- Fatliquor
- Fatliquor Principle.
- Fatliquoring Chrome-Tanned vs Vegetable-Tanned Leathers.
- Fatliquor Softening and Lubricating Properties.
- The Effects of Fatliquor on Leather Drying.
Fatliquor
Fatliquor plays a crucial role in the leather’s conditioning process by replenishing the fat and oil content that keeps leather supple and prevents stiffness or cracking. When applied, the water-encased fat and oil molecules penetrate the leather fibers. As the water gradually wicks away during the drying process, the fat and oil remain, hydrogen-bonding with the fibers, creating a breathable structure that enhances the leather’s elasticity and durability. Fatliquor 5.0 is essential for maintaining and restoring vachetta, aniline, nubuck, suede, and other leathers, preventing them from becoming brittle over time. Proper fatliquoring ensures that leather retains its tensile strength, resists breakage, and feels soft and luxurious.
Fatliquor Principle.
Almost all leathers, including nubuck, suede, hair-on, sheepskin, and shearling finished goods, will need periodic conditioning to replenish their diminishing fat and oil content to regain their softness and flexibility. This is attained in the fatliquoring process by introducing fat and oil into the leather so that the fibers are individually uniformly coated. The percentage of fat liquor on the weight of leather is quite small, 7-14%. The technique of distributing this small amount of fat and oil throughout the leather will affect its subsequent useful life. It is necessary to emulsify the fat and oil to allow a small amount to be spread uniformly over a large surface of the leather fibers.
In an emulsion with water, the fat and oil are dispersed in microscopically small droplets, giving it a white, milky appearance, just like milk is an example of a natural emulsion. The fat and oil droplets must remain as a milky emulsion until they penetrate the leather, not separate as large drops or as a layer of oil, which could not penetrate the leather fiber and would only give a greasy surface layer. Fatliquor, the lifeblood of leather, makes important improvements to its properties; they play a fundamental role in governing the softness, pliability, stretch, or hand; the ability to resist water; the resistance to abrasion, and the smoothness of the grain. The effect obtained will depend upon the type of leather, the quantity of fat and oil, how it is applied, and whether it is all on the surface or has penetrated the internal structure.
Fatliquoring Chrome-Tanned vs Vegetable-Tanned Leathers.
If the fiber structure is tightly woven, smooth, or finished, the leather will be firmer, making it more difficult for the fat liquor to penetrate the fibers uniformly. Chrome-tanned leather with diminishing fat liquor dries out firm, stiff, and hard. However, spreading a relatively small amount of fat liquor over the fibers readily reduces the hardness, improving the stiffness for its softness and stretchability. Vegetable-tanned leather with diminishing fat liquor is less hard than chrome leather; however, more fat liquor must be added to vegetable-tanned leather rather than chrome leather to obtain the same softness or stretchability. Normally, the leather becomes softer and stretchier as more fat liquor is used; however, excessive amounts of fat and oil may give an undesirable, greasy feel, or may interfere with redyeing and refinishing.
Fatliquor Softening and Lubricating Properties.
Fatliquor promotes the lubrication of adjacent fibers rubbing against each other or reduces the adhesion between them. Fatliquor is applied to the wet leather to prevent the fibrils from sticking together during drying. Fatliquor gross penetration into the inter-fiber spaces, the fat and oil molecules are hydrogen-bonded to the molecular leather fibrils. Fatliquor is ionic negative (-ve) charged, which gives a much firmer attachment to the ionic positive (+ve) charged leather fibril, with less migration during drying, thus less fiber collapse during drying, and hence a fuller leather.
The Effects of Fatliquor on Leather Drying.
Fatliquor is applied to the damp leather, ideally when the leather fibers are fully hydrated but little free water exists in the spaces between the fibers. Fatliquoring to completely dried leather fibers results in rapid absorption, often resulting in dark-colored, greasy patches. Moreover, the resultant leather is not as soft, resilient, or full as when fat liquor is applied to the damp, hydrated fiber. This is because without or insufficient fat liquor, and when the leather dries, the fibers shrink due to loss of water and come closer together, when cohesive forces come into play, cross-linking the fibril or fiber structure, making it firmer, harder, and less flexible or "crusty". These forces may be of the nature of Van der Waals forces or dipole or hydrogen bond forces, which would be much stronger. The degree of crustiness will depend upon the tanning type, being less with vegetable tanning, which may account for many of the hide's dipole forces, and more with the chrome tannages, where the effect is less.