Consider lignin's hydroxyl groups content and type, its molecular weight and content when converting it into epoxy resin

Lignin's natural phenolic structure makes it an attractive candidate for synthesizing bio-based epoxy resin. In the popular direct glycidylation route, finding the most suitable lignin has considerable importance. Hence, two key factors of lignin—molecular weight distribution and hydroxyl groups content—are discussed in this review. The relation of lignin's type and its content in the substrate of glycidylation on cured epoxy networks is also evaluated. Based on accurate determination, lignins with high total OH content, especially high phenolic OH content, are better candidates for epoxy resin, while lignins with high molecular weight and dispersity may not be the best choice. Modification of lignin on OH functionality or combination with other OH suppliers could also be beneficial. Comparatively speaking, lignin bio-oil, especially reductive catalytic fractionation (RCF) lignin, with its distinctive liquid form, tunable molecular weight distribution, high OH functionality and relatively well-defined molecular structure, tends to display a higher potential as a sustainable and safe alternative for epoxy resins.