Civil Engineering Reference
In-Depth Information
photoluminescence spectra of both raw and electrospun i bers indicated that cellulose
emitting centers are not af ected by the dissolution of cellulose in ionic liquids. Also
the use of nonvolatile solvents in electrospinning coupled to a water coagulation bath
allows the recovery of the ionic l uid, and represents a step forward in the search for
environmentally-friendly alternatives to the conventional approaches.
Cellulose i bers with diameters ranging from 500 nm to 10
m have been formed
by electrospinning cellulose from 1-butyl-3-methylimidazolium chloride solution into
an ethanol bath [99]. 10% (w/w) cellulose in 1-butyl-3-methylimidazolium chloride
were subjected to electrospinning at a voltage of 15-20 kV and working distance of 15
cm. h e l ow rate of the syringe pump was adjusted from 0.03 to 0.05 mL min
-1
in tan-
dem with the applied voltage, af ording i ber formation. h e i bers formed were directly
received in ethanol bath. h e RTILs selected for this study are completely miscible in
ethanol, while the cellulose is insoluble. Hence, as the i bers formed, the ethanol extrac-
tively removed the RTIL solvents, af ording pure cellulose i bers, which were collected
in the form of a tangled web. h e morphological studies of the cellulose i bers showed
the formation of highly branched, nanometer-to-micron-sized i bers with smooth sur-
face. It was found that the morphology and diameter distribution of electrospun i bers
depend on a variety of process parameters, including the solution concentration, sur-
face tension of solvent, applied voltage, and solution feed rate. h e high viscosity and
nonvolatility of the RTILs limited the i bers formed to mostly micron-sized diameters
and also contributed to the interconnected branched structures, and only a small per-
cent of nanoscale (~500 nm) i bers were observed. h e study suggested by using low-
viscosity RTILs and optimization of the spinning parameters, it should be possible to
prepare nonbranched nanoi bers of cellulose or its composites.
μ
12.6.2
N-methyl morpholine-N-oxide
h e N-methylmorpholine-N-oxide (NMMO) method allowed homogeneous cellu-
lose spinning solutions to be obtained in a relatively simple way. NMMO is among the
nonderivatizing solvents which can dissolve cellulose by breaking the intermolecular
forces and is considered as one of the direct solvents for cellulose, which is nowadays
applied in the industrial Layocell process. h is process is one of the modern and envi-
ronmentally-friendly industrial i ber-making technologies with direct dissolution of
cellulose without chemical derivatization. h e solvent does not produce toxic waste
pollutants, and can be recycled with over 98% recovery. At er dissolution in NMMO,
cellulose can be regenerated by rapid precipitation with an anti-solvent, which is usu-
ally water. However the dissolution in NMMO can change the crystal structure of cel-
lulose. Cellulose solution in NMMO/water for electrospinning has been reported by
many researchers. Kim
et al.
[100] reported nonwoven mats of submicron-sized i ne
i bers with diameters ranging from 250 to 750 nm by electrospinning of cellulose solu-
tion in NMMO/water system. h e i bers were collected in a water bath and coagu-
lated as excess solvent dif used into the bath. h e i bers emerging from the spinneret
landed on the collector, which rotated to briel y immerse the i bers into a water bath
maintained at 10°C. h e rate of disk rotation was optimized to prevent excess water
from building up on the disk and the i bers. h e resulting i ber morphology varied
