GB720030A - Improvements in and relating to the production of cellulose acetate threads, filaments, fibres and the like - Google Patents

Abstract

Threads and other filamentary products, including films, of cellulose acetate having an acetyl content of 58-62.5 per cent are produced by preparing a solution of the cellulose acetate in aqueous acetic acid by acetylation of cellulose using an acid catalyst, stabilizing the solution, so that it does not gel on standing for many weeks, by heating it in the presence of water, neutralizing the acid catalyst in the solution by the addition of ammonia or an amine or urea, and extruding the resultant solution (which is substantially free from metallic cations) into an aqueous coagulating bath which is also substantially free from metallic cations under such conditions that the acetic acid content of the bath does not exceed 40 per cent by weight and is preferably 10-30 per cent. The cellulose acetate solution may be spun into water or dilute acetic acid, and the concentration of the acid may be allowed to increase until it reaches a figure, e.g. about 25 per cent by weight, suitable for recovery of the acetic acid, e.g. by azeotropic distillation with ethyl acetate. In effecting the acetylation reaction the preferred solvent is acetic acid, but other solvents such as methylene chloride may be used instead of or in addition to acetic acid, provided that they are removed and, if necessary, replaced by acetic acid, before or during the stabilizing step. In an example, 100 parts of wood pulp pretreated with 100 parts of glacial acetic acid are acetylated with 260 parts of 90 per cent acetic anhydride in the presence of a further 500 parts of glacial acetic acid and 3 parts of sulphuric acid at a peak temperature of 45 DEG C., whereafter 40 parts of water, 2 parts of sulphuric acid and 140 parts of acetic acid are added; the solution is stabilized by heating it at 60 DEG C. for 75 minutes, and neutralized by adding 20 parts of triethanolamine dissolved in 100 parts of acetic acid. The solution is filtered and spun into water, and the products are stretched 40 per cent while still wet and collected under tension. In other examples methylene chloride is present during the acetylation step and removed after the neutralization step by distillation, the methylene chloride being replaced by acetic acid to prevent gelling of the solution. The solutions thus prepared are spun into water or aqueous acetic acid kept at 12-14 per cent concentration. Specifications 3973/11, [Class 2 (ii)], 509,702 and 575,661 are referred to.