Palm leaf manuscripts are a valuable part of world cultural heritage. Studying the mechanical properties of palm leaf manuscripts and their changes due to environmental influences is of great significance for understanding the material characteristics, aging mechanisms, and preventive conservation of these manuscripts. This study used dynamic vapor sorption (DVS) and a thermomechanical analyzer (TMA) to investigate the changes to the mechanical properties of palm leaf manuscripts in response to different relative humidity conditions and different time periods. The short-term study results show that exposure to varying relative humidities leads to changes in the equilibrium moisture content (EMC) of palm leaf manuscripts, causing the bending strength of the samples to decrease significantly with increasing humidity. The bending modulus initially increases and then decreases as the humidity increases. Moreover, the greater the desorption hysteresis of the samples, the more pronounced the changes to the mechanical properties. Therefore, a stable environment in terms of humidity can prevent changes in the mechanical properties of palm leaf manuscripts, thereby preventing the onset of degradation. The results of the long-term aging studies indicate that prolonged exposure to either very dry or very humid conditions greatly affects the mechanical properties of palm leaf manuscripts, which is detrimental to their preservation. The samples kept at 50% RH did not exhibit significant signs of deterioration, with no notable changes in their mechanical properties or chemical structure. This suggests that 50% RH is a relatively optimal humidity condition for the preservation of palm leaf manuscripts.

Palm Leaf Manuscripts represent a significant component of the world’s cultural heritage. Investigating their primary chemical components and understanding the transformations these materials undergo under environmental influences are crucial for elucidating their material characteristics and aging mechanisms and developing effective strategies for preventive conservation. This study utilized infrared absorption spectroscopy and X-ray diffraction analysis to examine changes in the primary chemical components of Palm Leaf Manuscripts under varying relative humidity conditions over extended periods. The findings reveal that dry environments lead to surface cracking, while humid environments promote mold growth, both of which contribute to the degradation of the primary chemical components. These degradative processes reduce cellulose crystallinity and thermal stability. The deterioration is particularly severe under high humidity, with hemicellulose degrading faster and more extensively than cellulose under the same conditions. After 200 days of aging at 10% RH and 90% RH, cellulose degradation reached 19.82% and 54.40%, respectively, while hemicellulose degradation was 34.78% and 64.28%. Correspondingly, the relative crystallinity of cellulose decreased by 8.01% and 13.11%. In contrast, samples maintained at 50% RH exhibited minimal deterioration, with cellulose and hemicellulose degrading by only 4.08% and 13.55%, respectively, and a 6.61% reduction in cellulose crystallinity. These results suggest that a relative humidity of 50% is optimal for the preservation of Palm Leaf Manuscripts. This study offers significant insights into the ageing mechanisms and preventive conservation of Palm Leaf Manuscripts, as well as other cellulose-based organic heritage materials.

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.

The mechanical properties of palm leaf manuscripts, a unique organic cultural heritage material, are strongly influenced by environmental conditions that directly determine their physical stability and long-term preservation. This study systematically examined the effects of natural and accelerated aging under different temperature, humidity, and light radiation conditions on the mechanical and chemical properties of palm leaf samples. Flexural strength and flexural modulus were measured to assess mechanical degradation, while FT-IR was employed to evaluate chemical structure changes. The results revealed that temperature had a pronounced effect on mechanical performance. At −20 °C, a temporary increase in flexural strength and modulus was observed due to the structural stabilization caused by frozen moisture, followed by a gradual decline attributed to ice crystal rupture and fiber damage. At 25 °C, degradation progressed steadily, while at 100 °C, the material underwent severe shrinkage and deformation, resulting in significant cracking and a subsequent sharp decline in its mechanical properties. Relative humidity also played a critical role: excessive dryness (10% RH) led to shrinkage and cracking, whereas high humidity (90% RH) caused microbial degradation and hydrolysis, both resulting in sharp declines in strength and stiffness. Samples aged at moderate humidity (50% RH) maintained superior mechanical stability. Light radiation further accelerated deterioration of mechanical properties, with UV exposure inducing the most significant loss due to photochemical reactions that disrupted lignin structures. FT-IR analysis confirmed that the degradation of cellulose and hemicelluloses was a significant cause of mechanical weakening. Overall, extreme environmental conditions accelerated both physical and chemical deterioration. Conversely, moderate and stable environments (around 25 °C, 50% RH, and limited light exposure) were found to be optimal for preserving the mechanical and structural stability of palm leaf manuscripts. These findings provide valuable guidance for the long-term conservation and environmental control of ancient organic manuscripts.