Crystallization and melting of polyethylene under high pressure. III. Mixed crystallization of two kinds of extended‐chain crystals

Abstract

Thermal behaviors of extended‐chain crystals of polyethylene formed during various crystallization processes and conditions under about 5000kg/cm² were studied by high‐pressure dilatometry and differential scanning calorimetry. The experiments indicate that by isothermal crystallization at small undercoolings for prolonged periods, the products show two endothermic peaks in the melting region of the usual extended‐chain crystals. This means of the presence of a bimodal lamellar thickness distribution in the extended‐chain crystals. A phase diagram has been made for pressures up to 5000 kg/cm². The experimental results confirm the existence of two kinds of extended‐chain crystals, i.e., ordinary extended‐chain and highly extended‐chain crystals, as suggested previously by the authors.