GB749955A - Degradation of rubber - Google Patents

Abstract

An aqueous dispersion of rubber is oxidized (degraded) by treatment with an alkali metal chlorite under non-alkaline conditions. The oxidation may be carried out under neutral or slightly acid conditions in the presence of an activator, e.g. formaldehyde, or, alternatively, at a pH of from 3 to 4. The effect of varying the temperature on the bleaching and plasticizing action is discussed. With a stabilized dispersion air or other free oxygen-containing gas may be passed through the dispersion during the oxidation to assist degration. The degradation may be stopped by adding a bisulphite. The degraded rubber may be chlorinated in its dispersed state or in solution in rubber solvent, e.g. carbon tetrachloride. In one example 2 gms. of sodium chlorite and 5.5 ccs. of aqueous formaldehyde of 40 per cent concentration were added to 100 gm. of 60 per cent natural rubber latex stabilized oleyl para anisidine sodium sulphonate, giving a mixture with a pH of 6. The mixture was heated for 17 hours at 60 DEG C. to oxidize the rubber and the product dried to give a rubber of plasticity 20 DEG Mooney. In another example the degradation was effected at 20 DEG C. in the presence of air bubbled through the latex. In a further example hydrochloric acid was added to 100 gms. of stabilized latex, to give a pH of from 3 to 4, and 2 gm. of sodium chlorite added, the whole being then heated for 48 hours at 60 DEG C. The remaining oxidizing agents was then removed by adding formaldehyde to give a white rubber of Mooney consistency 12. In a modification of this example, quantities of sodium chlorite less than 0.4 gm. per 100 gm. of latex were used.