Preparing a Core-Sheath Bicomponent Fiber of Poly(butylene Terephthalate)/Poly(butylene Succinate-co-L-lactate)

A core-sheath bicomponent fiber is melt-spun by co-extrusion of poly(butylene tereph thalate) (PBT) as the core and poly(butylene succinate-co-L-lactate) (PBSL) as the sheath. The resulting melt-drawn fiber is continuously guided to cold-drawing at 80°C. The core/sheath ratio of the melt-drawn fiber increases with increasing melt-draw ratio at a constant extrusion of the two polymers, because the melt viscosity of PBT is much higher than that of PBSL. The tensile strength of the final drawn fiber increases with increasing melt-draw ratio. The highest strength is obtained at a core/sheath ratio of 65/35. Scanning electron micrographs of the cross-sectioned fibers reveal that the adhesion of both polymers at the interface is strong. The core-sheath fibers are then treated with alkali or a lipase solution for hydrolysis of the PBSL sheath at mild conditions where PBT receives no hydrolysis. The treated fibers, consisting only of PBT, show a very smooth surface. Their tensile strength and orientation are slightly lower than those of the original bicomponent fibers, maintaining a high level of quality as apparel material. These data suggest that conjugate fibers consisting of biodegradable and ordinary polyesters can be used for the environmentally friendly denier reduction treatment of polyester fibers.