Blends of isotactic polypropylene and nitrile rubber: morphology, mechanical properties and compatibilization

Abstract

Morphology and mechanical properties of blends of isotactic polypropylene (PP) and nitrile rubber (NBR) have been investigated with special reference to the effects of blend ratio. Morphological observations of blends showed a two-phase system, in which the rubber phase was dispersed as domains in the continuous PP matrix at lower proportions of NBR (≲50%). The 30/70 PP/NBR blend was found to exist as a co-continuous system. Attempts have been made to correlate the changes in morphology with properties. The mechanical properties of blends were found to depend on the blend ratio. Various composite models, such as the series model, the parallel model, the Halpin-Tsai equation and Coran's model, have been used to fit the experimental mechanical properties. The effect of concentration of maleic-modified polypropylene (MA-PP) and phenolic-modified polypropylene (Ph-PP) as compatibilizers on the morphology and mechanical properties of the blend was also investigated. The compatibilizer concentrations used were 1, 5, 10 and 15 wt%. The domain size of the dispersed NBR particles decreased with the addition of a few per cent of the compatibilizer followed by a levelling off at higher concentrations. The levelling off was an indication of interfacial saturation. The mechanical properties of the blends were improved by the addition of the compatibilizer followed by a levelling off at higher concentrations. The levelling off was an indication of interfacial saturation. The mechanical properties of the blends were improved by the addition of the compatibilizers. The experimental results were compared with the current compatibilization theories of Noolandi and Hong.