Polyacrylonitrile fibers having a natural crimp and process for producing the same

Abstract

A naturally crimped polyacrylonitrile fiber having an asymmetrical cross section, the cross section having at least two large oblong lobes, the angle between at least two of these lobes being less than 90.degree., the fiber having an outer structure which has a relatively high density and has a variable thickness, this outer structure enclosing an inner structure which is porous and less dense than the outer structure. The process for producing crimped polyacrylonitrile fibers comprises spinning a solution of a polyacrylonitrile polymer into a cold bath at a temperature of less than 30.degree.C., this cold bath having low coagulation power for the polyacrylonitrile polymer and comprising 1,1,1-trichloroethane or mixtures of 1,1,1-trichloroethane with less than 25 percent of a solvent for the polyacrylonitrile, exposing the polyacrylonitrile to the cold bath for an exposure time of less than two minutes; drawing the partially coagulated filaments in a hot spinning bath at a draw ratio of greater than 200 percent, the spinning bath having a temperature between 60.degree.C. and a boiling point of the spinning bath, the composition of the spinning bath comprising either water or water mixed with up to 75 percent solvent for the polyacrylonitrile. The fibers are then washed followed by heat treating the fibers in a free state, without tension, so as to allow the same to naturally crimp.

Dependencies are inferred from the claim text.