AbstractA study of 11 variables of a modacrylic‐fiber wet‐spinning process has shown that the tenacity and stiffness modulus of the fiber depend primarily on the amount of stretch imparted during spinning and the solvent content of the tow at the time of stretching. The solvent content governs the degree of plasticity of the fiber during stretching and hence the degree of orientation achieved at a given stretch ratio. The solvent content, in turn, is determined primarily by the specific surface (fiber area per unit volume) through which solvent diffuses out of the fiber into the coagulating bath. As a result, the tenacity and stiffness modulus are invesely related to the denier per filament in the coagulating bath prior to stretching. The denier of the filament in the coagulating bath is determined by the concentration of fiber resin in the spinning solution, the volume of solution extruded per unit time, the velocity with which the fiber is withdrawn from the coagulating bath, and the number of holes in the spinnerette. These fundamental variables, along with stretch, determine the tenacity and stiffness of the spun fiber. The only other variable studied that affected the fiber physical properties was the drying temperature. Increasing the temperature slightly reduces both fiber tenacity and elongation. Variables having no influence on the mechanical properties over the range studied include length, temperature, and solvent concentration of the coagulating bath, residence time of the filaments in the coagulating bath, relaxation applied after stretching, and shear rate at which the spinning solution is extruded through the spinnerette orifi
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