Enhanced Flame Retardancy in Ethylene–Vinyl Acetate Copolymer/Magnesium Hydroxide/Polycarbosilane Blends

A polymer ceramic precursor material—polycarbosilane (PCS)—was used as a synergistic additive with magnesium hydroxide (MH) in flame-retardant ethylene–vinyl acetate copolymer (EVA) composites via the melt-blending method. The flame-retardant properties of EVA/MH/PCS were evaluated by the limiting oxygen index (LOI) and a cone calorimeter (CONE). The results revealed a dramatic synergistic effect between PCS and MH, showing a 114% increase in the LOI value and a 46% decrease in the peak heat release rate (pHRR) with the addition of 2 wt.% PCS to the EVA/MH composite. Further study of the residual char by scanning electron microscopy (SEM) proved that a cohesive and compact char formed due to the ceramization of PCS and close packing of spherical magnesium oxide particles. Thermogravimetric analysis coupled with Fourier-transform infrared spectrometry (TG–FTIR) and pyrolysis–gas chromatography coupled with mass spectrometry (Py–GC/MS) were applied to investigate the flame-retardant mechanism of EVA/MH/PCS. The synergistic effect between PCS and MH exerted an impact on the thermal degradation products of EVA/MH/PCS, and acetic products were inhibited in the gas phase.