The behaviour of styrene butadiene rubber/acrylonitrile butadiene rubber blends in the presence of chlorinated hydrocarbons

The behaviour of styrene butadiene rubber/acrylonitrile butadiene rubber (SBR/NBR) blends in the environment of chlorinated hydrocarbons, such as carbon tetrachloride, chloroform and dichloromethane, in the temperature range 32-52 degrees C has been investigated. Sulphur, dicumyl peroxide and a mixed system consisting of sulphur and peroxide were used as the vulcanising systems for the matrix. The effects of vulcanising agents, blend composition, solvents and temperature on the sorption characteristics were studied. The sulphur-vulcanised systems exhibited the highest solvent uptake and those with dicumyl peroxide as the vulcanising agent the lowest. This difference has been explained on the basis of the nature of cross links established between the polymer chains during vulcanisation. The solvent uptake increased with an increase in SBR content in the blends when carbon tetrachloride was used as the penetrant, whilst it decreased with SBR content when chloroform and dichloromethane were used as the probes. This behaviour has been explained on the basis of the polarity difference of the solvents. For a given blend system, the solvent uptake was maximum when dichloromethane was used as the solvent and minimum when carbon tetrachloride was used. This has been accounted for in terms of the difference in the size of the penetrants. The intrinsic diffusion coefficient, permeation coefficient, cross link density and interaction parameter were estimated from the sorption data. Thermodynamic parameters such as enthalpy and free energy changes were also calculated. These values indicate that the sorption process in the present systems is exothermic and is more spontaneous in sulphur-vulcanised systems. The experimental results, when compared with different theoretical diffusion models, have been found to be closer to Robeson's and Maxwell's models.