Bio-chemical Synthesis of Lignin-Derived Monomers for Bio-based Pressure Sensitive Adhesives

Abstract

In recent years, the development of bio-based polymers derived from lignin has garnered significant attention because of environmental concerns. Lignol, a monomer from lignin depolymerization, exhibits higher solubility than lignin and is synthesizable with other compounds. The lignin monomers extracted from lignocellulosic biomass consist of substances such as eugenol, dihydroeugenol, and isoeugenol. In this study, a lignin monomer with a vinyl functional group was synthesized, which can be utilized as green polymers for bio-based adhesives. Dihydroeugenol (DE), a lignin-derived aromatic compound, was the main substrate of this study. A DE-based acrylate was synthesized through a three-step enzymatic esterification process. The reaction conditions of the first and second steps were adjusted step by step based on the following parameters: solvent, immobilized enzymes (Lipozyme 435, Lipozyme TL IM, Lipozyme RM), molar ratio, temperature, and enzyme concentration. In the first step, dihydroeugenyl succinate (DiSu) was synthesized from the OH group of DE and one of the carboxyl groups of succinic anhydride (SuAn). In the second step, 4-hydroxybutyl acrylate (4HBA) was produced by 1,4-butanediol (BDO) and acrylic acid (AA). Lastly, the carbonyl group of DiSu and the hydroxyl group of 4HBA was esterified, generating a new green chemical, 4-(acryloyloxy)butyl dihydroeugenyl succinate (4ABDS). Through optimization, the final conversion of the first step was 60%, and 46.5% in second step. In the final step of the synthesis, the target monomer was produced at a quantity of 0.74 mmol, constituting 70% of the consumption of DiSu. The result of this study suggests the potential of bio-based adhesives to serve as environmentally friendly substitutes for petroleumbased adhesives in various sectors, including packaging, construction, and automotive.