Influence of castor oil-derived bio-resin on mechanical and visco-elastic properties of dynamic covalent imine bond based epoxy and its composite

The widespread use of thermoset composites has raised significant environmental and economic concerns due to their non-recyclable nature. This study addresses these issues by developing vitrimers and their composites featuring dynamic imine bonds synthesized from vanillin, 3,3 '-dimethyl-4,4 '-diaminodicyclohexylmethane, and epoxy. To enhance toughness and bio-content in the vitrimer and its composites, a green reactive monomer, epoxy methyl ricinoleate (EMR), was synthesized via the transesterification of epoxidized castor oil (ECO) and incorporated as the reactive diluent. The effect of EMR on bio-resin mechanical, thermo-mechanical, and relaxation times (tau) of the vitrimer was examined. The inclusion of EMR reduced the relaxation time, indicating improved dynamic bond exchange efficiency. EMR incorporation decreased the relaxation time, suggesting enhanced efficiency in the interchange of dynamic bonds. In addition, the incorporation of 20% EMR increased the impact strength of the epoxy vitrimer by 37.8%. The study also details the manufacturing and characterization of greener composites made with these vitrimers and flax fabric, which were evaluated for various mechanical and thermo-mechanical properties. Morphological analysis using a scanning electron microscope revealed good interfacial adhesion between the fiber and matrix. Furthermore, the flax fiber vitrimer-based composite demonstrated effective chemical recyclability. The results indicate that these composites possess mechanical and thermal-mechanical properties well-suited for lightweight engineering applications.