Patent GB-576909-A (GB)
Title: Improvements in the bleaching of organic materials
IPC: D06L4/70
Filed: 1944-01-31
Abstract: Organic materials other than cellulose, including artificial fibres, e.g. acetate rayon and nylon; bath sponges; walnut shells; synthetic resins, are bleached by subjection to the simultaneous action of a chlorite and a persulphate in aqueous solution maintained at pH not less than 7, alkali and alkaline earth chlorites, e.g. sodium or calcium chlorite being preferred. Effective persulphates include the salts of alkali and alkaline earth metals, especially sodium and potassium persulphates. Temperature, concentration and the ratio of chlorite to persulphate are variable over a wide range and the latter is materially reduced by employing, as adjuvants, alkali metal buffer salts, e.g. monosodium or disodium orthophosphates.  Bleaching may be effected by admixing the material with the persulphate in presence of water and subsequently adding the chlorite, maintaining the resultant mixture at a temperature ranging from room temperature to approximately 100 DEG  C. for an appropriate period and thereafter cooling and separating.  In examples: (1) acetate rayon fabric is improved in brightness by immersion for 2 hours in an aqueous solution at 40 DEG  C. and approximate pH 8 containing sodium chlorite and sodium persulphate; (2) sponge is bleached by immersion for 1 hour in an aqueous solution containing sodium chlorite and sodium persulphate at 50 DEG  C. and pH 8.ALSO:Organic materials other than cellulose, including carbohydrates, e.g. starch, are bleached by subjection to the simultaneous action of a chlorite and a persulphate in aqueous solution maintained at pH not less than 7, alkali and alkaline earth chlorites, e.g. sodium or calcium chlorite being preferred. Effective persulphates include the salts of alkali and alkaline earth metals, especially sodium and potassium persulphates. Temperature, concentration and the ratio of chlorite to persulphate are variable over a wide range and the latter is materially reduced by employing, as adjuvants, alkali metal buffer salts, e.g. monosodium or disodium orthophosphates.  Bleaching may be effected by admixing the material with the persulphate in presence of water and subsequently adding the chlorite, maintaining the resultant mixture at a temperature ranging from room temperature to approximately 100 DEG  C. for an appropriate period and thereafter cooling and separating.  In an example, crude corn starch, suspended in water, is bleached for 1 hour at 50 DEG  C. and pH 8, by treatment with an aqueous solution containing sodium chlorite and sodium persulphate.ALSO:Organic materials other than cellulose, including carbohydrates, e.g., sugar, are bleached by subjection to the simultaneous action of a chlorite and a persulphate in aqueous solution maintained at pH not less than 7, alkali and alkaline earth chlorites, e.g., sodium or calcium chlorite being preferred. Effective persulphates include the salts of alkali and alkaline earth metals, especially sodium and potassium persulphates. Temperature, concentration and the ratio of chlorite to persulphate are variable over a wide range and the latter is materially reduced by employing, as adjuvants, alkali metal buffers salts, e.g., monosodium or disodium orthophosphates. Bleaching may be effected by (a) admixing the materials, either molten or in aqueous solution, with a chlorite in presence of water and adding the persulphate thereafter, or (b) admixing the material with the persulphate in presence of water and subsequently adding the chlorite, maintaining the resultant mixture at a temperature ranging from room temperature to approximately 100 DEG  C. for an appropriate period and thereafter cooling and separating.  In an example brown sugar in aqueous solution is treated for 1 hour at 40 DEG  C. with an aqueous solution buffered at pH 8 and containing sodium chlorite and sodium persulphate, yielding a substantially colourless solution at pH 6.85.