The influence of crystallization conditions on radiation effects in polyethylene — II. Crystallization from concentrated solutions

Samples of Marlex 50 were crystallized from solution in the concentration range of 0.1 to 2 per cent and were irradiated with a dose of 20-megarad electrons. If crystallized at 70°C the materials were largely soluble, but if crystallization was conducted at 85°C the samples became two-thirds insoluble at from 0.4 to 0.6 per cent concentration upwards. Morphological examination of samples crystallized from 1 per cent solution revealed that the mode of crystallization was lamellar in all cases, but in the case of 70°C crystallization the lamellae were largely separated while in the 85°C case they were grown together in a compacted mass. After the latter was broken up by ultrasonic treatment this sample stayed fully soluble after 20-megarad electron irradiation. This finding indicates that the crosslinks are formed predominantly at the lamellar interfaces tying the lamellae together when these are in close contact. This might imply that the radiation is most effective at the sites where the chains fold. The present exploratory work shows the importance of the mode of packing of the lamellae, and indicates that this might be an important factor in distinguishing between the different morphologies observed in general.