Electrospinning of Chitosan (CHT) - Modern Trends in Chemistry and Chemical Engineering - page 84

Using concentrated organic acids such as acetic acid [24] and trifl ouroacetic acid
(TFA) with and without dichloromethane (DCM) [25-26] reported exclusively for
producing neat CHT nanofi bers. They similarly reported the decreasing of surface
tension and at the same time enhancement of charge density of CHT solution without
signifi cant effect on viscosity. This new method suggests signifi cant infl uence of the
concentrated acid solution on the reducing of the applied fi eld required for electrospin-
ning.
The mechanical and electrical properties of neat CHT electrospun natural nano-
fi ber mat can be improved by addition of the synthetic materials including carbon
nanotubes (CNTs) [27]. CNTs are one of the important synthetic polymers that were
discovered by Iijima in 1991 [28]. CNTs either single walled nanotubes (SWNTs) or
multiwalled nanotubes (MWNTs) combine the physical properties of diamond and
graphite. They are extremely thermally conductive like diamond and appreciably elec-
trically conductive like graphite. Moreover, the fl exibility and exceptional specifi c sur-
face area to mass ratio can be considered as signifi cant properties of CNTs [29]. The
scientists are becoming more interested to CNTs for existence of exclusive properties
such as superb conductivity [30] and mechanical strength for various applications. To
best of our knowledge, there has been no report on electrospinning of CHT/MWNTs
blend, except those ones [30-31] that use PVA to improve spinnability. Results showed
uniform and porous morphology of the electrospun nanofi bers. Despite adequate spin-
nability, total removing of PVA from nanofi ber structure to form conductive substrate
is not feasible. Moreover, thermal or alkali solution treatment of CHT/PVA/MWNTs
nanofi bers extremely infl uence on the structural morphology and mechanical stiffness.
The CHT/CNT composite can be produced by the hydrogen bonds due to hydrophilic
positively charged polycation of CHT due to amino groups and hydrophobic nega-
tively charged of CNT due to carboxyl and hydroxyl groups [32-34].
In current study, it has been attempted to produce a CHT/MWNTs nanofi ber with-
out association of processing agent to facile electrospinng process. In addition, a new
approach explored to provide highly stable and homogenous composite spinning solu-
tion of CHT/MWNTs in concentrated organic acids. This in turn present, a homoge-
nous conductive CHT scaffolds which is extremely important for biomedical implants.
EXPERIMENTAL
Materials
The CHT with degree of deacetylation of 85% and molecular weight of 5 × 10 5 was
supplied by Sigma-Aldrich. The MWNTs, supplied by Nutrino, have an average di-
ameter of 4 nm and purity of about 98%. All of the other solvents and chemicals were
commercially available and used as received without further purification.
Preparation of CHT-MWNTs Dispersions
A Branson Sonifier 250 operated at 30 W used to prepare the MWNT dispersions in
CHT/organic acid (90% wt acetic acid, 70/30 TFA/DCM) solution based on different
protocols. In first approach, 3 mg of as received MWNTs was dispersed into deion-
ized water or DCM using solution sonicating for 10 min (current work, Sample 1).