Incorporation of silica nanospheres into epoxy–amine materials: Polymer nanocomposites pp.823-844
Authors: (Francisco Torrens, Gloria Castellano, Institut Universitari de Ciència Molecular, Universitat de València, Edifici d’Instituts de Paterna, Spain, and others)
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.