Multifunctional Chitosan Nanofiber-Based Sponge Materials Using Freeze–Thaw and Post-Cross-Linking Method

The fabrication of porous sponge materials with stable structures via cross-linking diverse polymers presents significant challenges due to the simultaneous requirements for phase separation as a pore-forming step and cross-linking reactions during the fabrication process. To address these challenges, we developed a sponge material solely from natural-based polymers, specifically chitosan nanofibers (CSNFs) and dialdehyde carboxymethyl cellulose (DACMC), employing a straightforward, eco-friendly technique. This technique integrates a facile freeze-thaw method with subsequent cross-linking between CSNFs and DACMC. This method effectively addresses the difficulties associated with pore formation in materials, which typically arise from the rapid formation and precipitation of polyionic complexes during the mixing of anionic and cationic polymers, using ice crystals as a rigid template. The resultant sponge materials exhibit remarkable shape recoverability in their wet state and maintain light, stable porosity in the dry state. Furthermore, in comparison to commonly used commercial foams, this composite porous material demonstrates superior fire retardancy and thermal insulation properties in its dry state. Additionally, it shows effective adsorption capacities for both cationic and anionic dyes and metal ions. This method of using biobased polymers to produce porous composites offers a promising avenue for creating multifunctional materials, with potential applications across various industries.