Polyvinyl chloride is a light and heat sensitive material and due to defects in its polymer chain structure, it is inherently thermally unstable and is degraded during hydrochlorination processes, which is accompanied by discoloration of PVC. In fact, during the PVC extrusion and compounding, injection and calendering processes, which are accompanied by stress and heat, the degradation process of PVC begins with the release of active chlorine atoms.
