Manufacturing of isocyanate-based oligomeric dyes with high coloring capabilities: synthesis and application in the dyeing of organic chrome-free leather

Leather dyeing is a critical step in leather manufacturing, as it is responsible for providing leather products with an eye-catching visual aspect and adequate quality properties to meet customers' expectations. This step is becoming more and more challenging as the leather industry advances hand in hand with new environmentally friendly policies and regulations to achieve a safer and healthier planet by replacing the highly polluting Cr-based leather tanning technology with greener alternatives. As a result, achieving high-performance dyeing of organic chrome-free leather is one of the bottlenecks for the sustainable development of the leather industry. Herein, we propose a novel strategy to fabricate an isocyanate-based oligomeric dye (IBD) with high coloring capabilities (component content higher than 62.8%) based on toluene 2,4-diisocyanate and reactive red dye 180. This material has been tested for the dyeing of biomass-derived aldehyde (BDA)-tanned leather with excellent outcomes. The experimental results showed that the crust leather dyed with our novel IBD dyeing agent had higher color fastness and better fullness than the leather dyed with conventional anionic (CAD) or reactive red 180 (RRD-180) dyes. These excellent and promising results open new avenues in manufacturing high-performance organic Cr-free leather products and help to ensure the sustainable transition of the leather industry from Cr-based leather tanning to more sustainable alternatives, maintaining the final quality of the leather products.

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