A pre-tanning agent (OXD) which contains carboxyl, hydroxyl and tetra-amino groups was synthesized and applied in high exhaustion chrome tannage. This pre-tanning agent is able to react with the pendent amino groups of collagen and thus improves the hydrothermal stability when the additional carboxyl, hydroxyl and amino groups are introduced into the backbone of collagen. In the tanning process, the introduced carboxyl groups and the intrinsic carboxyl groups themselves of collagen coordinate with chromium and form uni- or multi-point bound chromium complexes, which seems to contribute to the final leather's excellent chromium combination fastness and high chrome exhaustion. In a practical tannage, hide or skin pre-tanned with 2wt% OXD-I followed by a traditional chromium tannage, the absorption of chromium increased from 70.6% to 96.5%, and the content of Cr(2)ZO(3) in the wastewater decreased from 1.76g/L to 0.16g/L. The shrinkage temperature of the leather also shifted from 104 degrees C to 114 degrees C. In a comparison with traditional chromium tannage, leathers pretreated with OXD followed by a chromium tannage showed good fullness and higher area yield as well as higher chromium combination fastness.

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Sichuan University