engleski

Epoxy-matrix composites filled with surface-modified SiO2 nanoparticles

To prepare polymer-matrix composites with good mechanical properties, inorganic fillers are modified by coupling agents in order to create an interphase. Composites based on epoxy resin and commercially available SiO2 nanoparticles were prepared. Nanoparticles were previously treated with a coupling agent, 3-glycidyloxypropyltrimethoxysilane (GLYMO), dissolved in toluene or in ethanol/water mixture (1/1 volume ratio). Successful modification of the nanoparticles was confirmed by infrared spectroscopy (FTIR), which displayed bands characteristic of C-H and epoxy group, and combined differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), which showed the additional mass loss due to organic modification. Composite materials were prepared by adding 0, 5 – 5 phr (parts per hundred parts of resin) of 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 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 TGA, and their glass transition temperature determined by DSC. Presence of the filler does not influence the curing mechanism of epoxy resin. All composites show improved mechanical properties (both hardness and tensile) in comparison with unfilled resin, especially for smaller nanofiller content, which can be explained by better dispersion of unmodified nanoparticles at lower contents. Poor dispersion at 5 phr is clearly visible in SEM micrographs. Samples prepared with nanoparticles modified in ethanol/water mixture exhibit significant increase of elongation at break, instead of brittle fracture characteristic of cured epoxy resin. We suggest that modified nanoparticles form loosely bonded agglomerates which act as a separate, elastic phase and have a toughening effect on the epoxy matrix. Glass transition shifts to higher temperatures in composites, and they exhibit improved thermal stability.

composite; epoxy; silica; nanofiller; properties

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