The photodegradation of polyethylene and polypropylene in the presence and absence of added titanium dioxide

The durabilities of polyethylene and polypropylene, in the presence and absence of added titanium dioxide, towards photodegradation have been assessed by the rate of oxygen absorption upon irradiation, measurement of photo-induced carbonyl compound and hydroperoxide formation using i.r. spectroscopy, and by measuring the change in tensile properties caused by irradiation. Oxygen absorption measurements are relatively insensitive and this method appears to be unreliable. Measurement of carbonyl compound and hydroperoxide formation by i.r. spectroscopy is suitable for polyethylene but not for polypropylene. The most sensitive method of following degradation appears to be the measuring of change in tensile properties. In general, the lower the photo-reactivity of added titanium dioxide, the greater its protecting action provided that the pigment is used at sufficiently high loading. It appears that the manner in which a pigment is dispersed in a polymer affects the performance of the pigment as a stabilizer.