In protecting cultural heritage, deacidification is used to stabilize acidic papers, ensuring the neutralization of acids present in the paper. But in the process of aging, several mechanisms of degradation occur simultaneously. Therefore, substances used to stabilize the paper should contain an antioxidant component in addition to the deacidifying component. The effect of the antioxidant (hindered amine light stabilizers—HALS type) on the stabilization of lignin-containing acid papers during accelerated aging was studied in this work. The effective deacidification component was magnesium; the solvent was hexamethyldisiloxane (HMDSO). The 4-amino-2,2,6,6-tetramethylpiperidine series of hindered amine light stabilizers (HALS) was selected as appropriate for creating a modifying system based on HMDSO. The modification system was tested on samples of a model test acid lignin-containing paper (NOVO) and naturally aged acidic paper from the real book. The addition of substances to the proposed deacidification system has a favorable effect on stabilizing the pH during aging and provides the inhibition of the oxidative degradation products and stabilization of the cellulose degree of polymerization. It was confirmed that the application of the system containing deacidification and an antioxidant component may increase the effectiveness of the protection of acid groundwood paper heritage objects. Adding a tested antioxidant to the proposed deacidification system has a favorable effect on stabilizing the pH value for a long time in accelerated aging.

From the perspective of deacidification and stabilization of paper as an information carrier, it is crucial to understand its interactions with water, including the transport of substances into and out of its structure, with consequences such as the swelling and shrinking of cellulose. Interactions of paper and water are significantly influenced by the paper’s structure, its composition, and the manufacturing process itself. The article focuses on studying changes in the water-paper interaction (liquid water and water contained in the moist air) on four model samples subjected to accelerated aging. The experiment is set up to simulate possible interactions occurring in the preservation/conservation processes of paper information carriers. The most significant result is the finding that an RH of 75% represents the ideal value of relative humidity for the treatment of paper information carriers, sufficient to ensure transport processes in the paper structure and at the same time not leading to excessive swelling or irreversible degradation of the paper yet. This point represents RH of the environment, where bound freezing water changes to free capillary water (second point from the isotherm). It is independent of paper composition and is not affected by aging.