Influence of hollow glass microsphere on flame retardancy of ethylene-vinyl acetate/9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide composites

To improve combustion resistance properties of EVA resin, a series of flame-retardant EVA composites were prepared by melt blending 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with hollow glass microspheres (HGM), abbreviated as EVA/HGM/DOPO. Attributable to the capture of free radicals by DOPO, the promotion of carbonation by HGM and the synergistic effects between HGM and DOPO, EVA/HGM/DOPO composites (4.0 wt% DOPO) exhibit better flame retardant performance, thermal stability, and smoke suppression performance. The limited oxygen index (LOI) results show that 4.0 wt% DOPO is replaced by HGM (EVA-5), the LOI value can be increased to the maximum value of 24.2%, and the vertical combustion reaches the V-2 level. Moreover, the peak of heat release rate (PHRR) value of sample EVA-5 was reduced by 26.5% and 42.8% in the microscale combustion calorimeter (MCC) and cone calorimeter test (CCT) compared to the pure EVA, respectively. The digital photographs and mass loss curves also give positive evidence of the synergistic condensed phase flame-retardant effects between HGM and DOPO. Particularly, the maximum smoke density (Ds, max) of EVA-5 composite is the lowest. The thermogravimetry analysis (TGA) results revealed that HGM/DOPO/EVA samples show higher thermal stability at high temperatures than EVA samples. Furthermore, the addition of HGM improved Young's modulus compared to EVA. These results suggested the synergetic effect of DOPO and HGM additions, the high efficiency of the proposed strategy and the wide application prospect of the produced EVA flame retardant composite materials.