Development of a fiber structure in poly(vinylidene fluoride) by a CO2 laser-heated drawing process

Abstract

Rapid and uniform heating by CO2 laser radiation can fix the position where necking occurs. Therefore, this study investigated the development of a fiber structure in poly(vinylidene fluoride) in continuous drawing by in situ measurement using synchrotron X-ray radiation with a time resolution of several hundred microseconds. Two neck-deformation behaviors were observed in the laser drawing: a moderate neck deformation under low drawing stress and a steep neck deformation under high drawing stress. The low drawing stress resulted in a mixture of α- and β-crystals in which the β-crystal was formed within 1 ms after the necking, earlier than the α-crystal. The development of the fiber structure under high drawing stress was almost complete in less than 1 ms, and the developed structure contained only β-crystals. Small-angle X-ray scattering images showed meridional streaks at low drawing stress, whereas a four-pointed pattern occurred under high drawing stress. Low drawing stress generated a long periodic structure that was defective in the periodic regularity of crystalline and amorphous regions, although the molecular chains were nearly oriented along the fiber axis. The high drawing stress resulted in a well-packed structure of adjacent fibrils with alternating amorphous and crystalline regions.