Flame retarding cardanol based novolac-epoxy/rice husk composites

The present study is based on the development of rice husk (RH) reinforced bio based epoxy composites for heat retardant properties. Cardanol based epoxidised novolac resin (ENR) was synthesized and toughened with commercial diglycidyl ether of bisphenol-A (DGEBA) and its chemical structure was characterised using Fourier transform infrared spectroscopy (FTIR). The curing studies by differential scanning calorimetry (DSC) and the thermal studies by thermogravimetric analysis (TGA) revealed that the thermal stability and char yield were accelerated by incorporation of rice husk to bio epoxy system albeit the tensile strength was found to decline slightly. The kinetic models Arrhenius, Broido and Horowitz–Metzger have been utilized to determine Ea value for thermal degradation of composites. The bio composite obtained with 11 wt% of RH on combustion showed enhanced thermal stability, high char yield, 34% limiting oxygen index value (LOI) and V-0 classification in UL-94 test. In addition the best results of the composites were compared with the reported works of similar kind and it revealed that the developed RH composites possess appreciable flame retardancy and tensile property. The analysis of char using FTIR, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) disclosed that the carbonaceous-silicate layer formed acts as a protective layer and imparts appreciable thermal and flame retardant properties to the composites. [Display omitted] •Rice husk incorporated cardanol based epoxy composite was developed.•Flammability and thermal stability of rice husk composites were found to be enhanced.•Kinetic studies revealed that the bio silica composite exhibits high Ea value.•Presence of silica in char formation was confirmed by SEM, FTIR and EDS.