Oriented chain-extended polyethylene

Abstract

Aggregates of polyethylene lamellae, whose average thickness can be increased progressively from about 200 to 2000 A and beyond have been produced by annealing drawn polymer hydrostatically. All lamellae share a common c axis orientation and have a surface free energy of 95 erg cm⁻². The physical texture of the resulting solids passes through three stages. First there is a chainfolded region in which the initial morphology of drawn material gradually gives way to a well-defined series situation. For annealing at 5 kbar this comprises lamellar thicknesses between about 500 and 1000 Å, these crystal interiors and interfacial regions have constant properties and only their relative proportion changes. Above this there is a discontinuity, associated with an endothermic process, and chain-extended layers appear. These have interlamellar regions with a greater mass deficit per unit area than do chainfolded crystals. The data support the hypothesis of Bassett and Turner (1972) that the endotherm represents a first order transition to a new phase which is necessary to the formation of chain-extended polyethylene.