The effect of chemically modified expandable graphite on flame-retardant properties of waterborne intumescent flame-retardant coating

Abstract

In this study, a modified expandable graphite material (mEG) with enhanced hydrophilic properties was successfully prepared with a natural graphite as the main raw material and polymeric 4,4′‐methylene diphenyl isocyanate (pMDI) as an interlinking agent, and polyethylene glycol (PEG) as surface modifier. X-ray diffraction (XRD) and volume expansion analyses verified the anion intercalation that produced the expandable graphite (EG). And the results of X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) raveled that 6.9% of PEG was chemically anchored on the expandable graphite (EG) surface. The contact angle of mEG was 39.6°, indicating that the surface is more hydrophilic than that of the EG surface (79.7°). The intumescent flame-retardant (IFR) coatings exhibited a more satisfactory flame-retardant effect when a mEG was added into the acryl resin matrix because of the synergistic effect of the dispersibility of mEG in the acryl resin matrix, resulted in the limited oxygen index (LOI) from 23 to 26%. Moreover, the total heat release (THR) of the IFR coating with mEG significantly decreased compared with that of the pure coating. The enhanced flame retardancy was due to the well-dispersed mEG in the acryl resin matrix, which may cause continuous carbon layer in the later stages of combustion.