MELTING BEHAVIOR OF ULTRAHIGH MODULUS LINEAR POLYETHYLENE

In the reported experiments, the differential-scanning calorimetry (DSC) behavior of drawn linear polyethylene (LPE) has been investigated as a function of draw ration and molecular weight. All the samples examined showed a dependence of the melting temperature on heating rate, an effect generally known as superheating. The magnitude of this effect, as well as the maximum melting temperatures, increased markedly at high draw ratio and high molecular weight. The highest melting temperature recorded was 145 degree C for a tape of draw ratio 25 and weight-average molecular weight of 312,000. It was concluded that the DSC data are consistent with previous wide-angle x-ray diffraction results in confirming that an extended chain morphology similar to that observed in pressure crystallized LPE is not present in these samples. Secondly, the superheating effects were examined in the light of the possible configurational constraints on the amorphous regions of drawn polymers, along the lines proposed by Zachmann. It is possible to understand the effects of draw ratio and molecular weight very well on this basis, in a manner consistent with previous structural results on these materials.