Patent GB-571954-A (GB)
Title: Improvements in or relating to the production of artificial textile materials, foilsand the like
IPC: D01F2/28
Filed: 1943-11-23
Abstract: An organic acid ester of cellulose of high viscosity characteristics is treated to separate the more hydrophile fractions from the less hydrophile fractions; the less hydrophile fractions are converted into artificial filaments, foils, or similar articles, and these articles are subjected to stretching after they have been brought into a softened condition by treatment with a gaseous or liquid softening agent.  The filaments, foils, or other articles may be subjected to saponification.  Removal of the more hydrophile fractions of the cellulose ester may be effected by fractional precipitation, or fractional extraction methods.  A mixture of solvent and non-solvent may be incorporated with a solution of the cellulose ester to cause precipitation of only a part of the ester, or the solid cellulose ester may be treated with a mixture of solvent and non-solvent in such proportions that either the more hydrophile or the less hydrophile constituents are dissolved.  Fractional precipitation may be effected when the cellulose ester is precipitated from an esterification solution.  The amount of water used for precipitation of cellulose acetate from its solution in acetic acid may be such that after the fractional precipitation the liquid medium contains 45 or 50 grams of acetic acid per 100 millilitres of solution.  A batch of cellulose acetate with a viscosity value of 60-90 may be stirred up with an aqueous solution of acetone containing 45-55 per cent of acetone by weight and the undissolved fraction is separated from the liquor. Instead of using water as the non-solvent, there may be used methyl, ethyl, or other alcohol.  Mixtures of alcohol and water may be used for the extraction.  The esters produced by removal of the more hydrophile constituents are substantially free from fractions having viscosities below 5 or 10.  The filaments or films may be produced from the cellulose esters by dry or wet spinning operations.  Cellulose acetate of a viscosity of 85, which has been extracted with 55 per cent aqueous acetone, may be employed.  Satisfactory filaments may be obtained even when using solutions containing less than 20 per cent of cellulose ester. The evaporative medium may be at atmospheric or higher temperature.  Stretching may be effected while the filaments are passing through wet steam, hot water, or an aqueous solution of dioxane.  Products of high tenacity are obtained.  Saponification may be effected by means of organic or inorganic bases, and it may be continued until regenerated cellulose products are obtained. High viscosity cellulose esters may be obtained by known methods, e.g. carrying out esterification in presence of a high proportion of acetic acid or other organic solvent for the cellulose ester, or using only a small amount of sulphuric acid as catalyst, or using a small amount of zinc chloride and hydrochloric acid as catalyst. Cellulose acetate which is soluble in acetone is regarded as of high viscosity if it has a viscosity of at least 40, i.e. if it yields a 6 per cent solution in acetone having a time of flow at least 40 per cent of that of pure glycerine measured under the same conditions; other esters and acetone-insoluble acetates are considered to be of high viscosity if, on complete saponification by a non-degrading method, e.g. by using an alcoholic solution of alkali containing only 1 or 2 per cent of the theoretical quantity of alkali necessary, a dilute cuprammonium solution of the regenerated cellulose obtained has a viscosity at least equal to that of a similar solution prepared from regenerated cellulose obtained by saponifying acetone - soluble cellulose acetate of viscosity 40.  Specifications 207,562, [Class 2 (ii)], 438,584, 438,585, 438,586, 438,587, 438,655, 438,656, 443,707, 443,773, 488,794 and 557,004 are referred to.