From Waste to Function: Valorization of Collagen-Based Wastes with Natural Deep Eutectic Solvents for Bioadhesive Applications

In this study, we propose a novel, environmentally, economically, and energetically sustainable approach for the valorization of vegetable-tanned leather waste, aiming at producing biobased adhesives with antibacterial properties and promising water resistance. The treatment of leather scraps was carried out using various Natural Deep Eutectic Solvents (NADES) in mild conditions (1 h, 60 °C), i.e., lactic acid:urea in a molar ratio of 2:1, choline chloride:lactic acid in a molar ratio of 1:1, and choline chloride dehydrated oxalic acid in a molar ratio of 1:1. The resulting bioadhesives exhibited excellent binding performances, in particular, on wood substrates. Structural modifications and its thermal behavior of collagen after the treatment were investigated using Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance (ATR-FTIR), Thermogravimetric Analysis (TGA and TGA/FTIR), Evolved Gas Analysis–Mass Spectrometry (EGA-MS), Pyrolysis–Gas Chromatography–Mass Spectrometry (Py-GC-MS), and proteomic techniques. Overall, this approach highlights a circular and green strategy for upcycling leather industry byproducts into high-performance materials, aligning with current goals in waste minimization and resource efficiency.