Compatibilising effect of carbon black on morphology of NR-NBR blends

It is proposed that a cion-polar filler can reduce interfacial energies bet ween polar and non-polar polymers. Experiments have been carried out to tes t this hypothesis using carbon black as the filler in blends of natural rub ber (NR) and a nitrile rubber (NBR) with an acrylonitrile content of 45%. B lends of NR-NBR (70/30) were prepared in an internal mixer with varying amo unts of carbon black. The dramatic decrease in domain size on addition of c arbon black was nonetheless lower than that predicted. Further experiments showed that the amount of carbon black available at the interface For compa tibilisation was influenced by preferential incorporation into the lower vi scosity elastomer (NBR). Thus, elastomers of similar viscosity should be ad ded to the mixer prior to the carbon black in order to maximise the amount of 'free' unwetted carbon black present when the elastomers are blended tog ether. Blending experiments carried out under these conditions resulted in a morphology close to the prediction based on thermodynamic theory.