Leather, “chrome-tanned

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 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-tanned leather has chromium bonded to the leather fibers. This chromium can act as a mordant for acid dyes resulting in fast colors and intense shading at the surface of the leather. 

The chrome tanning is one step in a compHcated series of leather operations leading from the raw hide to the finished products. Chrome tanning is the most important tannage for all hides except heavy catde hides, which are usually vegetable tanned. In heavy shoe uppers and soles, a chrome tanned leather is frequently given a vegetable retan to produce chrome retan leather. 

The Oeko-Tex label tests for and restricts a high number of chemicals in the product. It should be noted that chrome-tanned leather cannot receive the Oeko-Tex Standard 100 certificate due to stringent demands on chromium. Since around 85-90% of all leather in the world is tanned with chromium, the certificate is only valid for a minor part of the leather production. 

Chrome refractories, 21 518 Chrome-tanned leather, 9 225 Chrome yellow, 6 523, 554, 555t color, 7 332 for green, 6 555t... 

The complete and systematic examination of leather, including physical and mechanical tests 1 and chemical analysis, is carried out principally for tannin- or chrome-tanned leathers. The methods to be used in this examination arc given below and are preceded by the procedure to be followed in sampling. 

Figure 7.11 Chrome tanned leather from Overton Down experimental earthwork after 32 years of burial in a chalk environment. (Photo Experimental Earthworks Committee/R. C. Janaway. With permission.) (See color insert following p. 178.)...

A method is proposed for using chrome tanned leather wastes produced by the footwear and clothing industry as fillers in polymer matrices. A technique for processing the composite obtained by continuous extrusion is also demonstrated. In order to evaluate the technique, a series of PVC-leather fibre composites was prepared and extruded through a flat die to produce sheets. The process produced a leather-like sheet that could be used in several applications. The influence of the filler content on the processability and final properties of the composite sheets was evaluated. The tests revealed that the sheets were flexible and exhibited suitable water absorption levels for several applications in the footwear and clothing industry. Finally, the tests showed that this composite could be formulated and processed at high productivity levels and at a low cost. 28 refs. 

Large amounts of sodium dichromate, Na,Cto07 2Ho0, are used in the tanning of hides, to produce chrome-tanned leather. The chromium forms an insoluble compound with the leather protein. 

Oxidation states of chromium - -2, - -3, and -f-6. Oi es of chromium chronate, FeCr204, and crocoite, PbCr04. Chromium metal and its alloys ferrochrome, alloy steels, stainless steel. The aluminothermic process (Goldschrtiidt process). Electrolytic chromium. Chromium trioxide, chromic acid, dichromic acid, potassium chromate, potassium didiromate, sodium chromate, lead chromate. Equilibrium between chromate ion and dichromate ion. Chrome-tanned leather. Chromic oxide (chrome green) chromic ion, chrome alum, chromic chloride, chromic hydroxide, chromite ion. Chromous compounds. Peroxy-chromic acid. 

Igenal [BASF]. TM for a series of dyestuffs for chrome-tanned leather. Characterized by unusual tinctorial power. 

Leukanol [Rohm Haas]. TM for synthetic tanning assistants of the sulfonic type supplied in liquid and solid grades. Powerful dispersants for vegetable tannins, and bleaches for chrome-tanned leather. 

A very unportant process in converting hide to leather is tanning. In chrome tanned leather, the chromium is presented in a combined form with the hide protein. Though the chromium in leather is usually reported to be chromic oxide (Cr O ), this does not mean that the chromium is present as the oxide. 

Hannigan M V (1965), Evaluation of the relative serviceability of vegetable and chrome tanned leather for bookbinding , The Journal ofThe American Leather Chemists Association, 60(8)506-518. 

Oil-tanned chamois leather Alum-tawed skins Formaldehyde-tanned leather Aluminium-tanned skins Vegetable-tanned leather (hydrolysable) Vegetable-tanned leather (condensed) Chrome-tanned leather... 

Hammond CR (2002) The elements. In Lide DR, ed. CRC Handbook of Chemistry and Physics, 2002-2003, pp. 1-10. CRC Press, New York. Hansen MB, Rydin S, Menne T and Duus Johansen J (2002) Quantitative aspects of contact allergy to chromium and exposure to chrome-tanned leather. Contact Dermatitis 47 127—134. 

Chrome-tanned leather has a light blue color and tends to become stiff when dried. A lot of leather is... 

The predominant tanning technique in the world is chrome tannage (about 85%). As a multi-purpose material chrome tanned leather can be transferred to leather with different properties (to different leather types) by further processing. However, a significant quantity of vegetable tanned leather is manufactured, too. Part-tanned chrome-free - often termed wet white - leather is also produced, in small but growing quantity. 

As already stated, the polyphenols are firmly bormd to the collagen in leathers which have been subjected to vegetable tanning. In the TFG of a leather sample we may therefore expect that this bond will be broken and that fragmentation of both the tannin and the collagen will occur. Fig. 10 ows the TFG of an animal in treated only with chromium salts (chrome-tanned leather). For comparison. Fig. 11 pves the TFG of a chrome leather that has been further tanned with mimosa extract the characteristic, prominent zones of resorcinol (3) and pyrocatechol (2) show up clearly. The typical products of thermolysis of vegetable tanned and unfinished leathers are compiled in Table 5. 

The material obtained by the above-stated processing of waste buffing dust from chrome tanned leather is potentially applicable on cemented soles, wrapping sheets, lagging and noise damping materials, sealing materials, antivibration pads, and so on. 

The excellent properties of chrome-tanned leather opened up new fields of use and made possible the mass production of leather goods, for example in the shoe or apparel leather sector. This created the need for fashionable styling of these leather goods and for making them resistant to soiling and damage. It is this function that is performed by leather finishing [1-7]. 

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