THERMAL AND PHOTOOXIDATIVE BEHAVIOR OF NOVEL 4-SUBSTITUTED ALICYCLIC AMINO-2-HYDROXYBENZOPHENONE STABILIZERS IN POLYPROPYLENE AND HIGH-DENSITY POLYETHYLENE FILMS

The thermal and photooxidative stabilization activities of four light stabilizers based on 2-hydroxybenzophenone with alicyclic amine groups substituted in the 4-position have been examined and compared with those of 2-hydroxy-4-n-octoxybenzophenone (HOBZ) in polypropylene and high density polyethylene (HDPE) films at 0.1% w/w concentration infra-red absorption spectroscopy. From both carbonyl index and embrittlement times, both alkylpiperazine derivatives were found to be ineffective on exposure to QUV irradiation, whereas the propoxymorpholinyl and the hindered piperidine compounds were found to be more effective than HOBZ. All the stabilizers were synergistic with the commercial hindered phenolic antioxidant, Irganox 1010, especially the HOBZ. On the thermal ageing all the light stabilizers behaved as antioxidants, including the HOBZ. However, the hindered piperidine derivative was the most effective, exhibiting a stabilizing effect close to that of the Irganox 1010. In the presence of the Irganox 1010 weak antagonism was observed, with the HOBZ exhibiting the most effective stabilization. In HDPE the effects were different on irradiation, with all the 4-substituted amino benzophenones being effective. In this case the 4-amino hindered piperidine stabilizer was more effective than HOBZ. In the presence of Irganox 1010 strong synergism is common except for the bis-N,N-octylpiperazine derivative. On oven ageing all the stabilizers exhibited antioxidant behaviour with the 4-amino-piperidine derivative being the most effective. The antioxidant effect of Irganox 1010 was not impaired in HDPE apart from that with the propoxy-morpholino derivative. The steric hindrance, molecular, size and oxygen scavenging ability of the cyclic amine are all concluded to be important factors in controlling the antioxidant behaviour of the stabilizer with hydroperoxides playing a key role in the latter case. The results also demonstrate the importance of the ortho hydrogen bonded hydroxyl group in 2-hydroxybenzophenones as an active chain-breaking donor in photostabilization and not UV absorption. It is further concluded that the results show the potential for the development of a single stabilizer entity which will behave as an effective photothermal antioxidant.