Tough, Leaching-Resistant, and Photothermal Cellulose/Lignin Composites via Covalent Anchoring and Microphase Separation

Abstract Cellulose/lignin composites are promising sustainable materials but suffer from brittleness, lignin agglomeration, and lignin leaching in aqueous environments. Herein, an innovative strategy combining covalent anchoring and microphase separation is reported to overcome these long-standing challenges. By leveraging the differential hydroxyl reactivity of hydroxyethyl cellulose (HEC) and calcium lignosulfonate (CLS), a cross-linked HEC is constructed with partially covalently immobilized CLS. Subsequent solvent exchange induces the formation of hydrophobic microphases (100−300 nm), which can prevent CLS leaching in aqueous media via a phase-locking effect. The synergy of covalent anchoring and phase locking enables the uniform dispersion and leaching resistance of high-content CLS within MpS-HEC/CLS composites, thereby imparting excellent photothermal conversion effects. Meanwhile, plentiful small-sized microphases can effectively toughen the composites via forcing HEC segmental motion and suppressing the development of microcracks into macrocracks. Consequently, the optimized composite, MpS-HEC/CLS40, achieves a tensile strength of 114.5 ± 6.3 MPa and a toughness of 37.3 ± 1.6 MJ/m3, overcoming the classic strength-toughness trade-off. MpS-HEC/CLS40 also shows an exceptional photothermal effect with a surface temperature of 234.8 °C (dry state) and 95.6 °C (wet state) under 60 s of NIR irradiation, enabling good light-triggered shape memory performance and seawater desalination efficiency. This work provides an innovative and scalable approach to fabricating high-performance, multifunctional bio-based composites, which hold significant potential for intelligent devices and water purification technologies.