Waterless tanning: chrome tanning in ethanol and its derivatives

Abstract

An approach towards waterless tanning is crucial to address present challenges faced by humanity such as global warming and the depletion of water resources. Here, green solvent alternatives to water such as ethanol, ethyl acetate and ethyl lactate were employed for both pickle-based and pickle-less chrome tanning. The results show that an ethanol medium appears to be the best solvent for chrome tanning in terms of color, chromium uptake and other bulk properties of tanned leathers. Extensive studies indicate that chrome tanning in the ethanol medium leads to a higher exhaustion (87% for pickle-based and 95% for pickle-less), better chromium content, distribution and shrinkage temperature, and low chromium leaching in tanned leathers compared to water mediated tanning. Both visual and electron microscopic analyses demonstrate a comparable grain structure and fiber architecture in tanned and crust leathers. Similarly, the strength and organoleptic properties of crust leathers are also comparable between ethanol and water mediated tanning. The process enables the reduction of COD, BOD and TS loads in the composite liquor by 14–26, 21–28 and 42–46%, respectively. The leather properties are not altered upon recycling of the chromium containing ethanol liquor up to two times. These results suggest that it is possible to replace water with ethanol for chrome tanning, which offers great potential for sustainable leather manufacture with solvent recycling.