Optimizing soybean lecithin-based fatliquors for improved oxidative stability and leather performance

Fatliquoring agents play a crucial role in leather manufacturing by imparting softness, elasticity, and mechanical strength to the final product. Among the available raw materials, soybean lecithin has attracted considerable interest because of its wide availability, low cost, and high affinity for the collagen fiber network. However, its high degree of unsaturation makes it highly susceptible to oxidative degradation, leading to product instability, color changes, odor formation, and deterioration of leather properties. This study aimed to develop and evaluate soybean lecithin-based fatliquor formulations with enhanced oxidative stability. A 2 3 full factorial experimental design was employed to investigate the effects of three formulation factors: soybean lecithin acid value, surfactant type, and antioxidant concentration. Two soybean lecithins with different acid values were initially characterized by acid value, iodine value, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Fourier-transform infrared spectroscopy (FTIR). Subsequently, eight fatliquor formulations were prepared and monitored over a 60 day storage period for oxidative stability, color variation, thermal behavior, chemical changes, and emulsion stability. The formulations were applied to wet-blue leather, and their effects on physicomechanical properties were evaluated. The results demonstrated that oxidative stability depended on the interaction among formulation components rather than on a single factor. Lecithins with higher acid values exhibited lower oxidative stability, particularly when combined with the nonionic 7-EO ethoxylated fatty alcohol. Increasing the antioxidant concentration from 0.5 to 1.0 wt% significantly improved formulation stability, while sodium lauryl ether sulfate (SLES) enhanced emulsion stability and mitigated oxidative degradation. Application of different fatliquor formulations resulted in significant differences ( p < 0.05) in leather softness, tear strength, and elongation. The optimal formulation combined low-acid-value soybean lecithin, SLES, and 1.0 wt% antioxidant, providing improved oxidative stability while maintaining superior leather performance.