Synthesis of Eco-Friendly Additives for Sustainable Tanning Processes

Sustainability is a global level challenge for tanning industry whose production is based on Cr(III) salts for more than 90%, negatively impacting both biotic and abiotic factors in an ecosystem. Societal challenges are strongly pushing tanning industry to develop a more sustainable leather value chain. In fact, over the past 100 years, a lot of synthetic tannins have been developed for trying to replace chrome and to make the process more sustainable.1 An alternative tanning system, in fact, should not only satisfy environmental criteria, but should be also able to match the properties of chrome tanned leathers.2 For this reason, the wet white tanning process seems, nowadays, the only alternative to develop a less polluting process obtaining high quality products. In this respect, many efforts have been focused on the design of new environmental friendly and high-performance tanning products for industrial applications. This industrial PhD project has been developed in collaboration with the BI- QEM SPECIALTIES S.P.A., Leather and Footwear Research Institute (ICPI), Politehnica University of Bucharest, and FGL International S.P.A. In the first phase of this PhD project, a new supramolecular system based on bisphenol S and β-cyclodextrin was synthesized and used as a tanning agent and as an eco-friendlier and sustainable alternative to tannins currently on the market. Firstly, we investigated the formation of the supramolecular system, using 1D and 2D NMR, FT-IR, and high-resolution mass spectrometry and we studied the different interaction between β- cyclodextrin and the two isomers of bisphenol S. Secondly, we tested the obtained systems on raw hide to evaluate their efficiency in the tanning process on both a laboratory and pilot scale, in collaboration with FGL International S.P.A. In the project phase carried out at the Leather and Footwear Research Institute (ICPI), Bucharest, under the supervision of Dr. Elena Badea, the goal was to obtain a fully eco-sustainable re-tanning agent from sodium alginate, a biodegradable, renewable biomass, using the ultrasonic technology. The efficacy of the obtained sodium alginate products (SAD) was evaluated by micro-differential scanning calorimetry (micro-DSC)3 and attenuated total reflection mode infrared spectroscopy (FTIR-ATR). 4 The results so far obtained have confirmed the suitability of the various SADs as non-toxic and biodegradable re-tanning agents. [edited by Author]