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Leather production by alternative processes less pollutant than chrome tanning

In order to better recycle scraps and depuration sludges
generated in the tanning industry, free-chrome compounds
will be utilised in the industrial process.

The project intends to set-up cleaner tanning technologies using both the traditional tanning chrome salts, but without pickling and deliming treatment as separate phases and tanning agents poly-functional organic resins, 'as they are' or with metal compounds (chemically bound or additives). The possibility to obtain leather goods with technological characteristics similar to those of the skins processed with the traditional chrome tanning will be investigated. In the first case, trials will be performed on: - tanning of just de-haired and fleshed hides with potassic chrome alum. Such technology allows high quality products to be obtained without using salt, acids, and the chemicals usually utilised in deliming and fleshing processes. The working time is reduced, so is the pollution level of waste waters. In the second case, trials will be performed on: - pre-tanning techniques with these substances followed by tanning with chrome salts in order to obtain a better exhausting of the chrome bath; - tanning techiques with metallic-organic compounds with reduced amounts of chrome and other metals compared with traditional tanning; - tanning techniques with organic resins, completely excluding the metals. Such technologies represent the result of several studies and research works about the optimisation of the tanning phase and their application allows to obtain leather goods with excellent quality and to decrease the environmental impact produced by the leather manufacture. In fact in the last few years, a noticeable effort has been made in order to improve the knowledge of the chemical reactions involved in the chrome tanning process. State-of- the-art in interaction mechanisms among Cr+3 salts and leather proteins seems to show that the tanning action is connected to both functional tanning agents and geometric characteristics. In fact it seems that the mechanical properties of the tanned leather may be mainly attributed to the building up of bonds or bridges among collagen macromolecules chains and chrome aqueous-compounds having -OH groups able to link up with the functional groups and a suitable geometry to penetrate into the available interstices and fill them. It seems that the electric charges present on such compounds may hamper the penetration, but favour stabilisation by means of electrostatic bonds. The good quality of the product after the pre-tanning phase performed with polymeric functional resins suggests the possibility that at least a part of the chrome compound may be replaced by organic molecules with dimensions that can be moduled according to the polymerisation stage and functional groups able to bind themselves to the skin thanks to the cooperative capacity due to the macromolecule structure. These aspects will be exploited into the project with the objective to improve the chrome exhaustion and to lower notably its content in the exhausted waters. These concepts can be further developed in the framework of environmental protection and preserving the quality of the final product. In the short term, experimental trials on chrome compounds with polymeric species having suitable dimensions and functionality could be performed, whereas in the long term new polyfunctional organic resins and eventually alternative metal compounds will be studied. Moreover the project will study the application of new technologies for the finishing phase and in particular the use of a system of roller coating for the leather, instead of the traditional one using a spray painting procedure. The aim is to obtain a reduction of organic solvents (whether volatile or not) and aerosols, keeping at least the same final quality of the product. This will be obtained using microfoams (made by resins with a water-based solvent) and suitable machinery (rolls), which will allow the rugosities of the skin (scratches, cavities, wavy zones, etc.) to be filled better than the spraying process. Other advantages will be: high reduction of dispersed solvents and aerosols (also causing less expenses), no necessity for devices for aerosol abatment, better precision of microfoam deposition (the process may require only one run instead of two or three as is the case in the traditional one) and an improvement in the work environment. The project structure will be: 1) Characterisation of new tanning agents for producing leather goods with and without chrome; 2) Characterisation of new ecological products to be used in the re-tanning, dying, padding phases for producing ecological leather goods 3) Verification of the possibility to recycle the waste resulting from this tanning process (agriculture, energy, etc.) By using new tanning agents and products for the re-tanning, dying, padding phases, it will be possible to have leather for vamp and peltry with characteristics similar to those of the products at present on sale (such as padded hides, nabuk, etc.) Keywords: tanning, pollution, tanning agents.
Acronym: 
ECOLEATHER
Project ID: 
2 141
Start date: 
01-11-2001
Project Duration: 
24months
Project costs: 
2 800 000.00€
Technological Area: 
Market Area: 

Raising the productivity and competitiveness of European businesses through technology. Boosting national economies on the international market, and strengthening the basis for sustainable prosperity and employment.