Aging, paper deterioration

The main cause for paper deterioration in libraries and archives is the acid catalyzed hydrolysis of cellulose, the ingredient that gives permanence to the paper. The aging permanence of paper is closely coimected with the add concentration in the paper. The priority in preservation measures is in most cases the dead-dification of acid paper. Today, more than 70 years after Barrow s pioneering work, mass deacidification of books and archive materials has become a commerdal reality. 

Measurement of pH is a potentiometric technique frequently used for measuring the degree of the deterioration of materials that are subjected to natural aging. The determination of pH levels is commonly carried out on ethnographic objects manufactured with parchment or leather, and it is especially relevant in altered paper due to the formation of acidic compounds from the decomposition of the woodpulps and other raw materials, which can induce the hydrolysis of the cellulose and then decrease the resistance and mechanical properties of the document [29]. 

Old manuscripts printed on high grade paper with acid inks, in particular the iron inks commonly used in the Middle Ages, showed significantly greater deterioration than manuscripts printed with neutral or alkaline inks (2). 

Fold Loss Rate. A direct way of evaluating the effect of the morpholine process on the stabilization of paper is to measure the rate at which its folding endurance deteriorates before and after treatment. Figure 4 typifies the effect. The two lines are for the same paper aged in a dry oven at 100°C the line with the lesser slope reflects morpholine-treated... 

It is accepted that the strength properties of paper must be at a satisfactory level in the paper as manufactured in order to meet the necessary use requirements. Moreover, a paper of higher initial quality according to these tests may be expected to have a longer useful life than one of lower quality as progressive deterioration takes place if aging rates are similar under any established conditions. 

The examination of fold endurance and tensile strength of a series of polymer-paper systems under thermal accelerated aging indicates that only in the most favorable of circumstances is it possible to apply the Arrhenius equation to the system. It also seems unlikely that a sample addition relationship exists between the behavior of the individual components and their behavior as a system. A straight line plot of log folding endurance vs. aging time may reflect a fortuitous composite of several experimental variables leading to pseudo-first-order deterioration. 

Matched sets of folding endurance and tear resistance test specimens were prepared from each paper to be aged at several temperatures. Aging was done in forced circulation ovens that were supplied with air having a dewpoint of 53°F. At intervals, sets of test specimens were removed from the oven and tested to monitor the deterioration process. 

Figure 1. Machine direction folding endurance deterioration of an acid book paper upon heat aging...

A much more recent development is the morpholine process in which fifty books per hour are treated in an evacuated chamber with morpholine-water vapor (12). In its present form, it was effective on 95% of the papers treated, prolonging their life on average by a factor of 4-5 (Figure 7). Though it does not leave a titratable alkaline reserve in the paper, acid papers treated in this manner aged in the presence of 5 ppm S02 at 75 °C and 60% relative humidity deteriorate more slowly than if untreated. Recent tests of twenty treated books at the Library of Congress show that their pH has not declined in two years. The equipment for the process was set up in the Virginia State Library where 35,000 books were treated in the first seven months of operation. 

Figure 6. The effect of calcium content on rate of deterioration of papers rate of deterioration is taken from the slope of the log folding endurance vs. time of aging curve (9) FK dry, (O) FK humid, (A) NP dry, (A) NP...

Celluloses are similar to other linear polymeric materials in that they can possess one-dimensional order within an individual chain as well as three-dimensional order within an aggregate of chains. Increments in the levels of order occur during the isolation of native celluloses and also as a result of exposure to conditions that promote molecular mobility, such as elevated temperatures and immersion in plasticizing fluids. These increments generally result in embrittlement of the cellulosic materials. Similar effects are expected to occur upon aging of cellulosic textiles and papers over extended periods, and may be accelerated by hydrolytic cleavage of cellulosic chains. The implications of these effects for conservation practices, both with respect to recovery of function as well as in the assessment of deterioration, are reviewed. 

The Arrhenius treatment has been applied to aging studies on rubber (13), to predict the life of a polyester-glass laminate (14), to predict product stability of a thermosetting resin alone and in combination with two additives (15), in permanence tests on paper (16), to multi-component systems in which the principal component is paper (17), and to study the influence of temperature on the relative contributions of the oxygen-independent and oxygen-dependent processes to the total rate of newsprint deterioration (18-20). 

Many conservation treatments have been devised to slow down the rate of deterioration of paper. Often these treatments neutralize excess acidity in paper, which is an important factor in paper permanence. The probability of success with a new method is often determined by the use of accelerated aging tests and also by drawing parallels with existing methods thought to be effective. Many studies have investigated the best conditions for accelerated aging tests, but disagreement between laboratories is often found. However, even the best set of conditions produces a distortion of the results that would have occurred in ambient conditions. 

The paper and textile industries have been concerned about the aging, deterioration, and degradation of cellulosic materials at elevated temperatures for practical reasons, such as the performance of tire yarn and electrical insulation paper, and the problems involved in drying or processing the cellulosic materials in general. However, due to the practical nature of these problems, the reactions involved have often been measured in terms of loss of strength and other physical properties. 

Evidence exists that at least three reactions, hydrolysis, oxidation, and cross-linking, contribute to the deterioration of paper (4, 5, 6). The magnitude and rate of change of a specific physical property will depend on the extent one reaction proceeds relative to the others. It must also be recognized that each degradatlve reaction is affected differently by environmental variables and the results obtained from an accelerated aging test will depend on the selection of the environmental variables. It is therefore necessary to establish the relative importance of each environmental variable. 

The deterioration of paper in books and documents has been a concern for many years. Research by paper conservators indicates that books and manuscripts may be protected from aging by treatment with alkaline agents viiich neutralize the acidity of the paper as it develc s (3,, , 6,2). ie deaoidification process not oily neutralizes the acTdity of the oxidized cellulose, but also leaves an "alkaline reserve" in the paper to retard future deterioration. 

When an object turns fragile because of its age and the consequent deterioration of the material, as is the case of textiles, papers and many objects from... 

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