Tannins in tannins combine with active groups of skin collagen, which leads to new cross-linking between adjacent polypeptide chains and collagen molecules, thus enhancing the structural stability of collagen, improving the bending strength of leather, resisting the influence of chemical reagents and microorganisms, greatly increasing the contraction temperature of collagen and increasing its stability to damp heat.

Leather has been tanned and then processed into leather products of various styles for thousands of years. It belongs to one of the older industries. But people's research on tanning mechanism has only 200 years of history! Up to now, the research on tanning theory lacks enough detailed data, and it is difficult to make accurate and quantitative theoretical conclusions.

It is difficult to study for various reasons. Animal skin itself is very complicated. The fine structure and distribution of its basic components-skin collagen fibers and collagen molecules. , is not very clear, need further study. In addition, due to the increasing variety of tanning agents and the diversification of tanning methods in recent years, the research on the action mechanism of tanning agents is more complicated.

No matter what kind of leather raw materials, tanning agents and tanning methods are different, people have a basic judgment on the tanning effect of tanning agents:

(1) to improve the shrinkage temperature resistance of tanned skin and facilitate storage and transportation;

(2) Improve the anti-damp heat ability of collagen fiber;

(3) Improve the tolerance of collagen to chemicals, microorganisms and enzymes;

(4) Reduce the adhesion between collagen fiber bundles and fibers and fibrils;

 (5) Reduce the regularity of fine structure arrangement of collagen fibers;

 (6) Change the appearance of particle surface.

When judging whether a certain processing method is tanning or tanning with tanning agent, it can not be judged unilaterally according to a certain characteristic, but should be evaluated in combination with various characteristics.