Design for Recycling:
A Plastic Bottle
Recycler's Perspective
February 1992
prepared by
'
Richard A. Fleming
for The Partnership for Plastics Progress
i
The Society of the Plastics
Industry, Inc. ,
.
me Pnrtnershlpfor Plastics Progress has z n ~ o r p ~ j r u t e ~ l p oftbe
ros~~~~~~
former Councalf o r Solid WusteSolutwris
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,
ACKNOWLEDGMENT
While many in the industry kindly contributed their thoughts,
perspective, suggestions and examples during preparation of this
article, special appreciation goes to G. F. Schreiber, Plastic Recycling Alliance; Dr. R. A. L. Eidman, Du Pont; T. Kattray and E. A. Fox;
The Procter & Gamble Company; Dr. W. F. Carroll, Occidental
Chemical Corporation; and N. Liddell, John Brown, Inc.
..-
Contents
Introduction
1
Designing bottles for recycling
2
What “contaminants”impede recycling . . . and why
3
Design for recyclingTM:principles of container design
8
The real world: multilayer and commingled bottles
11
Other containers and other recycling processes
13
Designing for Recycling: An Educational Assessment
15
0 1992 Pai-tneiship for Plastics Progress
Printed on Recycled Paper
Introduction
T
he plastics industry and the United States Environmental
Protection Agency (EPA) agree on the four basic elements of our
national strategy for solid waste management: source reduction
(including composting), recycling, waste-to-energy incineration
and landfilling.Each has its place. Priority ranking will vary with locality,
the specific waste material mix, recycling plant capability and cost, and
with the perspective of the viewer.
This paper addresses recycling, the second element of the hierarchy.
It examines recycling of post-consumer plastics from the perspective
of those recyclers who purchase baled plastic bottles, recovered from
municipal waste, and convert them to salable flake or pellets.
The position and views expressed here are consistent with those
advanced both by the Coalition of Northeastern Governors (CONEG),
and by the Institute of Scrap Recycling Industries (ISRI). According to
ISRI, manufacturers must ensure that consumer products - plastic
ones as well as others - can be safely and economically recycled.
CONEG’S Preferred Packaging Manual states that packaging should be
designed to maximize compatibility with available recycling systems.
The plastics industry is committed to dramatic increases in the
reuse of plastic materials. Operating under the auspices of The Society
of the Plastics Industry, lnc. (SPI), the Council for Solid Waste
Solutions in March 1991, formally announced the ambitious goal of
achieving a 25 percent recycling rate for all plastic bottles and
containers by 1995. A concurrent goal is to increase the number of
communities that include plastics in their curbside collection programs to 4,000.
This industry initiative, coupled with strong citizen interest and
promoted by legislative activity, will generate a huge increase in
collection capability over the next several years. Today’s flow of
plastic bottles and other containers into the recycling industry will
turn into a torrent, and then a flood. While supply of raw material to
the industry will not be a problem, recovery of that material may be.
Recycling of plastic containers began with soft drink bottles (PET)
obtained from bottle deposit states. This feedstream was and is
homogeneous -more than 99 percent PET beverage bottles, and
clean ones at that. As plastics recycling expanded to include curbside
collection, HDPE milk bottles were collected. Today, many recycling
programs also collect mixed-color HDPE detergent/household bottles.
In some cases, all bottles and even rigid plastic packaging may be
2
DESIGN FOR RECYCLING: A PLASTIC BOTTLE RECYCLER’S PERSPECTIVE
collected. The diverse nature of collection programs results in
material streams that:
are enormously more heterogeneous in nature;
contain far more non-plastic contaminants;
are more difficult and expensive to recycle; and
are of lower economic value.
The original hand-sorting and PET-only processing operations are
giving way to newly introduced automatic sorting systems and multiresin processors. These systems are not yet capable of handling the
large variety of plastic packaging components, however. At the same
time, ingenious merchandising and technical personnel in the packaging industry, ever on the lookout for opportunities to differentiate
their products from competitive ones, will continue to change
container types and appearance. These changes can create containers
that are difficult to recycle via existing technologies.
If the plastics industry is to achieve stated container recycling goals,
efforts must be exerted not only to assure availability of raw materials
(collection programs), but also to make sure that competent recyclers
can develop economically sound businesses.
Reclamation systems will grow in capability as the industry grows.
In five to ten years, recycling should be capable of automatically
handling a wide variety of packaging designs, so that innovation in
both the plastics and packaging industry may continue to thrive.
During the interim period, however, more consideration needs to be
given to “fitting”packages into existing reclamation technologies so
that the industry has the time to grow and gain strength.
Designing bottles for recycling
Certainly many initiatives are needed in every step of the recycling
process, and many are underway. This paper, however, addresses only
the bottle design issue.
Those involved in design and construction of plastic bottles and
containers need to understand how container design affects ease and,
therefore, cost of recovery of plastic materials. Recycling compatibility needs to be included as a container design parameter. It should
be added to toddy’s long list or requirements, such as burst strength,
customer attractiveness, cost, shipping weight, regulatory status, etc.
The terminology Design f o r RecyclingTMis used to describe this
approach. It is both descriptive and appropriate. As CONEG concludes,
“Design for RecyclingTM”
is a trademark of the Institute of Scrap Recycling Industries,
Inc., 1325 G St., N.W., Washington, DC 20005.
RICHARD A. FLEMING
3
to facilitate recycling, a bottle design should take into account the
capabilities of today’s recycling processes.
Let us now consider design factors and how they influence
recyclability. Examples cited in the discussion mostly are bottles of
PET and high density polyethylene (HDPE), which constitute the
overwhelming bulk of raw material available to today’s recyclers of
post-consumer bottles. (Approximately 85 percent of all plastic
bottles are made from either PET or HDPE.) Nevertheless, the principles
are capable of general application.
What “contaminants” impede recycling.. . and
why
To consider how bottle design characteristics can create recycling
problems, two factors must be considered: 1) the type of separation
process employed by the recycler;and 2) the degree of value reduction
that unseparated minor components contribute to the final product.
In a typical recycling process for commingled bottles, the incoming
bale of crushed bottles first is positioned and restraining bands
removed. Then, the mixed commingled bottles are manually separated by type, e.g., clear PET bottles, HDPE milk jugs, etc. These bottles
after separation g o sequentially through 1)a grinder to produce flake;
2) air separation to remove loose label material; 3) a cleaning
operation to remove glue and water soluble materials;4) a hydrocyclone
to separate heavies (e.g., PET) from lights (e.g., HDPE); and finally ( 5 )
a series of driers.
Some processors invest in additional equipment to eliminate other
materials. Examples include systems for removing aluminum and
polyvinyl chloride from PET. Other process variations include use of
sink/float tanks in place of hydrocyclones.
Specifications or “typical property” listings are the vehicle by which
a seller and a buyer agree on characteristics of a sold/purchased
product. These define the agreement regarding impurities, and
normally are restricted to characterization data including deleterious
and commonly present contaminants. Therefore, they offer a quick
summary of what the industry today thinks are the factors that need
special attention for reclaimed soft drink bottles (see Table 1).Certain
contaminants are considered from the following perspective: the
ability of recyclers to accomplish separations with today’s technology
and the effects of unseparated impurities on product performance.
POLYMERS.
It is commonly true that the various packaging polymers
contaminate one another. Polymers within the same family (e.g., olefin
4
DESIGN FOR RECYCLING: A PLASTIC BOTTLE RECYCLER’S PERSPECTIVE
Table 1. Characterization factors for reclaimed PET soda bottle resin
Molecular weight
Inherent viscosity
Composition
Melting point
Physical characteristics
Density
Bulk Density
Particle size
Other
Odorb
Pesticides
Impurities
PVCa
Chloride
Aluminuma
Polypropylenea
Polyethylenea
Wooda
Papera
Watera
Off-color“
Heavy metals
GIuea
Ash
Dirt
Properties
Tensile strength
Elongation
Flexural modulus
Notched izod
Durometer hardness
Heat deflection
temperature
a. Most frequently cited contaminants
b. Often from milk, detergent, and perfume bottles
polymers such as HDPE, LDPE and PP) may be blended, but only up to
limited percentages and even then with some compromise in properties.
Polymers from different families are not melt co-processible.At the least,
the polymers will not bond to one another and at the worst they will
degrade one another.
The most mutually debilitating pair of contaminant polymers is
polyvinyl chloride (PVC) and polyethylene terephthalate (PET). PVC is
used in a variety of container types ranging from bottled water to salad
dressing, and exists in a commingled-bottle stream in other forms, as
well. These include PVC labels, liners, seals and gaskets.
When PVC products are made, the PVC is normally heated to
between 150 and 220 degrees Centigrade so that it flows into the
mold. It degrades rapidly at 230 degrees. The exact processing
temperature is defined by the amount and type of plasticizer used.
PET melts near 250 degrees Centigrade. PVC flake, therefore, will
degrade if present as contaminants in a batch of PET flake which is melt
processed at 280 degrees to form pellets, bottles or other articles of
commerce. At this temperature, PVC rapidly darkens, ultimately forms
a carbonaceous char, and, in the process, releases HC1 which rapidly
cleaves PET and reduces its molecular weight.
The current industry PET specification seems to be “zero PVC” for
many applications and u p to perhaps 300 ppm for others. New
automated technology for selectively identifying and separating PVC
bottles from a mixed container stream shows promise and was
commercialized during 1991.
RICHARD A. FLEMING
5
Some PVC bottles are amber or green, but most are clear. They
stress-whiten, unlike PET. In crushed bottles, a white crease indicates
PVC. However, crushed clear but dirty bottles of PET and PVC are almost
visually indistinguishable during the fraction of a second in which a
manual sorter must make a selection decision. Both exhibit brilliant
water-like clarity.
It is easy for manual sorters to mistakenly allow a PVC bottle to enter
a PET grinder, especially if the bottles are the same shape and size.
Subsequent separation from PET by density is not possible since flake
of rigid PVC and PET have almost the same specific gravity. Similarly,
no commercial technology is available today for selective removal of
other forms of flaked PVC such as labels, liners, seals and gaskets.
Conversely, for those recovering PVC or using it, PET is a contaminant though for a different reason. PET is a solid at temperatures used
for melt-processing of PVC.Unmelted particles of PET can mechanically plug processing machines. Or if PET ends up in the final product,
it normally is objectionable either for performance or aesthetic
reasons. The current maximum allowable concentration of PET in PVC
is 500 ppm.
METALS.Metal is present primarily as bottle caps. While large bottlers
are leading the industry to polypropylene caps, the need to separate
aluminum and steel caps will be present for several more years. There
are too many metal capped bottles in the municipal waste stream for
recyclers to economically remove caps by hand, or to simply discard
the bottles.
Metal fragments are undesirable because: 1) they can plug melt
delivery lines in processing equipment;2) are aestheticallyobjectionable;
3) can reduce physical properties of the final product; and 4) can reduce
electricalperformance parameters. Steel,harder than aluminum, can also
damage processing equipment from grinders to extruders.
Aluminum is present in applications other than bottle caps. For
example, some beverage cap liners have aluminum-lined seals.
Aluminum also is sometimes vacuum deposited on labels, but this
probably is not a problem because it is extremely thin (microinches)
and does not have mechanical integrity.
Removal of metals can be achieved several ways. Fortunately,
magnets can remove most steel contamination and, because aluminum is stable at PET processing temperatures, it can be removed by
melt filtration. For processors with melt filtering capability, aluminum
probably can be tolerated u p to 50 ppm. Otherwise, the customer’s
requirement may be “zero.”
6
DESIGN FOR RECYCLING: A PLASTIC BOTTLE RECYCLER’SPERSPECTIVE
Removal of aluminum from ground PET bottles is a challenge. Most
aluminum goes with PET in an aqueous sink/float or hydrocyclone
operation designed to separate HDPE by flotation.Some recyclers have
used “heavy medium” sink/float operations, with solutions dense
enough to float PET but not aluminum. One difficulty is that pieces of
plastic cap liners (often ethylene vinyl acetate, EVA) adhere to pieces
of aluminum cap and cause density of the composite to vary between
the two extremes. Others use electrostatic removal methods, but
again residual liner material reduces removal efficiency. For those
users requiring pelletized post-consumer recycled resin, melt filtering
during pelletization offers a final aluminum removal opportunity.
LABELMATERIAL. Information on the contents of a bottle is provided in
a variety ofways. Most, but not all bottles have labels. For example, many
milk jugs do not. Recyclers prefer labeling which either totally dissolves
in the cleaning step - or separates readily from the recovered plastic.
Labels are typically plastic (polypropylene or sometimes polyethylene), paper or plastic coated paper. The recycling process typically
uses an air classification operation to separate loose, flu@ label
material from the bulk plastic components. This generally works well
(especially if label adhesive is absent or minimal), and achieving
desired low levels of label contamination is normally accomplished
satisfactorily.
Nevertheless, many recyclers prefer paper to even a melt-compatible plastic label. While separation generally is satisfactory, the
operation does produce a substantial amount of paper sludge which
must be disposed of. Melt-compatible plastic labels minimize the
number of materials that must be separated but may contribute to
product color contamination.
“Labelless”printing of information directly on the plastic bottles
presents a special problem, since there is no method of separating the
dyes or pigments from the plastic. Consequently,for reasons discussed
below, heat transfer or other types of direct printing techniques are not
desired on clear bottles. The same printing techniques pose fewer
disadvantages for colored bottles - where there already is a large
concentration of pigments and dyes in the colorant system - so long
as the inks are melt processible with the bottle polymer.
PIGMENTS
AND DYES. Pigments and dyes are used in label advertising, in
color-coded caps, to color containers,to add identifying information,etc.
However, if not separated during processing, they can change the color
of recycled plastic resin.
RICHARD A. FLEMING
7
One advantage of label pigmentation is that the typical recycling
process effectively separates and removes labels -and any pigments
and dyes on the labels.
Colorless recycled resins are preferred. They can be used as such,
or easily colored to any tint by users. This is why clear soda bottles
and unpigmented milk jugs (without caps) are high value, and are
preferentially retrieved from commingled bottles constituting the
waste stream. The HDPE used for detergent bottles is a copolymer with
superior strength and stress crack resistant properties compared to
HDPE milk bottle homopolymer resin, but the pigments limit its
recycled end-use applications. This is why recyclers would like to see
reduced use of colorants which are inseparable from clear plastic
bottles. They prefer printing to be on labels versus printing on the
clear bottle itself.
Pigments in caps present a similar problem. There is no automated
technology now available for selectively removing colored bottle caps.
A miscellaneous mix of colored caps ground with milk jugs produces
a product (after melt processing) with colors ranging from off-white to
grey to olive drab. Generally these cannot be tinted to the bright
attractive colors on which most designers insist. Mixed color HDPE may
prove to be useful in a multilayer bottle where the outer (and
sometimes the inner) layer is of virgin resin, appropriately colored.
One final comment regardingpigments. It is most important that heavy
metals be absent. Spurred by growing legislative mandates, there is a
major industry effort to complete the job of eliminating lead, cadmium,
mercury and hexavalent chromium from pigments used in packaging
and other plastic materials. The presence of heavy metals in process
waste water can make it difficult to secure permits for sewer hookup.
ADHESIVES.
Adhesives come in many varieties and are used to secure
several components of a bottle: 1) base cup and bottle; 2) bottle and
label; 3) cap and liner; and 4) store-applied items such as price lists.
Many adhesives tend to yellow at temperatures above their recommended use range. When present as unseparated contaminants, they
can contribute undesirable color to recycled plastics, especially to PET
which is melt processed at relatively high temperatures.
Another difficulty is that insoluble adhesives tend to accumulate in
reclaiming equipment, eventually causing screen plugging and other
operating difficulties.
From the recyclers’ view, no adhesive is preferable. While this is
impractical for beverage bottle base cups, some bottles have shrinksleeve labels which require no adhesive. The next best situation is an
adhesive soluble in the recyclers’ wet processing operation. This
8
DESIGN FOR RECYCLING: A PLASTIC BOTTLE RECYCLER’S PERSPECTIVE
means ready solubility in a hot, mildly alkaline cleaning solution. If
an adhesive is required, recyclability is promoted by minimum usage
-such as affixing a label using a thin glue line, or spots of glue, rather
than with 100 percent coverage.
Design for recyclingTM:
principles of container
design
Each problem has at least one solution, though many today are not
demonstrated commercially. For example, PVC bottles can be removed
from a stream of mixed bottles after identificationusing x-ray techniques,
though these techniques don’t work well on much smaller PVC cap liners
and labels. Aluminum particles can be removed by apparatus utilizing
electrostatic principles. Fragments of paper and polypropylene labels
(after separation from polymer flake) are light and can be removed by
air classification.
All problems have solutions -but at a price. A recyclers’ solution
is needed by recyclers. They are squeezed by customers who want
consistent near-virgin quality at below-virgin prices. The preferred
recyclers’ solution is one characterized by no investment and no cost.
For them, the best solution is design f o r recycling. Design for
RecyclingTM
encourages the designer of a container to:
minimize component variety;
ensure component separability;
exclude undesirable melt-reactive combinations; and
avoid non-separable colorants.
MINIMIZE
COMPONENT VARIETY. A polypropylene bottle with a shrink fit
polypropylene label plus a polypropylene cap (same color as body)
recycles more easily and cost-effectively than one with a paper label and
aluminum cap. A PET bottle with a polypropylene label and a polypropylene cap (EVA liner) recycles better than one with a PVC label and an
aluminundfoamed PVC cap and liner.
Strictly from a recycler’s perspective, a clear PET bottle with a clear
PET base cup is better than a PET bottle with a black HDPE base cup.
However, if package performance requirements allow, it is better still
to have no base cup at all. An example is the new PET soft drink bottle
which eliminates the HDPE base cup. The use of a no-adhesive
polypropylene shrink-sleeve label together with a polypropylene
closure would further ease recycling.
ENSURE
COMPONENT SEPARABILITY.Whether the product in question is an
apartment building, an airplane, an automobile, a refrigerator, a
RICHARD A. FLEMING
9
10
DESIGN FOR RECYCLING: A PLASTIC BOTTLE RECYCLER’SPERSPECTIVE
detergent or beverage bottle, or a pair of gold-framedspectacles,the goal
is to be able to disassemble the item and reuse valuable components
when its useful life is over. The operating principle is that highest value
is obtained when individual materials are readily isolated.
Consider the PET beverage bottle as an example. A pound of clear
PET from the bottle and (separately) a pound of black HDPE from the
base cup are worth more than two pounds of a mixture of the two.
A pound of PET from the bottle and (separately) 5 grams of aluminum
from a cap are more valuable than a pound of PET contaminated with
5 grams of aluminum. In fact, this is why the term “contaminated”is
used. The minor component normally is termed a contaminant if it
reduces value.
There are, of course, many cases where minor components add
considerable value. Here, the term “contaminant”is not used. Terms
such as “additive,”“promoter,”“accelerator,”“enhancer,” “catalyst”
and “modifier”are appropriate in these cases.
In some applications, a minor component may be relatively
innocuous and act as a filler. Overall, however, purer is better. The
Design for RecyclingTMconcept recognizes that minor components
can be beneficial modifiers, can be neutral fillers or can reduce value
and be classified as contaminants.
With this perspective the question becomes, how can containers
be designed so that low concentration, value-reducing components
(contaminants) can be inexpensively separated by the manufacturing
operations most recyclers will be using?
EXCLUDEUNDESIRABLE MELT-REACTIVE COMBINATIONS. Nearly all plastic
bottles found in a commingled recycling stream are manufactured from
resins that are thermoplastic. They can be melted and frozen, remelted
and refrozen over and over again with little change in performance if it is done carefully.
However, it also is true that thermoplastics, like most materials, can
react chemically when hot-and
they must be heated to be
reprocessed and used again. It is important when designing plastic
containers to consider this point. Some polymers can react undesirably with one another during reprocessing. The qualification of
“undesirable”is required because there are some polymer/polymer
combinations where reaction does occur, but to only a small degree
and (for most applications) without undesirable consequences.
Some will degrade at processing temperatures required for others.
The consequence is that while all thermoplastics are individually
recyclable, some cannot be recycled in combination.
RICHARD A. FLEMING
11
A notable example discussed earlier is the combination of PVC and
PET. While either can be recycled alone, the combination causes
difficulty because the two polymers vary widely both in melting point
and in polymer stability.
AVOIDNON-SEPARABLE COLORANTS. Pigments or dyes used on labels or
directly on bottles, depending on design, can generate a significant
problem.
Consider again the design of a clear beverage bottle in which the
HDPE base cup is to be replaced with PET. This clearly is desirable in
light of the minimization of separate materialsprinciple. But, assume
the designer also wants to retain color coding of the base cuporange, green, blue, etc. This design then exhibits the “computer
virus” characteristic - upon subsequent melt processing, pigments
from the colored PET base cup will be inseparable from clear PET bottle
material. They will contaminate potentially huge amounts of otherwise high-value clear resin.
Contamination occurs because after grinding, recyclers commonly
separate the HDPE base cup from the PET body by sink/float or
hydrocyclone separation. Also, since in some markets green PET bottles
are of less value than clear ones, the color separation is performed first
and the two types are processed separately. Consider what happens
when HDPE base cups are replaced with colored PET.Flotation no longer
separates the base cup from the body. Processing lines will produce
clear bottle flake intermingled with flake of colored base cups. The high
value of the clear (and the green) PET are greatly reduced.
In summary, a better bottle design uses different materials which
are separable, rather than mixing clear and colored versions of the
same polymer.
The real world: multilayer and commingled
bottles
There are important factors this paper has not covered. It has addressed
neither the newer multilayer bottle designs, nor the commercially
important question, how does design of one bottle affect the recyclability
of others? Also, this paper does not explore implications of expansion
to include recycling of non-bottle containers such as jars, tubs and trays.
While a detailed discussion is beyond the scope of this paper, a few
general comments are appropriate.
MULTILAYER
BOTTLES. Multilayer bottles can present an additional
complexity, but not all multilayer bottles are alike. Sometimes the
12
DESIGN FOR RECYCLING: A PLASTIC BOTTLE RECYCLER’S PERSPECTIVE
bottle walls themselves are composed of different polymers, in a
layered construction.
The simplest and most easily recycled type is one in which an interior
layer is formed of recycled resin of the same polymer type as the virgin
outer layer and/or inner layers (e.g., the HDPE/HDPE laundry bottle).
This design employs the principle of minimizing component variability.
Another recent type, also easily recycled, contains alternative
layers of different polymers which have very low inter-adhesive
forces. These layers delaminate and separate easily during the
recycling operation, Le., they employ the principle of ensuring
component separability. An example is the PET/EVOH ketchup bottle.
A third multilayer type has a bottle wall formed of layers of different
polymers which do not mechanically separate with ease. With this
type, ready recyclability requires that the different and inseparable
polymers comprising the bottle wall be melt compatible, or employ
the principle of excluding undesirable melt-reactive combinations.
An example is the PP/adhesive/EvoH ketchup or jam bottle.
Recyclability is dependent on the particular resin combination and
the end use market for the polymer, but in most cases multilayer bottles
can be recycled as easily as those with monolayer walls - provided
they are designed with an understanding of, and an adherence to, the
principles enumerated in this paper. One of the advantages of
multilayer bottles is that they often represent substantial source
reduction - first in EPA’S hierarchy of waste management techniques.
“LOOKALIKE” BOTTLES. On a manual sorting line, operators select bottles
by type, not by polymer. If, for example, two bottles are visually similar,
they certainly cannot be quickly and accurately sorted - especially
when dirty and crushed. If they are compatible,no difficulty results from
their non-separation.However, if they are constructed of melt-incompatible polymers (for example, PVC and PET), then the recycling operator will
instruct manual sorters to accept neither bottle. The probability and
resulting financial consequence of cross contamination is just too great.
Like other problems, this one will yield to innovation. The solution
will come when polymer identification is accomplished at least in part
by some type of automated analytical instrumentation.
Automatic detection and separation of PVC bottles from PET bottles
is a new development moving from the laboratory to commercial
operation. However, until commercial scale equipment is installed
and operating effectively on their own line, recycling plant managers
still will prohibit collection of melt-incompatible “look alikes.”
Those bottles that cannot be identified (manually or automatically)
and separated must be processed as a mixed stream. Since value is
related to purity, mixed recycled plastics will bring a lower market price.
MELTFLOW VARIATION. Polymers, even of the same chemical composition, when mixed may lead to subsequent processing problems due to
differences in polymer structure, or molecular weight.
Some bottle components are blow molded, for example, the HDPE
laundry bottle and the water bottle. Other components are injection
molded, such as the beverage bottle base cup and the plastic bottle
cap. Yet another process, film extrusion, is used for the manufacture
of plastic labels.
These three processes each require different degrees of polymer
fluidity for suitable processing operability. This is achieved by
tailoring polymer molecular weight and structure.
The consequence of mixing, for example, equal amounts of lower
molecular weight PET having the higher fluidity needed for injection
molded base cups, with higher molecular weight (less fluid) PET
suitable for bottle bodies can be an intermediate molecular flow
optimal for neither process.
A reasonable question is, would recyclers prefer a clear PET blowmolded beverage bottle with a clear injection-molded PET base cup
(principle: minimize component variety) or with an injection-molded
HDPE base cup (principle: ensure component separability)? The
answer today is that the choice is not clear; both can be processed in
most plants.
What is clear is that a blow-molded beverage bottle with no base
is preferred over both.
Other containers and other recycling processes
has endorsed and promoted recycling of post-consumer plastic
containers, not just plastic bottles. Future inclusion of plastic jars, tubs,
trays, etc., will represent another substantial increase in the technical
challenge to the recycling industry. Complexity and availability of
feedstock will increase and, if contamination is allowed to increase,
value will drop.
By its nature, the type of recycling process described in this paper
is focused on identification,separation and processing of higher value
containers such as the PET beverage bottle and milk and detergent
bottles of HDPE. Addition of a multiplicity of smaller and lower volume
containers will make that job more challenging, and the new
SPI
14
DESIGN FOR RECYCLING: A PLASTIC BOTTLE RECYCLER’S PERSPECTIVE
feedstream components will have to be readily separated at costs
which the marketplace will judge to be satisfactory.
The conclusion is not that non-bottle materials should be ignored
by the recycling industry. Instead, if separation costs will be too high,
then new types of technology need to be developed for the use of
unseparated containers and flake.
In fact, research of this approach is underway. Automatic separation systems have been developed for separating bottles by resin type
and color, and work is progressing on separating bottles (extrusion
blow molding resins) from other rigid containers (injection blow
molding resins). Processes have even been developed to handle the
separation of mixed components within a container type, for example
grinding bottles then separating the resulting mixed polymer flake
using froth flotation techniques.
These technical advances will continue so that some day the
recycling of all types of plastic packaging will be technically and
economically feasible. At present, however, attention to how a
package is “designed for recycling”will be a tremendous help to the
fledgling recycling industry.
RICHARD A. FLEMING
15
Design for Recycling: An Educational Assessment
T
his assessment is designed to allow anyone to examine the
relative ease of recycling different styles of plastic bottles. It leads
to rough, educational and qualitative insights into recyclability. It
does not allow quantitativejudgements. The emphasis and intent
of the assessment is educational.
Ease of recycling is dependent on bottle design and construction.
Also, it is dependent on the precise recycling process employed. This
assessment is designed to be directly applicable to only one recycling
technology -one in common use today. In this process, the key
steps involve receipt of a bale of commingled crushed bottles,
breaking the bale mechanically to separate individual bottles, sorting
the bottles by type (manually or semi-automatically), then sending
bottles of each chosen type separately into 1) grinders; 2) cleaning
operations including separation of mixed flake by density; 3) drying
operations involving air separation of lights (label material) from
polymer flake; and finally; 4 ) packaging.
I.
Separations: How Many Materials to Separate?
A. Count the number of different polymers (fewer is better).
1. Name the body polymer(s)
2. Name the cap polymer
3. Name the cap seal polymer
4. Name the cap/seal adhesive
5. Name the label polymer
6. Name the label adhesive polymer
7. Name any other polymer used (base cup, handle, etc.)
8. Name any other polymeric adhesive used
B. Count the number of different metals (none is best).
9. Name the cap metal
10. Name the metal in the cap seal
11. Name the metal in the label
12. Name any other metal used
C. Count the types of paper used.
13. Plain paper
14. Plastic coated paper
15. Other type of paper
D. Count the number of non-plastic glues (not named above).
16. Count those soluble in warm alkali or detergent
17. Count those insoluble in alkali or detergent
E. Count other materials used which aren’t named above.
18. Name, if other material is used
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DESIGN FOR RECYCLING: A PLASTIC BOTTLE RECYCLER’S PERSPECTIVE
F. Count the total number of different materials listed above.
This determines “Product Complexity.” (In general, fewer is
better.)
11. Separations: How Easy to Achieve?
G. Mechanical separability.
19. Count the number of bonded combinations of materials
which are not readily mechanically separable after being
cut into W flake, e.g., cap/adhesive/seal (l), label/
adhesive/container (11, etc.
H. Chemical separability.
20. Count the number of combinations of materials and
material combinations which do not readily separate
within a minute after vigorous shaking (99.99 percent
separation) with a hot household cleaning solution at 150180’F.
I. Density separability.
21. Place a separated sample of each material type in room
temperature water; stir to mix without bubble generation.
Count the numerical difference between the number of
materials which float, minus the number which sink, as a
measure of effectiveness of sink/float separation.
111. Separations: Removal of Labeling Dyes and Pigments
J. Pigment/dye composition.
22. Count the number of otherwise clear plastic components
which contain labeling dyes and pigments.
IV. Separations: Chemical Consequences
K. Chemical reactivity.
23. Count polymer/polymer combinations which undergo
rapid chemical reaction to undesirable end products
when heated to the expected processing temperature.
Executive Summary
~
Recycling of plastic containers is here and growing. It began with soft
drink bottles, followed by unpigmented polyethylene milk jugs. Now,
however, essentially all bottles (and in many areas, rigid containers) are
being added to recycling programs. Plastic reclamation technologies are
still in the formative stages and are not yet able to handle the entire range
of package combinations. Therefore, we suggest that bottle designers/
producers review and adopt the following principles to maximize
compatibility of their packages with plastic reclamation processes:
1. Minimize component variety -The fewer kinds of materials (paper,
metal, glue and resin types), the better.
2. Ensure component separability -Each different material in a bottle
should separate in today’s typical recycling process employing
grinders, air classifiers, flake washing facilities and/or hydrocyclones.
3. Avoid melt-reactive material combinations - Such as PET and PVC in
the same package.
4. Avoid non-separable colorants - Such as direct printing on clear
bottles.
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DK.RICHARBA. F ~ ~ ; t r r w cis, president of P&E Consulting, Inc.,
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“Consultation on Plastics and the Environment.” Specialties include
recycled plastics, performance polymers and environmental issues
related to the manufxture, use and disposition of plastic materials and
products.
Following receipt‘of a Ph.D. in Physical Chemistry from Iowa State
University (1957), Dr. Fleming held a variety of polymer related
professional and managerial positions with DuPont through 1991.His
responsibilities included development of product and process technology for conversion of -post-municipal plastic waste to commercially useful products.
As Technology Manager -Recycling, he directed development of
‘ new and improved technology and operating procedures for two
large plastics recovery plants operated by the Plastic Recycling
Alliance LP. The PRA was created as a joint venture of DuPont and
Waste Management of North America.
Earlier DuPont activities included direction of worldwide programs
involving the invention, development and commercialization of
hundreds of higher performance engineering polymers in a wide
variety of generic polymer families.
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The Partnership for Plastics Progress
The Society of the Plastics Industry, Inc.
1275 K St., N.W., Suite 400
Washington, D.C. 20005
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-- 1-800-2-HELP-90
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