High temperature and fire properties of sustainable syntactic foam reinforced by end-of-life tyre-derived rubber particles

The management of end-of-life tyres faces challenges due to insufficient recycling infrastructure and technologies, as well as limited markets for the materials recovered from them. To mitigate this, waste rubber can be upcycled and used as filler material for polymer matrix composites. Before rubber-reinforced composites can be certified for fire-prone applications, their thermal and flammability properties must be understood. This research investigates the effect of rubber fillers on the thermal stability, flammability and flame spread characteristics of epoxy matrix syntactic foam. Thermogravimetric analysis, Fourier Transform Infrared spectrometry (FTIR), scanning electron microscopy and attenuated total reflection FTIR spectrometry were employed to elucidate changes in thermal degradation behaviours. The influence of rubber fillers on the flammability of syntactic foam was assessed using the cone calorimeter. The fire reaction properties of rubber-reinforced foam were affected by the intensity of the incident heat flux. Regardless of the incident heat flux, an increase in rubber content led to higher total heat release. At the lower heat flux of 35 kW/m², the fire growth rate increased with rubber content, but at the higher heat flux of 50 kW/m², the fire growth rate decreased as the rubber content increased. Importantly, all rubber-reinforced syntactic foams achieved a UL94 HB ranking and exhibited reduced flame spread rates compared to the unmodified foam. This study demonstrated the potential for upcycling waste rubber into sustainable engineering products and expanded the knowledge base on fire reaction properties and flame spread characteristics of such hybrid composite materials.