Epoxy resin (EP) is a thermosetting resin with excellent properties, but its application is limited due to its high brittleness and poor flame retardancy. Therefore, to solve this problem, a dispersion system of imidazole-containing ionic liquid ([Dmim]Es) and graphene in epoxy resin is designed based on the π–π stacking effect between imidazole and graphite layers. The study on the thermal and flame-retardant properties of the composites show that the modified [Dmim]Es–graphene nanosheets improved the flame retardancy, smoke suppression and thermal stability of epoxy resin. With the addition of 5wt% [Dmim]Es and 1% Gra, the exothermic rate (HRR) and total exothermic (THR) of the composites decrease by 35% and 30.2% compared with the untreated epoxy cross-linking, respectively. The limiting oxygen index reaches 33.4%, the UL-94 test rating reaches V-0. The characterization of mechanical properties shows that the tensile properties and impact properties increased by 13% and 30%, respectively. Through SEM observation, the addition of [Dmim]Es improves the dispersion of graphene in the EP collective and changes the mechanical fracture behavior. The results show that ionic liquid [Dmim]Es-modified graphene nanosheets are well dispersed in the matrix, which not only improves the mechanical properties of epoxy resin (EP), but also has a synergistic effect on flame retardancy. This work provides novel flame-retardant and graphene dispersion methods that broaden the range of applications of epoxy resins.

    Abstract
        Graphical abstract
    1 Introduction
    2 Experimental
        2.1 Materials
        2.2 Synthesis steps of ionic liquid [Dmim]Es
        2.3 Preparation of ionic liquid [Dmim]EsGra epoxy composites
        2.4 Characterization
    3 Results and discussions
        3.1 Characterization of [Dmim]EsGra
        3.2 Mechanical properties of the nanocomposite material
        3.3 Thermal stability of EP and nanocomposites
        3.4 Flame retardancy of EP [Dmim] EsGra composites
        3.5 Analysis on char residue
        3.6 Flame-retardant mechanism
    4 Conclusions
    Acknowledgements 
    References

• Chunhong Zhang(Jilin Province Key Laboratory of Carbon Fiber Development and Application, College of Chemistry and Life Science, Changchun University of Technology)
• Zice Xu(Jilin Province Key Laboratory of Carbon Fiber Development and Application, College of Chemistry and Life Science, Changchun University of Technology)
• Wenbo Sui(Jilin Province Key Laboratory of Carbon Fiber Development and Application, College of Chemistry and Life Science, Changchun University of Technology)
• Junbo Zang(Jilin Province Key Laboratory of Carbon Fiber Development and Application, College of Chemistry and Life Science, Changchun University of Technology)
• Yuhui Ao(Jilin Province Key Laboratory of Carbon Fiber Development and Application, College of Chemistry and Life Science, Changchun University of Technology)
• Lu Wang(Jilin Province Key Laboratory of Carbon Fiber Development and Application, College of Chemistry and Life Science, Changchun University of Technology)
• Lei Shang(Jilin Province Key Laboratory of Carbon Fiber Development and Application, College of Chemistry and Life Science, Changchun University of Technology)