Chloride formation and polymer coloration during thermal degradation of PVC stabilised with a Zn-Ca recipe

The part played by metallic chlorides, and especially zinc chloride generated during the stabilisation process of PVC with the zinc-calcium recipe, is analysed through a brief review of the mechanism established previously, a few additional data being presented. Correlations between polymer discoloration and chloride formation, estimated through a coulometric method based upon Ag⁺ ion precipitation in the presence of chloride ions, are analysed for different short-term and long-term secondary stabilisers. They allow the exact part played by each component to be explained.