Phosphorus-nitrogen containing polymer wrapped carbon nanotubes and their flame-retardant effect on epoxy resin

A novel phosphorus-nitrogen containing polymer wrapped carbon nanotubes (CNT-PD-x, x denoted the feed ratio) were facilely prepared via strong π-π stacking interactions between the poly(phenylphosphonic-4,4'-diaminodiphenyl-methane) (PD) and the walls of carbon nanotubes (CNTs). The content of polymer PD of CNT-PD-x can be controlled by adjusting the feed ratio of polymer monomers to CNTs. The structure and properties of CNT-PD-x were characterized by Fourier transformed infrared (FT-IR) spectroscopy, 1H nuclear magnetic resonance (1H NMR), transmission electron microscopy (TEM) and thermo gravimetric analysis (TGA) measurements. The CNT-PD-x was incorporated into epoxy resin for improving the flame retardancy. The LOI value reached to 33.6% when the mass fraction of CNT-PD-x (x = 20) was 4 wt%. Compared with CNTs, the same addition of CNT-PD-x (x = 10) reduced the PHRR and THR of epoxy resin more effectively. The results implied the gas-condensed phase flame-retardant effect of CNT-PD-x, which is ascribed to the combined action of the polymer PD and CNTs on the flame retardancy of epoxy resin.