GB652745A - Improvements relating to the saponification of filamentary material of an organic ester of cellulose - Google Patents

Abstract

Filamentary materials of organic acid esters of cellulose, having a tenacity of at least 2 grams per denier, are saponified in the form of a hollow cake enclosed in a fabric sock which passes through the hollow centre of the cake in contact with its inner surface. The ends of the sock are turned back towards each other so as to cover the ends and outer surface of the cake and to provide an overlap on said surface. The sock may be a circular knitted tube of cotton or a treated paper tube. The yarn is preferably twist-wound on to a mandrel covered with the fabric sock to form a cake (see Group IX), the ends of the sock being then turned back so as to enclose the finished cake, which is then removed from the mandrel. Alternatively the yarn may be wound into cake form and the mandrel removed prior to the insertion of the sock through the hollow centre of the cake. The yarn may be dry-spun or wet-spun and may be of cellulose acetate, cellulose propionate, cellulose butyrate or mixed esters of cellulose such as acetate-propionate or acetate-butyrate. They may have been stretched after their formation and while in a softened condition, e.g. in the presence of steam or hot water, by from 100 to 500 or 1000 per cent of their original length. Alternatively the yarns may have been stretched in the course of their formation by a wet-spinning process to obtain a tenacity of 2 grams per denier or more. Saponification of the yarn may be effected by placing the yarn cake covered with the sock in a rotating perforated spinning bucket and introducing the saponifying medium in the centre of the cake in the spinning bucket so that it is centrifugally distributed throughout the cake. The regenerated cellulose yarn thereby produced may be washed free of saponifying agent while still in the spinning bucket and in cake form. The saponifying agent may be an aqueous, alcoholic or aqueous/alcoholic solution of a basic agent such as caustic soda, caustic potash, methylamine, ethylene diamine or triethanolamine. The saponifying solution may also contain about 6-10 per cent by weight of sodium acetate. During saponification the yarn cake may be subjected to endwise pressure tending to cause axial contraction of the cake as the yarn shrinks. In the example a cellulose acetate yarn stretched to ten times its original length, wound in the form of a cake and covered with a fabric sock is placed in the spinning bucket of a centrifuge and a heavy annular plate is placed on the cake. A hot aqueous solution of caustic soda is fed to the rotating bucket and the saponified cake is then washed with hot water and dried. Data are given for the dry and wet tenacity and elongation of the finished yarn.