Rubber compositions

Natural rubber, a polystyrene type resin and an organic peroxide are intimately mixed and heated, e.g. on a mill, to a temperature sufficient for the peroxide to form free radicals to form a composition suitable for the reinforcement of natural rubber. Styrene, vinyl toluene, methyl and ethyl nuclear substituted styrenes and a -methyl styrene polymers and copolymers may be used and peroxides mentioned are benzoyl peroxide, cumene and t-butyl hydroperoxides and t-butyl perbenzoate. The composition may be used for shoe soles, floors, mouldings and extrusions. In an example, a blend with rubber, zinc oxide, sulphur, stearic acid and cyclohexylbenzthiazyl sulphenamide is vulcanized.ALSO:A homogeneous composition adapted for the reinforcement of natural rubber, is prepared by mixing and heating a mixture comprising natural rubber, polystyrene-type resin, and an organic peroxide to a temperature sufficient for the peroxide to break down with the formation of free radicals whereby the rubber becomes chemically linked with the polystyrene-type resin, which consists of a polymer or copolymer of styrene or a derivative obtained by substituting a hydrogen atom thereof with an alkyl group, e.g. nuclear methyl or ethyl substituted styrenes, or a -methyl styrene. The organic peroxide may consist of cumene hydroperoxide, benzoyl peroxide, tertiary butyl perbenzoate, or tertiary butyl hydroperoxide. The mixture may comprise 1 part by weight of natural rubber per 1 to 3 parts polystyrene-type resin, and 1 to 20 parts organic peroxide per 100 parts rubber, and is preferably heated for 5 to 30 minutes at 130 DEG to 160 DEG C. In one example 200 parts by weight polystyrene powder mixed with 10 parts tertiary butyl perbenzoate are milled into 100 parts pale crepe rubber at 150 DEG C. Amounts of 20, 30, and 40 parts by weight of the reaction product are milled into 80, 70, and 60 parts, respectively, of pale crepe, and vulcanizing and other ingredients, and the resultant mixes vulcanized. In a further example polyvinyl toluene is used as the polystyrene type resin.