Preparation and application of novel amphoteric acrylic retanning agents to improve dye absorption

Amphoteric acrylic polymers are some of the commonly used leather retanning agents, and possess assistant-dyeing function in contrast to traditional anionic acrylic retanning agents. To further enhance the cationic modification degree of anionic acrylic retanning agents, various amines (dimethylamine, diethylamine, dipropylamine, diethanolamine, dicyclohexylamine and diphenylamine) with different structural characteristics were selected as raw materials to prepare amphoteric acrylic retanning agents via the Mannich reaction. Then, the obtained amphoteric acrylic retanning agents were used in leather-making, and the retanning and assistant-dyeing properties were investigated. Compared with the anionic acrylic retanning agents, all amphoteric acrylic retanning agents have better assistant-dyeing owing to the presence of amino groups. The retanning agents modified by different amines exhibit different properties. The amination degree of the acrylic polymer retanning agent modified by diethanolamine was the highest (40.8%) and had better assistant-dyeing, which was confirmed by its highest dye-uptake (87.5%) and K/S value (17.0). The tensile strength of leather retanned with diphenylamine-modified acrylic polymer was the highest (23.6 MPa). The thickening rate of the leather retanned with dipropylamine-modified acrylic polymer was the highest (23.8%). Considering these properties, the overall performance of the amphoteric acrylic polymer modified by diethanolamine was found to be the best.