Kinetics of Crystal Nucleation in Polyethylene

Abstract

Observations of the freezing behavior of droplets of a linear polyethylene (Marlex-50) suspended in an inert medium have been made. It is possible to cool such suspensions of molten droplets to 85°—87°C before the majority of the droplets freeze, provided precautions are taken to minimize nucleation by the vessel walls. This indicates unambiguously that spherulites formed near 120°C (the usual crystallization range) are nucleated by heterogeneities in the melt. Analysis of experiments performed at various cooling rates indicate an end surface interfacial energy of rod-shaped nuclei of 168 ergs/cm2. This is similar to the estimates made of the fold-surface energy in crystals formed from dilute solution. The cooling-rate experiments also indicated that the transport processes in the production of the polymeric nucleus are similar to those involved in the production of nuclei of n-alkane crystals.