Biomass-derived aldehyde tanning agents with in situ dyeing properties: a ‘Two Birds with One Stone’ strategy for engineering chrome-free and dye-free colored leather

Abstract

High-profile chrome (Cr) pollution from tanning and potential health hazards from released leather dyes and pigments from leather products restrict the sustainable development of the leather industry. Herein, we report on a novel ‘Two Birds with One Stone’ strategy to simultaneously eliminate Cr and colorant pollutions using a Cr-free tanning agent with an in situ dyeing ability. Sucralose, containing an electron-withdrawing group (–Cl), was employed to fabricate a biomass-derived aldehyde tanning agent with in situ dyeing properties (BAT-iDP). This agent formed Schiff-base crosslinks between its aldehyde groups and the amino groups of collagen fibers (CFs), which efficiently dispersed and fixed the CFs, producing tanned leather with sufficient thermal stability (80.2 °C of shrinkage temperature) to meet commercial requirements. Simultaneously, the presence of an auxochrome (–Cl) in the structure of the Schiff-bases formed endowed the tanned leather with a brown color characteristic of leather. As a result, the tanned leather produced with our ‘Two Birds with One Stone’ strategy had excellent dyeing uniformity, color fastness to dry-wet rubbing and favorable mechanical strengths (14.7 N mm⁻² of tensile strength and 46.3 N mm⁻¹ of tear strength). This novel approach provides new insights for designing and developing multifunctional sustainable materials towards a greener and carbon-neutral leather industry.