Hydrolysis, paper deterioration

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. 

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]. 

A few animals (especially ruminants and termites) are able to metabolize cellulose, but even these animals depend on appropriate microorganisms in their intestinal tracts to hydrolyze the -1,4 links other animals, including man, cannot utilize cellulose as food because they lack the necessary hydrolytic enzymes. However, such enzymes are distributed widely in nature. In fact, deterioration of cellulose materials —textiles, paper, and wood —by enzymatic degradation (such as by dry rot) is an economic problem that is not yet adequately solved. Efforts to turn this to advantage through enzymatic hydrolysis of cellulose to glucose for practical food production have not been very successful (see Section 25-12). 

Oxidation and acid hydrolysis are the two principal deterioration mechanisms for paper, and recently chemiluminescence (CL) has been used to follow the oxidation of cellulosic materials at temperatures of 40 °C and below (I). CL is thought to be produced by the termination... 

Less recognized but also important is SO- damage to paper and leather. Paper products produced from about 1/50 on are embrittled by sulfur compounds converted to sulfuric acid which causes hydrolysis. Thus old books which are not stored in sealed cases undergo a gradual deterioration. Leather bindings are similarly affected. 

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. 

Polycarbonate is widely used in a nnmber of thermoplastic applications due to transparency and toughness. Copolymers of polycarbonate (PQ with polydimethyl siloxane (PDMS) fiirlher expand the property space to include extreme eonditions such as impact retention up to -60°C. It is known that hydrolysis of a carbonate linkage may lead to severance of polymer chains and may lead to deterioration of mechanical properties of polycarbonates under some conditions. Similarly for a molded part, physical aging at elevated temperatmes can also lead to deterioration of notched Izod impact of an amorphous polymer like polycarbonate . So, when a molded polycarbonate part is exposed to heat and humidity a combination of hydrolysis and physical aging may accelerate the property loss. Numerous approaches have been published in the past that leverage the use of various stabilizers to incrementally improve the performance. In this paper, we present the data for copolymers of polysiloxane with polycarbonate and their substantially improved heat aging and hydrolytic aging characteristics. 

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