The rapid deterioration of modern papers results from the use of acids, which break down the cellulose fibers into ever shorter segments and thereby weakening the paper. The acid deterioration may be accompanied by yellow or brown discoloration, a condition brought about by the use of alum-rosin compounds as sizing agents which generate sulfuric acid when atmospheric moisture is present.
The use of groundwood or unpurified wood fibers rather than chemically purified pulp is another factor in modern paper deterioration. The lignins or “glues” which hold the fibers together as wood degrade to form acids which weaken the paper.
Although most papers contain some unpurified wood fibers, the most common example of groundwood paper is newsprint.
Other factors influencing paper deterioration are: atmospheric pollutants such as sulfur dioxide, nitrogen dioxide, and ozone; the invisible radiation of sunlight and fluorescent light; the short wave lengths of visible light; the growth of microorganisms such as mold and bacteria; and insects and rodents which feed upon the paper.
(Source: Guidelines for Restoration and Preservation of Documentary Papers, Maps, Books, Maine State Archives, www.state.me.us/sos/arc/general/admin/doconsrv.htm)