Improvements in or relating to the manufacture of regenerated cellulose sheets, films, filaments, threads and the like produced from viscose

摘要

In the manufacture of regenerated cellulose sheets, films, threads, filaments and the like by the viscose process, the freshly-formed materials are treated, subsequent to desulphurising treatment and prior to a bleaching treatment, with a hot dilute aqueous solution containing a non-oxidising mineral acid, in a proportion of between 0.05 per cent and 1.0 per cent by weight, based on the weight of the solution, the sulphide sulphur content of the finished materials being thereby substantially eliminated. The preferred non-oxidising acid is sulphuric acid, but other mineral acids, e.g. hydrochloric or phosphoric acids, may be employed. The dilute aqueous solution of the acid is employed at a temperature of 80-100 DEG C. The preferred desulphurising agent is sodium sulphide in aqueous solution, the temperature of which is preferably 90 DEG C., but other known agents such as the sulphides of potassium, ammonium, or an alkaline earth metal or the sulphites or thiosulphates of sodium or potassium may also be used. For bleaching, a dilute aqueous solution of sodium hypochlorite is preferred although dilute aqueous solutions of other alkali metal or alkaline earth metal hypochlorites, or aqueous solutions of hydrogen peroxide, alkali metal perborates, percarbonates or chlorites may be employed. Examples are given, in one of which a regenerated cellulose film cast from viscose is washed with water, passed through a desulphurising bath comprising an aqueous solution of sodium sulphide at a temperature of 90 DEG C., washed with a counterflow of water at 90 DEG C., and passed through a 0.2 per cent aqueous solution of sulphuric acid at a temperature of 90 DEG C. The film is removed, washed with water at 35 DEG C., bleached by passage through an aqueous sodium hypochlorite solution, washed, impregnated with glycerine and dried.