Molecular weight evaluation of depolymerized poly(ethylene terephthalate) using intrinsic viscosity

A series of poly(ethylene terephthalate) (PET) depolymerization experiments versus time was proceeded under optimal experimental conditions with microwave radiation, in which the temperature was 220 degrees C, the pressure was 200 psi, the microwave power was 260 W, and the ratio of water to PET was 10 : 1. The relative viscosity of the feedstock PET grain and the residual solid products from depolymerization reaction at six different time, respectively, was measured in the solution of 60/40 (w/w) phenol/1,1,2,2-tetrachloroethane. Then the approximate intrinsic viscosity was calculated from linear and exponential extrapolation of reduced viscosity. Molecular weights were calculated by Mark-Houwink's equation, with values of K and alpha taken from the literatures. The results show that the molecular weights fell dramatically with increasing of reaction time, namely the number average molecular weight from 2.57 x 10(4) of the feedstock PET to 372 of the remained solid product at 240 min, and the weight average molecular weight of the samples fell from 3.89 x 10(4) to 408 correspondingly. The intrinsic viscosity decreased greatly with reaction, while the distribution of molecular weight turned to be steady. (C) 2008 Wiley Periodicals, Inc.