Synergistic dual-crosslinking and in situ silver functionalization for high-strength, photothermal, and antibacterial microfibrillated cellulose/alginate composite fibers

The escalating crisis of plastic pollution crisis necessitates the urgent advancements in development of sustainable material alternatives. A critical challenge is the fabrication of high-performance biodegradable fibers that can substitute non-degradable synthetic polymers. Natural polymers such as sodium alginate (SA) and cellulose feature excellent biocompatibility and renewability, yet their practical application are severely restricted by inferior inherent mechanical properties. To overcome this drawback, this study proposes a synergistic dual-crosslinking strategy. Specifically, microcrystalline cellulose was modified via a stepwise oxidation treatment to prepare dialdehyde- and carboxyl-functionalized microfibrillated cellulose (DTC). During fiber fabrication, DTC contributes to the construction of a robust ion-covalent crosslinking network: carboxyl groups chelate metal ions to form ionic crosslinks, while the aldehyde groups undergo condensation reaction with hydroxyl groups of sodium alginate to generate covalent bonds. Benefiting from this elaborate strctural design, the resultant composite fiber achieves a tensile strength of 445 MPa, which is 32% higher than that of pure alginate fiber. Furthermore, the incorporated aldehyde groups enabled the in-situ reduction of silver nanoparticles, which imparted exceptional near-infrared photothermal performance and superior antimicrobial activity. Under 250 mW/cm irradiation, the material reaches a photothermal temperature of 75.2 °C, and exhibits high antibacterial inhibition efficiencies of 97.7% against E. coli and 99.3% against S. aureus. This work develops a feasible and versatile strategy for the design and preparation of high-performance alginate-based materials and provides a generalized design principle for the fabrication of multifunctional sustainable composite materials.