Combined effect of hindered amine light stabilizer and ultraviolet absorbers on photodegradation of poly(vinyl chloride)

The combined effect of a basic hindered amine light stabilizer (HALS) and ultraviolet absorbers (UVAs) on casted poly(vinyl chloride) (PVC) films, during photodegradation, was studied by color change, ultraviolet‐visible (UV–vis) spectroscopy, Fourier‐transform infrared (FTIR) spectroscopy, and viscosity‐average molecular weight. It was found that the basic amine groups in the HALS (T770) could promote the dehydrochlorination, thereby accelerating the photooxidation of PVC films. Meanwhile, T770 could scavenge the radicals formed and restrain the aging of PVC to some extent. The above‐mentioned aspects were competing factors: the former played a dominant role during the first 100 h, while the latter counteracted the former effect to some extent between 100 and 300 h. A benzotriazole derivative (UV326) absorbs more UV radiation in the UV‐A region (320–400 nm), which mainly causes the photodegradation of PVC samples, than a benzophenone derivative (UV531). Thus, UV326 is a more efficient UV absorber than UV531 in prohibiting the photooxidation and chain scission of PVC films. The combination of T770 and UV326 effectively protected PVC films from dehydrochlorination and photooxidation. The combination of T770 and UV531 accelerated the dehydrochlorination and discoloration of PVC films. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers