Sur la dégradation thermique du chlorure de polyvinyle. III. Etudes cinétiques sous atmosphère d'air

Abstract

Abstract Polyvinyl chloride thermal degradation was carried out under air atmosphere from 150 to 250°C. and the kinetics followed, simultaneously by thermogravimetry and hydrochloric acid evolution measurements. The overall scheme of dehydrochlorination is the same under air and inert atmospheres: it is a chain reaction initiated by thermal instability of irregular structures initially present or created during the course of the reaction. Oxidation plays an important part in the activation of these structures and reduces all activation energies; furthermore, it creates new centers. Oxygen participates alao in propagation and termination of chains of reactions. With an increase in the reaction chains, simultaneously, backbone CC bonds are broken up, and the residue is formed by branched molecules small enough to remain soluble. All kinds of structures, but especially the polyenic ones, are oxidized. When their concentration and degree of oxidation are great enough, a further decomposition of these degraded parts into volatile oxidized products occurs; the velocity of this reaction is then nearly equal to that of macromolecular residue oxidation.