The non-halogen flame retardant epoxy resin based on a novel compound with phosphaphenanthrene and cyclotriphosphazene double functional groups

A novel flame retardant additive hexa-(phosphaphenanthrene -hydroxyl-methyl-phenoxyl)-cyclotriphosphazene (HAP-DOPO) with phosphazene and phosphaphenanthrene double functional groups has been synthesized from hexa-chloro-cyclotriphosphazene, 4-hydroxy-benzaldehyde and 9,10-dihydro-9-oxa-10- phosphaphenanthrene 10-oxide(DOPO). The structure of HAP-DOPO was characterized by Fourier transformed infrared (FT-IR) spectroscopy and 1H nuclear magnetic resonance (1H NMR) and 31P nuclear magnetic resonance (31P NMR). The additive HAP-DOPO was blended into diglycidyl ether of bisphenol-A (DGEBA) to prepare flame retardant epoxy resins. The flame retardant properties and thermal properties of the epoxy resins cured by 4, 4′-Diamino-diphenyl sulfone (DDS) were investigated from the differential scanning calorimeter (DSC), the thermogravimetric analysis (TGA), UL94 test, the limiting oxygen index (LOI) test and Cone calorimeter. Compared to traditional DOPO-DGEBA and ODOPB-DGEBA thermosets, the HAP-DOPO/DGEBA thermosets have higher Tgs at the same UL94 V-0 flammability rating for their higher crosslinking density and have higher char yield and lower pk-HRR at same 1.2 wt.% phosphorus content which confirm that HAP-DOPO has higher flame retardant efficiency on thermosets. The scanning electron microscopy (SEM) results shows that HAP-DOPO in DGEBA/DDS system obviously accelerate formation of the sealing, stronger and phosphorus-rich char layer to improve flame retardant properties of matrix during combustion.