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Research Centre Bulgaria
The nanocomposites for engineering applications are mainly based on thermoset or thermoplastic polymers, the
spectrum of the applied nanofillers becoming constantly wider. However, there are still technological problems
hampering the large scale application of these novel materials, mainly related to particle dispersion at nanolevel in the
polymer matrix and to the control on interfacial interactions, which are the basic factors for nanocomposite formation.
We have developed nano-reinforced thermosets by the incorporation of diamond (BAS, Bulgaria) and alumina (SASOL,
Germany) nanopowders in epoxy and unsaturated polyester resins. As varying the surface treatment by organic modifiers,
the state of dispersion and the agglomeration processes of nanofillers in the matrix polymers are controlled, by rheology
analysis. This study shows the utility of rheological, physical and mechanical studies in understanding the effects of
different nanoparticle reinforcement in thermoset polymer matrices, intended for protective coating applications.
Significant improvement of wear resistance has been found for nanocomposites, strongly dependent on the hardness of
the nanoparticles, degree of dispersion and interfacial interactions. At a relatively low volume fraction (0.5–5 vol%), the
diamond nanofiller improves the wear resistance of the matrix polyester resin with 11–35%, respectively. Moreover, the
effect of diamond and alumina are compared at a given volume fraction of 1.3 vol%, and it was observed that the wear
resistance improvement of the epoxy/alumina systems (~ 31%) is higher about 2 times of magnitude than that of the
polyester/diamond systems.
Epoxy and polyester nanocomposites with alumina show significant improvement in flexural modulus (about 22% at 1.3
vol% filler) compared to the pure epoxy resin. Moreover, the thermoset nanocomposites with alumina nanofiller treated
by targeted organic modifiers demonstrate relatively low values of water absorption. These are strongly related with the
attractions of the resin molecules at the large and active nanofiller surface, as well as the high degree of dispersivity.
Importantly, the maximal properties improvements seem to appear around the rheological percolation threshold (~ 3 vol%),
which is obviously due to the structural transition from the single floccules towards the three-dimensional network of
floccules, formed by nanoparticles in polymer matrix. Wear resistance improvement was related with the physical
properties of nanopowders – extreme hardness and good thermal conductivity.
The advantages of the thermoset nanocomposites developed make them an excellent alternative of conventional composites
for protective coating applications, providing broad possibilities of improving the existing characteristics as well as of
attaining new specific properties. The acquired novel properties are determined not only by the presence of the
nanodispersed phase in the polymer matrix but also by the new interfacial phenomena emerging on the boundaries
between phases. |
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