Effects of stretching on crystalline phase structure and morphology of hard elastic PVDF fibers

The phase characteristics and morphology of stretched hard elastic poly(vinylidene fluoride) (PVDF) fibers were investigated by X-ray diffraction (XRD) and wide-angle and small-angel X-ray scattering (WAXS and SAXS). It was indicated that alpha and beta phases coexisted in stretched PVDF fibers, stretching assisted in alpha to beta phase transformation. The beta/alpha ratios of stretched PVDF fibers were affected by stretching temperature, rate, and ratio. The P phase content of stretched PVDF fibers had an abrupt increase when stretched near 70 degrees C, and then it decreased with increasing stretching temperature. Besides, the beta/alpha ratio of PVDF fibers increased with stretching rate and ratio. The total crystallinity of PVDF fibers did not change much even on different stretching conditions. WAXS results indicated that the unstretched and stretched PVDF fibers all exhibited three strong equatorial streaks, with d-spacing (0.964, 0.488, and 0.439 nm) and (0.946, 0.494, and 0.480 nm), which suggested that PVDF fibers still remained the crystalline reflections of c-axis orientation even after being stretched. The long periods of stretched PVDF fibers, calculated from SAXS curves, increased from 19.04 to 39.75 nm. On the basis of these results, the P transformation mechanism of stretched PVDF fibers was also discussed. (c) 2007 Wiley Periodicals, Inc.