Leather Manufacture with Wattle Tannins

Abstract

Vegetable extract production in general has declined over the years as a result of decreased demand for vegetable-tanned leather. The use of wattle (mimosa) extract, however, has not been as adversely affected as has other extracts due to the advantages that wattle extract has in leather manufacture. Such properties as rapid tannin penetration, low salts content, and high solubility of wattle extract are shown to be ideal for traditional pit tanning operations and the Liritan tanning system. Wattle extract is also well suited for drum tanning and use thereof in processes such as the ‘Mimosa-cure,’ semi-chrome, chrome retan, and mimosa-alum is outlined. The last combination tannage is a chrome-free process and has been found to work best if carried out in two stages, initial wattle tanning, then aluminum sulphate retanning. Increasing the pH in subsequent basifying and neutralizing processes results in increased tannin aluminum complexation and hence crosslinking as measured by the hydrothermal stability of the mimosa-alum tanned leather. The properties of a number of specialty wattle based products are also noted, viz. ‘Mimosa GS’—light color, ‘Mimosa FS’—fast penetration, and ‘Mimosa-AL’—for wet white processes. These properties are discussed in relation to the theory and mechanism of wattle tanning.