Effect of multiwalled carbon nanotubes and phenethyl-bridged DOPO derivative on flame retardancy of epoxy resin

In this study, a phenethyl-bridged DOPO derivative (DiDOPO) was combined with multi-walled carbon nanotubes (MWNT) in epoxy resin (EP) to improve its flame retardancy. The introduction of only 10 wt% DiDOPO/0.8 wt% MWNT into EP increased the limited oxygen index (LOI) from 21.8% to 38.6%, achieving the UL 94 V-0 rating. The thermogravimetric analyses demonstrated that the presence of MWNT raised the char yield and formed thermally stable carbonaceous char. The decomposition and pyrolysis products in the gas phase were characterized by thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR), and found large amounts of phosphorus released into the gas phase. The flame-retardant effect evaluation by cone calorimetry testified that the MWNT improved the protective-barrier effect of the fire residue of EP/DiDOPO/MWNT, as shown by digital photo and scanning electron microscopy (SEM). Raman showed that MWNT could enhance the graphitization degree of the resin during combustion. Overall, these findings indicated that combination of DiDOPO with MWNT is an effective way in developing high-performance resins with attractive flame retardancy.