Bridging the Performance Gap: High‐Strength Lignin‐Reinforced Cellulose Papers With Plastic‐Like Barrier Properties

ABSTRACT Cellulose papers are sustainable alternatives to plastics but are often limited by poor water resistance and barrier properties. This study introduces a method to overcome these limitations by integrating softwood kraft lignin as a functional filler. Micronized lignin particles (4 µm) were produced via wet grinding and dispersed into a paper matrix at loadings up to 40%, followed by high‐temperature pressing (160°C) to soften the lignin. This process created a composite with exceptional interfacial bonding between the softening lignin and cellulose fibers, yielding outstanding mechanical properties: a tensile strength of 82 MPa, a folding endurance of 891 cycles, and a density of 1 g/cm 3 . The barrier properties were also significantly enhanced, with water vapor and oxygen transmission rates reduced to 287 g/m 2 ·d and 114 cm 3 /m 2 ·d·0.1 MPa, respectively, representing decreases of 67% and 73% compared to conventional paperboard. This work establishes a viable paradigm for creating high‐performance, fully biodegradable lignin‐cellulose composites that bridge the functionality gap between paper and plastic, demonstrating immediate potential for sustainable packaging and covering applications.