Nano-and micro-silica modification of epoxy polymers

Epoxy polymers reinforced with a premixed epoxy/nano-silica masterbatch or dry non-surface-treated nano-silica and ground micro-silica flour were compared. Cured plates of epoxy containing both nano-particles (up to 15 %wt) and micro-particles (up to 51 %wt) of silica were produced and tested. The glass transition temperature, T_g, of the epoxy was measured using differential scanning calorimetry (DSC), and no significant changes were observed. Scanning electron microscopy (SEM) observations, combined with energy-dispersive X-ray (EDX) analysis were performed to assess the particles dispersion and the chemical content of the microstructure. The tensile modulus was always found to increase due to the addition of silica. Experimental data was compared to theoretical predictions, including the Halpin-Tsai and Lewis-Nielsen models, and a reasonable agreement was obtained. The dielectric properties of the nano- and micro-particle composites were characterised by a series of electrical tests. Influences on dielectric permittivity, resistivity and dielectric loss were found, depending on the type of filler. High values of dielectric strength were measured. An improvement due to the micro-particles was found, while nano-silica had a slight negative effect. Premixed fillers were found to show a better dispersion in comparison with dry powder, with a direct consequence on dielectric permittivity and dielectric loss.