Grafting isocyanate onto graphene oxide for polyurethane composites to improve their thermal stability and mechanical properties

Modification of graphene oxide (GO) to apply to polymer composites has important potential for improving the mechanical properties and thermal stability of polymers. In this work, isophorone diisocyanate (IPDI) was used to chemically modify GO, and isocyanate-functionalized GO (IPDI-GO) was successfully synthesized at different reaction times and compounded with aqueous polyurethane (WPU) to prepare IPDI-GO/WPU composites. The test results indicated that the interlayer spacing of the prepared IPDI-GO has increased by 2.36 Å. Covalent bonds had been formed between isocyanate groups of IPDI and hydroxyl and carboxyl groups on the surface of GO. The atomic ratio of carbon to oxygen in IPDI-GO had increased from 2.79 to 4.05, and a characteristic peak of nitrogen (N) appeared. Moreover, the obtained IPDI-GO was insoluble in water, and hydrophobicity of the IPDI-GO/WPU composites was enhanced, and the contact angle increased from 63.8 to 92.6. The stability of IPDI-GO had been improved, it could stably disperse in the polar aprotic solvent DMF for 14 days without sedimentation. When modification time was 48 h and loading amount of the IPDI-GO in composites was 0.5 wt%, tensile strength of the IPDI-GO/WPU composite films increased by 33.1%. Additionally, thermal stability of the composite films improved compared to pure WPU. This work simulated the reinforcement mechanism of the composite films, as well. Graphical Abstract