THE MODE OF ACTION OF METAL STEARATE STABILIZERS IN POLY(VINYL CHLORIDE) .1. INFLUENCE OF PREHEATING ON MELT COMPLEXATION

Mixtures of calcium and zinc stearates (in a 1:2 ratio) were heated at different temperatures, in order to form the CaSt[ZnSt3] complex reported in the literature. Mixtures were added at 3 phr, to otherwise unstabilised poly(vinyl chloride) (PVC), and induction times for dehydrochlorination evaluated by thermogravimetric analysis and by HCl evolution. Unexpected behaviour was found when these materials were pre-heated at temperatures of 100, 130, 150 and 180-degrees-C. Pre-heated CaSt2 reduced the induction time to dehydrochlorination, whereas pre-heated ZnSt2 prolonged the induction time. When both soaps were pre-heated together the induction times to dehydrochlorination and hence discoloration of PVC were significantly extended. These observations have been explained by an evaluation of carboxylate anion-metal bridging using Fourier-transform infrared spectroscopy.