Leathers

Leather is the material made from animal skin by the process of tanning, which entails chemically altering the composition of the skin so as to make it durable and resistant to decay. Leather is therefore not a protein but a protein derivative. Although the tanning process alters the composition of skin, leather retains the fibrous structure and utilitarian frmctionality that make skin suitable for multifarious applications. Shelter, clothing, and decorative objects made from leather are, rmlike skin or hide, stable to physical, chemical, and biological decay under dry or wet conditions (O Flaherty et al. 1965  

Gustafson 1956). The essential differences between skin and leather are in their stability in damp and humid environments when damp or humid for extended periods of time, even at ambient temperatures, skin is gradually hydrolyzed into a viscous treacle leather remains practically unaltered even after prolonged immersion in boiling water (Stambolov 1969). 

Leather is an important material in the world economy, being used in footwear, clothing, luggage and upholstery. It is a complex substrate prepared from animal hides and skins by a long series of treatments. After the removal aU organic material and hairs the material is tanned, usually with chromium salts, which causes the protein chains to cross-link. After treating with oils or fats, to improve its handle, the leather is dyed. 

Leather can be dyed with acid, direct and mordant dyes. Many of the direct dyes were based on benzidine and its congeners but the German Ordinance, covered under the toxicity of certain azo dyes in section 2.3.1.1, has meant that this is no longer an option. To improve the light fastness of the dyed leathers, 1 2 premetallised azo dyes have also been used, but once again the use of metal complex dyes is becoming less favoured.  

Over 50% of leather is dyed black and 24% brown, the rest being largely coloured at the dictates of fashion. An example of a dye used in the dominant black shade area is Cl Direct Black 168 (2.51). 

Hide and skin processing for leather production involves several steps. These are socking, dehairing, bating, and tanning. Arunachalam and Saritha (2009) reported that hides and skins have a chemical composition of 60% to 65% water, 25% to 30% protein, and 5% to 10% fat with traces of minerals. 

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Colourless liquid with a strong peppermintlike odour b.p. 155" C. Manufactured by passing cyclohexanol vapour over a heated copper catalyst. Volatile in steam. Oxidized to adipic acid. Used in the manufacture of caprolactam. Nylon, adipic acid, nitrocellulose lacquers, celluloid, artificial leather and printing inks. 

Enzymes are used in baking, cheese manufacture, wine-making, brewing and distillation, pharmaceuticals, leather tanning, paper manufacture, adhesives, sewage disposal, animal feeds and in detergents. 

Slurry or slip casting provides a relatively inexpensive way to fabricate unifonn-thickness, thin-wall, or large cross section shapes [4o, 44, 45, 46, 42 aiid 48]. For slip casting, a slurry is first poured into a porous mould. Capillary suction then draws the liquid from the slurry to fonn a higher solids content, close-packed, leather-hard cast on the inner surface of the mould. In a fixed time, a given wall thickness is fonned, after which the excess slurry is drained. 

Chromates and dichromates are used in industry as oxidising agents, for example in the coal tar industry, in the leather industry (chrome taiming), and in the dye industry as mordants. Some chromates are used as pigments, for example those of zinc and lead. Chromates and dichromates are poisonous. 

All compounds of chromium are colored the most important are the chromates of sodium and potassium and the dichromates and the potassium and ammonium chrome alums. The dichromates are used as oxidizing agents in quantitative analysis, also in tanning leather. 

Poly(vinyl chloride) (PVC) has re placed leather in many of its appli cations PVC tubes and pipes are often used in place of copper... 

N Nitrosodimethylamine (formed dunng tanning of leather also found in beer and herbicides)... 

Dyeing accelerants Dyeing classes Dyeing of leather Dyeing paper Dyeing processes Dye initiators Dye-in-polymer systems Dye intermediates... 

Dyes for leather Dyes, natural Dyes, reactive Dyes, sensitizing... 

Leather chemistry Leatlier dyeing Leather dyes... 

Leather-like materials Leather processing Leather tanning... 

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