Self-healing and thermo bonding nanocellulose-vitrimer films

Abstract This study demonstrates the scalable fabrication of novel cellulose nanocrystal (CNC)-vitrimer composite films through a simple dip-coating process followed by in situ polymerization. FTIR analyses confirm rapid monomer uptake and complete vitrimer network formation within 8 h at 145 °C, evidenced by the disappearance of epoxide and carboxyl peaks and the emergence of ester linkages. XPS and diffusion-edited 1 H NMR provide evidence consistent with covalent attachment of vitrimer species to the CNC surface, supporting the formation of a chemically integrated hybrid interface. Cross-sectional SEM imaging uncovers a stratified architecture comprising vitrimer-rich surface layers, an unmodified CNC core, and a chemically fused transition zone that promotes strong interfacial adhesion. Rheological and stress-relaxation measurements confirm vitrimeric behaviour with a low activation energy of 38.8 kJ/mol and a topology freezing temperature of 40 °C, enabling thermally triggered network rearrangement. Incorporation of the vitrimer phase substantially enhances mechanical performance, increasing elongation at break from 1.5% to 4.4% and toughness from 41 to 76 kJ/m³. Vitrimer integration also significantly improves humidity resilience, at 50% RH, water-vapor permeability decreases to 2.4 × 10⁻¹² g/Pa·s·m, and at elevated RH the composite film maintains nearly an order-of-magnitude lower permeability than the control CNC film. In addition, the vitrimer layer introduces multifunctional capabilities, including thermally activated healing, heat-sealability at 180 °C via dynamic bond exchange, and UV-shielding properties. This study presents a novel general and scalable strategy for chemically integrating dynamic vitrimer networks with nanocellulose. It provides a new material design to overcome humidity sensitivity for multifunctional sustainable bio-based films.