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 andphosphaphenanthrene double functional groups has been synthesized fromhexa-chloro-cyclotriphosphazene,4-hydroxy-benzaldehyde and9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO). The structure of HAP-DOPO wascharacterized by Fourier transformed infrared (FTIR) spectroscopy and1H nuclearmagnetic resonance (1H NMR) and31P nuclear magnetic resonance (31P NMR).HAP-DOPO shows an obvious glass-transition temperature and melting point (Tg=82oC,Tm=186oC), TGA demonstrated that the onset decomposition temperature of HAP-DOPOis above200oC. Furthermore, the higher char yield (46.7%) at600oC of HAP-DOPOindicates that it has excellent flame retardant and charring properties.The additive HAP-DOPO was blended into diglycidyl ether of bisphenol-A (DGEBA)to prepare flame retardant epoxy resins. The flame retardant properties and thermalproperties of the epoxy resins cured by4,4′-Diamino-diphenyl sulfone(DDS) wereinvestigated from the differential scanning calorimeter (DSC), the thermogravimetricanalysis (TGA), UL-94test, the limiting oxygen index (LOI) test and Cone calorimeter.Compared to traditional DOPO-DGEBA and ODOPB-DGEBA thermosets, theHAP-DOPO/DGEBA thermosets have higher Tgs at the same UL94V-0flammabilityrating for their higher crosslinking density and have higher char yield and lower pk-HRR atsame1.2wt.%phosphorus content which confirm that HAP-DOPO has higher flameretardant efficiency on thermosets. Further study showed that phosphaphenanthrene andcyclotriphosphazene plays a major role to flame charring behaviors, respectively. Thescanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and X-raydiffraction (XRD) results shows that HAP-DOPO in DGEBA/DDS system obviouslyaccelerates the formation of the sealing, stronger and phosphorus-rich amorphous charlayer to improve flame retardant properties of matrix during combustion. The thermaldegradation behaviors of the phosphorus-containing epoxy resins were investigated by realtime Fourier transform infrared spectra (RTFTIR), thermogravimetric analysis/infraredspectrometry (TG-IR) and pyrolysis gas chromatography mass spectrometry (Py-GC/MS),the results suggested that the initial decomposition of phosphaphenanthrene ofHAP-DOPO, quench the OH and H radicals by releasing the PO2and PO radical groups and synergistically induce the formation of char layer by phosphazene andphosphaphenanthrene double functional groups.