Tannins vegetable

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. 

In retanning, vegetable tannins may be used in conjunction with or may be entirely replaced by synthetic tanning agents called syntans. The syntans and other specialty chemicals allow the creation of leathers not possible using vegetable tannins alone. 

More recently, a modification of the system described by Kreibich has been used extensively in industry with good success. Part A of the adhesive is again a standard phenol-resorcinol-formaldehyde (PRF) cold-setting adhesive, with powder hardener added at its standard pH. Part B can be either the same PRF adhesive with no hardener and the pH adjusted to 12, or a 50 to 55% tannin extract solution at a pH of 12-13, provided that the tannin is of the condensed or flavonoid type, such as mimosa, quebracho, or pine bark extract, with no hardener [118,135-137], The results obtained with these two systems are good and the resin not only has all the advantages desired but also the use of vegetable tannins and the halving of the resorcinol content makes the system considerably cheaper [118,135-137]. 

Haslam, E. (1966), Chemistry of Vegetable Tannins, Academic Press, London. 

Haslam, E., Natural polyphenols (vegetable tannins) as drugs possible modes of action, J. Nat. Prod., 59, 205, 1996. 

Plant polyphenols, also known as vegetable tannins, are a heterogenous group of natural products widely distributed in the plant kingdom. Tannins... 

Haslam E and Cai Y (1994) Plant polyphenols (vegetable tannins) gallic acid metabolism. Nat Prod Rep 11, 41-66. 

Haslam, E., Plant polyphenols (syn. vegetable tannins) and chemical defenses — a reappraisal, J. Chem. Ecol., 14, 1789, 1988. 

Boye,B.,Farnia, G., Sandona, G.,Buso, A. andGiomo, M. (2005) Removal of vegetal tannins from wastewater by electroprecipitation combined with electrogenerated Fenton oxidation. J. Appl. Electrochem. 35, 369-374. 

For many years, most of the leather in the United States was tanned with domestic tannins from hemlock and oak bark and from chestnut wood. Today only a small amount of tannin comes from these and other domestic sources. The most important source of vegetable tannin today is the wood of the quebracho tree, which grows mainly in Paraguay and Argentina. The tannin content of this tree and a few other sources of vegetable tannin are shown in Table 28.10. 

Leukanol [Rohm Haas]. TM for synthetic tanning assistants of the sulfonic type supplied in liquid and solid grades. Powerful dispersants for vegetable tannins, and bleaches for chrome-tanned leather. 

Analysis of vegetable tannins is used to determine the tannin content in the extract solution from the raw or spent materials. The tannin analysis method set up by the American Leather Chemists Association (ALCA, 1954a) is based on the absorption of materials from the extract by hide protein. It is not based on chemical analysis of a true tannin molecule. 

American Leather Chemists Association (ALCA) (1954a), ALCA Test Method A22, Nontannins and Tannins in Vegetable-Tannins Extracts, Lubbock, Texas, ALCA. 

---