Structure development in high-speed melt spinning of high-molecular weight poly(ethylene terephthalate)/polypropylene islands-in-the-sea bicomponent fibers

High-speed melt spinning of island-in-the-sea (SI) type bicomponent fibers with 74 islands consisting of high-molecular-weight poly(ethylene terephthalate) (HMW-PET) and polypropylene (PP) was achieved. The struc-ture and mechanical properties of the HMW-PET component (islands) in the SI fibers were significantly enhanced with increasing the take-up velocity, while those of PP component (Sea) were suppressed. These results were attributed to the concentration of spinning stress on the HMW-PET component exhibiting higher elongational viscosity in the spinline. Considerable interaction between the two components in the SI fibers contributed to uniform structure development of the island parts in the fibers and improvement of the melt structure in the spinline. These results further enhanced the mechanical property and spinnability of the island parts. The thermoplastic composites, manufactured using the high-speed spun SI fibers with the islands of fine diameter (approximately 1.9 mu m), exhibited a high tensile strength of approximately 1.0 GPa by microfiber-reinforced effect.