What Causes Acids to Be Present in Papers?
Impurities such as lignin, hemicellulose and hydrolyzed cellulose oxidize and produce substantial quantities of acidic degradation products. Alum-rosin sizing [Al2(SO4)3. 18H2O] added during the paper making process is a prime acid producer. Various deteriorative by-products, such as acetic acid, are produced as paper and film age naturally. These by-products of deterioration then catalyze (cause) further degradation reactions. This deterioration-from-within is responsible for the fact that pages adjacent within a book will deteriorate more quickly than if they were removed and stored individually. Acidic gases and pollutants from the atmosphere such as oxides of nitrogen and sulfur dioxide, form sulfuric and nitric acid. Other culprits are ozone, various peroxides, peroxyacl nitrates and cupric and ferric ions which promote carbohydrate acid through the oxidation of carbonyl and hydroxyl groups. There are also many indoor sources of deleterious pollutants and chemicals. For example, deteriorative agents such as formaldehyde, peroxides, formic acid, and acetic acid can be emitted by wood, plywood, particle board and chipboard. Protein-based glues and wool can yield sulfides. Fumes from an underground parking area can cause elevated interior levels of oxides of nitrogen, and sunlight entering a building can be responsible for increased photolytic reaction rates, resulting in concentrations of oxidative and acidic molecules such as ozone, peroxides, nitric acid and other nitrogen-containing molecules which are present at higher levels inside than outdoors. Acids also migrate from adjacent acidic materials, which is why we canít line an acid box with acid free paper and expect it to remain acid-free.