The effect of molecular weight on the physical and mechanical properties of ultra‐drawn high density polyethylene

A study has been made on the effects of molecular weight on the physical and mechanical properties of cold‐extruded high density polyethylene. Prior data indicate that such ultra‐drawn strands contain a significant fraction of extended‐chain crystals. Four samples, spanning the molecular weight range of 59,000 to 147,000, were cold‐extruded under the same conditions and were examined with respect to their melting point, degree of crystallinity, linear expansion coefficient, Young' modulus, strain to break, and tensile strength. The degree of crystallinity, linear expansion coefficient, and modulus did not change significantly with molecular weight. The melting point, strain to break, and tensile strength do increase with increasing molecular weight. This leads to the conclusion that the amount of extended‐chain crystals is invariant with molecular weight. Higher molecular weight polymers are seen as providing a greater number of the chains, thus giving the fiber a higher tensile strength.