Synergistic interlaminar toughening and strengthening of CF/EP composites via migration-stable PES/CNTs films

In this study, through a targeted experimental approach, polyethersulfone/carbon nanotubes (PES/CNTs) films with variable carbon nanotubes (CNTs) contents were fabricated by the phase inversion approach and employed in carbon fiber/epoxy (CF/EP) composites prepared by the vacuum-assisted resin infusion process to upgrade the toughness of composites. The dissolution of the PES/CNTs films in the epoxy resin was revealed to be controllable, which guaranteed a gradient distribution of polyethersulfone and CNTs between the layers. As observed, the CF/EP composites with PES/CNTs films containing 0.5 phr CNTs provided the optimized mode I fracture toughness with a 120.4% increase in G IC compared to the reference. Whereas, the G IIC of the composites with PES/CNTs film containing 1.0 phr CNTs was increased by 92.5%. Additionally, observation of the fracture surfaces of mode I and mode II specimens by scanning electron microscopy revealed that PES/CNTs films toughened CF/EP composites via three mechanisms: i) crack deflection and secondary microcracks initiation caused by polyethersulfone microspheres, ii) cracks bridging effect and pull-out from the epoxy matrix of CNTs and iii) CNTs distributed between epoxy matrix and polyethersulfone microsphere led to more energy consumption, which had a synergistic effect. This method overcomes the trade-off between toughness and stiffness in traditional interleaving methods, providing a new approach for the manufacturing of high-performance CF/EP composites.