Effect of bone glue concentration on the composition structure, surface properties, and thermal stability of Xuan paper

Based on the actual processing of Xuan paper surface sizing, we used bone glue solution with mass fractions of 0.5-2.5% to apply manual drag-dye surface sizing. Organic elemental analysis, scanning electron microscopy, surface pH determination, water contact angle measurement, dynamic vapour sorption, and thermogravimetric analysis were used to characterize the bone glue content, surface properties and thermal stability of the sized Xuan paper. Different bone glue concentrations were retained uniformly and effectively on Xuan paper. The surface morphology of Xuan paper changed significantly after sizing due to the bone glue coating on the fibres and the fibre network. With an increase in sizing concentration from 1.0 to 1.5%, the hydrophobicity of the sizing Xuan paper's surface increased considerably. The weak acidity of bone glue solution lowered Xuan paper's surface pH. Increasing bone glue concentration can boost Xuan paper's saturation moisture absorption. When bone glue concentration was over 1.0%, sized Xuan paper's moisture absorption rate increased, while sized Xuan paper with a concentration below 1.0% showed a slight inhibition of moisture absorption within a certain humidity range. The sized Xuan paper with a concentration of 1.0% had a more stable and slower hygroscopic reaction in the absorption-desorption cycle. As bone glue concentration increased, Xuan paper's initial moisture content decreased and then increased, with the lowest value for sized Xuan paper at 1.0% concentration. The sized Xuan paper with a concentration of 1.0% bone glue showed the best thermal stability. Surface sizing should have little effect on Xuan paper's calcium carbonate content, but bone glue complicated its thermal behaviour.