PHOTOAGEING OF RIGID PVC - I - FILMS CONTAINING CA ZN THERMAL STABILIZER/

The photo-oxidation (lambda > 300 nm, T = 40, 55 and 70 degrees C) of similar to 80 mu m films of PVC stabilised by Ca and Zn stearates was studied using gravimetry, IR and UV-visible spectrophotometry. The sta bilisers disappear in the early days of exposure according to a pseudo first-order process, presumably by HCl scavenging, which gives an ide a of the rate of HCl release during this period. The concentration of polyenes absorbing at lambda = 500 nm begins to increase rapidly when the stabiliser is totally consumed. At the same time, weight loss take s place, showing that there are more HCl elimination events than oxida tion events. These results are consistent with the following hypothese s: (a) oxidation is diffusion controlled; (b) long polyene formation i s HCl catalyzed; (c) conjugated sequences-(CH2 = CH2)(n)-with n = 10-1 2 result essentially from a thermal process; (d) the rate of carbonyl and hydroxyl build-up is nearly not influenced by the increase in poly ene concentration or rate of HCl evolution which can also be explained , at least partially, in terms of O-2 diffusion control of oxidation k inetics. (C) 1998 Elsevier Science Limited. All rights reserved.