Improvements in and relating to the production of regenerated cellulose filaments

Regenerated cellulose filaments capable of developing a crimp upon subsequent relaxation in an aqueous liquid are produced by extruding viscose into an aqueous acid coagulating and regenerating bath containing sulphuric acid and at least 16% of sodium and zinc sulphates, and conducting the filaments through the bath for a length of time approximately equal to that throughout which the liquid absorbed by the filaments remains alkaline or neutral, after which excess liquid is stripped from the filaments emerging from the bath and the filaments then pass through an aqueous acid regenerating bath in which or after which they are highly stretched. The neutral point is determined by carrying out a preliminary experiment in which bromcresol purple indicator is added to the viscose, the point at which the filaments change in colour from purple to yellow is observed, and the path length corresponding to this neutral point is measured. No indicator is used in the commercial production of filaments according to the invention. The first bath preferably contains at least 20% of sodium sulphate while the regenerating bath preferably contains less than 12% of acid and less than 16% of total salts. The bath in which the filaments are subsequently relaxed to impart to them a permanent crimp may be water or aqueous dilute acid or alkali. The degree of stretching is preferably at least 35%. The filaments may be cut into staple before or after the relaxing step. In an example, in which the path length corresponding to the neutral point is determined in a preliminary experiment as described above, and in which this path length is not exceeded, viscose is spun into an aqueous coagulating and regenerating bath at a temperature of 50 DEG C. containing 9.5% of sulphuric acid, 24% of sodium sulphate and 0.8% of zinc sulphate. The filaments are then conducted from the bath over a guide to strip off excess liquid and through an aqueous regenerating bath containing 5% of sulphuric acid, 6% of sodium sulphate and a very small percentage of zinc sulphate. The filaments are stretched 50% after removal from the regenerating bath and allowed to relax in a water bath.