Structure formation in stretched sheets of poly(butylene terephthalate)

Abstract

AbstractCrystalline and amorphous sheets of poly(butylene terephthalate) (PBT) were drawn in the temperature range of 20–150°C. The molecular orientation and the relative amount of α‐ and β‐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, α‐form crystals are partially transformed into β‐form crystals. Both α‐ and β‐form crystals are formed by drawing amorphous PBT sheets. The relative amount of α‐ and β‐form crystals is much more sensitive to drawing temperature than to draw ratio. The α‐form crystallinity is higher at higher drawing temperature and increases slightly with increasing draw ratio. The second moments of orientation functions of α‐ and β‐form crystals increase with increasing draw ratio, and the increase of the orientation function is suppressed at higher draw ratio. The orientation function of α‐form crystals is higher than that of β‐form crystals in a same sample.