Achieving flame retardancy and mechanical integrity via phosphites in bio-based resins

Bio-based flame retardant (FR) resins typically exhibit diminished mechanical properties compared with their petroleum-based counterparts. Recent experiments identified a promising FR phosphorus-bearing vanillin-based epoxy resin, EP2, that exhibited superior thermomechanical properties compared to that of petroleum-based diglycidyl ether of bisphenol A. However, the structure/property relationships of such phosphorus-containing bio-based resins are relatively under-explored and cannot be resolved via experiments alone. Here, molecular simulations are used to explore these relationships for a resin comprising EP2 cured with 4,4-diaminodiphenylmethane. The predicted thermomechanical properties are consistent with experimental observations, and critically, the structural analysis reveals the importance of the pendant phosphite group in the monomer as central to maintaining extensive hydrogen-bonding networks, giving rise to the excellent Young's modulus. This work provides the foundation for knowledge-based strategies to systematically improve the structure/property relationships in FR bio-based epoxy resins.