GB723897A - Novel rubber compositions - Google Patents

Abstract

A synthetic rubber is reinforced by adding a reaction product of lignin, or sulphonated lignin, and a methylene donor and dispersing a polymeric compound therein. Rubbers specified are polybutadiene and copolymers of butadiene with isobutylene, acrylonitrile or styrene and the polymeric compound may be polyvinyl acetate, butyral or chloride, polychloroprene or copolymers of vinyl chloride with vinyl acetate or vinylidine chloride. The methylene donor is preferably hexamethylene tetramine although paraformaldehyde may also be used. The compositions may be obtained by coagulation of aqueous dispersions of rubber, polymer and alkaline solution of lignin followed by milling and then heating with the methylene donor. Alternatively the components may be mixed dry or with the aid of dioxane. Carbon black may also be included. The products which may be vulcanized, e.g. with sulphur, are useful for soling footwear, making suitcases, battery cases, control panels and door knobs. Specification 709,991 is referred to.ALSO:Natural or synthetic rubber which is a polymer of an unsubstituted conjugated diene hydrocarbon or a copolymer of an unsubstituted conjugated diene hydrocarbon with a compound copolymerizable therewith is reinforced by adding a reaction product of lignin and methylene donor and dispersing a polymeric compound which is a polymer of a monomer containing the group CH2= 1/c - cl as a sole unsaturated group or a copolymer thereof with a compound copolymerizable therewith or a polymer of a diene hydrocarbon containing a CH2= 1/c - cl group or a polyvinyl acetal or polyvinyl acetate therein. The term lignin includes both the sulphonated and unsulphonated products. The methylene donor is preferably hexamethylene tetramine although polymers of formaldehyde such as paraformaldehyde may be employed in the presence of an alkaline catalyst. The rubber may be unvulcanized natural rubber, or polybutadiene, an isobutylenebutadiene copolymer, a butadiene-acrylonitrile copolymer, or a butadiene-styrene copolymer. The polymeric compound may be polyvinyl acetate, polyvinyl butyral, polyvinyl chloride, or copolymers of vinyl chloride with vinyl acetate or vinylidene chloride, or polymers of substituted diene hydrocarbons such as polychloroprene. In examples, natural rubber latex is mixed with unsulphonated lignin in caustic soda, polyvinyl chloride latex added and then the mixture precipitated with formic or hydrochloric acid. Hexamethylene tetramine is added, and then a vulcanizing mix consisting of sulphur, zinc oxide, stearic acid and mercaptobenzthiazole, with the optional addition of a condensate product of acetone and aniline, and calcium silicate is added and the whole vulcanized at 153 DEG C. The mix may be further reinforced by adding carbon black. Specification 709,991 is referred to.