Leather embrittled

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. 

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. 

As a preparative technique, the present radiation grafting process is useful for polypropylene and cellulose, however with leather care is needed, since the solvents tend to dry out this trunk polymer and embrittle it with time. Thus for many leather treatments, the radiation rapid cure processes mentioned at the end of this paper are to be preferred. 

The leather specimens are aged (a) at 50 °C for 7 days or (b) at 80 °C for 3 days. They are then assessed to see whether heat aging has resulted in embrittlement, yellowing or a change in the flexing endurance. 

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