Accelerated Aging of Paper: A New Test
Need for a Reliable Aging Methodology
The Library of Congress has developed a new accelerated aging test that closely simulates the natural aging of paper and provides a highly reliable evaluation of the longevity of papers, regardless of their pulp or chemical composition. A dependable accelerated aging test is at the heart of major preservation policy decisions that attempt to extend the life of library and archival collections.
Simple and Economic Design
In this test, preconditioned paper samples are sealed inside an airtight glass tube and are then heated at an elevated temperature in a simple laboratory oven. No longer needed are the expensive and problem-prone humid aging chambers required by currently-accepted accelerated aging tests to provide a controlled humidity and temperature environment. These aging chambers have also been the root cause of a lack of reproducibility of aging data among different laboratories, as the range within which environmental conditions fluctuate varies greatly among different chambers. The simpler and more economic design of the new test should enable many more laboratories to perform it.
Faster Test Simulates Natural Aging
The new test is also appreciably faster, requiring only 5 days to complete as compared to 30 days or longer for some other tests. Most importantly, this is the first time an accelerated aging test has been meticulously demonstrated to simulate the natural aging process. When naturally-aged papers are subjected to this test, the degrad-ation products already formed in nature increase in their concentration levels in proportion to the aging time. Moreover, no new or different chemicals, other than those already formed during natural aging, are produced in the accelerated aging process. Clearly, no new, unnatural chemical reactions are initiated in this accelerated aging test.
Development of the Test
In the development of this new methodology, a variety of acid and alkaline test papers -- bleached softwood kraft, cotton, and groundwood papers -- were aged as single sheets, as has been the accepted practice until now, but also in book-like stacks and within airtight glass tubes. Chemical analysis of degradation products formed in the aging process was used to compare (1) differences among the test methods and (2) the resulting chemical changes with those that occurred during the natural aging of similar papers. Accelerated aging within airtight glass tubes, which retained volatile degradation products best, showed the greatest similarity to natural aging.
New Insight: Spontaneous Formation of Acids in Paper
The chemical analysis of aged papers revealed for the first time that formic, acetic, lactic, oxalic, and other acids form spontaneously in the aging of all cellulosic papers, including highly stable cotton papers. Easily measurable concentrations of these acids were formed even in their natural aging at room temperature in a few short months. The formation of these acid molecules and their incessant accumulation was identified as a primary cause for the progressive increase of acidity in paper as it ages, which, in turn, leads to autocatalytic acid hydrolysis of cellulose in acidic papers. That is, acidic papers continue to deteriorate at an ever escalating rate. The same acids form in alkaline papers as well but are neutralized by the alkaline reserve. Until now, only acids introduced in the manufacture of paper and those absorbed from the environment have been believed responsible for the degradation of paper.
For further information on paper deterioration please see the brochure entitled: