Dual Fire Retardant Action: The Combined Gas and Condensed Phase Effects of Azo-Modified NiZnAl Layered Double Hydroxide on Intumescent Polypropylene

Abstract

Ternary nickel-substituted layered double hydroxide (C-LDH) was synthesized. It was intercalated with azobenzene-4,4'-dicarboxylic acid, using an ion exchange method to obtain organically modified NiZnAl-LDH (O-LDH). Both LDHs were melt-blended into polypropylene (PP) with intumescent fire retardant (IFR). The structure, morphology, thermal stability and combustible properties of intercalated LDH and its hybrid composite have been comprehensively characterized. SEM and EDX mapping show O-LDH exhibits better dispersion than ZnNiAl-CO3 LDH (C-LDH). Cone calorimetry shows the addition of IFR and LDH significantly reduced smoke and heat release rate. The composite with 1 wt% O-LDH, which showed dual gas phase and condensed phase fire retardant action, exhibited the lowest flammability with an LOI value of 29.3 % and achieved a UL-94 V-0 rating. In addition, incorporation of LDH improved the mechanical properties compared to PP/IFR composites. UV absorption showed that O-LDH could significantly improve the ultraviolet stability of PP composites.