Epoxidation of Methanol-Soluble Kraft Lignin for Lignin-Derived Epoxy Resin and Its Usage in the Preparation of Biopolyester

Abstract

Most commercial epoxy resins have been produced using toxic bisphenol A. Lignin can be utilized as green substitute for bisphenol A to produce bio-epoxy resins. Methanol-soluble kraft lignin was extracted by methanol fractionation for lignin epoxidation, and epoxidized into lignin-derived epoxy resin via two-step epoxidation consisting of epichlorohydrin addition and epoxide ring restructuring. Epoxidized lignin was selectively separated from non- or less-reacted lignin based on their solubility differences in organic solvents. The existence of epoxide groups in the lignin-derived epoxy resin was confirmed using FT-IR, 1H-NMR, and TGA analyses. Epoxidized lignin was used as a reactive lignin macromonomer to prepare biopolyester. The characteristics of the synthesized biopolyester were analyzed using FT-IR, and the thermal properties were analyzed by TGA. The thermal decomposition temperature of 5% weight loss (Td5) was determined to be 257.1°C, which is comparable to epoxy resins that are used in electronic applications.