Soluble Collagen Approach to a Combination Tannage Mechanism

Abstract

Although complex salts of CrIII sulfate are currently the most effective tanning agents, salts of other metals, including aluminum, have been used either alone or in combination with vegetable tannins or other organic chemicals. In the present study, the interactions of aluminum sulfate, and quebracho or chestnut tannins with collagen were investigated. A model system was devised to use soluble collagen in one compartment of an equilibrium dialysis cell and solutions of mineral or polyphenolic tanning agents in the other compartment. This study, by focusing on the effects of tanning agents on soluble collagen, rather than on intact hide, or powdered hide, gives a somewhat different perspective on the tanning process. The extraction of water from the collagen solution in the formation of aluminum/tannin complexes suggests that the lowering of water activity around the collagen may play a role in stabilizing a collagen/tannin/aluminum tannage. The most interesting finding is that aluminum which has little effect on collagen helical structure and stability does appear to connect collagen molecules in some manner to produce high molecular weight species that do not separate under the conditions of SDS PAGE. Comparison of the interactions of various combinations of minerals and vegetable tannins with collagen is expected to provide insight into a more generalized mechanism for tanning.