Dual Cross-linked Epoxidized Natural Rubber Reinforced by Tunicate Cellulose Nanocrystals with Improved Strength and Extensibility

Cellulose nanocrystals have been proved to be ideal reinforcing fillers for rubber. However, the increase in tensile strength always accompanies a reduction in extensibility. In this paper, epoxidized natural rubber (ENR) nanocomposites with dual cross-linking networks by incorporating tunicate cellulose nanocrystals (t-CNs) were prepared. Carboxyl groups were introduced onto t-CNs surface via grafting reaction with maleic anhydride (MAH). Interfacial chemical reaction between carboxyl groups on modified t-CNs and epoxy groups on ENR chains led to formation of covalent cross-linking network. Hydrogen bonds between hydroxyl groups on t-CNs and epoxy groups on ENR chains served as physical cross-linking network. Therefore, uniform dispersion and improved interfacial adhesion were achieved. Meanwhile, the covalent cross-linking network could provide strength and elasticity, while the reversible physical cross-linking network could serve as sacrificing element during stretching and dissipate energy. Therefore, dual cross-linked nanocomposites showed improved strength, modulus, extensibility, and decreased hysteresis compared with sole cross-linked nanocomposites.