Influence of thermal dehydrochlorination on the photooxidation kinetics of PVC samples

A series of PVC samples were thermally dehydrochlorinated under nitrogen. The amount of HCl was monitored and nine samples with increasing quantity of liberated HCl were obtained (from 0.03 to 2.0% of elimination of HCl, where 100% indicates the theoretically total removal of HCl from PVC). These samples were characterized with Raman and UV-Vis spectroscopy. Subsequently, the dehydrochlorinated resins were subjected to accelerated weathering with UV-B lamps and the kinetics of formation of the photoproducts were followed with FTIR spectroscopy, in order to study the influence of the presence of conjugated sequences on the photooxidation of PVC. The results show that the presence of conjugated sequences into the thermally degraded PVC samples (Raman spectroscopy indicates the presence of long conjugated sequences already at dehydrochlorination rates lower than 0.01%) does not influence either the mechanism or the kinetics of the photooxidation of the PVC chains. The mechanism of photooxidation is discussed.