Structural Characterization of Drawn and Annealed Poly(trimethylene terephthalate) Fibers

The changes in the structures of the glycol segment of poly(trimethylene terephthalate) (PTT) monofilaments caused by drawing and annealing were analyzed by 13C solid-state NMR relaxation, wide-angle X-ray diffraction (WAXD), IR spectroscopy, DMA, and DSC measurements. The 13C solid-state NMR relaxation and WAXD studies indicated that the drawn PTT consists of oriented crystalline, amorphous, and intermediate phases. The IR spectra indicated that three methylene bonds of PTT in the crystalline and amorphous regions adopt gauche–gauche and trans–trans conformations, respectively. The intermediate region consists of aggregates of molecular chains with a gauche conformation. On the other hand, as-spun and annealed PTT fibers consist of amorphous and intermediate regions. Although the proportion of intermediate to amorphous regions was unchanged on annealing, the molecular mobility was changed, i.e., the molecular mobility of the intermediate region decreased with increasing annealing time. The DMA and DSC measurements showed that the glass transition temperature (Tg) of PTT fiber increased by 20 °C on annealing for 144 h, whereas drawing induced a more significant increase in the Tg. The Tg of DR=3 sample was 50 °C higher than that of as-spun fiber, because of the existence of orientational crystallization in the drawn PTT.