Interlaminar toughening in flax fiber-reinforced composites interleaved with carbon nanotube buckypaper

Natural fiber-reinforced composites have advantages such as light weight, unique mechanical properties, good sound absorption, and heat isolation performances. However, low interlaminar properties of natural fiber-reinforced composite laminates caused by the poor interfacial properties between natural fibers and polymeric matrices have become one of the main obstacles for their applications. In this study, carbon nanotube buckypaper interleaf, which is network structures formed by carbon nanotubes, has been developed to utilize their potential for increasing interlaminar properties of flax fiber-reinforced composites. Synergistic effects between the buckypaper and the hierarchical structure of flax fibers on the interlaminar fracture toughness were investigated. The results obtained from double cantilever beam test indicated that the interlaminar fracture toughness of the composites was significantly improved with the addition of buckypaper. Fractured surfaces of the composites were observed with the aid of scanning electron microscopy. Improved interlocking between the flax fiber and the matrix by carbon nanotubes strengthened the interlaminar interfacial bonding, resulting in fiber fibrillation and matrix toughening. Improved impact performances also proved these mechanisms. Additionally, tensile tests confirmed that the introduction of buckypaper interleaves had no influence on the fiber-dominated in-plane properties.