The synergistic effect of metal soaps (zinc stearate and calcium stearate) and/or natural zeolite (clinoptilolite) on PVC thermal stability was investigated. For this purpose, PVC plastisol was prepared by mixing poly(vinyl chloride) (PVC) and dioctyl phthalate (DOP) and stabilized with different amounts of metal soaps and zeolite. Kinetic studies of dehydrochlorination at 140 and 160°C were done for unstabilized and stabilized PVC plastigels using 763 PVC Thermomat equipment. The stabilizing effect of zeolite on the increase in the induction period of the sample was considered to result from the absorption of HCl, a property that was thought to reduce the autocatalytic effect of HCl evolved at the initial stages of dehydrochlorination. Since the induction time of the sample having 0.53% of zinc stearate and 0.53% of zeolite was higher than those of the PVC plastigels having only zinc stearate or zeolite, the synergistic effect on thermal stability was observed at low levels of these additives.

The importance of flame-retardant and smoke-suppressed poly(vinyl chloride) (PVC) compositions is increasing gradually in the polymer industry since PVC releases smoke and toxic gases (hydrogen chloride, HCl) during heating at temperatures above 140 C with the result of dehydrochlorination reaction. In this study, the synergistic effects of zinc borate (ZB)-zinc phosphate (ZP) on the thermal stability of PVC were investigated using thermal techniques. The induction and stability time values of PVC plastigels were obtained at 140 and 160 C. The results revealed that PVC plastigels having only ZP and ZB retarded dehydrochlorination of PVC compared with the unstabilized sample. However, the plastigels with both ZB and ZP had a superior synergistic effect on char formation of PVC. Since the induction periods of the samples having both ZB and ZP were higher than those of the unstabilized samples having only ZB or only ZP, the synergistic effect was observed.

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