Thermal Stability, Flame Retardancy and Flame Retardant Mechanisms of Hollow Glass Microspheres/Montmorillonite/Epoxy Sheet Molding Compound Composites

Epoxy sheet molding compound (ESMC) composites have excellent mechanical properties, dimensional stability and electrical insulation, and are widely used in the automotive industry. In our previous work silane coupling agent modified, hollow glass microspheres (SiHGM) and montmorillonite (MMT) were incorporated to enhance the mechanical properties of the ESMC composites. It was found that the ESMC composites containing MMT (EP/SiHGM/MMT-1) exhibited excellent mechanical strength. However, the flammability of the epoxy resin (EP) limits the use of ESMC composites for applications that require good flame retardancy. In this paper we describe our research in which MMT was used to increase the flame retardancy of ESMC composites. The results showed that the addition of MMT made the ESMC composites have excellent flame retardancy. The limiting oxygen index (LOI) of the ESMC composites containing 1 phr MMT (EP/SiHGM/MMT-1) was 26.8%, which was 8.94% higher than that of the ESMC composites without MMT (EP/SiHGM/MMT-0). In addition, the peak heat release rate (PHRR), average heat release rate (AHRR) and total heat release (THR) of the EP/SiHGM/MMT-1 were 322.8 kW/m2, 95.3 kW/m2 and 38.6 MJ/m2, respectively, which were 22.6%, 8.2% and 8.0% lower than those of EP/SiHGM/MMT-0. The carbon monoxide production (COP) and carbon dioxide production (CO2P) of EP/SiHGM/MMT-1 were 0.0092 g/s and 0.2071 g/s, respectively, which were 34.3% and 22.8% lower than those of EP/SiHGM/MMT-0. The fire growth index (FGI) of EP/SiHGM/MMT-1 was 2.4, which was a decrease by 29.4% compared to EP/SiHGM/MMT-0. In addition, the flame retardant mechanisms were revealed. We suggest that MMT promoted dehydration and charring of the epoxy resin and helped construct an intact physical barrier, which had good blocking effects. The prepared composite has great application prospects for those occasions that require high flame retardancy. Thus, this work provides an innovative strategy for preparing low density epoxy composites with excellent flame retardancy and high mechanical properties.