STRUCTURE FORMATION IN STRETCHED SHEETS OF POLY(BUTYLENE TEREPHTHALATE)

Crystalline and amorphous sheets of poly(butylene terephthalate) (PBT) were drawn in the temperature range of 20-150-degrees-C. The molecular orientation and the relative amount of alpha- and beta-form crystals in the stretched sheets were studied by wide-angle X-ray diffraction (WAXD) and density measurements. When crystalline PBT sheets are drawn at lower temperatures, alpha-form crystals are partially transformed into beta-form crystals. Both alpha- and beta-form crystals are formed by drawing amorphous PBT sheets. The relative amount of alpha- and beta-form crystals is much more sensitive to drawing temperature than to draw ratio. The alpha-form crystallinity is higher at higher drawing temperature and increases slightly with increasing draw ratio. The second moments of orientation functions of alpha- and beta-form crystals increase with increasing draw ratio, and the increase of the orientation function is suppressed at higher draw ratio. The orientation function of alpha-form crystals is higher than that of beta-form crystals in a same sample.