One-Step Synthesis of Starch-Based Composite Chrome-Free Tanning Agents via In Situ Catalysis Using Hydrotalcites

The oxidation of starch into valuable chemicals holds great promise for the leather industry, but the catalytic efficiency of existing reactions is low. Moreover, residual catalyst in the reaction liquid is a potential environmental hazard. Herein, starch was oxidized by hydrogen peroxide and a magnesium aluminum iron hydrotalcite (MgAlFe-LDH) catalyst to introduce functional groups and nanomaterials, forming a starch-based hydrotalcite composite (OS-MgAlFe-LDH) in one step. This catalyst showed improved catalytic efficiency, and the generation of pollution was avoided. Moreover, the prepared OS-MgAlFe-LDH was suitable as a complex tanning agent for chrome-free tanning with improved efficiency, and MgAlFe-LDH acted as a crosslinking reinforcing agent. Using this tanning agent, the hydrothermal stability of crust leather was enhanced (shrinkage temperature: 75 °C). The tanned leather had high porosity (79.06%) and a uniform tanning agent distribution ascribed to the varying molecular weights of the components of the OS-MgAlFe-LDHs (weight-average molecular weight: 5438 g/mol). The binding energy between OS-MgAlFe-LDHs and the leather collagen (94.62 kcal/mol) was high, inhibiting the migration of OS-MgAlFe-LDHs from the collagen matrix. Thus, OS-MgAlFe-LDHs exhibited strong crosslinking performance with leather collagen. In summary, a sustainable and environmental-friendly tanning agent was prepared by a one-step synthesis in this work, offering a fundamental step for the preparation of biomass materials in the leather industry.