Nanoparticles can provide flame retardance to hosting polymers and act as nano fire extinguishers.Hydroxyapatite(Ca_5(OH)(PO_4)_3)(HA) is not hygroscopic,and is thermally stable up to 800 ℃,with18.5 wt%phosphorous content.It is this high phosphorous content that can provide HA with flame retardant properties.In this paper,we report on the continuous synthesis of ultrafine HA using a hydrothermal synthesis technique.The HA surface properties were changed from hydrophilic to hydrophobic by postsynthesis surface modification.The ratio of the HA nanoparticles and an intumescent agent known as Exolit AP750 was investigated to yield a self-extinguishing multi-component epoxy nanocomposite for extended application under extreme fire conditions.The HA/AP750/epoxy nanocomposite was able to resist a flame at 1700 ℃ and self-extinguish after the flame had been removed.The nanocomposite showed an enhanced flammability performance in standard cone calorimetry testing and formed a compact and cohesive protective char layer with a 50%decrease in peak heat released compared with virgin epoxy.Our aim was to establish the use of HA as an effective nanofiller with phosphorous-based flame retardant properties.The surface of this nano fire extinguisher was modified effectively with different surfactants for enhanced compatibility with different polymeric matrices.
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