The properties of unsaturated polyester based on the glycolyzed poly(ethylene terephthalate) with various glycol compositions D.J. Suh a , O.O. Park a , K.H. Yoon b, * a Center for Advanced Functional Polymers, Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusung-dong, Yusong-ku, Taejon 305-701, South Korea b Department of Polymer Science and Engineering, Kumoh National University of Technology, 188 Shinpyung-dong, Kumi, Kyungbuk 730-701, South Korea Received 7 September 1998; received in revised form 7 January 1999; accepted 1 March 1999 Abstract Unsaturated polyester (UP) based on the glycolyzed poly(ethylene terephthalate) (PET) with propylene glycol (PG), diethylene glycol (DEG) and their mixture was prepared and the influence of glycol compositions on the chemo-rheological behavior and the mechanical properties was studied. The glycolyzed products showed broad bimodal distribution in their molecular weights and the larger molecular weight oligomers were obtained with increasing DEG contents in DEG and PG mixtures. The gelation time of UP was delayed with increasing DEG contents. After 1 h curing, the final conversion level increased as the DEG contents increased. The tensile modulus decreased and the toughness of cured products increased with increasing DEG contents due to the flexibility of ether linkage in the DEG unit.  1999 Elsevier Science Ltd. All rights reserved. Keywords: Poly(ethylene terephthalate); Glycolysis; Unsaturated polyester 1. Introduction Recently, recycling of polymers has received a great deal of attention [1]. Poly(ethylene terephthalate) (PET) is one of the versatile engineering plastics which is used to manufac- ture films and bottles for packaging. The overall world consumption of PET amounts to about 13 million tons, of which 9.5 million tons are processed by the textile industry, 2 million tons are consumed in the manufacture of audio and video tapes, and 1.5 million tons are used in the manufacture of various types of packaging—mainly bottles and jars [2]. PET does not create any direct hazard to the environment, but due to its substantial volumes in the plastics waste stream and its high resistance to the atmospheric and biolo- gical agents, it could be thought of as a noxious material. Therefore, the recycling of PET will not only serve as a partial solution to the solid waste problem but also contri- bute to the conservation of raw petrochemical products and energy. Products made from recycled plastics can result in 50–60% energy saving as compared to making the same product from virgin resin [3]. In a recent study, Nadkarni et al. [4,5] suggested the synthesis of unsaturated polyester (UP) resin from PET waste and also investigated the kinetics of glycolysis on several glycols. Baliga and co-workers [6] carried out the glycolysis of PET with ethylene glycol (EG) using various metal-acetate catalysts. They found that glycolyzed products had 1–3 repeating units depending on the catalyst used. After synthesis of UP based on waste PET was suggested, researchers [7,8] tried to apply this unsaturated polyester to polymer concrete by replacing Portland cement as a concrete binder. Aslan et al. [9] compared the composite sheet containing unsaturated polyester developed in recycled PET to the analogous composite made of virgin unsaturated polyester resin. Abdel-Azim et al. [10] investigated the compressive strength of the polymer concrete using unsaturated polyester based on recycled PET. As shown above, the most previous works about recycling of PET were concentrated on the glycoly- sis. This is because polyols produced by glycolysis can be used for producing other polymers such as UP or polyurethane. In this work, we tried to compare the properties of unsa- turated polyester prepared by glycolysis of PET with propy- lene glycol (PG) and diethylene glycol (DEG) and their mixture. The cure behavior and the tensile properties of Polymer 41 (2000) 461–466 0032-3861/00/$ - see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S0032-3861(99)00168-8 * Corresponding author. Tel.: +82-546-467-4298; fax: +82-546-467- 4050. E-mail address: khyoon@knut.kumoh.ac.kr (K.H. Yoon)