Deterioration of Paper

Paper objects may suffer from damage by vermin, insect and microbial attack, theft, fire and flood. However, from a chemist s point of view there are two important mechanisms by which paper deteriorates, both of which may change its hue and make it weaker these mechanisms are acid-catalysed hydrolysis and oxidation. Papers vary a lot in their stability and the worst can become so brittle that they become unusable. Papers made from rags using traditional methods are usually extremely stable, but old papers made from poorly processed wood pulp are often very weak. 

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Another problem conservators face is the deterioration of paper by exposure to light it is discussed in Chapter 4. Paper is hydrophilic and may turn yellow over time. The importance of controlling the ambient atmosphere in which books are stored is brought out in Chapter 5, and yellowing is discussed in Chapter 6. 

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...

The principal task of PAPER CONSERVATORS is to slow down the processes of deterioration that occur in the objects in their care. Paper artifacts are made from papers having a wide range of stabilities some papers are quite permanent, whereas others degrade relatively rapidly. Additionally, the rate of deterioration of paper may increase because of improper storage conditions. 

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. 

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. 

The first comprehensive and systematic work on the reasons for deterioration of paper was performed by WJ. Barrow in the 1960s who firmly established the link between the acidity of paper and its permanence. Although we talk about the acidity of a sheet of dry paper, the acidity of paper, expressed as pH is only measured in an aqueous extract, generally produced by macerating 1 g of paper in 50 mL of pure water. 

In this section, we will concentrate on heat ageing which is intended to reproduce the effects of ageing in the dark and in the absence of air pollutants. Chemical reactions in general, and those which cause deterioration of paper in particular, slow down when the temperature is decreased and accelerate when the temperature is increased. In response to this fact, some libraries and archives have built stores that can maintain a low temperature to prolong the life of their collections. There is an equation that was defined by Arrhenius, which can be used to predict the effects of temperature on the rate of chemical reactions/ageing, here it is ... 

The deterioration of paper is manifested in several ways, for example, extensive discolouration and loss of mechanical strength can occur. The early detection of changes and their measurement needs special apparatus. 

In our cities, acid rain is responsible for extensive and continuing damage to buildings, monuments, and statues. It reduces the durability of paint and promotes the deterioration of paper, leather, and cloth. In short, we are just beginning to explore the effects of acid rain on human beings and on our food chain. 

The lack of paper permanence is attributable to both internal and external influences [4]. In addition to sizing materials, internal factors include the type of fiber, coatings, and the presence of acidic and metallic compounds. External variables are the conditions during storage and use. Heat and humidity accelerate the deterioration of paper, and atmospheric pollution is frequently the source of external acid attacks. A comparison of identical volumes stored in the Netv York Public Library and the Royal Library in The Hague proved the importance of proper storage, as the New York books were found to be in a far more advanced stage of deterioration [5]. 

Unfortunately, the low pH papermaking process has been associated with early deterioration of paper. Papers made in the past two centuries have been found to be very short-lived. This is especially troublesome to librarians and others concerned with archival records. 

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