Hide tanning

Other samples Include raw hide, tanned leather, condensed steam, etc. 

A considerable number of horse hides is annually imported from South America, sometimes as many as one hundred and ninety or two hundred thousand. The imported hides are much superior to those which find their way to the home market, on account of the latter belonging generally to old and worn-out animals, while the former have been flayed from the captured wild horses of the pampas, lyiug between the chains of the Andes. Ass and mule hides, tanned and so prepared, serve for the manufacture of scabbards the leather to called shagreen or shagri. 

Ammonium chloride is used as an ingredient of dry cell batteries, as a soldering flux, as a processing ingredient in textile printing and hide tanning, and as a starting material for the manufacture of other ammonium chemicals. 

Alloying agents in the manufacture of transistors, lasers, and semiconductors processing of glass, pigments, textiles, paper, metal adhesives, wood preservatives and ammunition hide tanning process pesticides feed additives pharmaceuticals 111, 12, 23,3121, 32, 341,3512, 3521,3522, 362, 372, 38... 

Use Manufacture of esters for solvents, flavors and perfume bases, disinfecting agent, varnish, deliming hides, tanning agent. 

USE Decalcifier. reducer in dyeing wool fast colors de-hairing and plumping hides, tanning, in sizes, electroplating, coagulating rubber latex aid in regenerating old rubber also in chemical analysis. 

In the leather and hide tanning industry, where calcium hydroxide is used to remove hair from hides and then to neutralize tanning solutions ... 

In hide tanning and dyeing procedures that use compounds of the element chromium ... 

Uses Mfg. of esters for solvents, flavors, perfume bases disinfectant preservative varnish deliming hides tanning agent buffer in cosmetics synthetic flavoring agent in foods and pharmaceuticals... 

Leather made by the crosslinking of proteinaceous hides (tanning) has been called "the most historic of useful materials". Reference to the tanner was made by the pla5rwright Aristophanes more than 2,500 years ago. 

Quinone is used as a feedstock to produce dyes and fungicides as well as hydroquinone, which is mainly used in photography. It has significant use in hide tanning to produce leather. 

Ionic Nature Nonionic Uses Degreaserfor hide tanning Features Stable in brine sol n. 

Tanning of hides by any of the primitive methods was a dirty job withHttle assurance of success. The tanner was a speciaUst generating little respect in the community. In some parts of the world, this ancient prejudice against tanners exists even as of this writing (ca 1994). The tanner in primitive societies was limited to making leather using the hides or skins available locally. Tanning materials were also limited to those in local supply. Techniques were dependent on the climate as well as avadabihty of materials. The leather made was for local needs. 

In temperate climates extracts from some plants were found to be excellent preservatives for hides and skins. The hides, with or without hair, were placed in pits in the ground, then covered with alternating layers of bark or leaves and skins. Water was added and later, ie, days or months depending on the thickness of the hide, the hides could be removed, washed, and oiled. The resulting leather is flexible and lasts essentially forever. This procedure was used well into the seventeenth century as the most common method of tanning. In some isolated primitive societies, the method is used in the 1990s. 

Leathermaking occurs in three broad steps (/) removal of aU materials that are not a part of the final product, (2) rendering the remaining hide substance biorefractive, ie, tanning, and (3) treating the stabilized taimed material to impart the characteristics desired in the final product. In aU steps the solubUity and reactivity of the components form the basis of the treatments employed. 

The manufacture of leather foUows the same general steps for a great variety of leathers (Fig. 2). The largest category of hides taimed is catde hides. Of the cattle hides chrome tanning of unhaired hides is by far the dominant system used throughout the world. The tanning of other types of hides and skins requires variations in the systems used for cattle hides (3). 

Fig. 2. Process flow diagram for the production of chrome-tanned cattle hide leather. Adapted from Ref. 3.

The grain layer is the most valuable part of the hide and serves as the outside of the shoe. Splitting aUows the grain layer to spread to the maximum area yield and also aUows an efficient use of the valuable tanning chemicals. 

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). 

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. 

The degree of pickle, ie, the amount and type of acid used, depends on the type of hides or skins and the taimage to be used. The pickle is in preparation for tanning and the chemistry of the subsequent taimage determines the pickle method. 

Control of chromium penetration, essential to permit tannage of the center of the hide, is accompHshed by pH adjustment. At a pH > 3.0 the reactivity of the hide to the chromium complex is greatiy increased. The pH is therefore raised gradually to the desired point by addition of a mild alkah, usually sodium bicarbonate. The chemistry of chrome tanning involves competing reactions that must be controlled for satisfactory results. 

The chrome-tanned leather is removed from the dmm and wmng to remove the absorbed tanning solution. The leather is then inspected for quaUty of the grain and other characteristics of importance for the leather being made. In large tanneries where very uniform hides are worked, the leather may be trimmed and spHt to the desired thickness. Hides spHt before tanning need no splitting at this point. 

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. 

The si2e of the vegetable tanning molecules and the coUoidal nature of the system result in the fixation in the hide of filling materials. The filling action is essentially an impregnation of the hide to form a dense firm leather. These properties are gready desired in sole and mechanical leathers. 

---