STRUCTURE OF THE AMORPHOUS PHASE IN HIGHLY DRAWN POLY(VINYL ALCOHOL) FIBERS

Wide-angle X-ray diffraction analysis of poly(vinyl alcohol) (PVA) fibres shows that the amorphous scattering at 2theta = 20-degrees concentrates on the equator, and the degree of concentration becomes stronger with increasing draw ratio. This indicates that the amorphous chains must be highly oriented in the highly drawn fibres. Small-angle X-ray scattering (SAXS) analysis shows that the meridional SAXS intensity of the highly drawn fibres decreases with increasing draw ratio, indicating that the amorphous chains are packed more densely. On the other hand, a new meridional diffraction peak appears at 2theta = 35.5-degrees (d = 2.52 angstrom) and the intensity becomes stronger with increasing draw ratio. The 2theta = 35.5-degrees diffraction peak is broader than the (020) diffraction (d = 1.26 angstrom) peak. The thermal expansion coefficient estimated from the 2theta = 35.5-degrees peak is positive, while that estimated from the (020) peak is negative above ca. 120-degrees. These results suggest that this meridional peak (2theta = 35.5-degrees) is not the (010) diffraction, which never appears in the normal PVA crystal but might appear in some disordered crystals, but is due to the intrachain scattering of a single amorphous chain with an almost planar zigzag conformation.