Improved interlaminar fracture toughness of carbon fiber/epoxy composites with a multiscale cellulose fiber interlayer

In this study, a multiscale cellulose fiber interlayer consisting of chopped flax fibers (FFs) and cellulose nanofiber (CNFs) was proposed for enhancing the interlaminar fracture toughness of carbon fiber/epoxy composites. The cellulose fiber interlayer was treated by waterborne epoxy to improve the interfacial compatibility with the epoxy matrix. The end-notched flexure results showed that the addition of the cellulose fiber interlayer in the carbon fiber/epoxy composites resulted in a remarkable increase in Mode II interlaminar fracture toughness, which was attributed to a synergistic effect of the FFs and the CNFs. The 3D network of the chopped FFs alleviated the agglomeration of the CNFs due to their good compatibility, leading to more fiber bridging and fiber pull-out during delamination. The presence of CNF further improved the interfacial properties of the FFs and epoxy matrix, which are beneficial for the fibrillation of flax fiber to hinder interlaminar crack growth. ●A multiscale cellulose fiber interlayer consisting of chopped flax fibers and cellulose nanofiber was proposed for enhancing the interlaminar fracture toughness of carbon fiber/epoxy composites.●Uniform dispersion of FF and CNF was achieved due to their good surface compatibility after the waterborne epoxy treatment.●The ENF test results showed that the addition of the multiscale cellulose fiber interlayer in the carbon fiber/epoxy composites resulted in a remarkable increase in Mode II interlaminar fracture toughness.