Thermal runaway of nylon 6–10 during drawing under constant load

Anhydrous nylon 6–10 filaments were cold drawn (by propagation of a preexisting neck) under constant load. The extension rate i, which is proportional to the neck velocity, was observed to be a continuous function of the load up to a certain critical extension rate ic above which i increased discontinuously (“runaway”) by approximately two orders of magnitude. If the filaments is in N2 gas, ic ≃ 0.4 cm/min, whereas if it is in He gas, ic ≃ 1 cm/min. The structure of the drawn filament produced by runaway is an opaque, microvoid structure which, after a suitable change in load, forms first in the center of a filament and spreads toward the surface. This instability is attributed to the heating of the shoulder of the neck during neck motion. An analysis based on the measured activation enthalpy for neck motion and the thermal properties of nylon and the gas is used to predict ic values that are in rough agreement with experiment.