Recyclable and Sustainable Natural Rubber Biocomposite Vitrimers Induced by Dynamic Anhydride–Epoxy Bonds

Research into rubber vitrimers as a sustainable alternative to traditional static crosslinked rubber systems for developing reprocessable and recyclable rubber materials is both promising and gaining substantial interest. This study aims to investigate the impact of cellulose nanocrystals (CNCs) and maleic anhydride-modified CNC (CNC-MA) as functional fillers in a natural rubber (NR) anhydride–epoxy transesterification vitrimer system. CNC modification and vitrimer thermomechanical properties (glass transition and vitrimer transition) of the resulting vitrimer composites were then evaluated using FTIR spectroscopy, NMR spectroscopy, XRD, tensile testing, DMA, DSC, swelling tests, etc. The resulting NR-MA vitrimers showed enhanced mechanical properties (20–37.6%, at 5 phr loading levels). Despite providing a modest improvement in mechanical properties, CNC-MA, acting as both a dynamic crosslinker and a reinforcing agent, displayed improved and superior interfacial compatibility at all loadings. Overall, sustainable modified nanofillers, such as CNCs, offer a promising strategy to dynamically crosslink rubber and overcome inherent filler–polymer incompatibilities, such that it can compete with traditional vulcanized rubber.