Relationship between the Structure of Modified Ricinoleic Acids via the Thiol–Ene Click Reaction and the Fogging Value of Fatliquored Leather
Yuehong Zhang, Chenyang Liu, Jianzhong Ma, Wenbo Zhang, Qianqian Fan, Zhonglei Ma
Abstract
Herein, hydroxylated, aminated, and carboxylated ricinoleic acids (RA-OH, RA-NH2, RA-COOH) are individually prepared via facile and efficient thiol–ene click reactions with renewable ricinoleic acid and commercially available sulfhydryl compounds as raw materials. The resulting modified ricinoleic acids are subsequently used as natural oils to prepare environmentally friendly fatliquors for automotive interior leather of a low fogging value. Further, the influence of the molecular structure of the three modified ricinoleic acids on the fogging value and free grease content of the fatliquored leather is systematically studied by molecular dynamics simulation theoretical predictions and regular experimental characterization. The introduction of −OH, −NH2, and −COOH to ricinoleic acid can increase its ability to form strong intermolecular interactions with leather collagen fibers, as confirmed by the Ebinding values from molecular dynamics simulations. The interaction strength of modified ricinoleic acids and leather collagen is in the order RA-OH > RA-COOH > RA-NH2 > RA, leading to a low migration rate of modified ricinoleic acids and an obvious lubricating effect on the collagen fibers. Among them, RA-OH shows the strongest intermolecular interaction with leather collagen and is difficult to migrate from the collagen matrix; thus, the RA-OH fatliquored leather exhibits the lowest fogging value of 6.38 mg, the lowest free grease content of 12.36%, and excellent softness and physical and mechanical properties. Overall, a combination of renewable ricinoleic acids with “green” thiol–ene click reactions provides a new strategy for the preparation of sustainable fatliquors for automotive interior leather of a low fogging value, and the wastewater after fatliquoring is also biodegradable, all of which contribute to the sustainable development of the fatliquors in the leather industry.