Free-Standing CNT Film for Interlaminar Toughening: Insight into Infiltration and Thickness Effects

Carbon fiber reinforced polymer composites have the advantages of being lightweight, having high strength and designability, and having been extensively used. However, the interlaminar toughness and delamination resistance of these composites are relatively poor due to their laminated structure and intrinsic brittleness of resin matrix. In this paper, commercialized free-standing carbon nanotube (CNT) films, drawn from CNT forests, were used to toughen the interlaminar interfaces of the composites. The effects of resin infiltration state and thickness of CNT films on the interlaminar toughening effect were systematically investigated. The results show that the pre-infiltration treatment of CNT films with acetone diluted epoxy resin solution can effectively improve the degree of resin infiltration. Compared with the samples containing untreated CNT film, the Mode I and Mode II interlaminar fracture toughness of the treated samples were significantly improved. The G_IC reached a maximum of 1412.42 J/m² at a CNT film thickness of 5 µm, which was about 61.38% higher than that of the baseline. At a CNT film thickness of 15 µm, the G_IIC reached a maximum value of 983.73 J/m², approximately 67.58% higher than that of the baseline. The corresponding toughening mechanisms were also systematically analyzed.