Melt rheological behaviour of natural rubber/poly(methyl methacrylate)/natural rubber-g-poly(methyl methacrylate) blends

Abstract

Melt rheological behaviour of natural rubber (NR) and poly(methyl methacrylate) (PMMA) blends has been studied with reference to the effect of blend ratio, processing conditions and graft copolymer concentration as a function of shear stress and temperature. The viscosity of the blend increases as the amount of NR increases. The observed values of viscosity are found to be higher than that calculated from additivity rule. In the case of solution cast samples the melt viscosity increases as the percentage of graft copolymer increases and the blend becomes more sensitive to temperature in the presence of graft copolymers. The influence of dynamic vulcanization of the rubber phase on the flow behaviour of the blends has been analysed. The die swell of the NR/PMMA blends was also evaluated in the presence and absence of graft copolymers. The morphology of extrudates has been analysed as a function of composition, graft copolymer concentration and shear stress conditions. Addition of compatibilizer reduces the domain size of the dispersed phase and stabilizes the morphology. It is also noted that state of dispersion are affected by conditions of blend preparation and extrusion. A shear rate-temperature super position master curve is constructed to predict the melt viscosities of the system as a function of temperature. The rheograms of 50/50 NR/PMMA with varying graft copolymer concentrations are found to coalesce into a master curve using modified viscosity and shear rate functions.