Impact properties and rheological behavior of exfoliated graphite nanoplatelet-filled impact modified polypropylene nanocomposites

Exfoliated graphite nanoplatelets (xGnP)-filled impact modified polypropylene (IMPP) composites were prepared at 2, 4, 6, and 8 wt% xGnP with and without the addition of a coupling agent and manufactured using melt mixing followed by injection molding. The coupling agent used in this study was polypropylene-graft-maleic anhydride. The nanoparticles used were xGnP with three different sizes: xGnP 5 has an average thickness of 10 nm, and an average platelet diameter of 5 μm, whereas xGnP 15 and xGnP 25 have the same thickness but average diameters are 15 and 25 μm, respectively. Test results show that nanocomposites with smaller xGnP diameter exhibited better impact properties for both neat and compatibilized composites. However, unnotched and notched impact strengths as well as fracture initiation resistance were dramatically deteriorated with the introduction of xGnP. Explanation of this brittle behavior in a nanoplatelet-filled IMPP is presented using melt flow index and transmission electron microscopy.