Abstract

Tannage experiments of New Zealand lambskins were carried out in different water-immiscible organic solvents: dichloromethane, trichloroethane, trichloroethylene and tetrachloroethylene with different vegetable tannins: sweetened chestnut, mimosa and sulphited quebracho (ATS) have shown, under the conditions of tannage, that according to the amount of water dispersed in the tanning bath (water coming from the pelts), the nature of tannin and the properties of the organic solvent that the tanning process may be compared to a gel emulsion phenomenon which prevents tannin from diffusing into skin. This effect is more marked in presence of quebracho and tetrachloroethylene. However, this emulsion may be avoided by adding a co-solvent (acetone) to the tanning bath. The experiments carried out in tetrachloroethylene-acetone show that, at an equal pelt moisture content, in the case of tanning with sulphited quebracho, the amount of acetone added is higher than in the case of the other tannins. Thus, these results indicate that the necessary amount of co-solvent is related to the hydrophilic and hydrophobic structural content of the tannin extract. Alternatively, tannage experiments were carried out in tetrachloroethylene medium by increasing the volume of tanning bath and in this case without adding co-solvent. In all cases, with tannage in chlorinated hydrocarbon media, tannin exhaustion is more complete and the shrinkage temperature of leather obtained is high and its quality is satisfactory. The feasibility studies of tanning in solvent media were prompted by the industrial scaling-up of a newly developed solvent degreasing process. The process solves the water pollution problem and gives complete recovery of the fats. As the chlorinated hydrocarbons separate easily from aqueous components they are recovered by distillation in a closed system which also allows recovery of the solvent in the skins by heating to 40°C for 2 h 30, this also aids tannin fixation.