GB389803A - Improved process for refining vegetable fibrous material - Google Patents

Abstract

In refining or bleaching vegetable fibrous materials by treatment with a solution of hypochlorous acid or its salts, the hydrogen ion concentration of the solution is maintained within the limits pH 4,5 to 8, preferably by the addition of one or more buffers. The treatment may be preceded or followed by alkaline treatment. According to the examples, (1) a bleaching solution is prepared by treating bleaching powder ("calcium chloride") solution with soda solution, and is brought to pH 6,6 by addition of sulphuric acid and a buffer solution comprising monopotassium and disodium phosphates; beech-wood sawdust is left in the solution at atmospheric or slightly raised temperature, yielding a white product free from lignin; (2) sodium hypochlorite ("sodium chloride") solution is brought to pH 5,6 by treatment with sulphuric acid and a phosphate buffer solution; the solution may be used to bleach soda cellulose, sulphite cellulose, or cotton, and if the bleached material is subjected to alkaline treatment, a refined cellulose suitable for artificial silk manufacture is obtained; (3) flax yarn is treated with dilute soda solution at 90-100 DEG C., washed, and bleached in a hypochlorite solution ("chlorine lye") brought to pH 6,8 by addition of a phosphate buffer; the material is then boiled with dilute soda solution, treated again with the bleaching solution, washed, treated with a dechlorinating agent, washed and dried; (4) cotton fabric is bleached and after-treated as in example 3.