Polymer Degradation and Stability 91 (2006) 894e901
www.elsevier.com/locate/polydegstab
Recovery of polyols from flexible polyurethane foam by
‘‘split-phase’’ glycolysis with new catalysts
Carolina Molero, Antonio de Lucas, Juan F. Rodrı́guez*
Department of Chemical Engineering, University of Castilla-La Mancha, Avda. Camilo Jose´ Cela s/n, 13004 Ciudad Real, Spain
Received 20 May 2005; accepted 22 June 2005
Available online 5 October 2005
Abstract
Polyurethanes (PU) represent one of the most important groups of plastics, so the increasing quantity of wastes makes their
recycling an urgent task. The general purpose of polyurethane chemical recycling is to recover constituent polyol, a valuable raw
material. Among the suitable processes, glycolysis, specially in two phases, allows better quality products. In this study glycolysis
reactions of flexible polyurethane foams were conducted in ‘‘split-phase’’ with different catalysts, in order to study their activity.
Diethanolamine, titanium n-butoxide as well as octoate salts, which are novel compounds for this application, showed suitable
catalytic activity. Reaction kinetics and glycolysis products were investigated. Times to reach complete conversion, chemical
properties of the polyol phase and its purity depend on the catalyst employed. The novel catalysts developed have been probed to be
a worthy and economic alternative to traditional catalysts.
Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: Polyol; Polyurethane; Recovery; Glycolysis; Catalysts
1. Introduction
In recent years, polyurethane (PU) materials have been
developed strongly in the world, proving it to be one of the
most versatile polymers. Since legislative measures for
wastes involve increasing economical costs and public
awareness of environmental issues has grown enormously, PU recycling is nowadays an urgent task. In the
chemical recycling, the urethane bonds can be broken
down releasing the polyols of the polymer chain by means
of a suitable reagent. In the literature processes have been
described based on hydrolysis and hydroglycolysis [1e4]
or methanolysis [5] which can convert the PU into a liquid
mixture of polyol and aromatic products. The reaction
* Corresponding author. Tel.: C34 926 295300x3416; fax: C34 926
295318.
E-mail address: [email protected] (J.F. Rodrı́guez).
0141-3910/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymdegradstab.2005.06.023
provides high conversion but leads to some drawbacks
associated with purification costs and toxicity. PU has
been also treated with esters of phosphoric acid [6] and
low weight alkanolamines [7,8], although glycolysis seems
more suitable to be applied on an industrial scale in order
to obtain quality recovered products.
In the glycolysis processes, the polyurethane chain is
degraded by successive transesterification reactions of
the urethane bond with low molecular weight glycols
with the aid of a catalyst. Several studies have been
published dealing with glycolysis of polyurethanes
[9e21], concerned mostly with formulation of glycolysis,
properties of the products obtained from the recycled
polyols and purification of the resulting products.
Among other reaction variables, the choice of catalyst
is an important factor affecting the properties of the
recovered products, as well as the time to reach the
complete degradation of the foam. Catalysts used in
polyurethane glycolysis include bases like amines,
895
C. Molero et al. / Polymer Degradation and Stability 91 (2006) 894e901
hydroxides and alkoxides and Lewis acids as well [22],
leading to different extension in secondary reactions.
Typical catalysts of hydrolysis such as alkaline
hydroxides have been used in glycolysis processes [23],
despite as reported by Simioni et al. [9] that hydrolysis
reactions were promoted by potassium hydroxide,
leading to higher contents of undesirable aromatic
amines. Acetates of Pb, Zn, Mn, Ca, Co and Cd have
been described as general catalysts in transesterification
reactions [24], although in the case of transesterification
of urethane bonds with glycols, only potassium acetate
and sodium acetate are mentioned in the literature
[10e12], leading to high amine values in the resulting
products. As well as aminolysis agent, alkanolamines
have been used as co-reagents. Borda et al. [13] studied the
dependence of the reaction time on the ratio of diethanolamine to ethylene glycol, whereas Hayashi et al. [14] also
included influence of monoethanolamine and triethanolamine. The increase in the amount of alkanolamine
provides advantage for the decomposition reaction,
although also increases the hydroxyl number and the
amine number. In the last years unspecified organometallic catalysts have been used in glycolysis processes
[15e17], specially in development of industrial-scale
processes [25,26]. Among organometallic compounds,
titanium n-butoxide has been reported [18,19] as selective
catalyst for the urethane group transesterification.
Due to the presence of glycolysis agent, in most of
the glycolysis processes above described polyols are
recovered in a liquid mixture of products containing
hydroxyl active groups. Nevertheless, better quality
products can be achieved from flexible foams using
a two-phase glycolysis, enabled by the higher molecular
weight of polyols used in these kind of polyurethanes.
By means of the use of excess amount of glycolysis
agent, much more than the stoichiometric quantity, the
reaction product splits in two phases, where the upper
layer is mainly formed by the recovered polyol from the
PU [20].
In this work, two-phase glycolysis reactions of flexible
PU foams based in polyether polyols have been carried
out with diethylene glycol (DEG) in presence of different
catalysts, in order to study their influence on the process:
diethanolamine, titanium n-butoxide and potassium and
calcium octoates as novel compounds for such applica-
tions. DEG was selected to study catalyst influence and
has since proved to be the most suitable low weight glycol
to recover polyols from flexible polyurethane foams by
split-phase glycolysis [20].
2. Experimental
2.1. Materials and methods
Industrial samples of flexible PU foam based on
polyether polyol [poly(propylene oxide-block-ethylene
oxide) M w 3500, functionality with respect to OH
groups of tree] and toluene diisocyanate (TDI) were
scrapped with an arbitrary diameter ranging from 5 to
25 mm. These foams had been prepared in the presence
of a cell regulator (surfactant), crosslinking agent,
catalyst, colouring agent, mineral loads and water as
a foaming agent. The scrap foam was reacted in a 1:1.5
mass ratio with diethylene glycol (DEG) (PS, from
Panreac, Spain). As catalysts we used diethanolamine
(DEA), titanium(IV) butoxide, potassium octoate and
calcium octoate (Table 1).
The glycolysis reactions were carried out in a jacketed
1 dm3 flask equipped with stirrer and refluxing condenser under nitrogen atmosphere to avoid oxidation.
The glycolysis agent was placed in the flask and when
the temperature raised up to the desired level, the
required quantity of scrap foam was added during an
hour by means of a continuous feeder at a constant rate,
according to its dissolution. This feeding rate selected
was 5 g minÿ1. The zero time for the reaction was taken
when all the foam was fed. Temperature was maintained
at 189 C during the feeding and the reaction.
2.2. Characterization
At given time intervals aliquots were sampled, cooled
and centrifuged to ensure the total separation of phases.
They were dissolved in tetrahydrofuran (THF from
Panreac, Spain) at a concentration of 1.5 mg mLÿ1 and
then filtered (pore size 0.45 mm). Gel Permeation
Chromatography (GPC) was used to determine the
molecular weight distribution (MWD) as well as
concentration of polyol in the products. Measurements
Table 1
Properties of the catalysts used
Catalyst
Purity
Concentration (by weight)
Supplier
DEA
Ti(IV) butoxide
K octoate
(potassium 2-ethylhexanoate)
Ca octoate
(calcium 2-ethylhexanoate)
98.0%
98C%
46.4% in decyl alcohol
(isomers mixture)
32.3% in Tb 200e220 C
petroleum distillate
Mass ratio to glycol 1:6
0.34% in the glycolysis agent
2.2% in the glycolysis agent
Panreac, Spain
Aldrich, USA
Nusa, Spain
2.2% in the glycolysis agent
Nusa, Spain
C. Molero et al. / Polymer Degradation and Stability 91 (2006) 894e901
were performed with a Shimadzu chromatograph
(Kyoto, Japan) equipped with two columns (Stryragel
HR2 and Styragel HR0.5) using THF as eluent at 40 C
(flow: 1 mL minÿ1) and a refractive index detector.
Poly(ethylene glycol) standards (from Waters, USA)
were used for MWD calibration and mixtures of
industrial starting polyether polyol and DEG were used
as concentration standards. The glycolysis products
were separated and their properties were analysed.
Hydroxyl number and acidity were determined by
standard titration methods (ASTMD-4274-88 and
ASTMD-4662-93, respectively). Amine values in products were determined by a titration method based on
ASTMD-2073-92, and the solvent was changed for
a mixture of 1:1 tolueneeethanol. Water content was
determined by KarleFisher method and the viscosity
was measured by a rotational Brookfield LVTDV-II
viscometer. All chemicals used in these analyses were of
the quality required in the standards. Chemical structure
of glycolyzate products was studied by Fourier Transform Infrared Spectroscopy using a Perkin Elmer
16PCFT-IR spectrometer; droplet samples were impregnated on KBr wafers.
5h
10 min
Intensity (a.u.)
896
2h
10 min
1h
10 min
I
10 min
The importance of catalyst lies in the fact that in
contrast to direct esterification, trans-reactions with
alcohol groups proceed very slowly in the absence
of catalysts under mild conditions [24]. A previous
experiment in absence of catalyst was carried out to
have a comparison reference on the ability of the
different catalysts for polyurethane degradation.
As mentioned before, two phases are obtained in the
split-phase glycolysis where the recovered polyol remains mainly in the upper layer. The GPC chromatograms of upper phase samples (Fig. 1) at different
reaction times demonstrate that as the time reaction
progresses, the polyurethane structure is degraded by
the glycol and converted into smaller fragments
(urethane oligomers), releasing polyol to the reaction
media. Although the intensity of peak I, originated
by these oligomers, decreases with the reaction time,
the decomposition process proceeds very slowly in
the absence of catalysts. After a reaction time of 5 h
the polyurethane chain is not yet completely broken, as
revealed by the polyurethane oligomer content. The
breakdown of the polymer chain allows the recovery of
the starting polyol (peak II), increasing their concentration as the urethane oligomers are decomposed. Peaks
III and IV, corresponding to a mixture of the main
adducts and peak V, corresponding to the reactant
glycol, also decreased their intensity and therefore their
concentration in the upper phase with the progress of
the reaction. The formation of the low weight glycolysis
III
V
10
3. Results and discussion
IV
II
12
14
16
18
Elution time (min)
Fig. 1. GPC chromatograms of upper phase samples obtained with
DEG in absence of catalyst as a function of time. Peak I Z urethane
dimers and higher oligomers; peak II Z recovered polyether polyol
(MpII Z 3627); peaks III and IV Z reaction by-products (MpIII Z 430,
MpIV Z 290); peak V Z glycolysis agent (DEG) (MpV Z 105).
products and the release of the polyol agree with the
mechanism of PU degradation under the action of
hydroxyl groups of the glycol. This mechanism involves
intermolecular transesterification of urethane and urea
bonds. The lasts are also present in the polyurethane
structure since they are formed in a small quantity in
polyurethane production as a result of using water as
foaming agent. Allophanate and biuret groups, which
are present in a reduced quantity in flexible foams, are
almost destroyed at the reaction temperature because of
their low thermal stability [27], yielding lower molecular
weight urethane and urea-containing products. Sterically crowded urethane groups and urea groups which
are more stable during alcoholysis may be preserved in
the PU matrix.
3.1. Glycolysis in presence of catalysts
Potassium and calcium octoates have been assayed as
novel catalytic compounds for the glycolysis process.
These salts have not been previously described for this
application.
897
C. Molero et al. / Polymer Degradation and Stability 91 (2006) 894e901
As a result of the glycolysis processes of a commercial
polyurethane waste in presence of catalysts, a tri-phasic
product is obtained. It is constituted by two liquid layers
and a small solid bottom layer. It has been found that the
top liquid phase is mainly formed by the recovered polyol
from the PU, polluted with a small amount of the bottom
liquid layer. In Fig. 2(a) the GPC chromatograms of the
industrial starting polyether polyol used for the foam
synthesis and the upper phase reaction product obtained
with potassium octoate as catalyst after 120 min of
reaction are shown. The main product in the upper phase
corresponds to the starting polyol which is completely
recovered with similar characteristics of the virgin one. It
is obtained without relevant loss of molecular weight
and similar polydispersity (Mwindustrial standard Z 3579,
P Z 1.053; Mwrecovered product Z 3325, P Z 1.067). This
fact shows that the polymer is basically recovered as it
was used in the polyurethane foam synthesis. Higher
Intensity (a.u.)
a)
industrial
standard
recovered
product
10
12
14
16
18
Elution time (min)
b)
molecular weight products are absent as a result of the
complete degradation of the polyurethane chain. The
bottom liquid phase is formed by low weight products:
mainly the excess of DEG used and aromatic by-products
derived from the starting isocyanates (peaks I and II)
similar to that obtained in absence of catalysts. Although
a little quantity of the bottom phase is dissolved in the
upper one, by decreasing its purity, all the recovered
polyol remained in the upper phase, as observed in
Fig. 2(b). In the chromatogram of the bottom phase
obtained there is not the characteristic peak of polyol
presence. The bottom solid phase, which comprises a low
percentage of the total quantity of glycolysis products, is
formed by the calcium carbonate used as mineral filler in
the PU formulation.
Oligomer content in the upper phase is related to the
rate of polyurethane decomposition and recovery of
polyol, and it is assumed that when it reaches the zero
value the complete degradation of the PU foam is
achieved. Fig. 3 shows the influence of the catalyst on
oligomer disappearance history in the upper phase as
well as in absence of them in order to compare their
destructing activity. All the catalysts studied, including
the novel substances, allow the complete breakdown
of the polyurethane chain, increasing noticeably the
decomposition rate against the non-catalysed process.
When no catalyst is used the glycol allows a partial
recovery of polyol only as an effect of temperature. In
agreement to the literature [18,19] the titanium alkoxide
can be successfully applied as catalyst to glycolysis
processes, reaching the complete degradation of the
polyurethane chain. However, the glycolysis carried out
in presence of DEA and both the octoates shows faster
disappearance rate than the process with the titanium
compound. The overall activity of alkoxides as catalysts
has been explained [28] as the result of various factors.
The most relevant of them are exchange reaction
DEG
Intensity (a.u.)
30
DEA
Ti butox.
K oct.
Ca oct.
no cat.
25
20
% weight
II
I
15
10
5
10
12
14
16
18
Elution time (min)
0
0
Fig. 2. GPC chromatograms of phases obtained with DEG and
potassium octoate in the glycolysis agent. (a) Upper phase: comparison
with the industrial starting polyol (Mwindustrial standard Z 3579,
P Z 1.053; Mwrecovered product Z 3325, P Z 1.067). (b) Bottom phase.
Peaks I and II Z main reaction by-products.
50
100
150
200
250
300
350
Reaction time (min)
Fig. 3. Evolution of oligomer content in the upper phase during the
glycolysis reaction of PU foams for different catalysts in presence of
DEG as glycolysis agent. Tr Z 198 C; Wglycol ag./Wfoam Z 1.5.
898
C. Molero et al. / Polymer Degradation and Stability 91 (2006) 894e901
capability of the original ligands with reactants, effects
on concomitant reactions and specially solubility in the
reaction medium. The solubility problem is solved for
octoates since they are amphiphilic molecules, where the
carboxylic acid group represents the hydrophilic part
and the hydrocarbon moiety represents the hydrophobic
one. In addition to these effects, titanium butoxide
stability can be affected by humidity, oxygen or
temperature, decreasing its activity against more stable
catalysts like DEA and octoates.
In order to design a polyol recovery process suitable
to be applied in industrial scale, the polyol content in the
upper phase should be as high as possible, avoiding
complex purifications. Polyol concentration history in
the upper phase has also been evaluated as a function
of the catalyst used, Fig. 4. As it was expected, the
appearance of polyol takes place in parallel to oligomer
disappearance. All catalysed reactions reach the plateau,
namely the total polyol release, against the process in
absence of catalyst. Once finished the release of polyol
to the reaction media, it is observed a high polyol
concentration in the upper phase for the catalysed
processes, greater than 80% by weight in all the cases.
Although the molar ratio of polyol recovered from the
PU matrix and by-products generated is 1:1, there is
a great difference between percentages in weight
observed of each one due to their so different molecular
weights. This fact implies that a change in the byproducts due to change of the degradation mechanism
(i.e. hydrolysis instead of glycolysis trans-reactions) does
not affect strongly to the concentration in weight of
polyol. Therefore the final concentration does not
change significantly with the type of catalyst used. In
addition, the polyol concentration depends basically
on its solubility in the glycolysis agent. The polyol
concentration varies by about 5% as a function of the
catalyst employed. Although in the first stages of the
90
80
reaction, DEA seems to be more active in the PU
degradation, potassium octoate reaches the same final
polyol concentration and in a period of time similar to
that required for DEA.
It can be observed in Table 2 that properties of upper
phases obtained without further purification, such as
viscosity, water content and acidity do not differ from
commercial requirements for starting polyols due to the
high polyol concentration. Though a decrease of
viscosity is expected because of the effect of dilution
by glycol phase, this property must be strongly
influenced by the reaction by-products present. They
are derived from the aromatic segments of the isocyanate used in the foam which pollute in small
quantities the polyol phase and increase their viscosity.
The glycolysis product obtained in absence of catalyst
still contains PU oligomeric chains, increasing the
viscosity value. Water content is slightly increased by
humidity absorbed during foam storage and glycol
content.
In spite of the fact that the properties previously
mentioned are almost similar to the starting polyol,
hydroxyl number becomes higher than that is required.
The lower molecular weight and functionality of the
glycol dissolved in the upper phase modify the resulting
hydroxyl value, increasing it as greater is the amount
dissolved. However, changes in the foam formulation or
an extraction to reduce hydroxyl value would make the
recovered polyols able to be used again in new flexible
polyurethane foams without decreasing the quality.
As a consequence of the degradation process of the
polyurethane, the recovered products contain amine
functional groups, reported as amine value in Table 2.
This amine value is mainly originated from primary
amines derived from the starting isocyanates employed in
the PU synthesis. In presence of water either as water
content of the glycol or as humidity adsorbed in the foam
from the surroundings, hydrolysis of urethane bond
happens in parallel to the glycolysis process. An instable
carbamate is formed (1), which at the reaction temperature decarboxylates readily to form aromatic diamines.
70
O
% weight
60
O
φ
50
R
HN
O
+ H2O
HO
R + φ
HN
(1)
OH
40
DEA
Ti butox.
K oct.
Ca oct.
no cat.
30
20
10
0
0
50
100
150
200
250
300
350
Reaction time (min)
Fig. 4. Evolution of polyol content in the upper phase during the
glycolysis reaction of PU foams for different catalysts in presence of
DEG as glycolysis agent. Tr Z 198 C; Wglycol ag./Wfoam Z 1.5.
H2N
φ +
CO2
These products are undesirable as they have a negative effect on PU synthesis because of their toxicity. On
the other hand, although the transesterification reaction
leads glycol transesterification carbamates for urethane
bonds, for urea bonds the resulting product is aromatic
diamines. The presence of diamines generated as a result
899
C. Molero et al. / Polymer Degradation and Stability 91 (2006) 894e901
Table 2
Properties of recovered polyols
Catalyst
Viscosity (cp)
Acidity
(mg KOH/g)
Water content
(% w/w)
OH number
(mg KOH/g)
Total amine
(mg KOH/g)
Primary amine
(mg KOH/g)
None
DEA
Ti(IV) butoxide
K octoate
Ca octoate
838
584
600
525
589
0.013
0.010
0.006
0.018
0.013
0.46
0.42
0.91
0.21
0.10
e
131
144
171
165
e
11.62
4.32
3.83
6.88
e
10.49
4.32
3.83
6.52
Raw polyol
560 G 30
0.100
0.10
48
e
e
primary amines in the final properties of the recovered
polyol. The presence of secondary amines in the product
obtained with calcium octoate may be produced as
a result of decarboxylation of transesterification carbamates, according to a secondary pathway proposed by
Borda et al. [13].
In Fig. 5 are shown the FTIR spectra of the starting
polyol used in the synthesis of the polyurethane foam (a)
and the upper phases obtained with DEA as catalyst (b)
and potassium octoate (c). The IR spectral examination
confirms the GPC results: the chemical structure of the
recovered polyols obtained by glycolysis is quite similar
to the virgin one. This is demonstrated by the presence
of absorption bands characteristic of the starting polyol
in the upper phase: intense stretching vibrations of the
aliphatic ether group at 1109 cmÿ1, overlapping the
band produced by CO groups associated to hydroxyl
end groups and stretching vibrations of these OH
groups at 3460 cmÿ1. There are absorption bands in
the spectral region of 2970ÿ2869 cmÿ1 due to stretching
of glycolysis in urea bonds cannot be nullified but they
only comprise a small quantity in flexible foams. For
that reason the way to minimize aromatic primary
amines quantity is related to the choice of catalyst.
Selective catalysts in the glycolysis process against
hydrolysis are able to reduce up to the minimum the
quantity of these undesirable products.
Titanium catalyst shows high selectivity to glycolysis,
as demonstrates its low amine content, showed in Table
2; however, this content is strongly increased when DEA
is used. The low primary amine content in the recovered
products using the novel catalysts studied points out
that they also promote glycolysis against hydrolysis,
acting as selective catalysts. In the case of potassium
octoate the amine content is even lower than that in the
process carried out with the titanium catalyst, showing
higher selectivity to the glycolysis. It is worth noting that
in the reaction where DEA is used, the secondary amine
groups of the catalyst also increase the total amine value
though their presence does not affect as negatively as
(a)
3487
(b)
1736
3468
1625
1521
(c)
1732
3478
1624
1537
4000
3000
2000
1500
1000
600
cm-1
Fig. 5. Comparison of polyols IR spectra: (a) industrial standard, (b) recovered polyol obtained by glycolysis with DEG and DEA as catalyst,
(c) recovered polyol obtained by glycolysis with DEG and potassium octoate as catalyst.
900
C. Molero et al. / Polymer Degradation and Stability 91 (2006) 894e901
vibrations of CH bonds in aliphatic carbons and in 1455
and 1373 cmÿ1 characteristic of bending vibrations of
methylene groups in the polyol chain. The upper phases
obtained are polluted in a small quantity by the main
products of the bottom phase, which makes the spectra
exhibit slightly different from that of pure polyol. The
glycol dissolved in the upper phase does not affect in
a significant way the absorption bands since its
molecular structure is similar to the constituent units
of one of the blocks of the polyol, except from the
increase of the quantity of hydroxyl groups (absorption
band at 3468 cmÿ1). The new absorption bands at 1736,
1625 and 1521 cmÿ1 in spectrum (b) and 1732, 1624 and
1537 cmÿ1 in spectrum (c) are related to transesterification and decarboxylated products which show partial
solubility in the upper phase, being the main pollutants
of the polyol.
Bands assigned to stretching vibrations of the C]O
bond in urethane groups [9,14,21] are found around
1690e1749 cmÿ1. According to this, the bands observed
at 1736 and 1732 cmÿ1 can be assigned to urethane
groups, particularly to those coming from toluene
diisocyanate because of the associated band at 1521
and 1537 cmÿ1, respectively. The band at 1625e
1624 cmÿ1 in both spectra can be assigned to primary
amines formed (bending vibrations of NH). The polyol
recovered with DEA as catalyst shows higher intensity
of the absorption band for these primary amines, in
conformity with the titration analysis results shown in
Table 2.
4. Conclusions
In this study glycolysis of flexible PU foams has been
investigated in presence of different catalysts in order to
obtain high quality recovered polyols via split phase in
a short reaction time. The traditional products DEA
and titanium n-butoxide have been employed as well
as two new catalysts for the process: potassium and
calcium octoates. All the catalysts assayed showed
appropriate activity compared with the non-catalysed
process, allowing the complete recovery of polyols from
the polyurethane matrix. Potassium and calcium
octoates, specially the first, have been found advantageous for the recovery process. Potassium octoate leads
to the complete degradation of the polymeric chain at
low reaction time and the recovery of the polyol in high
concentration. These reaction time and concentration
are comparable to those obtained with DEA, the most
active catalyst studied. One of the main advantages is
that the amount of octoate used represents only 15%
by weight of the DEA needed. On the other hand,
potassium octoate has shown high selectivity for the
glycolysis process, avoiding hydrolysis. In presence of
this novel catalyst the lowest primary amine content has
been obtained, improving the performance of titanium
butoxide. As a result, the novel catalysts developed have
proved to be of a low cost and improved alternative to
reported catalysts.
Acknowledgments
Financial support from REPSOL-YPF S.A. through
the General Foundation of the UCLM and a grant from
European Union and Consejerı́a de Ciencia y Tecnologı́a
(JCCM) are gratefully acknowledged.
References
[1] Grigat E. Hydrolyse von Kunststoffabfällen. Kunststoffe
1978;68:281e4.
[2] Gerlock JL, Braslaw J, Zimbo M. Polyurethane waste recycling.
1. Glycolysis and hydroglycolysis of water-blown foams. Ind Eng
Chem Process Des Dev 1984;23:545.
[3] Braslaw J, Gerlock JL. Polyurethane waste recycling 2. Polyol
recovery and purification. Ind Eng Chem Process Des Dev
1984;23:552.
[4] Bauer G. Alkoholyse-Chemisches Recyclingverfahren für PUR
und gemischte Kunststoffabfälle. Kunststoffe 1991;81(4):301e5.
[5] Asahi N, Sakai K, Kumagai N, Nakanishi T, Hata K, Katoh S,
et al. Methanolysis investigation of commercially available
polyurethane foam. Polym Degrad Stab 2004;86:147e51.
[6] Troev K, Grancharov G, Tsevi R, Tsekova A. A novel approach to
recycling of polyurethanes: chemical degradation of flexible polyurethane foams by triethyl phosphate. Polymer 2000;41:7017e22.
[7] Kanaya K, Takahashi S. Decomposition of polyurethane foams
by alkanolamines. J Appl Polym Sci 1994;51:675e82.
[8] Wal HR van der. New perspectives for the chemical recycling of
polyurethanes. UTECH’94 Conf., paper 51. The Hague; 1994.
[9] Simioni F, Modesti M, Rienzi SA. Recycling of polyurethane
waste. Cellular polymers int. conf., paper 36. London; 1991.
[10] Wu CH, Chang CY, Li JK. Glycolysis of rigid polyurethane from
waste refrigerators. Polym Degrad Stab 2002;75:413e21.
[11] Wu CH, Chang CY, Cheng CM, Huang HC. Glycolysis of waste
flexible polyurethane foam. Polym Degrad Stab 2003;80:103e11.
[12] Joo YL, Dukjoon K. Desaminated glycolysis of water-blown rigid
polyurethane foams. J Appl Polym Sci 2000;77:2646e56.
[13] Borda J, Pásztor G, Zsuga M. Glycolysis of polyurethane foams
and elastomers. Polym Degrad Stab 2000;68:419e22.
[14] Hayashi F, Omoto M, Ozeki M, Imai Y. General purpose
adhesives prepared from chemically recycled waste rigid polyurethane foams. In: Frisch KC, Klempner D, Prentice G, editors.
Recycling of polyurethanes. Lancaster: Technomic Publishing;
1999. p. 223e40.
[15] Simioni F, Modesti M. Glycolysis of flexible polyurethane foams.
In: Buist JM, editor. Cellular polymers, vol. 12. Shrewsbury:
Rapra Tech. Ltd; 1993. p. 337e48.
[16] Modesti M, Simioni F. Chemical recycling of reinforced polyurethane from the automotive industry. Polym Eng Sci 1996;36
(17):2173e8.
[17] Modesti M, Simioni F, Munari R, Baldoin N. Recycling of
flexible polyurethane foams with a low aromatic amine content.
React Funct Polym 1995;26:157e65.
[18] Simioni F, Modesti M, Rienzi SA. Polyol recovery from
elastomer polyurethane waste. Cell Polym 1987;6(6):27e41.
C. Molero et al. / Polymer Degradation and Stability 91 (2006) 894e901
[19] Simioni F, Modesti M. Controlled degradation of polyurethane
for recycling. Mater Eng 1991;2:127e44.
[20] Molero C, de Lucas A, Rodrı́guez JF. Recovery of polyols
from flexible polyurethane foam by ‘‘split-phase’’ glycolysis:
glycol influence. Polym Degrad Stab, in press, doi:10.1016/
j.polymdegradstab.2005.05.008.
[21] Bakirova IN, Valuev VI, Demchenko IG, Zenitova LA. Chemical
structure and molecular mass characteristics of products in the
glycolysis of flexible poly(urethane) foam. Polym Sci Ser A
2002;44(6):615e22.
[22] Bauer G. Recycling of polyurethanes. In: Weigand E, editor.
Recycling and recovery of plastics. München: Hanser Publishers;
1996. p. 518e37.
[23] Kresta JE, Xiao HX, Suthar B, Li XH, Sun SP, Klempner D.
New approach to recycling of thermosets. Macromol Symp
1998;135:25e33.
901
[24] Kricheldorf HR, Denchev Z. Interchange reactions in condensation polymers and their analysis by NMR spectroscopy. In:
Fakirov S, editor. Transreactions in condensation polymers.
Weinheim: Wiley-VCH; 1999. p. 1e78.
[25] Hemel S, Held S, Hicks D, Hart M. Chemisches Recycling von
PUR-Weichschaumstoffen. Kunststoffe 1998;88(2):223e6.
[26] Held S, Hemel S, Hicks D, Hart M. Chemical recycling pilot plant
for flexible polyurethanes. Everberg: Huntsman ICI Chemicals
L.L.C.; 2000.
[27] Ravey M, Pearce EM. Flexible polyurethane foam. I Thermal
decomposition of a polyether-based, water-blown commercial
type of flexible polyurethane foam. J Appl Polym Sci 1997;63:
47e74.
[28] Stanton MG, Gagne MR. The remarkable catalytic activity of
alkali-metal alkoxide clusters in the ester interchange reaction.
J Am Chem Soc 1997;119:5075e6.