Study on the Effects of Temperature and Relative Humidity on the Hygroscopic Properties of Palm Leaf Manuscripts

Palm Leaf Manuscripts are an invaluable part of the cultural heritage of the world. Due to their strong hygroscopic properties, Palm Leaf Manuscripts are particularly susceptible to fluctuations in environmental humidity. Therefore, studying the hygroscopic behavior of these manuscripts and understanding how it changes under different environmental conditions is crucial for exploring their intrinsic properties, aging mechanisms, and the development of effective conservation strategies. In this study, we employed the dynamic vapor sorption (DVS) method to investigate the changes in the hygroscopic properties of Palm Leaf Manuscripts under conditions of high temperature and high humidity. The results indicate that high-temperature environments reduce the number of adsorption sites and the hygroscopicity of palm leaves, weakening their physical adsorption and capillary action towards moisture while increasing the hysteresis in desorption, thereby enhancing the stability of palm leaves in fluctuating humidity conditions. Conversely, high-humidity environments increase the number of adsorption sites and the hygroscopicity of the leaves, strengthening their physical adsorption and capillary action, and reducing the hysteresis in desorption. The extent of these changes increases with the aging time of the manuscripts. The surface energy test results of the samples similarly indicate that exposure to high-temperature environments reduces both surface energy and hygroscopicity, while high-humidity environments increase surface energy and hygroscopicity. The infrared spectroscopy results show that in high-temperature environments, the crystallinity of cellulose within the palm leaves increases, whereas in high-humidity environments and under the influence of fungal erosion, both the cellulose and hemicellulose in the Palm Leaf Manuscripts undergo significant degradation, with the amorphous regions of cellulose degrading more than the crystalline regions.