Changes in Molecular Orientation of Nylon-6 Filament Yarns in Cold Drawing Process

The necking phenomena and molecular orientation of nylon-6 filament yarn in an industrial cold drawing process were observed by determining the value of birefringence (Δn) of drawn filament yarn. Further, the relation between the properties of drawn filament yarns and the drawing conditions were considered. The following results are obtained : (1) When the yarn is drawn under the industrial draw ratio 4.0, the value of birefringence (Δn) of the yarn passed through feed rollers becomes maximum at the end of the necking point, close to the feed roller. (2) Then, Δn is in equilibrium where the yarn speed is equal to the drawing roller speed. (3) Further, Δn becomes smaller between the drawing roller and the winding bobbin. (4) When yarn is wound under any tension, Δn becomes greater with the lapse of time and reaches to the constant value. (5) Δn increase asymptotically with the lapse of time when the yarn is drawn under the draw ratio 3.0, but Δn is approximately constant under the draw ratio 3.5, 3.6 and 4.0. The values of Δn of filament yarns drawn at the high drawing temperature are greater than those of yarns drawn at the low drawing temperature. (6) Variations of Δn under different drawing condition, e.g., draw ratio, humidity in a drawing chamber, etc., are also observed. (7) The determination of yarn properties under different drawing condition shows that the orientation behaviour in drawing process is related to the yarn properties. (8) The drawing tension, molecular orientation and crystalization under different draw ratio are determined and their behaviours are also analysed. (9) An attempt is successfully made to estimate the winding tension on a draw-twisting bobbin by determining Δn of the wound filament yarn.