Page 712 - Polymer-based Nanocomposites for Energy and Environmental Applications

Carbon nanotube-based nanocomposites for wind turbine applications 655

The average interlayer thickness of the cured composite laminates was 58 μm (23 wt
% PEK-C concentration), 65 μm (25 wt% PEK-C concentration), and 70 μm (30 wt%
PEK-C concentration) for the membranes with fiber diameters of 450, 750, and
950 nm, respectively. With the same weight loading of nanofibers, finer nanofiber sta-
bilized the crack propagation during delamination and assisted with maintaining the
flexure property. With the same average fiber diameter of 950 nm, increased
nanofiber interlayer thickness led to enhanced mode I delamination fracture toughness
and reduced flexure strength. The average crack initiation of strain energy release rate
2
2
for control sample is 151 J/m , while it is 249, 228, and 241 J/m for nanofiber-
reinforced samples with fiber diameters of 450, 750, and 950 nm, respectively [66].
Saghafi et al. [68] studied the effect of polyvinylidene fluoride (PVDF) nanofibers
to improve mode I fracture toughness of carbon/epoxy composites. Electrospinning
technique is used to produce PVDF nanofibers. According to their results, mode
I fracture toughness increased nearly by 43% at initiation stage of fracture and
increased nearly to 36% at propagation stage [68].
The brittle structure of matrix materials and delamination of composite laminates is
a big challenge to achieve. Van der Heijden et al. [69] studied the effect of poly-
caprolactone (PCL) nanofibers on the interlaminar toughness of resin transfer molded
glass fiber epoxy composites. Electrospinning method is used to obtain nanofibers
from PCL. The mode I fracture toughness is related to nanofiber content and addition
technique of nanofiber into laminates. When the electrospun PCL nanofibers were
produced over both sides of glass fiber webs, the fracture toughness enhanced nearly
2
100% with a value of 1200 J/m . Interestingly, while fracture toughness is increasing
with introducing PCL nanofibers between laminates, other mechanical properties like
tensile and dynamic mechanical properties were kept constant. The fracture toughness
2
2
of reference sample (without nanofiber addition and 475 g/m ) is 640 J/m , and it is
2
2
increased to 1230 J/m by toughening with 20 g/m nanofiber content in the
interlayers [69].
24.4 Nanocomposite coating for wind turbine blades

Wind turbine blades generally are made of glass or carbon fiber-reinforced epoxy or
polyester composite. This selection of raw materials is changeable depending on
required mechanical performance and chemical durability. It can be benefitted from
nanomaterials in situations where the macromaterials are inadequate. Nanomaterial-
based composites provide not only increment in product’s properties but also
multifunctional performances [70].
There are a few remedies to prevent the typical problems encountered over time on
wind turbine blades. Erosion is the primary inescapable problem for all materials
applied in water or on land as shown on wind turbine blades. In order to increase
the erosion resistance on the surface, gelcoat is applied on top of wind blade surface.
The speed and shape of the airfoil are also vital parameter for erosion. For erosion
resistance, the current solution is covering the turbine blades with polyurethane layer
as coating or tape [71,72]. Although these tapes lead to increase the aerodynamic drag,