Biodegradable leather: sodium alginate derivatives as re-tanning agents

Leather is a well-established biomaterial due to its unrivalled properties that make it irreplaceable for many traditional and modern applications . However, sustainability and mass production do not always go hand in hand, and obtaining sustainable and highly performing tannins is a global challenge. In the last years, alginate, a linear biodegradable polysaccharide, abundantly available, has seen an increase in the number of applications due to the improvement of its physicochemical properties by oxidation and functionalisation . Novel alginate-based materials have emerged as an excellent option to enhance the cross-linking effect with proteins while ensuring sustainability and bio-degradability. By controlling both the degree of oxidation and molecular weights, alginate derivatives for tanning industry have been obtained in the lab. In this work, re-tanning agents based on sodium alginate derivatives (SADs) were obtained by ultrasonic (US) treatments and used in lab micro-pilot tests. The working conditions (US frequency and intensity, time, temperature) and H2O2 or catalyst presence were varied to obtain a product with suitable viscosity and oxidation degree. Molecular weight of SAD samples was measured by gel permeation chromatography. The aldehyde groups presence was checked by Fourier transform infrared spectroscopy (ATR-FTIR). The SADs ability to bind to collagen in hide was evaluated by micro-Differential Scanning Calorimetry. The best SAD was synthetized on micro-pilot scale and tested as re-tanning agent in a wet white process. The final product showed enhanced tensile strength, tear load and breakage resistance. Leather water vapor permeability decreased, thus confirming that alginate irreversibly occupied the collagen interfibrillar spaces. These results represents a first step in the development of an industrial re-tanning product for high-performance wet-white leather without changing the current technologies, methods, and processes