Abstract
PTT (Polytrimethylene terephthalate)/PET (Polyethylene terephthalate) bicomponent filament is a new type of polyester fiber with excellent elasticity and other desirable fiber properties. It is used extensively in woven fabrics, however, when 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.