GB402106A - Improvements in processes for the de-esterification of filaments, yarns, fabrics andthe like of cellulose esters - Google Patents

Abstract

Filaments, yarns, fabrics, and the like, of organic esters of cellulose, are subjected to saponification by means of a medium comprising caustic soda, caustic potash, or other alkaline compound of an alkali metal, e.g. sodium silicate or trisodium phosphate, in quantity less than that necessary to effect the desired degree of saponification, and in presence of an auxiliary agent which is not a compound of an alkali metal, and is alkaline in character though less alkaline than the saponifying agent proper, or is capable of reacting with sodium or potassium acetate or other salt formed by the saponification of the cellulose ester to re-form the saponifying agent. Examples of such auxiliary agents are lime, baryta, strontia, or the corresponding hydroxides or basic salts. Such a reagent is present as a saturated solution or in the form of a fine suspension. The saponifying agent may be applied to the goods by bath or padding treatments, by spraying or printing methods, followed by batching the goods, or passing them over heated rollers. The filaments and yarns may be saponified while they are in warp formation, using, for example, the process of Specification 313,404, [Class 2(ii), Cellulose &c.] In order to render the saponification more uniform, there may be present in the saponifying media, buffer salts, e.g., sodium chloride, sodium acetate, or soaps, or substances such as glycerine. The degree of saponification varies from 2 per cent up to substantially complete elimination of the ester groups, according to whether the object is to confer upon the materials an affinity for cotton dyestuffs, increase the safe ironing point, or to produce a reconstituted cellulose yarn. The saponification process may be applied to textile materials containing cellulose esters of high viscosity characteristics, for example, up to 200 or more in the case of cellulose acetate, measured by comparing the viscosity of a 6 per cent acetone solution against a standard of glycerine taken as 100. Furthermore, the materials may be stretched, before, during, or after saponification, with a view to obtaining products of high tenacity, for example by the process of Specification 277,089, 323,790, [both in Class 2 (ii), Cellulose &c.], 370,430, or 371,461. The stretching may take place continuously with the production of the filaments as is described in Specifications 340,324, 340,325, 340,326, 340,436, 340,437, 343,062, and 378,858. In order to improve the extention of the filaments, they may be subjected to treatment with shrinking agents as in the processes of Specifications 380,504, 380,505, and 389,823. In examples, dry-spun cellulose acetate yarns which may have been stretched to 400 to 500 per cent of their original lengths are saponified in aqueous baths containing caustic soda and lime in various concentrations. In a further example, similar yarns, are saponified in an aqueous-alcoholic bath containing caustic soda and lime. Specifications 343,063 and 402,105 also are referred to.