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Mechanically Strong Multifilament Fibers Spun from Cellulose Solution via Inducing Formation of Nanofibers Kunkun Zhu, Cuibo Qiu, Ang Lu, Longbo Luo, Jinhua Guo, Hengjiang Cong, Feng Chen, Xiangyang Liu, Xin Zhang, Howard Wang, Jie Cai, Qiang Fu, and Lina Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b00039 • Publication Date (Web): 05 Mar 2018 Downloaded from http://pubs.acs.org on March 6, 2018

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ACS Sustainable Chemistry & Engineering

1

Mechanically Strong Multifilament Fibers Spun from Cellulose

2

Solution via Inducing Formation of Nanofibers

3 4

Kunkun Zhu1‡, Cuibo Qiu2‡, Ang Lu1, Longbo Luo2, Jinhua Guo1, Hengjiang Cong1,

5

Feng Chen2, Xiangyang Liu2, Xin Zhang3, Howard Wang3, Jie Cai1, Qiang Fu2*, Lina Zhang1*

6 7 8 9 10 11 12

1

College of Chemistry and Molecular Sciences, Wuhan University, No. 299 Bayi

Road, Wuchang District, Wuhan, Hubei Province, China, 430072 2

College of polymer science and engineering, Sichuan University, No.24 South

Section 1, Yihuan Road, Chengdu, Sichuan Province, China, 610065 3

University of Maryland, College Park, Maryland 20742, USA

13 14

‡ These authors contributed equally to this paper.

15 16

*Correspondence to: [email protected] (L. Zhang), [email protected](Q. Fu).

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ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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ABSTRACT: Mechanically strong cellulose fibers spun with environmentally friendly technology

2

have been tremendously concerned in textile industry. Here, by inducing the nanofibrous structure

3

formation, a novel cellulose fiber with high strength has been designed and spun successfully on a

4

lab-scale spinning machine. The cellulose-NaOH-urea solution containing 0.5 wt% LiOH was

5

regenerated in 15 wt% phytic acid/5 wt% Na2SO4 aqueous solution at 5 oC, in which, the alkali-urea

6

complex as shell on the cellulose chain was destroyed, so the naked stiff macromolecules

7

aggregated sufficiently in a parallel manner to form nanofibers with apparent average diameter of

8

25 nm. The cellulose fibers consisted of the nanofibers exhibited high degree of orientation with

9

Herman's parameter of 0.9 and excellent mechanical properties with tensile strength of 3.5 cN/dtex

10

at dry state and 2.5 cN/dtex at wet state, as well as low fibrillation. This work provided a novel

11

approach to produce high-quality cellulose multifilament with nanofibrous structure, showing a

12

great potential in the material processing.

13 14

KEYWORDS: High orientation, Nanofiber formation, Mechanically strong fibers, Parallel

15

self-aggregation, Environmentally friendly technology

16 17

INTRODUCTION

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The threats of the depletion of nonrenewable resources and environmental pollution caused by

19

petroleum-based polymer materials make a growing urgency to utilize naturally occurring polymers

20

to create new materials.1-3 Cellulose, as the most abundant natural polymer on earth, has attracted

21

much attentions, due to its renewability, wide availability, low-cost, biocompatibility and

22

biodegradability, etc.4-6 Regenerated cellulose fibers (RCFs), a typical class of cellulose-based

23

materials, are widely used in our daily life, and common in industries such as surgery, textile, water 2


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treatment, automotive industry, etc. As one of the oldest RCFs, viscose rayon has occupied an

2

important position in industry ever since 1892.7 Then N-methylmorpholine-N-oxide (NMMO) as a

3

new solvent, has been commercialized, leading to a new class of RCFs with the generic name of

4

Lyocell at the end of last century.8 Recently, the use of ionic liquid, as another novel solvent for

5

cellulose, is now a new avenue for fabrication of RCFs.9-11 Faced with the serious pollution

6

produced by the viscose method in China and India, the development of an environmentally friendly,

7

and low-cost approach to fabricate cellulose fibers with desired properties is still the key. In our

8

laboratory, a solvent of NaOH/urea aqueous solution with cooling, in which cellulose dissolution

9

can be achieved rapidly, has been developed, and from which novel cellulose multifilament fibers

10

have been spun.12 However, its further applications are hindered due to the mechanical strength,

11

which did not achieve high requirement in textile industry.

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Recently, we found that cellulose, chitin and chitosan exist as extended worm-like chains in

13

alkali/urea aqueous solution,13-15 and easily arrange in parallel to form nanofiber.16-18 Moreover,

14

mechanically strong cellulose-based or chitin-based bulk materials, such as films, hydrogels and

15

bioplastic, can be achieved through the construction of nanofibrous structure by controlling

16

regenerating cnditions.19-24 Usually, violent regeneration process generates inhomogeneous structure

17

and poor mechanical strength, whereas mild coagulation often leads to dense structure and high

18

strength of the regenerated materials. Thus, a worthwhile endeavor would be to construct high

19

strength nanofibril-structured fibers from the cellulose solution. Here, phytic acid, a coagulant with

20

low self-diffusion coefficients, was chosen to replace sulphuric acid to mitigate the regeneration

21

process, and the nanofibril-structured cellulose fibers were spun via a lab-scale spinning machine,

22

showing the excellent mechanical properties. This work opened up a completely new avenue to

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produce high quality cellulose multifilament fibers via a green pathway and new pattern. 3



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EXPERIMENTAL SECTION

3

Materials. The cellulose (cotton linter pulp) with an α-cellulose content of more than 95 % was

4

provided by the Hubei Chemical Fiber Co. Ltd. (Xiangyang, China). The viscosity-average

5

molecular weight (Mη) was measured with an Ubbelohde viscometer in cadoxen at 25 oC to be

6

7.5×104 (DP=460). The cotton linter pulp was dried in an oven at 60 oC for 4 h before use. All other

7

chemical reagents were purchased from Sinopharm Chemical Reagent Co., China and used without

8

further purifications.

9

Dissolution

of

Cellulose

and

Wet

Spinning.

The

aqueous

solution

containing

10

NaOH/LiOH/urea/H2O of 7:0.5:12:80.5 by weight was used as solvent of cellulose. To prepare the

11

spinning dope, cotton linter pulp in the desired amount was dispersed into the alkaline aqueous

12

solvent pre-cooled to -12 oC with mechanical stirring at ambient temperature. After removing air

13

bubbles by centrifugation at 7000 rpm for 30 min at 5 oC, a transparent cellulose dope with 5-6 wt%

14

concentration was obtained. The wet-spinning process of the nanofibril-structured cellulose fibers

15

(NCF) was performed on a lab-scale wet-spinning machine (Figure S1). The cellulose dope (5.8

16

wt%) was pushed from a sealed reservoir into a Zenith BPB-4391 gear pump using nitrogen

17

pressure (0.15 MPa), and then extruded through a spinneret cylinder (50 orifices; diameter, 160 µm)

18

into a coagulation bath of 15 wt% phytic acid/5 wt% sodium sulfate aqueous solution at 5 oC. The

19

resultant gel-state fibers were taken up on the Nelson-type roller I, and then drawn to the

20

Nelson-type roller II in hot water (60 oC). The residual salts and acids in the gel-state fibers were

21

washed out in a water bath until the pH of about 7, dried at 60 oC, and then collected on the take-up

22

roller. The flow rate of the cellulose solution through the spinneret holes was 7.46 m/min. The

23

multi-drawing processes were achieved by controlling the rotation rate of Nelson-type rollers I and 4


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1

II. The regenerated cellulose fibers were coded as NCF-1.0, NCF-1.5 and NCF-2.0, corresponding

2

to with draw ratios of 1.0, 1.5 and 2.0.

3

Fibrillation Test. Fibrillation was induced in aqueous NaOH solution at 80 oC using magnetic

4

stirring for 2 h. Degree of the fibrils was assessed by observing number of fibrils using an optical

5

microscope.25

6

Characterization. Solid-state

13

C NMR spectra were recorded on a BRUKER ACANCE III

7

spectrometer operated at a 13C frequency of 75 MHz using the combined technique of magic angle

8

spinning (MAS) and cross-polarization. The spinning speed was set at 5 kHz. The contact,

9

acquisition and delay times were 3ms, 50ms and 3s, respectively. A typical number of 1024 scans

10

was acquired for each spectrum. The fibers were ground into powders and dried at 60 oC under

11

vacuum before measurement. Atomic force microscopy (AFM) observations were carried out on a

12

commercial AFM (Cypher ES, Asylum Research) in an AC mode at room temperature. Silicon

13

probes with a spring constant of 2 N/m and resonance frequency of 70 kHz were employed. The

14

average tip radius was 28 nm. Scanning electron microscopy (SEM) images were taken on a

15

scanning electron microscope (FESEM, Zeiss, SIGMA) at an accelerating voltage of 5kV. The

16

gel-state fibers were frozen in liquid nitrogen, snapped immediately, freeze-dried and then sputtered

17

with gold to observe the cross-section with FE-SEM. The inner structure of the NCF at dry state

18

was firstly embedded in epoxy resin and then sliced along the fiber axis by microtome to obtain a

19

slice sample with the thickness of about 10 µm, which was sputtered with gold before observe.

20

X-ray diffraction (XRD) of the cellulose fibers was examined with a Rigaku Miniflex600

21

diffractometer operated at 40 kV and 40 mA in reflection mode with Cu Kα radiation (λ= 0.154 nm),

22

a scanning speed of 5 oC/min and a step-size of 0.02o over the 2θ range from 4o to 40o. In this case,

23

cellulose fibers were ground into particles to eliminate the effects of the crystalline orientation. The 5



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1

crystallinity of the samples were calculated from the relative integrated area of crystalline and

2

amorphous peaks through the following equation26 % =

3

× 100

(1)

4

where Acr and Aam are the integrated area of the crystalline and amorphous phases, respectively.

5

Two-dimensional wide-angle X-ray diffraction (2D WAXD) measurements were performed on a

6

Bruker D8 Advance diffractometer operated at 40 kV and 0.65 mA with a Cu anode via the

7

Debye-Scherer method. Both the degree of orientation (Π) and the Hermans’ orientation parameter

8

(f) from the (020) reflections in the 2D WAXD pattern were calculated by using following

9

equations27

10

=

11

=

(2)

(3)

(

12

!" # =

) ∑* %&' (

) ∑* %&'

(4)

13

where fwhm is the full width at half-maximum of the azimuthal distribution curve along the

14

equatorial (020) reflection. φ represents the azimuthal angle, and I(φ) is the intensity along the

15

Debye-Scherer ring. Small angle X-ray scattering (SAXS) was recorded on the GeniX 3D beam

16

delivery system using a MP-Xeuss 2.0 SAXS (BRUKER AXS, Inc.) with Cu Kα radiation (λ=

17

0.154 nm). The generator was operated at 40 kV and 0.65 mA. 2D SAXS patterns were obtained

18

using a HI-STAR detector and the specimen to detector distances were 1074 mm. The fiber bundles

19

were dried before the measurement and straightened. A typical image acquisition time was 45s.

20

Dynamic laser light scattering was measured with a commercial light scattering spectrometer

21

(ALV/SP-125, ALV, Germany) equipped with an ALV-5000/E multi digital time correlator and a

22

He-Ne laser (at 632.8 nm). The CONTIN program was used for the analysis of the dynamic 6


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1

light-scattering data.28 The hydrodynamic radius (z) of cellulose in dilute solution (2×10-4 g/ml)

2

was calculated by using the following Stokes-Einstein relation

3

/ 1

< , >. = 2340 5

* 6

(5)

4

where kB is the Boltzmann constant, T is the temperature in units of K, η0 is the solvent viscosity,

5

and Dz represents the translational diffusion coefficient. Rheological analysis was carried out in a

6

DHR-2 rheometer (TA instruments, USA) using a parallel plate of 40 mm diameter with a gap of

7

100 µm. The temperature sweep experiment was performed at a constant frequency of 1 Hz and

8

strain of 10% (linear viscoelastic regime) with a constant heating rate of 0.5 oC/min. Silicone oil

9

was used to avoid the evaporation of water during the test.

10

The cross-section and polarized optical micrographs of cellulose fibers were observed on an

11

optical microscope (Leica DMLP, Germany).The linear density of fiber was calculated in terms of

12

dtex, which are defined as the weight in grams per 10,000 m of the fiber. Tensile mechanical

13

properties of the cellulose fibers were measured at 23°C and humidity of 65% using a universal

14

tensile tester (LLY-06ED, Laizhou Electronic Instrument Co., Ltd. China) according to

15

ISO527-3-1995 (E). The stretching velocity was 20 mm/min. For each fiber prototype, the tensile

16

strength (σb) and elongation at break (εb) values were obtained from at least 20 independent

17

specimens with a gauge length of 20 mm under a certain pre-tension. The mechanical properties of

18

the fibers at wet state were measured according to GB/T 14244-2008.

19 20

RESULTS AND DISCUSSION

21

Formation of the cellulose nanofibers. In our findings, both of the stability and solubility of

22

cellulose in NaOH/urea were improved with addition of 0.5% LiOH (Figure S2), indicating that a

23

few LiOH could enhance the spinnability of the cellulose solution. The hydrodynamic radius 7



1

distributions (f(Rh)) of the cellulose dilute solution exhibited two peaks at 27 nm and 262 nm,

2

corresponding to the single cellulose chains and their aggregates, respectively (Figure1a).

3

Furthermore, nanofiber-like cellulose-alkali-urea complex with an average apparent height (h) from

4

1 to 3.3 nm and average apparent length (l) of 190 nm appeared even at low concentration in the

5

AFM images (Figure1b). These results indicated that rigid cellulose chains aggregated in parallel to

6

form nanofibers, which co-existed in the dilute solution. Moreover, immerging in phytic acid at 5 oC

7

led to the cross-linking networks consisted of the numerous long nanofibers (the cellulose chains

8

attached each other through the hydrogen bonds) with larger height (Figure 1c), indicating that the

9

aggregation and physical cross-linking of the cellulose chains occurred in the solution. This was

10

consistent with that previously reported in our laboratory, the extended cellulose chains easily

11

self-aggregated in parallel to form nanofibers through strongly intermolecular hydrogen bonding,29

12

and the cellulose and chitin materials consisted of nanofibers have been fabricated.14, 15, 20, 23, 29, 30 A

13

schema to describe the formation of the cellulose nanofibers during spinning process is proposed in

14

Figure 1d. During regenerating the cellulose solution in phytic acid at low temperature, the

15

alkali-urea complex as shell on the cellulose chain was destroyed, leading to the exposure of the

16

cellulose chains. Thus, the naked cellulose chains could self-assemble sufficiently in parallel

17

manner to form relatively perfect nanofibers, which then aligned easily along the spinning direction

18

into fibers during the spinning process.

19

To further understand the effect of the regeneration conditions such as diffusion rate of

20

coagulants on the nanofiber formation, the cellulose fibers were fabricated through syringes in three

21

coagulants including 7.3 wt% sulphuric acid, 9.3 wt% citric acid and 8.1 wt% phytic acid at

22

different temperature. The SEM images (Figure S3) indicated that the regenerated cellulose fibers

23

obtained from sulphuric acid and citric acid, coded as SF and CF, respectively, exhibited porous 8


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1

structure with pore wall, whereas the fibers regenerated with phytic acid (coded as PF) displayed

2

nanofibril structure, owing to the slower exchange between solvent and the phytic acid coagulant

3

with smaller self-diffusion coefficients (Figure S4). Clearly, the nanofiber formation depended on

4

the diffusion rate of the hydronium ions of coagulant. As shown in Figure 2, the hydronium ions

5

(H3O+) in phytic acid can slowly diffuse into the cellulose solution to destroy the NaOH-urea

6

complex shell, and the naked cellulose chains aligned sufficiently in parallel manner to form

7

relatively perfect nanofibers, because there was no violent fluctuation (including heat-induced

8

Brownian motion, rapid diffusion and exchange between solvent/non-solvent, etc.).31 Furthermore,

9

with a decrease of the regenerating temperature from 32 oC to 5 oC, the nanofibers in all fibers

10

appeared, suggesting that the mild regeneration condition was helpful for the parallel-self-assembly

11

of the cellulose chains. Moreover, all fibers exhibited a more compact structure with adding 5 wt%

12

Na2SO4 in coagulant (Figure S5), attributing to the increased osmotic pressure in the coagulation

13

bath, which caused the rapid dehydration of the interior regions of the hydrogel fibers.32 Importantly,

14

the nanofibers could help to improve the strength of the fibers, which also could be tuned by

15

changing the coagulant, regenerating temperature, and the adding of Na2SO4 (Figure S6). The

16

gel-state PF fabricated in 8.1 wt% phytic acid/5 wt% Na2SO4 at 5 oC had a tensile strength of 9.5

17

MPa, much higher than that of the gel-state SF (εb= 4.7 MPa) fabricated in 7.3 wt% sulphuric acid

18

at 32 oC. Thus, this regeneration condition, namely phytic acid/Na2SO4 aqueous solution at low

19

temperature, was chosen as the spinning condition on a lab-scale wet spinning machine.

20

Nanofibril structure of the NCF fibers. Cellulose is the most abundant renewable resource

21

(Figure 3a), so its utilization is sustainable. Here, cellulose was dissolved successfully in alkali/urea

22

aqueous solution at -12 oC to prepare dope (5.8 wt%). The gel-state fibers were spun from the

23

cellulose dope into the coagulation bath of 15 wt% phytic acid/5 wt% Na2SO4 aqueous solution at 5 9



1

o

2

gel-state fibers were washed out in a water bath until the pH of about 7, and then dried at 60 oC to

3

obtain the regenerated cellulose fibers, which exhibited good flexibility and a silk-like luster in their

4

appearance (Figure 3c).

C via wet-spinning process (Figure S1), as shown in Figure 3b. The residual salts and acids in the

5

Figure 4 shows the SEM images of the NCF fibers. The apparent diameter of the fibers could

6

vary from 69 µm to 37 µm by drawing, yet still maintained the homogeneous and smooth surface

7

(Figure 4a-c). The NCF fibers exhibited a circular/oval cross section (Figure 4d), similar to that of

8

Lyocell fibers and cuprammonium rayon, because of their physical regenerated process.33, 34 From

9

SEM images of the cross-section, the packed fibril bundles of highly aligned and

10

compartmentalized nanofibers with mean apparent diameter of 27 nm were observed (Figure 4e-f),

11

similar to the cellulose nanofibril structure in wood.35 Such a high orientation was due to the sliding

12

and rearrangement of the nanofibers induced by shear forces, which occurred during the drawing

13

process. To further validate the nanofibril structure of NCF at dry state, they were

14

epoxy-resin-embedded, sliced along the fiber axis by microtome, and then observed by SEM

15

(Figure 5a-b). Obviously, the nanofibers with an average apparent diameter of 25 nm appeared in

16

the NCF fibers. Moreover, the SEM images of the split fibers treated by ball-milling (Figure 5c-d)

17

also displayed the nanofiber patterns with the mean diameter of 24 nm. These results demonstrated

18

strongly that the NCF fiber was consisted of the cellulose nanofibers.

19

Drawing orientation of the NCF fibers. The maximum drawing ratio (DR) of the NCF reached

20

2.0 on a lab-scale spinning machine, which was important in the spinning process. Figure 6(a-c)

21

shows the 2D-WAXD patterns of the cellulose fibers under different drawing ratios. All fibers

22

exhibited the diffraction peaks of cellulose II, which were different from that of original cellulose I

23

(Figure S7), indicated that the structure transformed from cellulose I to II after the dissolution and 10


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1

regeneration. A similar result was also obtained from the 13C NMR spectra of the NCF (Figure S8).

2

Four main peaks appeared at 105.4, 87.9, 75.1, 63.1 ppm, assigning to the C1, C4, C5 (C3, C2), C6,

3

respectively, belonging to cellulose II.36 The C4 peaks of the NCF located at 87.9 ppm shifted to

4

higher magnetic fields than the cotton linter pulp (89.3 ppm) with a significantly lower intensity,

5

suggesting a decrease in crystallinity.37 Figure 6(d-f) shows the SAXS patterns of the NCF fibers.

6

All of the patterns displayed sharp and long equatorial streaks with very short meridional peaks,

7

indicating the presence of needle-shaped voids or a fibrillary structure aligned parallel to the fiber

8

direction and with a periodic lamellar arrangement of crystalline and amorphous. Meanwhile, the

9

NCF exhibited a pattern with colors when viewed between the cross polarizers (Figure 6g-i),

10

indicating the anisotropic structure of the fibers. With an increase of the drawing ratio, both of the

11

crystallinity and degree of orientation enhanced, supported by the results in Figure 6 as well as

12

Figure S9 and Table 1. More importantly, the NCF-2.0 fibers had a Hermans’ orientation parameter

13

of 0.9 (Table 2), similar to that of the commercial viscose rayon,34 indicating a high orientation of

14

the NCF fabricated by this lab-scale machine.

15

Mechanical properties of the NCF fibers. Mechanical properties are essential for an ideal fiber.

16

The tensile strength of the NCF at dry state increased from 2.0 cN/dtex to 3.5 cN/dtex by drawing

17

(Figure 7, Table 1), which were 1.8 times stronger than that of the cellulose fiber regenerated in

18

sulphuric acid (U-3-i, σb=1.9 cN/dtex),12 as a result of the nanofibril structure. Moreover, as shown

19

in Figure 7a and Table 2, the wet tensile strength of the NCF was 2.5 cN/dtex, higher than that of

20

Modal.38 This could be explained that the cellulose nanofibers greatly contributed to the

21

reinforcement, and their orientation further enhanced the tensile strength of the NCF fibers. At the

22

same time, NCF fibers exhibited low fibrillation compared with lyocell (Figure 8). The fibrillation

23

of lyocell fiber occurred even in water, and the fibril number increased with increase in the NaOH 11



1

concentration, whereas the fibrillation of the NCF fibers did not appear even at high alkali solution.

2

It was anticipated that the mechanical properties of the NCF cellulose fibers could be enhanced

3

significantly after further optimization of the spinning process in the industrialized production.

4

Therefore, by inducing the formation of nanofibers, the cellulose multifilament fibers exhibited a

5

great impact on the traditional methods in textile material field.

6

Furthermore, this method was advantageous in avoiding the utilization of toxic/explosive

7

chemical reagents and the release of toxic gas, it is an environmentally more friendly pathway.

8

Moreover, the production cycle (about 8 h) of our technology including the precooling of alkali/urea

9

aqueous solution, cellulose dissolution, filtration, degassing, and fiber spinning also displayed great

10

productivity in multifilament manufacture. Meanwhile, the cellulose fibers have been confirmed to

11

be easy to dye to deep vibrant colors.39 The coagulation bath after production could be recycled for

12

the cellulose regeneration by adding suitable sulphuric acid (Figures S10 and S11). Life cycle

13

assessment indicated that the environment load of this kind of the cellulose materials is at least 70%

14

less than that of PE from the local, regional and global perspectives.19 Therefore, this new pathway

15

offers great potential for producing high-quality cellulose multifilament fibers by using a low cost

16

and environmentally more friendly process.

17 18

CONCLUSION

19

In summary, highly strong multifilament fibers with nanofibril structure were spun from cellulose

20

solution in alkali/urea aqueous system by a relatively slow regeneration condition in phytic acid at

21

low temperature via a lab-scale wet-spinning machine. The stiff cellulose chains in the alkali-urea

22

aqueous solution could self-aggregate sufficiently in a parallel manner to form nanofibers under

23

mild regenerated condition, which was helpful to form the nanofibrous structure. The experimental 12


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1

results demonstrated that the multifilament fibers were composed of cellulose nanofibers with

2

apparent average diameter of 25 nm, and had high crystallinity of 65% and degree of orientation

3

with Herman’s parameter of 0.9. As a result, their tensile strength achieved up to 3.5 cN/dtex at dry

4

state and 2.5 cN/dtex at wet state, as well as low fibrillation. Moreover, the fabrication of the

5

high-quality cellulose multifilament was an environmentally friendly process with low cost and

6

short production cycle, suggesting great potentials in the textile industry.

7 8

ASSOCIATED CONTENT

9

Supporting Information

10

The Supporting Information is available free of charge on the ACS Publications website at DOI:

11

Schematic diagram of the wet spinning machine; Temperature dependence of the storage modulus

12

G′ and loss modulus G″ for cellulose-alkaline-urea solution; SEM images of the cross-section of the

13

SF, CF, and PF at different temperature; Two-dimensional DOSY spectrum of citric acid and phytic

14

acid at 298 K; Stress-strain curves of the gel-state SF, CF and PF; CP/MAS

15

cotton linter pulp, NCF-1.0and NCF-2.0; XAWD patterns of commercial viscose rayon and cotton

16

linter pulp.

17

AUTHOR INFORMATION

18

Corresponding Authors

19

* E-mail: [email protected] (L. Zhang).

20

* E-mail: [email protected] (Q. Fu).

21

ORCID

22

Lina Zhang: 0000-0003-3890-8690

23

Notes 13


13

C NMR spectra of


Page 14 of 30

1

The authors declare no competing financial interest.

2

ACKNOWLEDGEMENTS

3

This work was supported by the Major Program of National Natural Science Foundation of China

4

(21334005, 51421061), the Major International (Regional) Joint Research Project (21620102004).

5 6

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10 11 12 13 14 15 16 17 18 19

19



1 2

Figure 1. The hydrodynamic radius distributions [f(Rh)] of the cellulose alkaline solution (2×10-4

3

g/ml) at 5 oC (a). AFM images of the extremely dilute cellulose solution (2 ×10-7 g/ml) in alkaline

4

system before (b) and after (c) regenerating in phytic acid at 5 oC. The mean height and length of

5

wormlike pattern were 1-3.6 nm, and 190 nm, consistent with worm-like chains of cellulose. Two

6

peaks appeared at 27 nm and 262 nm in the hydrodynamic radius distributions pattern,

7

corresponding to the single cellulose chains and their aggregates, respectively. A schema to describe

8

the formation of the cellulose nanofibers during spinning process (d).

9 10

20


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1 2

Figure 2. The ionization state of sulphuric (a), citric (b) and phytic acid (c) molecules in water, and

3

the aggregation behaviors of cellulose chains regenerating in the acids, depending on the different

4

diffuse rate of the hydronium ions (H3O+) (d-f). Clearly, the larger of the acid molecules, the slower

5

of the diffusion of the acid, and the easier of the fabrication of cellulose nanofibers.

6 7 8 9 10

21



1 2

Figure 3. Abundant cellulose resource (a), the gel-state fibers during the wet-spinning process (b)

3

and the regenerated cellulose multifilament fibers (c).

4 5 6 7 8 9 10 11 12 13 14 15 16

22


Page 22 of 30

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1 2

Figure 4. SEM images of NCF-1.0 (a), NCF-1.5 (b), NCF-2.0 (c). Morphology of NCF-2.0

3

observed with optical microscopy (d). SEM images of the cross section of NCF-2.0 by freezing dry

4

(e, f), showing well aligned nanofibers.

5 6 7 8 9 10 11 12 13 14

23



1 2

Figure 5.The inner structure of the dried NCF prepared by slicing along the fiber axis direction (a,

3

b), and ball-milling (c, d).

4 5 6 7 8 9 10 11 12 13

24


Page 24 of 30

Page 25 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 2

Figure 6. WAXD patterns (a-c), SAXS patterns (d-f) and polarized optical micrographs (g-h) of

3

NCF-1.0 (a, d, g), NCF-1.5 (b, e, h) and NCF-2.0 (c, f, i). Scale bar: 60µm.

4 5 6 7 8 9 10

25



1 2

Figure 7. Mechanical properties of the NCF (a) and the comparison of mechanical properties of

3

various regenerated cellulose fibers (b), oval 1 represents the NCF from NaOH/LiOH/urea aqueous

4

system in this work; oval 2 to 7 represent the regenerated cellulose fiber from NaOH/urea aqueous

5

system,12 NaOH/ZnO aqueous solution,36 cuprammonium,33 NMMO,40 ionic liquid,41 NaOH/CS2,38

6

respectively. The scattering points in the figure are the value of the mechanical properties data of

7

cellulose fibers reported in references.

8 9 10 11 12 13 14 15 16 17 18 26


Page 26 of 30

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1 2

Figure 8. Optical microscope images of filaments (Lyocell, NCF-1.0, NCF-2.0) treated by NaOH

3

solution with different concentrations (0, 0.1, 0.4mol/L).

4 5 6 7 8 9 10 11 12 27



Page 28 of 30

1

Table 1. Crystallinity (χc), degree of orientation (Π), Hermans’ orientation parameter (f), and

2

mechanical properties of the NCF.

Sample

NCF-1.0 NCF-1.5 NCF-2.0

χc (%)

62 65 65

Mechanical Properties Π

0.83 0.85 0.86

f

0.83 0.88 0.90

Dry state

Wet state

σb (cN/dtex)

εb(%)

E (cN/dtex)

σb (cN/dtex)

εb (%)

E (cN/dtex)

2.0±0.1 2.9±0.1 3.5±0.1

24.0±1.7 9.1±0.6 7.7±0.3

78.4±0.2 117.1±2.8 127.8±9.6

1.4±0.3 2.3±0.1 2.5±0.1

26.0±6.7 9.9±0.7 8.7±0.4

27.8±2.8 51.0±2.9 69.0±5.3

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 28


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1


Table 2 Physical properties of the NCF and various regenerated cellulose fibers. Sample

NCF

Solvent

NaOH/LiOH/urea

DP

460

235-300

Viscose

Cross section

circular/oval

lobate

σb

εb

E (ε=1%)

(cN/dtex)

(%)

(cN/dtex)

2.0-3.5

8-24

78-137

This

1.4-2.5 (wet)

8.7-26 (wet)

28-69 (wet)

work 33, 38

f

χ c (%)

62-65

Ref.

0.83-0.90

25-30

1.8-2.5

18-23

24.8

1.0 (wet)

21.6 (wet)

7.1 (wet)

3.1

16.5

34.9

1.5 (wet)

18.3 (wet)

7.5 (wet)

0.58-0.90

NaOH/CS2

507

Modal

2

--

37

0.69

38

U-3-i

NaOH/urea

420-590

circular

56-62

0.56-0.64

1.3-1.9

2-18

--

12

RCF

NaOH/ZnO

560

circular

50-57

0.81-0.87

1.7-2.4

15-25

--

36

Ioncell-F

Ionic liquids

--

--

28-36

--

3.6-5.8

8.9-10.2

--

2.7-5.7 (wet)

10-12.4 (wet)

--

41

Lyocell

NMMO

1600

--

50-51

--

3.7-5.4

4.9-6.6

56-109

40

Cupro

cuprammonium

500

circular/oval

43

--

1.5-2.0

10-20

--

33

wet in the table means the date obtained from the fibers with wet state.

3 4 5 6 7 8 9 10 11 12 13 14 15 16 29



1

Abstract graphic

2

3 4

An outstanding mechanical properties and environment friendly multifilament fibers with nanofibril

5

structure is demonstrated to have an ultra-high tensile strength of 3.5 cN/dtex at dry state and 2.5

6

cN/dtex at wet state.

30


Page 30 of 30

Mechanically Strong Multifilament Fibers Spun ... - ACS Publications

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