Rheological behaviour of thermoplastic elastomers from polypropylene/acrylonitrile-butadiene rubber blends: effect of blend ratio, reactive compatibilization and dynamic vulcanization

The rheological behaviour of polypropylene (PP)/acrylonitrile-butadiene rub ber (NBR) blends has been investigated with special reference to the effect of blend ratio, compatibilization and dynamic vulcanization. The morpholog y of the extrudates and the size and distribution of domains were examined, PP/NBR blends show pseudoplastic behaviour, which is evidenced by the decr ease in viscosity with increasing shear rate. The melt viscosity of these b lends increased with increasing nitrile rubber concentration and shows nega tive deviation from the theoretically predicted values. Compatibilization o f the blends with phenolic-modified polypropylene (Ph-PP) increases the mel t viscosity at low concentrations of Ph-PP. The rheological behaviour of PP /BR blends was correlated with the blend morphology. Dynamic vulcanization has a decreasing effect on die swell values. The effect of temperature on t he melt viscosity of the blends was examined and attempts have been made to construct a shear rate-temperature superposition master curve. The melt-fl ow index values for these blends were measured and have been correlated wit h rheometer data to develop a master curve for different blend compositions . The morphological analysis indicates that compatibilization of the blends prevents the coalescence of dispersed NBR domains during annealing. (C) 19 99 Elsevier Science Ltd. All rights reserved.