Effect of annealing on the structure and properties of polyvinylidene fluoride hollow fiber by melt-spinning

Polyvinylidene fluoride hollow fibers were prepared by melt-spinning technique under three spinning temperatures. The effects of annealing treatment on the structure and properties of hollow fiber were studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), tensile test, and scanning electron microscopy (SEM) measurements. DSC and WAXD results indicated that the annealing not only produced secondary crystallization but also perfected primary crystallization, and spinning and annealing temperature influenced the crystallinity of hollow fiber: the crystallinity decreased with the increase of spinning temperature; 140 degrees C annealing increased the crystallinity, and hardly influenced the orientation of hollow fiber; above 150 degrees C annealing increased the crystallinity as well, and furthermore had a comparative effect on the orientation. The tensile tests showed that the annealed samples, which did not present the obvious yield point, exhibited characteristics of hard elasticity, and all the hollow fiber had no neck phenomenon. Compared with the annealed sample, the precursor presented a clear yield point. In addition, the annealed samples had a higher break strength and initial modulus by contrast with the precursor, and the 140 degrees C annealed sample showed the smallest break elongation. SEM demonstrated the micro-fiber structure appeared in surface of drawn sample. (c) 2006 Wiley Periodicals, Inc.