Inverse Chrome Tanning Technology Based on Wet White Tanned by Al-Zr Complex Tanning Agent

Abstract

In conventional leather production, the chrome in wet blue will be inevitably released into all the floats in post-tanning processes, which brings about a big amount of chromecontaining wastewaters, which can be difficult to treat. As a solution to this problem, an inverse chrome tanning technology based on wet white tanned by Al-Zr tanning agent (AZ) was investigated in present work. The AZ was the co-complexes of Al3+ and Zr4+ (9:1, mole ratio) with polycarboxylic acids synthesized in our laboratory. The wet white tanned by AZ had a shrinkage temperature (Ts) of 95oC under optimal tanning conditions, and therefore, it met the needs of splitting and shaving operations without generation of chrome wastes. More importantly, the wet white was suitable to be followed by retanning, dyeing and fatliquoring processes because of its satisfactory thermal stability and analogous electric charge characteristic to chrome leather. After fatliquoring and fixing by acid, chrome tanning was undertaken as final step. The leather with Ts around 110oC and comparable physical and aesthetic properties to conventional chrome tanned leather was obtained when 0.5-1% Cr2O3 was used in this inverse chrome tanning technology. The evident advantage of this technology is that no chrome was discharged in whole leather making processes except final chrome tanning and washing processes, and as a result, the volume of chrome-containing wastewater was largely reduced and easier to collect for recovery.