Photostabilising action of nickel(II) bis(1-phenyl-3-methyl-4-decanoyl-5-pyrazolate), (sanduvor NPU) in polypropylene. Thermal antioxidant action and its relationship to photostabilisation,importance of hydroperoxide decomposition and light stability as a function of concentration

The thermal antioxidant action of Sanduvor NPU in polypropylene film has been examined at the 0.1% w/w concentration level. Infra-red and second-order derivative u.v.-visible spectroscopic techniques were used to monitor degree of oxidation in the films and stabiliser photodecomposition behaviour respectively. Hydroperoxide analysis was employed to determine the degree of thermal oxidation of films in an air oven. It was found that the behaviour of Sanduvor NPU in polypropylene films as a thermal stabiliser parallels its mode of action when used a melt stabiliser. The metal complex is highly effective in inhibiting hydroperoxide formation during extreme oxidative conditions. Hydroperoxide decomposition appears to play no part in this behaviour due to the inability of the complex to destroy these chromophores in solution, and the effect it has is attributed to the very effective chain breaking acceptor mechanism, i.e. macroalkyl radical scavenging. The relationship between embrittlement time and concentration was studied by varying the stabiliser content of the polymer over a wide range. As in the case of other metal chelates, the relationship is not linear, a limiting concentration behaviour is observed. This effect is attributed to the formation during photooxidation of products which promote the degradation of the polymer. This effect has implications on the efficiency of commercial systems.