LAUSR

With increasing concern about the environmental pollution of petrochemical plastics, people are constantly exploring environmentally friendly and sustainable alternative materials. Compared with petrochemical materials, cellulose has overwhelming superiority in terms of mechanical properties, thermal properties, cost, and biodegradability. However, the flammability of cellulose hinders its practical application to a certain extent, so improving the fire‐retardant properties of cellulose nanofiber‐based materials has become a research focus. Here, cellulose nanofiber and alginate are extracted from abundant natural sargassum as high‐strength nanoscale building blocks, and then a sargassum cellulose fire‐retardant structural material is prepared through a bottom‐up hydrogel layer‐by‐layer method. The structural materials obtained incorporate excellent mechanical properties (≈297 MPa), thermal stability (≈200 °C), low thermal expansion coefficient (≈7.17 × 10−6 K−1), and fire‐retardant properties. This work largely improves the utilization of seaweed residue and natural polymers, providing a bio‐based fire‐retardant strategy, and has a wide range of development prospects in the field of fiber‐based high‐performance structural materials in the future.