Research Progress on the Synthesis and Modification of Bio-based Flame-Retarding Epoxy Resins

Abstract

Epoxy resins (EPs) are widely used in adhesives, coatings, encapsulation materials, and high-performance composites due to their excellent overall properties, such as excellent bond strength, dimensional stability, chemical resistance, etc. However, EPs have the significant disadvantage of insufficient flame retardancy, which limits their applicability. At the same time, increasing environmental concerns, such as global warming and the depletion of oil resources, require the exploration of alternatives, especially bio-EPs derived from sustainable sources. This review presents the research progress on intrinsic flame-retardant EPs, including those based on phosphate ester, phosphaphenanthrene, and cyclotriphosphazene, as well as their underlying mechanisms. Subsequently, the synthetic routes, structures, and properties of several representative bio-based flame-retardant EPs, such as eugenol-based, cardanol-based, rosin-based, vegetable-oil-based, and vanillin-based, were introduced. Finally, the development of bio-based flame-retardant EPs is envisioned, which can be further studied in terms of expanding raw material choices, optimizing synthesis and processing methods, comprehensive characterization and performance evaluation, life cycle assessment, and sustainability analysis. This review is instructive for the research on the synthesis of bio-based EPs and their flame-retardant modification.