Mechanical properties of modified aramid three-dimensional braided composites

Three-dimensional (3D) braided composites have good integrity and high stability, but aramid fiber (AF) has an inert surface and poor interfacial bonding with resin, which affects the mechanical properties of aramid 3D braided composites and limits their development. This paper used catechol/pyrogallol polyamine (CA/PGPA) to modify the AF. The effects of different mass fraction ratios of CA/PGPA and different reaction temperatures on the surface properties of AF and the mechanical properties of 3D braided composites were investigated. The results showed that after the CA/PGPA modification, fiber surface oxygen-containing groups increased, the roughness became more extensive, the fiber strength increased, and the interfacial shear strength increased. When AF-CAPG-II-40°C, the mechanical properties of the 3D braided composites were improved most significantly. Compared with unmodified composites, the bending modulus was increased by 70%, the compression modulus by 124%, and the shear strength by 55.7%. The epoxy resin modification was carried out based on AF-CAPG-II-40°C, and when the mass fraction of aramid nanofiber/graphene nanoparticle (ANF/G) was 0.7 wt%, 3D braided composites exhibited satisfactory mechanical properties. The bending modulus, compression modulus, and shear strength were increased by 15.3%, 23.3%, and 25.7%, respectively, compared with AF-CAPG-II-40°C.