Orientation of plane strain-compressed ultra-high-molecular-weight polyethylene

Abstract

Ultra-high-molecular-weight polyethylene (UHMWPE) samples of molecular weight 6 million were compressed using a channel die and characterized by wide-angle and small-angle X-ray scattering. The results were compared to previous studies performed on high-density polyethylene (HDPE) under the same compression conditions. Most deformation mechanisms exhibited by UHMWPE were also observed in HDPE. However, the onset of crystallographic and morphological orientation occurred at lower compression ratios in UHMWPE than in HDPE. Greater resistance to deformation and more extensive strain recovery were also exhibited by UHMWPE. These differences in deformation behaviour of UHMWPE and HDPE were attributed to the larger number of tie molecules and higher degree of entanglement within the amorphous regions of UHMWPE—a direct effect of its very high molecular weight. Our results clearly demonstrate that crystallographic texturing in UHMWPE, especially molecular orientation along the flow direction, can be controlled by channel die compression. This renders the method suitable for production of oriented samples for future studies of possible relationships between crystallographic texture and wear behaviour.