GB864798A - Bleaching processes and compositions - Google Patents

Abstract

A free-flowing solid bleaching composition comprises an inorganic persalt and, as particles separate from the persalt, a solid reactive organic ester of an aliphatic carboxylic acid which, when tested as described below, has a titre of at least 1,5 ml. 0,1 N sodium thiosulphate, the size of the ester particles being such that at least 70% of the ester is retained on a 60 mesh British Standard sieve. The test is carried out by adding the ester to 1,000 ml. of a solution containing 2,5 gm. sodium pyrophosphate, 0,615 gm. sodium perborate and 0,5 gm. sodium dodecyl benzene sulphonate at 60 DEG C., in an amount such that, for each atom of available oxygen present, one molecule of ester is introduced; after 5 minutes, a 100 ml. portion of the solution is withdrawn and pipetted on to a mixture of 250 gm. cracked ice and 15 ml. glacial acetic acid, 0,4 gm. potassium iodide is added and the liberated iodine is titrated with 0,1 N sodium thiosulphate, using starch as indicator. The ester is preferably one derived from an aliphatic acid having not more than 10 carbon atoms, e.g. acetic, propionic, butyric, caproic or caprylic acid, and is preferably an acylated phenol, e.g. sodium or potassium p-acetoxybenzene sulphonate. The ester, which preferably has a solubility in water at pH 10 of more than 0,1%, may consist of amorphous particles which have been precipitated from solution, e.g. during the formation of the ester, of crystals obtained by crystallization of the ester or of particles formed by agglomeration of the powdered ester, in which case a dispersing agent is preferably incorporated to assist dispersion when the bleaching composition is added to water for use. The bleaching composition preferably contains from 1/4 to 4 molecules of reactive ester to each atom of available oxygen in the persalt present. Suitable persalts are alkali metal perborates, percarbonates, perpyrophosphates and persilicates. The composition may also contain water-soluble binding agents, e.g. gelatin or starch, organic detergents which may be either soaps or soapless detergents, e.g. alkyl aryl sulphonates or alkyl sulphates, conventional detergent adjuncts, e.g. alkali-metal sulphates, sodium carboxymethyl cellulose and fluorescent brightening agents, and alkaline substances such as alkali-metal carbonates, orthophosphates, water-soluble condensed phosphates, e.g. tripolyphates or pyrophosphates, and silicates to give a pH of 9-11 when dissolved at a suitable concentration for bleaching. Detergent bleaching compositions preferably contain 10-50% by weight of organic detergent, 2-30% of ester and 1-15% of persalt. The compositions may be used to bleach cotton fabrics by dispersing them in water heated to 50 DEG -60 DEG C. in an amount to give a persalt concentration equivalent to from 0,001 to 0,1% available oxygen by weight of the liquor.ALSO:A free-flowing solid detergent bleaching composition comprises an inorganic persalt and, as particles separate from the persalt, a solid reactive organic ester of an aliphatic carboxylic acid which when tested as described below, has a titre of at least 1.5 ml. 0.1 N sodium thiosulphate, the size of the ester particles being such that at least 70% of the ester is retained on a 60 mesh British Standard seive. The detergent may be a soap or a soapless detergent, e.g. an alkyl aryl sulphonate or alkyl sulphate, and the composition may contain conventional detergent adjuncts, e.g. alkali metal sulphates, sodium carboxy methyl cellulose and fluorescent brightening agents. The test to which the ester must conform is carried out by adding the ester to 1,000 mls. of a solution containing 2.5 gm. sodium pyrophosphate, 0.615 gm. sodium perborate and 0.5 gm. sodium dodecyl benzene sulphonate at 60 DEG C., in an amount such that, for each atom of available oxygen present, one molecule of ester is introduced; after 5 minutes, a 100 ml. portion of the solution is withdrawn and pipetted on to a mixture of 250 gm. cracked ice and 15 ml. glacial acetic acid, 0.4 gm. potassium iodide is added and the liberated iodine is titrated with 0.1 N sodium thiosulphate, using starch as indicator. The ester is preferably one derived from an aliphatic acid having not more than 10 carbon atoms, e.g. acetic propionic, butyric, caproic or caprylic acid, and is preferably an acylated phenol, e.g. sodium or potassium p-acetoxy benzene sulphonate. The ester, which preferably has a solubility in water at pH 10 of more than 0.1% may consist of amorphous particles which have been precipitated from solution, e.g. during the formation of the ester, of crystals obtained by crystallisation of the ester or of particles formed by agglomeration of the powdered ester, in which case a dispersing agent is preferably incorporated to assist dispersion when the composition is added to water for use. The composition preferably contains from 1/4 to 4 molecules of reactive ester to each atom of available oxygen in the persalt present. Suitable persalts are alkali metal perborates, percarbonates, perpyrophosphates and persilicates. The composition may also contain water-soluble binding agents, e.g. gelatin or starch, and alkaline substances such as alkali metal carbonates, ortho-phosphates, water-soluble condensed phosphates, e.g. tripolyphosphates or pyrophosphates, and silicates to give a pH of 9-11 when dissolved at a suitable concentration for bleaching. The composition preferably contains 10-50% by weight of organic detergent, 2-30% of ester and 1-15% of persalt, the remainder being detergent adjuncts.