Periodic Micro-necking of Polyester Filament

Abstract

Periodic necking of micrometer order were generated in polyethylene terephthalate filaments by the crazing method which used tensile stress together with bending stress. PET filament passed to a bending point at a sharp blade (processing edge) under the constant tension. Cycles of the stress concentration and the relaxation were occurred at a pointed end of the processing edge, automatically. The morphology of periodic necking areas depended on the processing angle of bend at the point of the processing edge and the processing stress. Necked PET filament consisted of the necking length of 39-72 μm and the standard deviation of 2.8-6.9 μm for the processing stress of 27-32 MPa and the processing angle of 120 deg. Ratio of generated necking length per non-necking length was 0.2-1.8 (Processing angle: 136 deg.). Although PET filaments of the draw ratio 1.0 and 2.5 formed the periodic necking, those of the draw ratio 4.8 were drawn without the periodic necking. Almost conventional functional fibers were characteristic fibers in a cross sectional shape except thick and thin yarn, however, these periodic micro-necking PET fibers have specific shape in a fiber axis direction.