Epoxy-matrix composites filled with surface-modified SiO2 nanoparticles

Composites based on an epoxy resin, diglycidyl ether of bisphenol A and SiO2 nanoparticles, unmodified and surface-modified with a coupling agent 3-glycidyloxypropyltrimethoxysilane, were prepared. Successful modification of the nanoparticles was confirmed by infrared spectroscopy and combined differential scanning calorimetry and thermogravimetric analysis (DSC-TG). Composite materials were prepared by adding 0.5-5 phr (parts per hundred parts of resin) of modified and unmodified nanoparticles into the epoxy resin which was then cured with a poly(oxypropylene) diamine. Curing was followed by DSC, and cured materials were characterised by tensile and hardness testing. Morphology of fractured surfaces after tensile testing was investigated by scanning electron microscopy (SEM). Thermal stability of cured materials was studied by TG and their glass transition temperature determined by DSC. The presence of the filler was found not to influence the curing mechanism of the epoxy resin nor the degradation mechanism of the crosslinked epoxy-amine matrix. Glass transition exhibits a small shift to higher temperatures in composites, which also exhibit increased char formation-at lower filler content for the composite with unmodified nanoparticles and at higher for the one with modified nanoparticles. All composites show improved mechanical properties in comparison with the neat epoxy. For the unmodified particles, strength and modulus are particularly improved at lower nanofiller content due to their better dispersion, as observed by SEM. The modified nanoparticles contributed to a significant increase in elongation at break, increasing the toughness of the cured resin while retaining its strength and without having an adverse influence on the modulus.