Photo-stabilizing efficiency of N-substituted hindered amines in polypropylene: Effects of processing conditions and exposure to a protonic acid

The effects of exposure to processing conditions and strongly acidic gases on the photo-stability of polypropylene films stabilized with hindered amine light stabilizers (HALS) have been studied. A series of monofunctional hindered amines based on tetramethylpiperidine containing 〉NH〉NO〉NCOCH₃ and 〉N--OC(==O0CH₃ substituents in the piperidyl ring was compared with a bifunctional secondary amine. Exposure to heat and shear in a Brabender Plastograph caused loss by volatilization and decomposition of the 〉N O C(==O)CH₃ additive. All of the HALS derivatives formed salts upon exposure to gaseous HCl and their photo-stabilizing ability was greatly impaired although the monofunctional secondary amine was superior to the bifunctional amine under these conditions. The 〉N-COCH₃ additive was extensively decomposed by the HCl exposure.