結晶性高分子の大変形

抄録

In order to clarify the deformation mechanism of crystalline polymers, their structural changes during their uniaxial drawing were studied by electron microscopy, by the X-ray method at small and wide angles and by thermal analysis. Polyethylene (PE) was chosen for study as highly crystalline polymer, and polyethylene terephthalate (PET) as polymer of low crystallinity. In the case of the drawing of a commercial PE film having the so-called a-axis orientation along the machine direction, the long X-ray spacing increased at first with increasing draw ratio, showing maximum increase of ca. 14%, which corresponded with the macroscopic elongation at the yield point, and further elongation gave rise to rapid drop in the elongation range 100-120%, and then to levelling off. This long constant spacing was dependent only on the drawing temperature, irrespective of the original spacing, suggesting the melt-recrystallization mechanism occurring in the drawing process. The necking behavior was analysed theoretically by assuming that melting occurred by the mechanical force applied to the lamellar crystals. The results suggest that the melting occurs through interlamellar tie chains from which local unfolding takes place. Another type of (complete) unfolding may occur on drawing PET film of a low crystallinity, which results in formation of fringe micelle structure.