Objective Leather, as a natural polymer material, is widely used in the manufacturing of various products (e.g., shoes, clothing, bags, suitcases, sofas, car seat cushions) and serves as a pillar of China's light industry and a key export-oriented sector. However, the dominant chrome tanning method inevitably generates chromium-containing pollutants that threaten the environment and health. With increasingly stringent environmental regulations and growing awareness of green consumption, developing chrome-free tanning technologies has become urgent. Biomass-derived aldehyde (BDA), with advantages such as renewability, biodegradability and low formaldehyde risk, is regarded as an ideal candidate for green chrome-free tanning agents. Current research mainly focuses on the synthesis and application of BDA, but traditional processes remain water-intensive and cumbersome. In the context of green and low-carbon trends, simplifying processes to achieve energy conservation and emission reduction has gained significant attention. Therefore, this work proposed a BDA-based "one-pot" integrated processing technology for chrome-free leather, covering key steps from tanning to fatliquoring, and systematically evaluated the properties of the resultant crust leather, thereby providing new insights into green and efficient leather manufacturing.
Methods In this work, sodium chloride and BDA were first added to the drum. After sodium chloride was fully dissolved, the pickled sheepskin pelt was added. After the pelt was fully rewetted, sodium bicarbonate was added directly to raise the pH to 8.0, and the bath was heated to 40 ℃ and rotated for 2 h. Subsequently, a specified amount of formic acid solution was added to adjust the bath pH to 6.5. After running for 0.5 h, the tanned leather was processed under conventional post-tanning conditions without drainage. After the final aluminum salt treatment, the crust leather was obtained. The shrinkage temperature of leather at different stages, the thickening ratio, fiber dispersion, coloring performance, mechanical strengths, grain surface smoothness, softness, and fullness of crust leather were investigated. Moreover, the processing cycle and water consumption involved in this "one-pot" integrated processing technology were analyzed, with a comparison of the conventional tanning and post-tanning processing system (taking the chrome tanning system as an example).
Results Characterization results indicated that when the BDA dosage was only 2.0% (based on the weight of limed pelt), the shrinkage temperature of the crust leather was 74.4 ℃ with a high thickening ratio, indicating a satisfactory uptake of post-tanning materials. Besides, the tensile and tear strengths of the crust leather reached as high as 23.6 N/mm2 and 63.9 N/mm, respectively. Moreover, the crust leather had uniform coloring property, fine-grain surface, as well as excellent softness and fullness, indicating the favorable tanning and post-tanning effects of the BDA-based "one-pot" process technology system. Significantly, this novel one-pot process required only 8 h and 200% water, reducing the processing cycle by nearly 52 h and water consumption by 800% compared with the traditional chromium tanning and post-tanning process.
Conclusion This work successfully demonstrates that a highly integrated "one-pot" process technology system from tanning to post-tanning can be constructed based on the BDA with mild reactivity. While ensuring that the crust leather has satisfactory mechanical strength and sensory properties, it can significantly reduce processing cycle time and water consumption. This work not only offers a new technical reference for achieving green, efficient chrome-free leather manufacturing, contributing to the sustainable development of the leather industry, but also provides new high-value utilization methods for biomass resources.
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