Leather acid-deteriorated

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]. 

Materials and Structures. Building materials have become soiled and blackened by smoke, and damage by chemical attack from acid gases in the air has led to the deterioration of many marble statues in western Europe. Metals are also affected by air pollution for example, S02 causes many metals to corrode at a faster rate. Ozone is known to oxidize rubber products, and one of the effects of Los Angeles smog is cracking of rubber tires. Fabrics, leather, and paper are also affected by S02 and sulfuric acid, causing them to crack, become brittle, and tear more easily. 

Bindings covered with vegetable-tanned leather are washed with pure toilet soap, saddle soap, or mild, high quality surgical toilet soap and a 7-10% solution of potassium lactate. 0.25% of p-nitrophenol can be added as a fungicide, but this is not necessary if the temperature and relative humidity are constantly satisfactory (see p. 5). The lactate, when applied to new vegetable-tanned leather, is thought to protect the leather from the deleterious action of sulfuric acid which usually forms in leather when sulfur dioxide is absorbed. It is. probable that it has little efficacy once chemical deterioration has started, and for some years doubt has been cast on its effectiveness, even on new leather, despite favorable results in laboratory tests. However, it is used, and its use is advocated just in case it is beneficial. 

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. 

The results showed that while none of the books stored in the clean Welsh environment had deteriorated to any significant extent, nearly all the volumes subjected to London s acidic pollution exhibited evidence of decay, some within less than 10 years. In addition, the superior ageing properties of leathers prepared with hydrolysable tannins were confirmed. Of the various chemical analytical determinations undertaken, the only results to show any correlation with the degree of deterioration observed were those for the number of -terminal amino acid groups on the protein. This figure reflects the amount by which the collagen polypeptide chain had been broken and was considered to be evidence for hydrolytic deterioration. 

It can be concluded that chemical degradation of vegetable-tanned leather will occur in both polluted and unpolluted environments, and that both oxidative and hydrolytic reactions are always involved. The preponderant mechanism will depend on the exact conditions to which the leather is subjected. It should also be noted that the rate of decay of leathers exposed to the mainly hydrolytic effects of acidic urban atmospheres is much greater than the oxidative deterioration found with leathers held in cleaner rural surroundings. 

A number of techniques using similar concepts were developed over the years to treat leathers that had already deteriorated. Aqueous solutions of potassium lactate were routinely applied to the surface of bookbindings and other leather objects. Unfortunately, in many cases, the deleterious effects of the liquid water solvent on acidic leathers took place before the buffer salt neutralised the acid, resulting in dark, seriously embrittled leather. In order to avoid the effects of aqueous solutions, methods were tried employing ammonia vapour. The object was placed in an enclosed chamber over an open dish of ammonium hydroxide solution. However, ammonia vapour is a strong alkali and there is a danger that even with the use of dilute solutions, leathers that were too acidic would be transformed into ones which were too alkaline. Another alternative was to use an organic base such as imidazole in a non-aqueous solvent. However, this was also liable to result in leathers that were too alkaline. 

Wood-filled PVC has inferior mechanical properties because of lack of interaction. Treatment of wood filler with aminosilane improves acid-base interaction between filler and polymer to the extent that impact strength and tensile properties of composite are improved over unfilled PVC. Tensile properties of PVC were deteriorated when leather particles were used as a filler. But, after filler particles were treated with ethylene-vinyl acetate copolymer, a coating was produced on the surface of filler particles that promoted adhesion with PVC and improved mechanical properties.These are some recent examples of many applications of filler preparations to improve its interaction with PVC. 

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. 

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