Polyethylene crystallized from the melt under elevated pressure

Abstract

Abstract Polyethylene of the linear, low‐pressure type has been crystallized under pressure (up to 5400 atm.) from the melt. Crystallization conditions of constant supercooling and constant cooling rates were employed. The resulting solid was analyzed at atmospheric pressure. In contrast to solution crystallization under pressure above 2000 atm., extended chain lamellae of increasing thickness become dominant. These show a maximum melting point of 140°C. and in this research, densities of up to 0.994 g./cm. 3 . Combining these data on large crystals with the experimental maximum melting temperatures and thickness data on low and atmospheric pressure crystallized lamellae yields a surface free energy of 91 ergs/cm. 2 for folded chain lamellae crystallized at low pressure.