Improving the structural stability of TEMPO-oxidized cellulose nanofibril hydrogels through chitin nanofibril reinforcement and hydrothermal treatment

Hydrogels based on TEMPO-oxidized cellulose nanofibrils (TOCNF) are attractive sustainable materials but often suffer from poor structural stability and weak mechanical strength. In this study, surface-deacetylated chitin nanofibrils (ChNF) were incorporated to reinforce TOCNF hydrogels, and the effect of hydrothermal treatment on network structure and properties was investigated. Hydrogels were prepared at solid contents of 1.25 to 2.00 wt% by mixing dilute TOCNF and ChNF suspensions followed by centrifugation and hydrothermal treatment. Compared with TOCNF alone, TOCNF/ChNF hydrogels exhibited improved shape stability, higher viscosity, and enhanced shear-thinning behavior. Hydrothermally treated TOCNF/ChNF hydrogels maintained elastic behavior up to 74.6% strain, compared with 26.3% strain for non-treated TOCNF/ChNF hydrogels. The compressive strength increased markedly, reaching 36 kPa at 1.75 wt%, whereas TOCNF hydrogels showed only ~5 kPa. FTIR and XPS analyses indicated redistribution of intermolecular interactions after hydrothermal treatment without definitive evidence of covalent bond formation. SEM observations further revealed the formation of a more interconnected and densified porous network after hydrothermal treatment. Overall, ChNF reinforcement combined with hydrothermal treatment effectively improved the structural stability and mechanical performance of TOCNF hydrogels.