Textile & Clothing

Development of heavy-metal-free dye- and tanning agents and processes: application and process development

As an alternative to environmentally harmful chrome tanning, leather tanning tests have been conducted using tanning agents based upon sustainable raw materials. Extracts from the root of Sutton rhubarb and the overground parts of herbaceous knotgrass have proved to be suitable agents. 

Summary

Chrome tanning is the most effective process available in the leather tanning and processing industry. However, the chromium (III) salts used in the tanning process are associated with severe environmental pollution in the form of chromium-bearing wastewaters, sewage sludges and solid wastes.

The object of this project was the investigation of tanning agents based upon sustainable raw materials, as a means of reducing the release of heavy metals into the environment.  Specific analyses conducted were as follows:

  • 42 varieties of rhubarb roots and 2 varieties of herbaceous knotgrass were subject to chemical analysis, extraction and testing using the tablet test method;
  • Three process concepts for tanning, colouring and final dyebath processing have been developed.

Results:

  • Extracts from the root of the Sutton variety of rhubarb and the overground parts of herbaceous knotgrass have proved to be suitable for leather production, subject to the prior removal of insoluble tar.
  • Tar residues can be processed into a pickling medium, which may be applied prior to tanning or as a colouring agent.  By this method, it has been possible to achieve the residue-free processing of rhubarb extracts.
  • In comparison with chrome tanning, the resulting waste water contains more substances which are susceptible to chemical degradation and biodegradation.
  • Tanning by the use of plant extracts generates an additional cost of some 7 Euros per m2 of leather, which is acceptable for high-quality leather goods.

More Project Informations

Project title:  Development of heavy-metal-free dye- and tanning agents and processes: application and process development

Project number:  1481024/0

Project period:  1996 - 1999

Project region:  Germany (Saxony)

Project contact:

Herr Prof. Dr. rer. nat. Stoll

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Source: German National Library of Science and Technology Hannover (TIB)