Structural transformations in ultra-high-density polyethylene during high-pressure annealing followed by drawing

Structural transformations in ultra-high-density polyethylene films, prepar ed from a reactive powder by cold pressing with shear, were studied by X-ra y diffract-ion and DSC in the course of drawing or high-pressure annealing followed by drawing. The annealing under high pressure leads to samples hav ing a highly crystalline structure, comprising coarse crystals with an aver age effective longitudinal size of up to 100 nm, exhibiting high plasticity during the subsequent drawing. This behavior is related to a complicated m orphology of the material: the high-pressure annealing induces epitaxial cr ystallization of a partial melt on the rigid PE fibrils containing chain-ex tended crystals, which results in the formation of a row texture. It is sho wn that mechanical properties of the final oriented material can be signifi cantly modified by variation of the sample formation conditions.