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 can’t line an acid box with acid
free paper and expect it to remain acid-free.