The Properties Of Lightweight Microcellular Polycarbonate/Graphene Composites

Graphene has excellent electronic properties,remarkable thermal properties,unusual chemical stability and extraordinary mechanical properties. These remarkable properties make it an ideal choice as fillers of polymer-based functional composites. In this article, we will regard graphene as the filler of polycarbonate substrate, and prepare lightweight, high specific strength and high toughness and excellent conductive/electromagnetic interference shielding properties of microcellular polycarbonate (PC)/ graphene composites via supercritical CO2 as foaming agent.First of all, graphene nanosheets are prepared by oxidization of natural graphite and followed by thermal exfoliation under high temperature. Then, PC/graphene composites are prepared with solution method to prepare graphene of uniform dispersion. The excellent dispersion of graphene in PC matrix makes the composites have remarkable electrical conductivity, the electrical conductivity is as high as 36.5 S/m when graphene loading is 5 wt%, and the electromagnetic interference shielding is 26dB. The electrical conductivity of microcellular composites will have a slight decline, but can still maintain the excellent electrical conductivity. Although the microcellular foams have toughening effect on PC/graphene composites, but the addition of graphene makes composites brittleness, the Specific impact strength has gone down sharply from 6.14(kJ/m2)/(g/cm3) to 0.38(kJ/m2)/(g/cm3).Secondly, we use graphene nanosheets with different sizes (H5, M5, M15,M25) to replace thermal expanded graphene. we find that the weak dispersion of graphene nanosheets in PC causes poor electrical conductivity, the electrical conductivity is only 0.042 S/m when the loading of graphene nanosheets is 8 wt%, and the electromagnetic interference shielding is only 7dB. But graphene nanosheets greatly improve the mechanical properties, not only improve the tensile strength, but also greatly improve the ductility, for example the Specific impact strength has been improved by 3-5 times. When graphene nanosheets with thicker thickness or larger diameter are regarded as the filler of PC composites, the elongation at break will increase more and the tensile strength will decrease less at the same time.Finally, the addition of CNT into PC/TGO perfectly solves this problem. The addition of CNT into PC/TGO still can maintain excellent electrical conductivity, the electrical conductivity is as high as 9.7S/m when TGO loading is 4wt%, and the electromagnetic interference shielding is 18dB. More importantly, it also can have a more uniform cell structure which cell is smaller and cell density is greater. At last, the addition of CNT into PC/TGO will play an enhanced and toughening effect on the mechanical properties, which alleviates the problem that the addition of graphene makes composites brittleness.Above all, we found that the graphene nanosheets of thinner thickness,larger diameter and smaller specific surface area can make up for the defect of poor mechanical properties of TGO Joining CNT into PC/TGO can makes microcellular foaming composites of uniform cell structure、 excellent electrical conductive and mechanical properties.