Final report
Scoping study into food grade
polypropylene recycling
Scoping study for food grade polypropylene recycling, including technical
reprocessing trials, supply chain consultation and manufacturing trials.
Project code: MDP027
Research date: February 2009 to April 2010
Date: November 2010
WRAP’s vision is a world without waste,
where resources are used sustainably.
We work with businesses and individuals
to help them reap the benefits of reducing
waste, develop sustainable products and
use resources in an efficient way.
Find out more at www.wrap.org.uk
Document reference: WRAP 2010: Scoping study into food grade polypropylene recycling final report (WRAP project MDP027)
Written by: Dick Curry, Robin Hilder, Liz Morrish, Roger Morton, Nicola Myles and Chris Newman
Front cover photography: Polypropylene Packaging
WRAP and Axion Consulting believe the content of this report to be correct as at the date of writing. However, factors such as prices, levels of recycled content and
regulatory requirements are subject to change and users of the report should check with their suppliers to confirm the current situation. In addition, care should be taken
in using any of the cost information provided as it is based upon numerous project-specific assumptions (such as scale, location, tender context, etc.).
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Executive summary
Polypropylene (PP) is a versatile polymer (plastic) widely used in pots, tubs, bottles, punnets and trays to
package a variety of food products such as margarine, yoghurt, ice cream, sauces, microwavable products, meat
and vegetables. It is also used for packaging household cleaning and personal care products. The widespread
use of PP means it is the third most common polymer found in household waste in the UK after high density
polyethylene (HDPE) and polyethylene terephthalate (PET).
HDPE milk bottles and PET bottles are already recycled back to food grade plastic for new packaging. There is
significant commercial interest from retailers and food manufacturers in using recycled PP in their food packaging.
But although PP is regularly recycled into applications such as buckets and pallets, recycling it into food grade
packaging has not so far been possible.
This report describes the findings of the research into the feasibility of recycling post-consumer PP packaging to
produce food grade material, by adapting the existing technology used to produce food grade recycled HDPE in
the UK. The decision was taken to focus on the development of a recycling process for food grade polypropylene
because of the increased collections of mixed plastics within local authorities, with the knowledge that recycling
technical grade polypropylene alone would not meet the market demand.
The report concludes that producing food grade recycled PP is possible particularly for dry foods, but that
significant challenges remain to satisfy the requirement of European food safety legislation and achieve a
commercially viable process.
Key issues to recycling food grade PP
Under European Union (EU) legislation, plastic packaging for food can only be made from materials on a ‘positive
list’ of substances approved as safe. The simplest way of ensuring compliance is to exclude non-food packaging,
which is not subject to this restriction, from the input material to a recycling process. This has the additional
benefit of excluding contamination from non-food contents.
Achieving the threshold value for HDPE milk bottles, which is currently less than 1% non-food packaging, is
relatively straightforward as milk bottles are easy to recognise and separate from other HDPE packaging. PP
packaging is widely used for both non-food containers and a variety of food containers and has a wide range of
shapes, sizes and colours and therefore presents a far more difficult challenge. The integral or directly printed
labelling in multiple colours on PP containers also presents an additional challenge. Very few printing inks are
approved for direct food contact situations and there is a risk that the inks used could decompose to harmful
substances during the recycling process.
Technical challenges that need to be overcome before recycled PP can be used for food contact packaging
include:
„
developing a cost-effective system to obtain efficient separation of food contact and non-food contact PP
containers in household waste;
„
ensuring contaminants (from misuse of food containers in a second use, external contamination, processing
additives and printing inks) are removed from the PP in order to meet the standards set by the EFSA; and
„
obtaining recycled product with acceptable colour and odour.
Recycling food grade polypropylene
In order to establish the baseline capabilities of the unmodified HDPE technology, a large scale recycling trial was
carried out at a HDPE recycling plant using near infrared (NIR) sorted bales of mixed PP obtained from a plastic
reprocessor. The bales contained about 50% by weight of PP food packaging and a two-stage hand-picking
system proved necessary to ensure 99% food contact material was processed. The separated containers were
flaked, washed with a hot caustic soda solution and dried before being turned into pellets using a two-stage
vacuum extraction and extrusion process.
Detailed analysis of the recycled PP produced showed that whilst the process was very efficient at removing the
vast majority of the contaminants, small quantities of low volatility contaminants remained following processing
using a HDPE plant at levels above the EFSA limits.
Scoping study into food grade polypropylene recycling
1
Properties of the recycled PP
Sample trays and pots from the recycled PP pellets were produced in trials at two commercial packaging
manufacturers. The pellets could be processed by both extrusion/thermoforming and injection moulding at up to
100% recycled content, as well as at more commercially realistic levels of 25% and 50%. The recycled PP was
an opaque beige colour and had a slight, but noticeable, odour.
The recycled PP was found to be technically suitable in punnets for dry and semi-dry foods (for example
mushrooms) at up to 100% recycled content. But for products like margarine with a full fat content, it would be
suitable at no more than 5% recycled content. Intermediate levels would be acceptable for other foods such as
fish (15%) or meat (20%).
Additional investigations
Recycling PP using a HDPE plant did not remove all contamination and traces of low volatility contaminants were
identified as one of the key issues in producing a food grade recycled PP. Additional investigations were
undertaken at laboratory and pilot scale to establish the potential routes to improving the decontamination of
both flake and melt. Process temperature and residence time were found to be the most critical factors. The
need for high levels of input material sorting was also confirmed by investigating a number of individual
packaging types.
Packaging supply chain
A consultation exercise with the PP packaging supply chain explored the levels of interest of using a food grade
PP in packaging applications. Little recycled PP is currently used in packaging because little is currently available.
There is certainly interest from all levels of the supply chain – retailers, brand owners, food manufacturers and
packaging manufacturers – in using recycled PP, if a recycling system existed that could meet regulatory
standards and company food performance standards.
Conclusions
This study has provided valuable insights into the potential for using recycled PP in food grade packaging. It
proved it is possible to produce recycled PP suitable for dry food applications, but the trial material was not
cleaned sufficiently to allow it to be used at 100% recycled content for liquid and full fat applications. Further
investigations are necessary to produce a commercially viable process capable of satisfying the stringent
requirements of European food safety legislation.
Recommendations for future work include:
„
identify a credible, automated method for recovering food contact containers from mixed PP post-consumer
waste;
„
optimise the recycling process to improve product colour and odour, as well as the removal of the low level
volatile contaminants;
„
„
„
analyse different types of PP packaging to identify sources of product odour and contamination;
tailor analytical techniques for the assessment of material purity for food grade packaging to recycled PP; and
carry out more detailed studies on the fate of the label printing inks during the recycling process.
Scoping study into food grade polypropylene recycling
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Contents
1.0
2.0
3.0
4.0
5.0
Introduction ............................................................................................................................. 8
1.1
Background to the project......................................................................................................8
1.2
Aim of the project..................................................................................................................8
1.3
Project objectives ..................................................................................................................8
1.4
Project partners.....................................................................................................................9
1.5
Project sequence and methodology ........................................................................................9
Assessment of PP packaging in the UK waste stream ........................................................... 13
2.1
Background......................................................................................................................... 13
2.2
Compositional analysis .........................................................................................................14
2.2.1
Hand sorting analysis ..............................................................................................14
2.2.2
Bulk hand sorting analysis ....................................................................................... 24
2.2.3
Hand sorting container categories sorted from the picking line .................................. 26
2.2.4
Conclusions ............................................................................................................27
2.3
Packaging supply chain ........................................................................................................27
2.3.1
Retailers.................................................................................................................29
2.3.2
Food manufacturers ................................................................................................30
2.3.3
Packaging manufacturers ........................................................................................31
2.3.4
Labelling system suppliers .......................................................................................32
2.4
Forms of packaging .............................................................................................................33
2.5
Labelling systems ................................................................................................................ 34
2.6
Conclusions......................................................................................................................... 34
Phase 1 - Large scale technical recycling trials ..................................................................... 36
3.1
Methodology ....................................................................................................................... 36
3.1.1
Large scale recycling trial ........................................................................................36
3.1.2
Recycling process used for the trial ..........................................................................36
3.2
Feed materials and product yields ........................................................................................37
3.2.1
Feed material .........................................................................................................37
3.2.2
Negative pick food and non-food contact material..................................................... 37
3.2.3
Positive pick food contact ........................................................................................38
3.2.4
Hand sorting process ..............................................................................................40
3.2.5
Mass balance observations ...................................................................................... 40
3.2.6
Plant throughput.....................................................................................................42
3.2.7
Provisional challenge test ........................................................................................42
3.3
Contamination removal results .............................................................................................43
3.3.1
Label/ink removal products......................................................................................46
3.4
Polymer properties .............................................................................................................. 46
3.4.1
Physical property testing .........................................................................................46
3.4.2
Colour ....................................................................................................................48
Phases 2 and 3 - Investigation of potential areas for improvement identified in phase 1 .... 49
4.1
Phase 2 and 3 methodology .................................................................................................49
4.2
Phase 2 - Laboratory investigations ......................................................................................49
4.2.1
Results from Phase 2 ..............................................................................................49
4.2.2
Basic degassing parameters.....................................................................................53
4.2.3
Effects of temperature on vacuum chamber degassing.............................................. 54
4.2.4
Post supermarket packaging samples ....................................................................... 56
4.3
Phase 3 – Pilot scale investigations .......................................................................................57
4.3.1
Process condition changes.......................................................................................58
4.3.2
Cleaning efficiency ..................................................................................................58
4.3.3
Recyclate properties................................................................................................58
4.3.4
Melt filtration ..........................................................................................................59
4.4
Phase 2 and 3 conclusions ...................................................................................................59
4.5
Recommendations ...............................................................................................................59
Food grade testing ................................................................................................................. 60
5.1
Methodology ....................................................................................................................... 60
5.2
Testing regime and protocols – methodology and results ....................................................... 60
5.2.1
Migration testing methodology.................................................................................60
Scoping study into food grade polypropylene recycling
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6.0
7.0
5.2.2
Migration testing results and discussion.................................................................... 61
5.2.3
Organoleptic testing methodology............................................................................ 64
5.2.4
Organoleptic testing results and discussion............................................................... 65
5.3
Conclusions......................................................................................................................... 66
Packaging manufacture trials ................................................................................................ 67
6.1
Polypropylene polymer types................................................................................................67
6.2
Suitability of PP recyclate for food use ..................................................................................67
6.3
Methodology ....................................................................................................................... 67
6.4
Manufacturing trials ............................................................................................................. 68
6.4.1
Sharp Interpack ......................................................................................................68
6.4.2
RPC Containers .......................................................................................................72
6.5
Results and discussion .........................................................................................................75
6.6
Conclusions......................................................................................................................... 75
Conclusions and recommendations........................................................................................ 76
7.1
Mass balance ...................................................................................................................... 76
7.2
Physical properties............................................................................................................... 76
7.3
Phase 2 and 3 small scale laboratory investigation and pilot scale trial .................................... 76
7.4
Packaging manufacturing trials.............................................................................................77
7.5
Gas chromatography assessment by Fraunhofer IVV and PIRA of rPP in comparison to virgin PP
77
7.6
Provisional theoretical addition rate for food contact.............................................................. 78
7.7
Key recommendations for further work following this scoping study ....................................... 79
List of Figures
Figure 2 PP packaging bale.......................................................................................................................... 15
Figure 3 Stockport MBC kerbside plastic sample composition .........................................................................16
Figure 4 Ice cream tubs and containers ........................................................................................................ 18
Figure 5 Margarine tubs (yellow).................................................................................................................. 18
Figure 6 Detergents .................................................................................................................................... 18
Figure 7 Yoghurt tubs.................................................................................................................................. 19
Figure 8 Margarine tubs (non-yellow) ........................................................................................................... 19
Figure 9 Coloured general food packaging .................................................................................................... 19
Figure 10 Clear general food packaging ....................................................................................................... 20
Figure 11 Food trays (clear) ........................................................................................................................ 20
Figure 12 Food trays (blue) ......................................................................................................................... 20
Figure 13 Food trays (other)........................................................................................................................ 21
Figure 14 Sauce bottles............................................................................................................................... 21
Figure 15 Beverage bottles.......................................................................................................................... 21
Figure 16 Personal hygiene products............................................................................................................ 22
Figure 17 Household cleaning products ........................................................................................................ 22
Figure 18 Large non-food contact items ....................................................................................................... 22
Figure 19 Unidentifiable fragments .............................................................................................................. 23
Figure 20 Hand pick trial results................................................................................................................... 24
Figure 21 Comparison between positive pick and hand pick...........................................................................25
Figure 22 Comparison of reject fraction from positive and hand picks ............................................................26
Figure 23 PP packaging supply chain............................................................................................................ 28
Figure 24 Greenstar WES PP recycling process configuration ......................................................................... 36
Figure 25 Vacurema Advanced extrusion system...........................................................................................37
Figure 27 250µm screen pack...................................................................................................................... 41
Figure 28 Cleaning efficiency based on selected headspace peak areas .......................................................... 43
Figure 29 Selected relative peak areas for oligomers and limonene ................................................................44
Figure 30 Relative peak areas of rPP and PP homopolymer............................................................................ 44
Figure 31 Relative peak areas for positive and negative pick flake and pellet .................................................. 45
Figure 32 Comparison between positive and negative pick pellets with a long vacuum history ......................... 45
Figure 33 Phase 2 Micro pellets and phase 1 die face cut pellets.................................................................... 50
Figure 34 Twin screw extruder – the various processing zones can be seen along the screws.......................... 51
Figure 35 Twin screw extruder with both vacuum vents attached .................................................................. 51
Figure 36 Micro-plunger extruder used to prepare standard pellets from flake ................................................ 52
Scoping study into food grade polypropylene recycling
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Figure 37 Extruder melt degassing cleaning efficiency...................................................................................53
Figure 38 Vacuum chamber with temperature controller................................................................................55
Figure 39 Vacuum chamber - sample supports ............................................................................................. 55
Figure 40 Oligomer cleaning efficiencies at various vacuum chamber temperatures ........................................ 56
Figure 41 Cyclohexane GC/MS trace............................................................................................................. 61
Figure 42 99.7% ethanol extraction GC/MS trace..........................................................................................62
Figure 43 Acetic Acid GC/FID trace .............................................................................................................. 63
Figure 44 10% Ethanol GC/FID trace ........................................................................................................... 64
Figure 45 250g punnet................................................................................................................................ 68
Figure 46 Poultry tray ................................................................................................................................. 71
Figure 47 430ml snack pot .......................................................................................................................... 72
List of Tables
Table 1 PP packaging categories .................................................................................................................. 15
Table 2 Separation results from hand sorting ................................................................................................ 23
Table 3 Summary of discussions with companies in the packaging supply chain .............................................. 29
Table 4 PP yield comparison with HDPE recycling process .............................................................................. 41
Table 5 Physical property test results............................................................................................................ 47
Table 6 Colour measurements ...................................................................................................................... 48
Table 7 Levels of post consumer contaminant in Phase 3 flake compared to the Phase 1 pellet (100%)............ 52
Table 8 Samples for processing in the vacuum extruder system ..................................................................... 54
Table 9 Comparison of the levels of selected contaminants compared to the Phase 1 pellet ............................. 57
Table 10 Food simulants.............................................................................................................................. 60
Table 11 Odour testing results ..................................................................................................................... 65
Table 12 Taint testing results....................................................................................................................... 65
Table 13 Chilled impact tests on rPP samples................................................................................................ 69
Table 14 Edge deflection test on rPP samples ............................................................................................... 70
Table 15 Base compression tests on rPP samples .......................................................................................... 70
Table 16 Colour measurements on rPP samples ............................................................................................70
Table 17 RPC trial process conditions ........................................................................................................... 72
Table 18 RPC Containers dimension check and drop weight impact testing ..................................................... 73
Table 19 Snack pot colour at three recyclate levels measured with white and black background ...................... 74
List of Appendices
Appendix 1 Supply chain consultation list
Appendix 2 Fraunhofer IVV report (phase 1)
Appendix 3 Pira International migration test report (phase 1)
Appendix 4 Pira International organoleptic (taint and odour) test report (phase 1)
Appendix 5 Phase 2 and 3 technical report
Appendix 6 Sorema washing trial report (phase 3)
Appendix 7 EREMA extrusion trial report (phase 3)
Appendix 8 Pira International test report (phase 3)
Appendix 9 Pira International test report (phase 3)
Appendix 10 LyondellBasell investigation report Scoping study into food grade polypropylene recycling
5
Glossary of terms
Block copolymer
Copolymer
EFSA
FID
Food contact
Food grade
FTIR
GC
GC/MS
HDPE
HIPS
Homopolymer
Hydrocarbon
Injection moulding
IPM
Jayplas
KT
Mass balance
MFR
MRF
Negative picking
Non-polar substances
Oligomer
PE
PET
Plasticiser
Polar substances
Polyolefin
Positive picking
PP
rPP
A term to describe the type distribution of a second monomer within a copolymer, a
block referring to sequential runs. A polypropylene block copolymer, refers to a
polypropylene homopolymer/copolymer of mixed ethylene composition where
molecules of ethylene/propylene rubber coalesce during melt processing to form a
toughening separate phase
A polymer formed from the polymerisation of two or more types of monomers
European Food Standards Authority
Flame ionisation detector: a GC non-specific detector with proven sensitivity for carbon
containing species
Polymer or packaging which has been used in contact with food
Polymer or packaging that is originally manufactured under conditions which make it
suitable for use in food contact applications
Fourier Transform Mid Infra-red spectroscopy: an analytical technique permitting the
characterisation of principally organic species
Gas Chromatography: analytical technique used to separate volatile components from
a mixture
Gas Chromatography/Mass Spectroscopy: a refined analytical technique combining gas
chromatography with mass spectroscopy to identify the eluted species
High density polyethylene
High impact polystyrene
A polymer formed from the chemical process of polymerisation using one type of
precursor molecule, known as monomer
A chemical compound comprising, at least, carbon and hydrogen
Plastic melt processing technique; plastic granules are converted into a viscous melt
by heat and shear prior to injection into a metal tool under, typically, high pressure.
Cooling of the tool permits ejection of the cooled, now rigid, moulded article
Isopropyl myristate
J&A Young Ltd - Polymer Recycling Facility
‘Krystallationstrockner’ meaning crystallisation dryer in German. The name is a
carryover from the PET drying process for which the system was developed
A mass balance shows the quantities of materials going into and out of a process.
This allows for instance the overall efficiency of the system to be assessed and losses
to be identified
Melt Flow Rate; a rheological test method providing an approximate measure of
molecular weight and so providing an assessment of ease of flow within subsequent
melt processing equipment
Materials Recovery Facility
A hand sorting arrangement where the target material is left on the picking belt and
only the contaminants are picked from the sorting belt by the sorting staff and
transferred to collection bays
Substances with relatively small differences in charge within the molecular structure
Commercial thermoplastics typically possessing a distribution of species of varying
chain length. Species of lowest chain length are referred to as oligomers
Polyethylene
Polyethylene Terephthalate
Plasticisers are substances added to hard plastics such as polyvinyl chloride to adjust
the hardness and flexibility of the finished product
Substances with large differences in charge within the molecular structure
Polyolefins are polymers produced from alkene monomers. The simplest is
polyethylene which is made from ethylene followed by polypropylene made from
propylene
Hand sorting arrangement where the target material is picked from the sorting belt by
the sorting staff and transferred to collection bays
Polypropylene
Recycled polypropylene
Scoping study into food grade polypropylene recycling
6
Surrogates
Thermoforming
Surrogates are chemicals used to simulate classes of potential contaminants in a
challenge test. They are chosen to have a range of physical and chemical properties
such as polarity, volatility and molecular weight
Plastic melt processing technique; plastic sheet is heated until softened whereupon it
is formed in a tool by the action of air or vacuum
Acknowledgements
Axion Consulting and WRAP would like to thank the partners that have worked on this project. Greenstar WES
for hosting the phase 1 technical trials and providing valuable support and expertise. Fraunhofer IVV and Pira
International for their time, support and expertise, Sorema and EREMA for hosting the phase 3 pilot scale
demonstration trials and LyondellBasell for their work on characterising the application suitability of the recycled
polypropylene.
Scoping study into food grade polypropylene recycling
7
1.0
Introduction
1.1
Background to the project
The Waste & Resources Action Programme (WRAP) commissioned a scoping project to evaluate the production of
food grade polypropylene (PP). This involved considering whether the existing recycling process that has been
developed to produce food grade high density polyethylene (HDPE) can be adapted to recycle PP and meet
European Food Safety Authority (EFSA) requirements. This project represents the first piece of work aiming to
recycle post consumer PP packaging back into food contact applications.
There is a growing demand for food grade recycled PP (rPP) amongst brand owners and supermarkets who wish
to put PP food packaging onto the market that contains recycled content. By increasing the proportion of
packaging that can be recycled back into high value food grade packaging applications, less packaging waste will
be sent to landfill and the impact on the environment will be minimised through rPP substituting virgin PP in the
manufacture of new food packaging.
This is the final report for the overall scoping study and covers a number of key areas of work:
„ Compositional analysis of PP in the household waste stream;
„ Consultation work with the PP supply chain including retailers, brand owners, packaging manufacturers
and polymer suppliers;
„ Technical reprocessing trials of PP packaging (phase 1);
„ Small scale laboratory investigation (phase 2) and pilot scale technical trials (phase 3) including hand
sorting, washing and extrusion stages;
„ Migration and organoleptic testing; and
„ A number of manufacturing trials to produce rPP packaging samples.
The report provides a summary of each area of work, with further information being provided in a number of
more detailed reports as appendices.
This report is designed to be used by recyclers of packaging plastics in the UK who may be considering a move
into production of food grade rPP from household waste. It should also be of interest to packaging technologists
working for producers of fast moving consumer goods and retail groups. It is assumed that readers of this
document have some technical knowledge of plastic packaging and the processes that are used to produce it.
1.2
Aim of the project
The aim of the project was to determine if the existing recycling process developed for food grade HDPE can be
adapted to recycle PP and meet EFSA food grade standards.
1.3
Project objectives
The objectives of the project were:
„ Undertake a compositional analysis of post consumer PP packaging in the UK waste stream;
o Research how much PP is used in packaging, in what form, the presence of labels and printing;
o Detailed compositional analysis of PP packaging;
„ Consultation work with the PP supply chain, including retailers, brand owners, packaging manufacturers
and polymer suppliers;
o Understand what grades of PP are used in packaging and in what form, explore level of interest
from the supply chain in using rPP in packaging, identify barriers and opportunities for using rPP;
„ Conduct technical reprocessing trials (phase 1);
o Test large scale hand sorting process to identify food contact and non-food contact packaging;
o Use existing food grade HDPE recycling process (at Greenstar WES) to produce finished rPP pellet
from sorted food contact material only and from mixed food contact and non-food contact material;
o Measure yields of the overall recycling process;
o Measure the composition of contaminants in the finished rPP resin, assessing if the recycling
process could be optimised further to produce food grade rPP on a commercial basis;
o Conduct a preliminary provisional challenge test to identify if the cleaning efficiency of the recycling
process is able to meet food grade standards;
„ Conduct small scale laboratory investigation and pilot scale technical demonstration trials (phases 2 and
3);
o Assess, on a smaller scale, if hand sorting can achieve a food contact threshold purity of greater
than 99%;
Scoping study into food grade polypropylene recycling
8
Use the Sorema washing process to partially process the food contact PP packaging into clean
washed flakes;
o Use the EREMA Vacurema extrusion process to produce finished rPP pellet from the Sorema cleaned
flakes;
o Measure the contamination levels in the washed flake and finished pellets;
„ Perform food grade testing on rPP pellet, including migration tests and organoleptic tests; and
„ Conduct trials with packaging manufacturers to produce packaging with a rPP content.
o
1.4
Project partners
The scoping project has been led by Axion Consulting and involved a number of key project partners:
„ Axion Consulting: provides innovative processing solutions for recycling waste materials. It has a wide
range of clients within the recycling and process industries and key areas of work include practical
development of new processing and collection methods, as well as business planning and support;
„ Greenstar WES: the Greenstar WES group of companies specialise in the recycling of plastics and
chemicals and also operates its own packaging compliance scheme. The recycling operations produce
high quality recycled plastics, including PP, polyethylene (PE) and polystyrene (PS). Greenstar WES
hosted the phase 1 technical recycling trials and compositional analysis work at its Wilton facility;
„ Fraunhofer IVV: the Fraunhofer Institute for Process Engineering and Packaging IVV perform contract
research and development work for industry. The activities are partly supported by publicly-funded
investigative applied research projects, as well as by the participation in scientific, standardisation and
industrial bodies. Fraunhofer IVV delivered the headspace GC analytical work for the scoping study;
„ Pira International: is a worldwide authority on the packaging, printing and paper industry supply chains.
It provides market research, strategic and technical consulting, testing, publications and conferences to
help clients understand market trends, identify opportunities, meet compliance requirements, network and
develop strategies to grow their businesses. Pira International delivered analytical work for the study,
including the migration and organoleptic tests;
„ Sorema: a division of Previero, design, construct and install complete plastic recycling processes from the
initial size reduction stage through to flake washing and cleaning step. Polyethylene terephthalate (PET)
and HDPE bottle recycling plants are Sorema’s speciality. Sorema hosted the phase 3 pilot scale washing
trial at its test facility in Italy;
„ EREMA: design and manufacture high tech plastic recycling systems with a specific focus on the extrusion
stages. EREMA hosted the phase 3 pilot scale extrusion trial at its test facility in Austria; and
„ LyondellBasell: LyondellBasell is a global leader in polymers, chemicals and refining with a vertically
integrated structure stretching from the crude oil wellhead, through refining to the production of olefin
derivatives. LyondellBasell is ranked as number one globally for polypropylene capacity. It has provided
technical support in terms of characterising the application suitability of the rPP produced by the technical
trials. A report of their findings can be found in Appendix 10.
1.5
Project sequence and methodology
This section of the report gives an overview of the practical tasks and trials delivered during the scoping project.
There were a number of key stages to the project including large scale demonstration trials, small scale
laboratory investigations, pilot scale work and analytical testing. Figure 1 shows the timeline sequence for the
project, with the three phases of work shown in different colours.
Scoping study into food grade polypropylene recycling
9
Figure 1 Project sequence
Phase 1 - Initial small scale hand sort to measure the approximate composition (Section 2.2.1)
The aim of the small scale hand sort was to identify the approximate mix of materials in a PP packaging stream.
Packaging was sorted by a bulk Near Infrared at a Plastics Recovery Facility (PRF) to get an indication of the
separation issues likely to be involved in food grade PP recycling.
Phase 1 - Conveyor hand sort of 24 tonnes (Section 3.0)
Axion worked with Greenstar WES during March 2009 to deliver the phase 1 production scale recycling trials at
Greenstar WES’s plastic recycling facility in Teeside. The large scale conveyor hand sort involved hand sorting
bales of PP, supplied by Jayplas, to separate food contact from non-food contact material. The food contact PP
fraction from the phase 1 hand sort became the feed material for the subsequent phase 1 washing and extrusion
trial.
Phase 1 - Preparation of provisional challenge test sample (Greenstar WES) (Section 3.2.7)
The sample for the provisional challenge test was generated over a two week period, consisting of a mix of
polymer flakes and surrogate chemicals. The objective of the provisional challenge test was to provide data on
the likely effects of dilution and the interaction of surrogate vapours with the uncontaminated flake within the KT
temperature gradient.
Phase 1 - Large scale washing and extrusion trial, plus provisional challenge test (Greenstar WES)
(Section 3.0)
The large scale washing and extrusion trial was conducted using the full scale HDPE recycling plant at Teeside.
The conveyor hand sorted material was processed through the Greenstar WES washing and drying process to
produce a clean washed flake, which was then fed to the Vacurema vacuum extraction and extrusion process.
The Vacurema system comprises two vacuum chambers, in which the flakes are stirred and heated under
vacuum, followed by an extruder fitted with a melt filter which has back flushing capability.
The provisional challenge test was also conducted at the Greenstar WES facility, which involved adding the
provisional challenge test material to the washed flake feeding into the Vacurema extrusion system once the
process had reached steady state.
Phase 1 - Organoleptic and migration tests (Pira International) (Section 5.0)
As part of the overall scoping project a testing regime was developed, through discussion with retailers and
packaging manufacturers within the supply chain, which included both migration and organoleptic testing. The
initial food grade testing of the samples from the Greenstar WES trial provided data to the packaging
manufacturers before they conducted the manufacturing trials. The organoleptic testing assesses for odour and
Scoping study into food grade polypropylene recycling
10
taint problems. The aim of the migration tests were to prove that the intended applications and use would not
yield quantitative migration of harmful species and species over threshold limits.
Pira International was commissioned to undertake the migration analyses and the organoleptic testing of the rPP
material. Both the migration and organoleptic tests used packaging from the Sharp Interpack manufacturing
trial.
Phase 1 - Packaging manufacture trials (RPC and Sharp) (Section 6.0)
Two packaging manufacturers, Sharp Interpack and RPC Containers, ran trials to produce a number of packaging
samples with different levels of recycled content using the rPP material generated from the phase 1 trials.
The packaging application chosen for the initial manufacturing trial with Sharp Interpack was a black vegetable
punnet (250g capacity). A follow-up trial was also conducted to produce a poultry tray following feedback and
discussions with Sharp Interpack. RPC Containers manufactured a snack pot application (430ml capacity) for
trialling the rPP.
Information was obtained from each manufacturing trial including packaging samples, retail customer feedback,
processing information and an assessment of fitness for use.
Phases 2 and 3 practical trials (Section 4.0)
Based on the results and findings from the phase 1 trials at Greenstar WES two further phases of technical work
and demonstration trials were delivered to investigate the potential areas for improvement identified in phase 1.
The work consisted of:
•
Phase 2: Small scale laboratory investigations; and
•
Phase 3: Pilot scale demonstration trials.
The aim of the second and third phases of work and trials was to establish why certain materials (low volatility
but specific migration relevant contaminants) were persisting into the finished rPP and how best to change the
processing parameters and techniques in order to improve their removal.
Phase 2 - Laboratory scale investigations – melt degassing (Hilder Business and Technology
Services) (Section 4.0)
Phase 2 was a laboratory scale investigation to assess the potential for various process modifications to be made
in the Phase 3 pilot scale trials. During phase 1 a number of problems and issues were identified. The second
phase of work was delivered at laboratory scale so that the research could be carried out under carefully
controlled conditions, enabling particular parameters to be changed in sequence. This level of control would not
have been possible at a pilot or production scale. The work involved a comprehensive evaluation of the effects of
processing conditions and packaging material selection at laboratory scale. This specific part of the laboratory
scale investigation focused on assessing vacuum melt degassing.
Phase 3 - Static/table hand sort to prepare samples for further test work (Section 4.3)
During the hand sorting at Greenstar WES in phase 1; two significant problems were identified. The first issue
was that surging of material onto the feed belt resulted in the sorting capacity of the belt being temporarily
exceeded. The surging was caused by large ‘chunks’ of the input bales falling periodically onto the feed belt
during manual bale breaking. The second problem was that after sorting the transfer belt fed directly into the
granulator making quality control assessment difficult.
In addition, the hand sorting selection process was designed to promote accurate selection of food packaging.
This was achieved by instructing the sorters to select only that packaging that they could easily identify as food
contact packaging. In practice this meant that only about half of the available material could be picked.
Since the pilot trials required significantly less material it was possible to use static sorting tables. This meant
that the sorters had more time to evaluate the packaging allowing both improved quality control and much higher
yields of food grade packaging being selected.
Phase 3 - Washing trial (Sorema) (Section 4.3)
The washing trial, held at Sorema in Italy, processed the food contact PP packaging material from the static hand
sort. The objective of the trial was to produce a batch of washed PP flake for further processing in the
subsequent extrusion trial. The trial was also used to determine the suitable operating conditions, including
detergent selection, for the hot washing process in order to achieve maximum label, ink and adhesive removal.
Scoping study into food grade polypropylene recycling
11
Phase 2 - Laboratory scale investigations – vacuum chamber and individual packaging types (Hilder
Business and Technology Services) (Section 4.0)
Additional laboratory scale investigations, considered as part of phase 2, included vacuum chamber tests and
assessment of individual packaging types. The vacuum chamber tests took the hot washed flake from the
Sorema trial and assessed the cleaning efficiencies for various oligomers. The laboratory investigative work
helped recommend suitable settings for the phase 3 pilot scale extrusion trial at EREMA. Three samples of
consumer pre-waste chain plastic packaging were also evaluated to assess the potential contaminant risk from
individual classes of packaging.
Phase 3 - Vacurema trials (EREMA) (Section 4.3)
Following on from the Sorema washing trial was the Vacurema extrusion trial, held at EREMA in Austria. Based
on the results from the phase 1 work at Greenstar WES and the Phase 2 laboratory scale work, the aim of the
trial at EREMA was to maximise both the process temperature and residence time in order to improve the
cleaning efficiency.
Phase 3 - Analysis (Pira International) (Section 4.2)
Samples produced from the Vacurema trials at EREMA were subjected to analysis by Pira International.
Scoping study into food grade polypropylene recycling
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2.0
Assessment of PP packaging in the UK waste stream
2.1
Background
This part of the overall scoping study focused on assessing the quality and composition of the PP packaging
stream which is produced by materials recovery facilities (MRFs) in the UK. MRFs can receive a full range of
recyclable plastics from kerbside recycling collections and tend to use Near Infrared (NIR) sorting machines to
positively pick containers which reflect the characteristic NIR spectrum for each polymer type that the MRF
decides to target for segregation.
Smaller MRFs of this type tend to only target PET and HDPE containers as these are the dominant polymer types
in the container fraction of the UK packaging waste stream. A proportion of this material can be supplied back
into food grade applications via a select number of reprocessors. Larger size MRFs can have sufficient economy
of scale to be able to dedicate NIR sorting machines to other polymer types. PP is the next polymer stream that
these MRFs are likely to target because it is a valuable polymer type and is usually the next most abundant
polymer stream after HDPE and PET 1. At present only a small proportion of the municipal MRFs in the UK are
believed to target PP packaging material.
If however a market for this fraction can be developed then it would be relatively straightforward to install NIR
sorting equipment at existing MRF. Depending on what solution is found for the problem of separating food
contact from non-food contact packaging, it may also be possible to perform this selection at the same.
Presently, there are no PP food contact plastic recycling processes that comply with Commission Regulation (EC)
No 282/2008 2. The role of EFSA is to review and approve applicant processes to ensure regulation compliance.
Whilst there is no explicit target set in the legislation for a minimum sorting threshold, the plastics reprocessing
sector commonly accepts that a 99% previous food contact specification should be used. In general it is widely
considered to be Good Manufacturing Practice (GMP) for food contact recycling and the following sources all use
or recommend the generally accepted specification of 99% or greater food contact material:
„ The Fraunhofer IVV recommends that, in the case of HDPE milk bottles, >99% prior food contact material
is required as the input material to the process;
„ ILSI (International Life Sciences Institute) has also recommended this benchmark threshold;
„ EU directives indicate a high sorting efficiency is required although the interpretation of the exact wording
is not clear cut;
3
„ WRAP recycled HPDE project : the specification for the input material states >99% prior food contact
material; and
4
„ WRAP HDPE Feasibility Study : recommendation by ILSI and the German Federal Institute for Risk
Assessment (BfR).
This level is considered to be a general guideline and the actual level may depend upon the polymer type and its
prior use.
Recycling operations are required to address the question of minimising adventitious contamination 5 of articles
returned for recycling. Preliminary sorting may reject unsuitable articles – those that are not food grade plastics
or are identifiably contaminated. The remaining contaminating substances not detected in these preliminary
stages will be further reduced in concentration by dilution with food contact material. The subsequent clean-up
stages undertaken during the recycling process are aimed at eliminating those contaminants residing on the
surface or those penetrating the surface of the material.
1
WRAP Project Commercial Scale Mixed Plastics Recycling MDP021
2
Commission Regulation (EC) No 282/2008 of 27th March 2008 on recycled plastic materials and articles intended to come into
contact with foods
3
WRAP PLA0017, Food Grade HDPE Recycling Process: Commercial Feasibility Study, Final Report, June 2006, Ed Kosoir, page
15 http://www.wrap.org.uk/downloads/PLA0017_Commercial_Feasibility_Study_Final_Report2.52aff9bc.3153.pdf
4
WRAP, Develop a food grade HDPE recycling process, June 2005, Frank Welle, page 3
http://www.wrap.org.uk/downloads/Full_wrap_HDPE_Recycling_final_reportV141205.4bf0364b.2332.pdf
5
Adventitious Contamination – contaminants: any unwanted substance that deliberately or inadvertently comes into contact
with the packaging material before it is collected for recycling and that therefore that may contaminate the plastic and
negatively influence the quality of the product with which a recycled packaging material is brought into contact. Dr.F.Welle IVV
Fraunhofer.
Scoping study into food grade polypropylene recycling
13
In contrast, ingredients of plastics (additives and processing aids) and their degradation products are less likely to
be removed by the cleaning process. Therefore, if non-food grade plastics enter the recycling process, the parent
polymer can be indistinguishable from food grade material but there is a risk (albeit small) of non-approved
additives or other ingredients being introduced. Thus, any recycling operation must demonstrate the capability to
select and use only food contact feedstock material.
The assumption that HDPE achieved levels (>99%) may be sufficient for PP material could be flawed, because
the target threshold may need to be higher because of the presence of materials which don’t have food contact
approval or ‘non-positive list’ substances within in-mould labelling printing inks. These chemicals, or their
degradation products, will be mixed into the polymer when it is melted during the recycling process and these
substances will not necessarily be removed by all recycling processes.
Since all PET is manufactured at food grade standard there is not a problem with the polymer and in the case of
HDPE the main food containers are milk bottles which are easy to recognise and select. As a result, it is relatively
simple to use a final hand pick before the recycling process to ensure that less than 1% of the feed material is
from non-food contact applications.
In comparison to PET and HDPE, PP is used more widely for non-food contact containers in household packaging
(for example a bleach bottle) and is also used in a wider variety of types of container with different coloured print
and label systems. NIR sorters that are set up to target PP cannot currently discriminate between food contact
and non-food contact PP containers and they cannot discriminate between packaging and non-packaging PP
items.
2.2
Compositional analysis
A comprehensive compositional analysis exercise was conducted in three ways for this study:
„ Hand sorting samples of material from a bulk PP packaging sorting plant;
„ Positively picking a large volume of food contact material from a bulk sample of PP packaging from a
sorting plant; and
„ Positively picking specific categories of container from a bulk sample of PP packaging and then analysing
these containers by brand, packaging type and type of label.
2.2.1 Hand sorting analysis
Aim
The aim of this analysis was to identify the approximate mix of materials in the PP packaging feed stream from a
bulk NIR sorting MRF and to get an indication of the separation issues likely to be involved in food grade PP
recycling. The hand sorting analysis also provided the source of PP packaging for the subsequent large scale
technical trials.
Method
Greenstar WES sourced 40 tonnes of waste PP packaging from the automated plastic sorting plant operated by
Jayplas.
Scoping study into food grade polypropylene recycling
14
Figure 1 PP packaging bale
A 70kg sample from the corner section of a single randomly selected bale from this consignment was removed for
hand sorting. The statistical sampling analysis undertaken indicated that this would be a meaningful sample size
for this sort. See section 2.2.3 for further detail.
The 70kg sample was hand sorted initially into categories of packaging type and then following lengthy
inspection, including weighing, into subcategories as illustrated below.
Table 1 PP packaging categories
Container category
Tubs and pots
Trays
Bottles
Cleaning products
Caps
Blacks
Non-assignable items
Container sub-category
Yoghurt pots
Margarine tubs (yellow colour)
Margarine tubs (non-yellow colour)
Food product packaging (clear)
Food product packaging (non-clear)
Ice cream tubs
Food trays (blue colour)
Food trays (clear)
Other food trays
Beverage bottles
Sauce bottles
Household cleaning products
Personal hygiene products
Detergents
Closures
Notable non-food items
Small fragments
This created a total of eighteen categories and photographs of the sorted samples are shown in figures 4 to 19.
Statistical basis for sample selection
Axion previously carried out hand sorting and sampling from mixed household packaging plastics with Stockport
Metropolitan Borough Council 6 (Stockport MBC). This work measured 13% PP in a large kerbside collection trial
6
Stockport Council Plastic Collection and Sorting trials, Report by Axion Recycling for WRAP Project KTF 0009, June 2005
Scoping study into food grade polypropylene recycling
15
for household plastic including films. Excluding the 29% films that were also collected in this trial, the calculation
implies around 18% PP would be found in the container fraction rather than 13% as illustrated below.
Figure 2 Stockport MBC kerbside plastic sample composition
More recent confidential sampling and sorting work undertaken for various commercial clients has shown a lower
amount of PP in MSW. Data from clients that are collecting plastic bottles at the kerbside indicate a lower
percentage of PP (around 3-5%) in the container fraction.
In the trial in Stockport each household that participated in the kerbside collection (around 40% of households)
put out an average of 1.74kg of plastics every two weeks during the four months of the trial. This trial requested
householders to segregate all types of plastic in a single collection sack for recycling. The composition of the
waste was measured by hand sorting of regular samples. 29% films were measured in this collection, implying
that the average amount of rigid containers (bottles, tubs, trays and other containers) put out by each household
for recycling was around 1.24kg per fortnight (30kg/year).
Recoup’s annual plastic collection survey 7 measured a total of 169,000 tonnes of plastic bottles collected through
kerbside collections in 2008 and estimated that 18 million households had access to these collection schemes. In
recent surveys for local authorities average kerbside collection participation rates have been in the range of 4070%. Not all households put out recyclables for every collection, for example if a kerbside scheme has large
collection containers and a weekly collection frequency, a householder may not need to set out their recyclables
on every collection. From previous experience it is expected that the set-out rate for each individual collection is
around 20 percentage points less than the long-run participation rate. Assuming an average participation rate of
55% for UK local authorities then the average set-out rate for a single collection is likely to be around 35%.
For a set-out rate of 35% then the total UK kerbside plastic container collection of 169,000 tonnes will have come
from plastic put out by around 6.3 million households (27kg per household per year). If the majority of these
collections take place on a fortnightly basis then the average collection of plastic per household each fortnight will
be 1.03kg/ collection. This is in line with the measurements taken from the Stockport kerbside project mentioned
above. Assuming a 1.08kg collection rate per household and an average of 5% PP in the household container
fraction, then the amount of PP sent for recycling by a typical household is around 50g per fortnight.
Assuming that the whole bale used for this compositional analysis work came from a single fortnightly collection
then the 70kg sample taken for hand sorting in this trial would have come from approximately 1,500 households.
The sampling model estimates that a sample from 1,500 sources where the sample is split into fractions of
around 5% each, will give an error of 5% +/- 1% on the measurement of each fraction with a confidence limit of
95%. Sorting of a sample from 7,000 sources (around 330kg) would be required to reduce this error to +/0.5%.
The sorting task was time consuming to undertake, taking three people two days to sort the 70kg sample as
described below. Following the same degree of hand sorting for a larger sample of material would have been
7
UK Household Plastics Packaging Collection Survey, Recoup, 2009
Scoping study into food grade polypropylene recycling
16
difficult to deliver within the timescales for the task and it is believed that this additional effort would not have
improved the accuracy of the sort significantly.
The hand sorting analysis provided a categorisation and quantification of principal PP packaging forms present in
the household waste stream. An understanding and appreciation of the types of packaging forming the infeed
material for the technical trials has a value for the interpretation of the final trial results.
Results
The fractions separated in the hand sort are shown in the photographs below. The choice of categories of
packaging identified and sorted followed from their relative ease of identification and form. Thus margarine tubs,
for example, were visible as both yellow and non-yellow categories.
Scoping study into food grade polypropylene recycling
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Figure 3 Ice cream tubs and containers
Figure 4 Margarine tubs (yellow)
Figure 5 Detergents
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Figure 6 Yoghurt tubs
Figure 7 Margarine tubs (non-yellow)
Figure 8 Coloured general food packaging
Scoping study into food grade polypropylene recycling
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Figure 9 Clear general food packaging
Figure 10 Food trays (clear)
Figure 11 Food trays (blue)
Scoping study into food grade polypropylene recycling
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Figure 12 Food trays (other)
Figure 13 Sauce bottles
Figure 14 Beverage bottles
Scoping study into food grade polypropylene recycling
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Figure 15 Personal hygiene products
Figure 16 Household cleaning products
Figure 17 Large non-food contact items
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Figure 18 Unidentifiable fragments
Table 2 Separation results from hand sorting
Category
Tubs and pots
Trays
Bottles
Cleaning products
Caps
Weight (Kg)
24.0
8.5
5.5
7.5
1.5
%
35
12
8
Category subset
Yoghurt pots
Yellow margarine pots
Non-yellow margarine tubs
Clear food product packaging
Weight (Kg)
1.15
3.00
3.81
%
2
4
6
5.71
8
Non-clear food product packaging
7.35
11
Ice-cream tubs
2.90
4
Blue food trays
0.80
1
Clear food trays
5.45
8
Other food trays
2.30
3
Beverage bottles
1.65
2
Sauce bottles
3.81
6
Household cleaning
2.36
3
Personal hygiene
2.60
4
Detergents
2.86
4
2
Closures
1.5
2
11
Black plastics
1.0
1
Black plastics
1.00
1
Non-assignable
21.0
30
Notable non-food objects
5.65
8
Small fragments
15.10
Total
69.0
22
99%
Clearly identifiable food contact items comprised 56% of the weight of the total sample. 11% by weight were
non-food contact items and 33% of the material by weight was closures, black items, large non-container objects
and small fragments. Some of this material would have been food contact but could not be clearly identified as
such.
Scoping study into food grade polypropylene recycling
23
Figure 19 Hand pick trial results
Five random samples from each of the 18 categories were tested in the laboratory at Greenstar WES using a
Fourier Transform Mid Infra Red (FTIR) Spectrometer. In total, seven out of the 90 items analysed had been
wrongly sorted by the NIR sorting machine, representing a mis-sorting rate of 8%. The mis-assigned containers
were as follows; a yoghurt pot identified as HDPE, three beverage bottles (two PET and one HDPE), a household
cleaning item identified as high impact polystyrene (HIPS) and two detergent containers identified as HDPE. Missorting can arise through a number of scenarios; including the signal being wrongly derived from a packaging
label composed of another plastic material rather than the body of the packaging. Also baling and compaction
can cause items to become inadvertently entwined, again leading to analysis errors.
2.2.2 Bulk hand sorting analysis
A bulk hand sort of 13 tonnes of PP bales from Jayplas was conducted, producing a sample of 3.5 tonnes of
positively picked food contact material for washing, extrusion, conversion to packaging and subsequent taste and
smell testing. The results of this bulk sort were analysed to:
„ Confirm the fraction of food contact material that was measured in the initial hand sort;
„ Identify the likely mix of container types in positively picked food contact material;
„ Measure the practical picking rate that is possible for a positive hand sort; and
„ Provide samples for more detailed analysis.
Method
Initially 13 tonnes of material were sorted by between four and five hand pickers on the sorting belt at Greenstar
WES, over two sessions of 14 hours each. Samples were taken and analysed at regular intervals in order to
assess the accuracy of the positive pick being undertaken. The throughput of the picking line was also
measured. A further 12 tonnes of bales were sorted after the initial exercise, in order to increase the size of the
food contact sample to 5.7 tonnes for the technical reprocessing trial.
Scoping study into food grade polypropylene recycling
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Originally it had been expected that the food contact fraction in the feed would be large enough to allow the
material to be sorted by a negative pick – just pulling out the non-food contact materials. However, the lower
than expected food contact content of the PP feed required a change in the sorting strategy, to a much slower
and more labour intensive positive pick in order to pull out the food contact material and then a second negative
pick of this food contact fraction in order to remove the remaining contaminants.
Results
Nine samples of about 2kg each were taken at regular intervals during the first positive hand picking trial in order
to assess the quality of the pick as it was taking place. Each sample was sorted on site to measure its
composition and these were kept segregated for further off-site analysis.
The average composition of the nine positively picked samples is shown below, plotted together with the
corresponding hand pick results. It can be seen there is reasonable agreement between the figures.
Figure 20 Comparison between positive pick and hand pick
The proportion of non-food containers in the samples varied from 0% to 24%, with an average of 7.5%. This
indicated that a further negative hand pick was required before the washing step of the technical trial in order to
ensure that 99% food contact material was present in the feed to the washing and extrusion process.
The composition of two samples from the reject fraction from the positive hand pick was also analysed by hand
and compared to the initial scoping hand sort results. Again this composition matched well with the initial sort.
Scoping study into food grade polypropylene recycling
25
Figure 21 Comparison of reject fraction from positive and hand picks
Overall the positive picking exercise recovered 5.7 tonnes of positively picked material from 25 tonnes of baled
PP-rich material. A picking rate of 26kg/hr per person could be derived from the 48 hour duration, using a 4.5
strong team of operators.
Following the positive pick, a negative pick was undertaken, with a higher throughput per hour (but a further
yield loss of around 7%). This was required to ensure a supply of 99% food contact material into the wash
process.
2.2.3 Hand sorting container categories sorted from the picking line
Objective
The mix of polymer types, label and print systems and additives in the PP packaging stream is likely to be more
varied than for HDPE and PET streams. These components have potential to complicate the recycling process for
food grade PP. Some of the additives and printing inks used may be difficult to remove in the washing process or
may potentially create problematic degradation products in the extrusion step. High levels of non-food contact
material with migrating potential could raise the sorting thresholds required, to levels above 99%, thus
presenting a significant challenge to practical sorting accuracies.
The aim of this part of the hand sorting exercise was to identify the likely mix of polymer types, print types and
additives used in different types of food contact containers. This information should help in the design and
development of the food grade recycling process.
Method
The statistical sample size analysis for the initial hand sort identified that a minimum sample size of 50-100kg is
needed in order to measure the mass distribution with an accuracy of +/- 1% when the material is split into
around 20 categories and the sample comes from around 1,500 sources.
For a sort by container design within the individual container categories, the number of individual items which is
sorted must not be vulnerable to sampling error. The sampling model estimates that if containers within an
individual category are of around five different types (20% of each), then about 200 items must be selected from
each category for more detailed assessment in order to achieve an accuracy of +/- 5% with a 95% confidence
Scoping study into food grade polypropylene recycling
26
limit. About 200 items from each category that were collected and sorted during the bulk positive pick were
bagged off and transported to the laboratory for further analysis.
The key packaging technology factors were noted for each category, for example whether the packaging was
thermoformed or injection moulded and the following information recorded for the individual items selected from
each category: brand name, weight, labelling type, colour, size, wall thickness and polymer type.
2.2.4 Conclusions
The key conclusions from the compositional analysis work are:
„ The positive hand pick using a conveyor belt collected approximately 25% from the 50% available food
contact material from the feed stream. This means that the positive hand picking exercise managed to
extract about half of the available food contact material. Much of the food contact material is difficult to
identify positively, partly because of the wide variety of container brands in the stream and partly because
the containers are often severely deformed after baling;
„ The positively picked food contact stream still contained about 7.5% non-food contact material so the
material needed a further negative pick to ensure 99% non-food contact prior to washing and extrusion;
„ The most frequently occurring containers in the positively picked material were margarine and ice cream
tubs; and
„ The cost of hand sorting is not commercially viable to allow the development of a commercially viable food
grade PP recycling process based on hand-selection of 99% food contact material, particularly as the
recovery of food contact material from the mixed PP feed is low.
The percentage of food contact material in bulk PP packaging from a NIR sorting MRF is around 50%. This is too
low to allow a negative hand sort to remove non-food contact items up to the current limit of >99% food contact
material in the feed to the food contact recycling process. Future research work may permit the use of
technology, such as refined automated sorting, to attain EFSA process approval without the use of extensive and
expensive hand-sorting. Furthermore, developments in the area of marking technology, coupled with advanced
detection for example, may improve sorting rates of food contact applications towards meeting the demanding
levels of accuracy required.
Instantaneous positive hand picking rates of up to 60kg/hr per picker were measured during this exercise but
over a full shift the average rate was around 25kg/hr. Improvements to bale breaking, feeding system and
ergonomics / operator comfort could well lead to 50kg/hr rates being achieved. Assuming an operator’s hourly
pay rate of £10/hr and achieving a sorting rate of 25kg/hr, it can be deduced that a sorting cost per tonne of
£400 is clearly a significant cost. Achieving a doubling of productivity to 50kg/hr would half this to yield £200 per
tonne. The additional negative picking was considered to add a further nominal £100 per tonne sorting cost to
the £400 per tonne for the positive pick.
2.3
Packaging supply chain
This part of the scoping study has investigated the supply chain for PP food packaging by interviewing eight
major retailers, 18 food manufacturers and four packaging manufacturers. Three suppliers of inks and labelling
systems, together with a number of other organisations within the food industry have also been contacted.
The interviews and consultation exercise with these organisations sought to gain an understanding of their
respective roles in the supply chain, their understanding of issues relating to food contact recyclate use.
The forms of packaging produced including important components such as labelling and the inter-relations
between the supply chain members.
All the companies interviewed are listed in Appendix 1.
Discussions with these companies have indicated that the existing supply chain for PP packaging can be
summarised as shown below.
Scoping study into food grade polypropylene recycling
27
Figure 22 PP packaging supply chain
Polymer suppliers
Labelling
system suppliers
Packaging
suppliers
Food
manufacturers
Retailers
The outcome of discussions with the retailers, food manufacturers and packaging suppliers is summarised in
Table 3 below and presented in more detail in the following sections. The feedback in this report has been
anonymised.
Scoping study into food grade polypropylene recycling
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Table 3 Summary of discussions with companies in the packaging supply chain
Retailers
Food manufacturers
Interviewed
8
18
Clear commitment to
using recyclate
8
18
2
Would like the option
of using rPP
8
all recognise very little
is available in UK
currently
12 yes
4 cautious
1 no
1 use of PP not relevant to
this study
2 yes
2 cautious
Currently substituting
PP with PET
2 yes
3 yes
2 aware of retailer pressure
but currently resisting this
Require transparency
in packaging
A reason for the move
to PET
A reason for those moving
to PET. Others required
limited opacity.
Concerned about
colour
No comments about
colour
2 household name brands
who saw colour as an
important part of product
marketing
Driven by customer
requirements
8
10
Driven by customer
requirements
3 making more use of
stuck-on labels
7 use stuck-on labels or
sleeves
9 yes, provided it met
relevant food contact
standards
8 cautious
1 no
Use on-polymer
printing or in-mould
labelling
Looking at recycling
friendly labels
Prepared to take
non-food packaging
material
Aware of generally
accepted guideline
on use of plastics
from prior-food
contact applications
Use food grade
polymer for non-food
applications
8
all would require this
to meet relevant food
hygiene standards
Packaging
manufacturers
8 contacted
4 provided information
Driven by customer
requirements
Also raw material
premiums are important
Driven by customer
requirements
Dependent upon
application
Will use if customer
requires
Very cautious, generally
no
None
None
2
1 insists on this
Not relevant
2
2.3.1 Retailers
Retailer commitment
The retailers that were interviewed expressed a commitment to packaging minimisation and recycling. To varying
degrees they already use rHDPE and rPET and would see rPP as a further development of their current practices.
All were clear that rPP would need to come from a certified recycling process and to be demonstrated to meet all
relevant food contact standards and regulations. One went beyond this to say they would require additional
testing using their own products. They had experience of rHDPE and rPET passing migration tests but still
leading to qualitative tainting of products, for example a perceptible odour from the packaging.
Scoping study into food grade polypropylene recycling
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Issues with recycling PP
Retailers were aware that PP recycling is at a much lower level than HDPE and PET. They attributed this to low
availability of recycled material since PP packaging in the household waste stream is not collected as
systematically as other types of plastic. They also recognise that PP packaging covers a much more diverse
range than with HDPE and PET and that there is no single predominant form of packaging comparable to a HDPE
milk bottle or a PET soft drinks bottle. This, coupled with the wide range of colours used by some food
manufacturers to promote their brand image, leads some of the retailers to feel that complex collection and
sorting systems will be required and that a number of discrete streams, each with fairly low tonnage, will be
produced. As a result some doubted if the quantities would sustain an economic and commercially viable
recycling system. Some said they supported a change from PP to PET in view of greater clarity in the packaging,
more established recycling systems and therefore greater availability of recyclate.
Roles and responsibilities
The retailers typically describe their role as defining the performance standards required by packaging,
particularly in terms such as food hygiene and shelf life. Only one retailer mentioned the visual appearance of
packaging as being important. However, as discussed below in more detail, food manufacturers and packaging
manufacturers described retailers as being deeply interested in the visual appearance of food on the shelf and
saw clearer packaging becoming increasingly required. Retailers see the responsibility for the detailed
specification of packaging to meet these performance standards lying with the food manufacturer and the
packaging supplier. They prefer the upstream companies to make use of their own expertise and to have some
economic freedom as to how best to meet customer requirements. Individual retailers may go some way beyond
this, for example to ask suppliers to provide options which they can evaluate, but still stop well short of
stipulating detailed technical specifications. Knowledge of the grades of PP involved or the manufacturing
processes by which particular types of packaging is produced was limited and, in some cases, non-existent within
the retailers interviewed.
Labelling systems
There was appreciation that labels which could not be removed could present a food contact issue if the PP were
recycled into food packaging. Companies generally seemed not to have been involved in the technical details of
labelling systems in the past, although some now do seem to be asking for labels that do not impede recycling.
There was also some recognition that the food industry generally may need to change its practices in this area,
with a suggestion that specific guidelines from a regulatory agency may be helpful. One company was able to
provide contact details for a supplier of inks for packaging printing who was known to have done work on the
environmental characteristics of the inks they produce.
Food contact packaging
The fact that food grade PP was commonly used in non-food packaging was recognised by several retailers, with
one insisting on it for many personal products. However there was no awareness amongst the retailers of the
generally accepted recommendation with the sector that any plastic being recycled into food contact packaging
should come 99% from prior food-contact applications. Some felt that, if a regulator issued such a guideline, it
should be followed rigorously. Others thought that, if rPP were to become available, prior food contact should
not be an absolute requirement. Provided a PP recycling scheme, operating on post-consumer waste, could be
demonstrated to provide scrupulously clean plastic that would meet their food performance standards, they
would not be concerned about prior use. Some companies were surprised that such a recommended minimum
threshold exists. One thought it illogical, since some food-stuffs, for example those with high fat contents, could
lead to migration effects that were as significant to the polymer as contact with non-food products.
2.3.2 Food manufacturers
Food manufacturing takes two broad forms and there is not a clear-cut division between the two. Whilst some
manufacturers operate in one or other area, some will operate in both. The distinction is important in terms of
the role food manufacturer’s play in the packaging supply chain.
1.
Manufacturers of ‘own brand’ goods for major retailers described their role very much in terms of
responding to the requirements of their retail customers. They generally seem not to have the
technical expertise to give detailed technical specifications to packaging manufacturers but relied
on them to provide packaging that will be fit for purpose; and
2.
Manufacturers of household name brands that will be stocked by retailers seemed to have a
greater level of knowledge about plastics although, even here, their role seemed to be to work with
a packaging supplier to achieve an acceptable form of packaging, rather than issuing firm
Scoping study into food grade polypropylene recycling
30
specifications of grades and properties. The importance of colour was mentioned by several
manufacturers, who saw it as an important aspect of their brand identity and product marketing
even if, as they recognised it to be, it is an impediment to effective recycling. Packaging colour is a
key method of product differentiation and therefore of particular value to brand owners rather than
for private labels supplying retailers own-brand products.
Food manufacturers commitment
In many cases, views on use of rPP were similar to those of the retailers. Little rPP is actually used because there
is little available currently. If it were available, and provided it came from an accredited recycling system and
met all food standards, most would be prepared to use it. However the level of enthusiasm for rPP clearly varied
between the companies interviewed. Some companies had a clear commitment to use of recycled materials and,
if rPP became available, they would evaluate it proactively. Others were interested in recycled material as a
means of extending the options available to meet retailers’ requirements and, possibly, as a means to contain
costs. Some thought that the views of their retail customers could be the important factor in deciding to use rPP.
A small number seemed to be very reluctant to use it, due to their perceptions of the practicalities of recycled
material. They thought the range of colours in which PP appears and the range of labelling systems that are in
use would lead to rPP just not meeting their own requirements or those of their retail customers. Even where
discoloration was not the issue, the likelihood of rPP being noticeably less clear than virgin PP was seen as an
issue. There was also a recognition that additional colouration costs would occur to achieve a particular package
appearance.
Switching to other polymers
Several manufacturers reported a drift away from PP in the recent past to, usually, PET. A common reason given
was that PET is clearer and therefore fits with consumers’ preconceptions that clarity of packaging indicates
quality of foodstuff. Some also said that PET recycling systems were already established. The pressure for this
seems to have come from the retailers, although it was not reported as an important issue in the interviews with
them. One manufacturer of household name products reported making this change for their own marketing
benefits opposite competitors. The trend was expected to continue, although there were some food companies
who were strongly resisting it. They believe PP is the appropriate packaging for some applications and that the
solution lies in establishing sensible PP collection and recycling systems.
Labelling systems
Many of the food manufacturers recognised that the labelling systems currently used may be an obstacle to
effective recycling. Some systems are material specific to either PET or PE, for example, self-adhesive labels or
labels on an outer wrapping film. Additionally, many use direct printing or in-mould labels. Usage of these is
probably increasing, even though some companies recognise the subsequent impact on recyclability. PP
substrates can be used for the latter but, in all cases, inks, varnishes, photo-initiators and other materials will not
be certified as food grade. One manufacturer commented that other recycled polymers and recycled cardboard
are now starting to exhibit noticeable levels of contaminants from the printing used in prior applications and
would expect rPP to follow the same trend. Few of the food manufacturers appeared to have investigated
alternatives that would be food compatible and none could report any specific development work being done in
this area.
Food contact packaging
None of the food manufacturers interviewed seemed to be aware of the generally accepted recommendation
within the sector that any plastic being recycled into food contact packaging should come 99% from prior food
contact applications. Some were cautious about this but others commented that, if rPP were to become
available, prior food contact need not be an absolute requirement. Provided a PP recycling scheme was fully
accredited and could demonstrate that it provided scrupulously clean plastic that would meet their food
performance standards, they would not be concerned about prior use. Some saw the retail customers as taking
the final decision on this issue.
2.3.3 Packaging manufacturers
Switching to other polymers
Packaging manufacturers tended to reinforce the view expressed by some of the food manufacturers that there is
a move from PP packaging to either PET or HDPE. Both of these other polymers have well established collection
and recycling systems in place. The greater clarity of PET was also a factor in some cases. The label and sleeve
Scoping study into food grade polypropylene recycling
31
types used with PET and HDPE packaging both have effective and established removal strategies (caustic
washing and air separation) which have been demonstrated to achieve good separation yields.
Packaging manufacturers commitment
They were clear that very little rPP is available and therefore very little is currently used. One company reported
importing some rPP material from Germany for use in non-food packaging. If it were to become available within
the UK, then it would be examined to see if it offered any advantages for food packaging, although there was
clearly considerable caution as to the need to scrupulously demonstrate that the rPP met all food standards. One
manufacturer pointed out that costs to the companies in the food supply chain that would arise from a packaging
related food contact problem could run into hundreds of thousands of pounds in direct costs plus even more in
adverse publicity and loss of reputation. Any polymer processor supplying rPP for use in food packaging would
need to be well indemnified. It was suggested that the only practical way forward would be to use a small
proportion, for example 10% rPP with virgin PP and then increase over time as the tonnages available and the
confidence in the consistency of the rPP increased.
Labelling systems
The problems that direct print or in-mould labelling systems can create for recycling were well recognised by this
part of the supply chain. Companies stated that food compatible materials were used for substrates, inks,
varnishes and other materials, although the reason given was to prevent off-set transfer from the outer surface
of one container to the inner surface of another when they are stacked during storage prior to filling. There was
no knowledge about the degradation products that could be produced from inks during plastic recycling but
contacts were provided at major labelling or ink suppliers for this to be followed in more detail.
Food contact packaging
One packaging manufacturer said they were aware of the generally accepted recommendation within the sector
that any plastic being recycled into food packaging should come from at least 99% from prior food contact
applications and fully supported it. Even where there was no knowledge of the generally accepted minimum
threshold, it was thought to be a sensible position to take and one that packaging manufacturers would follow.
One company was adamant that they would prefer to confine the use of rPP from UK sources to non-food
packaging. There was no recognition that such a chosen application could conceivably yield levels of migration in
excess of limits of concern.
2.3.4 Labelling system suppliers
Grades of ink
Ink manufacturers recognise that labelling for food packaging is a complex issue. There are grades of ink
available that are described as ‘food-compatible’ or ‘low-migration’. This means that the rate of migration
through the packaging is low enough to not present a food hygiene issue within the shelf life of the foodstuff, or
to prevent off-set transfer from one item of packaging to another arising during the storage of the packaging
before filling. ’Standard’ grades of ink exhibit higher migration rates through plastics and are therefore not
described as ‘food-compatible’. However, according to one ink supplier, some packaging companies do use them
for food packaging.
Food contact packaging
The discussions held with the sector for this project found that with one exception which is discussed below, ink
manufacturers do not produce inks that are approved for use in direct food contact situations. They are also
aware that inks will degrade at the temperatures encountered in a plastics recycling process and that the
degradation products may well be harmful. For example, the pigment in yellow ink (i.e. margarine tubs) will
degrade to dichlorobenzidine, which is a known carcinogen. The European Printing Inks Association (EuPIA), the
trade body for this industry sector, supports this view. They are clear that any use of rPP for food packaging
would need very specific testing with the foodstuffs concerned in order to demonstrate that there were no food
hygiene issues. No distinction was drawn from potential different sources of ink i.e., from direct printing and inmould labelling.
One supplier of in-mould labels uses PP substrates printed with inks that do not have food contact approval. He
overcomes this by using a top coat of a lacquer that does carry food-contact approval but expected there would
be problems with the decomposition products of both the inks and the lacquer if PP packaging was recycled.
Scoping study into food grade polypropylene recycling
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The UK Food Standards Agency’s (FSA) work has been concerned only with migration through packaging into
food, rather than with the composition of inks. While there are currently no specific controls on inks that may be
used for food contact applications, they are subject to the general requirements of Commission Regulation
1935/2004. This requires manufacturing practices not to allow ink constituents to migrate into food in quantities
that could endanger human health or affect the nature or quality of the food. The FSA has stated that, should
inks enter a recycling process as a result of having been applied directly to the source plastic, the recycler will
have to remove any substances not on the list of approved substances in Commission Directive 2002/72/EC, or
demonstrate that they are present in concentrations that do not pose a risk to human health.
At present, these problems have not arisen with HDPE or PET packaging since labelling systems have been
chosen which can be easily removed during recycling, i.e. stuck-on labels or external sleeves. The ink
manufacturers see PP packaging as a much more difficult issue due to the widespread use of direct printing or inmould labels. They see it as inevitable that substances which have not been food contact approved, or which are
definitely harmful, will be presented at the inner surface of any packaging made from rPP.
New inks
One ink supplier has developed some inks to meet new sustainability requirements. It allows paper and card to
be safely composted, although they are paler than traditional inks, are generally felt to have a “washed-out” look
and are therefore not always popular. It also has a limited range of inks that are suitable for direct food contact
and that can be used on plastic packaging. However their cost is a significant multiple of the cost of other inks
and they are only available in a limited colour range so, again, are not commonly used. The inks will decompose
at the temperatures involved in plastic recycling. No work has been done to determine the decomposition
products in detail but they will not be food contact approved materials. In principle the industry could develop
new food contact inks that would enable PP to be recycled but there would need to be a clear demand for them
to justify the development cost. For example, the cost of the toxicological tests on a new pigment, as required by
REACH legislation, is said to be between £0.5 and £1 million. If regulators took action that led in that direction, it
was thought that the food industry would respond by changing to a different type of packaging and/or a different
labelling system, rather than incurring these additional costs.
2.4
Forms of packaging
All of the companies interviewed have been willing to talk about use of PP or rPP in general. However, little
detailed information has been provided on the manufacturing processes used for making different types of
packaging and even less information on grades of PP or required properties. There are clearly differences of
approach to similar types of packaging between manufacturers. Some have commented that they only really use
a single grade of PP but meet the requirements of different forms of packaging by varying the wall thickness or
other physical features in the packaging, or by including additives. The information that has been received is
summarised below for the five packaging types that were identified during the compositional analysis part of this
project as being of most significance within the waste stream.
Microwaveable
This is a broad category of packaging and will apply to any product where high temperatures will be involved. As
well as microwavable products such as ready meals, soups and sauces, there are also a number of products that
are packed while still hot, even if they are subsequently held at refrigerator temperatures. PP is also used for
cups in hot drinks vending machines.
Some companies use homopolymer whilst others use a homo and co-polymer mix. One company quoted
proportions of 60-40. Barrier layers are not used in these applications. Several food companies said they use
single layer plastic but one referred to a triple layer product. The reason for using a triple layer pack is that the
skeletal waste left from thermoforming pots from sheet material can be recycled back into the inner layer. One
packaging company has advised that, if the sheet and the pots are made in the same factory, then the skeletal
waste can legitimately be recycled within the factory operation. If the sheet material is delivered to a food
manufacturer who produces his own pots, then the waste cannot be recycled.
Sauce bottles
As well as sauces, this would include other products such as salad cream. These use homopolymer with an
Ethylene Vinyl Alcohol (EVOH) barrier layer and are made by extrusion blow moulding. One company said the
EVOH represents less than 0.1% of the total package weight and therefore should not be a problem for recycling.
However another suggested there are adhesive layers at each PP-EVOH interface which may present problems,
Scoping study into food grade polypropylene recycling
33
particularly if they degrade during recycling. There is a clear move from PP to PET in this category. It provides a
clearer package product, permitting store shelf package differentiation against the ‘hazier’ polyolefin sauce
bottles.
Ice cream tubs
These are made from homopolymer or from PP-PE copolymer. Some companies have talked about designing the
package to possess adequate low temperature impact strength at low package weight. The use of a consistent
thin wall design and through use of good design principles permit these conflicting requirements to be met.
Others talked about inclusion of plasticisers as the means of avoiding brittleness, even though this can lead to
rather opaque plastic. One company interviewed used PP-PE copolymer to achieve adequate low temperature
strength with a thin-wall.
Margarine tubs
This category covers a wider range of products than just margarine, with butter, cream, custard, yoghurts and
other deserts also included. The generic characteristic is that they are food stuffs that are packed cold and held
at refrigerator temperatures.
Companies have described these as being made from thin-walled PP-PE copolymer, with no barrier layers. They
are made either by injection moulding or by thermoforming from sheet. One company has said the former is
used for premium branded products whilst the latter is used for others. Both single-layer and triple-layer sheets
are used for thermoformed tubs, with skeletal waste being recycled into the middle layer. However some
retailers do not like triple-layer materials for thin-walled packaging due to the risk of pin-holing at corners or
other sharp changes in profile, which would allow food to come into contact with the middle layer.
Trays
These are generally homopolymer, without barrier layer, and are made by thermoforming. Otherwise, they seem
to vary significantly depending on the foodstuff. High clarity packaging has been said to be important for meat
products, leading to high levels of plasticiser being used. Coloured trays are used for vegetables.
2.5
Labelling systems
Labelling systems seem to be recognised as a problem for recycling by companies at all stages in the supply
chain. However the responses to the problem vary enormously. Some use labels on an outer wrapping film
rather than on the actual food container, so as to segregate the non-recyclable elements from the more
recyclable part of the packaging. Others regard the labelling as an important part of the brand image or are
concerned to maximise the efficiency of their manufacturing process. This may result in in-mould labelling being
chosen, even though it is recognised as not the best choice if the plastic packaging is to be recycled.
The result is a wide variety of labelling practice. Nothing has been found to suggest that “package X normally
uses label Y”. On the contrary, different labels are used on essentially the same type of packaging, depending on
the preferences of the companies involved.
2.6
Conclusions
The key conclusions from the supply chain work are as follows:
„ Little rPP is used because little is currently available. Most companies would be prepared to use it
provided a recycling system existed that was demonstrably capable of meeting regulatory standards and
company food performance standards;
„ There is very little knowledge of the generally accepted recommended threshold for plastic being recycled
into food contact applications to have come 99% from prior food contact applications. A few companies
think this is sensible but many would have no problems with PP recycled from non-food applications, again
provided the necessary regulatory and performance standards were met;
„ A move from PP to PET has been reported, although not quantified. Retailers seem to have led this move
on the basis that PET is clearer, and therefore plays to consumer perceptions over food quality, and in
view of there being established recycling schemes for PET;
„ Some household name food manufacturers see distinctively coloured PP as an important part of their
brand identity. They do not wish to change this even though they recognise it could be an obstacle to
recycling;
„ Labelling systems are recognised as an obstacle to recycling. Some companies have chosen stuck-on or
sleeve labels, similar to those used on HDPE or PET, to avoid the problem. However there is widespread
Scoping study into food grade polypropylene recycling
34
use of direct-print or in-mould labels. Some companies use these latter types of labels as a part of their
brand identity, regardless of the issues that may be raised for recycling; and
„ This project found there were virtually no printing inks approved for food contact situations. Those that
do exist are expensive and have a limited range of colours and are therefore rarely used. Labels are
therefore at the non-contact surface or are protected by a top-coat of a lacquer that is approved for foodcontact. Of the inks that are used some, at least, will decompose to potentially harmful products during a
PP recycling process. Use of rPP in food contact situations will require specific testing to establish that
inks or decomposition products, or any other chemicals used in labelling systems, have either been
removed during recycling or are not present at the new food contact surface in a way that creates food
hygiene issues.
Scoping study into food grade polypropylene recycling
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3.0
Phase 1 - Large scale technical recycling trials
3.1
Methodology
3.1.1 Large scale recycling trial
Axion worked closely with Greenstar WES during March 2009 to deliver the phase 1 production scale recycling
trials, using the commercial HDPE milk bottle recycling plant in Teesside. The technical trials covered the
separation, cleaning and reprocessing of baled PP derived from the Jayplas Plastics Recovery Facility (PRF) in
Leicestershire.
The core aims of the trial programme were:
„ To separate a 10te batch of food contact PP containers from baled PP supplied by a typical large UK
packaging PRF;
„ To “hot caustic wash” this material using a standard recycling process of the type used for HDPE
packaging in the UK;
„ Take the washed food contact PP flake to steady state in the EREMA vacuum degassing process that is
typically used to produce food grade HDPE recyclate; and
„ Evaluate the resulting PP pellet for food contact suitability.
Secondary aims of the trial programme were:
„ Undertake an assessment of a hot-water wash rather than a caustic soda wash. Greenstar WES has
demonstrated the effectiveness of this promising improvement for HDPE reprocessing in terms of the
environmental impact of the process;
„ Greenstar WES has modified its Vacurema to provide enhanced volatile extraction. An assessment was
made of the extraction using its Vacurema using a conventional process to ensure the results and findings
were applicable to comparable operators within the sector; and
„ Scoping of a ‘provisional challenge test’ for rPP food packaging. Challenge testing seeks to replicate the
most demanding chemical conditions anticipated during unconventional consumer use of packaging and
then check the efficiency of the removal of volatiles present. The purpose of the provisional challenge test
was to generate data for future refinement in a future formal challenge test.
3.1.2 Recycling process used for the trial
The technical reprocessing trials were conducted using the full scale HDPE recycling plant operated by Greenstar
WES at Teeside. The process configuration used for the trials is summarised below in Figure 23.
Figure 23 Greenstar WES PP recycling process configuration
Scoping study into food grade polypropylene recycling
36
3.2
Feed materials and product yields
Bales of PP supplied by Jayplas were broken open and subjected to hand picking to separate food contact from
non-food contact material. The hand sorting processes used are described in more detail in Section 3.2.4 below.
As stated earlier, some of the material was subjected to an initial positive hand pick in order to identify and
separate food contact material and then a negative hand pick to further remove any mis-sorted items. The
remainder of the material was only given a negative hand pick in order to remove obvious non-packaging items.
The hand sorted (positive then negative picked) material was then passed through the Greenstar WES proprietary
washing and drying process, which includes a wash process supplied by Sorema of Italy. The process separated
and cleaned the target PP material and separated it from other plastics and other gross contaminants present.
The washing and drying process produced a clean washed flake, which was then fed to the Vacurema vacuum
extraction and extrusion process. The equipment used was a VACUREMA ADVANCED 1716TE supplied by EREMA
of Austria. This comprises two vacuum chambers in which the flake is stirred and heated under vacuum, followed
by an extruder with a melt filter with back flushing capability.
Figure 25 Vacurema Advanced extrusion system
3.2.1 Feed material
The mixed baled PP feed material used for these trials was supplied by Jayplas, with 50 tonnes of this material
being used during the trial. Prior experience of HDPE and PET bottle sorting led to an expectation that a high
yield of readily identifiable food contact PP applications could be expected. In practice, the proportion of the bale
that could be readily hand sorted formed about 25%. It was decided to increase the sample size to also study
the negatively picked (mix of food contact and non-food contact items) to test a range of processing conditions.
A smaller sample of material was also generated, from subsequently positively picked material. This was to yield
close to certain levels of food contact packaging in order to simulate optimised sorting conditions and material
suitable for migration and organoleptic (taste and odour) testing.
3.2.2 Negative pick food and non-food contact material
26 tonnes of PP bales were subjected to a negative hand pick in order to provide feed material for the trials. The
aim of the negative pick was to remove obvious items of the incorrect polymer type, black items which could
Scoping study into food grade polypropylene recycling
37
cause likely difficulty with subsequent NIR automated sorting, non-packaging items and containers having
unsuitable prior contents such as paint.
3.2.3 Positive pick food contact
24 tonnes of PP bales were subjected to a positive pick to identify and extract containers that had clearly been
used for food contact applications, such as meat trays, margarine tubs, soup containers, beverage bottles and
sauce packaging. Overall the positive picking exercise recovered 5.6 tonnes of positively picked material from 24
tonnes of baled PP-rich material.
The quality of the intensive hand sorting was measured and yielded between 0% and 24% non-food contact
material. The average of 4.1% fell short of the below 1% threshold, so a further negative pick was required to
ensure that the target of 99% or higher value of prior food contact material was met. Material was then fed
directly to the washing step.
The output of extruded food contact pellet after the washing and extrusion stages was a total of 3.17te. This
gave an overall yield of 13% extruded pellet from the feed material. 2.25te of the material was classed as ‘good’
food contact pellet. A further 0.92te was not classed as food contact material because it represented transitional
mixed material, containing both non-food contact material and positively picked 99% food contact material.
The overall mass balance for the positively picked material is shown on the next page in Figure 26.
The 18.1te of non-food contact material from the positive picking process was used to set up the washing and
extrusion processes at the start of the trial. From this quantity 2.25te of start-up pellet was generated following
Vacurema extrusion processing and 5te of washed flake was also produced.
Scoping study into food grade polypropylene recycling
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Figure 26 Mass balance for the positive pick process
Scoping study into food grade polypropylene recycling
39
3.2.4 Hand sorting process
All of the hand sorting in this trial was based on qualitative distinctions between containers which could be
interpreted differently by individual sorters. This made the sorting process inherently variable. Language barriers
did not appear to be a problem for positive picking. Most of the sorting staff had very limited English language
skills. It was very difficult to assess the composition of the reject stream from the positive picking process as
there was no easy access for obtaining samples of this material.
The biggest issues with the hand sorting process were:
„ Efficient bale breaking;
„ Surging when feeding: new sorting staff required extended assistance to learn how to feed material
consistently;
„ Sorting staff training, particularly where individuals do not have English as their first language; and
„ Staff motivational issues, as hand sorting is an unpleasant job to undertake.
The most effective quality control technique appeared to be a visual inspection of the bags as they were filled.
Other observations from the hand sorting process were:
„ Some non-food packaging was difficult to identify, for example:
o Green tea shampoo (this was read as tea and therefore considered as food contact);
o One particular washing powder tub lids seemed to make all sorting staff think it was an ice
cream container; and
„ The negative pick sorting instruction – to remove non-packaging items and packaging of concern - was
not intuitive like ‘pick food contact’.
Section 2.2.4 of this report provides a consideration of the commercial aspects of hand sorting.
3.2.5 Mass balance observations
Hand pick
This study sought to achieve the generally accepted minimum threshold within the sector of 99% food contact
grade polymer, which in practice is taken to mean “was previously in contact with food” since the provenance of
the material cannot otherwise be readily identified. Whilst non-food contact PET is seen as relatively
unproblematic, since all PET currently manufactured is food contact quality regardless of the application and PET
inherently has a low capacity to absorb potential contaminants. With a lack of universal food contact approval
and a much higher capacity of absorb contaminants, polyolefins such as PP and PE, are see by the regulators as
much more problematic. Consequently, a very efficient removal of material not previously in contact with food is
required on a precautionary basis.
There is provision within the legislation to make a technical argument that testing and quality control systems
could form an effective barrier to the inclusion of unsuitable additives to food contact rPP, but as this lacks the
robustness of the previous food contact route, it is difficult to place this well within a Good Manufacturing Practice
(GMP) regime.
EFSA has currently not approved any food contact recycling process, although it is assumed that the current
commercial HDPE milk bottle operations that do sort to 99% milk bottle purity will be accepted. Final yields of
23% (unwashed damp packaging, inclusive of labels) following hand picking were significantly lower than the
higher 80% levels achieved with HDPE / PET bottle processes. However, reasonable agreement was achieved
with the compositional analysis part of this scoping study. Practical sources of this apparent discrepancy include
the following:
„ Residual contents in packaging especially domestic cleaning items;
„ Accuracy of the pickers recognition of food contact PP items;
„ The efficiency of the initial bale-breaking operation leading to packaging items becoming crushed together
and becoming hard to separate;
„ Operator positioning and the design of the work stations was also a significant issue; and
„ Excessive surging and ineffective distribution of the material on the belt was a problem since individual
articles are perceived more easily.
Scoping study into food grade polypropylene recycling
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Washing / drying
Greenstar WES operates the process commercially for HDPE and generally expects a washing /drying yield of
80%. The flake yield in this study yielded 67% for food-contact items and 50% for non-food contact items. The
probable sources of this drop include the following:
„ Fluids packaged using PP can be ‘stickier’ than those used with HDPE and so remain in contact at point of
disposal;
„ Labelling of PP packaging can be more intricate and extensive including in-mould labelling; and
„ PP packaging can include components of other polymer types, in the form of heat-seal lids and trigger
sprays.
Extrusion
Losses at the melt filtration stage averaged around 9.5% once the system was purged and had reached steady
state. This contrasts with around 2% when Greenstar WES process baled natural HDPE.
The EREMA extruder at Greenstar WES uses a sophisticated melt filter with a back-flush system. During the trial
the back flush system was triggered much more frequently than when running recycled HDPE or PET. EREMA’s
experience is that the normal screen change rate for recycled PET with a 100µm screen is one back-flush per
hour. This trial used a coarser 200 µm screen and recorded nine to ten back-flushes per hour, with a filter
change every hour. Each back-flush used about 7kg of material.
EREMA took sample screens from the trial, boiled them in xylene to remove the residual PP and took photographs
of the un-melted residues on the screen.
Figure 27 250µm screen pack
The material caught on the screen was analysed by Greenstar WES using a Fourier Transform Mid Infra Red
(FTIR) spectrometer. It appears that the main contaminant is 100µm polyamide (PA) film. This is possibly due
to the top barrier film used within long life meat “modified atmosphere” packaging. The total mass of this
material in the washed flake is probably relatively small but because of its high aspect ratio it is very good at
blocking filters. These filtration problems could probably be addressed by using a high capacity continuous filter
such as the EREMA LASER FILTER or Ettlinger ERF.
Table 4 PP yield comparison with HDPE recycling process
Loss from hand sorting process
Loss from wash process
Loss from extrusion process
Food contact PP
77%
35%
9.5%
Negative picked PP
5%
43%
9.5%
HDPE
~5%
~20%
~2%
Scoping study into food grade polypropylene recycling
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3.2.6 Plant throughput
Hand picking
A positive hand sort means that every item that is to be recycled must be picked off the belt by the sorting staff,
which limits the capacity of the overall process to the picking capacity of the individual sorters. The bulk positive
pick for this trial indicated an average picking rate of 26kg/hr per sorter. This could possibly be increased to
around 50kg/hr with improvements to the bale breaking and feeding system and improvements to the
ergonomics and comfort of the picking stations. A further negative hand sort was required to remove around 4%
incorrectly picked containers as the material was fed into the wash process. The inefficiency and high cost of the
sorting methodology used would certainly be prohibitive if used commercially.
Washing and extrusion
The feed rate to the washing and extrusion steps was very similar to the throughputs measured by Greenstar
WES when processing HDPE material. However the output rate was significantly lower, roughly in proportion to
the higher loss of yield when processing PP compared to HDPE as shown in Table 4.
3.2.7 Provisional challenge test
The aim of a challenge test is to quantify the cleaning efficiency of a recycling process for the types of
contaminants which are most likely to be found in practice. In a challenge test the trial material is soaked for a
period of several days or weeks, depending on the ambient temperature and polymer type, in a ‘cocktail’ of
chemicals called surrogates. The surrogates are selected to simulate the type of chemicals/substances which
may potentially be found as contaminants in the packaging waste stream, either through external contamination
of packaging during use or through misuse of packaging in a second use, for example for storage of paint
thinners or fuel. The surrogates therefore need to cover a range of chemical physical properties for instance,
typical volatilities or polarities of likely migrating contaminants.
Surrogates are added to the trial mixture at concentrations significantly higher than are likely to be found in
practice, in order to test a ‘worst case’ scenario. For the provisional challenge test undertaken as part of this
scoping project, 100g of each of the surrogate chemicals was added to 100kg of flake, giving a concentration of
1000ppm (0.1%) in the sample for each chemical.
A provisional challenge test was the agreed approach rather than a formal challenge test. This was due to no
suitable large scale study of UK post consumer PP food packaging previously being conducted so there was
insufficient data available in advance of this project that could be used to predict exactly which surrogates should
be used. It was also not possible to predict accurately exactly how much challenge test flake would be required
for the high output machine being used. For both these reasons the decision was taken to conduct an internal
provisional challenge test as part of the phase 1 processing trial at Greenstar WES. The objective of the
provisional challenge test was to gather sufficient data for the Fraunhofer IVV to be able to design a formal
challenge test should the phase 1 trials show that the plant as configured was capable of processing the target
input material to food grade pellet.
The surrogate chemicals chosen for the provisional challenge test were similar to those normally used in
challenge tests for HDPE, with two additional surrogates added:
„ Surrogates: all identifiable by headspace gas chromatography (GC) – toluene, chlorobenzene, methyl
salicylate, phenyl cyclohexane, benzophenone and methyl stearate; and
„ Additional surrogates: dioctyl adipate which requires use of solvent extraction GC to evaluate and
limonene which can be found in food packaging (and thereby not strictly a surrogate) but can be readily
identified by GC.
The surrogate chemical/polymer flake mixture was generated over a two week period. A steel drum held at
ambient temperature with daily rolling was used to contain and to further disperse the surrogate constituent
solvents. Final inspection of the mixture suggested that a satisfactory dispersion had been achieved.
During the trial, the provisional challenge test material was added to the washed flake feeding into the Vacurema
extrusion system once the process had reached steady state.
Scoping study into food grade polypropylene recycling
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3.3
Contamination removal results
The headspace chromatography results from both Greenstar WES and the Fraunhofer IVV did not show the
presence of any surrogate material within the limit of detection (LOD) of this technique. This means that it was
not possible to quantify the cleaning efficiency for high levels of single shot contamination. The most likely cause
of this was a combination of lower than expected absorption of the surrogates into the contaminated flake due to
low ambient temperature, combined with higher than expected dilution of the surrogates through cross-migration
with the uncontaminated material on the large production plant.
However it has been possible to measure it under normal operating conditions. This was done by examining the
headspace results for a number of oligomers which could be detected in the flake and pellets, as well as the
virgin PP. It was also possible to use the limonene peak, which has a retention time = 8.45 minutes in the IVV
GC and could be clearly seen in all of the rPP flake and pellet samples.
Figure 28 shows the cleaning efficiency for the food contact material was only slightly higher than for the
negative material and that it was nearly constant across a wide range of volatilities. This means that the cleaning
efficiency is effectively independent of input concentration and only marginally dependent on increases in vacuum
residence time, beyond the normal steady state operation of the Vacurema.
Figure 28 Cleaning efficiency based on selected headspace peak areas
Looking at the pattern of peak heights, shown in Figure 29, it can be seen that there are large differences
between the values for the two virgin samples tested (homopolymer and copolymer). Although this is thought to
be more of a reflection of process variations during post reactor processing at the polymer manufacturers, rather
than a generic difference between homo and copolymer per se.
Scoping study into food grade polypropylene recycling
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Figure 29 Selected relative peak areas for oligomers and limonene
Comparing the homopolymer to the rPP pellet in Figure , it can be clearly seen that in most cases the level of
oligomers in the rPP is well below the levels found in the virgin material. This indicates that the Vacurema
process has a high capacity for removal of low molecular weight species.
Figure 30 Relative peak areas of rPP and PP homopolymer
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What can be seen from the comparison between positive and negative pick inputs and outputs in Figure 31 is
that, with the notable exception of limonene, the pattern of oligomer concentrations is relatively constant despite
the radical difference in the type of packaging present.
Figure 31 Relative peak areas for positive and negative pick flake and pellet
However since a modest difference could be seen between the residual levels in the positive and negative pick
pellets, it was felt important to compare samples with comparable vacuum histories. This was because the
positive pick flake was subjected to a longer period of vacuum processing due to the difficulties in obtaining a
good seal to the extruder vent ports during the delivery of the technical trial at Greenstar WES.
Fortunately a number of samples taken during process stoppage and shutdown of the negative pick material were
available. As can be seen below, under similar vacuum conditions the efficiency for both sorts appears to be
similar.
Figure 32 Comparison between positive and negative pick pellets with a long vacuum history
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Summary
The key results from the contamination removal work are:
„ The cleaning efficiency of the Vacurema, as configured for the technical trial at Greenstar WES, under
steady state conditions was found to be 92%;
„ Excluding the 11.03 minute peak, where the level of residual oligomer was consistently but unusually high,
a cleaning efficiency of 97% was achieved for the positive pick material. It is felt that the major
contributing factor here was, as discussed, the increased residence time under vacuum;
„ It was not possible to investigate the effects of chamber temperature, but basic diffusion physics would
suggest that raising this by an additional 10°C, which should not run an unacceptable risk of flake
clumping, would be very helpful; and
„ The method of determining the cleaning efficiency via the polymer oligomer concentrations opens up the
possibility of continuous monitoring during production to complement process validation tests using
artificial surrogates.
Full details of the test work conducted by the IVV can be found in Appendix 2.
3.3.1 Label/ink removal products
The colourmetric analysis of the rPP showed that the material contained substantial amounts of titanium dioxide
as well as yellow organic pigments. It has not been possible thus far to determine whether these pigments are
predominantly from polymer pigmentation or residual printing ink. The latter would be of significant concern
since these would be thermally unstable as well as not being approved for direct food contact. The presence of
such pigments suggests that difficulties would be encountered in the possible subsequent colour matching of this
material, at reasonable cost, to deep black or white colours.
Decomposition of diarylide process yellows to 3,3-dichlorobenzidine could have been detected down to 2ppb
using the standard photometric test for PAAs (polyaromatic amides). However, this was not tested for during this
programme of work.
The thermal stability of pigments used in inks varies considerably, however it would be possible to produce inks
where all of the component colours would be stable at extrusion temperatures. That said, degradation products
from the binder systems used, would still be a concern and the cost of some of the thermally stable pigments is
very much higher than the standard ones.
The thermal stability of inks is less important for HDPE milk bottle recycling for two main reasons. Firstly the
labels used on milk bottles are relatively easy to remove, meaning that relatively little ink passes into the extruder
and secondly the pigments used for the two main colours, that is blue and green, have very good thermal
stability. Yellow pigments, which are a cause for concern in PP packaging, tend not to be found in HDPE
packaging.
3.4
Polymer properties
3.4.1 Physical property testing
Test bars were moulded from a selected number of samples of rPP pellet made from:
„ Positively picked food contact material;
„ Negatively picked food and non-food contact material; and
„ The reject fraction from the positive hand sort (which is depleted in food contact material). This is the
material that was used for set up of the washing and extrusion system.
Each material was tested for:
„ Melt Flow Rate (MFR) using a 2.16kg weight at 230˚C;
„ Notched and un-notched Izod impact strength (ISO180 A / U);
„ Titanium and Calcium concentration by X-ray Fluorescence (XRF);
„ Tensile strength, elongation at yield and break; (ISO 527-1); and
„ Flexural modulus.
The results of these tests are summarised and assessed in Table 5.
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Table 5 Physical property test results
Physical property test results Positive pick pellet (99% food contact) Octabin #1 Negative pick pellet (contains both food and non‐food contact) Drum #6 Octabin # 4 Bag #6 (17/03/09) Bag #3 (19/03/09) Depleted flake from positive pick (contains less food contact) Bag #1 (05/03/09) MFR reading (g 10min‐1) 10.14 8.28 8.40 7.08 8.03 12.77 Notch Izod Impact 25.0 kJ/m2 15.1 kJ/m2 18.3 kJ/m2 17.6 kJ/m2 21.2 kJ/m2 15.7 kJ/m2 Standard Deviation 4.6 kJ/m2 1.5 kJ/m2 5.0 kJ/m2 8.2 kJ/m2 8.4 kJ/m2 5.8 kJ/m2 Unnotched Impact 4 x NB 4 x NB 4 x NB 5 x NB 5 x NB 3 x NB Ti ‐ ppm 7982 7462 6751 5140 4893 4992 Ca ‐ ppm 2195 1851 1513 1148 1052 558 Tensile Strength 27.4 MPa 27.5 MPa 27.7 MPa 27.6 Mpa 28.6 MPa 28.2 MPa Elongation at Yield 9.1% 10.2% 9.2% 10.1% 10.6% 11.1% Elongation at Break 78.8% 110.2% 70.3% 107.0% 251.2% 160.8% Flexural Modulus 1.59 GPa 1.57 GPa 1.57 GPa 1.56 Gpa 1.56 GPa 1.49 GPa Scoping study into food grade polypropylene recycling
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The key observations of the physical property testing results are as follows:
„ Levels of calcium and titanium appear to be linked and are higher in the positive pick material, perhaps
because both titanium dioxide and calcium carbonate are used in food contact containers to produce
opacity. Candidate calcium species include calcium stearate used as a lubricant / wetting agent and
calcium carbonate used as a film anti-block additive;
„ The flexural modulus results are consistent with unfilled PP;
„ Melt Flow Rate (MFR) and impact strength appear broadly similar between negative and positive picked
material; and
„ Elongation at break is somewhat better for the negative pick material than the positive pick material. This
appears to be due to composition differences rather than problems with melt filtration.
3.4.2 Colour
The colour of the test bars used in the physical property tests was measured using a colour spectrophotometer,
which translates the colour measurements into standard colour measurements of:
„ dL – lightness;
„ da – yellow /blue: the yellow spectrum gives a positive result and the blue spectrum gives a negative
result;
„ db – red/ green: the red spectrum gives a positive result and the green spectrum gives a negative result;
and
„ dE – root mean square of dL, da and db.
A dE colour difference of 1.0 is generally accepted to be the minimum colour difference that is visible to the
human eye.
Table 6 Colour measurements
Positive pick pellet
(99% food contact)
Octabin #1
Negative pick pellet
(contains both food and
non-food contact)
Drum #6 Octabin # 4
Bag #6
Bag #3
(17/03/09) (19/03/09)
Depleted flake
from positive
pick (contains
less food
contact)
Bag #1
(05/03/09)
dL
(lightness)
100
101.5
97
80
83.5
84.9
Da
(yellow +/blue -)
0
-2.9
-1.3
-2.7
-2
-4.2
Db
(red+/green-)
0
-2.7
-2.6
-14.6
-15
-17.4
0
2.6
2.7
16.5
15.3
15.7
dE
The key observations of the colour measurement results are as follows:
„ Within each category the colour seems to be reasonably constant, as there is a relatively low delta E
between samples even considering the time difference between the sampling of them;
„ There was a significant difference in colour between the positive and negative picked material, with the
positive pick material being lighter in colour than the negative pick material. It was not possible to
determine the source of this colour difference at this stage; and
„ The material has high opacity; no difference was detected in the lightness colour difference (dL) over
black and white backgrounds at 700µm colour wavelength.
Scoping study into food grade polypropylene recycling
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4.0
Phases 2 and 3 - Investigation of potential areas for improvement
identified in phase 1
Based on the results and findings from the phase 1 trials at Greenstar WES two further phases of technical work
and demonstration trials were delivered to investigate the limiting factors identified in phase 1. The aim of the
second and third phases of work and trials was to establish why certain materials (low volatility but specific
migration relevant contaminants) were persisting into the finished rPP and how best to change the processing
parameters and techniques in order to improve their removal.
The work consisted of:
„ Phase 2: Small scale laboratory investigations; and
„ Phase 3: Pilot scale demonstration trials.
Please refer to appendix 5 for a more detailed technical report covering the work from phases 2 and 3.
Additionally trial reports for the phase 3 pilot scale demonstration trials (Sorema and EREMA) can also be found in
appendices 6 and 7.
4.1
Phase 2 and 3 methodology
The presence of small quantities of low volatility, but specific migration relevant contaminants, was the major
obstacle to achieving a high level of potential rPP addition from the phase 1 work. In particular isopropyl
myristate migrated at a level of 190ppb in isooctane but the threshold is 10ppb, so there would be 19 times too
much isopropyl myristate at 100% rPP. This means that rPP levels would need to be diluted at a rate of 20:1 (no
more than 5% rPP recycled content) in fat contact packaging such as margarine tubs. This estimate is made by a
pro-rating approach but would need to be checked and confirmed experimentally.
The objective of the second and third phases of work and trials was to establish why these materials were
persisting into the finished rPP and how best to change the processing parameters and techniques in order to
improve their removal.
The work was divided into two interlinked phases; the first (phase 2) being a comprehensive evaluation of the
effects of processing conditions and packaging material selection at laboratory scale. The second (phase 3) being
a pilot scale implementation of the findings from the small scale work.
The small scale laboratory work (phase 2) focused on:
„ Dependence of vacuum degassing of the flake on temperature (potential to improve vacuum chamber
cleaning efficiency);
„ Dependence of melt degassing (potential to improve melt cleaning) on;
o Temperature;
o Residence time;
o Throughput;
o Rate of surface renewal; and
„ Risk factors associated with food contact and non-food contact packaging input (potential to reduce input
contamination by improved sorting).
The pilot scale work (phase 3) also gave the opportunity to review the detailed implementation of the three
critical phases of the recycling process:
„ Selection of food contact packaging;
„ Washing to remove surface contamination; and
„ Vacuum degassing, melt filtration and extrusion.
4.2
Phase 2 - Laboratory investigations
The principle conclusion of the phase 1 investigations (Greenstar WES technical trials) was that the Vacurema
system had once again proved to be very capable of removing volatile contaminants up to limonene. Phase 2
was an initial laboratory investigation to assess the potential for various process modifications to be evaluated in
the phase 3 additional pilot scale trials.
4.2.1 Results from Phase 2
In the previous work (phase 1 trials) on the flake input material it was difficult to establish clear levels of input
contamination due to the small number of flakes that could be sampled and the random variation between them.
Scoping study into food grade polypropylene recycling
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Headspace analysis typically uses a sample of ~1g (30 flakes) and so has maximum sampling errors of +/- 18%,
whilst at 50 to 100g (1,500 to 3,000 flakes) this falls to +/- 2.5% and +/- 1.8% respectively.
Thus by melting and mixing a larger sample of flake in an extruder it has been possible to greatly reduce this
variation, allowing a direct assessment of cleaning efficiency for individual contaminants using GC/MS (gas
chromatography/mass spectroscopy).
Given the large number of samples to be evaluated it was decided to use extraction with 99.7% ethanol at 40°C
for 48 hours rather than food simulant migration testing. Since some of the input material was flake and others
pellets of various sizes and shapes, the samples were converted to standardised micro-pellets, in preparation for
the extraction testing, by matching the strand line speed to the throughput to ensure uniform pellet diameter.
This meant that all the samples had identical and very high surface areas, ensuring uniformly high levels of
extraction and that they could all be referenced back to the phase 1 pellet for which specific migration values had
already been determined. The relative concentration in the various samples was determined by taking the ratio
of peak heights for particular molecular ion weights.
The standard parameters used during micro pelletising were 150g/h throughput and 120rpm screw speed with
the barrel running from 120°C to 230°C and die set to 210°C. It should be noted that micro-pelletising only
works for substances which have low volatilities; otherwise an unpredictable amount of high volatility substances
would be lost during the mirco-pelletising stage.
Figure 33 Phase 2 Micro pellets and phase 1 die face cut pellets
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Figure 34 Twin screw extruder – the various processing zones can be seen along the screws
Figure 35 Twin screw extruder with both vacuum vents attached
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Figure 36 Micro-plunger extruder used to prepare standard pellets from flake
As well as being an extremely useful output of this project, this approach should also be a major help to
producers of rHDPE. It gives a quantitative basis for quality assurance, risk assessment and process development
that has previously been missing due to the inability to make a clear assessment of the input material. The
approach tracks contaminant concentration from input to output, which allows the actual cleaning efficiency of a
plant to be monitored, on a continuous basis if required. A challenge test only shows the cleaning efficiency in
response to a single catastrophic event and therefore does not provide a good picture of the response of a
system to low level pervasive contamination, which is the day to day problem recyclers of high diffusivity
polymers such as HDPE or PP are faced with.
Looking at all the flake samples tested within phases 2 and 3 only modest variations were seen between
comparable samples, indicating that the contaminants were widely present rather than being concentrated in a
small number of flakes. If this had been the case, then even at the much larger sample sizes used, only a small
number of contaminated flakes would have been present resulting in large sampling errors.
Table 7 shows selected low volatility (C12-C15 range) post contamination levels for the three samples of phase 3
washed input flake tested. This shows that input levels of low volatility contaminants found in the phase 3 flake
were much lower than those found in the phase 1 pellet.
Table 7 Levels of post consumer contaminant in Phase 3 flake compared to the Phase 1 pellet (100%)
Benzophenone
n-Hexyl salicylate
a-Hexycinnamaldehyde
Isopropyl Myristate
Sample 12
Sorema hot
wash
22%
11%
17%
33%
Sample 24
Sorema hot
wash
19%
16%
6.5%
16%
Sample 25
Sorema cold
wash
23%
12%
13%
41%
This means even prior to the Vacurema super cleaning it can be expected that the migration performance of even
the cold washed flake would be much better than the phase 1 pellet for these low volatility contaminants. Since
no significant difference could be seen between hot and cold washing, it appears that this difference was due to
Scoping study into food grade polypropylene recycling
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differences in the input flake, with the phase 3 flake simply being cleaner than the phase 1 pellet, rather than any
changes to the washing regime between phases 1 and 3.
Taking the average level for isopropyl myristate of ~30% would imply that a cleaning efficiency of approximately
85% would be sufficient to reduce the concentration to a level that would allow the packaging made from this
material to have migration levels below the required 10ppb. However in order to clean the phase 1 pellet itself a
cleaning efficiency of 95% would be required. It should be noted however that these figures are estimates based
on the extraction behaviour in 99.7% ethanol rather than the actual migration performance using food simulants.
The phase 2 testing was divided into three parts:
„ Basic vacuum degassing behaviour of the Phase 1 pellet;
„ The effect of temperature on vacuum chamber degassing; and
„ Samples of individual post supermarket packaging.
4.2.2 Basic degassing parameters
In the basic testing regime a matrix of tests was performed, in which individual processing parameters were
varied in turn whilst others were held constant. The aim of the investigative tests was to quantify the melt
degassing kinetics in order to establish the relative importance of particular parameters, issues such as thermal
degradation were considered secondary at this stage.
The basic control parameters investigated by the laboratory scale work were:
„ Barrel temperature;
„ Screw speed; and
„ Mass flow.
These parameters interact in a complex manner to influence:
„ Rate of surface renewal;
„ Residence time;
„ Fill level; and
„ Melt temperature.
Melt temperature, rate of surface renewal and residence time were found to be the most significant factors for
good extruder cleaning efficiency.
Figure 37 Extruder melt degassing cleaning efficiency
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Table 8 shows the full processing parameters for the samples in Figure 37.
Zone 3
Zone 4
Zone 5
Die Pressure
4
120
125
195
200
200
200
6.6
7
5
2
230°C
150
3.7
120
125
204
230
230
210
6
7
5
3
260°C
151
3.7
120
125
215
260
260
215
6
8
5
4
80rpm
150
4
80
125
204
230
230
210
5.5
7
5
5
200rpm
147
4.5
200
125
207
230
230
210
6
8
5
6
75g/h
73
3.8
120
125
204
230
230
210
3.8
5
5
7
Two passes
148
4
120
125
204
230
230
210
6
8
5
Sample
Vac 2
Zone 2
152
Vac 1
Zone 1
200°C
Torque
1
Throughput
RPM
Table 8 Samples for processing in the vacuum extruder system
What can clearly be seen is that melt temperature has a significant effect on cleaning efficiency but the other
parameters are also very important. The best results were obtained for:
„ Highest temperature;
„ Lowest throughput; and
„ Highest residence time (two passes).
What also can clearly be seen from this analysis is that there is a limit to effective cleaning in terms of the
residence time of the contaminants, which for the extruder seem to lie in the region of 15 to 17 minutes.
During the phase 1 technical trials however, the extruder was kept deliberately cool at ~170°C to minimise
possible ink degradation. Based on the laboratory findings it was decided to run the vent port in the phase 3
pilot trials much hotter at ~260°C. Both the MFI data and the relative concentrations of Irgafos 168, and its
oxidation product, suggested that processing at this temperature should have little effect on the PP itself.
Compared to the vacuum chamber, residence times in the extruder were much shorter typically in the region of
60 seconds, with an estimated 20 seconds in the vacuum zones at 120rpm. Despite this the cleaning
performance was very good and the extruder was able to clean the phase 1 pellet to more than the targeted 95%
efficiency. The influence of up-scaling on the cleaning performance is unknown and further work is required to
assess it.
4.2.3 Effects of temperature on vacuum chamber degassing
Results for oligomers in the small vacuum chamber agreed well with the performance seen in the KT
(‘Krystalltrockner’ or crystallisation dryer, which for HDPE and PP recycling is the first of two vacuum chambers)
over a similar residence time. Cleaning efficiency was dependent on temperature, but only moderately so. There
was a steady decline in cleaning efficiency from C12 to C24 oligomers, with only around 15% of the C24 being
removed. It is assumed that the oligomers are part of the bulk of the polymer and not a surface feature.
Generally, with high diffusion rates, it is thought that contaminants tend to equalise through the flakes. This is
unlike PET, where high molecular weight substances can accumulate on the surface only. Achieving food grade
approval should not be prohibited by the steady decline in cleaning efficiency as the C24 oligomers will be
relatively slow at migrating so there may be a relatively high threshold concentration. If the input material is
below the threshold concentration then there is not a problem, otherwise it should really be possible to remove
the oligomers.
Whilst the oligomers themselves are not strictly speaking contaminants since they are simply the short chained
fraction of the PP, as seen in Phase 1, they do provide a good indication of cleaning performance at different
volatility levels. This is because unlike the post consumer contaminants they form a family of nearly identical
chemical substances where the boiling point is dependent only on the number of propylene units (C3).
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Figure 38 Vacuum chamber with temperature controller
Figure 39 Vacuum chamber - sample supports
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Figure 24 Oligomer cleaning efficiencies at various vacuum chamber temperatures
In Figure 2440 the material was held in the vacuum chamber for 120 minutes with a 15 minute warm up under
a carbon dioxide blanket and a cool down under vacuum.
Both the vacuum chamber and the extruder were able to remove 100% of the oligomers up to C12 but the
extruder was able to remove five to six times as much of the C24 oligomers as the vacuum chamber thus
suggesting that the performance of the extruder is better than the vacuum chamber.
Some very light oily deposits were seen on the vacuum chamber lid when a silicone rubber seal was used. It is
believed that this was due to the lower temperature of the lid. It is estimated that there was probably a 20°C
temperature difference between the lid and the body with the seal in place. With the exception of the shower gel
packaging sample, raising the temperature of the unheated lid by removal of the seal and running on the flat
metal faces, prevented light deposits from forming. This was considered significant since condensation within the
vacuum system can severely limit or indeed halt the movement of vapours on their way to the condenser or
vacuum pump. Pipe work diameter plays a role here but the sort of condensation observed simply adds a further
risk to the process. The use of large diameter piping as well as minimising vertical rises or trace heating would
minimise or remove this risk factor.
4.2.4 Post supermarket packaging samples
Three samples of consumer pre-waste chain plastic packaging were evaluated to assess the potential
contaminant risk from individual classes of packaging:
„ A butter substitute was selected to represent the common yellow margarine/butter fraction in the
packaging waste stream;
„ An un-pigmented chicken drumsticks and thighs tray was selected for the thermoformed packaging
example; and
„ A shower gel product with aromatherapy oils for the personal care category of packaging.
The post supermarket packaging samples did not show the complex pattern of post consumer contaminants.
Compared to the phase 1 pellets the following levels of typical contaminants were seen.
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Table 9 Comparison of the levels of selected contaminants compared to the Phase 1 pellet
Benzophenone
n-Hexysalicylate
a-hexycinnamaldehyde
Isopropyl Myristate
Margarine
0%
0%
0%
0%
Meat trays
0%
0%
0%
0%
Shower gel / mouth wash
0%
38%
51%
17428%
One particularly interesting feature of the margarine tubs chromatograms were the strong peaks for fatty acid
esters, which were the reaction products of the ethanol and fatty acid residues from the margarine. These peaks
were also found in all the samples produced from post consumer waste, implying that even under the very severe
caustic hot wash conditions it is not possible to remove all of the fat residues from the packaging. It is possible
that the fat was absorbed into the PP but the working assumption so far has been that it sits on the surface.
Further test work would be required to resolve this issue. The one peak that was significantly reduced by the hot
washing process following cold washing was for oleic acid.
As demonstrated in Table 9, shower gel bottles showed massive isopropyl myristate contamination from mouth
wash exposure even after vacuum chamber and extrusion. Just 0.03% of such material would bring the final
pellet to the 10ppb migration level. Very high levels of light stabiliser and slip additive were also found. The
functional requirement for these is not known.
Meat trays produced exceptionally clean rPP with almost no detectable substances, apart from the Irgafos 168
anti-oxidant, and also no fatty acid ester peaks.
4.3
Phase 3 – Pilot scale investigations
The following section details the three pilot scale demonstration trials, which were all interlinked:
„ Selection of food contact packaging by a hand sorting trial;
„ A washing trial with Sorema to remove surface contamination; and
„ An extrusion trial with EREMA to test the Vacurema system.
Although the pilot scale trials required substantially less input material it was still necessary to process
approximately 2 tonnes of packaging through a hand sorting regime in order to produce a sufficient quantity of
infeed material for the trial. It was once again possible to separate the NIR sorted PP packaging to >99%
previous food contact in the two stage hand sort. This was conducted using static sorting tables rather than a
picking belt as was done in phase 1. This allowed for a much higher selection rate of the food grade packaging,
with around 90% of the food contact fraction being recovered. At 52% the food contact content of the input was
similar to the phase 1 input material.
The costs of doing so were however more than three times higher than in the phase 1 hand sorting trial. A total
of three days with four sorters and two supervisors were required to produce 892kg of material, at an
approximate cost of £1,880/tonne.
Whilst very good selection was achieved in terms of previous food contact the handpicked material contained
some 10% of non-PP polymers; PET, HDPE, PVC and PS were all identified. Whilst it is relatively straightforward
to remove PET and PVC on the basis of their much higher density, PS and HDPE are more challenging since they
have densities much closer to that of PP and water. PS however tends to be less of a problem than HDPE, so
long as it is not foamed. However, there can be a wide range of reasons as to why PS might be found in the
floating PP fraction, for example, air bubbles and PP flake attachment are two possible reasons.
The washing trials at Sorema in Italy demonstrated that removal of paper labels was highly effective since these
are broken down to pulp that could be filtered in the water treatment plant. Removal of plastic labels was
however poor since they are waterproof, meaning that the washing media has to get behind the label from the
edges and dissolve the adhesive in order to detach the label from the flake.
Even with the use of very strong alkali detergent packs it was not possible to remove the on-polymer and plastic
label inks in the hot caustic wash, meaning that both the ink binders and pigments were transferred to the
extrusion process, where they will have been subject to thermal degradation. Following the hot wash a number
of additional contaminants were seen in comparison to the cold wash. Some of these are believed to be residues
from the detergents used in the washing process.
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Overall yield however from the phase 3 washing was consistent with phase 1 at 61%. The main losses were
water and residual contents, labels, non-PP polymers and fines.
4.3.1 Process condition changes
Reflecting the results from both phase 1 and phase 2 the pilot scale trials at EREMA attempted to maximise both
process temperature and residence time.
Whilst it was only possible to make modest increases in the reactor temperature, from ~120°C in phase 1 to
~140°C in phase 3, running the equipment in the batch KT pre-heating Prime mode allowed the average
temperature in the first chamber to be raised from ~60°C to ~110°C. It also ensured that the absolute minimum
residence time was 60 minutes at process temperature since material could not track from the feeder to the
extruder as it can in the continuous Advance mode.
4.3.2 Cleaning efficiency
Once again the cleaning efficiency of the Vacurema was found to be primarily dependent on vacuum chamber
residence time. Vacuum venting of the extruder, even at the much higher temperature of ~270°C, did not
substantially improve on the cleaning achieved in the vacuum chambers.
The estimated migration levels of isopropyl myristate for the best samples collected towards the end of the trial
were around 13ppb. This gives a maximum addition rate (recycled content) of 77% for phase 3 pellet instead of
5% for phase 1 in full fat applications. However 25ppb was the typical estimated value achieved implying
maximum addition rates of 40%.
As previously indicated these estimations are however based on simply pro-rating against the migration value
recorded for the Phase 1 pellet by ratio of the mass spectrometry (MS) peak heights. Given that they are quite
close to the specific migration limit of 10ppb and very significantly below the phase 1 result, a more sophisticated
modelling technique or indeed specific migration testing would be necessary to give a definitive value.
However more than half of this improvement was due to lower starting levels in the phase 3 input flake and the
average isopropyl myristate cleaning efficiency was around 60%.
4.3.3 Recyclate properties
The MFR of the pellet samples decreased towards the end of the trial. Although unexpected, it would not make
any difference to whether the material could be thermoformed or injection moulded, as all the materials will
require additives to modify the MFI anyway. It is thought that the thickness of the flakes also increased at this
point. This is significant as this may also have contributed to the higher cleaning efficiencies seen at the end of
the run, since the distribution of polymer types and therefore applications would have been different to the
average profile being processed.
Unlike the majority of the substances identified the concentration of two contaminants, styrene dimer and 2,4dimethylbenzaldehyde (DMB), increased with residence time in the vacuum chamber. Both are decomposition
products and show quite clearly that account must be taken of, not only of the contamination found on or in the
post consumer packaging, but also of its behaviour at the temperatures found during flake and melt processing.
Ink binders and pigments are of particular concern here, since whilst suitable for indirect food contact at
everyday temperatures some of their high temperature breakdown products are known to be harmful.
In line with the findings from the small scale investigations processing at 270°C instead of the 170 to 240°C used
in phase 1 did not significantly affect either the MFR or the levels of Irgafos 168 antioxidant, confirming that little
degradation of the rPP occurred.
The phase 3 pellets however had a noticeable odour, strong enough to fail an odour test, and increased levels of
headspace volatiles compared to the phase 1 pellet. This indicates that some higher volatility material (boiling
point < C12 oligomers) was produced during melting and melt filtration. If the contamination causing the poor
melt filtration was removed, it would not be there to degrade and produce higher volatility material, meaning the
melt temperature would be lower because the screw would not have to work so hard.
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4.3.4 Melt filtration
During phase 1 the melt filtration issue was the presence of small quantities of polyamide film heat welded to the
rims of meat trays. At the higher melt temperatures used in phase 3 any polyamide would have melted so it is
not possible to assess whether this was also present in the phase 3 input flakes.
It was not possible to melt filter at 60µm due to excessive pressure build-up resulting from high levels of
particulate contamination. Changing to 100µm screens did allow the material to be filtered, but significant
material losses occurred during ‘back-flushing’. This was a considerable improvement on the results achieved in
phase 1 in which a 200µm filter was used. The filtration level is very dependent on the levels of solid
contamination, such as label fragments, which need to be removed before the extrusion process. At full
production scale the contamination issue would need to be dealt with in order to reduce the screen use rates and
ensure a high level of filtration can be achieved if required. In general, the finer the filtration, the more universal
the potential end applications. Ideally the screen size should be kept below 160µm, which is the point at which
contamination would be generally visible to the naked eye. The much higher elongation at break values
recorded for the phase 3 pellet, which were nearly twice that for the phase 1, reflects the reduction in large
particulate contamination.
It was possible to effectively remove the odour from the high volatility substances by vacuum degassing on the
twin screw extruder.
The colour of the rPP was light green rather than the fawn colour seen in phase 1. This is however more
consistent with the principle packaging and inks colours of blue and yellow. This would restrict the range of
pastel shades that could be made in comparison to the phase 1 product. Opacity was of a similar level to phase
1.
4.4
Phase 2 and 3 conclusions
The levels of input contamination found in the phase 3 flake were much lower than in the phase 1 pellet,
indicating that significant variation may be expected in commercial production and that the levels seen in phase 1
may not be the highest that will be encountered.
The level of rPP recycled content would once again have been limited by isopropyl myristate. Typically the output
had estimated migration levels of ~25ppb which would limit the addition rate (recycled content) to 40%.
Critically the Vacurema cleaning efficiencies for isopropyl myristate were found to be around 60%, which leaves
the process highly dependent on input contamination levels, which are expected to vary considerably.
An additional issue was the formation of volatiles (C12-C15 range) during the phase 3 melt filtration and extrusion
stages, which resulted in a noticeable odour and increased headspace volatiles. This and the formation of
styrene dimer as a breakdown product within the vacuum chamber suggests that efficient cleaning of melt as well
as flake is an important factor in ensuring low levels of food contact relevant substances in the final product.
A small twin screw extruder was capable of reducing input levels of isopropyl myristate from both the phase 1
pellet and Phase 3 flakes and pellet to below the GC/MS limit of detection (LOD) levels which would allow rPP
addition rates of 100%. It was also possible to largely eliminate the odour. It is however important to note that
no data is currently available on the scale up economics and technical feasibility for the multi screw extruder
route, as this was beyond the scope of this project.
4.5
Recommendations
The key recommendations from the second and third phases of the scoping project are:
„ Improvements to the cleaning efficiency of the Vacurema system through vacuum chamber
modifications should be quantified; and
„ The technical feasibility and costs of twin or multi screw extruder super cleaning should be quantified
both as a post Vacurema step as well as in direct flake to pellet processing.
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5.0
Food grade testing
5.1
Methodology
The governing legislation for recycled plastic coming into food contact materials is the ‘Commission Regulation EC
282/2008’ 8 and the ‘Plastic materials and articles in contact with food (Eng) Regulation 2009’. The purpose of the
legislation is to establish the requirements to be met by plastic materials containing recycled plastic and intended
for food contact.
The role of EFSA is to provide risk assessment guidance and to help compliance with EU directives. A guideline
document relating to their recycling food contact process outlines numerous steps a reprocessor must undertake
to prove food safety. Within this proof is required that intended applications and use would not yield quantitative
migration of harmful species and species over threshold limits.
Migration testing combined with Gas Chromatography/Mass Spectroscopy (GC/MS) is used to demonstrate
compliance with this requirement. Mass spectroscopy is an analytical method with great sensitivity that can
identify the chemicals being separated into peaks by the gas chromatogram. However the process itself must
operate within a properly audited quality control system following the principles of good manufacturing practice.
In addition the ability of the process to deal with incidents that might result in high levels of contamination being
present in the input material has to be demonstrated by a challenge test.
5.2
Testing regime and protocols – methodology and results
As part of the overall scoping project a testing regime was developed, through discussion with retailers and
packaging manufacturers within the supply chain, which included both migration and organoleptic testing.
5.2.1 Migration testing methodology
Migration testing measures the amount of material dissolving out of the plastic into a contact medium. There are
limits set for both the sum total of all species migrating, as well as limits for the migration of individual
substances.
A number of chemical stimulants representative of particular classes of food are used rather than actual food
substances. The time, as well as the temperature, of exposure reflects the expected storage conditions.
Exposure can either be by filling or immersion depending on the test piece geometry.
Pira International was commissioned to undertake the migration analyses. Its testing laboratory is accredited to
ISO/IEC 17025:2005 (United Kingdom Accreditation Service). A full report of the migration study can be found at
Appendix 3. The Statutory Instrument 2009, No. 205 provides for four food simulants as detailed in Table 10.
Table 10 Food simulants
Abbreviation
Food stimulant
Simulant A
Distilled water or water of equivalent quality
Simulant B
3% Acetic acid (w/v) in aqueous solution
Simulant C
10% ethanol (v/v) in aqueous solution, except that the concentration of
ethanol solution shall be adjusted to the actual alcoholic strength of the
food if it exceeds 10% (v/v)
Simulant D
Rectified olive oil having the characteristics specified in paragraph 3 or,
subject to paragraph 5, any of the fatty food simulants specified in
paragraph 4
Simulants B, C and D were used for the migration testing; however for analytical reasons 95% ethanol (v/v) and
isooctane were used in place of rectified olive oil. The chosen test durations and temperatures are specified as
8
Commission Regulation EC 282/2008 amending EC Regulation 2023/2006 Statutory Instrument
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simulating standard shelf conditions and thereby ensuring validity with all types of aqueous, fatty, alcoholic and
acidic foods.
The appropriate test standard for the migration testing was ISO 13130 Part 1. The migration studies were
conducted at 40°C for ten days, except for isooctane which was conducted for two days at 20°C. This difference
is due to isooctane being a more effective solvent than ethanol and therefore the time of the test is adjusted to
simulate what would happen if olive oil was used (which is what isoctane is simulating). These test conditions
gave results with validity for shelf storage of products up to 40°C for periods of more than 24 hours. The
migration testing was conducted on the 100% rPP 250g black extruded / thermoformed punnets from the Sharp
Interpack manufacturing trial (see Section 6.4.1for further information). Test pieces were cut from the whole
punnets because a number of the 100% rPP containing punnets contained base pin-holes. A control sample of
virgin PP punnets was also included in the testing regime.
Post migration the simulants were assessed using GC with a flame ionisation detector (FID) which permitted
quantitative determination of whether the contaminants identified exceed the 10ppb limit. GC/MS of samples of
the positive pick material and a virgin PP control, using 99.7% ethanol, were used to determine the chemical
composition of the contaminants and their retention time in the GC column.
Prior work with the IVV Fraunhofer that was carried out on granulate and mouldings used a GC/headspace
analysis with capacity to study relative levels of lower molecular weight species. GC/MS can identify and quantify
species including the higher molecular migrating species of interest to food safety.
5.2.2 Migration testing results and discussion
In order to establish baseline qualitative information about the extractable materials in the rPP, solvent extraction
was performed on both the rPP and the control virgin polymer blend of homo and copolymer, which was provided
by Sharp Interpack.
Since the extraction rate is dependent upon the relative polarities of the solvents and substances, a non polar
solvent, cyclohexane, and a more polar one, 99.7% ethanol, were used. The cyclohexane extraction showed
significant quantities of hydrocarbon material in the form of propylene oligomers in both the virgin and rPP
samples as seen below in Figure 41.
Figure 41 Cyclohexane GC/MS trace
As was the case for the IVV headspace GC investigations, this shows a regular repeating structure of oligomers with retention time, it is thought, representing the stepwise increase in chain lengths by a single propylene unit.
The intensity of the peaks also followed a smooth distribution curve centred on a retention time of 14 to 15
minutes.
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The peak heights and thus concentrations were higher for the rPP than the virgin material, but there are clear
differences in the peak height distribution within the cluster of oligomers, with the dominant peak in the rPP
occurring around 0.4min earlier than that in the virgin.
Within the scope of these tests it has not been possible to conclusively determine how much of these differences
were due to the initial manufacturing and service life of the packaging and how much was due to differences in
the virgin polymer used.
This contrasts quite strongly to the headspace results where the oligomer concentrations in the rPP were lower
than in the virgin. However the extraction process is capable of identifying much higher molecular weight
substances than headspace. This can clearly be seen by the fact that benzophenone, which is at the limit of
headspace detection, is seen about half way through the extract GC/MS chromatogram (Figure 41).
Looking at the section of the chromatograms for both cyclohexane (Figure 41) and ethanol (Figure 42) below
around 9 minutes which would equate to hydrocarbon boiling points in the region of ~220°C, it is clear that the
oligomer concentrations in the rPP are substantially lower than those present in the virgin. Given the higher
levels in the less volatile oligomers this is a good indication of the effectiveness of the Vacurema removal of
volatile substances.
Since PET has very low diffusivity, that is it is relatively difficult for materials to pass into, out of or through the
polymer, it is only the most mobile/volatile materials that can migrate at levels that are of concern for food
contact applications. The less mobile/volatile material remains effectively locked within the polymer rather than
crossing into the food. Polyolefins such as HDPE and PP have a very different structure and contaminants find it
much easier to move through these polymers; which means that even quite large/non-volatile molecules can
migrate out of these polymers at concentrations that cause problems in terms of food safety.
That means that challenge testing of both rHDPE and rPP needs to include surrogates with much lower vapour
pressures than PET and it is not clear that vacuum extraction is an effective method of removing such species.
It should however be remembered that the extraction analysis conducted within this scoping project did not
include input flake oligomer quantification. As a result, there was no surrogate based assessment of the cleaning
efficiency in the high molecular weight region. This means that we cannot determine the extent to which
improved vacuum extraction would offer the possibility of satisfactorily cleaning the post consumer polymer.
The chromatogram from the ethanol extraction is very different to that from cyclohexane extraction, which shows
the differences in extraction due to of the relative polarity and structure of contaminant, matrix and solvent.
Figure 42 99.7% ethanol extraction GC/MS trace
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Firstly comparing Figure 41 and Figure 42, the scale should be noted as the axis for the ethanol trace is only a
quarter the height of the cyclohexane one. Secondly, although the virgin material still shows a repeating pattern
of oligomers no such structure can been seen for the rPP. The majority of the peaks were however still found to
be hydrocarbons.
The presence of significant quantities of higher molecular weight oligmers is in contrast to HDPE where this
region is sparsely populated. The most likely explanation for this is to be found in the stability of the base
polymers themselves since the polymer chains of PP, unlike PE, are relatively easy to cut through by, shear,
thermal and chemical stress. This means that with PP, short chain end fragments will be produced under normal
processing and service conditions.
Since these fragments, even when present in raised concentrations, are a normal feature of PP they do not in
themselves represent a barrier to the use of the rPP for food contact applications. However as they effectively
mask portions of the chromatogram they may hide non-positive list substances including, in the worst case,
potential carcinogens or other harmful materials.
Thus alternative analytical methods will be required if food contact use of post consumer rPP is to satisfy the
basic principles of food safety.
Looking at the substances not directly related to the polymer, or its breakdown products, which were identified by
the extraction work, these included both food packaging approved material from the positive list as well as
substances that are not included on this list and therefore banned from use in packaging. The positive list
substances such as Irgafos 168, an antioxidant, and erucamide, a slip agent, are well known process aids and
almost universally used. However it is not clear at present where the substances not on the positive list
originated from, but some may well be fragrances from non-food applications. An example of this is the presence
of hexyl salicylate.
For food contact use of the rPP the migration concentration of the non-harmful, non-positive list materials need
to be less than 10ppb, which is a widely used although not an officially recognised limit of detection/significance.
The positive list material has set migration limits often in the ppm range.
Migration testing
The aqueous simulants B, 3% acetic acid and C, 10% ethanol showed low levels of a number of substances,
mainly hydrocarbons, in comparison to the virgin control. The overall migration limit should not exceed 60ppm
and all the non-positive list materials must be less than 10ppb.
Figure 43 Acetic Acid GC/FID trace
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Figure 44 10% Ethanol GC/FID trace
Further investigation would be required to confirm that the species are of polymeric origin or not, since the
concentrations in the virgin sample were too low to be able to make an effective comparison. In addition the
concentrations are estimates based on an assumption that the specific response of the flame ionisation detector
FID detector is linear in comparison to the marker substances such as pentadecane. N.B. the time baseline for
the FID GC work is much longer than that for the GC/MS due to the use of different columns.
The concentration of these species was however in the region of 10 to 20ppb meaning that including a modest
factor of safety use of the rPP at ~30% would be possible whilst observing the 10ppb threshold. This value is
however only a simple estimate and would need to be confirmed by investigation of samples containing reduced
concentrations of rPP.
At present there are no food simulants for dry or semi-dry foods such as mushrooms. These are much less
sensitive to contamination from packaging due to poor contact between the surfaces of the food and packaging
which are both rough at a microscopic level. The absence of a liquid, i.e. water, also limits migration. Thus the
tests with 10% ethanol and 3% acetic acid are much more severe and could therefore be seen as an extreme
worst case.
It is possible that a much higher level of rPP could therefore be properly used for instance for vegetable punnets.
The picture for the two fatty simulants was less favourable, which is however in line with the extraction work,
which showed the presence of significant quantities of non-polar species.
Two non-positive list substances in particular were identified and the highest concentration recorded was for
isopropyl myristate, IPM, at 190ppb.
Based on this full fat contact would be allowed at no more than 5% recycled content, however this would require
investigation with real systems. One rider to this is that the legislation does allow for the use of a factor to reflect
the specific fat content of fatty foods. For instance fish has a factor of 3 and meat a factor of 4 to 5, meaning
that the maximum concentrations may be 3 or 4 to 5 times higher respectively for packaging containing these
kinds of foods.
It should be noted however that these figures are a snap shot from a particular rPP sample, obtained by a
particular sorting method. Therefore before reaching a conclusion on appropriate addition rates for rPP, the likely
range of contamination would have to be considered further.
5.2.3 Organoleptic testing methodology
Organoleptic testing assesses the odour and tainting capacity of materials on the basis of the perceptions of a
panel of testers. The test pieces are placed in sealed containers for one day at room temperature before being
Scoping study into food grade polypropylene recycling
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assessed. Taint is evaluated on the basis of the change in taste of a chocolate button that has been in contact
with the packaging surface for that time.
Pira International was also commissioned to undertake organoleptic testing on the rPP samples. A full report of
the organoleptic testing can be found at Appendix 4. Eleven 100% rPP packaging samples (again obtained from
the Sharp Interpack manufacturing trial) were tested for odour and taint according to Paper and Board Intended
for contact with foodstuffs (sensory analysis) odour (pt 1), off-flavour, taint (pt2) EN 1230 parts 1 and 2 (2001).
The taint test is used to evaluate whether a material may bring about a change in the taste (flavour) of the food
to be in contact with the material. As previously stated, chocolate was used as the flavour absorbing medium for
these tests and a panel of testers score the level of taint. Odour
The key conditions for the odour tests were as follows:
„ Sealed container;
„ 24 hours sample storage at 23°C; and
„ Assessment by testing panel
o 0 - No perceptible odour
o 1 – Odour just perceptible
o 2 – Moderate 0dour
o 3 – Moderate odour
o 4 – Strong odour
Taste / Taint
For the taste/taint tests the key conditions were:
„ Sealed container;
„ Chocolate buttons in contact with surface of the test sample;
„ 48 hours sample storage at 23°C; and
„ Assessment by testing panel
o 0 – No perceptible off flavour
o 1 – Off flavour just perceptible
o 2 – Moderate off flavour
o 3 – Strong off-flavour
5.2.4 Organoleptic testing results and discussion
Table 11 presents the results of the odour testing undertaken by Pira International.
Table 11 Odour testing results
Number of assessors assigning
each odour rating
Odour rating
0
1
2
3
4
Mean
Recycled PP trays
0
6
2
2
0
1.6
Descriptions of odour
Cloves, detergent, plastic soapy,
slightly metallic
The results from the testing panel show that some assessors reported relatively strong odours, but the majority
experienced slight or no apparent odour. What is not clear at present is whether improvements to the washing
techniques are required to reduce the concentration of residual contents or if this will need improved extraction
of contaminants from the plastic itself.
Table 12 presents the results of the taint testing undertaken by Pira International on the rPP samples.
Table 12 Taint testing results
Taint rating
Recycled PP trays
Number of assessors assigning
each taint rating
0
1
2
3
4
4
5
1
0
0
Mean
0.7
Significance
Not significant
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Unlike the odour testing no statistically significant difference was found between the control samples and test
samples exposed to the sample of rPP.
5.3
Conclusions
The key conclusions from the food contact testing work are as follows. Despite the very efficient separation of
food contact material, non-food contact substances were found at levels of up to 20 times the required threshold.
There are two possible likely sources of this material:
„ Contaminants in the residual non-food packaging content; and
„ Contaminants absorbed from non-food packaging and in the input bales prior to sorting and washing.
Looking at the potential for contamination from the residual non-food contact at 2%, this would imply for
instance a concentration of isopropyl myristate in the region of 10ppm. Further investigations are required to
establish if this is a credible route. It would however put isopropyl myristate contamination at a level similar to
that of limonene, which is found in practically all post consumer packaging and indicates that the isopropyl
myristate was widely spread through the input material at more than trace levels.
Given the high diffusivity of PP the second exposure route that is the residual content cross contamination, must
also be considered highly problematic, since the once NIR sorted comingled food contact and non-food contact
packaging spends an indeterminate period with substantial cross contamination of residual content (for example,
a food grade shower gel in contact with a food contact mushroom punnet).
Washing of the packaging pre or post NIR would be a substantial help, as would separation into food and nonfood contact materials as early as possible in the collection chain.
Despite these problems it does appear that rPP could be used for dry, semi-dry and aqueous food packaging
applications, at a recycled content level of up to 30%. A substantial amount of additional work would be required
to produce a technical dossier for approval by EFSA. It is likely that EFSA approval would not be achieved at the
current time due to the following reasons:
„ The spectral responses of a number of PP oligomeric species may have obscured the potential presence of
species of concern. The development of reliable analytical techniques is required to deal with the much
more complex exposure scenarios, especially in respect of ink breakdown products and the inherent
problems stemming from the significant levels of polymer oligomers;
„ The intensive level of hand sorting required to attain a prior food contact level of around 99%, may not
satisfy EFSA. The use of marking/tagging technology may be required with automated sorting to reduce
the potential for human error during manual sorting. The identification of non-positive list species may
reinforce this potential view; and
„ An assumption of a >99% prior food contact sorting level has been made based upon experiences of
relatively more straightforward food contact recycling processes such as with PET. EFSA could take a
rigour view upon the potential impact of non-food contact in-mould labelling and their non-food contact
printing inks and require a demonstrated higher level of sorting efficiency.
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6.0
Packaging manufacture trials
6.1
Polypropylene polymer types
Three main types of PP polymer types are used in household packaging:
„ Homopolymer PP: this is a translucent polymer, with high Heat Distortion Temperature (HDT), with a
lower impact strength (particularly at low temperatures) and is used for applications such as closures and
soup pots;
„ Block copolymer PP: this polymer has a lower transparency and generally a lower HDT, with a higher
impact strength (particularly at low temperatures) and is used for applications such as ice cream
containers and for chilled foods; and
„ Random copolymer PP: this polymer has a high transparency and the lowest HDT. It is a product with the
greatest flexibility and possesses reasonable impact strength. Typical applications requiring high
transparency are bottles and salad bowls; Homopolymer and copolymer (random and block) PP polymer
types may be used with either of the two main types of moulding process (extrusion/thermoforming or
extrusion blow moulding) and therefore can be made with different melt flow characteristics as follows:
„ Thermoforming and blow moulding: used for meat trays and bottles, with a low MFR (Melt Flow Rate) (1
to 4); and
„ Injection moulding: used for thin walled packaging, such as soup pots, with a high MFR (33 and higher).
6.2
Suitability of PP recyclate for food use
The MFR of around 8 to 10, measured in both the positively and negatively picked recyclates produced in these
trials, is consistent with a broad mixture of polymer types used. The recycled polymer does not appear to be
suitable for any application requiring transparency or translucency due to its colour and titanium dioxide loading.
Assessment of the heat distortion temperature (HDT) and low temperature impact strength would be required if
the rPP was to be considered for applications such as food trays or ice cream tubs.
The MFR could be raised by adding peroxide to cut the polymer molecules into shorter lengths at the extrusion
stage and in order to make it suitable for injection moulding applications. However tests would be required to
determine the effect on the impact strength of reducing the already short polymer chain length of the high melt
flow blend component. This blend component comes from from injection moulded containers in the feed
material.
Although the GC/MS analysis of oligomers and post consumer contaminants indicates a very good cleaning
efficiency for more volatile contaminants (based on the initial GC headspace analyses) the material does still have
a significant odour and colour. Higher molecular weight oligomeric species, as determined through GC/MS, may
be contributing strongly to odour. Other species derived from inks, pigments and product residues and their
degradation products may also be contributing.
Unlike HDPE milk or PET beverage bottles PP packaging comes in a very wide range of shapes, sizes and colours.
This makes it relatively difficult to separate food contact packaging from packaging that has been exposed to a
wide variety of non-food materials.
Whilst PET with its low diffusivity absorbs contaminants only very slowly and in small quantities, PP which has
high diffusivity will absorb relatively large quantities of such non-food materials. This makes the need to achieve
a high degree of separation all the more important.
6.3
Methodology
A number of companies that would potentially be interested in delivering a packaging manufacturing trial were
identified as part of this scoping project. The companies were identified through the supply chain consultation
work (covered in Section 2 of this report) and through contacts provided by WRAP. A number of leading retailers
were also consulted to determine if they were interested in working on the project and their packaging
manufacturers on the trials. Once the manufacturers were identified (three in total), it was agreed collectively
what packaging application would be produced and at what recycled content levels.
For each manufacturing trial up to 200kg of granulate rPP material was supplied to the manufacturer/trial host.
Each manufacturer ran a trial to produce a number of packaging samples, at different levels of recycled content.
A quantity of set-up material was also supplied to Sharp Interpack as transitional material to be run to establish
stable production conditions ahead of the use of the prime recyclate.
Scoping study into food grade polypropylene recycling
67
Information was obtained from each manufacturing trial including packaging samples, retail customer feedback,
processing information and an assessment of fitness for use. Samples from one of the trials were used in the
migration and organoleptic testing undertaken by Pira International.
6.4
Manufacturing trials
6.4.1 Sharp Interpack
Sharp Interpack is an established UK manufacturer of in extrusion / thermoformed packaging. Its polyolefin and
aPET products are typically sold to UK supermarkets such as ASDA, M&S, Tesco and Sainsburys.
The packaging application chosen for the initial manufacturing trial was a black “250g” vegetable punnet. A
follow-up trial was also conducted on a”S4-35 poultry tray” following feedback and discussions with Sharp
Interpack. Figure 45 shows both items.
Figure 45 250g punnet
The initial manufacturing trial was conducted simulating the standard production punnet polyolefin composition of
a proprietary blend of PP homopolymer and copolymer + 2% black masterbatch (concentrate of pigments with a
polymeric carrier). The first trial was run with black masterbatch, chosen as it was expected that this was to be
of more interest commercially. Following discussion Sharp Interpack also ran a second manufacturing trial, with
no black masterbatch to assess the production of a ‘natural’ rPP application.
PP is a versatile plastic material capable of use with and without modification with other components. The use of
PP copolymer/homopolymer blends for such packaging items is common. The homopolymer gives a degree of
stiffness and the copolymer provides low temperature toughness. Blend dynamics are primarily governed by
price and achieving an acceptable package stiffness-toughness balance. Block copolymer materials typically
command a premium of £40/tonne over a typical homopolymer price of £815/tonne. 9 The essential difference in
9
LME European Polypropylene cash settlement 2nd November 2010
Scoping study into food grade polypropylene recycling
68
the materials is the presence of an ethylene/propylene rubber within the copolymer material. This rubber
component confers a degree of low-temperature impact strength with a corresponding modest reduction in
rigidity.
The extrusion/thermoforming process consists of an extruder with a long die producing a sheet. This feeds a
thermoforming unit, where the sheet enters an oven to soften it prior to being formed to accept the form of a
tool by vacuum or air. Parts can then be stamped or cut from the surrounding (skeletal) sheet. It is standard
practice within this manufacturing sector for the production line to reuse its own skeletal regrind (post industrial
waste) back into the process. For these manufacturing trials, however, no skeletal regrind was used.
For the first trial with the 250g punnet three levels of rPP content were used.
Formulation 1: 98% rPP and 2% black masterbatch. The key observations of this trial are:
„ Extruder settings were found to be identical to those used in normal production;
„ Barrel heater settings: 180°C (feed) increasing to 200°C (die);
„ It was observed that the material had lower melt strength than that of virgin material, and drew slightly
onto the cooled feed wheel prior to thermoforming. Melt strength is a feature of the plastic emerging
from the die. Good melt strength indicates easy set-up for the following process, however, inadequate
melt strength can prevent successful control for, in this case, the thermoforming operation;
„ A similarity to the melt strength of aPET was noted;
„ A different, but not mal-odorous, smell was noted during processing;
„ No additional fuming noted at the extruder die;
„ Material was pulled by vacuum into the cavities with no issues;
„ Sheet passed through the trim-press with no issues;
„ Punnets passed through the restacker and nested together well;
„ Punnets were appreciably more flexible than normal production;
„ Punnet colour was not of the same depth of black as achieved in normal production – the jet-black colour
had been lost, but this was considered to be probably still be acceptable; and
„ A slight odour to the stack of warm punnets.
Formulation 2: 48% (PP-Co + PP-Homo), 50% r-PP + 2% black masterbatch. The key observations from this
run:
„ Material was pulled by vacuum into the cavities with no issues;
„ Sheet passed through the trim-press with no issues;
„ Punnets passed through the restacker and nested together well; and
„ Punnets were appreciably more flexible than normal production but closer to the performance of virgin
material than those samples produced from the processing of Formulation 1.
Formulation 3: 73% (PP-Co + PP-Homo), 25% r-PP + 2% black masterbatch. The key observations were as the
second formulation but reported as closer to as expected from virgin processing.
Prior to trialling the rPP material, Sharp Interpack conducted a number of characterisation analyses concluding
that the material possessed a high proportion of PP block copolymer, deriving 12% ethylene by a quantitative
FTIR spectroscopy technique. They also confirmed that the material had a low level of volatiles (as measured by
GC head-space analysis). Furthermore, ash content (residual fillers and particulate pigments etc) was found to
be 1.2%. This value was considered to be in line with titanium readings and slightly low if calcium levels are
included.
Following processing, the strength of the punnets was compared against punnets made from virgin material.
Chilled impact and base deflection tests were also conducted on the samples. Measurements were made using a
Lloyd LR10 machine in accordance with internal test protocols at Sharp Interpack.
The punnets were stored at +4°C for 24 hours prior to testing. The three tests have been devised to simulate
physical abuse in the field. In each test, nine punnets were tested, and the percentage that passed was
recorded. Any sample which exhibited a crack, tear or perforation was deemed a failure.
Table 13 Chilled impact tests on rPP samples
Test
Control
25% rPP
50% rPP
100% rPP
Scoping study into food grade polypropylene recycling
69
500g Weight Drop
Flange Crush
Base Crush
89%
78%
44%
89%
89%
56%
100%
100%
67%
100%
100%
91%
A Lloyds LR10K machine was used to measure the force to deflect the short edge of the punnets by 10mm, and
the central base deflection by 20mm.
Table 14 Edge deflection test on rPP samples
Test
Edge Deflection
Base Deflection
Control
18.7N
15.0N
25% rPP
21.0N
17.9N
50% rPP
17.0N
13.5N
100% rPP
15.1N
10.9N
A Lloyds LR10K tensometer machine was used to measure the force to compress the complete punnet by 8mm.
Table 15 Base compression tests on rPP samples
Test
Base Compression
Control
100N
25% rPP
110N
50% rPP
65N
100% rPP
56N
The key results from these tests are:
„ All levels of recyclate (25%, 50% and 100%) improved the chill impact performance;
„ There were no obvious differences amongst the samples in any of the deflection tests; and
The higher levels of recyclate (50% and 100%) did affect the flexibility, and these two sets of samples had
significantly reduced compression/top-load performance in comparison to the control sample.
Table 16 Colour measurements on rPP samples
L*
A*
B*
Virgin
8.12
0.53
-0.51
25%
14.13
0.48
-1.83
50%
16.10
0.34
-2.28
100%
16.46
0.40
-2.52
The L* (intensity) values indicate that there is a noticeable and expected darkening of the poultry tray upon
increasing recyclate level. Differences in A* (red-green) and B* (yellow-blue) are of a lower level and if a value
of 1 is generally able to be perceived by eye then changes appear to be of a low level.
Following discussion with Sharp Interpack ran a second manufacturing trial. The chosen application was a
poultry tray and black masterbatch was not added so to assess the potential of manufacturing a ‘natural’ rPP
product (Figure 46). For this trial a more modest addition rate of 10% and 20% recyclate was used. The virgin
content of the natural tray trial was composed of 50% PP-Co and 50% PP-Homo PP. The key observations and
findings from this trial are:
„ There were no processing issues when forming the poultry trays; and
„ Their mechanical performance is very similar to that of virgin material.
Scoping study into food grade polypropylene recycling
70
Figure 46 poultry tray
The key results and observations from the Sharp Interpack manufacturing trial are very positive and are
summarised below:
„ No issues were encountered during the manufacturing trials in terms of melt strength, thermoformability,
trimming or nesting / de-nesting or unacceptable level of nibs (entangled polymer appearing as a visible
surface bump);
„ At 100% recycled PP content a reduction in the depth of black achieved was noted but this was not
considered to be excessive;
„ There were no excessive process fumes noted and processing odours, whilst different from normal, were
not considered an issue;
„ Mechanical properties appeared to be heavily influenced by the incorporation of the ethylene/propylene
rubber rich recyclate. The flexibility of the 25% recyclate punnet was identical to the virgin punnets. The
flexibility of the 50% recyclate punnets was only down by 10%, and was considered acceptable;
„ The chilled impact strength of all the punnets containing recyclate was greater than the virgin material; no
cracked, split or perforated samples were reported;
„ Lowered rigidity was reported at the higher recyclate levels. It is not known whether the rigidity obtained
was deemed unacceptable;
„ A number of in-hole defects were apparent within the 100% r-PP thermoformed punnets. The principal
cause of these would be the excessive drawing of polymer around particulate contamination and the likely
origin would be the use of 250 micron size Vacurema filters. The choice of a smaller filter size would
certainly have reduced or eliminated the occurrence of thermoformed pin-holes;
„ An unexpected rise in 25% r-PP compression force was noted compared with the control and higher
recyclate loadings (50% and 100%). It is possible that a degree of significant additional crystallisation
nucleation has occurred in the recyclate content samples compared with the control sample. Higher levels
of crystallisation would yield higher modulus and stiffness values. At higher loadings, the stiffening effect
of crystallisation behaviour has been masked by the increasing levels of ethylene/propylene rubber
present;
„ A production system using r-PP content could have the virgin component’s ratio optimised to generate the
desired stiffness/toughness balance for a package. Commercial benefit might be possible from this
refinement since the tougher PP copolymer commands a premium over homopolymer; and
„ Additionally, the extruded form’s melt strength would probably be also enhanced by use of such a
composition. Use of such a formulation adjustment would probably overcome any processing related
difficulties or concerns.
Scoping study into food grade polypropylene recycling
71
6.4.2 RPC Containers
RPC Containers is a multinational rigid packaging manufacturer supplying injection stretch blow/extrusion blow
moulded, injection moulded and extrusion / thermoformed items from 45 operations in 12 countries. It supplies
a number of sectors, including building/construction, food/drink and personal care.
RPC Containers considered that an opaque application would be suitable for a manufacturing trial. The rPP melt
flow rate of 9 was considered to be low and so not of immediate interest for general thin wall injection moulded
packaging. Injection moulded high volume food contact applications manufactured by RPC Containers typically
feature the use of clarified PP in hot-runner fed multi-impression tools. This allows these containers to be used
for applications which can have wall sections as low as 0.5mm thick. In-mould and post-mould decoration can
also be used with such packaging.
A snack pot application (430ml capacity) was recommended for a trial due to its higher wall section (minimum
0.7mm) and its commercial use in black. A cold-runner fed single impression tool was made available for a trial.
Polypropylene block copolymer is used in this application, which possesses a combination of good processability
and excellent stiffness/toughness balance at both room temperature and also during its short period of hot-water
contact in use. The material has a MFR of 33.
Figure 47 430ml snack pot
The trial was started with 100% virgin PP block copolymer to establish stable machine cycling. The rPP material
was then introduced to the machine and process changes necessary to re-establish suitable mouldings were
noted.
Table 17 RPC trial process conditions
Control
rPP @100%
Change
Over Point
(mm)
12
8
rPP @ 50%
rPP @ 20%
12
12
Type
0.38
0.46
Holding
Pressure
(Bar)
50
75
0.44
0.42
60
55
Fill time
(Sec/1)
4.6
4.8
Polymer
Temperatures
(°C)
230
230
4.7
4.7
230
230
Cycle time
(sec/1)
Scoping study into food grade polypropylene recycling
72
During the manufacturing trial melt temperatures were kept constant so that the influence of other machine
parameters could be better seen as recycled content decreased from 100% to 50% and 20%. Adjustment of
multiple process parameters simultaneously to remedy a defect can obscure the effects of key parameters.
Consequently, melt temperature was fixed so that changes to holding pressure could be noted. The key
observations and findings from the trial are as follows:
„ Significant holding pressure increases were necessary to achieve good parts with increasing recycled
content;
„ Slight increases in fill time were also evident with increasing recyclate level;
„ Pots of good gloss and freedom from streaks were achieved at all recyclate levels, suggesting that
adequate dispersion of the recycled material had been achieved;
„ No gross shot-to-shot problems were reported during processing;
„ A slight puckering of whitened material could be seen at the gate (tool entrance). These, however, were
not seen as problematic and might easily be alleviated through process condition refinement;
„ A small number of black specks were apparent on the majority of the submitted samples. These black
specks could be due to the scouring effect of using a lower melt flow material after the processing of an
easier flowing material. Carbonised degraded material can form on the metal surfaces inside the melt
processing equipment. This degraded material can ‘flake-off’ over time and this can be exacerbated by a
change in the material being processed.
RPC undertook a number of in-house tests on the manufactured samples and the key results are summarised in
Table 18.
Table 18 RPC Containers dimension check and drop weight impact testing
Type
Average height
Control
PIR @100%
PIR @ 50%
PIR @ 20%
Expected
108.52
108.51
108.43
108.35
108.30 109.30
Average
internal
diameter
82.04
82.07
82.00
82.03
81.75 82.25
Average
external
diameter
92.41
92.26
92.14
92.14
92.15 92.65
Shot to
shot %
Impact
height
Product
weight
0.30
0.60
0.65
0.30
< 0.50
200
150
150
150
[email protected]
20.62
20.05
20.04
20.01
21.0 + - 1.0
Dimensional quality
RPC Containers make dimensional quality checks by using an automated coordinate measurement machine. It is
important to measure and monitor any variability in pot dimensions to ensure a consistent process has been
established. In addition it is important to check that expected tolerances are being met and consistency being
achieved so that secondary operations such as foil-lidding can be carried out to an acceptable standard.
The results from the trial show that height and internal diameter tolerances have been met, whereas average
external diameter values are at and below the lower tolerance limit. These variances could be due to using a
limited number of moulding parameters (intentionally) in order to achieve acceptable mouldings. A repeat trial
aiming to achieve the target dimensions by using a wider range of machine parameters may have yielded the
required levels.
A dimensional based shot-to-shot dimension check indicated that excessive variation is seen at 100% and 50%
recyclate levels. The control standard is matched at a recycled content of 20%.
Packaging strength
An in-house drop weight impact test was used to assess packaging strength. A round 500g striker was dropped
upon a package in height increments of 50cm to point of failure. The impact location is chosen to be away from
the highly orientated gate (tool entrance) region. Usually, approximately 20 packages provide a close indication
of the average drop height.
The impact height recorded fell short of the 100% virgin level target for all the recycled content samples. This
could be due to higher levels of moulded-in-strain (arising from polymer chain orientation in the direction of flow)
due to higher moulding pressures, which resulted in a weakening of the parts. Increasing the melt temperatures
Scoping study into food grade polypropylene recycling
73
or lowering moulding pressures, for example, could have alleviated this to some degree but could also have had
negative implications for cycle time.
An inferior impact performance of the recycled content samples compared to virgin material could be regarded as
inevitable to some degree. The presence of particulates and contamination in the recyclate may also have
contributed to the material’s mechanical properties.
Summary
The trial was performed using a single-impression tool which yielded good quality parts, despite higher than usual
holding pressures. Critical dimension and impact performance fell short of that expected of virgin block
copolymer PP.
It is also worth noting that many high volume food packaging injection moulded applications require not only
clarity but also the ability to fill multi-impression (4+) tooling, in order to achieve high quality in parts
approaching 0.5mm minimum wall section. For injection moulded food packaging applications a rPP material
should have a MFR greater than 9 (rPP of composite origin) and be closer to 30 (as used by RPC Containers). For
RPC Containers, this particular concern significantly outweighed the shortcomings of the material in terms of
mechanical properties or dimensional characteristics.
Blending of a minor fraction of rPP (of low MFR) into a higher melt flow virgin PP may provide improvements to
the overall flow and therefore enable the production of thin-wall packaging. However, such a scenario may lead
to the formation of visible streaks arising from poor recyclate mixing. In general, higher flow minor-fraction
materials are easier to mix into lower flow major-fraction materials than the converse scenario. Another
approach is the blending of a minor fraction of very high flow virgin into the major fraction of a recycled PP
material. In this scenario, both good flow and good mixing may be achieved.
Colour and appearance
The three recycled content levels (100%, 50% and 20%) achieved a ‘fawn’ colour with only slight translucency.
Colour studies were performed to indicate changes with increasing recyclate content. Furthermore,
measurements were made to see if any visible impact was made by probable contaminant degradation during
melt processing.
Table 19 below provides colour data using the 20% recyclate level as a baseline. Values, as previously,
mentioned indicate comparative differences in intensity (L), red-green (da), green-blue (db) and a cumulative
colour space change (dE). Measurements were taken against both white and black backgrounds.
Measurements indicate the expected darkening of each blend comprising higher levels of recycled content. At
each level there was a difference between white and black background intensity (L) measurements, which will
relate to a degree of opacity at that material composition. The presence of high colour strength printing inks
from in-mould-labels and printing within a recyclate will contribute to overall colour. The degradation of these
components will lead to the loss of their colour strength as a consequence of the shear and thermal load
encountered during melt processing. The changes in L white to L black ratio follow the increasing levels of
obscuring titanium dioxide levels with increasing recycled content. Degradation in printing inks, for example,
would tend to follow changes in da (red/green) and db (blue/yellow).
Table 19 Snack pot colour at three recyclate levels measured with white and black background
rPP Content
Background
L
da
db
dE
Lwhite to Lblack
20%
White
Black
White
Black
White
Black
100
86.26
89.16
86.71
86.95
87.29
0
-4.09
0.81
-1.99
-0.69
-1.01
0
-12.81
-4.02
-8.12
-7.12
-7.3
0
14.94
9.12
12.39
11.76
11.61
115.9%
50%
100%
102.8%
99.6%
Scoping study into food grade polypropylene recycling
74
6.5
Results and discussion
In all trials, it was a notable achievement that the rPP proved to be capable of being processed by both
extrusion/thermoforming and injection moulding. Whilst this was, in-part, due to the choice of packaging items
being of straightforward design, in the case of the thermoforming application this only required modest drawdown depths (the depth the sheet has to be drawn through forming). In the case of the injection-moulding
application, a package whose wall section was high compared with other injection moulded food packaging
containers.
The good homogeneity of the material was also indicated through high part consistency in each trial.
The recycled material was capable of being master-batch coloured to a tolerable depth of black. Natural rPP
trials yielded parts with nominal translucency but of a general fawn colour.
In no trial was processing odour cited as being an issue, furthermore, the level of visible particulates were not
considered excessive.
Some 100% rPP punnets, however, possessed numerous pin-holes which are considered to be a consequence of
the Vacurema melt filtration being performed at a modest 250 micron level. Unfiltered particulate contamination
tends to cause voiding around them when the sheet is drawn during thermoforming.
The high rubber content yielded flexible thermoformed punnets of good mechanical performance.
Polymer blend ratios between homopolymer and copolymer could conceivably be tailored to mimic virgin blend
performance with incorporating recyclate levels. An unexpected rise in 25% rPP compression force was noted
compared with the control and higher recyclate loadings (50% and 100%). Further investigations would however
be required to determine whether this effect is reproducible and establish what factors influence this behaviour.
Injection moulding mechanical performance, however, suffered due to a possible combination of high levels of
moulded-in-stress and also the presence of a non-optimised rubber morphology, particulate content and
contamination.
6.6
Conclusions
The conclusions from this stage of the project are that successful processing/manufacturing trials were conducted
using both extrusion/thermoforming and injection moulding techniques. Neither of the packaging manufacturers
involved in the trials commented upon an unacceptable odour of the rPP material. Furthermore, set-up time in
each trial was straightforward and did not present any issues.
In the case of the Sharp Interpack trial with the black thermoformed punnets, the achieved performance came
close to that expected from virgin polymer products. Formulation refinements are expected to meet the target
performance of virgin material.
Some thermoformed packages from the RPC Containers trials, however, revealed unacceptable pinholing. It is
thought that the use of finer Vacurema melt filters may be able to alleviate this problem.
The natural product trials revealed that the rPP material possessed a fawn/biege colour, which would almost
certainly require disguising through the use of colour matchbatch in a commercial application.
The mechanical performance of the injection moulded pots fell short of the level set by the virgin material.
However, the levels of moulded-in-strain caused by the high viscosity rPP may have contributed to this result.
Emphasis was placed on the need for a higher MFR grade product, closer to 30 than 9, for use within thin walled
injection moulded food contact applications.
Scoping study into food grade polypropylene recycling
75
7.0
Conclusions and recommendations
7.1
Mass balance
The NIR sorted input bales were found to contain approximately 50% by weight of food packing. To comply with
the generally accepted minimum requirements for recycling polymers for use in food contact applications this had
to be increased to at least 99%. In the absence of any gross difference between food and non-food applications
the only method available was hand picking. It was found that by positively picking material identified by
operators as food packaging it was possible to raise the food packaging content to ~95% in a single pass.
However, a second pass where incorrectly selected non-food packaging was removed, was required to achieve
the target of greater than 99%. The combined yield of the two hand sorting processes was ~25% of the initial
input.
The subsequent washing and extrusion processes resulted in the losses that reduced the final yield of previous
food contact polymer to ~13% of the input bale. It should be noted however that the yield of polymer was
substantially higher since these losses include water, product residues and labels. However at present precise
figures for these elements are not available.
7.2
Physical properties
The rPP produced had an MFR of 8 to 10 g/10 min, which lies between typical extrusion grades ( less than 4
g/10min) and injection moulding grades (greater than 20 g/10min). This reflects the fact that the rPP is a blend
of material from both types of application. Furthermore the rPP material contains both homo and copolymer PP,
as well as impact modified grades.
The notched impact and tensile strength of the material, as well as its flexural modulus, were found to be
acceptable for a wide range of applications. The low temperature impact strength was found to be in some cases
superior to virgin homo-polymer.
In terms of appearance the rPP had a very opaque beige colour and a light odour. Although the odour was found
to be only moderate in organoleptic testing of 100% rPP samples, both this and the optical properties would limit
in particular the maximum concentration at which the rPP could be used in commercial applications.
7.3
Phase 2 and 3 small scale laboratory investigation and pilot scale trial
The use of GC/MS chromatography, combined with melt homogenisation of the input flake, appears to be a very
effective method of directly assessing cleaning efficiency of individual contaminants, without the need to resort to
large scale challenge testing. The information gained gives direct insights into the ability of process modifications
to deal with contaminants in concentrations that occur in ‘real world’ recycling systems.
The largest single difference identified in the course of phases 2 and 3 was that the input flake had significantly
lower levels of contamination than the output pellet from the phase 1 trials. This implies that the input flake for
the phase 1 trials had very much higher levels of contamination, possibly by as much as an order of magnitude.
The small scale trial work identified melt and flake temperature as significant factors in increasing cleaning
efficiency. Based on this the temperature of both the vacuum chambers and the extruder in phase 3 was raised
in comparison to the phase 1 configuration. However, without reassessing the phase 1 samples using the new
GC/MS techniques it is not possible to establish by how much this change improved extraction of the
contaminants. It is expected that the adoption of a Vacurema Prime configuration rather than the continuous
Advanced mode will also have improved cleaning efficiencies.
The KT and Reactor vacuum chambers were shown to be capable of removing material in the volatility range of
isopropyl myristate at cleaning efficiencies in the range of 60%, under continuous operating conditions, and up to
80% during the run out of the system. This indicates that there is scope to improve on the steady state cleaning
efficiency. It would therefore seem sensible to quantify the effects of water and air stripping in the vacuum
chambers.
The small scale trials also showed that twin screw extruders are capable of cleaning to a very high efficiency in a
single pass direct from washed flake. However despite the relatively high melt temperatures in the phase 3 trial
Scoping study into food grade polypropylene recycling
76
the cleaning efficiency of the Vacurema vent port was very low. This is in line with previous investigations during
the development of the rHDPE process.
Melt stripping is a common technique for the production of virgin polymers, where low levels of residual
monomers and solvent have to be removed. Since this technique can be used with both single and twin screw
extruders it would be an area where the performance of the existing installed Vacurema equipment could possibly
be improved. This means the improvement could potentially be achieved without the need to move to multiscrew extruders, which would have substantial capital investment issues.
Whilst it was possible to show that hand sorting under controlled conditions is capable of meeting the
requirement for >99% previous food contact material, it is not able to achieve similar levels of polymer purity.
This was found to be one of the principle factors in the relatively low yield of the washed PP flake. The reliability
of this technique in industrial production is also not expected to be capable of maintaining regulatory compliance,
given the considerable statistical difficulty of combining viable sample sizes and the need for sampling errors to
be substantially below 1%.
When combined with the exceptional high cost of conducting a two stage, high quality hand sort it is clear that
the commercial production of food grade rPP will be critically dependent on the development of an automated
selection technique. The growing use of natural blow moulded HDPE containers suggests that such techniques
may also become necessary in the future to secure the continued production of food grade rHDPE.
7.4
Packaging manufacturing trials
The rPP could be both thermoformed and injection moulded on conventional commercial equipment at 100%
recycled content rates.
During thermoforming trials at 100% recycled content some issues were noted with the melt properties due to
the relatively high MFR, but these could be controlled by normal process parameters. The resulting products had
slightly lower ambient impact strength but slightly higher chilled impact strength. However some pin holing due
to solid contamination was noted in high stretch regions during vacuum forming, indicating that improvements in
the melt filtration would be required in commercial production. This would also be expected to improve impact
behaviour.
By contrast in injection moulding the relatively low MFR resulted in increased clamping force requirements and
injection times. In spite of this it was possible to manufacture relatively thin walled containers with a good
surface finish.
However since it is unlikely that the rPP would be used at 100% recycled content commercially, the majority of
the process issues could be addressed by selecting a grade of virgin material for the blend with either a higher or
lower MFR than the original polymer respectively, so that the flow properties of the resultant blend are much
closer to the current system.
7.5
Gas chromatography assessment by Fraunhofer IVV and PIRA of rPP in comparison to
virgin PP
Post consumer rPP shows elevated levels of both oligomers and contaminants. However, as was the case for
HDPE, the Vacurema process was highly effective at removing the volatile substances that form the majority of
the post consumer contamination. Both headspace and extraction GC showed low levels of these substances, as
well as oligomer concentrations that were lower than for typical virgin polymer. Based on the reduction in
oligomers cleaning efficiencies of 90 to 95% were seen. Headspace GC can provide an insight into the relative
volatility and thereby size and concentration of extractable species. In contrast, GC/MS permits quantification of
these species and also, by nature of the prior extraction into a solvent, an insight into species of inherent lower
volatility.
Interestingly, whilst the exact pattern of post washing contamination was highly variable, little difference could be
seen between the average levels in positively picked and negatively picked material, except for a much higher
level of limonene in the later.
Using extraction GC/MS it was also possible to look at the non-volatile oligomers and contaminants it could be
seen that the oligomer concentrations were higher in the rPP than in the virgin material. This reflects the much
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lower cleaning efficiency in respect of low volatility material, which sets a limit to the type of contaminant that
can be removed by the Vacurema process.
The significance of this limit is much less for polymers with a low diffusivity such as PET than for polyolefins such
as HDPE and PP, since low diffusivity polymers both absorb less contaminants and also then effectively trap these
materials resulting in very low levels of migration in use. In the absence of a method of removing such low
volatility material from the recyclate, it is the need to prevent them from entering the recycling process in the
first place that is behind the greater than 99% previous food contact threshold limit.
Whilst a great deal of the migratable material from the rPP was found to be either typical polymer oligomers or
positive list additives, such as anti-oxidants and slips agents, some significant concentrations of non-positive list
materials could also be identified. This means that the Vacurema process, in isolation from the other stages of
the complete recycling chain, might not be effective in adequately reducing the presence of all anticipated nonpositive list species and so could impact upon the potential use of the recycled polymer. A number of process
modifications to the set up used are available, including optimised stirring blades for the vacuum chamber,
extruder screw and design modifications which may be helpful in extending the range of contaminants that can
be removed. But effective sorting and prevention of residual content cross contamination will remain the only
effective barrier for some of the ultra low volatility substances identified.
The highest levels of migration, 190ppb, were recorded for isopropyl myristate, a cosmetic and personal care
additive, under simulant conditions for prolonged fat contact at room temperature (10 days at 40°C - 95%
ethanol and two days at 20°C – isooctane). Whilst this is approved for use as food flavouring and as a
component of mouth wash it is not currently on the positive list for packaging materials. A large number of other
peaks of post consumer origin were however seen and it may also be the case that still more substances were
present but were masked by the complex pattern or polymer oligomers. This unexpected result may require the
development of further refined characterisation techniques.
7.6
Provisional theoretical addition rate for food contact
Reflecting the need to reduce the levels of non-positive list migration to the widely accepted limit of 10ppb for
benign unlisted substances, the maximum concentration of this rPP that could be used for full fat contact at room
temperature, for example margarine tubs, would be less than 5%.
The maximum concentration of rPP would however be dependent both upon the food type and the storage
conditions. For instance under chilled conditions, for example a pâté pot, rates of migrations would be
considerably reduced and so a higher addition level of rPP permissible. Indeed were the testing to be performed
under the conditions used for HDPE milk bottles (ten days at 20°C – 95% ethanol) then an approximately fourfold reduction in migration might be expected and so the maximum rPP content could be raised by a
corresponding amount.
Likewise different foods have different sensitivity, which is reflected in the legislation, by the use of multipliers.
Thus for fish and meat a factor of three and four respectively may be applied to the fat stimulant migration test
results, meaning that a maximum rPP of 15 and 20% would be allowable.
The picture for aqueous foods is much better, with much lower levels of migration being recorded for both 3%
acetic acid and 10% ethanol. Working on a precautionary basis to allow for potential masking by oligomers a
maximum room temperature rPP content was set at 30%.
For dry and semi dry foods, such as mushrooms, there is currently no simulant testing prescribed, since rates of
transfers would be very low due to the lack of liquid and also poor contact between the food substance and the
packaging. In this case it is possible that use of rPP up to 100% would be permissible.
However it should be noted that further work is required to develop tests methods to exclude the issue of
oligomers masking hazardous materials, such as ink decomposition products. In addition these figures are based
on a simple linear extrapolation which would require verification by tests on actual blends of virgin and rPP
material.
Furthermore the use of rPP would require the submission to and acceptance of a technical dossier by EFSA so
that the entire recycling process can be assessed.
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7.7
Key recommendations for further work following this scoping study
In order to make the rPP suitable for use at commercially significant rates of incorporation of recycled material,
the twin enabling issues of odour and non-positive list contamination need to be addressed. Critical to this
process is the identification of the source of both, which will require the analysis of individual classes of packaging
to assess the contribution that they make, both in terms of residual contents and substances absorbed into the
polymer packaging.
Cross-contamination would be the easier of the two to deal with, since it would require only improvements to the
washing regimes, whilst absorbed substances from non-food contact applications would require further
improvements to the sorting process, possibility to levels well in excess of 99%.
At a commercial level, improvements in both yield and the cost of sorting are required to offer an adequate
return on the expected sales price of rPP. This means identifying a credible, automated method of sorting food
contact from non-food contact packaging. Furthermore, it has to be capable of achieving the sorting levels
determined from the odour and non-positive list investigations. An initial review of the options available for
marking food packaging identified three basic approaches:
„ Existing labelling system;
„ Marking the polymer; or
„ Coating the finished packaging.
The chosen route would require the following essential features:
„ Compliance with food packing legislation;
„ Suitability for established sorting technology;
„ High rates of positive identification with associated low rates of false positives; and
„ Deactivation through conventional recycling processes to prevent mis-identification in the second recycling
loop.
Furthermore during the primary recycling process, deactivation or removal of the marking/tagging substance
would be required in the anticipated scenario of recycled food packaging being processed into non-food contact
applications. This would prevent accumulation of the marking/tagging substance in the non-food contact
recyclate stream. A detailed review of each of these options is given in Appendix 5.
To meet regulatory requirements the potential for oligomers to interfere with the GC-FID assessment of specific
migration needs to be assessed and analytical techniques specifically tailored to the needs of rPP developed. As
part of this, the potential for carcinogenic breakdown products from inks need to be reviewed and measured to
prevent or minimise this. The design of a robust challenge test will also be vital for the preparation of a technical
dossier for approval by EFSA.
Finally improvements to the specification of the product should be targeted. These should include, for instance,
reducing the size and quantity of particulate contamination through better melt filtration in order to improve
impact and thermoforming behaviour. Improvements to the colour performance by changes in design practice in
partnership with the packaging industry; for instance by reducing opacity by lowering levels of titanium dioxide or
reducing the amount of on-polymer printing and in-mould labelling would also improve market acceptance and
maximum rPP addition rates.
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www.wrap.org.uk/foodgradepp