Effect of boron and phosphate compounds on physical, mechanical, and fire properties of wood–polypropylene composites

Physical, mechanical, and fire properties of the injection-molded wood flour/polypropylene composites incorporated with different contents of boron compounds; borax/boric acid and zinc borate, and phosphate compounds; mono and diammonium phosphates were investigated. The effect of the coupling agent content, maleic anhydride-grafted polypropylene, on the properties of the composites with fire-retardant was also investigated. The composites with the zinc borate had the highest dimensional stability and strength in the bending, tensile, and izod impact, followed by the monoammonium phosphate, borax/boric acid, and diammonium phosphate treatments. The treatments produced modest improvements in fire performance as indicated by reductions in the heat release rates. Best results were achieved with the phosphate treatments. The Scanning Electron Microscope–Energy Dispersive Spectroscopy elemental mapping of the samples revealed that the outer surface of the wood fibers was coated by some crystalline deposits of the fire-retardants.

► The WPCs with the zinc borate had the highest water resistance and strength values.
► Best fire performance were achieved with the phosphate treatments.
► Surface of wood fibers was coated by some crystalline deposits of fire retardants.