Study on the properties of synergistic flame retardant PA66/aluminium hypophosphite composites

The halogen-free flame retardant (HFFR) polyamide-66 (PA66) composites filled with aluminium hypophosphite (AHP) had been prepared by melt compounding method using a twin-screw extruder. The thermal degradation behaviour, flame retardancy, microscopic morphology of carbon slag, smoke release and mechanical properties of HFFR PA66 composites had been investigated by thermogravimetric analysis (TGA), cone calorimeter, UL-94 vertical test, limiting oxygen index (LOI), scanning electron microscopy (SEM), NBS smoke density chamber, ultimate tensile and IZOD notched impact testing. The research results indicated that the flame retardancy and char-forming of PA66 composites had been dramatically improved, especially for sample A-7 with the addition of synergistic agent zinc borate (ZB). Due to the addition of ZB, a very obvious expansion phenomenon was observed during the combustion process, and the combustion residue presented a honeycomb-like microstructure with many dense pores. The addition of ZB not only had a significant synergistic flame retardant effect with AHP on PA66 composites, but also greatly reduced smoke release during combustion, which was crucial for reducing fire hazards. Mechanical testing showed that the addition of synergistic agents ZB and organic montmorillonite (OMMT) can reduce the negative effects of AHP on tensile strength, elongation at break, and impact strength, which was beneficial for practical engineering applications.