Deformation mechanisms in biaxially drawn polyethylene

The crystal orientation of solid-state biaxially drawn solution-crystallized ultra-high-molecular weight polyethylene (UHMW-PE) film has been revealed from flat-plate wide-angle x-ray scattering (WAXS) patterns and interpreted in terms of crystal plasticity. A slightly drawn film (λ ≤ 3 × 3) possesses only a (100) planar orientation, whereas in a highly drawn film (λ ≥ 6 × 6), a mixed (100) and {110} planar orientation is present. Crystal deformation is found to proceed both by slip on (100) and {110} planes, resulting in a (100) texture in a similar way to crystal deformation in uniaxially drawn polyethylene and by {110} 〈110 〉 transverse slip and/or {310} twinning which results in a {110} texture. It is postulated that during transverse slip or twinning, the molecules deform without chain extension. As a consequence, neither the molecular draw ratio nor the tensile properties change significantly for macroscopic draw ratios above 10 in contrast to the data obtained for uniaxially drawn polyethylene.