Design and adhesion mechanism of multi-component natural polysaccharide-based adhesives for paper fracture repair

Cracks and losses in paper-based cultural relics critically threaten structural integrity and aesthetic coherence. Repairing paper fractures under stringent conservation criteria remains challenging, particularly when avoiding synthetic materials. Here, we designed film-forming adhesives composed of four polysaccharides, with curdlan as the primary component and chitosan, xanthan, and locust bean gum as synergistic texturizers that suppressed nanocrystal formation. The optimized formulation C9C1XL1 (1.215 wt% curdlan, 0.135% chitosan, 0.05% xanthan, 0.05% locust bean gum) achieved a tensile strength of 0.74 ± 0.05 kN/m in torn-edge raw Xuan paper fractures after accelerated aging, exceeding the cross-direction strength of intact paper with minimal chromatic shift. It also proved effective on bamboo paper and naturally aged wood pulp paper. SEM and confocal microscopy revealed a dual-role adhesion mechanism: curdlan formed a transparent film matrix filling interfiber voids for bulk mechanical support, while water-soluble polymers coated fiber surfaces, anchoring the fiber network through mechanical interlocking. Additionally, protruding cellulose fibers at repair sites functioned as load-bearing elements, substantially reinforcing tensile strength. The adhesive exhibited antifungal activity against the paper-degrading fungus Aspergillus niger, and showed promising reversibility (>90%) as evaluated by morphological analysis and fluorescence reduction. This study provides new insights into polysaccharide-based adhesives for paper conservation.