Polyethylene networks crosslinked in solution : preparation, elastic behaviour and oriented crystallization. Part 3.—Oriented crystallization of swollen networks

Abstract

This paper describes an investigation of the crystallization of stretched polyethylene networks swollen to equilibrium in p-xylene. The retractive force during crystallization of the elongated networks shows a strong increase in contrast to the usual decrease in dry networks. The increase in force is often preceded by a smaller decrease during which slight turbidity is observed in the still swollen sample. The material obtained has a shish-kebab morphology identical to that obtained by flow-induced crystallization from solution. The strain dependence of the dissolution temperature is very small. This is shown to be largely due to the geometrical effect of swelling shifting the extensions of the chains to a high level. The effect of increasing dilution upon stretching is shown to be of lesser importance.

For the dry unstrained networks it is shown that the trapped entanglements contribute significantly to the melting point depression in addition to that caused by the crosslinks. The contribution per entanglement is much less than the contribution per crosslink.