Fat-liquoring:
It is an important operation in leather manufacture in that the application of fatty emulsion enable it to surround the individual leather fibre with fatty substances or softening compounds which are firmly fixed to prevent their migration.
Objectives of Fat-liquoring:
1. Deposit of fatty substances in the Interfibrillar spaces in order to give the leather desire softness & handle properties.
2. Primary function is to prevent the fibre structure resticking during drying.
3. Correction or control of physical properties like tensile strength, split tear strength, wetting properties or water repelling properties, waterproofness, permeability to air & water vapour, water absorption & moisture storage-capacity, thermal & electrical conductivity.
Properties of Fat-liquor:
1. Raw oil:
Which not get fixed to the leather fibre but lubricate the latter.
2. Emulsifier:
Which emulsify the raw oil & carry them inside of leather & at the same time will get fixed to the leather fibres & slightly prevent the free movements of raw oil by their power of adhesion.
3. Continuous phase:
Acts as a vehicle for the oil-droplets surrounded with emulsifier.
Principle of Fat-liquoring:
1. Fats & oils of highest lubricating power should only be selected for the preparation of fat-liquors, so that small amount can produce sufficient softness to leather.
2. The emulsifier may or may not process any lubricating power but carry the lubricating oil deep into inside of the leather without facing any resistance during penetration into the leather.
3. The strength of both hydrophobic & hydrophilic ends of emulsifier should be as high as possible but between them hydro-phobic side should be slightly stronger.
4. Develop the opposite charge into the neutralized leather.
Mechanism of Fat-liquoring:
1. The neutral oil is transported into the pelts as an oil in water emulsion.
2. The emulsifying agent interact with the leather, reducing or eliminating its emulsifying power.
3. The neutral oil is deposited over the fibre structure - the level of the hierarchy of structure depends on the degree of penetration.
4. The water removed by drying, allowing the neutral oil to flow over the fibre structure.