Thesis (M.Eng.)--Chulalongkorn University, 1991

Low density polyethylene and high density polyethylene films sensitized with aromatic ketones or aromatic diketones were exposed outdoor for six months. The degradation of sensitized polyethylene films were also studied by irradiation with medium pressure mercury lamp. The effect of photosensitizers and the progress of degradation were studied by measuring the changes in tensile strength, elongation at break, gel formation, molecular weight and fourier transform infrared absorption. The relative infrared absorbance of the carbonyl and vinyl groups increased regularly during the whole exposure time. The elongation at break and molecular weight decreased with exposure time. An accelerating factors for outdoor exposure and irradiation with medium pressure mercury lamp were calculated. From the results, it was found that the photosensitizers accelerated the degradation. Regarding to the type of photosensitizers, polyethylene films sensitized with thioxanthone, derivatives of benzophenone and of anthraquinone show a higher degradation rate than ones sensitized with benzophenone and anthraquinone. In addition to this, the degradation of high density polyethylene is faster than that of low density polyethylene.