Abstract
The DSC method has been applied for the study of melting behaviour of polyethylene [PE] films in dependence on the number of repeated stretching λ. Some samples have been subjected to annealing and etching by nitric acid. The melting process characteristics have been correlated with structural parameters. It was found that the longitudinal dimension of a crystallite l, calculated from the value of long period and degree of crystallinity, had increased slightly with increasing λ. A rise in the melting point temperature Tm with increasing λ has not been caused so much by the value of l but has been related to the decrease of σe values—the specific free surface energy of the edges of crystallites. The values of σe, calculated according to the Thomson formula, have significantly decreased with increasing λ and have increased after annealing of the samples. The etching process has been accompanied by increase of σe. The structural changes, occuring during stretching, annealing and etching of PE samples, have had their significance presumably in amorphous zones and the end facets of crystallites, affecting also σe and, consequently, Tm values.
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