Abstract
The hexagonal phase of a constrained ultra-drawn polyethylene (PE) fiber (UDPF) was studied in detail. The melting process of the constrained UDPF was examined at atmospheric pressure by DSC and X-ray measurement. The hexagonal phase appears prior to melting in the constrained UDPF. The phase diagram showing the pressure change of the hexagonal phase was determined by high pressure DTA up to about 600 MPa. The temperature range of the hexagonal phase increases with pressure and coincides with that of so-called “high pressure phase” (HPP) of it above about 300 MPa. That is, the hexagonal phase of the constrained UDPF is the same as HPP. The phase diagrams of three kinds of PE samples, two constrained UDPFs and a bulk sample composed of extended-chain crystals, determined by high pressure DTA, were compared with one another. The constraining force applied to these PE samples considerably raises the melting temperature of HPP, while it has almost no effect on the transition temperature from orthorhombic phase to HPP. By constraining force, HPP of UDPF appears even in the low pressure region that includes atmospheric pressure.
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Tsubakihara, S., Nakamura, A. & Yasuniwa, M. Hexagonal Phase of Polyethylene Fibers under High Pressure. Polym J 23, 1317–1324 (1991). https://doi.org/10.1295/polymj.23.1317
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DOI: https://doi.org/10.1295/polymj.23.1317