Effects of phthalate and sulphonic acid ester plasticisers on TiO 2 catalysed photodegradation of PVC

Abstract

The effects of two plasticisers, one phthalate and one sulphonic acid ester, on the photodegradation of TiO₂ pigmented polyvinylchloride films are reported. The loading of each plasticiser was altered in the range 0–70% relative to the polyvinylchloride and the effects on the rates of photomineralisation were determined using a closed loop flow system to detect the carbon dioxide evolution. All plasticiser additions lead to an initial acceleration in CO₂ evolution over the non-plasticised cases. Non-plasticised films show a marked acid catalysis due to HCl evolution which leads to an acceleration in the rate of oxidation with time. Following initial rapid oxidation of preadsorbed plasticiser, the phthalate systems demonstrated a reduced rate of CO₂ production and no acid catalysis. The sulphonic acid ester plasticiser is broken down to produce sulphonic acid and sulphuric acid fragments which are sufficiently acidic to catalyse the TiO₂ when plasticiser loadings are >50%. The carboxylic acid fragments from the phthalates seem incapable of catalysis even at the highest levels used in the present work.