Biodegradable Retanning Material from Tannery Trimming Waste: Extraction, Preparation and Application

The leather industry has long grappled with environmental challenges associated with waste disposal. One ton of wet-salted hides or skins generates approximately 650 kg of solid waste. The majority of trims and hair waste remain underutilized, with hair often discarded or used inefficiently. We initiated the creation of a retanning agent devoid of formaldehyde by utilizing discarded tannery trimmings, with the goal of promoting a circular economy approach in the leather processing industry in our sustainability efforts. Optimal hydrolysis conditions were determined, involving an alkaline (3.75% w/w NaOH) pre-treatment followed by thermal hydrolysis at 100 °C for 5 hours, effectively maximizing the use of trimmings. Similar treatments were applied to hair waste, particularly red sheep hair, yielding successful hydrolysis. Keratin hydrolysate-g-methacrylic acid (KH-g-MA) copolymers were synthesized through in situ polymerization, employing hydrolysates in a redox system. Characterization was carried out using dynamic light scattering and Fourier transform infrared spectroscopy. These newly developed copolymers were applied as retanning agents in the leather industry, enhancing leather qualities such as fullness, grain tightness, and color brightness. Moreover, they improved leather mechanical strength and reduced the need for post-tanning chemicals. This innovative approach not only addresses solid waste issues but also contributes to greener leather processing, thereby fostering a more sustainable environmental landscape.