A new extra situ sol-gel route to silica/epoxy (DGEBA) nanocomposite. A DTA study of imidazole cure kinetic

Silica nanoparticles were obtained through the Stober method, from mixtures of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTS). The nanoparticles were dispersed in tetrahydrofuran (THF) and coupled to bisphenol A epoxy resin (DGEBA) through surface amino groups. After removing THF non-isothermal cure was performed at different heating rates (2-20A degrees C/min), using imidazole (2-4 wt%) as curing agent. For the sake of comparison bare DGEBA epoxy polymers were also prepared with similar schedule A nanocomposite of well-dispersed silica nanoparticles (5 wt%) in a fully cured epoxy matrix was easily obtained. Lower cure kinetics were observed with silica addition. This was attributed to reduction of the imidazole volume concentration. Cure activation energy was not influenced by silica presence, whereas it changed with the imidazole content. Therefore, experimental results suggested that silica had only an indirect effect (the reduction of the imidazole molar concentration) on the epoxy matrix cure kinetics. Glass transformation temperatures, T (g), as high as 175A degrees C were recorded. The nanocomposite glass transformation temperature depended on the heating rate of the cure process, the imidazole and silica content. T (g) changes as high as 40A degrees C were detected as a function of the heating rate. At higher imidazole content no differences in T (g) values between bare polymer and the nanocomposite were observed. This suggests that a higher imidazole content assures a better interconnection between the compatibilizing epoxy shell around the nanoparticles and the epoxy matrix. The new proposed methodology is an easy route to engineer both nanocomposites structure and interfacial interactions, thus tailoring their properties.