GB692023A - Process for the continuous manufacture of rayon from viscose and rayon manufactured by such process - Google Patents

Abstract

In the manufacture of rayon, films, &c. by a continuous process in which viscose is extruded from a spinning nozzle or slit into a spinning bath in which partial decomposition of the cellulose xanthate occurs, the further decomposition is carried out in two stages in which (1) the extruded material is treated with an aqueous solution of an inorganic acid and at least one inorganic salt in which the molar ratio of acid to the salt or salts is less than one until the xanthate ratio in the extruded material is less than about 0.02, and (2) after being freed from acid solution containing salt by washing with water the extruded material is treated with an aqueous solution of acid either containing no salt or in which the molar ratio of acid to salt is greater than one until the xanthate ratio in the product has fallen to below 0.003 and preferably to 0.002. The extruded material is then desulphurized and bleached in known manner. The first stage after-treatment bath may contain 0.5-6 per cent by weight of H2SO4 and correspondingly 1-10 per cent Na2SO4 and may be at a temperature of 60-95 DEG C. The second stage after-treatment bath may contain 0.5-6 per cent by weight of H2SO4 and percentages of Na2SO4 to give a H2SO4 : Na2SO4 molar ratio of about 3 : 1, the bath temperature being 60-95 DEG C. and preferably 80-95 DEG C. In the example, viscose is spun into a coagulating bath at 50 DEG C. containing 8 per cent by weight sulphuric acid, 17 per cent sodium sulphate and 2 per cent zinc sulphate. The filaments of freshly coagulated and partially undecomposed cellulose xanthate are drawn as a sheet from the spinning bath into an after treatment bath at 80 DEG C. prepared by diluting the spinning bath until its sulphuric acid content is 4 per cent or less. The threads are then drawn through a bath of water at 50 DEG C. and thereafter through three liquid baths at 80 DEG C. containing 4 per cent by weight sulphuric acid and less than 1 per cent salts. The desulphurization of the threads is then completed and followed by bleaching and oiling in the usual manner. The process increases the speed with which desulphurization and bleaching of the threads or films can be carried out. Specifications 17503/02, [Class 2], 432,692, 467,500 and 570,159 are referred to. The Specification as open to inspection under Sect. 91, refers also to the completion of the decomposition of the residual xanthate in the extruded material by the use of oxidizing agents such as hydrogen peroxide, potassium persulphate, chloric or perchloric acid, sodium chlorite or hypochlorite, and sodium nitrite. Solutions containing 0.5-2 per cent of sodium hypochlorite, to be used at room temperature, or 0.2-1 per cent of sodium chlorite, to be used at 10 DEG C., are preferred. This subject-matter does not appear in the Specification as accepted.