Abstract:
The rheological behavior of linear low density polyethylene (LLDPE), natural rubber (NR) and their blends were studied by a cone-and-plate rheometer in dynamic mode at a frequency ranges from 0.1-100 rad/sec and a capillary rheometer in steady mode at high shear rates. Maleic anhydride (MA) was added to the blends as a compatibilizer. The presence of a single tan 8; i.e. a single glass transition temperature, indicated that the compatibility of LLDPE/NR blends was improved by the addition of maleic anhydride. The results illustrated the effects of blend ratio, maleic anhydride concentration, shear stress/shear rate and temperature on melt viscosity and melt elasticity of the blends. Addition of NR caused the increase in viscosity and modulus. But blend viscosity reduced at high shear rate while the storage modulus increased. SEM analysis of the fracture surfaces of the compatibilized blends showed that the addition of a small percentage of the compatibilizer was enough to decrease and stabilize the domain size of dispersed NR phase. Without MA, the morphology was altered by shear rate due to the change of viscosity with shear rate. Dynamic mechanical properties of the blends were also investigated. Master curves of G' and G” for the blend system were constructed by using the time-temperature superposition principle. It was observed that the master curves of the blends did not fall on the same curve due to morphological changes induced by the viscosity difference and the drop-coalescence mechanism. Fine calcium carbonate was used as a filler in the blends. It was found that viscosity of the filled blends increased significantly with amount of filler at low frequency.
