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265 S. Schoolhouse St. Boynton Beach, FL 33435ing, the hides are soaked in clean water to remove the salt left over from curing and increase the moisture so that the hide or skin can be further treedT o prevent damage of the skin by bacterial growth during the soakg period, biocides, typically dithiocarbamates, may be used. Fungicides such as 2-thiocyanomethylthiobenzothiazole may also be added later in the process, to protect wet leathers from mold growth. After 1980, the use of pentachlorophenol and mercury-based biocides and their derivatives was forbidden.[by whom?]Liming (leather processing)After soing, the hides and skins are taken for ling: treatment with milk of lime (a basic agent) that may involve the addition of "sharpening agents"(disulfide reducing agents) such as sodium sulfide, cyanides, amines, etc. The objectives of this operation are mainly to: 1.Remove the hair and other keratinous matter2.Remove some of the interfibrillary soluble proteins such as mucins 3.Swell up and split up the fibres to the desired extent 4Remove the natural grease and fats to some extent 5.Bring the collagen in the hide to a proper condition for satisfactory tannage"The weakening of hairis dependent on the breakdown of the disulfide link of the amino acid cystine, which is the characteristic of the keratin class of proteins that gives strength to hair and wools"(keratin typically makes up 90% of the dry weight of hair). The hydrogen atoms suppliedby the sharpening agent weaken the cystine molecular link whereby the covalent disulfide bond links are ultimately ruptured, weakening the keratin. To some extent, sharpening also contributes to unhairing, as it tends to break down the hair proteins.The isoelectric point of the collagen in the hide (this is a tissue-strengthening protein unrelated to keratin) is also shifted to around pH |
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