Vegetable-tanning

The apphcation of vegetable tanning materials has an additive effect on the leather. The more vegetable tannins appHed the more the leather becomes like vegetable-tanned leather. The color is changed, the fullness of feel increases, and the leather can be worked and embossed like vegetable leather. 

Any vegetable tanning extract used commercially is a complex mixture of related substances. The individual tanning properties of the extracts have been extensively studied and are weU known in the industry. 

The si2e of the vegetable tanning molecules and the coUoidal nature of the system result in the fixation in the hide of filling materials. The filling action is essentially an impregnation of the hide to form a dense firm leather. These properties are gready desired in sole and mechanical leathers. 

Vegetable-tanning materials in commercial quantities come from many different countries. Quebracho is a principal tanning material from South America. Wattie or Mimosa is suppHed from several African sources. India and other Asian countries supply a variety of materials including Myrabolans, Gall Nuts, and Tara Pods (3). 

The vegetable-tanning materials are commercially extracted using hot water. The extraction is normally done in countercurrent extractors that permit the final removal of the extracts with fresh water. The dilute extracts are then evaporated to the desired concentration in multiple effect evaporators. Some extracts may be further dried by spray drying or any other means that proves effective without overheating the extract. Extract preparation depends on the type of extract, the si2e of the operation, and the desired concentration of the final product. 

The chrome tanning is one step in a compHcated series of leather operations leading from the raw hide to the finished products. Chrome tanning is the most important tannage for all hides except heavy catde hides, which are usually vegetable tanned. In heavy shoe uppers and soles, a chrome tanned leather is frequently given a vegetable retan to produce chrome retan leather. 

Howes, F. N. (1953), Vegetable Tanning Materials, Butterworth, London. 

Howes, E., 1953, Sumac. In Vegetable Tanning Materials, Butterworths Scientific Publications, London, pp 209-218. 

Howes, F.N., "Vegetable Tanning Materials" Butterworths, London,1939. 

Cationic dyes were the first synthetic organic dyes employed for dyeing leather, initially for dyeing of vegetable-tanned leather. Currently, brilliant cationic dyes are used for enhancing the brilliance of the shades obtained with 1 2 metal-complex dyes. 

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. 

Vellum. There is a great deal to be said for this material which has proved durability and is certain to last much longer than any present-day vegetable-tanned leather. Difficulties can arise with full-vellum bindings... 

A. Cassano, J. Adzet, R. Mofinari, M. G. Buonomenna, J. Roig, and E. Drioli, Membrane treatment by nanofiltration of exhausted vegetable tanning liquors from the leather industry. Water Research 37, 2426-2434 (2003). 

Use Vegetable tanning, retanning of chrome-tanned upper leathers, dyeing, ore flotation, oil-well drilling fluids, flavoring. 

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