Epoxy composites find application in the aerospace industry. Although epoxy is a high-performance polymer, its fracture toughness is compromised due to its highly cross-linked nature. Nanomaterials such as carbon nanotubes...

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The aerospace industry has started shifting toward polymer composites, especially epoxy-based composites. Because epoxy is inherently brittle, it must be suitably reinforced to enhance its fracture properties and make it suitable for aerospace applications. In this regard, we studied surface-modified Ti 3 C 2 nanosheets as toughening agents for aerospace-grade epoxy composites. Ti 3 C 2 T x (T = O, OH, and F) nanosheets were synthesized by acid etching of the Ti 3 AlC 2 precursor and further functionalized with polyethyleneimine (PEI) to improve their degree of exfoliation and enhance their degree of interaction with the epoxy matrix. Epoxy composites containing 0.1, 0.5, and 1.0 wt % PEI−Ti 3 C 2 T x nanosheets were synthesized. These composites were studied for their curing behavior and mechanical properties. The isoconversional Starink method was used to calculate the curing activation energy. Compared to neat epoxy, the PEI−Ti 3 C 2 T x nanosheets showed a catalytic effect on curing by lowering the curing activation energy. A 40% higher compressive strength was observed in 0.5 wt % PEI−Ti 3 C 2 T x /epoxy composites, compared to neat epoxy. The K IC and G IC of the 0.5 wt % PEI−Ti 3 C 2 T x /epoxy composite were 70 and 140% higher than those of neat epoxy, respectively. The fracture properties improved due to crack deflection, crack blunting, and enhanced filler−matrix interaction. At 1.0 wt % PEI−Ti 3 C 2 T x loading, the nanosheets began agglomerating, which caused a reduction in the mechanical properties. The storage modulus and T g of the PEI− Ti 3 C 2 T x /epoxy composites were also significantly higher than those of neat epoxy. It was observed that blank Ti 3 C 2 T x did not cause a remarkable improvement in the properties of epoxy composites. Hence, PEI functionalization was instrumental in achieving uniform filler dispersion and favorable filler−matrix interaction.