Hierarchical assembly of biomass fiber–lamella–macromolecule networks for biocomposites with high strength and water-resistant sealing

Enhancing mechanical strength and water resistance in cellulose fiber-based materials is crucial for their adoption as sustainable alternatives to petroleum plastics. However, achieving these improvements through a simple, economical, and ecofriendly approach remains a major challenge. Here, we present a chitosan (CS)-driven multiscale assembly and rearrangement strategy that produces fiber-lamella biocomposites with outstanding mechanical strength and water resistance, achieved without any chemical modification, thermal treatments, or mechanical pressing. This method leverages synergetic electrostatic interactions, hydrogen-bonding, and hydrophobic association where negatively charged microscale pliable pollen lamella and positively charged macromolecular CS sequentially assemble within pulp fibers to form dense, water-resistant networks. Relying solely on the spontaneous organization of the three components, the resulting fiber/pollen-CS (FP-CS) biocomposites exhibit superior mechanical strength (~80 MPa) and maintain water stability for up to 100 d. Remarkably, they also enable seamless water-resistant sealing through simple CS application, facilitating ecofriendly production of straws, packaging, and water-resistant patches. This green, scalable, and energy-efficient process uses only biomass feedstocks to produce high-performance biocomposites, offering a promising sustainable alternative to conventional plastics.