Traditional handmade bamboo paper has a long history. Since the Song Dynasty, bamboo paper has been widely used in writing and printing. Bamboo paper comprises a large proportion of paper cultural relics, which have precious cultural value. However, many bamboo paper relics are degraded by factors such as temperature, humidity, acid, and alkali in the environment, resulting in aging and the paper becoming yellow and brittle during long-term storage. The aging mechanism of paper is a complex issue in cultural heritage conservation, which hinders the protection of paper cultural relics. Therefore, studying the mechanism of paper aging is the basis for implementing effective protection measures, which are crucial for effectively preserving bamboo paper cultural relics. This study examined the aging behavior of bamboo paper. Traditional handmade bamboo paper samples from Zhejiang Province, whose production technology is listed in the first batch of national intangible cultural heritage in China, were aged artificially by exposure to dry-heat conditions. The microstructure and micro-morphology of the aged bamboo paper were investigated via Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The tensile strength was tested, and the thermal stability was detected by thermogravimetric analysis. The moisture absorption ability was measured by dynamic vapor sorption. The relationship between the effects of aging on the microstructure of paper and performance degradation was revealed. The chemical structure of bamboo paper changed after aging, including the decreased relative intensities of the OH and CO-C stretching vibrations, and new functional groups for C=O generated by the fiber molecular chain were broken. The fiber surface of aged bamboo paper becomes fragmented after prolonged aging, eventually leading to the collapse of the fiber structure. The crystallinity of cellulose increases initially and then decreases due to damage to the fiber structure, suggesting that the crystalline and amorphous regions of cellulose are affected differently by aging. The changes in the microstructure of aged bamboo paper also affect some of its properties. Aged bamboo paper gradually loses its mechanical strength due to degradation of the molecular chains inside the fiber. A persistent decrease in the characteristic pyrolysis temperature of bamboo paper after aging was observed due to damage in the cellulose crystallization region: The initial pyrolysis temperature of 5% mass loss (T-0.05), the temperature of 50% mass loss (T-0.5), and the temperature of maximum mass loss (T-max). Therefore, the thermal stability of bamboo paper deteriorated. Furthermore, the capillary structure, hemicellulose, and amorphous regions of the aged bamboo paper were damaged, decreasing the ability of moisture absorption. The deterioration of the tensile strength, thermal stability, and moisture absorption of aged bamboo paper was caused by the destruction of the chemical structure and crystallinity of the paper fibers. These findings will promote research aimed at protecting aged paper cultural relics. Therefore, in addition to the macroscopic properties of aged paper, more attention needs to be paid to analyzing the microstructure of paper when planning a protection plan for paper cultural relics and evaluating the protection effect, which is vital for achieving a better protection effect.
