5—THE TORQUE IN HIGHLY TWISTED NYLON 6 MONOFILAMENTS

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Abstract
Theoretical considerations have lead to the following formula for the torque M in highly twisted monofilaments with a circular cross-section: where d = the filament diameter; ρ/d = the relative radial distance from the axis; τ[ρ/d] = the shear stress at ρ/d from the axis. With this formula it appears to he possible to compare the torques in highly twisted filaments which have been subjected to different treatments before twisting, in such a way that the influence of the resulting differences in diameter can be separated from the effects of the differences in molecular structure. The infiuence of the differences in diameter can be eliminated by changing over from the observed torque M to the “reduced torque” M 1 (= M/d 3, d = filament diameter), i.e., the torque which would exist in the filament under geometrically similar conditions if this filament had a diameter of unit length. Experiments were made on nylon 6 monofilaments in order to investigate the effect of processes, such as drawing and heat-setting under various conditions of time, temperature and tension, on the “reduced torque” and its torsional relaxation. The value of the reduced torque increases with the drawing of the monofilament. This applies to a smaller extent to the set filaments. In this case, a maximum reduced torque occurred in filaments set under rather different conditions as regards time and tension, provided that the filaments have a birefringence of at least 0·054. The reduced torque of filaments increases as the setting temperature is raised. The various filaments show only small differences in torsional relaxation.

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