engleski

Influence of surface modification of silica nanofiller on properties of epoxy matrix composites

Modification of polymer materials with nanoparticles is a common method for preparation of nanocomposite materials with improved final properties. In order to improve interaction between the filler and the polymer matrix, surface modifiers are used. We have prepared and characterized composites based on epoxy resin and commercially available SiO2 nanoparticles (AEROSIL® 300, Evonik Degussa GmbH). Influence of surface modification with an organically modified silane, 3 glycidyloxypropyltrimethoxysilane (GLYMO), was investigated. Nanoparticles were mixed with a solution of GLYMO in ethanol/water mixture (1/1 volume ratio) at 60 °C. Infrared spectroscopy (FTIR) and combined differential scanning calorimetry and thermogravimetric analysis (DSC-TGA) proved the presence of GLYMO on the surface of modified nanoparticles, but it was not possible to determine whether it was covalently bonded to the nanoparticles. Composite materials were prepared by mixing 0, 5 and 5 phr (parts per hundred parts of resin) of modified and unmodified nanoparticles into an epoxy resin (diglycidyl ether of Bisphenol A) which was then cured with a poly(oxypropylene) diamine. Curing was followed by DSC, and cured materials were characterised by mechanical and hardness testing (Table I). Morphology of fractured surfaces (after mechanical testing) was investigated by SEM. Presence of the filler does not influence the curing mechanism of epoxy resin. All composites show improved mechanical properties in comparison with unfilled resin. For the unmodified filler the improvement is more significant for smaller nanofiller content. This can be explained by better dispersion of unmodified nanoparticles at lower contents. Poor dispersion at 5 phr is clearly visible in Figure 1 c) and d). For modified particles, influence of filler content is less significant, and there is only a small increase in modulus. On the other hand, elongation at break increases significantly, which is uncharacteristic for usually very brittle cured epoxy. We suggest that modified nanoparticles form loosely bonded agglomerates (where surface modifier acts as binder for the agglomerate) which act as a separate, elastic phase and have a toughening effect on the epoxy matrix. Traces of elastic deformation and pullout at break are visible in Figure 1 f) and h). Toughening can also explain the poor improvement of the modulus for modified particles, since it generally decreases stiffness. Improved hardness is typical of particle-filled composites, and it does not depend greatly on the surface modification.

epoxy resin ; nanocomposites ; SEM ; silica ; surface modification

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