Oxidative stabilization mechanism of poly(vinyl chloride) pitch

We have investigated the oxidative stabilization mechanism of poly(vinyl chloride) (PVC) pitch by thermogravimetric analysis (TGA) and Fourier transform-infrared spectrometry (FT-IR). Rapid weight gain was observed in the initial stage of stabilization due to the autoacceleration. The weight gain was thought to result from the conversion of methyl and methylene groups into carbonyl groups producing aldehyde, ketone, alcohol, and water. As stabilization proceeds, formation of ether and carboxylic acid was observed, which were the oxidation products of aldehyde and primary alcohol. The rate of weight gain became low after the initial stabilization stage, Aromatic anhydride was formed by dehydration of carboxylic acids at high temperature and long stabilization time. Weight loss, resulting from decarboxylation of carboxylic acid evolving carbon dioxide, was observed under stabilization conditions of 290 degrees C for 24 h. As stabilization temperature increased, the maximum value of weight gain and duration of autoacceleration decreased showing the formation of aromatic anhydride. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.