Investigating the moisture sorption behavior of naturally and artificially aged bamboo paper with multi-analytical techniques

Hygroscopicity affects the chemical and physical stabilities of paper-based historical relics. In this research, the moisture sorption behavior of naturally aged bamboo paper dating from the Qing Dynasty to the Republic of China, and artificially aged and untreated modern bamboo paper was investigated using dynamic vapor sorption analysis (DVS). The results were fitted by sorption models to analyze the regularities of changes in the moisture absorption of aged bamboo paper. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the chemical and physical structures of aged bamboo paper. It was found that untreated and aged bamboo paper showed similar moisture sorption isotherms at 25 °C, indicating that aging did not alter the sorption mechanism of paper. Guggenheim Anderson de Boer (GAB) and Hailwood Horrobin (H–H) models provided good fits to the experimental data and meaningful physical parameters regarding the effective sorption surface area (SGAB), monolayer water content (W0), and multilayer water content (Ws), showing that the SGAB, W0, and Ws of naturally and artificially aged bamboo paper were decreased. Results of FTIR demonstrated that the levels of hydrophilic groups decreased, causing a reduction in the effective adsorption sites of naturally and artificially aged bamboo paper, which was the principal reason for a decrease in their hygroscopicity. The fiber structure damage of naturally and artificially aged bamboo paper was observed through microscopic morphology, which has different influences on the capillary adsorption of paper depending on the extent of degradation.