High performance cellulose fibers regenerated from 1-butyl3-methylimidazolium chloride solution: Effects of viscosity and
molecular weight
Jiaping Zhang
,1 Naoki Yamagishi,2 Yasuo Gotoh
,1,2,3 Antje Potthast,4 Thomas Rosenau4
1
Department of Materials Science and Engineering, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan
2
Graduate School of Science and Technology, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan
3
Institute for Fiber Engineering, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan
Division of Chemistry of Renewable Resources, Department of Chemistry, University of Natural Resources and Life Sciences Vienna,
4
Muthgasse 18, A-1190 Vienna, Austria
Correspondence to: Y. Gotoh (E-mail: ygotohy@shinshu-u.ac.jp)
ABSTRACT: In the present study, we focused on several factors affecting the utility of 1-butyl-3-methylimidazolium chloride (BMIMCl) for
obtaining higher performance fibers. The dependence of the spinnability and tensile strength of the fibers on the zero-shear viscosity of the
spinning solutions was investigated based on differences in the molecular weight of the cellulose, pulp concentration, and the pH of
BMIMCl. We demonstrated an appropriate viscosity range of 2000–4000 Pa s−1 (100 C) for spinning dopes to obtain good spinnability
and high tensile strength. The pH of the BMIMCl and the molecular weight of the cellulose clearly impacted tensile strength. The high
molecular weight of cellulose contributed to high mechanical properties of the regenerated cellulose fibers. Optimizing the molecular weight
and concentration of the cellulose based on the appropriate viscosity allowed us to prepare high performance cellulose fibers with a tensile
strength of 1.15 GPa and a Young’s modulus of 42.9 GPa. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48681.
KEYWORDS: cellulose and other wood products; fibers; ionic liquids; mechanical properties; textiles
Received 27 June 2019; accepted 19 October 2019
DOI: 10.1002/app.48681
The ongoing depletion of fossil fuel reserves, and increasing environmental concerns such as climate change and the accumulation
of plastic waste, have led to growing research interest in cellulose,
the most abundant renewable resource. Cellulose is typically
manufactured as regenerated cellulose fibers for use in clothing
but also holds promise as other industrial materials, such as tire
cord,1 because it is renewable and has attractive mechanical properties and thermal stability. According to Adusumali et al.,2
regenerated cellulose fibers are suitable as reinforcing materials
for high fracture toughness composites, although their strength
and modulus performed less than glass fiber.
straightforward manufacturing process involves dry-jet wet spinning and allows efficient recycling of the solvent. Ionic liquids
(ILs) have drawn much attention as an alternative type of direct
solvent since the report by Swatloski et al.3 This approach allows
the formation of regenerated cellulose fibers by dry-jet wet spinning, similar to the Lyocell method. The antisolvent (H2O in this
case), which possesses strong affinity for ILs, can destruct the Hbond between cellulose and ILs, and thus help reform the Hbond between cellulose chains for regeneration.4 Many studies
have investigated the regeneration of cellulose from IL solutions
in different forms, such as fibers,5 films,3,6 foams,7 and hydrogels/
aerogels8,9 for various applications.
High-strength regenerated cellulose fiber is typically generated
using the viscose method but this approach uses the volatile,
environmentally harmful, compound carbon disulfide and thus
alternative methodologies are required. For example, the
increasingly popular Lyocell method uses N-methylmorpholine
N-oxide monohydrate as a direct solvent for cellulose, and the
Numerous studies on regenerated cellulose fibers spun from
ILs via dry-jet wet spinning have investigated the effects of various cationic bases, anions, and alkyl chains on the properties
of ILs including solvation and viscosity,10 which would affect
the spinnability and the properties of spun fibers. Chen et al.11
reported the preparation of regenerated cellulose fibers from
INTRODUCTION
Additional Supporting Information may be found in the online version of this article.
© 2019 Wiley Periodicals, Inc.
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the imidazolium-based ILs 1-butyl-3-methylimidazolium chloride
(BMIMCl), 1-ally-3-methylimidazoluim chloride, and 1-ethyl3-methylimidazolium acetate, and found that the tensile strength
and hence degradation of the spun fibers varied depending on
the solvent. Imidazolium-based ILs containing halides reacted
with the cellulose, causing degradation at elevated temperatures
(>90 C).12,13 A series of studies were conducted using
1,5-diazabicyclo[4.3.0]non-5-enium acetate, a nonimidazoliumbased IL solvent that allows a low processing temperature and
thus prevents cellulose degradation, and regenerated cellulose
fibers with high tensile strength were obtained.14,15
However, with the exception of several patents,16,17 to the best of
our knowledge, the reported tensile strengths of regenerated cellulose fibers using ILs are generally below 900 MPa. This is far
lower than the strength of “Bocell” regenerated cellulose fibers
(1.3–1.7 GPa) reported by Boerstoel and coworkers and produced
using an anisotropic cellulose/superphosphoric acid solution.18
The strength of Bocell indicates that strong regenerated cellulose
fibers can be made using other non-IL based spinning processes,
although the relatively complex mixing process required to prepare the solution, limits its commercialization potential. In contrast, the one-step IL-based spinning process is an attractive
alternative to the traditional viscose process and the other processes mentioned above for regenerated cellulose fibers because
some ILs exhibit unique characteristics, including the ability to
directly dissolve cellulose, high thermal stability, and amenability
to recycling.19 We reported regenerated cellulose fibers with a
tensile strength of about 1 GPa generated using BMIMCl as a solvent after optimizing several dry-jet wet spinning processing
parameters, such as the draft ratio and the air gap atmosphere.20
We believe the strength of regenerated cellulose fibers spun from
BMIMCl solutions can be further improved by optimizing the
solution composition. Chen et al.11 investigated the combined
effects of raw materials and solvent systems, and reported the
importance of the molecular weight of cellulose for high tensile
strength. Our studies with BMIMCl confirmed that the solvent,
solution state, and molecular weight of the cellulose affect the
spinnability and fiber strength, and indicated that the strength of
regenerated cellulose fibers can be further improved using
BMIMCl.
Herein, we used BMIMCl as the cellulose solvent and explored
the effect of solution viscosity and cellulose molecular weight on
the spinnability and tensile strength of the spun regenerated
fibers. The influence of the pH of BMIMCl on the thermal stability of cellulose during the dissolution and spinning processes was
also investigated.
EXPERIMENTAL
Materials
Three dissolving cellulose pulps (A, B, C) with different degrees
of polymerization (DPw) were used. The number-average molecular weight (Mn), weight-average molecular weight (Mw), DPw,
and dispersity (Đ, Mw/Mn) are shown in the insert of Figure 1.
The method used to determine the molecular weight is described
in the Analytical Methods. The manufacturer-reported alpha cellulose content of the three pulps ranged from 96.8 to 98.0%.
Figure 1. Molecular weight distribution of the raw dissolving pulps. Mn,
Mw, DPw, and Đ are shown in the insert table. [Color figure can be viewed
at wileyonlinelibrary.com]
Other information about pulps is summarized in Table S1,
Supporting Information.
Several BMIMCls with different pH values were obtained from
Nippon Nyukazai Co., Ltd. (Tokyo, Japan) and Sigma-Aldrich
Japan (Tokyo, Japan), and were used without further purification.
The pH values were determined for 5 wt % BMIMCl aqueous
solution at ambient temperature.
Preparation of Spinning Dopes
The pulps were pulverized by a food mill (Iwatani IFM-720G,
Tokyo, Japan) and dried at 100 C for 3 h. A given amount of
each cellulose was then mixed with BMIMCl in a stainless-steel
vessel and allowed to swell in an oven at 60 C for 30 min, then
the swollen mixture was forcefully stirred in a kneader at 90 C
for 1 h. Complete dissolution was confirmed using a polarized
optical microscope (Olympus BHT-P, Tokyo, Japan) under
crossed Nicols.
Dry-Jet Wet Spinning
Regenerated cellulose fibers were prepared by a dry-jet wet spinning process, as described in our previous report.20 The spinning
dopes were heated to 100 C and extruded into a coagulation
bath (water) after passing through a 15 cm air gap. The throughput rate of the spinning dope and the winding speed were fixed
at 0.1 mL min−1 and 107 m min−1, respectively, except for the
data shown in Figure 2 where fibers were prepared at varied
winding speeds according to the corresponding maximum winding speeds. The temperature for coagulation bath was generally
set at 15 C, except for the results related to the effect of coagulation temperature where temperature of 5–25 C was tested. The
spun fibers fixed on bobbins were soaked in water for one night
to remove residual solvent and then dried at room temperature.
Analytical Methods
Rheology. The rheological properties of the spinning dopes were
measured at 100 C using a rotational rheometer (Malvern
Kinexus pro+, Worcestershire, UK) with two round parallel
plates (diameter of the upper plate: 25 mm). The gap between the
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conducted according to Potthast et al.23 and Siller et al.24 Activated samples were placed in new 4 mL vials and 9% w/v N,Ndimethylacetamide (DMAc)/lithium chloride solution (1 mL) was
added to each sample. The vials were vortexed for 20 s and
placed in the rotary shaker again for over 20 h to dissolve the
samples, then the samples were diluted 1:3 with pure DMAc and
filtered through polytetrafluoroethylene syringe filters (0.45 μm)
before SEC-MALS analysis. The SEC-MALS system was
described in detail previously by Röhrling et al.25 The calculations
were based on a refractive index increment of 0.136 mL g−1.
Figure 2. Empirical dependencies of tensile strength (black closed symbols)
and maximum winding speed (blue open symbols) on the zero-shear viscosity (η0) of the spinning dopes. Three types of pulps (A, B, and C) were used
to prepare spinning dopes with cellulose concentrations between 6 and
14%. Pulps A, B, and C are represented as triangles, squares, and circles,
respectively. The trends for the empirical dependencies of tensile strength
and maximum winding speed on η0 are shown by dotted lines. [Color figure
can be viewed at wileyonlinelibrary.com]
plates was 0.5 mm. Viscosity measurements were performed in
steady flow mode with a shear rate (_γ) ranging from 0.1 to
10 s−1. Viscoelastic measurements were performed in oscillation
mode with a frequency-sweep range of 0.6283–62.83 rad s−1. The
zero-shear viscosity (η0) was obtained by fitting the complex viscosity data based on the three-parameter cross model.21
Tensile Property. Testing standard of JIS L 1013: 2010 was used.
The tensile properties of the fibers were evaluated by conditioning all the samples at 20 C and a relative humidity of 65% for
12 h prior to the test. The fiber fineness was measured using a
fineness tester (Search DC-21A; DENICON, Kyoto, Japan). Tensile measurements were made using a tensile tester (Shimadzu
EZ-SX, Kyoto, Japan) equipped with a 5 N load cell. The gauge
length and tensile speed were set at 20 mm and 20 mm min−1,
respectively. In addition, a very small preload of up to 0.002 N,
which did not affect the results, was applied to the fiber at a
speed of 1 mm min−1 to avoid an initial slack. At least 15 measurements were performed for each specimen to ensure data
accuracy and repeatability.
Molecular Weight Distribution. The molecular weights of the
cellulose raw materials and regenerated cellulose fibers were measured by size exclusion chromatography coupled to multiangle
light scattering (SEC-MALS). The pulverized pulp and
regenerated fiber samples were activated with dimethyl sulfoxide
(DMSO) before dissolution, as reported by Silbermann et al.22
Each sample (ca. 12 mg) was transferred to a 4 mL brown vial,
then 4 mL DMSO was added. The vials were placed in a rotary
shaker (IKA KS 260 basic, Staufen, Germany) for over 2 h at
room temperature to allow the cellulose to swell and aid subsequent dissolution. Excess DMSO was removed by filtration before
the sample was dissolved. Dissolution and measurements were
Wide-Angle X-ray Diffraction. Wide-angle X-ray diffraction
(WAXD) images of regenerated cellulose fibers were obtained
using an X-ray generator (Rigaku RAmicro7, Tokyo, Japan)
equipped with an imaging plate with a resolution of 3000 × 3000
pixels. The X-ray source was a Cu Kα line (0.15418 nm) generated at 40 kV and 20 mA. The exposure time was set to 20 min
and the camera distance was fixed at 150 mm. FIT 2D software
was used to export the 2D images after compensating for air scattering. Integrated diffraction intensity profiles were obtained
using Display software (Rigaku). The full width at half-maximum
intensity (H) of the azimuthal diffraction distribution for the
ð110Þ plane was used to determine the crystallite orientation (fc)
using the equation fc = (180 –H )/180 . The crystallite size (D)
was estimated by using the Scherrer equation, D = Kλ/βcosθ,
where the Scherrer constant, K, has a constant of value 0.918, β is
the full-width at half-maximum intensity of the deconvoluted diffraction peak (a Gaussian function was used for fitting), and θ is
half of the diffraction angle 2θ.
Birefringence. The total molecular orientation (f ) of regenerated
cellulose fibers was determined using the equation f = Δn/Δn0,
where Δn is the birefringence of the fiber and Δn0 is the intrinsic
birefringence (0.062).26 Δn was determined using a polarizing
microscope (Olympus BX51) with a Berek compensator. For each
sample, the average value from six tests was used as the final
value.
RESULTS AND DISCUSSION
Relationship Between Spinning Dope Viscosity and Tensile
Strength
The effect of the viscosity of the spinning dope on the spinnability and tensile strength of the prepared fibers was measured
by varying the molecular weight and concentration of the cellulose. Figure 2 shows the empirical dependencies of the tensile
strength of the spun fibers (left vertical axis) and the maximum
winding speed of the spinning dopes (right vertical axis) on η0 of
the spinning dopes. Various BMIMCls acquired from Nippon
Nyukazai and Sigma-Aldrich Japan were used. Since the throughput rate was fixed at 0.1 mL min−1, the maximum winding speed
represents the spinnability of the spinning dopes.
The tensile strength was generally obtained from fibers prepared
at about 85% of the maximum winding speed for corresponding
spinning dopes. However, there were exceptions for spinning
dopes with high viscosity, where the winding speed was reduced
to less than 50% of the maximum winding speed for stable spinning. In this study, a spinning that lasted over 1 min was
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recognized as stable spinning. The η0 value of the spinning dopes
was controlled by using three pulps of different DPs and varying
its concentration in the dope. The dependence of η0 on pulp concentration of spinning dopes was shown in Figure S1, Supporting
Information. If η0 was below 1500 Pa s−1, the winding speed of
the spinning dopes was almost constant at about 124 m min−1
and the tensile strength of the prepared fibers varied slightly from
760 to 890 MPa. When η0 was increased up to 4000 Pa s−1, the
winding speed improved to around 150 m min−1, indicating that
the force of the spin line to the water resistance generated in the
coagulation bath was high. In this region, the maximum winding
speed and tensile strength increased gradually with increasing viscosity and were highest at about 3500 Pa s−1. Below 3500 Pa s−1,
the tensile strength tended to improve as the maximum winding
speed increased. However, large variation was observed for spinning dopes with η0 values around 3500 Pa s−1, perhaps due to
differences in the molecular weight of the cellulose, as discussed
in the “Effect of Cellulose Molecular Weight on Fiber Properties”
section. Spinning dopes with η0 values over 3500 Pa s−1 resulted
in remarkably reduced winding speeds due to the strong elasticity
of the spinning dopes hindering smooth flow, and the tensile
strength of the prepared fibers decreased due to their low winding speed. The above empirical dependence of tensile strength
and maximum winding speed on η0 indicated that η0 values from
about 2000 to 3500 Pa s−1 were appropriate for our experimental
conditions and cellulose/BMIMCl spinning dopes.
Influence of Solvent Quality on Solution Viscosity and Tensile
Strength
Here, we expand on the relationship between viscosity, spinnability, and tensile strength. The results in Figure 2 unexpectedly
showed wide variation in the tensile strength of the fibers
although the pulp and cellulose concentrations remained constant
for preparing the spinning dopes, likely due to variations in the
pH of the BMIMCl. This was further investigated by using two
kinds of BMIMCl, with pH values of 5.8 and 7.6, to prepare the
spinning dopes (referred to as L-pH and H-pH, respectively, as
shown in Table I). Figure 3 shows logarithmic plots of
γ_ -dependent η before and after the spinning process, where “after
spinning” means that an elapsed heating time at 100 C was
about 5 h to simulate because the whole spinning process generally took about 5 h in our study. H-pH dope tested before spinning had a higher viscosity than the L-pH dope, at a low γ_ up to
~3 s−1. This result can be explained with the cellulose in H-pH
dope having a higher molecular weight immediately after the
solution preparation process (e.g., Mw of 182.6 kDa for the H-pH
and 120.9 kDa for the L-pH samples). In addition, compared with
spinning dopes before spinning, the shear viscosity dramatically
decreased for L-pH dope after spinning, whereas it remained
essentially unchanged for H-pH dope, suggesting that the pH of
used BMIMCl resulted in different thermal stabilities of the spinning dopes.
Molecular weight measurements of L-pH and H-pH fiber prepared using different heating times during spinning were carried
out to investigate why the viscosity of the spinning dopes changed. The 0 h samples were fibers formed at the start of the spinning process and the 3 h samples were produced after 3 h of
heating at 100 C. Figure 4 shows the molecular weight
Table I. Composition of Spinning Dopes Containing BMIMCl with Different pH Values
Cellulose
BMIMCl
Concentration
(wt %)
Supplier
Sample code
Pulp
pH
L-pH
Pulp B 9
Nippon Nyukazai 5.8
H-pH
Pulp B 9
Nippon Nyukazai 7.6
distribution curves of fibers spun from different spinning L-pH
and H-pH dopes. As predicted, the L-pH fibers have lower
molecular weights than the H-pH fibers. Moreover, a remarkable
shift to lower molar masses was seen for L-pH fibers spun after
3 h heating, from 120.9 to 80.5 kDa. In contrast, the molecular
weight distribution curves for H-pH fibers with and without 3 h
heating were the same.
Next, we investigated the effect of the pH of BMIMCl on the tensile strength of the regenerated cellulose fibers and the results are
shown in Figure 5. Regenerated cellulose fibers were prepared
from L-pH and H-pH under the same conditions. The tensile
strength of H-pH fibers was higher than that of L-pH fibers. Furthermore, the tensile strength of L-pH fibers decreased greatly
(approximately 25%) after 3 h heating. On the other hand, the
tensile strength of H-pH fibers remained relatively stable at
around 890 MPa, although deviation increased slightly after spinning. This deviation may be due to an increase in a low-molecular-weight component of cellulose caused by 3 h heating,
resulting in a slight reduction in spinning stability. We conclude
that the use of high pH BMIMCl, which does not lower the
molecular weight of cellulose, greatly helps increase the tensile
strength of prepared fibers.
Figure 3. Rheological properties of the L-pH and H-pH spinning dopes
before and after the spinning process. [Color figure can be viewed at
wileyonlinelibrary.com]
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acidic component likely reduces the molecular weight of the
cellulose. Furthermore, the molecular weight of cellulose
decreased little when BMIMCl with a pH of 5.7 purchased from
Sigma-Aldrich was used to prepare cellulose solutions
(Figure S2). Consequently, the utility of BMIMCl for preparing
regenerated cellulose fibers cannot be based solely on the pH of
the BMIMCl and these other causes are currently under investigation in our laboratory.
Effect of Cellulose Molecular Weight on Fiber Properties
We studied the effect of the molecular weight of cellulose on
obtaining high strength fibers. Spinning Dopes A, B, and C with
almost the same η0 values were prepared using three pulps by
adjusting the polymer concentration (Table II). BMIMCl (pH of
5.7) from Sigma-Aldrich was used because it gave spinning dopes
with good thermal stability at 100 C.
Figure 4. Molecular weight distribution of regenerated cellulose fibers spun
after different heating times (0 and 3 h) from L-pH (black) and H-pH (red)
spinning dopes. [Color figure can be viewed at wileyonlinelibrary.com]
The degradation of cellulose in BMIMCl at high temperature
(≳90 C) has been studied intensively.27–29 According to Ahn
et al.,27 the molecular weight of cellulose in BMIMCl solution
decreases as the dissolution time increases, due to the acid
hydrolysis of cellulose being accelerated by ionic bonding
between chloride anions and imidazolium cations. Alkaline
additives such as sodium hydroxide28 and N-methylimidazole29
are effective for stabilizing the molecular weight of cellulose.
Similarly, in the present study, BMIMCl with pH of 7.6 reduced
undesirable degradation of the cellulose molecular chains during
the spinning process and high strength fibers were obtained.
Based on the above results, we believe that an unidentified
The η0 of the spinning dopes affects the tensile strength of the
prepared fibers and thus the concentration of cellulose was
adjusted to prepare spinning dopes with similar η0. Table II
gives the detailed compositions of the spinning dopes and the
rheological properties of the corresponding spinning dopes are
shown in Figure 6. Measurements obtained in steady flow
mode (left) clearly show that all three spinning dopes exhibited
shear thinning behavior despite some differences in
_
γ-dependent
viscosities in the range 0.13–10 s−1. Cellulose chains
in Dope C tended to orientate easily due to increased γ_ , indicating
that this high molecular weight cellulose was more sensitive to
shear flow. Moreover, as shown in the right panel of Figure 6, the
storage modulus (G0 ) and loss modulus (G00 ) were low for the
spinning dope containing high molecular weight cellulose since
the concentration of cellulose had been decreased to obtain a η0
value similar to the other samples. Furthermore, the angular rate
(ω) of the crossover point indicated by asterisks shifted to the left
as the molecular weight of the cellulose increased. This trend
indicates that higher molecular weight dopes had longer relaxation times, and thus likely higher molecular orientation and
higher tensile properties compared to lower molecular weight
cellulose.
Figure 7 shows typical stress–strain curves of regenerated cellulose fibers spun from spinning Dopes A, B, and C. Fibers with
high tensile strengths over 1 GPa were prepared from all three
spinning dopes when the coagulation temperature was 5 C.
Additionally, the tensile strength and Young’s modulus of the
regenerated cellulose fibers were improved by increasing the
molecular weight of the cellulose, as shown in detail in Table III.
Table II. Composition of Spinning Dopes with the Same Zero-Shear
Viscosity
Figure 5. Tensile strength of regenerated cellulose fibers spun from L-pH
and H-pH spinning dopes. Then, 0 and 3 h represent the heating time of
the spinning dopes while spinning. [Color figure can be viewed at
wileyonlinelibrary.com]
Sample code
Pulp
Cellulose
concentration
(wt %)
Dope A
A
13
3422
Dope B
B
9
3420
Dope C
C
6
3487
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Zero-shear
viscosity, η0
at 100 C (Pa s−1)
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Figure 6. Rheological properties of spinning Dopes A (black triangles), B (blue squares), and C (red circles): steady flow mode (left) and oscillation mode
(right). [Color figure can be viewed at wileyonlinelibrary.com]
The diameter of prepared fibers decreased in an order of Fiber
A > Fiber B > Fiber C, since the pulp concentration of
corresponding spinning dopes was adjusted to keep their viscosity similar. WAXD photographs revealed that all the prepared
fibers had the Cellulose II form, with a high fc around 0.95; a typical photograph is shown in Figure 8. The structural parameters
(crystallite size D, crystallite orientation fc, and total molecular
orientation f ) were evaluated to investigate the structure–
property relationship of the fibers but no significant trend was
observed in the parameters shown in Table III. This finding indicates that the crystallite size and molecular orientation did not
correspond to different mechanical properties for the highly oriented fibers prepared in this study. We think the number of tie
molecules binding to the crystallites and/or defects at the molecular chain ends may play vital roles here.
The coagulation temperature during spinning appeared to have
different effects for spinning dopes with different molecular
weights of cellulose (and thus different concentrations of cellulose). The tensile strength of fibers spun from spinning Dopes
A and B was enhanced by reducing the coagulation
temperature from 25 to 5 C. In terms of spinning dopes with
low molecular weight and high concentration of cellulose, this
decreased temperature might help decrease the mutual diffusion
of solvent and antisolvent, providing uniform structures and
thus superior strength. In contrast, the tensile strength of fibers
spun from spinning Dope C changed little with coagulation
temperature in our experimental range. This indicated that the
structure formation induced by coagulation temperature probably be different for the spinning dope with high molecular
weight and low concentration of cellulose. Besides, for Dope C,
the maximum winding speed dropped almost 25% at a coagulation temperature of 5 C compared with 25 C. We think the
low coagulation temperature resulted in slow solidification of
the cellulose gel near the first roller and thus quick break-up of
the spin line. The decreased Young’s modulus and molecular
orientation of Fiber C prepared using a coagulation temperature of 5 C supports this speculation indirectly, since the orientated cellulose chains could relax during the slow coagulation
process and thus give a negative effect on the final properties
of the fibers.
Figure 7. Typical stress–strain curves of regenerated cellulose fibers spun from spinning Dopes A, B, and C. The temperature of the coagulation bath was
varied from 5 to 25 C. [Color figure can be viewed at wileyonlinelibrary.com]
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0.82
0.82
0.947
4.24
4.20
3.13
3.01
2.86
5.5 1.2
5.5 1.0
42.8 4.5
1159.7 142.5
1153.7 80.9
7.4 0.4
7.6 0.3
15
25
42.9 2.8
3.00
0.946
0.80
0.85
0.949
0.956
4.69
4.53
2.91
3.13
2.85
3.00
6.6 2.0
4.9 0.5
37.0 1.5
40.8 2.9
919.5 90.0
1153.8 77.7
9.4 0.5
7.6 0.3
25
5
Fiber C
0.82
0.85
0.948
0.949
4.12
4.46
2.90
2.98
3.36
2.83
5.7 0.9
5.7 1.3
37.5 2.1
981.0 107.2
37.7 1.6
1066.5 83.3
9.1 0.6
9.2 0.7
5
0.84
4.28
2.95
7.7 1.1
34.6 3.0
11.1 1.3
25
908.8 109.3
3.04
0.941
0.83
0.950
0.947
4.44
4.14
3.08
3.05
2.89
2.99
6.0 0.8
7.1 1.8
35.2 2.9
988.4 98.4
36.8 2.7
1019.2 113.6
10.7 1.6
10.8 0.9
5
15
15
Fiber B
Sample
Fiber A
Elongation Crystallite size, D
Young’s
at break
(nm) (110) (nm) (020) (nm)
Tensile strength (MPa) modulus (GPa) %
110
Temperature of
coagulation bath ( C) Diameter (μm)
Structural parameters
Mechanical properties
Table III. Summary of the Mechanical Properties and Structural Parameters of the Regenerated Cellulose Fibers
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Crystallite
Total molecular
orientation, fc orientation, f
ARTICLE
Figure 8. WAXD photograph of regenerated cellulose Fiber C coagulated
at 5 C.
CONCLUSIONS
In this work, we investigated the effects of solution viscosity and
cellulose molecular weight in order to prepare high performance
regenerated cellulose fibers from cellulose/BMIMCl solutions via
dry-jet wet spinning.
First, we found that the zero-shear viscosity of the spinning
dopes significantly influenced the spinnability and thus the final
mechanical properties of the spun fibers. Spinning dopes with
zero-shear viscosities of between 2000 and 4000 Pa s−1
(at 100 C) provide adequate flowability and entanglement of the
cellulose chains independent of DPw and concentration of cellulose. Acidic BMIMCl results in severe hydrolytic degradation of
the cellulose during spinning, resulting in reduced viscosity and
decreased strength of the spun fibers. Consequently, pH adjustment of BMIMCl is vital, and BMIMCl with a pH of 7.6
inhibited undesirable degradation of the cellulose during the
spinning process.
Second, increased molecular weight of the cellulose combined
with lower pulp concentration contributed to high mechanical
properties of the regenerated cellulose fibers. As a result, high
performance regenerated cellulose fibers with a tensile strength of
up to 1.15 0.08 GPa and a Young’s modulus of up to
42.9 2.8 GPa were prepared from a cellulose/BMIMCl solution.
To the best of our knowledge, these are the highest values
reported for fibers spun from cellulose/BMIMCl solutions.
ACKNOWLEDGMENTS
This work was supported by a grant-in-aid for the Shinshu University Advanced Leading Graduate Program by the Ministry of
Education, Culture, Sports, Science and Technology (MEXT),
48681 (7 of 8)
J. APPL. POLYM. SCI. 2019, DOI: 10.1002/APP.48681
ARTICLE
WILEYONLINELIBRARY.COM/APP
Japan. In addition, this work was also supported by JSPS
KAKENHI Grant Number 15H01789.
15. Asaadi, S.; Hummel, M.; Hellsten, S.; Härkäsalmi, T.;
Ma, Y.; Michud, A.; Sixta, H. ChemSusChem. 2016, 9(22),
3250.
CONFLICT OF INTEREST
16. Sugimoto, K.; Koide, M. WO2012074019 (2011).
The authors declare no conflict of interest.
17. Sugimoto, K. JP 2013-241703 A (2013).
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