Antioxidant interaction between organic phosphites and hindered amine light stabilizers: Effects during photoxidation of polypropylene .2.

The behaviour of mixtures of hindered amine light stabilizers (HALS), their nitroxyl radical, and alkylamine analogues, with aromatic and aliphatic phosphites during photoxidation of polypropylene (PP) has been examined. The photostabilizing performance of the above mixtures of stabilizers was compared with that of the individual antioxidants and with the performance of a number of synthesized bifunctional stabilizers containing aromatic phosphite or phosphonite and either of the above HALS or related functions in the same molecule (referred to as 'HALS-Phosphites or 'HALS-Phosphonite'). Combinations of the hindered aryl phosphite Irgafos 168, with the hindered amine Tinuvin 770, the tertiary amine Tinuvin 292 and the bis-nitroxyl-analogue of Tinuvin 770, gave antagonistic effects at most molar ratios examined. Furthermore, in all cases, the extent of antagonism was reduced with increasing the amount of Irgafos 168 in the mixtures. Combination of the aliphatic phosphite, trilaurylphosphite, TLP, with Tinuvin 770 in PP, on the other hand, has shown synergistic effect under photoxidative conditions. The HALS-Phosphites and HALS-Phosphonite examined have shown better stabilizing efficiency than the corresponding mixtures of the individual stabilizers. (C) 1997 Elsevier Science Limited.