Abstract
The molecular weight effect on the morphology of high molecular weight polyethylenes (HMW-PE, 2.2×105 and 6.9×105) crystallized at 590 MPa was studied by scanning electron microscopy. The external shape of the band of the HMW-PE is as that of the medium molecular weight PE (MMW-PE); however with increasing molecular weight the band comes to be comprized of long fibrils. It is suggested that the band of HMW-PE is formed by the parallel arrangement of fibrils. Thermal analysis on the pressure-crystallized PEs in a molecular weight range from 4×103 to 2.5×106 was also performed, and the molecular weight dependence of the melting temperature and heat of fusion was obtained. The heat of fusion of the pressure-crystallized sample decreases linearly with logarithm of molecular weight. The melting temperature increases linearly with logarithm of molecular weight in a molecular weight region lower than about 105. Above 105, the melting temperature for the pressure-crystallized powder sample is higher than about 146°C and increases slightly with molecular weight. This considerable increase of the melting temperature is caused by the superheating effect.
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Yasuniwa, M., Tsubakihara, S. & Nakafuku, C. Molecular Weight Effect on the High Pressure Crystallization of Polyethylene. Polym J 20, 1075–1082 (1988). https://doi.org/10.1295/polymj.20.1075
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DOI: https://doi.org/10.1295/polymj.20.1075
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