Highly effective flame retarded epoxy resin cured by DOPO-based co-curing agent

A highly effective 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based flame retardant (D-bp) was successfully synthesized via the addition reaction between DOPO and Schiff-base obtained in advance by the condensation of 4,4'-diaminodiphenyl methane (DDM) and 4-hydroxybenzaldehyde. D-bp was used as co-curing agent to improve the flame retardancy of DDM/diglycidyl ether of bisphenol A (DGEBA) system. Non-isothermal curing kinetics, thermal and flame-retardant properties of cured epoxy resins were studied by differential scanning calorimeter (DSC), thermogravimeric analysis (TGA), UL94 vertical burning test, limited oxygen index (LOI) and cone calorimeter test. The morphology of residues after cone calorimeter test was observed by scanning electron microscope (SEM). The results revealed that the epoxy thermosets exhibited excellent flame-retardancy and passed V-0 rating of UL 94 test with LOI of 39.7% when the phosphorus content was only 0.5 wt%.