Melt-Drawing of Ultrahigh Molecular Weight Polyethylene: Effect of Molecular Weight

Melt-crystallized films of three kinds of ultrahigh molecular weight polyethylenes (UHMW-PE's) having Mv‘s of 1.0-6.0 × 106 were tensile-drawn in the temperature range of Td = 140-160°C, slightly above their static melting temperatures (133-135°C). The effects of Mv on the melt-draw behavior and the tensile properties of the resultant drawn products were studied. The deformation of the entanglement networks in molten UHMW-PE, which occurred during the melt-drawing, induced the chain extension, orientation and crystallization depending on the drawing variables. For a given Mv, the ductility increased with increasing the Td, reaching a maximum at a specific Td, which increased with the sample Mv. At yet higher Td's, the ductility decreased rapidly with the Td. The optimum Td, as defined by the Td where the highest tensile properties were achieved, increased with Mv from 140°C for the lowest Mv to 155°C for the highest Mv. Although the tensile properties for a given Mv increased with the draw ratio (DR) at a given Td, those at a given DR decreased with increasing the Td. As a result of the specific effect for each of these drawing variables on the ductility and tensile properties, the highest tensile modulus of 88 GPa and strength of 1.3 GPa were obtained for the UHMW-PE with the highest Mv. These values are among the highest ever reported for the melt-drawing of UHMW-PE.