Preparation and application of a novel biomass-based amphoteric retanning agent with the function of reducing free formaldehyde in leather

Non-toxic and biodegradable retanning agents have received increasing attention over recent years driven by the tough environmental targets for leather cleaner manufacturing. Herein, a novel biomass-based amphoteric retanning agent, which can reduce free formaldehyde significantly, was prepared using hydrolyzed collagen and oxidized valonia extract as the raw materials. In this investigation, collagen was derived from chromium-containing waste leather by in situ hydrolysis, and oxidized valonia extract was obtained after laccase catalysis of valonia extract. A Schiff’s base reaction occurred between the laccase-catalyzed valonia extract and hydrolyzed collagen. Notably, the leather retanned using the oxidized valonia extract modified collagen retanning agent was comparable and surpassed a market glutaraldehyde modified collagen retanning agent exhibiting superior shrinkage temperature, thickness, mechanical properties, dyeing properties and free formaldehyde removal function (free formaldehyde removal rate is 70.2%). This study provides a method for preparing an outstanding multifunctional non-toxic amphoteric retanning agent and offers a method for sustainable development of leather.