Improvements relating to the production of regenerated cellulose filaments

Regenerated cellulose filaments are made by extruding viscose having a cellulose content of 4-6% and a caustic soda content approximately half that of the cellulose, the cellulose having an average degree of polymerization of at least 300 and the viscose having a salt figure of at least 10 and a ball-fall viscosity of 50-200secs., into a coagulating bath at 20 DEG -30 DEG C. containing 2,0-3,5% by weight sulphuric acid, less than 15% by weight anhydrous sodium sulphate and not more than 0,02% by weight anhydrous zinc sulphate as an impurity, limiting the length of the immersion path so that the filaments may be stretched by at least 80% of their original length on emerging from the bath, stretching the filaments by at least 80% in air immediately after they have emerged from the bath and subsequently completing the regeneration of the filaments. Preferably the salt figure of the viscose is at least 13 and the ball-fall viscosity 100-200, the coagulating bath containing 1-10% anhydrous sodium sulphate. Filaments having deniers up to 4,5 may be made using an immersion path of not more than 6 inches, and filaments having deniers up to 3 using an immersion path of not more than 3 inches. Regeneration may be effected in a warm dilute (e.g. 2% by weight) sulphuric acid bath at 60 DEG C. Filaments so made show a high ratio of wet-to-dry tenacity, low extensibility, no skin-core differentiation and low water imbibition.