Improving performance of polypropylene through combined use of calcuim carbonate and metallocene-produced impact modifier

Polypropylene (PP) composites containing calcium carbonate (CaCO₃) filler and/or impact modifiers were prepared and investigated as a function of composition. The effects of surface treatment of filler particles and type of impact modifiers were studied. Characterization of composite microstructure was discussed in relation to the mechanical properties. The results show that the balance of mechanical properties of PP, as presented by the modulus and impact strength, can be achieved through combined use of low-cost CaCO₃ filler and impact modifiers. The use of stearic-acid-coated filler and metallocene-produced ethylene-octene copolymer (EOR) impact modifier was found to give the best balance. The composite containing 20% of coated CaCO₃ and 20% of EOR exhibited comparable modulus and, remarkably, 20 times higher impact strength than the unfilled PP. Cavitation around the filler particles in accordance with plastic yielding are important mechanisms for energy dissipation in that composite.