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Microwave assisted glycolysis of poly(ethylene terepthalate) for preparation of polyester polyols



The generic aim of the present work is to reduce the time required for glycolytic depolymerization of PET by employing microwave irradiation instead of the conventional heating process. Glycolysis of PET was performed in the presence of glycols of different molecular weight under microwave irradiation. Experimental conditions like PET : glycol ratio, reaction time and concentration of glycerol were optimized to maximize the product yield. In the presence of ethylene glycol, bis-(hydroxyethyl) terephthalate (BHET) could be obtained in excellent yields in significantly lesser time (30 min) as compared to 8–9 h by conventional heating process. The BHET yield could further be increased by a second step glycolysis of the residual oligomers. This increased efficiency of the microwave assisted process has been attributed to the high microwave absorption capacity of glycols which results from their high loss factor. PET could also be glycolysed in the presence of higher glycols, however the reactivity of diols was found to decrease with increase in the molecular weight. The polyols obtained were reacted with aromatic diphenylmethane diisocyanate to prepare polyurethane foams, which were characterized by various techniques for determination of their physical, mechanical and structural properties. The compressive strength of the polyurethane foams was found to be inversely proportional to the molecular weight of the glycolysed polyol used for its preparation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013