Unique Gelation of Polyethylene Glycol-Modified Lignin in Hot Ethanol and Its Application to the Synthesis of Epoxy Resin with a Large Lignin Content

Abstract

Glycol lignin is one of the novel lignin derivatives extracted from softwood meal and is expected to be an industrially important organic resource. Here, we show the peculiar aggregation behavior of glycol lignin in ethanol and the production of an ethanol-containing gel. The gel could be simply obtained by stirring glycol lignin powder in hot ethanol for several minutes. Furthermore, the gelled glycol lignin could be easily and homogeneously mixed with a traditional epoxy chemical, bisphenol A diglycidyl ether, in any ratio without any additional solvent and/or heating, resulting in an easy production of epoxy resin using wood-based lignin resources. Since the residual ethanol in the mixture could be easily evaporated before the curing process, thermosetting hard epoxy resin with glycol lignin contents of up to 90 wt % was prepared through the homogeneous mixing with the gel. Quantitative analysis of the equilibrium reaction between ethanol and glycol lignin using a gas adsorption analysis tool was investigated to understand the gelation behavior. It was suggested that the ethanol molecules were stored between polyethylene glycol molecular chains in glycol lignin, which generates a unique chemical character of this novel lignin derivative material.