Orientational Crystallization of Ultrahigh Molecular Weight Polyethylene under Tension: Effect of Thermal Fixation

A series of samples with different morphology is obtained by the monolithization of an ultrahigh molecular weight polyethylene nascent powder at different temperatures. The elastoplastic properties of films pressed at 135°C that have the greatest ability to achieve high orientational elongations are studied in detail. It is shown that the deformation of ultrahigh molecular weight polyethylene crystals at elevated temperatures contains a noticeable elastic component and, at the time of unloading of the stretched “spatulas,” their elastic contraction occurs; as a result, the residual elongation and disorientation of chains decrease. Relaxation processes can be reduced if the deformable sample with fixed ends is cooled rapidly. Orientational crystallization during thermal fixation promotes an increase in the degree of crystallinity and the Hermans orientation factor and, accordingly, facilitates improvement in the mechanical properties of the sample.