Abstract: series of multi-carboxyl polymer (OP) with varying molecular weights and carboxyl contents were used as ligands of zirconium salt in chrome -free tanning. The tanning performance of OP -Zr complex was evaluated by shrinkage temperature, softness, zirconium distribution and extent of fiber dispersion of the leather. When the carboxyl content of OP was similar, the lower molecular weight of OP resulted in better tanning performance. However, the carboxyl content of OP played a more essential role in the tanning performance compared with its molecular weight. In this study, OP4-2 with medium carboxyl content (carboxyl content 4.65mmol/g, Mn 3986g/mol) was chosen as the best ligand of zirconium sulfate, leading to the best comprehensive properties of the crust leather. The shrinkage temperature reached 86 ℃. Meanwhile, the crust leather showed the highest softness, the most uniform zirconium distribution and the highest extent of fiber dispersion.

Key words: chrome-free tanning, zirconium, complex, molecular weight, carboxyl group