Abstract
The change in fine structure of polyethylene terephthalate (PET) yarns textured by the false-twisting process was studied. To simulate a false-twisting textured yarn of multi-filament yarns, the three-filament yarns of PET were used instead of the single monofilament yarns whose behavior wasCdiscussed in the Part 1.
In the twisting and heat setting stages, the degree of orientation of the molecular chain in the crystalline region de creases with increasing the number of twists accompanying the increase in the inclination of a filament itself and fibrils. Especially it was noted that the lamellar crystals were tilted in the region of more than 138 tpm and that the folded plane which is the interface between the crystalline and amorphous regions is normal to the fiber axis. The crystallinity, the crystallite size and the lattice distortion within the crystallites were scarcely changed.
In the untwisting stage, the direction of filaments and fibrils almost recovers accompanying the recovery of crystal orientation. However, the tilt of lamellae within the fibrils is preserved so that the interface becomes inclined away from the plane normal to the fiber axis. The crystal lattice distortion increases with an increase in the number of twists.
