Civil Engineering Reference
In-Depth Information
Figure 12.6
SEM images at dif erent magnii cation (100x-5000x) of cellulose i brous mats obtained by
electrospinning from molten cellulose/NMMO solutions electrospun with dif erent spinning parameters
(cellulose content in the spinning solution 3 wt%, applied voltage ~30 kV, temperature of needle100°C).
(a) and (b) working distance 9.5 cm, temperature of spinning head 110°C, (c) and (d) working distance
11 cm, temperature of spinning head 100°C. (Adapted from Reference [81]).
solvent system has sui cient volatility to evaporate during electrospinning. However,
LiCl is the dissolved salt in the system which will remain on the i ber, hence post-
treatment of the i ber is required to remove the salt. h is solvent has been shown to
dissolve cellulose from dif erent sources over a large range of cellulose concentrations
without side reactions. h e presence of lithium chloride, not any other salt, has been
proven to be necessary to bridge the electrostatic interaction between DMAc and cel-
lulose [104]. Previous studies of cellulose in LiCl/DMAc systems have shown that at
elevated temperature (>80°C), degradation of cellulose was registered [105]. It has been
reported that the crystalline polymorph cellulose I forms to cellulose II when cellulose
is treated with water or methanol, and forms cellulose III when cellulose is treated with
liquid ammonia [69, 106] .
h e incorporation of a coagulant bath also stabilized i bers electrospun from LiCl/
DMAc [75, 100, 107]. Kim
et al.
[107] varied the composition of cellulose solutions in
LiCl/DMAc solvent to determine the range of concentration or viscosity suitable for
electrospinning. h e major variables considered in this study were the electric i eld
strength/gradient and volumetric feed rate of the cellulose solution. h e ef ects of other
parameters, including material or temperature of the collector were also investigated.
Submicron-sized cellulose i bers were obtained via electrospinning cellulose in lithium
chloride/DMAc without its derivatization. Pretreated cellulose powders were dissolved
