The aging of Springhill™ offset paper, a typical alum-rosin-sized book paper from a few years ago, was undertaken under several different aging conditions. Experimental data on the deterioration of physical, optical and chemical data were obtained. However, for the sake of brevity, only the data on loss of fold endurance are summarized in Table 1. For each aging condition, a relative lifetime " T ", which equals three half-lives for the MIT fold number, is calculated as a convenient measure of the rate of degradation.
As might be expected, single sheets aged at 80°C /65% RH age just a little more slowly than those aged at 90°C /25% RH. Stepping up the relative humidity from 25 to 50% and maintaining the temperature at 90° doubles the rate of degradation. At 90°C and 50% RH, paper in stacks ages twice as fast as single sheets. Sheets sealed inside PET or polypropylene, which is less permeable to moisture, aged at about the same rate as the sheets within paper stacks when both, the stacks and the encapsulated sheets aged at the same rate. However, when the same encapsulated sheets were aged in a dry oven at 90°C, the rate of deterioration of paper slowed by as much as six times. Evidently, the porosity of the plastic films permits the moisture to escape, reducing the moisture content of paper. Finally, sheets sealed within aluminized PET and aged at 100°C are shown to have a relative lifetime of only 6 hours when 10 sheets are enclosed inside the sealed bag, as compared with 15 hours for a single sheet inside the same enclosure. These relative lifetimes compare with 12 days for the same paper when aged conventionally as single sheets at 80°C and 65% RH.
There is no virtue in a mere acceleration of the rate of degradation. However, it is a big plus when it is accompanied by a more realistic aging method and also does not require specialized and expensive equipment such as a humid aging chamber. Humid aging experiments have also been carried out in closed containers over salt solutions. However, having learned the role that degradation products play in the aging of paper, one might question the use of such experimental setups since all solutions would tend to absorb these compounds.
Further work in progress in our laboratories is aimed at the study of a variety of variables in sealed enclosure aging. These include the effect of moisture content and air volume inside the enclosure, and a comparison of activation energies among different accelerated aging methods. If the Arrhenius relationship does not hold at higher temperatures, the rate of this aging technique is fast enough to allow us to go to appreciably lower temperatures. In other experiments the degradation products from different accelerated aging methods will be compared with those extracted from naturally aged books. The greater the number of commonalties we can find with natural aging, the more acceptable an accelerated aging method will become.
We need to introduce a word of caution about the use of aluminized PET bags. Within a few days of the aging process, degradation of PET reaches such an advanced state that the whole bag just crumbles. We believe that acid hydrolytic degradation of polyester induced by the products of degradation of cellulose is the cause. An empty bag without any paper in it does not degrade noticeably even after weeks of aging. Therefore, we have discontinued the use of such bags and are now using capped glass tubes, which are much more convenient too.
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