Novel multi-component flame retardant system based on nanoscopic aluminium-trihydroxide (ATH)

Abstract

Inorganic hydroxides represent more than 50% of flame retardants (FRs) sold globally. This is due to their low cost, low toxicity, and minimum corrosivity. Aluminium tri-hydroxide (ATH) is the largest FR in use. This paper reports on a novel continuous flow fabrication of nanoscopic ATH with consistent product quality. TEM micrographs demonstrated nanoplate structure with 25nm size. XRD diffractogram revealed highly pure crystalline structure free from defects and any interfering substances. The made-up ATH has the potential to deliver a flame retardant action (heat sink action) to the hosting polymer by absorbing heat, releasing water, and forming a protective oxide layer (Al2O3). This oxide layer can prevent further polymer degradation. The effectiveness of ATH heat sink action was evaluated with thermal analysis techniques including TGA and DSC. The phase transition of ATH to corresponding oxides during its endothermic decomposition was verified with XRD. The synergism between the ATH heat sink and intumescent action (provoked with a phosphorous-based FR agent known as AP750) was employed to develop self-extinguishing multi-component epoxy nanocomposite. The developed nanocomposite was able to resist direct flame source at 1700°C; it demonstrated superior flammability performance using cone calorimeter testing. The peak heat released was decreased by 58%, and the time to peak heat released was extended by 35%. The synergism between ATH and AP750 was ascribed to the ability of the protective oxide layer (Al2O3) (resulted from ATH decomposition) to crosslink the phosphoric acid chains (resulted from AP750 decomposition) and to form aluminium phosphate (AlPO4). This catalytic action was demonstrated by conducting XRD of the developed char layer.