Leather manufacture

The leather making operations can be divided into three major groups  

The next steps often carried out together are deliming and bating of the pelt. The pH is decreased to about 8 by addition of weak acidic inorganic or organic salts or acids. Residual lime is removed from the pelt. Bating is performed with enzymes like trypsin or bacterial proteases to clean the pelt, to remove degraded protein residues. 

In the finishing process the surface of the leather is treated to obtain special effects and to protect it against mechanical damages, to make it more user-friendly. In the finishing polymer binders, dyestuffs, pigments, waxes and others are sprayed or applied to the leather surface. 

Processes with extremely high (liming) or low (pickling) pH values do not favour to the growth of microorganisms. However, the semi-processed states like wet blue or wet white provide due to their water content (about 40%) and their pH (about 4,0) an ideal breeding ground for mould and yeast. 

Finished ready-for-use leather, vegetable tanned leather and crust may have a different water content depending on the environment. A water content below 12 15% inhibits the proliferation of micro-organisms. However, sporogenic species may have released spores which withstand unfavourable conditions, e.g. great heat and dryness, but will germinate to a metabolic active state again as soon as favourable conditions appear. 

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Albumen has the largest number of acid and basic groups. It is the most soluble of the proteins present in a hide. The albumen is not a fibrous material, however, and therefore has no value in the leather. Keratin is the protein of the hair and the outermost surface of the hide. Unless the hair is desired for the final product it is removed by chemical and/or physical means. The elastin has Htde acid- or base-binding capacity and is the least soluble of the proteins present. The lack of reactivity of the elastin is a detriment for most leather manufacture. The presence of elastin in the leather greatly limits the softness of the leather. 

Figure 9.1 Main aspects of traditional leather manufacturing process...

PCP was widely applied by the leather industry before the 1990s for improving the biocidal activity of raw hides and skins. Due to the risk of transformation into dioxin during burning, the use of PCP and its salts and esters in leather manufacturing is not allowed in the EU according to EU Regulation 1997/2006 (Annex XVII) [12],... 

This review of literature on tannin degradation shows that our knowledge of this topic is only very slowly improving. Only a handful of laboratories are currently involved in this area. Of these, the Indian laboratories have made several interesting investigations recently, presumably because they are very active in leather manufacture and need to control the toxicity of their tannery effluents. 

BLMRA British Leather Manufacturers Research Association... 

M Culloch considers that the leather manufacture ranks third or fourth in importance, being inferior in money value to those of cotton, wool, and iron, whilst others are disposed to think that it is quite as important as cottcn. A glance at the extent of this branch of trade will show at once how much it has merited tho... 

In preparing this account of the leather manufacture, much of the information, besides what has been derived from private sources, has been obtained from Doctor Mobpjt S able work on Tanning, Knapp S Technology, So mm art, Dumas, Parnell, Sullivan, the Catalogue of the Irish Industrial Exhibition, and other authorities. 

Leather Bating Enzymes Enzymes used in leather manufacture lo remove flesh from hides. The enzymes generally are derived from hog and beef pancreas and consist of mixtures of enzymes that attack both proteins and lipids,... 

E. Heidemann fundamentals of Leather Manufacturing, Eduard Rother Verlag, 1993. 

Corner obtained a position with the British Cotton Industry Research Association, Manchester, in 1928, working initially in the rayon department where she developed a fascination with microanalysis. As a result of her acquired background, she was promoted to Head of the Microanalytical Section then in 1945, she obtained a similar post with the British Leather Manufacturers Research Association. Two years later, Comer was invited to become Head of the newly formed Microanalytical Section of the Chemical Research Laboratory (later the National Chemical Laboratory). 

By 1921, her original work on proteins led to an invitation to join the British Leather Manufacturers Research Association, a move which, according to Marjory Stephenson, probably robbed this country of a distinguished professor of biochemistry. 59(a) As a final contribution to her original research field, Jordan Lloyd wrote the classic work The Chemistry of Proteins, published in 1926, for which Hopkins wrote the introduction (a second edition, co-authored with Agnes Shore, appeared in 1938).60... 

It was Jordan Lloyd who turned leather manufacture from a craft industry into a scientific process. In 1927, she was appointed Director of the Association, a post in which she served until her death in 1946. For a women to head such a large scientific organisation was an amazing accomplishment for the period. Her predecessor, Robert Pickard,61 commented in his obituary of her ... 

Ornes and Roddy (1960) investigated the elastin content of animal skin before and after treatment for leather manufacture. Two methods were used for the determination of elastic tissue. In the first, squares of limed calfskin, after deliming, were treated with a commercial pancreatic preparation containing elastase to dissolve the elastin. The squares were then autoclaved for 4 hr at 15 lb steam pressure, and the residue was treated alternately with hot 0.5 N HCl and hot water to remove lime and acid. Finally the residue was extracted with acetone to remove fat and was... 

Procter, Principles of Leather Manufacture, Spon, 1903, p. 206. See also Stiasny and Das, J. Soc. Ghem. Ind., 1912,31,753, for a careful research on the reaction between sodium thiosulphate and a mixture of potassium diohromate and sulphuric acid. 

E. Heidemann, Fundamentals of Leather Manufacture, Eduard Roether KG, Darmstadt, 1993. 

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