Green Synthesis of Cutting-Edge Nonionic Surfactants Derived from Lignin

Surfactants play a crucial role in both everyday life and industrial applications. Unfortunately, most are still derived from fossil sources and are not biodegradable, highlighting the need for nontoxic, biologically derived alternatives. Lignin is a biopolymer found in lignocellulosic biomass, which represents a renewable source of bioaromatic compounds rich in phenolic moieties, making it suitable for further modifications. However, its recalcitrance to chemical and biochemical processes hinders its conversion to value-added products. In this work, a sustainable synthetic process for the preparation of new biobased surfactants under mild conditions was developed. The starting material was vanillic acid (VA), which is a lignin-derived model compound. VA esters were prepared by exploiting several primary aliphatic alcohols with different chain lengths (C4–C10) to obtain the nonpolar tail, achieving a complete conversion after 45 min at 120 °C. The polar head was synthesized by direct coupling with glycerol carbonate in neat conditions, replacing the use of toxic epichlorohydrin, and improving yields (63.1% vs 20.5%). The resulting products were characterized by using the pyrene fluorescence method to prove their surfactant behavior and measure their critical micelle concentration (CMC), showing a correlation between the length of the nonpolar tail and the CMC. The C8 derivative showed the lowest CMC, with an estimated value of 5.05 × 10^–5 M. This work demonstrates the potential for converting lignin-derived platform chemicals into renewable nonionic surfactants for a wide range of applications.