DRAWING OF LOW-MOLECULAR-WEIGHT POLYETHYLENE GEL FILMS AND ULTRAHIGH-MOLECULAR-WEIGHT POLYETHYLENE MELT FILMS

Gel films of low-molecular-weight polyethylene (LMWPE) were prepared b y partial melt under compression. The gel films could be readily stret ched up to 20 times at 135-degrees-C. The Young's modulus is in the ra nge 32-34 GPa. This value is slightly higher than that of melt-crystal lized ultrahigh-molecular-weight polyethylene (UHMWPE) drawn to 40 tim es at the same temperature but is much lower than that (> 200 GPa) of UHMWPE gel films drawn to 300. This behavior is discussed in terms of the morphology of the gel film as studied by wide-angle X-ray diffract ion, small-angle X-ray scattering, and birefringence measurements. It turns out that the Young's modulus, 32-34 GPa, of the LMWPE gel film i s attributed to a suitable degree of chain entanglement to assure effe ctive transmission of the drawing force associated with a significant crystal transformation from a folded to a fibrous type. In spite of th e perfect orientation of the c-axes, however, the Young's modulus of t he LMWPE gel film is much lower than that of the UHMWPE gel films with a draw ratio of 300. This is thought to be due to low crystallinity a nd short length of extended crystal chains.