Construction of a Chrome-free Tanning System Based on Highly-oxidized Starch–Zirconium Complexes

Chrome-free leather manufacture is one of the major focuses of leather industry. In this work, a chrome-free tanning system based on highly-oxidized starch–zirconium complexes (HOS–Zr) was constructed. Particle size and charge properties analyses revealed that the small size (2.5 nm) and the low cationic species content (45.1%) of HOS–Zr at low pH facilitated its uniform penetration in leather at the initial stage of tanning, and the large size (89–169 nm) and the high cationic species content (77.5%) of HOS–Zr after basification contributed to its stable crosslinking between collagen fibers. A 3% HOS–Zr offer (based on the weight of ZrO2) imparted wet white with sufficient tanning effect. The physical properties of HOS–Zr crust leather were remarkably better than those of lactic acid–zirconium crust leather and were comparable to those of chrome crust leather. Wastewater in HOS–Zr tanning system showed a reduction in TOC load by 40.0% and higher biodegradability compared with chrome tanning system. As a result, this work provided a practical and sustainable approach to eliminate chrome in leather manufacture.