GB893440A - Improvements in bleaching processes and compositions - Google Patents

Abstract

Synthetic textile fibres discoloured by use are bleached by treating them with an aqueous solution having a pH of 5-8.5 containing chloride ions in combination with monopersulphate ions, the monopersulphate being present in a concentration giving 20-1,200 parts of active oxygen per million of solution and the gram-ion ratio of chloride ions to monopersulphate ion being 0.5-10 gram-ions of chloride to one gram-ion of monopersulphate ion. The source of chloride ions may be an alkali or alkaline-earth metal chloride and the source of monopersulphate ions may be an alkali or alkaline-earth metal monopersulphate, preferably "oxane", a mixture of KHSO5, KHSO4 and K2SO4 in mole proportions of 2 : 1 : 1. The bleaching solution may also contain alkaline salts, e.g. sodium carbonate, sodium tripoly phosphate, pyrophosphates and other buffer salts, but preferably a mixture comprising, for each part by weight of "oxane", about 0.6-1.2 parts by weight of potassium carbonate and about 0.3-0.6 parts by weight of sodium dihydrogen phosphate, or boric acid, citric acid or Na2H2P2O7 in equivalent amounts, the mixture supplying 0.008-0.016 parts by weight of hydrogen ion. Fluorescent brightening agents, carboxymethyl cellulose alkali metal salts and detergents may also be present. Specified fibres are nylon, polyethylene terephthalate and polyacrylonitrile and mixtures thereof with cotton. Solid bleaching compositions, suitable for bleaching discoloured synthetic fibres, comprising an alkali or alkaline-earth metal monopersulphate, an alkali or alkaline earth metal chloride and a buffer adapted to maintain a pH of 5-8.5 when the composition is dissolved in water to give a concentration of active oxygen of 20-1,200 parts per million, are also described. Specifications 428,142, 428,148 and 893,439 are referred to.