The effect of crystallization conditions on radiationinduced crosslink formation in polyethylene

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Abstract
Annealing treatment before irradiation was observed to change the radiation-induced gelation behaviour of single crystals. After a decrease on short annealing times the gel content increases on prolonged annealing and approaches the behaviour of the bulk. Variations in lamellar contact are invoked to account for this behaviour. In other experiments single crystal samples were irradiated first and annealed subsequently. It was found that even a high degree of crosslinking which might be expected to immobilize the chains did not prevent re-folding. The conclusion is reached that the folds are preferential sites where the crosslinks form, the ineffective ones giving rise to small rings which can thread through the lattice on re-folding. Lattice distortions are expected to occur during this process and are in fact indicated by the x-ray diffraction pattern.