Karayandis.pdf

Chemical Recycling of PET by Glycolysis:
Polymerization and Characterization of the
Dimethacrylated Glycolysate
George P. Karayannidis,* Alexandros K. Nikolaidis, Irini D. Sideridou, Dimitris N. Bikiaris, Dimitris S. Achilias
Laboratory of Organic Chemical Technology, Department of Chemistry, Aristotle University of Thessaloniki,
GR-541 24, Thessaloniki, Macedonia, Greece
E-mail: karayan@chem.auth.gr
Received: June 19, 2006; Revised: September 8, 2006; Accepted: September 8, 2006; DOI: 10.1002/mame.200600243
Keywords: chemical recycling; dimethacrylated oligoesters; glycolysis; poly(ethylene terephthalate); UV-curable formulations
Introduction
Poly(ethylene terephthalate) (PET) is a semi-crystalline
thermoplastic polyester showing excellent tensile and
impact strength, chemical resistance, clarity, process-
ability and reasonable thermal stability.[1]
Although its
main application was by far the textile industry, tremen-
dous quantities of this material are consumed in the
manufacture of video and audio tapes, X-ray films, food
packaging and especially of soft-drink bottles. PET does
not create a direct hazard to the environment, but due to its
substantial fraction volume in the plastics waste stream and
its high resistance to atmospheric and biological agents, it
could be considered as a noxious material.[2]
PET accounts
1338 DOI: 10.1002/mame.200600243 Full Paper
Summary: In the framework of chemical recycling of poly-
mers, leading to the generation of secondary value-added
products, PET flakes taken from post-consumer soft drink
bottles, were glycolyzed with DEG. The oligomers obtained
were analyzed for their molecular weight and characterized
by FT-IR and POM. Subsequently, dimethacrylated oligo-
esters of PET glycolysate (PET-GLY-DMA) were synthes-
ized by methacrylation of the glycolyzed PET product. The
resulted monomer PET-GLY-DMA was studied by FT-IR,
POM and DSC. Thermal polymerization of this monomer
was carried out at 80 8C in the presence of benzoyl peroxide
as initiator. A UV-curable formulation was also prepared on
the basis of neat PET-GLY-DMA, as well as by mixing PET-
GLY-DMA with styrene, using DMPA as photoinitiator.
Nanoparticles of SiO2 were dispersed into PET-GLY-
DMA/styrene copolymers as reinforcing agents and the
mechanical properties of resins formed were studied.
Preparation of methacrylated PET glycolysate.
Macromol. Mater. Eng. 2006, 291, 1338–1347 ß 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

for 8% by weight and 12% by volume of the world’s solid
waste.[3]
PET recycling represents one of the most successful and
widespread examples of polymer recycling. The main
driving force responsible for this extremely increased re-
cycling of post-consumer PET is its widespread use,
particularly in the beverage and food industry. PET bottles
are characterized by high strength, low weight and
permeability of gasses (mainly CO2) as well as by their
aesthetic appearance (good light transmittance, smooth
surface), while they do not have any side effect on the
human organism.[2]
Many attempts are currently directed
toward recycling of PET waste, because of the interests in
environmental protection, energy preservation and eco-
nomic benefits.[4]
PET bottle collection in Europe (Euro-
pean Union member states plus Norway, Iceland, Switzer-
land, and all EU candidate countries) is growing steadily.
In 2004, 665 000 t were collected, an 8.4% increase in
comparison with 2003. By 2009, it is forecast that Euro-
pean PET collection will increase to more than 1 Mt.[5]
Among the different recycling techniques (primary,
mechanical, chemical recycling and energy recovery),
the only one acceptable according to the principles of
‘‘Sustainable Development’’ is chemical recycling, since it
leads to the formation of the raw materials from which the
polymer is made, as well as of other secondary value-added
products.[6]
Chemical recycling has been defined as the
process leading to total depolymerization of PET into
monomers, or partial depolymerization into oligomers and
other chemical substances. The main methods used for this
purpose are glycolysis, methanolysis, hydrolysis (alkaline,
acidic and neutral) and other processessuch as aminolysisand
ammonolysis.[7]
Glycolysis makes it possible to employ very
low amounts of reactants, as well as applying lower
temperatures and pressures, in contrast with other methods
such as supercritical methanolysis and thermal degrada-
tion,[8–12]
while hydrolysis under acidic or basic conditions
may cause corrosion and pollution problems.[13,14]
Recently,
a growing interest has been observed in PET glycolysis for
the manufacture of specialized products such as un-
saturated polyesters,[15–18]
polyurethanes,[19–22]
vinyl
esters,[23–25]
epoxy resins,[26]
and polymer concretes.[27,28]
Baliga et al.[29]
carried out the glycolysis of PET with
ethylene glycol (EG) using various catalysts. They found
that glycolyzed products had 1–3 repeating units, depending
on the catalyst used. Halacheva and Novakov[30]
have
investigated the chemical structure of the oligoesters pro-
duced from PET glycolysis with diethylene glycol (DEG)
and they have pointed out the existence of secondary
hydroxyl groups of the products obtained at a large excess of
DEG. Glycolysis of recycled PET was also investigated by
Chen et al.,[31,32]
Mansour and Ikladius,[33]
Michel et al.[34]
and Troev et al.[35]
Moreover, the mechanism of formation
and applications of PET glycolysates have also been studied
in the literature.[36–39]
In our previous work,[18]
PET was depolymerized with
DEG at different DEG/PET molar ratios and the oligomers
obtained were identified and subsequently used as raw
materials for the synthesis of alkyd resins.
Farahat and Nikles[23–25]
provided results on the glyco-
lysis of PET with DEG and a new application for the
obtained oligoester diols/polyols, by converting the hydro-
xyl terminals into acrylate/methacrylate groups. These new
acrylated/methacrylated oligoesters were tested as UV
curable monomers, either alone or as mixtures with other
commercially available diacrylate/dimethacrylate mono-
mers. They gave promising results, from the point of view
of their curability by UV and their mechanical properties,
in order to work as novel binder systems for solventless
magnetic tape manufacturing.
Atta et al.[3,26]
performed the glycolysis of PET with
DEG or tetraethylene glycol (TEG); an epoxy resin was
then prepared by the reaction of glycolyzed products with
epichlorohydrin. New diacrylate and dimethacrylate vinyl
esters were also synthesized by the reaction of the terminal
epoxy groups with acrylic and methacrylic acid. These
vinyl esters were used as cross-linking agents for unsatu-
rated polyester resin diluted with styrene and the resulted
resins were evaluated in coating applications of steel.
The aim of the present investigation was to apply the
dimethacrylated oligoesters, produced from PET chemical
recycling, as potential raw materials for the production of
UV-curable formulations, used as enamel paints or coat-
ings for metallic surfaces in the automotive industry. For
this purpose, depolymerization of PET was firstly conduc-
ted using DEG and the oligomers produced were then
characterized. Then the hydroxyl end-groups of the glyco-
lyzed PET product (PET-GLY) were converted into meth-
acrylate groups and the dimethacrylated oligoesters of PET
glycolysate (PET-GLY-DMA) obtained were studied.
UV-polymerization was chosen for the resulted monomer,
to give solvent-free systems and allow rapid curing, as well
as a low curing temperature for in-line production. Finally,
nanoparticles of SiO2 were dispersed into PET-GLY-DMA/
styrene copolymers as reinforcing agents and the mechan-
ical properties of the final resins were studied.
Experimental Part
Materials
PET flakes were prepared from post-consumer clear PET
bottles, after the removal of polyethylene caps and the
poly(propylene) label. The bottles were cut and fed to a rotary
cutter with a maximum size of 6 mm. Diethylene glycol
(DEG), acetic anhydride, triethylamine (TEA) and styrene
monomer were all supplied by Fluka AG. Methacryloylchlor-
ide (MAcCl), and manganese acetate [Mn(CH3COO)2 4H2O]
with a purity of 99% were obtained from Aldrich and used
without further purification. Fumed hydrophobic nanoparticles
Chemical Recycling of PET by Glycolysis: Polymerization and Characterization . . . 1339
Macromol. Mater. Eng. 2006, 291, 1338–1347 www.mme-journal.de ß 2006 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim

of silica (SiO2) were supplied by Degussa AG (Hanau,
Germany) under the trade name AEROSIL1
R 974. The
photoinitiator used was 2,2-dimethoxy-2-phenylacetophenone
(DMPA) from Aldrich, while the initiator for the thermal
polymerization was benzoyl peroxide (BPO) from Fluka AG.
Tetrahydrofuran (THF), used as a solvent in gel permeation
chromatography (GPC), was obtained from Riedel-de-Haen.
All other chemicals used were reagent grade.
Glycolysis of PET
A continuously stirred 500 mL round-bottom four-necked
flask was charged with 150 g (0.781 mol per repeating unit) of
PETwaste flakes and 84.6 g of diethylene glycol (correspond-
ing to a DEG/PET molar ratio of 1.02). Manganese acetate,
0.6 wt.-% based on weight of PET, was added as trans-
esterification catalyst. The flask was immersed in an oil bath
and heated for 4 h at 210 8C. The reaction was carried out
under reflux in an argon atmosphere. After the 4 h period, the
reaction product was allowed to cool at room temperature,
dissolved in a suitable amount of dichloromethane and fil-
tered. The filtrate was washed several times with distilled
water in order to remove traces of unreacted DEG, the
produced EG and the remaining catalyst. After phase sepa-
ration, the organic layer was collected and dried over an-
hydrous Na2SO4. Finally, purified oligoesters were obtained
after removal of the solvent by rotary evaporation.
Synthesis of PET-GLY-DMA
In this procedure, 69 g of PET glycolysate were dissolved in
300 mL CH2Cl2 in a 500 mL round-bottom four-necked flask,
equipped with a magnetic stirrer, inlet to inert gas (argon),
thermometer and a 100 mL additional funnel. After cooling
the content under an argon purge to 0 8C with an ice bath,
35 mL of TEA were introduced and 25 mL (0.254 mol, 5%
excess) of MAcCl were added dropwise through the funnel
over a 50 min time span. The mixture was kept at 0 8C for 3 h,
allowed to reach room temperature and remain there for an
additional 18 h. The insoluble TEA salt was then filtered and
the filtrate was washed twice with 300 mL of 1 M aqueous
NaOH saturated with NaCl and several times with distilled
water. After phase separation, the organic layer was collected
and centrifuged. The synthesized product was then isolated,
dissolved in 300 mL of a CH3OH/CH2Cl2 (50:50 v/v) mixture
and dried over anhydrous CaSO4. The purified PET-GLY-
DMA was obtained after removal of the solvents by rotary
evaporation.
Homopolymerization and Copolymerization of the
Prepared Monomer
PET-GLY-DMA was homopolymerized in order to produce
UV-curable films. Mixtures containing PET-GLY-DMA and
styrene (50:50 w/w), as well as a series of mixtures containing
PET-GLY-DMA and styrene (50:50 w/w) and silica nano-
particles in several ratios (corresponding to 0.5, 1 and
2.5 wt.-% SiO2) were also copolymerized. Films were obtained
by spreading the monomer or the mixture of monomers on a
glass surface for a thickness of about 1 mm, controlled by using
a doctor’s knife. Curing was performed by the addition of 1
wt.-% of DMPA in each case (lmax ¼ 253.7 nm) and UV
irradiation using a Hanovia high-pressure quartz mercury-
vapor lamp (Model L 679A-36) at the output intensity of 450 W.
The distance chosen between films and lamp was 10 cm, while
the irradiation time was 30 min per side of the film. In addition,
films of pure PET-GLY-DMA were obtained as mentioned
above by thermal polymerization at 808C for 2 h, in the
presence of BPO as initiator.
Characterization of the Glycolyzed PET,
PET-GLY-DMA Resins
The molecular weight distribution and the average molecular
weight of the glycolyzed PET product were determined by Gel
Permeation Chromatography (GPC). The instrument used was
from Polymer Laboratories and included a pump (Marathon
III HPLC pump), an Evaporative Mass Detector (PL-EMD
950) and a Plgel 5m MIXED-D column. The sample was
dissolved in THF at a constant concentration of 0.2 wt.-%.
After filtration, 25 mL of the sample was injected into the
chromatograph. The elution solvent was also THF at a
constant flow rate of 1 mL min1
. Calibration of GPC was
carried out with standard polystyrene samples (Polymer
Laboratories).
The content of hydroxy end-groups (hydroxyl number, HN)
of the oligoester diols obtained was determined by titration
with 1 N KOH solution. About 1.5 g sample was accurately
weighted and added to 10 ml acetylating solution, containing
10 vol.-% acetic anhydride in pyridine, in a round-bottomed
flask. The flask was fitted with a vertical reflux condenser and
heated to 80 8C for 2 h. Afterwards, 10 ml of water were added
and the heating was continued for 10 min at 100 8C. The
mixture was then cooled at room temperature and 10 ml of
methanol were added from the top of the condenser. The
resulting solution was titrated against 1 N KOH standard using
phenolphthalein as indicator. A blank run was also performed.
The values obtained provide a measure of the number average
molecular weight.
The chemical structure of the glycolyzed PET product, as
well as the extent of the methacrylation reaction were
confirmed using a Perkin-Elmer spectrophotometer (Model
Spectrum One).
Phase identification of the glycolyzed PET product and
PET-GLY-DMA was performed by polarized optical micro-
scopy using a Nikon OPTIPHOT-2 polarizing microscope,
equipped with a Linkam THMS 600 heating stage and a TP 91
control unit. Heating rates were 10 8C min1
.
Tg measurement and thermal polymerization study of
PET-GLY-DMA in the absence of initiator were performed
using a differential scanning calorimeter of Perkin-Elmer
(Pyris 1) equipped with the Pyris software for Windows and
calibrated for temperature and enthalpy with indium.
Tensile tests were performed using an Instron 3344
dynamometer, in accordance to the ASTM D638 method at
room temperature. Prior to measurements the samples were
1340 G. P. Karayannidis, A. K. Nikolaidis, I. D. Sideridou, D. N. Bikiaris, D. S. Achilias

conditioned at 50 5% relative humidity for 36 h, placed in
a closed chamber containing a saturated Ca(NO3)2
4H2O solution in distilled water (ASTM E-104). Tensile tests
were performed under the condition that the crosshead speed
of tensile tester was set at 5 mm min1
and the initial gauge
length was fixed at 22 mm. Five measurements were con-
ducted for each sample, and the results were averaged to
obtain a mean value.
Results and Discussion
Glycolysis of PET and Characterization of the
Glycolyzed Product
The alcoholysis of PET with diethylene glycol proceeds
according to the reaction shown in Scheme 1. The alcoho-
lysis consists of the transesterification of PET and the
depolymerization of its polymer chain, resulting in the
decrease of its molecular weight. Using a small excess of
glycol in the depolymerization of PET, the oligoesters
obtained have mainly two hydroxyl end-groups, that is,
mixtures of oligoester diols are formed.[30]
The choice of
DEG to carry out the glycolysis is usually determined by
the necessity of having good flexural properties in the
UV-cured resin, since the long chains containing this gly-
col improve flexibility.
In the present study, the glycolysis of PET was carried
out using an initial DEG/PET molar ratio of 1.02, to obtain
a small degree of depolymerization and, as a consequence,
oligomers of relatively high molecular weights. These
could partly maintain the primary features of PET and
impart improved mechanical properties to the cured film of
the final dimethacrylated product. This means that the
presence of more terephthalate repeating units between the
cross-links can result in the existence of harder domains
and better separation between the cross-links in the packed
cross-linked structures, leading to improved mechanical
properties.[23,24]
The number average molecular weight, Mn, of the
obtained glycolysate was calculated by determining the
hydroxyl number (HN), which was found to be 196.2 mg
KOH/g of the sample. Based on this value the Mn calcu-
lated was found to be 572. The number (Mn) and weight
(Mw) average molecular weights of the polyester oligomers
produced and the polydispersity of the molecular weight
distribution obtained from GPC were 880, 990 and 1.13,
respectively. It was noticed that the number average
molecular weight measured by GPC was higher than that
obtained from the hydroxyl number. If it is considered that
the oligoester produced is a trihydroxy-compound,[23,24]
the Mn estimated based on the HN, becomes equal to 858,
that is very near with that obtained from GPC (880). The
greater than one polydispersity of the molecular weight
distribution revealed that the distribution was not uni-
modal. Actually, three distinct peaks (trimodal shape) were
identified (Figure 1). That means that PET glycolysis using
DEG results mainly in three kinds of oligoesters. On trying
to identify the oligoester diols produced, the structure in
Scheme 2 was proposed,[30]
According to this structure, if
one replaces m with 0, 1 and 2 the following molecular
weights are obtained: 342, 534 and 726, respectively. By
comparing these values with the values obtained by GPC, it
can be concluded that the above structure is confirmed with
m ¼ 0, 1 and 2.
The FT-IR transmission spectrum (Figure 2) confirms
the proposed chemical structure for the glycolyzed PET
product. The characteristic peaks for the PET glycolysate
as shown in Figure 2 are the following:
3 429 cm1
(–OH), 3 030 cm1
(–H arom.), 2 953 cm1
(–CH2–), 1 718 cm1
(–C–
–O–ester), 1 612 and 1 506 cm1
(–C–
–C– arom.), 1 274 cm1
(–C–O–C–ether).
Scheme 1. The alcoholysis of PET with diethylene glycol.

By using a hot-stage polarizing optical microscope
(POM), a significant amount of crystallites dispersed in the
viscous amorphous phase was observed at room tempera-
ture. So the glycolyzed PET product could be characterized
as a semi-crystalline substance. That is probably why the
glycolysate performs as a semi-solid and opaque material.
Crystallization might be related to the molecular species of
lower molecular weight, namely the oligomers correspond-
ing to the proposed structure for m ¼ 0 and 1. By increasing
the temperature to 37 8C, a movement of the crystallites
into the liquid amorphous phase was detected, due to its
fluidization. At 65 8C these crystallites were shown to be
melted or dissolved in the amorphous phase. Furthermore,
the above changes were completed at 80 8C. Up to 120 8C
no other change was observed. During the slow cooling of
the sample, new spherulites appeared possessing a dark
Maltese cross pattern.
Synthesis and Characterization of PET-GLY-DMA
The methacrylation reaction of PET glycolysate could be
represented by Scheme 3. MAcCl was chosen as the
methacrylation agent instead of acryloylchloride (AcCl),
because the presence of methyl groups at the a-carbon
atom of the ester chain generally imparts higher resistance
to both UVand thermal oxidations, while increasing the Tg
of the final product.[40]
Furthermore, the direct esterifica-
tion reaction with methacrylic acid, in the presence of
methanesulfonic acid or p-toluenesulfonic acid as ester-
ification catalysts, was avoided, because the Mn values of
the methacrylated products by these methods were report-
ed to be slightly lower than that of the starting oligomers,
indicating the occurrence of an acidic degradation reaction,
which does not affect the methacrylic functionality.[41–43]
The excess of MAcCl was intended to cause the meth-
acrylation of as many hydroxyl end-groups of PET
glycolysate as possible. Dichloromethane was proved to
be a more effective solvent of the glycolyzed PET product
for the methacrylation reaction than THF, without resulting
in by-products. In our first effort using THF as solvent
some oligomers of polytetrahydrofurane were produced,
which did not separate from the reaction mixture by the
rotary evaporator. Triethylamine was used as a basic
scavenger, in order to remove the HCl as triethylamine salt,
(C2H5)3Nþ
H Cl
. To avoid the hydrolysis of MAcCl and
the polymerization of the corresponding acid, as well as to
control the temperature of the reactant mixture, meth-
acrylation was conducted at 0 8C, because it is an exo-
thermic reaction. The washes with the aqueous solution
of 1 M NaOH aimed at the hydrolysis of the MAcCl excess,
dissolved in the organic phase, to the corresponding acid
Figure 1. Molecular weight distribution of the glycolyzed PET
product.
Scheme 2. Proposed structure of the oligoester diols resulting from PET glycolysis using DEG.
m ¼ 1–3.
Figure 2. FT-IR spectrum of the PET-GLY.

Scheme 3. Preparation of methacrylated PET glycolysate. m ¼ 1–3.
Figure 3. FT-IR spectrum of the PET-GLY-DMA. Figure 4. DSC traces of the PET-GLY-DMA.

and hence at the removal of the latter as methacrylic salt in
the aqueous phase.
As shown by the FT-IR transmission spectrum (Figure 3),
the progress of the methacrylation reaction is confirmed by
the reduction of the broad band at 3 535 cm1
, corres-
ponding to the –OH group (against the FT-IR spectrum of
the glycolysate), and the appearance of a new band at
1 637 cm1
, corresponding to the newly formed meth-
acrylate group. The higher intensity of the peaks at 2 957,
1 722 and 1 271 cm1
against the intensity of the peak at
1 637 cm1
, reveals a larger ratio of methylene, ester and
ether groups against the methacrylate groups in the chemical
structure of PET-GLY-DMA.
Similarly to the glycolysate, PET-GLY-DMA was found
by POM to consist of a significant amount of a crystalline
phase dispersed in the viscous amorphous phase at room
temperature (semi-crystalline substance) and consequently
giving a semi-solid and opaque material. By heating the
Scheme 4. Photochemical homopolymerization of PET-GLY-DMA by UV irradiation.

sample up to 120 8C and cooling it slowly to room tem-
perature, a behavior similar to that of the glycolysate was
observed. Heating PET-GLY-DMA again up to 220 8C, no
movement of the amorphous phase was detected, while the
little crystallites did not change. This attitude could be
attributed to thermal polymerization of the substance,
which might have been initiated at the end of the first
heating (120 8C) and led to a cross-linked structure and a
trap of the two phases. During cooling the sample again to
room temperature, no change was observed, obviously due
to its polymerization.
The DSC thermogram (Figure 4) shows that by a first
heating of the PET-GLY-DMA from 50 to 120 8C, the Tg
of the sample appeared at 30 8C.
This rather low value of Tg could be attributed to the
flexibility that the segments of ether and methylene groups
impart to the oligomer chains. Despite the low value of
Tg, the material performed as a semi-solid mass at room
temperature, perhaps due to the presence of crystals
detected by using POM into the amorphous phase, which
retained the stiffness of the material. In addition, the broad
endothermic peak at the temperature area of 40–90 8C
Scheme 5. Photochemical copolymerization of PET-GLY-DMA with styrene by UV irradiation.

maybe confirms the total fluidization of the amorphous
phase, as well as the total melting or dissolution of the
crystals, effects which were also observed by POM. By a
second heating of the same sample from 50 to 220 8C, the
Tg was found to be increased to 23 8C, while the exo-
thermic peak recorded at 130 8C supports the possibility of
a thermal polymerization of PET-GLY-DMA at the
particular temperature. The additional increase of Tg from
23 to 12 8C, as well as the loss of the exothermic peak at
130 8C observed by a third heating of the same sample
(from 50 to 150 8C), just confirms the above claim.
Homopolymerization and Copolymerization of the
Prepared Monomer
The UV-homopolymerization of the PET-GLY-DMA
monomer with DMPA as photoinitiator is shown in
Scheme 4. The dispersion of DMPA in the semi-solid
monomer was achieved by using methanol-dichloromethane
50:50 v/v mixture as diluent. After the casting of this
formulation on a glass plate and the evaporation of the
diluent the photopolymerization followed.
The above homopolymer did not harden enough even
after 30 min of irradiation. This behavior could be attri-
buted to the relatively low concentration of double bonds in
the structure of the monomer. Furthermore, the films that
were produced by this homopolymerization were rather
flexible, due probably to the flexible methylene– and ether
groups in the structure of the PET-GLY-DMA. So, styrene
was used as the co-monomer of the PET-GLY-DMA in
order to act as a reactive diluent; on the one hand, aiding
the dispersion of DMPA and SiO2 into the semi-solid
PET-GLY-DMA monomer, as well as the molding of the
material into film; and on the other hand participating in a
copolymerization process with PET-GLY-DMA, leading to
the formulation of cross-linked films with improved
mechanical properties. In both cases, the polymerization
of the films was macroscopically confirmed by the fact
that they hardened after the UV-irradiation. The UV-
copolymerization reaction of the PET-GLY-DMA mono-
mer with styrene is shown in Scheme 5,
Nanoparticles of SiO2 were used as a reinforcing agent.
These fine inorganic particles exhibit huge surface areas
due to their small size. For this reason a satisfactory
dispersion and adhesion in the copolymer matrix and thus
an improvement in the mechanical properties were ex-
pected. This adhesion could be also attributed to the pre-
sence of hydrophobic methyl groups at the SiO2 surface,
which are quite friendly to the organic material.
The thermal polymerization of PET-GLY-DMA at 80 8C
for 2 h in the presence of benzoylperoxide (BPO) was
considered to be adequate, as the polymerized material
yielded a quite hardened and brittle film.
Figure 5. Stress-strain curves of PET-GLY-DMA/styrene copo-
lymers containing different amounts of SiO2.
Figure 6. Young’s modulus of PET-GLY-DMA/styrene copoly-
mers containing different amounts of SiO2.
Figure 7. Tensile strength at break of PET-GLY-DMA/styrene
copolymers containing different amounts of SiO2.

Mechanical Properties of the Resin
Films Produced
PET-GLY-DMA/styrene and PET-GLY-DMA/styrene/
SiO2 specimens performed as tough and brittle materials
by their fracture in the dynamometer (Figure 5). Especially,
the samples containing SiO2 exhibited a slightly lower
Young’s modulus than the specimens of PET-GLY-DMA/
styrene copolymer (Figure 6), perhaps due to the presence
of nanoparticle agglomerates and their inefficient disper-
sion into the copolymer matrix. A similar behavior can be
seen in Figure 7, where the tensile strength at break of
PET-GLY-DMA/styrene copolymers containing different
amounts of SiO2 is shown.
Conclusion
In this work, PET glycolysis for the production of the
dimethacrylated glycolysate PET-GLY-DMA was carried
out. By finding the Mn of the PET glycolysate according to
end-group analysis, it is obvious that the glycolysis of
post-consumed PET using a small excess of DEG is
attainable. The above glycolysate can be easily converted
to the respective dimethacrylated product, which could be
applied as a raw material in the acrylic coating industry. In
the frame of chemical recycling, a significant amount of
post-consumed PET could be used as raw material in a
value-added application in the near future, instead of end-
ing up at city landfills. Certainly, the whole attempt requi-
res further investigation in order to help the polymerization
of the produced dimethacrylated monomer. The presence
of the silica did not have a clear effect on the mechanical
properties of the films, probably due to its inefficient
dispersion into the copolymer matrix.
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