Synthesis and characterization of a new phosphorus‐containing furan‐based epoxy curing agent as a flame retardant

Summary In this study, 5‐hydroxymethyl‐2‐furfural (HMF) was used as a renewable resource for preparing an epoxy curing agent (furan‐based flame retardant, FBF), and a phosphorus‐containing functional group was also incorporated to enhance the flame retardancy of FBF. FBF was easily synthesized, and the total yield was 83%. 2‐Methyl imidazole was chosen as an accelerant to reduce the activation energy for the reaction of FBF with diglycidyl ether of bisphenol A (DGEBA). The DGEBA cured with FBF showed a low glass transition temperature and cross‐linking density compared with those of DGEBA cured with isophorondiamine (IPDA) and 4,4′‐diaminodiphenylmethane (DDM). However, the FBF‐cured DGEBA exhibited a comparable tensile strength with that of the DGEBA‐IPDA and DGEBA‐DDM systems (81.96 MPa) and a significantly higher tensile modulus (1721 MPa) owing to the H‐bonding via oxygens of the phosphorus group of FBF in the network structure. The DGEBA cured with FBF showed a high char yield and a high limitation of oxygen index value (29.7%) compared with those of the IPDA‐ and DDM‐cured ones. The cone calorimeter measurement also showed that the DGEBA‐FBF system had a low heat release rate, total heat release, and smoke production rate, indicating the improved flame retardancy mediated by FBF.