The mode of action of metal stearate stabilisers in poly (vinyl chloride): II. Influence of pre-heating on induction times and carbonyl formation

Abstract

Evaluations of HCl evolution from PVC doped with different combinations of pre-heated CaSt 2, ZnSt 2 and their mixture were made, in order to consolidate previous findings from weight loss measurements, 1 where the induction times to degradation increased when ZnSt was pre-heated and subsequently combined with CaSt 2 and when their mixture was pre-heated, but diminished when CaSt 2 was pre-heated and subsequently combined with ZnSt 2. Dehydrochlorination results were in agreement with previous loss of weight analysis data where, for both, a distinctive behaviour was found at the pre-heating temperature of 150 °C. FTIR analyses, in the carboxylate region, of samples degraded at 5, 10, 15 and 20 min show the appearance of carbonyl groups at 1705 cm −1 while the complex CaSt[ZnSt 3], which it has been suggested forms on heating, disappears throughout the degradation time. Lower amounts of carbonyl groups were found when the pre-heated mixture of soaps and the pre-heated ZnSt 2 were added to the PVC, supporting the results obtained from the induction time evaluations. X-ray diffraction analyses and molecular modelling studies support the formation of such a complex between the metal stearates.