Modified silica xerogel derived from groundnut hull ash by alkyl-ammonium salt for epoxy nanocomposites: Synergistic effects on thermal stability and flame retardancy

•Low-cost silica xerogel was synthesized from groundnut hull ash by sol−gel method.•Highly dispersed silica xerogel was obtained by alkyl-ammonium salt modification.•Modified silica xerogel was used as filler in preparation of epoxy nanocomposites.•Physicochemical and thermal properties of epoxy were improved with silica xerogel.•Nanocomposites including modified silica xerogel showed enhanced thermal stability. In this study, silica xerogel was synthesized from groundnut hull ash using sol−gel method. Amorphous silica xerogel showed promising properties such as high thermal stability, low thermal conductivity and bulk density. Agglomerations in silica xerogel were observed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses. To provide homogeneous dispersion of silica xerogel, modification process was carried out using tetrabutylammonium bromide (TBAB). Good interfacial interaction between modified silica xerogel and epoxy had synergistic effects on properties of epoxy nanocomposites. Epoxy nanocomposites including modified silica xerogel exhibited lower water sorption and higher corrosion resistance than that of silica xerogel. Char residue of neat epoxy was increased from 15.3% to 18.0% with 2 wt% modified silica xerogel as per thermogravimetric analyses (TGA). Epoxy nanocomposite including 2 wt% modified silica xerogel was classified as V−0. Thermal conductivity of neat epoxy was reduced to 0.22 W/(m K) with modified silica xerogel.