The effect of the type of polyethylene on the grafting of styrene on polyethylene—II. Grafting initiated by pre-irradation in air and by chemical initiators

Abstract

Low and high density polyethylenes were irradiated in a cobalt-60 source in air at a low dose rate. Differences in behaviour in grafting were observed. The form of the kinetic curves, the temperature effect and the effect of the foil thickness suggest that there are different grafting mechanisms depending on the type of polyethylene. It is concluded that the grafting reaction is initiated by peroxides in low density polyethylene and by free radicals in high density polyethylene. When graft copolymerization was initiated by chemical initiators such as azo iso butyronitrile and benzoyl peroxide, in all cases higher grafting rate was obtained for low density polyethylene. It is assumed that chain transfer to branched low density polyethylene is much more effective than that to linear polyethylene. Thicker foils are grafted at a higher rate in low density polyethylene. The thickness effect often observed in polyethylene grafting must be mainly ascribed to structural differences, affecting the termination rate constant.