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Copolymers of tannins and waste lignocellulosic materials with synthetic materials for non-toxic, environment-friendly chromesbstitutes in leather tanning

Toxic chrome salts are used for the production of 70% of today's soft leather. The project proposes synthesising copolymers of non-toxic vegetable tannins and waste lignocellulosic materials (both derived from the forestry industry) with (i) acrylic acid, (ii) aminoplastic resins, and (iii) by reacting natural vegetable tannins with small amounts of non-toxic nitroalcohols. It will also show that these compounds can substitute toxic chrome salts, either completely or at least partially (in re-tanning operations), to produce acceptable soft leather.


The final report outlines the technology developed for and the research and results obtained in the manufacture of flexible soft leather by total and partial substitution of toxic chrome salts by the use of a vegetable tannin coreacted in situ with a variety of different melamine-urea-formaldehyde (MUF) polycondensation resins. These conclusions were reached for more than 130 leather treatment combinations tried.
Successful total and partial substitution of toxic chrome salts by the use of a vegetable tannin coreacted in situ with an MUF resin is possible, and was achieved in leather tanning and retanning. The results obtained compared perfectly to those of chrome-tanned leather both as regards colour and light fastness. Even more importantly as regards leather shrinkage temperature exceptional improvements were indeed achieved. In the case of chestnut tannin only some further, slight improvements on this might be needed in some formulations and were introduced by mixing with other tannins, in particular mimosa. Glutaraldehyde and oxazoladine initial confirmatory experiments have already been done but do not improve further on what was obtained with the vegetable tannin/MUF copolymers.
A completely new MUF resin for leather treatment was developed far superior and far cheaper than the obsolte commercial MUF resins available now. This result is certainly a commercial probability.
The good results ontained applied to all three tannins finally tested, namely chestnut, mimosa and quebracho tannin extracts. This is fundamentally important, indicating that this approach is usable successfully with any type of hydrolysable and/or polyflavonoid tannin extracts, rendering possible for tanning even species currently discarded, like European and other pine bark tannin.
New systems of analysis of the leathers produced were developed, refined and compared with the results of classical analysis. Electron Spin Resonance (ESR or EPR) kinetics and UV ageing kinetics have been used extensively and correlated with the colour and light fastness obtained by UV and traditional colorimetrical methods with interesting new scientific findings. Equally, Thermomechanical analysis (TMA) of the tension of leather as a method to investigate the correlation of classical shrinkage temperature was investigated for the first time, and yielded insights as to what occurs in shrinkage at molecular level: not explored hitherto. Equations correlating the results of the traditional leather shrinkage test with the TMA test were obtained, as were equations correlating the parameters for a proper colour evaluation system with the light-fastness of the leather produced.
Mixed leathers were manufactured in Italy based on a mix of vegetable tannin and a syntan to which was coupled the same MUF resin. This gave excellent results and a particularly light-coloured, almost white, leather.
The results were applied at factory level in a series of bulk plant trials in the UK. The results supported the lab results, especially as this concerns shrinkage resistance to high temperatures as well as light stability. A low degree of 'drawing' of the leather was observed in full-scale industrial trials, but this was minimised with appropriate industrial treating techniques. The industrial trials indicated that the system developed is most apt for soft upholstery leather tanning and retanning.


Scientist responsible for the project

Rue de Merle Blanc, 27 Box 1041
88051 Epinal CEDEX 9
France - FR

Phone: +33 3 29 81 11 50
Fax: +33 3 29 34 09 76


Project ID QLRT-1999-00913
Organisation University Henri Poincare - Nancy 1
Area 5.2
Start date 01 February 2000
Duration (months) 36
Total cost 860 000 €
Total EC contribution   430 000 €
Status Completed

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