Lignosulphonates in Tanning
The use of lignosulphonates in tanning was already common knowledge in the last century. Originally only raw lignosulphonates compounded with calcium salts were used with varying results.
Later, however, it was realized that lignosulphonates or the so- called cellulose extracts, have to be free from calcium and iron, if these comparatively cheap tanning agents were to enjoy extensive industrial application.
Our lignosulphonate was the first practically calcium- free lignosulphonate that was also practically ash-free. For this reason it can be said that LIGTAN played a major role in promoting the intensive application of lignosulphonates in the tanning industry.
The excellent suitability of ligninas a tanning agent lies in the irreversible bonding property of lignosulphonates with the skin substances. However, the bonding properties of vegetable tannins and those of lignosulphonate differ in some aspects. Today it is generally agreed that vegetable tanins bind with the skin proteins in at least the following two ways:
- Co-ordination – based on the hydrogen bonding of the phenolic structures of the vegetable tannin on the peptise groups of the skin proteins and
- Saline bonding – between the vegetable tannins and the amino groups of skin proteins.
The lignosulphonate acids in bond almost exclusively with the skin proteins, which is why cannot completely replace vegetable tannins in the tanning process.
On the other hand the vegetable tannins provide a comparatively limited bonding with the amino group of skin acids. For this reason one can safely say that the vegetable tanning agents and the lignosulphon acids complement each other in the tanning process. This explains the excellent absorption of the tanning liquids by the skin substance when LIGTAN is added to the tan liquor.
By adding lignosulfonate, up to 25% of vegetable tanning agents can be saved irrespective of the type of leather being processed.