comparative characterisation of man-made regenerated ... - Lenzing

Lenzinger Berichte 87 (2009) 98-105
COMPARATIVE CHARACTERISATION OF MAN-MADE
REGENERATED CELLULOSE FIBRES
Thomas Röder 1 , Johann Moosbauer 1 , Gerhard Kliba 1 , Sandra Schlader 2 , Gerhard
Zuckerstätter 2 , and Herbert Sixta 3
1 Lenzing AG, Department FE, A-4860-Lenzing, Austria
2 Kompetenzzentrum Holz GmbH (Wood K plus), A-4021 Linz, Austria
3 Helsinki University of Technology, 02150 Espoo, Finland
Phone: (+43) 07672-701-3082; Fax: (+43) 07672-918-3082; E-mail: t.roeder@lenzing.com
Presented during the 8 th International Symposium Alternative Cellulose Manufacturing, Forming, Properties 03-
04 th September 2008 Rudolstadt/Germany
Man made cellulose fibres show a large
bandwidth of properties depending on
their manufacturing process. Despite
the differences in structure and
morphology, molecular weight and its
distribution, fibre properties and cross
section, crystallinity and orientation, the
chemical substrate is always cellulose in
the modification II. The great variability
of their properties is the basis for the
manifold use of these fibres all over the
world.
Commercial man made cellulose fibres
of different types (viscose, cuam and
high modulus rayon, tire cord, lyocell)
are compared against experimental
Introduction
98
regenerated cellulose fibres (e.g.
fortisan, fibre B “bocell”, lyocell).
Numerous characterisation methods
(e.g.: REM, Raman/WAXS, SEC, NMR,
fibre properties) are used to highlight
similarities, differences, and
characteristics of cellulose fibres.
Structure – property – relationships will
be presented and discussed.
Keywords: man made cellulose fibres,
fibre properties, viscose, lyocell, modal,
fortisan, bocell, cuam, celsol
__________________________________________________
In contrast to cotton the use of cellulose
pulp made from wood to produce textiles
needs a forming procedure based on
cellulose dissolution followed by a
forming (and a regeneration) step.
The history of man-made cellulose fibres
started in 1846 with the discovery of
cellulose nitrate by Karl-Friedrich
Schönbein. In 1892 the first factory was
built in Besançon (France) by Comte
Hilaire de Chardonnet producing
“Chardonnet silk”. Cuprammonium rayon
was discovered in 1857 by Eduard
Schweizer, the first factory was built in
1899. Viscose (cellulose xanthate) was
discovered in 1891 by Cross, Bevan, and
Beadle.
Nowadays a great variety of man-made
cellulose fibres is known. But only a few
are produced in industrial scale: viscose
(CV, staple and filament), modal (CMD),
lyocell (CLY), cupro (CUP), acetate (AC),
and triacetate (CTA).
The fibres are divided into two categories:
cellulose fibres (e.g. CV, CMD, CLY,
CUP) and cellulose derivative fibres (e.g.
AC, CTA). We will focus on the cellulose
fibres only.

Cellulose fibres can be produced via
cellulose derivatisation followed by
regeneration (involving the destruction of
the derivative, e.g. viscose) or via
dissolution in a non-derivatising solvent
(e.g. NMMO, Cuoxam, ionic liquids) and
consequent regeneration.
Fibre samples
In this study various commercial fibres are
compared with a great variety of
experimental fibres. Commercial fibres are
viscose fibres (viscose, tire cord viscose,
polynosic fibres), modal fibres, cupo fibres
(Asahi Kasai), and lyocell fibres (Tencel ® ).
Fibres based on cellulose derivatives are
Fortisan® fibres:
A saponified cellulose acetate prepared by
dry spinning a solution of cellulose acetate
in acetone (Celanese Corp., sample kindly
provided by Prof. H. Chanzy, Grenoble,
France). Fibres are highly oriented. The
yarn is no longer produced.
“Fibre B” (Bocell):
Anisotropic solutions of cellulose in
superphosphoric acid spun via air-gap into
acetone and saponification in water/soda.
Fibres have high tenacities and are highly
oriented (developed by H. Boerstoel (Akzo
Nobel), sample kindly provided by Dr. S.
Eichhorn, Manchester, UK).
Viscose fibres:
Cellulose xathogenate dissolved in sodium
hydroxide and spun via wet spinning
process into sulphuric acid/ sodium
sulphate/ zinc sulphate. Modal fibres are
produced by a modified viscose process.
Celsol fibres:
Cellulose is dissolved in sodium hydroxide
and regenerated in water (Institute of
Chemical Fibres, Lodz, Poland).
Fibres based on direct dissolved cellulose
are
Cupro fibres:
Cellulose dissolved in tetraaminecopper
dihydroxide (complexation) and
Lenzinger Berichte 87 (2009) 98-105
99
regenerated in water (Asahi Kasai).
Lyocell fibres:
Cellulose is directly dissolved in
NMMO/water (Tencel®) or ionic liquids
and spun through an air gap and
precipitated in water.
Cellulose solvents, resulting fibre types
and their characterisation
The cross section is a structural parameter
of the fibre which is accessible via
microscopy. Fibre diameters around 10
microns allow the use of light microscopy
as well as scanning electron microscopy.
Independent of the used solvent system for
cellulose similar cross sections can be
made (Figure 1) assuming the use of
similar spinnerets. However, the same
solvent system but a modified spinning
bath leads to different cross sections
(Figure 2). For viscose the acid
concentration (same dope, same machine,
all the other parameters are the same)
influence the regeneration of the cellulose
xanthate. A lower acid content leads to a
“softer” regeneration. However, high acid
content results in a massive loss of degree
of polymerization (DP).
The commercially available viscose type
fibres CV, CV tire cord, CMD, and
polynosic (Figure 3) differ in DP of
cellulose (source), spinning process, and
after treatment. Their fibre properties vary
over a wide range. Nevertheless, further
diversification needs the use of other
solvent systems. Higher tenacity, e.g., is
available by using the lyocell process.
Crystallinity increases, too. The solvent for
the commercial Lyocell process is
NMMNO (Tencel®). Similar to Lyocell,
BISFA defines a cellulose fibre obtained
by a spinning process from an organic
solvent mixed with water."Solventspinning"
means dissolution and spinning without
derivatization. Therefore, every spinning
process using ionic liquids to dissolve and
to spin cellulose is a Lyocell process.

Examples for these are given in Figures 1
and 4. The shape and the overall properties
of these fibres are comparable to Tencel®
fibres.
The use of special pulp sources (e.g. cotton
linters pulp) and special spinning
conditions allows the manufacturing of
fibres with higher tenacity and higher
modulus. However, the fibre properties are
in the same range as for NMMO fibres,
which could be improved by the named
changes in pulp source and spinning
conditions, too.
NMMO and ionic liquids are the most
recent cellulose solvents used and lie in the
focus of actual research. Other solvents for
cellulose like hydrates of inorganic salts,
e.g., zinc chloride and lithium perchlorate;
lithium chloride and dimethylacetamide
(DMAc); and metal complex solvents, e.g.,
copper ethylendiamine (Cu-en), are known
and some are used for analytical purpose
(LiCl-DMAc for SEC; Cu-en for intrinsic
viscosity measurement), but they are not
Lenzinger Berichte 87 (2009) 98-105
100
used to make fibres.
Another interesting approach is the
CELSOL concept: Cellulose is dissolved
in sodium hydroxide. Known from the
viscose process, where cellulose reacts
with sodium hydroxide to sodium
cellulose, sodium hydroxide is able to
dissolve hemicellulose and shorter
cellulose molecules. The idea is to use
sodium hydroxide directly without
cellulose xanthate as for viscose to
produce man made fibres. The
disadvantage is in the limited solubility of
longer cellulose chains. Therefore,
presumably only fibres lower than viscose
quality will be possible.
During World War 2 a process for
manufacturing of cellulose silk for
parachutes was developed: Fortisan®
(Figure 4). These fibres have a high
crystallinity, high orientation, and high
modulus. Therefore they are very lean and
thin. Fortisan® was produced via a dry
spinning process.
Figure 1. SEM figures of regenerated cellulose fibres with round shape.
Figure 2. Influence of acid content in spinbath for viscose types of fibres.

Lenzinger Berichte 87 (2009) 98-105
Figure 3. SEM figures of different viscose types of fibres.
Figure 4. SEM figures of regenerated cellulose fibres with different cross sections.
Table 1. Fibre data.
Tenacity Elongation Tenacity Elongation BISFA modulus Commercial/
titre cond. cond. wet wet modulus cond. experimental
[dtex] [cN/dtex] [%] [cN/dtex] [%] [cN/tex/5%] [cN/tex/%] fibre
Tencel® 1,3 40,2 13,0 37,5 18,4 10,8 8,8 com.
polynosic 1,8 38,2 9,7 26,0 11,0 12,1 n.a. com.
cupro 2,5 22,3 24,3 17,6 51,3 5,0 9,9 com.
EMIM-Cl 1,7 43,0 9,6 35,9 11,6 14,0 8,1 exp.
BMIM-Cl 1,5 50,1 9,3 39,4 10,4 17,8 n.a. exp.
CV 1,4 23,9 20,1 12,5 22,0 2,4 5,3 com.
CV tire cord 1,9 52,3 15,1 38,4 22,9 3,1 11,1 com.
CMD 1,3 33,1 13,5 18,4 14,1 5,2 6,3 com.
fibre B 1,6 89,4 6,8 75,8 7,9 39,0 23,5 exp.
EMIM-Ac 1,8 44,7 10,4 38,1 11,9 13,2 10,0 exp.
Fortisan® 0,7 23,9 3,2 27,7 5,1 27,0 n. a. exp.
Celsol 3,32 16,96 7,8 7,2 11,2 4 n. a. exp.
Up to now the highest crystallinity,
orientation, and tenacity is known from the
so-called “fibre B”. This experimental
fibre is produced from liquid crystalline
solution of cellulose in superphosphoric
acid and spun into acetone followed by
saponification. This has similarities to the
old Fortisan® process where cellulose
101
acetate is spun into acetone, too.
In contrast to viscose type fibres (wet
spinning) all these fibres are produced via
air-gap in a dry-wet (Lyocell) or in a dry
spinning process (followed by
saponification: Fortisan®, fibre B).
Characteristic fibre data are given in Table
1.

Structural parameters and fibre properties
Fibre properties can be varied within a
wide range by using the same dope and the
same spinning process. The level of
stretching determines the tenacity and
elongation level. A high degree of
stretching results in a relatively tearresistant
and low-strain fibre.
The product of tenacity and elongation is
called “working capacity”. This “working
capacity” is mainly determined by the
process and the solvent used. The
molecular weight of the cellulose should
be in an optimum range for the used
solvent. The length of cellulose chains
should be high enough to be able to form
fibres. Cellulose chains should, however,
not be too long, since this would increase
the viscosity of the dope too much. For
every manufacturing process there exists a
different optimum range. Structural
parameters like orientation are mainly
influenced by the stretching during fibre
making. The liquid crystalline structure of
the dope for “fibre B” is one reason for the
high crystallinity of the fibres. The
structure of the cellulose inside the dope,
the width of cellulose molecular weight
distribution, and the velocity of
regeneration process mainly determine the
crystallinity of the fibres. WAXS (wide
angle X-ray scattering) is the standard
method for the determination of
crystallinity of man-made cellulose fibres
(Hermans and Weidinger 1949) [1].
The information concerning crystallinity of
cellulose II can be obtained by other
methods as well, e.g. Fourier Transform
(FT) Raman, FT-infrared (IR), or solid
state
13 C NMR (nuclear magnetic
resonance) spectroscopy. Raman and IR
based methods normally use a calibration
with WAXS data [2] [3]. Therefore these
methods can only be as good as the
reference method itself.
One of the factors determining the
properties of cellulose fibres is the
Lenzinger Berichte 87 (2009) 98-105
102
Tenacity cond [cN/tex]
50
40
30
CLY, same dope, different draft
20
0,10 0,15 0,20 0,25 0,30 0,35
f 2
C(WAXS) *X IR
Figure 5. CLY fibre manufacturing with the same
dope at various draft levels – correlation of tenacity
and structural parameters orientation and
crystallinity.
Figure 6. WAXS versus FT-Raman crystallinity
[2].
alignment of the fibrillar elements relative
to the fibre axis. A relationship between
the degree of orientation and the tensile
strength of viscose fibres was put forth by
Krässig and Kitchen [4]:
Strength or tenacity in the conditioned
state
FFc ~ f 2 c
and strength or tenacity in the wet state.
FFn ~ f 2,5 tot
The classical method to quantify
orientation of polymer fibres is wide angle
X-ray scattering (WAXS). The WAXS
results were compared with Raman results
to obtain a Raman-based method to
determine the degree of orientation of
cellulose II (Figure 7 and 8).

Lenzinger Berichte 87 (2009) 98-105
Figure 7. Calibration of crystalline fibre orientation - WAXS versus Raman.
Figure 8. Calibration of total fibre orientation – WAXS versus Raman.
The higher resolution of Raman
spectroscopy can be used as a tool for
determining the local fibres orientation.
Another common method to measure the
fibre orientation is the birefringence. A
microscope equipped with polarisers and a
compensator is used. The birefringence n
is obtained by dividing the measured
retardation of polarised light by the
respective fibre thickness. By relating n
to the maximum birefringence of cellulose
nmax, the orientation factor f (Hermans’
orientation factor) can be calculated
according to f = n/nmax. Factor f = 1
means perfect orientation parallel to the
103
fibre direction, f = 0 for random
orientation, and -1 for perfect transverse
orientation. This method is very useful for
fibres with a round cross section, e.g.
lyocell, and no crimp and distortion.
Unfortunately, most of commercial fibres
have no round cross section, are crimped,
or both. This results in large differences of
orientation values.
According to Krässig and Kitchen [4] a
linear correlation between the degree of
orientation and the fibre tenacity in
conditioned as well as in wet state was
found. Especially a series of CLY made
from the same dope spun under different
drafts showed a very good correlation

(Figure 5). The comparison of different
man-made cellulose fibres used for
analytical method development is given in
Figures 9 and 10. Despite the CV tire cord
the fibres showed more or less a linear
correlation between tenacity and fibre
orientation.
Tenacity cond [cN/tex]
60
50
40
30
20
10
f C ...degree of orientation of crystalline regions
X IR ...crystallinity determined by infrared spectroscopy
0
0,0 0,1 0,2
f
0,3
2
C(WAXS) *XIR Lenzinger Berichte 87 (2009) 98-105
CLY
CMD
Polynosic
CV
Cupro
CV tire cord
Figure 9. Correlation between tenacity
(conditioned state) and structural parameters –
crystalline fibre orientation and crystallinity.
Tenacity wet [cN/tex]
45
40
35
30
25
20
CLY
15
CMD
Polyosic
10
CV
5
0
Cupro
CV tire cord
0,00 0,05 0,10 0,15
f 2.5
tot(WAXS) *XIR Figure 10. Correlation between tenacity (wet state)
and structural parameters – total fibre orientation
and crystallinity.
As mentioned above, the molecular weight
distribution is another important
parameter. State of the art is the
determination of the molecular weight
distribution by size exclusion
chromatography (SEC). Essential is the
choice of a suitable solvent system, e.g.
LiCl-DMAc. Another possibility is the use
of cellulose derivatives, e.g. cellulose
nitrate. In this study SEC based on LiCl-
DMAc was used (Figure 11).
104
differential molecular weight
differential molecular weight
1,5
1,2
0,9
0,6
0,3
0,0
1,5
1,2
0,9
0,6
0,3
0,0
fortisan
fibre "B" bocell
CV tire cord
3,5 4,0 4,5 5,0 5,5 6,0
log molar mass
CV
polynosic
celsol
3,5 4,0 4,5 5,0 5,5 6,0
log molar mass
Figure 11. Comparison of molecular weight
distribution of man-made cellulose fibres.
Lyocell fibres (Tencel® and ionic liquid
fibres) have a higher molecular weight
than viscose fibres. The spectrum depends
on the used pulp. While the cellulose is
degraded in the ripening step in the viscose
process, the degradation during the lyocell
process is prevented by added stabilizers.
Therefore, the molecular weight of lyocell
fibres is mainly determined by the used
pulp. Normally, the degradation during the
lyocell process should be less than 10%.
The elastic modulus (Young’s modulus) is
the linear slope of stress (tenacity) versus
strain (elongation). It is a measure of the
stiffness of a material. A higher elastic
modulus means a higher resistance of the
fibre against deformation. A comparison of
typical stress-strain-curves is given in
Figures 12 and 13. The highest value for
the elastic modulus and tenacity as well
was reached by fibre “B” (bocell). The
lowest value was determined for viscose
fibres. To get fibres in between these two
values, the solvent and/or the

manufacturing process has to be chosen
carefully.
tenacity cond [cN/tex]
Figure 12. Stress-strain curve of viscose type man
made fibres.
tenacity [cN/tex]
40 CV tire cord
CMD
CV
30
20
10
0
0 2 4 6 8 10 12 14 16 18 20
50
40
30
20
10
0
0 5 10 15 20
elongation [%]
Lenzinger Berichte 87 (2009) 98-105
Tencel
Fortisan
Fibre B
Figure 13. Stress-strain curve of high modulus fibres
compared with Tencel®.
Conclusions
elongation cond [%]
Man-made cellulose fibres are manifold
and open a fascinating field of research
and application. The further development
of these fibres will surely direct to some
surprising properties and facts. After more
than 100 years of viscose fibres, even there
the development is not completed.
105
Acknowledgements
The authors thank Dr. Hans-Peter Fink and
Dr. Andreas Bohn (IAP Golm, Germany)
for the WAXS measurements concerning
crystallinity, Prof. Dr. Peter Zipper and Dr.
Boril Cernev (University of Graz, Austria)
for the WAXS measurements concerning
orientation, and Anneliese Flachberger
(Lenzing AG, Austria) for the textile
measurements.
We would like to thank Prof. Dr. Henry
Chancy (Grenoble, France) for the kind
donation of the Fortisan fibre, Dr. Frank
Dürsen (Obernburg, Germany) for the
viscose tire cord fibres, Dr. Birgit Kosan
(TITK Rudolstadt, Germany) for the ionic
liquid fibres, and Dr. Stephen J. Eichhorn
(University of Manchester, UK) for the
fibre “B” (bocell).
References
[1] P. H. Hermans and A. Weidinger. Xray
studies on the crystallinity of
cellulose, J. Polymer Sci. 4 (1949) 135-
144.
[2] T. Röder, J. Moosbauer, M. Fasching,
A. Bohn, H.-P. Fink, T. Baldinger, and
H. Sixta. Crystallinity determination of
native cellulose -comparison of
analytical methods, Lenzinger Berichte
86 (2006), 85-89.
[3] T. Baldinger, J. Moosbauer, and H.
Sixta. Supermolecular structure of
cellulosic materials by Fourier
Transform Infrared Spectroscopy (FT-
IR) calibrated by WAXS and 13 C
NMR, Lenzing Berichte, 79 (2000) 15
- 17.
[4] H. Krässig and W. Kitchen. Factors
influencing tensile properties of
cellulose fibres, J. Polymer Sci. 51
(1961) 123-172.