Research On The Elasticity Of PTT/PET Bicomponent Fibier

PTT(Polytrimethylene terephthalate)/PET(Polyethylene terephthalate) side-by-side bicomponent fiber is composed of PTT and PET polymer, this fiber combines PTT and PET property, and exists helical crimp, so it's also called "self-crimping fiber". The structure similar to the spiral coil spring brings the fiber to great extended performance, excellent bulkiness and elastic recovery, which make it a unique elastic fiber.Currently, the researches of PTT/PET composite fiber mainly have focused on the spinning process and the product performance (such as crimp configuration, tensile properties and elastic properties etc.), but there wasn't sufficient research on the relationship between crimp structure and fiber's elastic properties, and the fracture mechanism of PTT/PET fiber. Based on existing research, the elastic elongation and fracture property of PTT/PET fiber were tested, and the relationship between them and spinning process,after processing was analyzed. The fracture morphology of PTT/PET fiber was tested and analyzed, the prediction equation of breaking strength and elastic elongation of PTT/PET fiber were summarized. The conclusion was verified by the spinning practice, which provided reference for PTT/PET filament flexible design. The following were the four main results:1. The tensile properties (including elastic elongation) of PTT/PET bicomponent fibers spun by different spinning process were tested and analyzed, and found that under certain technology condition, with the increase of PTT component content (40%-60%), breaking elongation and elastic elongation of PTT/PET fiber increased, but the breaking strength decreased was not decreased simply. With the increase of hot plate temperature (draft temperature,80-100℃), the breaking elongation and elastic elongation of PTT/PET fiber increased insignificantly, the breaking strength decreased. With the increase of drawing ratio (1.95-2.35), the breaking elongation and elastic elongation increased firstly and then decreased, the breaking strength of B series of PTT/PET fiber decreased, and the breaking strength of K series of PTT/PET fiber increased. With the increase of intrinsic viscosities of PTT component, breaking elongation and elastic elongation of most PTT/PET fiber increased, the breaking strength of PTT/PET (component ratio:50/50) decreased, but the breaking strength of PTT/PET (other component ratio) increased. The breaking elongation and elastic elongation of B series of PTT/PET fiber is better than K series, but the breaking strength is lower than K series of PTT/PET fiber's, B series of PTT/PET fiber K series of PTT/PET fiber was spun by different spinneret.2. The fracture mechanism of PTT/PET fiber was analyzed according to the tensile fracture morphology and single fiber's stress-strain curve, the two components of both B series and K series of PTT/PET fiber is combined closely, the PTT component would be fractured almost simultaneously after the PET component fractured. The simultaneous of fracture of the two components of B series is greater, which makes B series of fiber's breaking strength is lower than K series. B series of fiber's self-elongation (which reflects the elongation of PET components) is lower than K series'. Based on the theory of multi-forces composition, the fractured strength calculation formula was derived for PTT/PET fibers, and the difference was small between the theoretical and measured fractured strengths. The stress-strain curves of PTT/PET filament showed that with the increase of PTT component content, there would be more volatility on the curves, and the self-elongation of PTT/PET fiber is larger, but numbers of the volatility had little effect on breaking strength.3. On the basis of the Denton's theory of bi-component fibers curvature, the elastic modulus of PTT and PET, the fractional differential shrinkage between PTT and PET components, and the structural parameters of PTT/PET fiber's cross-section, the crimp curvature of PTT/PET fiber was estimated. The fitting equation was obtained by the calculation result and the measured elastic elongation. According to the equation and the curvature formula, the fiber elastic properties of PTT/PET fiber can be predicted at the preliminary design stage, which provided reference for development of new fiber.4. Spinneret would decide the cross-sectional shape and the shape of interface of two components of PTT/PET fiber. Custom two special spinneret, and two series of PTT/PET fibers were spun-AB series (B-type) and the AK series (K-type), with the different component ratio (30/70,50/50 and 70/30). By observing the fiber cross-sectional and longitudinal shape, analyzed the relationship between spinneret and fiber structure; the validity of the conclusions above was verified through experiments. The differences between calculated elastic elongation and measured elastic elongation of the two series of PTT/PET fiber was small, and showed the same trends, which could authenticate the validity of the fitting equation of the crimp curvature and the elastic elongation preliminarily.