Chemistry Reference
In-Depth Information
Nanotube Composites
Regardless of biological properties, the electrical, mechanical, and thermal properties
of biopolymers need to be reinforced using suitable filler for diverse applications.
Following discovery of CNTs, their usage as filler in polymer matrix improves the
bulk properties compared to neat matrix [79]. Ajayan et al. in 1994 introduced CNTs
as filler in epoxy resin through the alignment method [80]. Later, many studies have
focused on CNTs as excellent substitute for conventional nanofillers in the nanocom-
posites. Recently, many polymers and biopolymers have been reinforced by CNTs. As
mentioned earlier, these nanocomposites have remarkable characteristics compared
with bulk materials due to their unique properties [81].
There are several parameters affect the mechanical properties of composites in-
cluding proper dispersion, large aspect ratio of fi ller, interfacial stress transfer, well
alignment of reinforcement, and solvent choice [82].
Uniformity and stability of nanotube dispersion in polymer matrix are most im-
portant parameters for evaluation of composite performance. In fact the prefect fi ller
distribution is a prerequisite for effi cient load transfer from matrix to fi ller [83]. The
correlation between effective dispersion and functionalization and their effects on the
properties of CNT/polymer nano-composites were extensively investigated. In over-
all, it has been showed that the proper dispersion enhances a variety of mechanical
properties of nanocomposites [71].
Fiber aspect ratio, defi ned as “the ratio of average fi ber length to fi ber diameter.”
This parameter is one of the main effective parameters on the longitudinal modulus
[84]. CNTs generally have high aspect ratio but their ultimate performance in a poly-
mer composite is different. The high aspect ratio of dispersed CNTs could lead to a
signifi cant load transfer [85]. However, the aggregation of the nanotubes decreases the
effective aspect ratio of the CNTs. This is one of the processing challenges regarding
to poor CNTs dispersion [86].
The interfacial stress transfer is essential for load transfer process while external
stresses apply to the composites. Experimental observation showed that fi llers take a
signifi cant larger share of the load due to CNTs-polymer matrix interaction. Also, the
mechanical properties of polymer nanotube composites represent an enhancement in
Young's modulus due to adding CNTs [87]. Wagner et al. investigated the effect of
stress-induced fragmentation of MWNTs in a polymer matrix. The results showed
that generated tensile through polymer deformation can be thoroughly transferred to
CNTs [88].
The CNT alignment in polymer matrix is extremely effective parameter to ex-
plain the properties of CNT composites. Quin Wang et al. [89], for instance, assessed
the effects of CNT alignment on electrical conductivity and mechanical properties
of SWNT/epoxy nanocomposites. The electrical conductivity, Young's modulus, and
tensile strength of the SWNT/epoxy composite rise with increasing SWNT alignment
due to increase of interface bonding of CNTs in the polymer matrix.
Umar khan et al. in 2007 examined the effect of solvent choice on the mechanical
properties of CNTs-polymer composites. They were fabricated double-walled nano-
tubes (DWNT) and polyvinyl alcohol (PVA) composites into the different solvents
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