Structure and deformational behavior of high-pressure annealed ultra-high-molecular-mass polyethylene with different initial morphology

Deformational behavior and structural rearrangements upon high-pressure ann ealing and subsequent tensile drawing were studied by X-ray diffraction and differential scanning calorimetry for PE samples with different morphologi es: films obtained by the solid-state extrusion of a reactor powder, single -crystal mats of ultra-high-molecular-mass polyethylene, and bulk samples o f linear PE with a medium molecular mass prepared by melt crystallization o f the polymer. It was found that the structure of annealed samples is quali tatively the same and shows a complex heterogeneous character. In addition to the dominating crystals with extended chains, the material also contains a marked fraction of epitaxially crystallized crystallites with folded cha ins (a row texture). As the annealing temperature is increased, the fractio n of the row-texture material increases. For the film of ultra-high-molecul ar-mass PE, the effect of temperature of the preliminary tensile drawing on the structure and properties of the annealed samples was studied. In singl e-crystal mats annealed at a high pressure, the fraction of the row texture is much lower than that in the films prepared by the solid-state extrusion of reactor powders, because the optimum entanglement network in single-cry stal mats and a well-defined size of the fold lead to a smaller diffusion o f the boundaries of the p-T phase diagram of ultra-high-molecular-mass poly ethylene, The presence of crystals with folded chains epitaxially crystalli zed on central fibrils is the necessary but not the sufficient condition fo r the high deformability of PE films annealed at high pressure. Deformabili ty is controlled not only by the ratio between the fractions of crystallite s with folded and extended chains, but also by the plasticity of fibrils co ntaining crystals with extended chains, which is governed by the network of molecular entanglements.