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 M-v's of 1.0-6.0 x 10(6) were tensile-drawn in the temperature range of T-d = 140-160 degreesC, slightly above their static melting temperatures (133-135 degreesC). The effects of M-v 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 T-d, reaching a maximum at a specific T-d, which increased with the sample M,. At yet higher T-d's, the ductility decreased rapidly with the T-d. The optimum T-d, as defined by the T-d where the highest tensile properties were achieved, increased with M, from 140 degreesC for the lowest M-v to 155degreesC for the highest M-v. Although the tensile properties for a given M-v increased with the draw ratio (DR) at a given T-d, those at a given DR decreased with increasing the T-d. 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 M-v. These values are among the highest ever reported for the melt-drawing of UHMW-PE.