Cellulose Nanofibers (CNF)/Carbon Fiber Composites With Enhanced Flexural Strength for Structural Applications

Cellulose Nanofibers (CNF) are produced from plant cellulose microfibers through a facile synthesis process. These fibers are discontinuous, very graphitic, and extremely compatible with the majority of polymer processing techniques; they can be dispersed isotropically or anisotropically. Since they are available in a free-flowing powder form, the dry carbon fiber can be physically modified with the addition of CNF. The effect of the CNF compositions, their morphology on carbon fiber, and subsequent mechanical properties are explored in this paper. The CNF composite nanofiber networks are introduced as interleave layers to improve the interlaminar shear strength (ILSS) of an epoxy/carbon fiber laminate composite. Dry carbon fiber is coated by different volume fractions of CNF (0.6 wt.%, 0.8 wt.%, 1 wt.%) through the strong bath sonication process. Laminates are fabricated by modifying dry carbon fiber surface with CNF resulting in a considerable improvement in the mechanical characteristics as compared to a neat sample. The application of CNF composite nanofiber networks as an interleaved layer in an epoxy/carbon laminate increases the delamination resistance of the ILSS in both 0.8wt% and 1 wt.% CNF enhanced laminates by 27.2%, and 12.4% respectively, but no significant difference is found for ILSS in 0.6 wt.% CNF enhanced laminate. Moreover, a significant improvement is observed in flexural modulus for 0.8 wt.% CNF coated carbon fiber laminate. This suggests that CNF can enhance the delamination resistance and flexural strength of an epoxy/carbon fiber laminate undergoing delamination and deformation. This result is attributed to crack path modification, and load energy absorption by higher modulus CNFs reinforced nanofibers interleave in the laminate resulting in a higher shear modulus to the networks.