Accelerated Aging of Paper: Can it Really Foretell the Permanence of Paper
Measurement of Rates of Degradation
The experimental setup for accelerated aging, which we have discussed extensively so far, provides only part of the methodology that needs to be standardized. We also need a broad consensus on what properties of paper we need to quantify the degradation of paper as it ages. Ideally, we should measure selected properties among each of the three dimensions that paper presents to us, namely, physical, chemical and optical.
Most research laboratories come to develop a preference for a selected set of tests that they may have practiced over long stretches of their history, just as there are tests that are liked, there are also those that are not liked. However, few tests for physical testing of paper arouse as much passion as the fold endurance test. It has been said that this test is not functional, it is too time-intensive, and that it fluctuates too wildly to be of any practical use. The NISO committee on permanent paper saw it fit to drop this test from its requirements and place its confidence entirely on a tear resistance requirement.
At the Library of Congress, we have recently completed a lengthy study on a comparison of a host of physical and chemical properties. In this study, three very different papers were subjected to accelerated aging at 90°C and 50% RH for a period of 90 days. The decline in several physical, chemical and optical properties was measured periodically. Selected data for some physical properties are shown in Figure 4. The percent loss in MIT fold endurance, tensile energy absorption, tear and burst is presented as a function of aging time for a single test paper. Clearly, the fold endurance test is much more sensitive than the other three tests. While percent loss in tear resistance is only about 35 percent and that in tensile energy absorption is almost 40 percent, fold endurance has lost 90 percent of its initial value. The sensitivity of this test more than makes up for its high standard deviation.
In fact, its high standard deviation is mainly a result of its high sensitivity to the homogeneous structure of paper. Besides, the high standard deviation can easily be lowered by an appropriate statistical treatment if desired. However, for measuring the physical properties of weak paper, fold endurance is at a decided disadvantage, unless it were to be modified in some way. This is not intended to be an exhaustive discussion of the physical properties of paper, for it would not be complete without an honorable mention of the zero span tensile test.
Table of Contents - Introduction - Status of Accelerated Aging of Paper - Research in Accelerated Aging of Paper - Comparison of Accelerated Aging of Paper in Stacks and Sheets - Aging of Paper Sealed within Polyester Film - Inadequacy of Single Sheet Accelerated Aging Methods - Accelerated Aging within Sealed Enclosures - Comparison of Accelerated Aging Methods - Accelerated Aging under Light -Measurement of Rates of Degradation - Conclusion - References - Supporting Documents