Preparation of nano zinc borate and investigation of flame-retardancy of ternary combination nano zinc borate/red phosphorus/expandable graphite on HDPE

Nano zinc borates were successfully synthesised from aqueous solutions of zinc sulfate, boric acid, and sodium hydroxide via the precipitation method. The effects of pH, temperature, and surfactants on the structure and morphologies of nano zinc borates were investigated. The nano zinc borates obtained at the pH of 7 to 8 were well-crystallised monophase Zn[B3O4(OH)3]. The morphologies of nano zinc borates were highly impacted by the reaction temperature and the surfactants. At the range of temperatures from 70 to 80oC, the nano zinc borates were nanoplates of 40-50 nm in thickness. The nano zinc borates grew out of the surface to form nanorods at 90oC and nanowhiskers at 100oC. The nano zinc borates modified with surfactants tended to form larger and thinner plate-like nanoparticles. In the presence of Tween 80, petal-like nano zinc borates were achieved. The petal-like nano zinc borates showed good flame retardant synergistic effects with red phosphorus and expandable graphite on high-density polyethylene matrix. Additionally, the nano zinc borates nanopetals significantly improved the mechanical properties of red phosphorus/expandable graphite/high-density polyethylene composites.