Efficient and green approach for the esterification of lignin with oleic acid using surfactant-combined microreactors in water

Abstract

A green, effective, and feasible reaction for esterification of lignin with oleic acid in water at room temperature was investigated. A surfactant-combined system (p-toluenesulfonic acid/4-dodecylbenzenesulfonic acid) was designed to simultaneously solubilize kraft lignin and disperse the oleic acid, producing microreactors for esterification. Esterification using a higher 4-dodecylbenzenesulfonic acid dosage at room temperature was found to be a good option, and an increasing oleic acid dosage had no effect on improving the degree of esterification. Structural characterization analyses confirmed the successful esterification of lignin with oleic acid, indicating the effectiveness and feasibility of esterification of macromolecules in water. Due to the introduction of a long flexible aliphatic chain, the lignin ester showed a noticeable decrease in glass transition temperature, an obvious increase in contact angle, and exhibited excellent thermoplasticity, processability, and hydrophobicity. Additionally, lignin-ester nanoparticles were prepared through the micellization of p-toluenesulfonic acid. Therefore, the method of esterification using surfactant-combined microreactors in water is promising for high value-added utilization of lignin.