Natural fat content in leather production

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In raw sheep skin about 25 -30 % fat is found. Goat skin contain about 10 -15 % less fat than sheep. This fat content require different % ratio in different kind of leather. Mostly it is extracted from skin fibers through degreasing. If it does not remove properly it increased fattening practices disturb the leather production process and produce eruptions and staining of the leather. Therefore most of the natural fat has to be removed or, with a lower fat content, be disturbed over the cross-section of the skin.
This process is often executed after bating by a treatment with surface-active substances, mostly by adding fat-dissolving organic degreasing agents.
Requirement of fat content in different type of leather
Type of leather fat requirement
Shoe lining leather less than 10 %
Sole leather 3-4 %
Garment leather 4-10 %
Gloves leather 4-10 %
Technical leather 12 % cold-stuffed
17 % hot-stuffed
25 % Burned-in max
Fat content test method in leather
Fat forms a heterogeneous group of compounds which have the common property of not dissolving in water but dissolving in organic solvents. This property of specific solubility is made use of in extracting fats from tissues, free from any water-soluble matter.
A soxhlet extractor is used for solvent extraction of the fat from the leather samples. 10-15g of the dried leather sample are packed in thimbles and inserted into the soxhlet extractor and 40⁰ - 60⁰ c petroleum ether is used as the extracting solvent. The period of continuous extracting is 8 hours. At the end of this period the solution is transferred to a pre-weighed beaker and solvent is6 recovered by simple distillation. When the solution is free of organic solvent the weight is determined again. The difference in weight gives the weight of the fat.
Estimation of free fatty acids
The conventional titration against standard NaOH solution is used. For this purpose, the fatty acid is suspended in 50% ethanol solution and this is titrated standard 0.1N Na0H solution using phenolphthalein (1% ethanolie solution) as indicator. The end point will be the appearance of a faint but permanent pink colour. From the volume of NaOH used, the normality of the fatty acids can be calculated.