Annealing of stirrer-crystallized polyethylene

Abstract

A small portion of highly superheatable, but relatively low melting polyethylene crystals was discovered by calorimetric measurements on stirrer-crystallized polyethylene from solution. This portion corresponds probably to the fibrous backbone in these crystal aggregates discovered by electron microscopy. Annealing greatly increased the amount of superheatable material in the other portion of the polyethylene crystals, an effect not observed in the usual solution-grown crystals. The annealing was accompanied by a slight increase in crystal perfection as reflected by the true ultimate melting point. This latter increase is beyond the level normally reached on annealing solution-grown crystals, but not beyond that reached in slowly cooled melts. This unusual annealing behavior must be induced by the fibrous backbone. We associate increasing superheating with increasingly extended chain crystals and the comparatively low melting points with imperfections within such crystals.