Mini-Review on the Synthesis of Lignin-Based Phenolic Resin

The use of biomass in phenolic resin can not only improve performance and reduce costs but can also reduce pollution and protect the environment. Lignin is a biopolymer with a three-dimensional network structure formed by three phenylpropane units of p-hydroxyphenyl, guaiacyl, and syringyl connected by an ether bond and carbon–carbon bond, containing a large amount of phenol or an aldehyde structure unit. It is an effective way to improve the economy, protect the environment, and reproduce the resin via the synthesis of high-performance biophenolic resin polymer materials by modification or depolymerization of lignin. This review describes the latest developments in the preparation of phenolic resins by modification or depolymerization of lignin, focusing on the modification of its original functional groups by phenolization, demethylation, and hydroxymethylation, as well as chemical depolymerization methods. The properties of thermosetting or thermoplastic phenolic resins as prepared by different lignin modification methods are compared, and the future research directions for the synthesis of biomass-based phenolic resins are prospected.