Kinetic study of the photostabilisation of polypropylene films by an hydroxyphenylbenzotriazole

PP films of similar to 100 mu m thickness containing 0%, 0.05% or 0.15% by weight of 2(2'-hydroxy-3'-tert.butyl-5'-methylphenyl)-5-chlorobenzotriazole (TINUVIN 326) were exposed in photochemical reactors equipped with a fluor escent lamp at 40 degrees C, 55 degrees C and 70 degrees C. The stabilizer disappearance was monitored by UV spectrophotometry, whereas the polymer ox idation was followed by IR spectrophotometry and gravimetry. Two distinct k inetic regimes were observed. At low temperature, stabilization results ess entially from the screen effect. The stabilizer is destroyed by chemical (o xidation) reactions, the end of induction period corresponds to a stabilize r loss of abo ut 30%. At high temperature, the stabilizer loss is essential ly governed by a physical evaporation/diffusion process. But UV stabilizer displays a noticeable antioxidant effect. A possible explanation of this re sult is that at T greater than or equal to 70 degrees C, POOH thermolysis t ends to become faster than photolysis (for the light source and the intensi ty under study). (C) 1999 Elsevier Science Ltd. All rights reserved.