Flame retardancy and thermal degradation of intumescent flame retardant EVA composite with efficient charring agent

Abstract

Intumescent flame retardant ethylene-vinyl acetate (EVA) composites with ammonium polyphosphate (APP) and efficient charring agent (CNCA-DA) were prepared through melt blending. The effect of APP and CNCA-DA on the flame retardant properties and thermal degradation of EVA were investigated by the means of limited oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TGA), cone calorimeter test (CCT), scanning electron microscopy (SEM), laser Raman spectroscopy (LRS), and Fourier transform infrared (FTIR). The results from LOI and UL-94 showed that the intumescent flame retardant (IFR) containing CNCA-DA and APP was very effective in flame retardancy of EVA. When the mass ratio of APP and CNCA-DA was 3:1, the IFR showed the best effect, and when the IFR loading held 30%, the LOI value reached 32.1%. It was also found that when the IFR loading held only 20%, the flame retardancy of EVAP/IFR can still pass V-0 rating in UL-94 tests, meanwhile, its LOI value reached 27.0%. As for CCT results, IFR could clearly change the decomposition behavior of EVA and formed an intumescent char layer on the surface of the composites, consequently resulting in efficient reduction of the flammability parameters, such as heat release rate (HRR), total heat release (THR), smoke production rate (SPR), and mass loss (ML). In addition, the morphological structures which were observed by digital photos and SEM manifested that IFR could promote to form the continuous and compact intumescent char layer. The analysis of LRS and FTIR indicated that EVA/IFR could form POP and POC connected structures as well as polyaromatic structure. When APP and CNCA-DA were combined together, the suitable strength of char layer was obtained to improve the flame retardant properties.