Synergistic flame retardant effects between hollow glass microspheres and magnesium hydroxide in ethylene-vinyl acetate composites

A series of flame retardant ethylene-vinyl acetate (EVA) composites, with different content of magnesium hydroxide (MH) and hollow glass microspheres (HGM), have been prepared. The synergistic flame retardant effects of HGM with MH in EVA/MH blends have been studied by limiting oxygen index (LOI), UL-94 tests, cone calorimeter test (CCT), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), respectively. The LOI and UL-94 results show that when 2.00 wt% magnesium hydroxide (MH) is substituted with HGM, the LOI value can be raised to the maximum value of 42.1 among all samples. The data obtained from the CCT test indicate the heat release rate (HRR) of EVA/MH/HGM sample with 1.00 wt% HGM reduced by 37% when compared with EVA/MH sample without HGM. The digital photo graphs and scanning electron microscope (SEM) of char residues after CCT give positive evidence that the synergistic flame retardant effects between HGM and MH can be described that HGM mixed with MH can decrease the melt viscosity of EVA/MH/HGM, and promote the homogeneous dispersion of MH. HGM also can promote the formation of compact charred layers and prevent the charred layers from cracking, which effectively protects the underlying materials from burning. The TGA results reveal that EVA/MH/HGM samples show higher thermal stability at high temperature than EVA/MH sample.