Fiber Structure Development and Crimp Formation in Bicomponent Fibers Prepared from Post-Consumer Poly (ethylene terephthalate) Bottles

Abstract

Side-by-side bicomponent fibers consisting of poly (ethylene terephthalate) (PET) with different molecular weights, i. e. high molecular weight virgin PET and low molecular weight PET recycled from post consumer bottles were prepared by melt spinning, continuous drawing, and postdrawing heat treatment processes. The effects of process conditions on the higher-order structure and crimp formation of resultant fibers were investigated. The structure of each component in the bicomponent fibers was evaluated through an analysis of birefringence and Lorentz density, which are based on refractive index measurements using an interference microscope. Distinct crimp formation was observed for the high-speed spun fibers prepared at take-up velocities higher than 5km/min. In comparison with the respective single component fibers, the birefringence of the high molecular weight component increased and that of the low molecular weight component decreased. Accordingly, there was a significant birefringence difference between the two components in the high-speed spun bicomponent fibers with severe crimp formation. Intensive crimp formation was also observed for fibers prepared by drawing the melt spun fibers at relatively low take-up velocities to a draw ratio close to their respective limits. In these drawn fibers, the birefringences of both components were high and the birefringence difference between the two components was small in comparison with the high-speed spun fibers. For fibers drawn at various drawing temperatures, a smaller radius of curvature in the crimps was observed for fibers with a larger birefringence difference between the two components. When a combination of polymers with smaller molecular weight difference was used, a similar degree of crimp was observed for bicomponent fibers with the smaller birefringence difference. In other words, there is no universal relationship between the birefringence difference between the two components and the radius of curvature, and the relation varies depending on the combination of polymers used for the preparation of fibers. High temperature heat treatment of fibers drawn at low drawing temperatures was found to be a most effective method for the preparation of crimped fibers with small radii of curvature. In these fibers, surprisingly, the radius of curvature decreased with decreasing birefringence difference between the two components.