Fabrication of well-dispersed cellulose nanocrystal reinforced biobased epoxy composites using reversibility of covalent adaptable network

Cellulose nanocrystal (CNC) shows great potential in reinforced composites but it is difficult to disperse in epoxy thermosets due to its poor dispersity in epoxy monomers. Herein, we reported a novel approach to disperse CNC in epoxidized soybean oil (ESO)-derived epoxy thermosets uniformly by using the reversibility of dynamic iminecontaining ESO-derived covalent adaptable network (CAN). The crosslinked CAN was deconstructed by an exchange reaction with ethylenediamine (EDA) in dimethyl formamide (DMF), leading to a solution of deconstructed CAN with plenty of hydroxyl and amino groups, which could form strong hydrogen bonds with hydroxyl groups of CNC and thus facilitated and stabilized dispersion of CNC in the deconstructed CAN solution. Epoxy composite with well-dispersed CNC was finally achieved by a reformation of CAN through the removal of DMF and EDA. In this way, the epoxy composites with CNC content up to 30 wt% were successfully prepared and showed drastically reinforced mechanical properties. The tensile strength and Young's modulus of the CAN were improved by up to -70 % and -45 times with the incorporation of 20 and 30 wt% CNC, respectively. The composites showed excellent reprocessability without significant loss in mechanical properties after reprocessing.

Automated summary

A new method was developed to disperse cellulose nanocrystals (CNC) in epoxidized soybean oil (ESO)-derived epoxy thermosets uniformly by utilizing a reversible dynamic imine-containing ESO-derived covalent adaptable network (CAN). The findings showed that the dispersion of CNC was facilitated and stabilized by the formation of strong hydrogen bonds between the hydroxyl groups of CNC and the hydroxyl and amino groups in the deconstructed CAN solution.