Upcycling leather waste: The effect of leather type and aspect ratio on the performance of thermoplastic polyurethane composites

Leather is among the most traded commodities globally, despite being one of the most ancient engineered natural materials and a by-product of the meat industry. This reflects its high perceived commercial value as well as its unique physical properties such as tear and wear resistance, thermal stability, and breathability. However, transforming animal hide into leather is a complex process that involves several carcinogenic chemicals which heavily impact the environment. Moreover, the low yield of final leather products, combined with the lack of viable end-of-life options, has drawn significant attention from the research community. Herein, we systematically explore the potential for upcycling leather waste by incorporating it into thermoplastic polyurethane (TPU). TPU composites with various contents of leather waste (5 to 30 wt%), sourced from different tanning methods and with different particle size distributions, were prepared by melt compounding and studied for their morphological, thermal, and mechanical properties as well as tear and abrasion resistance. It was demonstrated that enhanced mechanical properties (Young's modulus 305 MPa) and abrasion resistance are significantly influenced by the average particle size of the leather waste, with the highest aspect ratio (61) of wet blue leather providing the best performance.