Authors: (Francisco Torrens, Gloria Castellano, Institut Universitari de Ciència Molecular, Universitat de València, Edifici d’Instituts de Paterna, Spain, and others)
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Abstract:
Composites of silica nanospheres, coated with cross-linked epoxy–amine, were
synthesised and examined by 29Si-magic-angle-spinning nuclear magnetic resonance
spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy and
scanning electron microscopy. The most representative fact is that epoxy-modified
nanospheres lost less weight at high temperatures. At temperatures greater than 300ºC the
loss of weight for epoxy-modified nanospheres was rather lower than for unmodified
nanospheres. This helped them to retain their structures as the loss of weight can have
adverse effects on network defects, because of the loss of crosslinks by unit of volume.
The mechanical properties of epoxy nanocomposites, strengthened with silica spherical
nanoparticles unfunctionalized, with silica nanospheres functionalized with amine, with
silica nanoballs functionalized with epoxy, or with both silica nanoparticles
functionalized with epoxy and silica nanospheres functionalized with amine, increase up
to reinforcement percentages of 3–5%, as reflected in the study of the storage modulus in
shear performed in dynamic mechanical analysis. Improvements are observed in the
glassy and rubbery states, without affecting the glass transition temperature of the
material. From these strengthening percentages the mechanical properties begin to
decrease but keeping, in all the studied reinforcement percentages, a mechanical
behaviour higher than the one of the pristine epoxy resin. For low strengthening
percentages, the samples reinforced with both nanospheres functionalized with amine and
epoxy show higher mechanical behaviour. As the strengthening percentage increases,
materials reinforced with silica nanoballs functionalized with epoxy groups show a
mechanical behaviour higher than the rest. To improve the mechanical properties in these
systems, it is important to arrive to a compromise between the percentage of added
strengthening versus type of reinforcement. The parameter determining the flow stress is
the cohesion of the solid state, which is represented by the storage modulus in shear. |
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