Amphiphilic polyimide-graphene nanoplatelet aerogel composites with high mechanical stability and enhanced thermal insulation properties for oil sorption applications

Abstract

This study presents the fabrication of new polyimide (PI) aerogel composites through incorporation of graphene nanoplatelet (GNP) in PI matrix. A series of PI aerogel composites with various GNP concentrations were synthesized in a three-step gel preparation method, followed by a supercritical drying procedure. The role of GNP in tuning and optimizing various properties of aerogel composites including physical, thermal, and mechanical properties was discussed. The fabricated aerogel samples showed a significant reduction of shrinkage from 16% for pristine PI aerogel to only 6% in the presence of 0.5 wt% GNP. Further characterizations showed that incorporation of 0.5 wt% GNP also resulted in the highest pore volume (3.5 cc/g), highest surface area (404.5 m2/g), lowest density (∼ 0.04 g/cm3), and outstanding thermal insulation property (thermal conductivity of only 25.47 mW/m.K). When GNP was incorporated into the solid backbone, it was noticed that even at a very low concentration of 0.1 wt%, the modulus was increased over two times, and the maximum modulus of around 8 MPa was obtained. Such an enhancement in mechanical properties showed that GNP with ultrahigh aspect ratio can not only control and tailor the nanostructured assembly of PI aerogel composites but also due to the better entanglement with polymer chains, a stronger 3D porous network was formed, and thus, GNP can act as a reinforcing filler. Eventually, the sorption capacity and kinetics were determined using various solvents including methanol, acetone, toluene, hexane, and diesel to demonstrate the application of aerogel composites in oil sorption. The results showed that the highest sorption capacity was obtained for PI aerogels with 0.5 wt% GNP, and it could reach 7.3 ± 0.2 g/g for diesel which was significantly higher than the one for pristine PI aerogels. Unlike the previously reported PI aerogel composites where the enhancement of a specific property would often be associated with the deterioration of several other properties, this study showed that various properties of PI aerogel composites can be improved and optimized through the incorporation of GNP and the control of the aerogel synthesis. The proposed materials can therefore be used as high-performance thermally insulating materials and hold great potential for the removal of oil pollutants and organic solvents.