Civil Engineering Reference
In-Depth Information
Most of the polymers are dissolved in suitable solvents before electrospinning. When
the solid polymer or polymer pellet or powder is completely dissolved in a proper
amount of solvent called polymer solution, it is then introduced into the capillary tube
for electrospinning. h e electric i eld is subjected to the end of the capillary tube that
contains the solution l uid held by its surface tension and an electric charge is induced
on the liquid surface due to this electric i eld. When the applied electric i eld reaches
a critical value, the repulsive electrical forces overcome the surface tension forces.
Eventually, a charged jet of the solution is ejected from the tip of the Taylor cone and
an unstable and rapid whipping of the jet occurs in the space between the capillary
tip and collector which leads to evaporation of the solvent, leaving a polymer behind
[25, 55, 56] . h e jet is only stable at the tip of the spinneret and at er that instabil-
ity starts. Mutual charge repulsion and the contraction of the surface charges to the
counter electrode cause a force directly opposite to the surface tension [57]. h us, the
electrospinning process of ers a simplii ed technique for i ber formation [58] . Both the
dissolution and the electrospinning are essentially conducted at room temperature with
atmosphere conditions. However, some polymers may emit unpleasant or even harmful
smells, so the processes should be conducted within chambers having a ventilation sys-
tem. Furthermore, a dc voltage in the range of 10-50 kV is necessary to generate i bers
by electrospinning. One must be careful to avoid touching any of the charged jet while
manipulating. It is noted that the same polymer dissolved in dif erent solvents may
all be electrospun into nanoi bers. Polymers melted at high temperature can also be
made into nanoi bers through electrospinning. Instead of a solution, the polymer melt
is introduced into the capillary tube. However, dif erent from the case of polymer solu-
tion, the electrospinning process for a polymer melt has to be performed in a vacuum
condition [59-61] . h e capillary tube, the traveling of the charged melt l uid jet, and the
metal collecting screen must be encapsulated within a vacuum.
Currently, there are two standard electrospinning setups, one with vertical spinning
head and the other with horizontal spinning head. With the expansion of this technol-
ogy, several research groups have developed more sophisticated systems that can fab-
ricate more complex nanoi brous structures in a more controlled and ei cient manner
[62, 63] .
12.5
Electrospinning of Cellulose
Cellulose is an important target for energy conversion and medical applications.
Its benign properties, namely biocompatibility, biodegradability, and regenerative
properties, make cellulose an environmentally-friendly material. Cellulose i bers are
nowadays being used as the basis of functionalized materials and i ber-reinforced
composites [64]. Fibers in the nanometer range display improved properties, such
as high surface energy and glass transition temperatures, high thermal and electrical
conductivities, and enhanced surface reactivity [26-46]. h e preparation of micro-and
nanoi bers of polymers may be accomplished by a variety of physical-chemical meth-
ods. However in the case of cellulose, it must be noted that cellulose is neither fusible
nor soluble in most common solvents, which implies that specii c methods need to
