Natural weathering,photo and thermal degradation of the two-phase system poly(vinyl chloride) and poly(isobutylene)

Natural weathering, photo-oxidative and thermo-oxidative degradation have been compared for poly(vinyl chloride) (PVC) and poly(isobutylene) (PIB) and nine of their blends covering the entire composition range. The degradation techniques used include heating in an air oven at 100°, u.v. irradiation and natural weathering. Studies on the morphology of the blends show that the state and mode of dispersion of the elastomer in films of the blend are influenced by composition. PIB is substantially less stable than PVC and does not act as a good modifier for PVC in freshly prepared samples. Considerably improved mechanical properties were obtained when the polyblends were partially degraded presumably because of the interactions between the polymers. The changes in the chemical properties were monitored by i.r. measurements. The presence of PIB in PVC up to 20% gave optimum stabilization to PVC whereas small amounts of PVC in PIB destabilized PIB considerably. The presence of PIB in a PVC-PIB blend leads to considerable suppression of dehydrochlorination at 100°. The blends became more stable than the homopolymers. The effect of PIB is chiefly to stabilize PVC; a mechanism is proposed. Equations have been developed to allow evaluation of the role of PIB as an effective stabilizer for PVC.