Effects of different amine-functionalized graphene on the mechanical, thermal, and tribological properties of polyimide nanocomposites synthesized by in situ polymerization

To make clear the effect and mechanism of graphene functionalized by amines on the morphology and properties of PI nanocomposites, graphene functionalized by different amines (AFG), including ethylenediamine, diethylenetriamine and p-phenylenediamine (EG, DG and PG, respectively), was prepared and used to synthesize a series of PI composites by in situ polymerization. Different amines with varying chains were chemically grafted onto the graphene oxide surface via reactions, which was confirmed by Fourier transform infrared spectrum, X-ray photoelectron spectroscopy and Raman spectrum. Aliphatic triamine underwent effective modification because of its reactivity and molecule structure; however, the aromatic amines did not cause an obvious effect as in other amines. Different loading amounts of AFG were incorporated into the polyimide matrix. It is found that the Young's modulus of 1.0DG/PI was 1.73 GPa, which increased by 86.02% from neat PI (0.93 GPa). The temperatures for 5% weight loss of 1.0DG/PI (541.8 degrees C) were obviously higher than that of neat PI (521.5 degrees C). Tensile tests and TGA showed that the loading of DG resulted in a great improvement in the mechanical and thermal properties compared with other amines. The tribological properties and mechanism were discussed. The friction coefficient of 1.0DG/PI (0.263) decreased by 51.9% from that of neat PI (0.547). The minimum wear rate is 1.895 x 10(-5)mm(3)/Nm for 0.5DG/PI, which was a 46.3% decrease from neat PI. The results showed that DG, as a stiff fulcrum, reinforcer and lubricant, significantly reduced the friction coefficient and enhanced the wear resistance of the polyimide composites. These data will be of great value for improving the interfacial effects between graphene and polymers and developing polymer materials and application areas. (C) 2018 Elsevier Ltd. All rights reserved.