Gargano, Marika (2023) Green chemistry and circular economy as alternative strategies for the traditional leather manifacturing industry. [Tesi di dottorato]

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During the last decades, the increasing social and political attention to environmental sustainability has driven the industrial sectors towards the development of cleaner and closed-loop productions. Leather industry is one of the most fitting instances of the green transition. Although it is originally based on the principles of Circular Economy, being leather the result of the recovery and valorization of a by-product of the meat industry, nowadays this industrial sector is labeled as one of the most polluting, due to the high polluting procedures and the huge amounts of wastes produced. The green transition of tanning industry is, therefore, aiming to the development of alternative biotechnological approaches to traditional methods and focusing on the recovery of wastes produced. In this scenario and in a Circular Economy perspective, the present PhD project has been defined. The objectives of the project are related to the development of green strategies for tanning processes, by i) recovering leather solid wastes through the extraction of collagen and ii) applying the extracted collagen in leather processing, replacing the polluting chemicals that are conventionally used. For the first part of the project, four different kind of tanned solid wastes have been treated to extract collagen. Two cost-effective enzymatic extraction methods were developed and optimized in terms of amounts of chemicals, reaction time and extraction yields. The extracted collagen was characterized and it results that the developed extraction methods allow extracting high quality collagen. To employ back collagen in the leather processing, an enzymatic-mediated cross-linking reaction between collagen and casein was set up ex situ and optimized on the basis of the percentage of high molecular weight moieties formed. In the second part of the project the extracted collagen has been applied as filling agent for low quality leather and as finishing agent during the last part of leather processing. Regarding the filling, the optimized cross-linking reaction was exploited in situ, re-designing the re-tanning process. It results that leather treated with collagen appeared more uniform, well-filled and more pleasure at the touch than the leather treated with conventional re-tanning process. Finally, the extracted collagen was used as component of finishing formulation, allowing to develop an eco-friendly finishing system and to obtain treated leather with characteristics comparable to those of leather treated with the top-of-the-range finishing formulation.

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