Self-Crimping Configurations And Properties Of PTT/PET Side-By-Side Bicomponent Fiber

As a new and fiber forming polymer, PTT (Polytrimethylene terephthalate) was successfully industrialized by Shell Chemical Corp. and DuPont Corp. separately. PTT/PET fiber is produced via the conjugated spinning method to make the bicomponent fiber, which has self crimps because the different shrinkage of PTT and PET components. The fiber develops high frequency spatial helical crimp geometries similar to the appearance of a telephone wire. In addition, the PTT component has the "Z" macromolecule chain which gives the fiber low modulus and high elastic recovery. These crimps offer exceptional good stretch and wrinkle recoveries, and bulk to the yarns and fabrics. Although polyurethane based fibers (spandex) can provide comparable elasticity to fabrics, PTT/PET fibers are easier to dye, higher dimensional stability and more resistant to chlorine bleaching, sunshine and high temperature. PTT/PET fiber is very popular in textile industrial circle, and the commercial international brands have Invista's T400, Huvis's ESS and Hyosung's X55. All of the patents of producing the bicomponent fiber were owned by the overseas factories. Although the domestic factories have the similar fiber production, they didn't have their own technological property right to produce this fiber.In this research, we aimed to investigate the configuration and properties of the self-crimpsing of this fiber. We also make analysis on the crimps' mechanical formation of PTT/PET fiber, and the factors affecting on the crimp configuration. Some obtained important parameters which are useful for designing new PTT and PET bicompoent fiber. The method of predicting the stress-strain properties of crimps was also verified. The results gave some experimental suggestions and theory basis to produce the new fibers. The main work and results of this thesis will be presented in the following.Four commercial PTT/PET fibers were selected to investigate the crimp configurations. The two components of fibers were verified by FTIR (Fourier Transform Infrared Spectroscopy) and fiber dyeing experiment. The optical microscope investigation results present that the shapes of the sample PTT/PET fibers have gourd-shaped, round and dumbbell-shaped, the component ratio is 40/60,60/40 and 50/50 accordingly. PTT/PET fibers have different crimps when the environment is changed, the preliminary spun PTT/PET fiber have loose and inconspicuous helical crimps configuration. When the fiber was treated in heat treatment, the crimps became much more compacter. Based on the investigation of crimps configuration, four parameters were selected to indicate the crimp configuration, they are crimp radius, helixes pitch, crimp curvature and axial uniformity. The results of measuring the parameters show that with the increasing of helixes pitch and crimp radius, the crimp curvature will decrease. The cross-sectional shape is the vital factor to acquire higher crimp curvature, the fiber cross section with larger ratio of long and short axis has the advantage to obtain higher crimp curvature. PTT/PET fiber samples don't have higher axial uniformity, and the fiber with gourd-shaped cross-sectional shape has the highest axial uniformity.As a new elastic fiber result from crimp structure, it is necessary to set a standard method to measure the stretch and resilience of PTT/PET fiber. To apply a suitable pretention is the first important parameter needed to confirm. After several exploring experiments, the pretention was confirmed as 0.001±0.0001cN/dtex for measuring the tensile properties of-PTT/PET fiber. The experiment results show the elongation of PTT/PET fibers have two parts including the elongation of crimps and fiber oneself. Especially, the crimp elongation of PTT/PET fiber has the low modulus and higher elongation. The heat treatment has obvious influence on the fiber elongation, the elongation ability of treated fiber could reach as high as 450%～600% and the crimp elongation is 300%-450%. The 6 times stretch experiments results show the elastic recovery of PTT/PET fiber self is between the pure PTT and PET fiber, and the elastic recovery of treated fiber is above 80% when the elongation at 150%. The excellent elasticity of treated fiber comes from the crimp configuration.The crimp mechanism of PTT/PET fiber is same as that of common side-by-side bicomponent fibers. In order to investigate the effects of different factors on crimp structures, some models were built to calculate the second moment of PTT/PET fibers with complex cross-sectional shapes. Based on the Denton's crimp curvature model of bicomponent fiber and measured cross-sectional parameters of PTT/PET fiber, the crimp curvature calculation model of PTT/PET fiber was built.Another model was built in order to analyze the relationship among the parameters of crimp configuration. When the model was used to analyze the crimp configurations of PTT/PET fiber sample, the analytical result shows that the crimp curvature of fiber in the lower possible value, and the crimp radius tend to maximum but the helical pith tend to minimum. The result also indicates that the crimp configuration of PTT/PET have the minimum helical pith which is the diameter of the filament yarn. The minimum helical pith could be got by the cross-sectional area of single fiber and the yarn block coefficient. The ratio between the measured and minimum helical pith is in the range of 1.39～2.The elasticity of PTT/PET fiber is come from the crimp configuration whose stretch property is associated closely with the usability of fiber. The stress-elongation model of crimps could be built by parameters of crimp configuration and geometric distribution of two components. Model I is Holdaway model based on the crimps configuration is helical curve. Applied model I to express the stress-crimp extension of PTT/PET fiber, the results present the classical characterization of crimp configuration elongation, but there is a gap between the measured and model value. The model II which followed the mechanical principle of yarn, the exact stress-crimp extension curve could be obtained by this model with corrected elastic modulus.There are two important unknown factors in the built crimp curvature calculation equation, the elastic modulus ratio and differential shrinkage of PTT and PET components. We found that both of the crystallinity of PTT and PET component are almost the same in the three fiber samples, so the elastic modulus of the same components could be regarded as same in different fiber samples. The average elastic modulus ratio of PTT and PET components is 0.573 which is calculated by the stress-strain curve and cross-sectional area of two components. As soon as the elastic modulus ratio and the crimp curvature calculated by measured crimp radius and helical pitch were known, the differential shrinkage of PTT and PET components could be got in the range of 6.70%～8.57% by solving the equations. It was found that as the elastic modulus ratio increased, the crimp curvature increases rapidly when the m increases from 0 to 0.5, and then approach to a stable value when m is larger than 0.5. The crimp curvature increased continuously as the differential shrinkage increased. After the experimental and theory analysis, the PTT and PET polymer are the best choice to make the bicomponent fiber.When PTT/PET fiber used in knitted fabrics it has a tendency of showing severe random uneven surfaces. The causes of this problem and ways to overcome it were investigated. Fabric surfaces and yarn crimp configurations of several knitted fabrics made with PTT/PET bicomponent filaments were studied by optical microscopy. Attempts to adjust the tensions and yarn speeds during knitting could not eliminate the unevenness entirely, especially when the fabrics were wet-heat treated. From microscopy and heat-treatment studies, the major cause for this unevenness was found to be due to the development of tight crimp configurations, which produced reversal points and changed the helical crimp directions after heat-treatment. They caused light to reflect differently, and the random tight crimps caused fabric to protrude and, therefore, the unevenness. This problem was mitigated by using PTT/PET filaments made by a new yarn manufacturing method, which controlled the development of crimp configurations and prevented the formation of reversal points and helical crimp direction changes.The most important thing for PTT/PET fiber is that it could give the fabric excellent elastic. PTT/PET fiber is usually used as in the fabric with medium elasticity, such as the free elastic suit, fitness skirt, etc. The influences of important structural variables on the elasticity of woven fabrics made of PTT/PET weft filaments by testing 3×11 samples with different weave structures, PTT/PET contents, weft densities and yarn twists. Fabric elasticity is described by two indices, fabric strain and resilience in tensile testing. The experiments results indicate that twill and stain weaves have greater potentials in obtaining high elasticity than a plain weave. Fabric elasticity increases with the increase of the PTT/PET content in the weft yarn, but the change becomes insignificant after the PTT/PET content exceeds 66.7%. Increase in weft density has a negative effect on fabric elasticity, while the weft twist limits crimp formation of PTT/PET filaments and thus undermines the fabrics elasticity noticeably. The built-in helical crimps in the PTT/PET filament result in good yarn elongation and recovery, and therefore can influence the elasticity of fabric. The PTT/PET fiber could not shrink more than the space between adjacent warp filaments during the heat-setting process. Hence, lowering warp density and having adequate finishing temperature and time can help the fabric to gain more elastic potential.