Conservation of Paper
Because of natural chemical processes that can attack and degrade paper, librarians and conservationists rely on chemical strategies to preserve our written heritage.
Few of us spend a great deal of time pondering the chemistry of paper. Perhaps when having a piece of artwork, a diploma, or an award framed, the option of having an “archival quality” acid free 100 percent cotton rag mat may be mentioned. When looking through a box of mementos, we notice that newspaper clippings from our youth or from the lives of older relatives are yellowed and fragile, but that simply seems to be an indication of the age of the information. For universities, librarians, and government laboratories as well as the pulp and paper industries, the question of how to preserve our written heritage takes on a very important and very chemical focus.
Paper degrades due to several different types of chemical reactions. First, acid that is present from the paper-making process or introduced from the atmosphere attacks the cellulose in paper fibers, which weakens the polymers and makes the paper more brittle. In a second process, atmospheric oxidation discolors white paper turning it yellow or brown over time.
To address the more critical issue of acid damage, mass deacidification processes are designed to neutralize the acid in the paper and add an extra residue of a weak base to prevent future acidification as a means of halting the degradation process. One of the challenges of creating such a process is that since water tends to swell the paper fibers, it is generally avoided in the process. Most of the various deacidification methods involve a neutralizing agent such as diethyl zinc or magnesium oxide suspended in either a gas or a highly volatile solvent to allow the treatment agent to diffuse throughout the book.
Paper that has severely deteriorated and is falling apart can be strengthened by treating it with several different monomers which create new polymers that integrate with the paper’s cellulose, thus strengthening the paper. Because those methods are irreversible, they are substituted by laborious processes using handmade papers and natural adhesives for the most precious archives such as the Magna Carta, signed in 1215 A.D. But both options are important for the preservation of our written and illustrated past.
Advice from the Library of Congress about how to preserve paper artifacts can be found at http://www.loc.gov/preservation/care/paper.html