Preparation and assistant-dyeing of formaldehyde-free amphoteric acrylic retanning agent

Abstract With the enhancement of environmental protection consciousness, concerns have been raised about non-toxic and biodegradable leather retanning agents. According to the European standard 2002/231/EC, the free formaldehyde content of leather products should be less than 150 mg/kg. As one of the retanning agents in the market, the content of free formaldehyde in the Multifunctional retanning agent (MTA) is 372.22 mg/kg and higher than the limit value. In this work, glutaraldehyde as an alternative of formaldehyde was used to modify acrylic polymer and an amphoteric acrylic retanning agent was prepared. Then it was used in retanning process, and its retanning and assistant-dyeing properties were investigated. The results showed that the free formaldehyde content of amphoteric acrylic retanning agent modified with glutaraldehyde was only 4.17 mg/kg. Meanwhile, the presence of amino groups in the amphoteric acrylic retanning agent improved the dyeing properties of leather by electrostatic attraction. Compared with the leather treated with anionic acrylic retanning agent, the residual dye concentration of the dyeing effluent of the retanned leather with amphoteric acrylic retanning agent decreased from 17.4 mg/L to 10.0 mg/L, and the dyed leather had better resistances to friction and water-washing. In addition, the BOD5/COD value of the wastewater after Mannich base polymer retanning was only 0.32, indicating that the retanning agent was biodegradable. Moreover, the leather retanned with amphoteric acrylic retanning agent had good thermal stability, fullness and physical and mechanical properties. Graphical abstrac