The synergistic effects of boroxo siloxanes with magnesium hydroxide in halogen-free flame retardant EVA/MH blends

Abstract

The synergistic effects of boroxo siloxanes (BSil) with magnesium hydroxide in halogen-free flame retardant EVA/MH blends have been studied by cone calorimeter test (CCT), Fourier transfer infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), mechanical properties measurements, limiting oxygen index (LOI), UL-94 and torque tests. The LOI and UL-94 data show that when 3 wt% boroxo siloxane substituted for the magnesium hydroxide (MH) can increase 8% LOI values of the EVA/MH blends and keep the V-0 rating. The data obtained from the CCT tests indicate the heat release rates (HRR) reduced by about 23% for the EVA/MH sample with 3 wt% BSil when compared with the EVA/MH sample without BSil. The experimental observations from the torque, FTIR, TEM and SEM give positive evidence that the synergistic effects mechanism of BSil with MH can be described to: (i) BSil react with MH and increases the melt viscosity; (ii) BSil promote the homogeneous dispersion of MH; (iii) BSil promote the formation of compact charred layers and prevent the charred layers from cracking, which effectively protects the underlying polymer from burning. The TGA and dynamic FTIR spectral reveal that EVA/MH/BSil samples show slower thermal degradation rate and higher thermal degradation temperature than the EVA/MH sample. The mechanical tests show that the mechanical properties of EVA/MH/BSil blends are markedly improved by suitable amount of BSil.