Civil Engineering Reference
In-Depth Information
the electrospinning. h is phenomenon is attributed to decreasing viscosity of the spin-
ning solution by the addition of co-solvent, which helped the whipping motion. By the
stable whipping behavior, the cellulose solution was uniformly elongated and i bril-
lated, which resulted more uniform i bers with thinner diameter. h e quantitative anal-
ysis of variation in i ber diameter showed that in both cases i ber diameter decreased
with increasing the amount of co-solvent. A signii cant dif erence in i ber diameter
was observed with type of co-solvent used. h e average and the standard deviation of
the i ber diameter in the i ber web prepared from the solution with DMF were signii -
cantly smaller compared to the one with DMAc, which is attributed to the dif erence
of charge-induced partial polarity of the co-solvent. In comparison with DMAc, DMF
has higher partial polarity by the electrical charge for spinning, hence the solution with
DMF would have a better chance to be ef ectively elongated during the whipping pro-
cess. h e improved whipping produced i ner and more uniform i bers.
In conclusion, the type and the concentration of the co-solvent showed signii -
cant ef ects on the spinnability and the diameter and the properties of the i ber. It was
observed that when weight ratio of co-solvent against ionic liquid increased, the spin-
nability was improved with stable whipping and splaying motion. Regardless of the co-
solvent type, the higher co-solvent concentration resulted in i ner i ber diameter, better
web uniformity, higher crystallinity and better thermal stability. Compared to DMAc,
DMF showed more of a signii cant inl uence on the i ber diameter and the crystallinity.
h e addition of the co-solvent produced more uniform i bers due to reduced viscosity
and the partial polarity of the co-solvent [97].
Recently, Härdelin
et al.
electrospun [78] cellulose with various concentrations of
ionic liquid and co-solvent. h e dif erent co-solvents used were DMAc, DMF, and
DMSO. h e co-solvents were added to modify the viscosity, electrical conductivity, and
surface tension of the cellulose solutions. h e study found that the solubility of cellulose
in ionic liquids is highly af ected by changes in solvent properties on the molecular level
in the binary solvent systems. h e dif erence in molecular structure of the co-solvents
and the interactions between co-solvent and ionic liquid is explained by the dif erence
in dissolution power of the co-solvents.
h e study used pulp sheets as the cellulose source and all solutions were prepared
under similar conditions and same procedure. h e pulp sheets were cut in small qua-
dratic pieces, about 1 mm in size, and dried in an oven at 80°C for 12 h before use.
An appropriate amount of co-solvent, DMAc, DMF, or DMSO, was added to the pulp
and was allowed to absorb the co-solvent, for roughly one min. h en ionic liquid was
added to the mixture and stirred at 80°C for 12 h in a sealed container, which generated
a clear and homogenous solution. h e reason for i rst adding co-solvent to the pulp fol-
lowed by ionic liquid was to enhance the ionic liquid dif usion rate into the pulp. It was
found that by using this method, the dissolution process was simplii ed and less time
consuming. h e clear and homogenous solution was then subjected to electrospinning
and collected the i bers on a rotating collector with a 10 cm diameter covered with an
aluminum foil. h e collector was partly submerged in a water bath to achieve precipita-
tion of the cellulose solution into solid polymer i bers. h e applied voltage was varied
from 10 to 15 kV depending on the solution. Other spinning parameters were kept
constant. h e distance between the tip of the needle to the collector was 10 cm, solution
