Role of pigments in the stability of polyethylene systems

Full Paper: The photodegradation processes of high-density polyethylene (HD PE) films containing either a phthalocyanine-based pigment, or a rutil (TiO 2)-based pigment, as well as of the unpigmented films stabilised differentl y were investigated during photo-ageing, applying mechanical, gel content a nd XPS measurements. The phthalocyanine pigment-containing film showed degr adation characteristics (abrupt decrease of elongation at break after short irradiation period, no gel formation, high concentration of oxygen-contain ing functional groups on the surface) similar to those of the films contain ing a Low amount of stabiliser. The behaviour of the TiO2-containing film a nd that of the unpigmented films containing a higher amount of stabiliser w ere also similar (slow decrease of elongation at break, increase of gel con tent, lower amount of oxygen-containing functional groups on thr surface). The concentration of oxygen-containing functional groups in samples pigment ed with phthalocyanine increased remarkably with increasing processing temp erature. The results suggest that the phthalocyanine pigment influences the photostability indirectly, through reduction of the thermal stability of p olymer due to the adsorption of the thermal stabiliser by the phthalocyanin e pigment. Coating the surface of phthalocyanine with reactive surfactant i mproved the photostability of the HDPE film.