Page 24 - Polymer-based Nanocomposites for Energy and Environmental Applications

Introduction of polymer-based nanocomposites 3

There are several applications for thermoplastic resin systems via their special
capabilities for cost reduction in manufacturing and damage tolerance enhancement.
Moreover, these polymers often sustain in their initial properties regardless their
reheating or reforming. Akca et al. [3] studied the thermoplastic materials and matrix
toughness influences on the long-term behavior of fiber composites. In addition, due
to linear molecular structure, thermoplastic polymers are tougher than thermoset types
with highly cross-linked molecular structure. This linear structure provides easy
sliding of the molecules among each other, which makes a mechanism for the mechan-
ical energy consuming and toughness improvement. Hence, by using a thermoplastic
polymer matrix rather than a thermoset material, both ductility and toughness of the
composite will be ameliorated [13]. However, thermoplastics have less strength and
chemical stability in high temperature range against the thermosetting polymers but
show more resistant to impact damage and cracking [14]. As a brilliant factor for
thermoplastic polymers, these types of polymers can be recycled [3]. By utilizing
these matrices, thermoplastic composites can be reinforced by carbon, glass, metal,
biobased materials, etc. In this field, modern industry demands several types of
thermoplastic composites; also, various efforts are directed toward the new modeling
development in order to decrease time and costs [15].

1.2.2 Thermosetting polymer matrixes

Thermosetting resins are characterized as low-viscosity liquids or low-molecular-
weight solids that need additives as cross-linking agents to be formulated and cured.
Also, these polymers can be doped with fillers or fibrous reinforcements to improve
final demanding properties such as thermal and mechanical [12]. Among the curing
process, which is engaged by pressure and heat, the thermoset resins fully polymerize
and gradually harden with polymerization completion and the cross-linking of the
polymer molecules. These polymers illustrate some unique characteristics via their
three-dimensional cross-linked structure including good resistance to solvents, high
stability in dimensions, and resistance to high temperature [14]. The molecules of
thermosets can react freely to provide covalent bonds; thus, the cross-linking is gained
in one gigantic molecule among the polymer sample as an exothermal reaction. This is
due to the effect of molecular arrangement to a lower energy state than the random
molecular orientation of the liquid. Consequently, these molecules are bounded
together via covalent bonds and cannot be melted through reheating [16,17].
Thermosetting resins include different types of polymers such as epoxies, polyes-
ters, bismaleimides, vinyl esters, and polyamides [12]. There are various researches
that used thermoset matrices in polymer composite systems, especially PNCs.
Gorowara et al. [18] studied the molecular factors of glass fiber surface coatings in
thermosetting composite systems containing polymer matrix/glass fiber. In this
research, multicomponent glass fiber sizing was investigated for the full coating
packages used in commercial glass fiber manufacture. Kim et al. [19] investigated
experimentally and analytically the influences of the size of silver flakes and their
distribution on the thermal and electric conductivities of a polymer-based composite.
Another study [20] represented a molecular dynamics (MD) simulation technique to