Phase structure and mechanical properties of ternary polypropylene/elastomer/nano-CaCO3 composites

This work is focused on properties improvement of polypropylene (PP) by incorporating ethylene-octene copolymer (POE) and nanosize calcium carbonate. Two types of CaCO3 nanoparticles (stearic acid treated and untreated) and two processing sequences (one-step and two-step mixing) were used to adjust the phase structure of the ternary composites. The experimental results indicated that the one-step mixing generated segregated dispersion of POE and CaCO3 nanoparticles in PP. The two-step process resulted in core-shell structures 100-200 nm in size throughout the matrix, in which POE acts as the shell part encapsulating one or two nano-CaCO3. These specific phase structures were independent on the surface features of CaCO3 nanoparticles. In comparison with PP/POE blend or neat PP, notched impact toughness of the ternary composites of PP/POE/nano-CaCO3 was significantly increased. Meanwhile, stiffness and tensile strength of the latter were almost unchanged or slightly enhanced. It is believed that the synergistic effect of both the POE elastomer and CaCO3 nanoparticles should account for the balanced performance of the ternary composites. (C) 2007 Published by Elsevier Ltd.