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Qin, Lu, Sun, and Rogers (2010) extracted the high molecular weight
chitin from crustacean shells using 1-ethyl-3-methylimidazolium
acetate ([C2mim]OAc) as solvent, at the same time, chitin films
and fibers were prepared as well. Zhu, Han, Cheng, and Wu (2011)
studied the dissolubility of chitosan in four kinds of imidazole-
1-ethyl-3-methylimidazolium acetate ([Emim]Ac), and found that
and Li (2006) claimed that chitosan could be dissolved in 1-butyl-
3-methylimidazolium chloride ([Bmim]Cl) to form a semi-clear
good solvent for chitosan with different deacetylation degrees and
molecular weights, and the prepared chitosan solution presents rel-
ative low viscosity, furthermore, the chitosan fibers was prepared
(Li et al., 2012b). Nonetheless, there are still few reports on the
preparation of chitosan fibers using ILs as solvent.
The aim of this work is to show a method to prepare chitosan
fibers with high tenacity using binary ionic liquid system as sol-
vent, which is composed of glycine hydrochloride (Gly·HCl) and
[Bmim]Cl. A homogeneous chitosan solution was prepared, and
the chitosan fibers were manufactured by wet and dry-wet spin-
ning processes respectively. The prepared chitosan fibers were
characterized by FT-IR and WAXD, which provide the informa-
tion on the dissolution and regeneration process of the materials.
SEM was used to visualize the morphology of the prepared fibers,
and strength testing was used to evaluate its mechanical perfor-
mance. Furthermore, the possible reaction during the dissolution
and regeneration was investigated as well.
extraction method, then in vacuum for 48 h. A purified [Bmim]Cl
was obtained.
Their 1H NMR spectra are shown as follows:
Gly·HCl: 1H NMR (400 MHz, D2O, TMS), ı4.65 (2H, s).
[Bmim]Cl: 1H NMR (400 MHz, D2O, TMS), ı0.88–0.92 (3H, t),
1.23–1.28 (2H, m), 1.75–1.79 (2H, t), 3.87 (3H, s), 4.17–4.20 (2H,
t), 7.75 (1H, d), 7.83 (1H, d), 9.35 (1H, s).
2.3. Preparation of spinning solution and chitosan fibers
The preparation of spinning solution was described as followed,
a certain amount of chitosan powder was added into 10 wt.%
Gly·HCl/[Bmim]Cl solvent system to form 5 wt.% chitosan disper-
sion, and heated at 80 ◦C under mechanical stirring for 1 h to obtain
a homogeneous, viscous (the viscosity is about 5 Pa s at 80 ◦C) and
amber solution. The obtained solution is stable, can be stored at
room temperature for at least a number of months without any
phase separation, and there have not obvious viscosity decrease
as well. In general, it is necessary to filtrate the solution with the
400 mesh filter and remove the bubble under vacuum in order to
satisfy the spinning requirement.
The preparation of chitosan fibers was described as followed,
holes (60 m diameter) under the 0.4 MPa compressed air, then
immersed in an ethanol coagulation and 5 wt.% sodium hydrox-
ide solution successively. The schematic representation of spinning
process is shown in Fig. 1a, diameter of all the rollers is 17.5 cm.
The fibers, which are collected between coagulation bath and neu-
tralization bath were named as primary chitosan fibers. The fibers
which are collected after washing bath and air dried were named
as regenerated chitosan fibers, as shown in Fig. 1b. The fibers
A and B are prepared by wet and dry-wet spinning technique
respectively, its density and moisture content under equilibrium
conditions at 25 ◦C and 65% relative humidity are 1.45 g/cm3, 12.5%
and 1.46 g/cm3, 11.4% respectively.
2. Experimental
2.1. Materials and reagents
2.4. Characterization
Chitosan powder (800 cP, 1 wt.% in 1% acetic acid at 25 ◦C;
dried at 105 ◦C until constant weight before use. Its viscosity aver-
age molecular weight (Mv) is about 9.76 × 105 g/mol, which is
calculated by the Mark–Houwink equation according to reference
(Wang, Bo, Li, & Qin, 1991). Glycine and hydrochloric acid (HCl,
36–38 wt.%) were purchased from Sinopharm Chemical Reagent
Co. Ltd., and used as received. Industrial-grade N-methylimidazole,
1-chlorobutane and ethanol (content >99.5%) were purchased
from Shanghai Jiachen Chemical Co. Ltd. (Shanghai, China). N-
methylimidazole and 1-chlorobutane were purified by distillation
before use, ethanol was used as received.
2.4.1. Microscopy
The surface morphology of the prepared chitosan fibers was
studied in a Jeol Jsm-5600lv (Jeol Ltd., Tokyo) scanning electron
microscope (SEM). The fibers were washed with ethyl ether for
several times and sputter-coated with gold. For the observation
of cross section, the fibers were fractured under liquid nitrogen.
2.4.2. Thermo gravimetric analyzer (TGA)
Thermal analysis of the chitosan samples was performed on a
TG 209 F1 Iris (Netzsch Gertebau GmbH, Germany) under nitro-
gen atmosphere. In each experiment, about 5–10 mg sample was
filled in an aluminum pan and the TG was recorded by raising the
temperature from 50 ◦C to 1000 ◦C at a heating rate of 10 ◦C/min.
2.2. Synthesis of ILs
2.4.3. Fourier transform infrared spectroscopy
Gly·HCl and [Bmim]Cl were synthesized as follows. 37.5 g
glycine and 60.9 g HCl aqueous solution (36–38 wt.%) were added to
a round-bottomed flask fitted with magnetic stirring, until glycine
was fully dissolved. The mixture was kept at 60 ◦C for 6 h, and cooled
to room temperature. Water was removed through vacuum dis-
tillation, the residue was washed with ethanol three times, and
kept in vacuum for 24 h, and a white crystalline of Gly·HCl was
obtained. [Bmim]Cl was prepared as follows. The mixture of puri-
fied N-methylimidazole 41.05 g and 1-chlorobutane 55.54 g were
added to a round-bottomed flask fitted with reflux condenser and
magnetic stirring, kept in 80 ◦C for 24 h, ethyl acetate was used to
remove the residual N-methylimidazole and 1-chlorobutane using
Fourier Transform Infrared Spectroscopy (FT-IR) was performed
on Nicolet 8700 (Thermo Electron Corp, USA) at room temperature.
The fiber samples were cut into powder and mixed with KBr to
prepare pellets. All spectra were recorded with an accumulation of
32 scans with a resolution of 4 cm−1 in the range of 4000–400 cm−1
.
2.4.4. Wide angle x-ray diffraction
Wide angle X-ray diffraction (WAXD) analysis was performed
for raw chitosan, primary chitosan fiber and regenerated chitosan
fiber, using a Rigaku D/Max-2550 (Rigaku Corp, Tokyo) with Cu
radiation operated at 40 kv and 200 mA, from 5◦ to 60◦ in steps of
0.02◦.