Carbon fiber/epoxy vitrimer composite patch cured with bio-based curing agents for one-step repair metallic sheet and its recyclability

Vitrimers have gained a great deal of attention from researchers, yet research on its application is still lacking. This study, a novel bio-based vitrimer was developed from epoxy (EP) and bio-based curing agents, that is, cashew nut shell liquid (CNSL) and citric acid (CA), and then reinforced by carbon fiber. The vitrimers with different ratios of acid to epoxy (R ratio) at 0.30–0.40 contained ester and ether linkages. All EP/CA/CNSL vitrimers showed the stress relaxation over 70–100°C due to transesterification. The vitrimers were applied as polymer matrices for the carbon fiber composites and then used as repair patches. By using the carbon fiber-reinforced vitrimer with the R ratio of 0.30, patch repair on a damaged alloy sheet revealed that approximately 98% of the tensile strength of the damaged alloy sheet was recovered. The vitrimer can be dissolved from carbon fiber composite to recover carbon fiber. The recovered carbon fiber retained good tensile strength compared to the pristine composite. Based on this study, the EP/CA/CNSL vitrimers showed the comparable thermomechanical properties with the epoxy vitrimer cured by the petroleum-based curing agent. The vitrimer composite patch could therefore be an alternative new repair method to extend the service life of damaged structures.