A trade-off study toward highly thermally conductive and mechanically robust thermoplastic composites by injection moulding

In order to achieve high thermal conductivity (TC) for graphene-reinforced thermoplastic polymer composites, many efforts have been made to reduce the interfacial thermal resistance. However, good mechanical properties may be conflicting with thermal properties due to the poor interaction bonding between matrix and fillers. In this work, graphene sheets (GSs) filled thermoplastic polypropylene (PP) composite are prepared by three different moulding methods: i) melt extrusion with subsequent injection moulding, ii) single injection moulding and iii) hot-pressing. The relationship among processing methods, microstructures and properties are systematically demonstrated in detail. It is found that single injection moulding can be used to realize a random distribution of the filler with modest size to keep good mechanical properties, and an acceptable conductive network in the matrix to improve the thermal transfer ability of the composites. As a result, high TC of 2.07 Wm(-1)K(-1) and tensile strength of 24 MPa are simultaneously achieved for 20 wt% GSs/PP composite, realizing a tradeoff between thermal and mechanical properties. Finite element simulation is also conducted to perceive the dependence of the thermal properties on the size and distribution of GSs filler. We think that this work provides an instructive route to design thermoplastic composites with overall consideration of thermal and mechanical properties and allows a considerable step to its industrial application.