THE USE OF SODIUM-HYDROXIDE HYDROLYSIS TO STUDY THE FINE-STRUCTURE OFUNDRAWN AND DRAWN HIGH-SPEED SPUN POLY(ETHYLENE-TEREPHTHALATE) FIBERS

The fine structures of undrawn and drawn high-speed spun poly-(ethylen e terephthalate) (PET) fibers, 0.86 dL/g intrinsic viscosity, formed a t speeds from 1615 to 3329 m/min, were investigated. Increasing the sp inning speed and drawing resulted in greater levels of orientation and crystallinity in the untreated fibers. The relatively high molecular weight of the PET yielded undrawn products of higher orientation and c rystallinity than those obtained by workers using PET of lower molecul ar weight but spun at similar speeds. A linear relationship between co hesive and optical anisotropy was found for the undrawn and drawn fibe rs. Aqueous sodium hydroxide hydrolysis was utilized to reveal the pre sence of any radial variations in structure. In the undrawn fibers, hy drolysis revealed that a more oriented layer was present very near the fiber periphery at higher spinning speeds. In the drawn samples a sma ll but significant progressive decrease in birefringence was generally observed as the center of the fiber was approached. The drawing proce ss appears to produce fibers without a skin-core structure and less su sceptible to tenacity loss due to surface defects.