Maleic Anhydride-Modified Lignin Reinforced Multi-Crosslinked Composite Coating for High Wet Strength and Recyclable Paper

Plant fiber-based paper is renewable and biodegradable but suffers from poor water resistance and weak wet mechanical properties. To overcome these challenges, a CPML-Fe coating system was developed, which comprises a composite coating made from carboxymethyl cellulose (CMC), poly(ethylene glycol) diglycidyl ether (PEGDE), and maleic anhydride-modified lignin (ML), integrated with Fe3+ ions through post-treatment. This coating formed a multi-crosslinked network on the paper surface and within the fiber interstices via β-hydroxy ester bonds, Fe3+–O coordination bonds, and hydrogen bonds, effectively overcoming the inherent drawbacks of paper. The wet tensile strength of the CPML-Fe coated paper increased from 2.21 MPa to over 39 MPa, while the wet strength retention rate improved from 4.21% to more than 72%. In a 72 h water immersion test, the tensile strength consistently remained above 37.88 MPa, demonstrating exceptional long-term water stability. Notably, the CPML-Fe coating exhibits pH-responsive behavior, allowing it to be de-crosslinked through pH adjustments and separated from the paper fibers, thereby enabling fiber recovery and reuse. The CPML-Fe coating significantly enhances water resistance and mechanical properties while preserving the paper’s inherent environmental friendliness, providing a novel approach toward eco-friendly paper-based alternatives to plastics.