Hierarchical Assembly of Cellulose Fibrils and Tannin in Biocomposite Foam: Scalable Production via Oven Drying and Customizable Metal Ions Release for Antimicrobial Activity

Advanced cellulose-based foams are urgently needed as sustainable packaging materials in an era of prioritizing environmental consciousness. However, transferring the mechanical properties of cellulose fibers into porous structures is always limited by gas entrapment during foaming and irreversible structural collapse upon liquid evaporation. Herein, a hierarchical assembly strategy combines cationic cellulose nanofibrils (CCNF) with a dynamic covalent tannin/borate (T/B) complex to fabricate 3D continuous foams with distinct lamellar structure via oven drying is proposed for scalable production. CCNF assembles the T/B complex onto cellulose fibers by electrostatic attraction and hydrogen bonding, while the reversible covalent bonds among T/B complex impart shear-thinning and self-healing properties, thereby ensuring foamability (exceeding 300%) and structural stability. Moreover, the T/B foam offers a versatile platform for customization with metal ions (Fe³⁺, Cu²⁺, and Ag⁺), allowing the tailoring of physical and mechanical properties. At an optimized tannin addition of 10%, the 10T/5B-Fe foam exhibits the highest normalized strength above 410 Pa/density, while maintaining an ultralow density of 9.2 mg cm^- ³. Additionally, the pH-responsiveness of T/B complexes enables the release of metal ions for long-term antimicrobial activity. This study demonstrates a green and scalable strategy for functional foam production, offering new possibilities for next-generation antimicrobial packaging materials.