ROLE OF METAL-OXIDES IN THE THERMAL-DEGRADATION OF POLY(VINYL CHLORIDE)

Thermal degradation of poly(vinyl chloride) has been studied in the pr esence of metal oxides by a thermogravimetric method. It follows a two -step mechanism. In the first step chlorine free radical is formed as in the case of pure PVC, and in the second step chlorine free radical replaces oxygen from metal oxide to form metal chloride and oxygen fre e radical. Subsequently, the oxygen free radical abstracts hydrogen fr om PVC. Formation of metal chloride is the rate-controlling step. The metal chlorides formed during the thermal degradation either volatiliz e or decompose simultaneously to lower metallic chlorides depending on the boiling point or the volatilization temperature.