Process for spinning polyacrylonitrile filament having low degree of crimp and high cimp reversibility

944,424. Crimped composite artificial filaments. E. I. DU PONT DE NEMOURS & CO. Feb. 15, 1960 [Feb. 16, 1959], No. 5319/60. Heading B5B. Dry spun composite filaments comprising at least two linear fibre-forming synthetic polymers of differing shrinkage potentials so distributed in the filaments that each filament has at all points along its length two or more distinct components comprising respectively the said different polymers arranged contiguously and bonded together in a side-by-side structure in which the outer surface of each component forms part of the surface of the composite filament, having 10 to 18 helical crimps per inch of extended length and an equilibrium crimp reversibility of 25 to 50% may be produced by dry spinning solutions of the component polymers simultaneously through separate but contiguous sectors of single orifices under conditions of high gas and cell temperatures, high gas flow rate and low spinning speed such that the residual solvent content of the as-spun composite fibre is less than the amount indicated by curve 1 of Fig. 8 of the drawings. The points of extrusion of the spinning solutions are preferably positioned so that the component of lower shrinkage potential faces the centre of the spinning cell and that of higher shrinkage potential faces the periphery of the cell. Preferably, also the spinning solution of the component of lower shrinkage potential is less concentrated than that of the other component. The component of " lower shrinkage potential " is that which, if in the form of a homogeneous filament, would shrink less under the action of hot water. In Fig. 8 curve 1 shows the maximum permissible residual solvent content and curve 2 shows the preferred residual solvent content, both as a function of filament denier. The equilibrium crimp reversibility is determined as follows: A single filament is separated from a tow of drawn, unrelaxed filaments and a three-inch length of the filament is attached to opposite sides of a rectangular wire frame with 30% slack between the ends. The frame and filament are then immersed in boiling water for 15 minutes to develop the crimp. The crimped filament is then transferred to a viewing holder so that about 10% slack is present and the filament length between the clamped ends is about 2.5 inches. The filament is dried by storing it and the holder for 18 to 24 hours at 70‹ C. in a stoppered test tube containing a desiccant and the tube is allowed to cool to 25‹ C. and the total