Patent GB-687054-A (GB)
Title: Improvements in reclaiming mixtures of vulcanized natural rubber and synthetic rubber scraps
IPC: C08J11/10
Filed: 1951-06-29
Abstract: In reclaiming mixtures of vulcanized natural rubber and vulcanized butadiene-styrene copolymer rubber scraps, the scraps are heated in a non-alkaline medium for a time sufficient to soften the natural rubber portion to a Mooney viscosity, measured at 180 DEG  F., of 20-40 and soften the butadiene-styrene copolymer rubber to a Mooney viscosity, measured at 180 DEG  F., of 50-140, and the softened mixture is heated with sodium, potassium, calcium or ammonium hydroxide, potassium or sodium carbonate, trisodium or tripotassium phosphate, or sodium or potassium sulphite, whereupon the natural rubber portion increases in viscosity at a greater rate than the butadienestyrene copolymer portion to give a uniform reclaimed rubber of Mooney viscosity, measured at 180 DEG  F., of 50-180.  According to an example, ground scrap containing 25 per cent of cellulose fibres, and a rubber portion comprising 4 parts of vulcanized natural rubber to 1 part of vulcanized GR-S is heated under pressure in a digester for 5 hours at 388 DEG  F. with pine and rosin oils as softeners, dicresyl sulphide as plasticizer, calcium chloride as defibring agent, and water, sodium hydroxide is then added, and the heating at 388 DEG  F. is continued, with mixing, for 30 minutes more; according to another example, a similar ground scrap, mixed with coal oil fraction, carbon black, and rosin oil, is heated for 16 minutes by pressure and mechanical action in a Banbury mixer under 200 lb./sq. inch ram pressure, the temperature reaching 500 DEG  F. aqueous sodium hydroxide is added, and mixing and heating is continued for 3 minutes.ALSO:In reclaiming mixtures of vulcanized natural rubber and vulcanized butadiene-styrene copolymer rubber scraps, the scraps are heated in a non-alkaline medium for a time sufficient to soften the natural rubber portion to a Mooney viscosity, measured at 180 DEG  F., of 20-40 and soften the butadiene-styrene copolymer rubber to a Mooney viscosity, measured at 180 DEG  F., of 50-140, and the softened mixture is heated with sodium, potassium, calcium or ammonium hydroxide, potassium or sodium carbonate, trisodium or tripotassium phosphate, or sodium or potassium sulphite, whereupon the natural rubber portion increases in viscosity at a greater rate than the butadiene-styrene copolymer portion to give a uniform reclaimed rubber of Mooney viscosity, measured at 180 DEG  F., of 50-180.  According to an example, ground scrap containing 25 per cent of cellulose fibres, and a rubber portion comprising 4 parts of vulcanized natural rubber to 1 part of vulcanized GR-S is heated under pressure in a digester for 5 hr. at 388 DEG  F. with pine and rosin oils as softeners, dicresyl sulphide as plasticizer, calcium chloride as defibring agent, and water, sodium hydroxide is then added, and the heating at 388 DEG  F. is continued, with mixing, for 30 min. more; according to another example, a similar ground scrap, mixed with coal oil fraction, carbon black, and rosin oil, is heated for 16 min. by pressure and mechanical action in a Banbury mixer under 200 lb./sq. in. ram pressure, the temperature reaching 500 DEG  F., aqueous sodium hydroxide is added, and mixing and heating is continued for 3 min.