Providing Natural Organic Pigments with Excellent Tanning Capabilities: A Novel "One-Pot" Tanning-Dyeing Integration Strategy for Sustainable Leather Manufacturing

Engineering high-performance chrome-free colored leather is currently a tough challenge in the leather industry. Herein, we report on a novel tanning-dyeing integration strategy based on converting natural cochineal carmine (Car) into an effective tanning agent (DCar) without losing its dyeing capabilities via periodate oxidation. Initially, DCar was used as a tanning-dyeing agent, leading to tanned-dyed leather with well-dispersed and fixed collagen fibers (CFs) and a shrinkage temperature (Ts) of ca. 70 degrees C. Subsequently, this leather was filled and fatliquored to be prepared for the subsequent aluminum fixation of the CFs matrix, which was facilitated by the excellent metal complexation capabilities of DCar. This dual integrative process resulted in successful simultaneous leather tanning and dyeing. Consequently, the resultant crust leather had a Ts of ca. 80 degrees C with an outstandingly dispersed and fixed CFs network and excellent softness, fullness, and commercializable mechanical strength (tensile strength: 13 N/mm2; tear strength: 54 N/mm). Besides, it also had a highly marketable brown color, a smooth grain surface, and excellent coloring uniformity and fastness. These results open the door for a new paradigm, i.e., providing natural pigments and dyes with tanning properties to develop novel and benign dual tanning- dyeing agents for the leather industry.