Page 702 - Polymer-based Nanocomposites for Energy and Environmental Applications

Carbon nanotube-based nanocomposites for wind turbine applications 645

particles. Generally, nanoclays have many classes such as montmorillonite, hectorite,
halloysite, bentonite, and kaolinite. In nanocomposite materials, nanoclays are incor-
porated in limited amounts mostly <5 wt%, and these amounts allow their dispersing
in the polymer matrix.
The life cycle of wind turbine blades produced from polymer composites is sup-
posed to be 20–25 years with minimum maintenance and repair. Thus, there should
be intense research to increase the reliability and lifetime of polymer matrix compos-
ites [27]. Nanoengineering of matrix or fiber/matrix interfaces of nanocomposites by
nanoclay has studied. Mishanaevsky et al. [28] have investigated the potential and
results of nanoclay reinforcements for the improvement of the mechanical properties
of polymer composites using continuum mechanics and micromechanics methods and
effective phase model. Their computational investigations demonstrated that the
nanoreinforcements and nanomodifications have a potential to improve mechanical
properties, strength, and stiffness of polymer fiber-reinforced composites to be used
for wind energy applications [28].
Effect of the addition of pristine and organo-modified nanoclays on the water
absorption and mechanical properties of glass fiber/unsaturated polyester resin com-
posites for wind turbine blades was studied by Rull et al. [29]. They have analyzed
mechanical properties and water absorption behavior of the composites in which
nanoclays included and compared it with those of conventional unsaturated polyester
(UP)/glass fiber-reinforced composites. The pristine clay increased water absorption
rate of the composite and decreased the mechanical performance of the material due to
its hydrophilic nature and low compatibility with the UP resin. Water absorption
behavior and mechanical performance of the UP-tributyl hexadecyl phosphonium
bromide (UP-TBHP)-modified bentonite/glass fiber composites were found to be
almost identical to those of the conventional UP/glass fiber-reinforced composites.
The best results were obtained when the octadecyl ammonium chloride (ODA)-
modified bentonite was used as nanoreinforcement. This is because of the higher
compatibility of ODA-modified bentonite with the polymeric matrix improved the
dispersion of the clay in the polymer and reduced the water absorption of these
composites (37% with respect to the UP/glass fiber composites) and retained the
mechanical properties almost equal to the dry composites [29].
The effect of the unmodified and modified clays on the polyester matrix was also
studied by the same research group [30]. They developed fiberglass-reinforced
UP-bentonite composites by the vacuum bagging technique. Composites with and
without clay were prepared using six mats of glass fibers using the same matrix/cat-
alyst/accelerator ratio as for the matrix, and the clay content was kept constant at
4.3 wt% in all samples with clay. Transmission electron microscope (TEM) images
of nanocomposites were illustrated in Fig. 24.4. It shows the silicate platelets that
are dark and the tactoids (elongated particles) that are composed of unseparated clay
layers. The tactoids could be from nonmodified clays (clay 1) or organophilic (mod-
ified) ones with high-clay concentrations. This morphology could be observed when
there is no compatibility between the clay and the polymer. For clays 3 and 4 with low
clay contents (1, 2.5, and 5 wt%), a higher number of disordered structures and exfo-
liated layers were observed, especially when compared with the former image [30].