GB867662A - Preservation of rubber latex - Google Patents

Abstract

Natural rubber latex is preserved by adding to it a small amount, e.g. 0,2% to 0,5%, preferably 0,25%, based on the weight of latex, of ammonia or other preserving base, e.g. alkali metal hydroxide or mono-, di-, or tri-alkylamine, and either a small amount, e.g. 0,0025 to 0,2%, preferably 0,02 to 0,1%, based on the weight of latex, of a polyamine polycarboxylic acid which forms a complex with magnesium ions having a stability constant of not greater than 1 X 109, or an alkali metal metal salt of such acid. Preferred acids have a molecular structure in which at least one valency of each nitrogen atom is linked through one or more methylene groups, preferably four such groups, e.g. 1,2 cyclohexylene diamine tetra-acetic acid, diethylene triamine penta-acetic acid, triethylene tetramine hexaacetic acid etc.; polyalkylene ether polyamine polycarboxylic p acids can also be used, e.g. ethylene glycol-bis-beta-amino ethyl ether N, N1-tetra-acetic acid. The acid or salt thereof is added to an ammonia-preserved latex which has been desludged and creamed, e.g. by centrifuging, to a dry rubber content of 60% and which preferably incorporates up to 0,5%, preferably from 0,01 to 0,2%, by weight of the latex, of a water-soluble soap, e.g. ammonium oleate or laurate, together with a similar amount of a precipitant for magnesium, e.g. ammonium fluoride, phosphate, or silicate. The Provisional Specification discloses the further addition to the latex of a bactericide, e.g. boric acid, 2 : 21-dihydroxy-5 : 51-dichloro-diphenylmethane, or an anti-biotic, e.g. sulphanilamide. Specification 708,056 is referred to.