S1

Supplementary Information

High Modulus Regenerated Cellulose Fibers Spun

from a Low Molecular Weight Microcrystalline

Cellulose Solution

Chenchen Zhu1, Robert M Richardson

2, Kevin D Potter

1, Anastasia F Koutsomitopoulou

1,

Jeroen S van Duijneveldt3, Sheril R Vincent

1, Nandula D Wanasekara

4, Stephen J

Eichhorn4*

, Sameer S Rahatekar1*

1. Advanced Composites Centre for Innovation and Science (ACCIS), Department of

Aerospace Engineering, University of Bristol, Queen’s Building, University Walk, Bristol

BS8 1TR, UK

2. H H Wills Physics Laboratory, Physics Department, University of Bristol, Tyndall

Avenue, Bristol BS8 1TL, UK

3. School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK

4. College of Engineering, Maths and Physical Sciences, University of Exeter, Stocker Road,

Exeter EX4 4QL, UK

Total number of pages: 10 (S1-S10) including 3 Equations, 7 Figures and 0 Tables.

S2

25 °C 40 °C 60 °C

70 °C 75 °C 80 °C

Clearing Temperature of Cellulose/EMImDEP Solutions

When the solutions are heated above the clearing temperature (Tc)1, the solution becomes

isotropic and the anisotropy pattern disappears. To study Tc, 12.4 wt%, 15.2 wt% and 18.0

wt% cellulose/EMImDEP solutions were heated from 25 °C to 90 °C, while polarized optical

micrographs were taken at different temperatures, respectively (Figure S1-3). The anisotropy

of cellulose/EMImDEP solutions diminished gradually as the temperature increased and

finally disappeared at Tc. For the 12.4 wt% and 15.2 wt% cellulose/EMImDEP solutions, 75

°C< Tc <80 °C (Figure S1-2); while for the 18.0 wt% solution, 85 °C< Tc <90 °C (Figure S3).

Given these differences in Tc, a fiber spinning temperature of 80 °C was used for further

studies.

Figure S1. Typical anisotropy transition of 12.4 wt% cellulose/EMImDEP solution heated

from 25 °C to 80 °C.

S3

25 °C 40 °C 60 °C

80 °C 85 °C 90 °C

Figure S2. Typical anisotropy transition of 15.2 wt% cellulose/EMImDEP solution heated

from 25 °C to 80 °C.

Figure S3. Typical anisotropy transition of 18.0 wt% cellulose/EMImDEP solution heated

from 25 °C to 90 °C.

Diameter Measurements of Cellulose Fibers

SEM images of 12.4 wt%, 15.2 wt% and 18.0 wt% cellulose were taken for diameter

measurements. Their average diameters as obtained from images such as those shown in

25 °C 40 °C 60 °C

70 °C 80 °C 75 °C

S4

Figure S4 are given in Table 1. With the same draw ratio, no significant differences in the

average diameters were observed for 12.4 wt% (22.0±1.4 µm), 15.2 wt% (23.1±1.1 µm), and

18.0 wt% (20.8±3.0 µm) fibers.

Figure S4. Average diameters for 12.4 wt%, 15.2 wt% and 18.0 wt% cellulose fibers

measured from SEM images.

Cross-section Observation of Cellulose Fibers

To confirm the accuracy of fiber diameter measurements using SEM images, cross-sections

of regenerated cellulose fibers were imaged using light microscopy. Six to eight randomly

picked filaments of 12.4 wt%, 15.2 wt% and 18.0 wt% cellulose fibers were mounted

vertically and parallel to each other into a cylindrical resin mold. A combination of PRIME™

20LV epoxy resin and PRIME™ 20 slow hardener purchased from Gurit (Newport, UK) with

a mix ratio (weight) of 100:26 was used for the molds. After filament mounting, the molds

S5

C

B

A

were cured at room temperature for 2 days. They were then polished perpendicular to the

filament axis direction using a Buehler Beta™ grinder polisher and a Vector™ power head

(Esslingen am Neckar, Germany). The cross-sectional shapes of fiber filaments mounted in

resin molds for 12.4 wt%, 15.2 wt% and 18.0 wt% cellulose fibers were observed using a

ZEISS Axio Imager 2 microscope (Cambridge, UK), with torch light brightening in a

direction perpendicular to the fiber axis.

Figure S5. Typical optical micrographs of cross-sections of (A) 12.4 wt%, (B) 15.2 wt% and

(C) 18.0 wt% cellulose fibers mounted in resin molds.

S6

The cross-sections of 6-8 randomly selected filaments of 12.4 wt%, 15.2 wt% and 18.0

wt% cellulose fibers mounted in resin molds are shown in Figure S5. It is found that these

fibers have circular cross-sections, similar to NMMO-type filaments but different from the

typical serrated shapes observed for viscose2.

Machine Compliance (Cs) Study of Cellulose Fibers

The existence of machine compliance (Cs) during tensile testing may affect the accuracy of

mechanical properties data. Therefore, it is necessary to calculate this parameter. Compliance

(Cs) is attributed to the influence of the load system and the specimen-gripping system on the

crosshead displacement. This influence results in a difference between the recorded crosshead

displacement and the true specimen displacement according to Equation S13, where ∆L is the

recorded crosshead displacement, ∆l is the elongation of the specimen gauge length, Cs is the

system compliance and F is the force required to fracture the specimen.

∆� = ∆� + ��� (S1)

In a single fiber, the tensile strain can be calculated using Equation S2, where ε is the

tensile strain, σ is the tensile stress, E is the Young’s modulus, A is the cross-sectional area of

a single fiber and l0 is the original gauge length.

=

�=

�

��=

∆�

�

(S2)

With a combination of Equations S1 and S2, Cs can be calculated using Equation S3:

∆�

�=

∆�

�+ �� =

�

��+ �� (S3)

S7

Therefore, ∆L/F of ten fiber tensile specimens were calculated for 12.4 wt%, 15.2 wt% and

18.0 wt% cellulose fibers with gauge lengths of 12, 20 and 30 mm. A linear curve was fitted

to this parameter as a function of reciprocal gauge length for 12.4 wt%, 15.2 wt% (Figure

S6A-C). According to Equation S3, the calculated values of Cs are similar for 12.4 wt% (-

0.00018), 15.2 wt% (-0.00016) and 18.0 wt% (-0.00023) cellulose fibers; these values are

small, indicating that machine compliance does not significantly influence the results.

Arridge et al. showed that the load becomes better diffused across the entire cross-section

as a fiber’s aspect ratio (length/diameter) increases, resulting in the effective Young’s

modulus (E) approaching the true value4. To avoid the potential end effect of a fibers’ aspect

ratio on Young’s modulus, a linear curve was fitted according to the average E of ten

cellulose fiber specimens as a function of reciprocal gauge length of 12, 20 and 30 mm for

12.4 wt%, 15.2 wt% and 18.0 wt% cellulose fibers (Figure S7 and Table 2). The intercept of

a linear fit to these data will give an estimation of E at an infinite gauge length. In Figure S7,

the slopes of these linear fits are small: -0.028, -0.012 and – 0.025. The small slopes observed

indicate that the average Young’s modulus is relatively insensitive to changes in gauge

length.

S8

Figure S6. Tensile system compliance estimated by the ratio of displacement to load as a

function of reciprocal gauge length of 12, 20 and 30 mm of (A) 12.4 wt%, (B) 15.2 wt% and

(C) 18.0 wt% cellulose fibers.

A B

C

S9

Figure S7. Average Young’s modulus of (A) 12.4 wt%, (B) 15.2 wt% and (C) 18.0 wt%

cellulose fibers, with three gauge length of 12, 20 and 30 mm.

A B

C

S10

REFERENCES

(1) Boerstoel, H.; Maatman, H.; Westerink, J. B.; Koenders, B. M. Liquid crystalline

solutions of cellulose in phosphoric acid. Polymer 2001, 42 (17), 7371-7379.

(2) Fink, H. P.; Weigel, P.; Purz, H. J.; Ganster, J. Structure formation of regenerated

cellulose materials from NMMO-solutions. Prog. Polym. Sci. 2001, 26 (9), 1473-1524.

(3) Standard test method for tensile strength and Young's modulus of fibers. 2003 ed.;

ASTM International: West Conshohocken, PA, 2008.

(4) Arridge, R. G. C.; Barham, P. J.; Farrell, C. J.; Keller, A. Importance of end effects in

measurement of moduli of highly anisotropic materials. J. Mater. Sci. 1976, 11 (4), 788-790.