Writing paper was once widely used, and a large number of archives with writing paper as the carrier were kept in archives, such as manuscripts, letters, diaries, etc., which were mostly written on this kind of paper. Due to the defects of modern papermaking technology and the poor preservation environment, archives with writing paper as the carrier are easily corroded by acidic substances and even face devastating damage. Exploring and establishing a reasonable large-scale deacidification process has become an extremely difficult task for archives departments. Deacidification of archival paper is an extremely important link in the restoration of paper archives. It refers to the neutralization of acidic substances in paper and the precipitation of a certain amount of alkaline substances (alkali reserves) in the paper to neutralize the acidic substances produced in the subsequent natural aging process, aiming to delay the aging speed of paper and increase the life of paper. At present, the domestic large-scale deacidification system is still dominated by aqueous solution deacidification, but this is also limited to very few libraries and archives. Commonly used deacidifiers are: carbonates, bicarbonates, hydroxides, metal oxides, amine compounds, metal alkanes, metal alkoxides, amino-substituted silanes, borax, etc. Most of these various deacidification agents act on the paper to be treated by soaking, spraying or brushing. Based on the type of stabilizer selected in the deacidification agent, the deacidification process system can be roughly divided into: aqueous phase deacidification, non-aqueous phase deacidification, and dry deacidification process.
In recent years, the non-aqueous phase deacidification system using alkaline magnesium oxide (MgO) particles as deacidification agents and organic solvents (perfluoroheptane, cyclohexane, isopropanol, etc.) as stabilizers has become a hot topic in academic and applied research at home and abroad. However, the current research on the MgO particle deacidification system mainly focuses on the preparation of alkaline particles of different sizes and the search for a better deacidification agent stabilization system, while the research on the aging behavior after deacidification is relatively blank.
Chen Ling and Huang Xiaoxia from the School of Information Resources Management of Renmin University of China once systematically explained the series of aging behaviors of acidic writing paper archives after deacidification by the MgO system from the perspective of chemical reaction kinetics in the article “Aging Behavior of Non-aqueous Phase MgO Deacidification System in Paper Archives Deacidification” from the perspective of chemical reaction kinetics, and combined with complete physicochemical characterization to confirm the correctness of the kinetic theory. At the same time, standard ultraviolet, dry heat and wet heat aging experiments were used as research methods to explore the changes in the physical and chemical properties of the acidic writing paper used in archives after being deacidified by micron- and nano-sized alkaline magnesium oxide (MgO) particle deacidification solutions under different external conditions.
The original author used micron- and nano-sized MgO non-aqueous phase deacidification systems to deacidify the acidic writing paper used in archives, and focused on combining dry heat, ultraviolet and wet heat aging tests to analyze the changes in the physical, chemical and optical properties of the deacidified writing paper during the aging process. From the SEM and EDS analysis results, it can be seen that compared with the micron-sized MgO particles that aggregate on the surface of the paper in blocks, the nano-sized MgO particles are smaller, have good dispersion and can micro-penetrate into the shallow surface of the paper. The pH of the deacidified writing paper is significantly increased but still acidic. After three aging processes, the deacidified paper samples maintain a good pH value, among which the paper samples treated with nano-sized MgO show better pH aging results. After dry heat and UV aging, the mechanical properties of the deacidified writing paper in the transverse and longitudinal directions changed little. With the increase of wet heat aging time, the number of folding endurance of the deacidified paper sample decreased exponentially, and the tensile strength remained unchanged. The whiteness of the three groups of experimental paper samples decreased significantly after UV and dry heat aging, and the chromaticity difference changed greatly (all greater than 1.5). With the increase of wet heat aging time, the chromaticity and whiteness difference of the three paper samples showed a nearly linear change process (3~15 days). The two deacidification systems did not significantly improve the mechanical properties of paper, but both could slow down the yellowing rate of paper.
Overall, the MgO non-aqueous phase deacidification system has a good deacidification effect on acidic archives with writing paper as the carrier, which can slow down the aging rate of fibers and increase the life of acidic writing paper archives.