Flammability characterization and synergistic effects of expandable graphite with magnesium hydroxide in halogen-free flame-retardant EVA blends

Abstract

The flammability characterization and synergistic effects of different types of expandable graphite (EG) with magnesium hydroxide (MH) in halogen-free flame-retardant (HFFR) ethylene vinyl acetate (EVA) blends have been studied by cone calorimeter test (CCT), thermogravimetric analysis (TGA), limiting oxygen index (LOI), and UL-94 test. The results show that the particle size and expansion ratio of EG have a great effect on the flammability of the HFFR EVA/MH/EG blends. The EG with bigger particle size and higher expansion ratio can apparently increase the LOI value and improve the UL-94 flammability properties of EVA blends. The data obtained from the CCT indicate that the heat release rate (HRR), the effective heat of combustion (EHC), and the mass loss rate (MLR) of EVA/MH/EG blends decrease remarkably with increasing the particle size and expansion ratio of EG. However, the specific extinction area (SEA) data show that the addition of EG can apparently increase the smoke emission of EVA/MH/EG blends. The TGA results show that the thermal stability of EVA/MH/EG blends increase with increasing the EG particle size and expansion ratio.