The effect of crystallization conditions on radiation-induced crosslink formation in polyethylene

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Abstract
The effect of lamellar packing in polyethylene single crystals on radiationinduced crosslinking was examined. As a follow up of an earlier exploratory experiment by Salovey and Keller the stacks of crystal layers were systematically loosened and dispersed by ultrasonic treatment. This led to large reductions in the radiation-induced insolubility with only slight change of molecular weight. It could be shown that even these small changes had no effect on the gelation which accordingly was entirely due to the state of aggregation of the lamellae. This is in agreement with the proposition that the links which lead to networks are the ones between lamellae. It was concluded that initially molecular links between layers are scarce even in the compact unirradiated crystals and attention is drawn to the fold surface as a possible source of cohesion. Some new observations on the morphology of compact crystals and results on their irradiation while in suspension are reported relevant to the problem of lamellar packing.