In situ study of fiber structure development of poly(butylene terephthalate) in a continuous laser-heated drawing process

Abstract

The structural development of poly(butylene terephthalate) (PBT) fibers was analyzed using in situ wide angle X-ray diffraction and fiber temperature measurements during CO 2 laser-heated drawing, in which the necking position on the running fiber could be fixed by CO 2 laser irradiation. The measured parameters were determined as functions of the elapsed time after necking with a time resolution of 0.3 ms. The as-spun PBT fibers, which exhibited a low-oriented α-crystalline structure, were drawn to a draw ratio of 5 using laser heating. The (001′) reflection, which indicates a quasi-smectic fibrillar structure, was not observed before crystallization in contrast to measurements of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalene dicarboxylate) (PEN). The α-crystal was transformed into an oriented β-form crystal at the necking position, and the developed β-crystallites exhibited increased size and altered orientation 2 ms after necking. The fiber temperature increased rapidly at around T g, and the rearrangement of the β-crystal primarily occurred as the fibers temperature rose from 100 to 160 °C. The oriented β-crystal of the drawn fiber transformed into the oriented α-crystal when the drawing tension was released. © 2012 The Society of Polymer Science, Japan (SPSJ) All rights reserved.