In situ self-assembly of pulp microfibers and nanofibers into a transparent, high-performance and degradable film.

Despite the significant properties of fossil plastics, the current unsustainable methods employed in production, usage and disposal present a grave threat to both energy and environment. The development of degradable biomass materials as substitutes for fossil plastics can effectively address the energy-environment paradox at the source. Here, we prepared novel micro-nano multiscale composite films through assembling and crosslinking nanocellulose with coniferous wood pulp microfibers. The composite film combines the advantages of microfibers and nanocellulose, achieving a maximum transmittance of 91 %, foldability, excellent mechanical properties (tensile strength: 51.3 MPa, elongation at break: 4 %, young's modulus: 3.4 GPa), high thermal stability and complete degradation within 40 days. The composite film exhibits mechanochemical self-healing and retains properties even after fracture. Such exceptional performance fully meets the requirements for substituting petroleum plastics. By incorporating CaAlSiN:Eu into the composite film, it enables dual emission of red and blue light, thereby being able to promote plant growth and presenting potential as a novel sustainable alternative for agricultural films. By assembling microfiber and nanocellulose, such novel strategy is presented for the fabrication of high-quality biomass materials, thereby offering a promising avenue towards environment-friendly resource-sustainable new materials.