Lignin-enhanced wet strength of cellulose-based materials: a sustainable approach

Cellulose is the most abundant renewable polymer resource in nature and cellulose-based materials are expected to serve as viable replacements to petroleum-based plastic products. However, the poor wet strength of cellulose limits its application as a high-strength material. Lignin is another abundant natural polymer in the biosphere. Inspired by the natural structure of wood fibers, researchers have added lignin to cellulose-based materials to effectively improve the wet strength while maintaining the environmentally friendly nature of these materials. This review comprehensively summarizes the current studies and describes the mechanisms underlying lignin-induced enhancement in the wet strength of wood fibers and cellulose-based materials. In addition, the influence of various methods for preparing cellulose-based materials is analyzed based on the introduction of ionic or chemical crosslinking or the thermal curing of lignin/cellulose-based materials to improve their wet strength. The use of environmentally friendly methods to improve the wet strength of cellulose-based materials is key in advancing the applications of these two abundant biomass resources. Finally, the future prospects of cellulose-based materials with lignin-enhanced wet strengths are discussed. This review contributes to the understanding of the physicochemical changes of lignin in cellulose-based materials and provides theoretical support for the wet strength of lignin-enhanced cellulose-based materials.