Tanning Performance of a Novel Chrome-Free Complex Tanning Agent: Penetration and Distribution

Penetration of tanning agent in leather plays an important role in tanning performance and properties of finished leather. A novel complex tanning agent composed of Al–Zr salts and highly-oxidized starch ligand, named TWLZ, was used for chrome-free tanning. The masking effect of highly-oxidized starch reduced the electropositivity of metal complexes, which should help penetration of TWLZ and moderate its fixation during tanning. The effects of tanning agent dosage, basification method and pretreatment method on the distribution of TWLZ in leather were investigated. Using 8% TWLZ and basifying with magnesium oxide benefited the penetration and distribution of TWLZ throughout the cross-section of leather. Pretreatment with an amphoteric organic tanning agent could regulate the charge state of the hide, balance the penetration and fixation of TWLZ, and thus show uniform distribution and satisfactory tanning performance. This work will guide the establishment of TWLZ chrome-free tanning system.