Chemical analysis of leather

Materials used for leather dyeing are usually acid dyes, direct dyes, mordant dyes (Thorstensen, 1993) and reactive dyes (Shao and Zhao, 1984). Basic dyes are primarily used for dyeing vegetable tanned leather (Sandoz, 1949). 

Based on the production processes of leather, this chapter will discuss the chemical tests which allow identification of leather from its synthetic substitutes and analyses of tanning materials. Some tests of important leather properties, such as pH, fat, chrome and ash content will also be described. The azo dye tests will be illustrated here since many countries have already adopted mandatory regulations 

Resin finishing and coating are widely used to improve the leather properties (Thorstensen, 1993). Chemical analyses of finishes and coating are often required. Description of such analyses can be found in Chapter 6 and Chapter 7 of this book, respectively. 

Leather making produces a large quantity of effluents, which contain a considerable amount of chromium. Chapter 9 of this book discusses the treatment of wastewater including heavy metals. Section 3.3.2 of this chapter will discuss the analysis of chromium content in solutions and the recycling of chromium briefly. 

This chapter does not purport to explain all of the safety concerns. The users of the following test methods must have knowledge of and obey all the laboratory safe policies to avoid injury during testing. 

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Analysis of vegetable tannins is used to determine the tannin content in the extract solution from the raw or spent materials. The tannin analysis method set up by the American Leather Chemists Association (ALCA, 1954a) is based on the absorption of materials from the extract by hide protein. It is not based on chemical analysis of a true tannin molecule. 

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. 

Part of the sample (about ioo grams), to be used for chemical analysis (see later), is then reduced to small pieces and these by means of a suitable mill to a woolly powder when this is not possible, as with oiled leather, the sample is cut with a knife into very small fragments. The sample thus prepared is kept in well closed vessels. 

After the surface layer of the leather sample is peeled off, the sample can be observed under a microscope. The collagen fibres of leather differ in appearance from non-woven fabrics and from the uniform polymers of coating and lamination in the synthetic substitutes. However, some artificial leathers in the market do better than the real leather. It has been reported that some leather substitutes with super-microfibres of nylon, polyester and polypropylene can have similar views of cross-section under the microscope (Cheng, 1998). A combination of the bum test, the chemical test, the infrared spectroscopic analysis and/or the microscopic... 

No matter what the source of chromium tannages, either from raw materials or from recycled solutions, care must be taken to maintain the quality of the leather. This can be only achieved by constant chemical analysis and chemical control. The chromium content in the solution can be tested by the following two methods, titration and atomic absorption analysis ... 

Analysis of the chemical composition of mink s leather tissue before and after impact of microorganisms testifies to reduction of the quantity of fatty matter with simultaneous relative increase of collagen proteins and mineral substances quantity (specifically observed in the raw material) (Table 2). 

Butylphenol-formaldhydharze. Dermatosen 27 49-52 Shono M, Ezoe K, Kaniwa M-A, Ikarashi Y, Kojima S, Nakamura A (1991) Allergic contact dermatitis from para-tertiary-butylphenol-formaldehyde resin (PTBP-FR) in athletic tape and leather adhesive. Contact Dermatitis 24 281-288 Snell FD, Ettre LS (1973) Encyclopedia of industrial chemical analysis, vol 17. Interscience Publishers, USA, pp 9-10... 

A characteristic example of the performance of IC/ICP-OES is the spedation of chromium [190,191]. Due to it widespread use in industrial applications such as chromium plating, dye manufacturing, and preservation of wood and leather materials, chromium concentrations in environmental samples are monitored on a routine basis. Both the US EPA and the European Union have specified maximum admissible chromium concentrations in their respective drinking water directives. As with many other trace elements, chromium (Cr) is typically found in more than one chemical form, each of which with different chemical properties and behavior, such as bioavailability and toxicity. The spedation analysis of chromium is a challenging task, since the stability of different chromium species is easily affected by conditions during sample collection and treatment. For... 

Several methods have been used for the characterization of refuse. Some of these have been derived from the techniques employed for the characterization of solid fuels such as the proximate and ultimate analyses. The reader will recall from the previous section that by proximate analysis we mean the moisture, volatile, fixed carbon, and ash content of the refuse. The ultimate analysis gives the actual chemical composition of the refuse. Still another classification which is frequently employed provides a breakdown of the refuse components according to their origin, viz., glass, leather, paper, etc. 

The International Union of Leather Technologists and Chemists Societies has developed, mostly binding, Methods of chemical leather analysis (I.U.C. methods) and Methods of physical leather testing (I.U.P. methods). The German DIN sheets for testing leather have in most cases been conformed to the above methods. I.U.F. (International Union Fastness) describes guidelines and test methods drawn up by the International Fastness Commission for leather dyes and dyed leathers. 

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