Fabrication of surface-modified magnesium hydroxide using Ni2+ chelation method and layer-by-layer assembly strategy: Improving the flame retardancy and smoke suppression properties of ethylene-vinyl acetate

Abstract

A novel magnesium hydroxide-polyphosphazene-Ni2+ (MH-PZPN-Ni) was synthesized by the layer-by-layer assembly strategy and Ni2+ chelation method. Post modification, the composite was incorporated into ethylene-vinyl acetate (EVA). The morphology, composition and structure of the MH-PZPN-Ni composites were comprehensively characterized by scanning electron microscopy, transmission electron microscope, Fourier transform infrared, X-ray diffraction and X-ray photoelectron spectroscopy. MH-PZPN-Ni could efficiently increase the flame retardancy and smoke suppression of EVA. The MH-PZPN-Ni (60 wt %)-incorporated EVA composite showed a limiting oxygen index value of 30.4 % and was rated as a UL 94 V-0 material. Cone calorimeter test results showed that the peak heat release rate and total heat release of EVA/MH-PZPN-Ni were decreased by 85.8 % and 56.7 %, respectively when compared to pure EVA. The morphology, structure, and chemical composition of the char residue and the pyrolysis products formed during the decomposition of the EVA composites were analyzed to investigate the flame-retardant mechanism of the modified EVA matrix. The production of ammonia (during the process of PZPN-Ni decay) and the water vapor formed due to the combustion of the H· and OH· radicals were found to dilute the concentration of the generated combustible gases. The denser char layer effectively blocked the heat and mass transfer. At the same time, the use of the Ni catalyst resulted in a significantly low production of various volatile products (such as CO and aliphatic and aromatic compounds). Moreover, PZPN-Ni enhanced the mechanical properties of EVA. The elongation at break increased by 74.9 %.