Hide, bating

Deliming and Bating. The limed hides have a pH around 12. Because chrome tanning is done at pH 2—4, the lime must be removed for pH adjustment. In addition, the undesirable materials in the hide, ie, both natural and the degradation products from the unhairing, must be removed (7,9). 

For deliming, ammonium salts and acids are used. The proportion of ammonium salts to acids and the type of acids employed is a matter of the tanner s choice. The acid neutralizes the lime, Ca(OH)2, thereby adjusting the pH. The ammonium salts have two functions to buffer the solution to a pH required for bating, and to form calcium ammonium complexes. The acidity and the complex formation solubilize the calcium and serve to bring the hide to the desired pH. 

The usual procedure in the manufacture of chrome-tanned leathers is the use of a continuous bate, pickle, and tan method. The hides or skins remain in the dmm from the lime washing through the chrome tanning stages. The entire process usually takes about 22—24 hours. The bate, pickle, and tan can be done faster, but most tanners find that a one-day cycle fits well into production scheduling and results in a quaUty leather. 

Chrome Tanning. The original chrome tanning was a two-bath process. The unhaired hides, delimed and bated, were treated with a solution of sodium bichromate [10588-01-9]. The amount of bichromate used was about 3—5% based on the weight of the hides. The bichromate was absorbed or adsorbed into the hide, the solution drained, and the hides refloated. Sodium bisulfite was added and two important reactions resulted in the formation of a basic chromium and coUoidal sulfur in the hide. This gave a chrome taimage and also helped to fiH the hide with the soHd sulfur. This cmde system, which continued in the industry in some types of leather for over 50 years, is obsolete. 

Enzymes in the Tannery. The processing of skins and hides for leather (qv) has been based on enzymes ever since 1908 when Otto Rn hm patented the first standardized bate based on pancreatic enzymes (78). Leather chemistry research helped to improve understanding of the bating process, and at the same time spurred on developments to improve leather processing (79). 

Prior to the bating process, the hides are delimed with ammonium sulfate and/or ammonium chloride. Proteases are then appUed. The early preparation proposed by Rn hm was pancreatic trypsin. The use of a bating enzyme makes the hides soft and supple to prepare them for tanning. A new microbial protease, Pyrase 250 MP (82) (Novo Nordisk A/S) has been found to be a promising substitute for pancreatic trypsin [9002-07-7] which is more expensive because it must be extracted from pancreatic glands. 

Beize,/. corrosive corrosion (Dyeing) mordant disinfectant disinfection (Med.) caustic, cauterisation (Leather) bate, drench (Metal.) pickle etching staining stain, beizempfladlich, a. sensitive to corrosion, mordanting, etc. (see beizen). beizen, r.2. corrode mordant cauterize steep bate, drench (hides) etch pickle blanch (metals) disinfect stain sauce (tobacco) ... 

Proteinases in the Leather Industiy. Protease enzymes are used in the processing of skins and hides into leather, in particular for the removal of hair and wool, and for increasing the pliability (called bating) of leather. 

The use of enzymes for the manufacture of leather played a major role for the industrial scale production of enzymes. For the preparation of hides and skins for tanning, the early tanners kept the dehaired skins in a warm suspension of the dungs of dogs of birds. Wood was the first in 1898 to show that the bating action of the unpleasant dungs was caused by the enzymes (pepsin, trypsin, lipase) which they contained. In the context... 

In the tanning process hides are first washed or soaked, hair and keratinous debris are removed, bated (enzymes are used to break down non-collagenous components, which are washed out) and the hide is acid-pickled to prepare for the addition of the chromium salt. Contemporary processes are exclusively based on one-bath procedures and utilize chromium(III). The older two-bath process is now obsolete, mainly because it involved the in situ reduction of chromate, a major environmental and toxicological hazard (cf. chromate toxicity p. 947) to chromium(III) on the hide. A useful review of the history of chromium tannage processes is available.1205... 

Bating,—With respect to the removal of lime from the skin, it has been found that no amount of scraping and rinsing is capable of making a perfect separation, a portion of the earth being retained in the pores of the skin, combined w, tk, perhaps, some of the decomposing tissue, and with the grease and fat of the hide, as a lime soap. These combinations, if not altered and VOL. it. 

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,... 

Application of pancratic enzymes in the leather industry for the bating of hides. Rohm... 

Oropon. DR.ohm Haas] Protease enzymes for bating hides brfore tanning. 

Processes carried out at a pH of 7-9 represent the most efficient use of this type of enzyme. The first industrial process involving this type of protease was in the bating of hides to remove the debris from the skin after liming, and to impart softness and air exchange to the finished leather. Although pancreatic bates are still in general use proteases derived from Aspergillus flavus-oryzae and Bacillus subtilis now supple ment them. 

Excrement Tubs. — The excrement tubs bate )> 01 the contrary, exert a very energetic action, since they effect a true digestion of the hide, which first of all softens, but which then may deteriorate profoundly if the attack is prolonged too far. Two... 

As tanning requires acid conditions, the hides have to be delimed before further processing. By addition of ammonium salts and acids, a neutral pH is achieved. Proteolytic enzymes are added to eliminate undesirable byproducts from the connective tissue and to break down elastin in the hide (so-called bating), because elastin may make the leather too firm and stiff. 

The term tannins also attributed to proanthocyanidins (condensed tannins) was defined by Bate-Smith and Swain in 1962 as water soluble phenolic compounds having molecular weights between 500 and 3,000 Da and, besides giving the usual phenolic reactions, they have special properties such as the ability to precipitate alkaloids, gelatine and other proteins. Tannins have been widely employed in the tanning process converting hide collagen in leather [292]. 

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. 

Others. Used in bating hide and in desizing fabrics. 

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