Nanocellulose reinforcement of epoxidized natural rubber: Enhancing strain‐induced crystallization for high‐performance bio‐composites

Abstract Nanocomposites of cellulose nanofiber (CNF) and natural rubber (NR) have been regarded as promising soft biomaterials for industrial products. However, the CNF was unsatisfactory for NR reinforcement because of poor mixing between CNF and NR. In this study, we explored the combined use of silane‐treated CNF and epoxidized natural rubber (ENR20, 20% epoxide content) to enhance the compatibility and reinforcing ability of CNF in NR‐based nanocomposites. The CNF/ENR20 nanocomposites containing 5 phr of CNF were prepared via an eco‐friendly latex mixing method. Structural observation showed all the CNF/ENR20 nanocomposites exhibited nano‐aggregated CNFs consisting of intertwined nanofibers with varying sizes depending on the types of CNFs. The addition of untreated CNFs (U‐CNFs) and silane‐treated CNFs significantly improved the modulus and tensile strength of the ENR20, notably with U‐CNFs. The U‐CNFs led to a remarkable 75% increase in tensile strength due to mutual entanglement between nano‐aggregated U‐CNF and ENR as well as hydrogen bonding despite larger aggregates. Novel model describing the effect of CNF rotation and strong CNF‐ENR adhesion on strain‐induced crystallization was revealed through WAXS/SAXS in ENR20 composites. Based on these findings, the morphological design with key structure of CNF nano‐aggregates enabled the development of high performance CNF‐reinforced rubber nanocomposites. Highlights CNFs (13 nm) were modified using two types of alkoxy silanes. 5 phr CNFs significantly enhanced the mechanical properties of ENR20. CNF rotation during stretching promoted molecular orientation. U‐CNFs reinforced ENR20 due to mutual entanglement and H‐bonding. A new model was proposed for strain‐induced crystallization process of U‐CNF/ENR.