Abstract

Preliminary extraction of wattle tanned hide powder in aqueous acetone followed by secondary extraction in a number of aqueous media incorporating dirnethylformamide, dioxan, diethylene glycol dirnethly ether, urea and lithium bromide, serve to demonstrate the high degree of tannage reversibility in terms of reduction in the amounts of combined tannins and shrinkage temperature. Dirnethyl formamide and dioxan at 20 moles °/ in water removed all except 15 to 20% of tans on a dry hide substance basis with shrinkage temperatures close to raw pelt. This is consistent with the view that secondary valence forces, particularly hydrogen bonds, are chiefly responsible for the major portion of tan fixation.

The stripping power of the extractant media at various concentrations has been examined in relation to their effects on the hydrothermal stability of untanned collagen. While no consistent relationship was apparent, it would appear that in the case of most of the mixtures of organic solvent with water, the increasing stripping power with increasing proportion of organic solvent reached a maximum and then declined probably due to the opposing effect of dehydration of the pelt.

The removal of the solvent resistant portion of wattle extract, gives a fully solvent reversible tannin in spite of preparative oxidative darkening, nd yielded leather with normal thermal stability. This proves that re sistance to solvent leaching is not primarily a function of the protein, and that it is not necessary to have main bond linkages to achieve the normal thermal resistance of vegetable tannage.

These results appear to disprove theories of vegetable tannage which invoke the idea of “main bond reinforcement” and “quinone-type link ages” in the case of wattle tannins.