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TOLEDO (SPAIN)SYNTHESIS OF UNSATURATED POLYESTER RESIN FROMGLYCOLYSED POSTCONSUMER PET WASTES
I. Duque-Ingunza1, R. López-Fonseca1, L. Flores-Giraldo1, I. Acillona2,
B. de Rivas-Martín1, J.M. Laza3, J.L. Vilas3, S. Arnaiz2, J.I. Gutiérrez-Ortiz1*
1Department of Chemical Engineering, 3Department of Physical Chemistry,
Faculty of Science and Technology, Universidad del País Vasco/EHU, E-4808, Bilbao, Spain
2GAIKER-IK4, Technological Centre, 202, E-48170 Zamudio, Spaine-mail: itxaso.duque@ehu

Abstract
In this work the production of secondary value-added products, such as unsaturated polyester resins (UPE), derived from thechemical recycling of polyethylene terephthalate (PET) was examined. Glycolysis of PET waste granules was carried out
using excess ethylene glycol in the presence of sodium carbonate as catalyst. High yields (80%) of the monomer bis(2hydroxyethyl terephthalate) were obtained. This recovered monomer was polyesterified with maleic anhydride to form
unsaturated polyester resins. Upon addition of styrene monomer, UPEs were casted by crosslinking reaction using methyl
ethyl ketone peroxide and cobalt octoate as initiator and catalyst, respectively. The polyesterification reaction was followed
by GPC and the cured resin was subjected to various characterization techniques in order to determine its chemical, physicaland mechanical properties.

Keywords: PET wastes, recycling, glycolysis, unsaturated polyester resin, bis(2-hydroxyethyl) terephthalate

1. Introduction
Poly(ethylene terephthalate) (PET), a semi-crystalline
thermoplastic polyester that is extensively used indiverse applications -textiles, high strength fibers,
photographic films, disposable soft-drink bottles, andothers- is also one of the largest components of the postconsumer plastics in landfills.
The principle of chemical recycling is to convert highmolecular weight polymers into low molecular weightsubstances via chemical reaction. PET can be
depolymerized into monomer or low molecular weightoligomers via glycolysis reaction in excess ethylene
glycol [1,2]. Further, the monomer, bis(hydroxyethyl)
terephthalate (BHET) thus obtained can be used asbuilding blocks to synthesize other polymers with higher
economical values such as unsaturated polyesters,polyurethanefoams,polyisocyanuratefoams,copolyesters, polyurethane coatings, alkyd resins, lowtemperature curable resins, or UV curable resins [3,4].
The purpose of this research is to develop a new methodof producing unsaturated polyester resins (UPR) from theBHET obtained via glycolysis of PET wastes.

2. Materials and Methods
Glycolysis of PET waste granules was carried out using
excess ethylene glycol in the presence of zinc acetateand sodium carbonate acting as catalysts. Experiments
were carried out in a batch reactor at atmosphericpressure. After a specified time interval the product(BHET) was separated through two consecutive steps

interiores libro.indd 131(extraction with hot water followed by crystallization). TheBHET was quantified by gel permeation chromatography(GPC) and subjected to various characterization
techniques, namely elemental analysis (EA), differential
scanning calorimetry (DSC), Fourier transform infrared
spectroscopy (FTIR) and nuclear magnetic resonance(NMR).
UPR was prepared by the polyesterification reaction of
the recovered BHET with maleic anhydride. Synthesis
was carried out in a round-bottom flask connected to adistillation condenser. Afterwards, unsaturated resin wasmixed with styrene 35% weight and hydroquinone wasalso added in order to inhibit initiation of thepolymerization. In order to cure the resin, methyl ethyl
ketone peroxide (MEKP) and cobalt octoate were used,
as initiator and catalyst, respectively, at a weight ratio of
100:0.5:0.5.
The polyesterification reaction was followed by GPC andthe cured resin was subjected to various characterization
techniques: differential scanning calorimetry, Fouriertransform infrared spectroscopy, flexural dynamic
mechanicalthermalanalysis(DMTA)
andthermogravimetric analysis (TGA). Curing behaviors(curing time and temperature) were also analyzed.

3. Results and Discussion
Glycolysis of PET wastes
The effect of various operation parameters on thecatalysed glycolysis of PET waste was investigated inorder to efficiently recover its purified monomer. The
yield of monomer increased with an increase in EG:PET

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6th International Symposium on Feedstock Recycling of Polymeric Materials

molar ratio, temperature, amount of catalyst and reaction
time until the reaction reached equilibrium conditions [1].
Hence, a yield of high purity BHET close to 80% could be
attained at 196 ºC, with an EG:PET molar ratio of 7.6:1
and using zinc acetate as catalyst with a concentration(PET:catalyst molar ratio) of 380:1.
In an attempt to find an alternative to zinc acetate, ahighly active catalyst for the process but with aconsiderable environmental impact, several eco-friendly
simple salts were examined namely, sodium carbonate,sodium bicarbonate, sodium sulphate and potassium
sulphate. From the comparison of the efficiencies it was
found that sodium carbonate could depolymerize PET
wastes almost as efficiently as zinc acetate does at thecost of using a slightly higher concentration in thereaction mixture. The environmental impact of theglycolysis process can be markedly diminished since theuse of Zn cation (commonly used) is avoided.
The purity of the recovered BHET after PET waste
glycolysis, was determined by means of a number ofanalytical techniques, and the results were comparedwith those corresponding to a commercial BHET sample
provided by the Aldrich Chemical Co. From all theseobservations it was concluded that the product fromglycolysis was highly pure BHET.
Synthesis of unsaturated polyester resins
The effect of various operation conditions on the UPR
synthesis was investigated. The molecular weight of theresin increased with reaction time and temperature as
showed by GPC analysis (Fig. 1).

Fig. 1. UPEs GPC chromatographs.
Firstly, the amount of hydroquinone used for inhibiting
undesired polymerization was optimized. The same resin
varying amounts of hydroquinone (0.05-0.045% wt) wascured with MEKP and cobalt octoate as initiator andcatalyst respectively, and then was analyzed by DMTA. A
sinusoidal load was applied to the sample and the real(E´) and imaginary (E´´) module were measured. Theratio E´´/E´ is defined as the loss tangent or the damping(tanδ). The tanδ peak temperature was taken as theglass transition temperature (Tg). The tanδ and Tg
decreased when the amount of hydroquinone increased.
Thus, the resin obtained with higher amounts of inhibitor

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presented inferior thermal properties. 0.02% wt waschosen as the optimal amount.
After optimizing the curing conditions, UPE synthesizedunder different conditions were compared. Glasstransition temperature (Tg) of cured UPE resins wasanalyzed from DSC thermograms. It was observed thatTg increased with an increase in the reaction time andtemperature. As example, Tg(4h, 150 ºC)= 55 ºC, Tg(6h,150 ºC)= 63 ºC, Tg(8h, 135 ºC)= 77 ºC and Tg(8h, 150ºC)= 82 ºC. Tg of the prepared resin varied from 50 to 85ºC. This range of temperature for the glass transition waswithin the range expected for a fully cured UPR [5].
FTIR spectra were recovered for all synthesized resins.
All of them showed the same spectra. The absorption at3400, 3000-2800, 1750 and 1300 cm-1 corresponded toOH, C-H, C=O and C-O stretching, respectively. A sharp
peak around 750 cm-1 was related to the para-sustituted
aromatic ring, which is characteristic of PET [4].

4. Conclusions
Recycling of PET waste through glycolysis wassuccessfully performed, cracking the polyester intomonomer. Polyesterification of the monomer with maleic
anhydride was completed to obtain an unsaturatedpolyester resin. The unsaturated resin was cured withMEKP and cobalt octoate, and analyzed with various
characterization techniques.

References[1] R. López-Fonseca, I. Duque-Ingunza, B. de Rivas, S.
Arnaiz, J.I. Gutiérrez-Ortiz. Chemical recycling of postconsumer PET wastes by glycolysis in the presence ofmetal salts. Polym Degrad Stab 95 (2010) 1022-1028.
[2] S. Mishra, A.S. Goje. Kinetics of glycolysis ofpoly(ethylene terephthalate). Waste powder at moderatepressure and temperature, J Appl Polym Sci 87 (2003)
1569-1573.
[3] D.E. Nikles, M.S. Farahat. New motivation for thedepolymerisation products derived from poly(ethyleneterephthalate) (PET) waste: a review. Macromol MaterEng 290 (2005) 13-30.
[4] A.R. Zahedi, M. Rafizadeh, S.R. Ghafarian.
Unsaturated polyester resin via chemical recycling of offgrade poly(ethylene terephthalate). Polym Int 58 (2009)1084-1091.
[5] J. Grenet, S. Marais, M.T. Legras, P. Chevalier, J.M.
Saiter. DSC and TSDC study of unsaturated polyester
resin. Influence of the promoter content. J Therm Anal
Cal 61 (2000) 719-730.

Acknowledgements
The financial support for this work provided by theSpanish Ministerio de Ciencia e Innovación (CTQ200806868-C02-01 and CTQ2008-06868-C02-02) andDiputación Foral de Bizkaia (DIPE08/13) are gratefully
acknowledged. Also the supply of post-consumer waste
samples of PET by ECOEMBES is acknowledged.

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