Development of metal-graphene-filled hybrid composites: Characterization of mechanical, thermal, and electrical properties

Production and properties of thermally and electrically conductive polymeric composites containing conductive micro and nano fillers are investigated. Mechanical, electrical, and thermal properties of the produced nano and hybrid Polyamide 6-based composites filled with graphene nanoplatelets and metal microfibers are studied. The influence of nanofiller content and geometrical characteristics on the thermal conductivity of the composites are studied through experiments and finite element modeling. The results show the influence of nanoplatelets aspect ratio and lateral dimension on the thermal conductivity of the composites. Furthermore, combination of graphene nanoplatelets and metallic micro-scale fillers leads to significant improvements in thermal and electrical conductivities. In fact, graphene nanoplatelets act as conductive bridges in minuscule gaps to increase the number of contacts in the constructed network. The combination of the two different fillers increased the mechanical properties up to 120% compared to the metal reinforced composites, indicating stronger interfaces between the fillers and polymeric matrix. Rheological investigations also confirm the effectiveness of hybridization. Furthermore, the influence of annealing on the conductivities of the specimens are studied. Adding an annealing step following the nanofiller inclusion within the composites resulted in 151 and 72% enhancement in the thermal and electrical conductivities, respectively. Stress relaxation and reorientation of metal fibers in combination with additionally constructed nanofiller networks have been attributed to the observed enhancements. The involved mechanisms in the observed behaviors are studied using optical and electron microscopies.