Effect of the combination of a benzotriazole-type ultraviolet absorber with thermal stabilizers on the photodegradation of poly(vinyl chloride)

The effect of the combination of a benzotriazole type of UV absorber (UV326) with different types of thermal stabilizers, including an organic calcium complex and an organotin mercaptide, on the photodegradation of poly(vinyl chloride) (PVC) was investigated by color difference measurements, UV-vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and viscosityaverage molecular weight (M_η) determinations. Films of PVC containing 0.5 phr of UV326, with or without 2 phr of thermal stabilizer, were prepared by solution casting and subjected to accelerated UV weathering under xenon light with an irradiance of 0.51 W/(m² nm) at 65°C. The results revealed that both UV326 and the mixture of UV326 with the organic calcium complex displayed good performance in inhibiting the photodehydrochlorination and photooxidation of PVC. In contrast, the combination of UV326 and the methyltin mercaptide remarkably accelerated the discoloration of PVC when the irradiation time increased from 300 to 400 h because of the UV sensitivity of the organotin. However, carbonyl index data indicated that a hydrogen abstraction reaction did not take place between UV326 and the methyltin mercaptide, so that the photooxidation of the PVC film was prevented effectively during the whole period of exposure, a result which may be attributed to the strong steric hindrance effect of the tert-butyl group at the 3-position of the phenyl ring in UV326. The changes of M_η were in good accordance with the results obtained from other characterizations. J. VINYL ADDIT. TECHNOL., 16:175-182, 2010.