Mechanism of smoke suppression by metal oxides in PVC

The amount of smoke suppression induced in PVC by some metal oxides was measured as a function of temperature. The amount of CO₂ evolved in the combustion was also measured simultaneously with smoke emission. Our results show that in a smoldering condition smoke occurred almost immediately, whereas CO₂ occurred at a later stage. A good correlation was found between smoke density and char yield in nitrogen, and the amount of benzene suppression, induced by metal oxides, also correlated well with the char yield. These facts are taken as evidence that crosslinking catalyzed by metal oxides is the principal mechanism of smoke inhibition and that char oxidation is responsible for the reduction of char yield.