Neutral hydrolytic depolymerization of PET (Polyethylene terephthalate) waste was studied using 0.5-L high pressure autoclave at the temperatures 100, 150, 200, 230, and 250 degrees C at autogenious pressures 15, 80, 230, and 451 psi (pound per square inch) and time intervals of 60, 90, 120, and 150 min, respectively. The obtained terephthalic acid (TPA) was characterized by measuring its acid value and recording FTIR spectra. Depolymerization of the PET by neutral hydrolysis was found to be first order with velocity constant in the order of 10(-2) min(-1). Energy of activation and frequency factor were obtained by slope and intercept of Arrhenius plot, which were found to be 99.58 KJ mole(-1) and 2.9 X 10(8) min(-1) respectively. Effect of temperature on rate of depolymerization reaction was also studied and optimized: rate of reaction increased drastically on increase in temperature from 150 to 200 degrees C. Modified shrinking core model based on acid values focused the light on depolymerization of the PET into TPA by fragmentation due to formation of pores and cracks. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 2179-2183, 2008