Aging time improves adhesive performance of handmade starch paste for restoration of ancient Chinese books and its mechanism of action

In the restoration of ancient Chinese books, handmade starch paste serves as a paper adhesive, distinguished from traditional starch paste preparation methods. It involves special processes such as starch washing and aging, relying entirely on the artisanal expertise throughout the entire process. The study recreates the process of making handmade starch paste for the restoration of traditional ancient books and investigates the effects of aging time on the apparent viscosity, rheological properties, and adhesive performance of the paste. The results indicate that during aging, the pH of the starch paste decreases significantly, but it has a minimal impact on its apparent viscosity, rheological properties, and paper softness. However, it notably enhances the adhesive performance, with the optimal results observed after 3 days of aging. This is attributed to the decrease in residual protein content in the starch, as well as the significant improvement in swelling power and solubility of the starch. The results of infrared spectroscopy and XRD testing reveal that there are no significant changes in the molecular and crystalline structures of starch during the aging process. The acidic environment produced by starch fermentation promotes protein hydrolysis, emerging as the primary reason for the improved adhesive performance of the paste.