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

It is proposed that a non-polar filler can reduce interfacial energies between polar and non-polar polymers. Experiments have been carried out to test this hypothesis using carbon black as the filler in blends of natural rubber (NR) and a nitrile rubber (NBR) with an acrylonitrile content of 45%. Blends of NR-NBR (70/30) were prepared in an internal mixer with varying amounts of carbon black. The dramatic decrease in domain size on addition of carbon black was nonetheless lower than that predicted. Further experiments showed that the amount of carbon black available at the interface for compatibilisation was influenced by preferential incorporation into the lower viscosity elastomer (NBR). Thus, elastomers of similar viscosity should be added to the mixer prior to the carbon black in order to maximise the amount of ʹfreeʹ unwetted carbon black present when the elastomers are blended together. Blending experiments carried out under these conditions resulted in a morphology close to the prediction based on thermodynamic theory.