On the 3D printing and flame retardancy of expandable graphite-coated polylactic acid

Abstract

In this study, we made a flame-retardant coating layer composed of expandable graphite (ExG) (carbon source), ammonium polyphosphate/boric acid (acid source), melamine (blowing agent), and epoxy/amine resin/hardener system (binding agent). At varying ExG amount, the coating was deposited onto the surface of 3D printed polylactic acid (PLA) by dip coating method. The fire resistance performance of 3D printed PLA was measured in terms of burning rate and burning duration. Surface morphology and thermal stability of the coated samples were investigated by scanning electron microscopy (SEM) and thermogravimetric (TGA) analysis. Residual char after burning was also analyzed by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis. Addition of 9.8 % w/w ExG in the coating formulation showed good adhesion and increased fire resistance of PLA. The coated specimens exhibited high thermal stability, increased residual weight and enhanced surface structure by TGA and SEM analysis. Lastly, FTIR and XRD results revealed the presence of graphite and boron phosphate in the residual char.