A study of fiber extrusion in wet spinning. I. Experimental determination of elongational viscosity

Abstract

AbstractElongational viscosities were measured in a wet‐spinning apparatus. The advantage of this procedure lies in the fact that excellent temperature control can be maintained and that gravity effects can be neglected for a horizontally spun fiber. As a spin dope, an aqueous solution of polyacrylonitrile (PAN) consisting of approximately 10% polymer and 40% sodium thiocyanate (NaSCN) was spun into a coagulating bath of varying NaSCN content, up to a concentration at which spinning was no longer feasible. Fiber diameters were measured photographically as a function of distance from the spinnerette. Spinning tension readings were made on a multifilament bundle using a calibrated tensiometer. To eschew the influence of the hardening effect arising from mass and heat transfer, the temperatures of the spin dope and coagulating bath were kept constant, while the solvent concentration of the coagulating bath was varied up to a maximum limiting value. In this manner, the theoretical condition of no hardening is approached, and the experimentally determined elongational viscosity approaches a limiting, concentration‐independent value. The rheological properties of the spin dope were determined independently in a jet thrust measurement device. Some of the experimentally determined results on elongational viscosity versus rate of elongation were presented and discussed in the light of the theoretical prediction based on various constitutive equations.