1986 Volume 43 Issue 3 Pages 133-138
The temperature dependence of the elastic modulus E1 of crystalline regions of poly (vinyl alcohol) (PVA) in the direction parallel to the chain axis has been investigated by X-ray diffraction. The value of E1 for the (020) plane of PVA was 235 GPa from room temperature to 110°C. However, it decreased abruptly near 110°C, and was 167 GPa at 180°C. The lattice spacing of the (020) plane decreased with increasing temperature up to 180°C. This means that molecular contraction occurs at high temperature. Further, this change is more pronounced in the higher temperature range. The thermal expansion coefficient α (020) changes discontinuously aroun4 110°C (<110°C; α (020) =-3.3×10-6K-1, >110°C; α (020) =-9.9×10-6K-1). These phenomena and the results of dynamic mechanical measurements and infrared spectroscopy show that the mobility of chain molecules in the crystalline regions, i. e., incoherent thermal vibration of crystal lattice, increases beyond 110°C, and that this causes the decrement of E1 at high temperature.
