ORIENTATION OF PLANE STRAIN-COMPRESSED ULTRAHIGH-MOLECULAR-WEIGHT POLYETHYLENE

Ultra-high-molecular-weight polyethylene (UHMWPE) samples of molecular weight 6 million were compressed using a channel die and characterize d by wide-angle and small-angle X-ray scattering. The results were com pared to previous studies performed on high-density polyethylene (HDPE ) under the same compression conditions. Most deformation mechanisms e xhibited by UHMWPE were also observed in HDPE. However, the onset of c rystallographic and morphological orientation occurred at lower compre ssion ratios in UHMWPE than in HDPE. Greater resistance to deformation and more extensive strain recovery were also exhibited by UHMWPE. The se differences in deformation behaviour of UHMWPE and HDPE were attrib uted to the larger number of tie molecules and higher degree of entang lement within the amorphous regions of UHMWPE - a direct effect of its very high molecular weight. Our results clearly demonstrate that crys tallographic texturing in UHMWPE, especially molecular orientation alo ng the how direction, can be controlled by channel die compression. Th is renders the method suitable for production of oriented samples for future studies of possible relationships between crystallographic text ure and wear behaviour. (C) 1998 Elsevier Science Ltd. All rights rese rved.