Exfoliated graphite nanoplatelet-filled impact modified polypropylene nanocomposites: influence of particle diameter, filler loading, and coupling agent on the mechanical properties

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 (PP-g-MA). 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 flexural and tensile properties for both neat and compatibilized composites. For composites containing a coupling agent, tensile and flexural modulus and strength increased with the addition of xGnP. In the case of neat composites, both tensile and flexural modulus and strength decreased at higher filler loading levels. Increasing xGnP loading resulted in reduction of elongation at break for both neat and composites containing coupling agent. Explanation of this brittle behavior in a nanoplatelet-filled IMPP is presented using scanning electron microscopy and transmission electron microscopy.