MELTING AND CRYSTALLIZATION OF ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE WITH APPEARANCE OF HEXAGONAL PHASE-II - STRAIN-INDUCED CRYSTALLIZATION OF THERMAL-CONTRACTED SAMPLE
S. Tsubakihara et M. Yasuniwa, MELTING AND CRYSTALLIZATION OF ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE WITH APPEARANCE OF HEXAGONAL PHASE-II - STRAIN-INDUCED CRYSTALLIZATION OF THERMAL-CONTRACTED SAMPLE, Polymer Journal, 28(7), 1996, pp. 563-567
Strain-induced crystallization of a thermal-contracted sample, prepare
d from highly-drawn ultra-high molecular weight polyethylene (UHMW-PE)
, was examined by the wide angle X-ray diffraction method using a high
temperature elongating apparatus. X-Ray diffraction measurements were
isothermally carried out al three characteristic temperatures 148, 15
2, and 156 degrees C, above the melting point. At each temperature, th
e molten sample was elongated in steps up to the break ratio, and chan
ge of the X-ray equatorial diffraction pattern was recorded with a pos
ition sensitive proportional counter. At 148 degrees C below the ortho
rhombic to hexagonal transition point determined by thermal analysis o
f a constrained sample, the strain-induced crystallization of the only
orthorhombic crystals occurred in the elongation. On the other hand,
the hexagonal crystals grew together with the orthorhombic ones at 152
degrees C that corresponds to the transition point, and at a yet high
er temperature of 156 degrees C, the only hexagonal ones grew. Such te
mperature dependence of the structure of growing crystals was discusse
d on the basis of the free energy diagram proposed in Part I to explai
n the melting process of the constrained UHMW-PE.