The Changes of PP Crystal Orientation in the Polypropylene/Polyamide 6 Blend Fiber by Annealing.

Abstract

The changes of X-ray diffraction patterns with annealing were investigated for polypropylene/polyamide 6 (hereafter “PP/PA6”) blend fibers. An annealing under a free end at the melting point of PP or higher, induced the extreme reduction of the c-axis orientation of PP crystal, and the development of anisotropic a*-axis orientation. In the samples annealed under a constant length or the samples with low heat shrinkage, the c-axis orientation of PP crystal remained unchanged and the a*-axis orientation was developed. X-ray diffraction patterns of the blend fiber during heating revealed that the diffraction peak of PP crystal completely disappeared around 170°C or higher, although the blend fiber annealed at a constant length for two hours at 200°C, showed a clear c-axis orientation of PP crystal.It is inferred that the PP crystals melt during annealing of the blend fiber at the melting point of PP or higher. Since the oriented PA6 phases keep their macroscopic shape during annealing, molecular chains of PP can't form a random coil but partly keep the original orientation which might enhance an anisotropic c-axis orientation.