Washington, D.C. 20540
A commonly held view is that paper deterioration slows down over time and that highly acidic paper will actually remain in usable condition indefinitely if it is properly stored and handled.
Research here at the Library of Congress and at other institutions, however, clearly demonstrates that the degradation and embrittlement of paper does not in fact stop. Research completed this year, based on extensive analysis of deterioration byproducts from naturally and artificially aged papers, confirms that accelerated aging is a valid and reliable test to predict paper longevity.
The research also demonstrates that:
All cellulose-based papers spontaneously generate aliphatic acids such as acetic, formic, oxalic and lactic acids as they age.
Measurable concentrations of these acids have been observed to form at room temperature within a few months of the formation of paper. These acids form even in alkaline papers, although they are probably neutralized soon enough in such papers.
Acids attach themselves to the paper matrix through hydrogen bonding and are not easily dissipated into the environment, particularly when paper is stacked or bound in a book. The accumulation of these acids within closed books continues inexorably and is the basis of a constant and continuous increase in the rate of degradation of paper.
There are some modern paper-based materials (books and manuscripts) that become brittle and basically unusable within only a few decades of their creation. Yet others printed or handwritten on paper made hundreds of years ago survive in nearly pristine condition.
Why do some papers deteriorate rapidly while others appear to be little affected by the passage of time?
The answers are found in the composition of paper, the causes of its deterioration, and the conditions under which it is stored. Early papers were made by hand from cotton and linen rags. Most early papers, especially those made from about the 12th to the middle of the 19th century, are strong and durable. If properly stored, the majority of books published during that period are still in excellent or good physical condition.
But most modern book papers, unless they are of the types designated as permanent-durable or acid-free, have an expected useful life of only a few decades and will not last even that long if they are housed in improper environments.
The primary reason that modern papers deteriorate fairly rapidly is that they are acidic — a condition brought about largely by the use of alum-rosin compounds as sizing agents during the manufacturing process. In the presence of moisture, the sizing agent generates sulfuric acid that destroys the paper.
Another factor that promotes deterioration of some modern papers, such as the newsprint in mass-produced newspapers, is the use of groundwood in its manufacture. This pulp is made by the mechanical grinding of wood that is then made into paper without first purifying it chemically. Papers made by this process are substantially weaker than those made of chemically purified wood pulp (like we often see in books).
Also in newsprint, lignin remaining in the pulp degrades to form acids and peroxides that further promote the aging process. Newspapers (made from this groundwood) are more subject to degradation by light than most of the papers used to print books.
Additional factors contributing to the deterioration of paper include atmospheric pollutants; ultraviolet radiation in sunlight and fluorescent light; and microorganisms such as mold.
For those materials that are acidic but not already highly embrittled, we can save many of them today through use of a new technology known as Mass Deacidification. Deterioration of paper due to its chemical composition and other factors can be dramatically minimized by treating the paper with a process that neutralizes the acids in the paper.
Deacidification treatment enables libraries and archives today to treat books and manuscripts so they will remain in usable condition for several centuries rather than becoming brittle and unusable in only a few decades.
We have already saved over 1/3 million books at the Library with Mass Deacidification and have plans, recently approved by Congress, to use this technology in future years to extend the useful life of millions of books as well as unbound manuscripts and other paper materials in our custody.
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