Nanocomposites are near-molecular blends of polymer molecules (thermoset or thermoplastic resins) and nano-scale particles. A nanoscale particle is a material with at least one dimension in the nanometer range, which is 50,000 times smaller than conventional fillers. When these infinitesimal particles interact with the polymeric matrix at molecular level, many physical and physico-chemical properties are greatly enhanced. Several types of minerals are appropriate to produce nanoparticles: octasilicates, mica fluoride, montmorillonite, etc. This later, which is a natural clay, seems to have the widest acceptability because of its low cost and low loading levels. To obtain nanoparticles (or nanoclays in this case), montmorillonite particles are modified with organic compounds, such as alkyl ammonium salts. These compounds act as compatibility agents that will bond the particles to the resin and will disperse the particle layers (individual sheets forming the platy structure of Montmorillonite) through a process called exfoliation. Once exfoliated, nanoparticles have a flexible structure characterized by its astoundingly small thickness, measuring only about one nanometer.
Nanocomposites exhibit multiple property enhancements. In the case of GFRP rebars, the improved properties are:
Nanoparticles reduce the porosity of the resin and create a path tortuosity because of its platelet structure. In some cases, significant effect of nanoclay on water diffusion characteristics have been obtained. Hydrophobic enhancement would clearly promote both improved nanocomposite properties and diminish the extent to which water would be transmitted through to an underlying substrate such as the rebar core. Therefore, applications in which contact with water or moist environments is likely could clearly benefit from materials incorporating nanoclay particles.
Nanoparticles have reinforcing properties on several mechanical properties such as tensile resistance, flexion resistance and stiffness. The magnitude of the improvement depends on the type of resin and presence of other filler/fibres.
Heat Distortion Temperature was shown to increase with nanoclay-modified materials.
Nanoparticles create more interlinked structures in the matrix and often increase Tg by 10-20°C
The presence of an inorganic nanoparticles reduces the distortion of resins upon heating.
Nanoclays reduce the flammability of polymeric materials. Heat release rates were found to diminish substantially by nanoclay incorporation. The flame retardant effect is due to a carbonaceous-char layer which develops on the outer surface during the combustion. This surface char rich in nanoclay becomes an insulator and a mass transport barrier (reducing oxygen supply and combustion product release).
Barrier effect to gazes and liquids has a protection effect on the resin.
Sag control is the ability of the liquid resin to properly wet out and adhere to glass fibres prior to curing.
The objectives of this work are to fabricate and characterize nanoclays and nanocomposites with vinyl ester, a thermoset resin, and to evaluate their water absorption/desorption behavior. Three types of treatment have been performed on two different clays: montmorillonite and bentonite. One of the treatment gave an ordinary clay, another one a nanoclay and the last one an intermediate clay. The untreated and modified clays, and two commercial nanoclays, were mixed to vinyl ester resin to produce composites, the clay content of which, were 1, 3, and 5%. The clays and their composites were characterized using common chemical analysis techniques: Elemental Analysis, Fourier Transform Infrared Spectroscopy, X Ray Diffraction, and Differential Scanning Calorimetry. The results have confirmed that one of the modified clay was a nanoclay. Some of the composites (and nanocomposites) were conditioned in water during several weeks, at room temperature or 60oC, and their water content measured at short and long term. The results show that the equilibrium moisture content increases with the amount of clay and that the "intermediate" clay- and the nanoclay (lab-made and commercial)-containing composites absorb less water than "ordinary" clays, but more than pure resin. However, the water diffusion coefficient of nanocomposites strongly decreases with nanoclay content and was found to be reduced by more than 4 for 5% nanoclay containing samples.
In progress.
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Testing3 |
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1 Including characterization of nanocomposites by X Ray diffraction and other techniques if necessary
2 Water absorption testing; thermomechanical analysis (DMA), thermal analysis (DSC), thermal stability (TMA), flame resistance
3 Same as 2 plus mechanical testing (tension, flexion, etc…)
* Conducted with Pultrall Inc
The obtained results are very promissing to develop perfectly durable nanocomposites products. More research will be conducted in this area through the coming years.
Cousin, P., Wang, P., and Benmokrane, B (2004), "Preparation and Characterization of Nanoclays and their Composites with Vinyl Ester Resin and Study of Water Absorption," submitted to the Journal of Composite Materials.