Abstract
The drawability and physical properties of dried poly(vinyl alcohol) (PVA) gel films prepared from N-methylpyrrolidone (NMP) and ethyleneglycol (EG) solutions were compared. X-ray diffraction and differential scanning calorimetry showed that PVA/EG gels had higher values of crystallinity than PVA/NMP gels. The drawability of dried PVA/NMP gels was higher than that of PVA/EG gels at all drawing temperatures. Although the maximum draw ratio of dried PVA/NMP gel films increased with molecular weight, the extent of the increase is much less than in the case of polyethylene gel films, partly because the highest molecular weight available in this study was lower than in the case of ultra-high-molecular weight polyethylene. The highest draw ratio achieved was about 28 × for a dried PVA/NMP ( DP = 14400, 2 wt%) gel film and its tensile strength and modulus were 1 GPa and 30 GPa, respectively. The α c relaxation temperature ( T α c ) of PVA shifted to high temperature with increasing draw ratio, approaching the melting point, while the second-order crystal transition point remained at 120°C. This implies that the α c relaxation is related to molecular motion in the crystal-amorphous boundary.
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