Processing Leather using Deep Eutectic Solvents

Leather processing is a significant source of aqueous waste particularly in LEDCs. Most of the waste arises from processes such as hair removal, fat removal, chromium tanning, and dyeing. The main concept behind this thesis is to determine whether leather can be processed using deep eutectic solvents, DESs. These are mixtures of quaternary ammonium salts and hydrogen bond donors. They have physical and chemical properties which can be tuned by varying the type and amount of the components. The idea is to include the DES as an active ingredient using a minimum amount of fluid in the processing and an ideal scenario would be for all the DES to be absorbed into the leather. The first part of the study investigated the stability of collagen with DESs. It was found that no denaturing of the collagen occurred even after exposure for 2 days at elevated temperature. It was shown that the DES was able to leach out some of the chromium but this had only a small effect on the mechanical strength and the shrinkage temperature. The leather absorbed a large amount of DES which changed the morphology of the surface but this could be reversed when hydraulic pressure was applied to the sample and almost all the DES was squeezed out of the sample. The DES acted as a lubricant when left in the leather. In the second part of the study, post tanning processes were attempted using DESs. It was shown that dyeing could be effectively carried out using hydrophobic dyes and the advantage of this was that there was no apparent leaching when the sample was washed. Post-tanning with vegetable tanning agents was shown to be successful although extended tanning times did result in more leaching of chromium. The final part of the study showed that a post-tanning process could be used to treat an ovine hide using half the concentration of active ingredients that would classically be used in an aqueous process. Both processes produced leathers with the same mechanical and optical properties but the green metrics for the DES treated leather were better than the traditional method. It was also shown that particles such as graphite could be infused into leather using DESs.