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CELLULOSE PROCESSING WITH CHLORIDE BASED IONIC LIQUIDS

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					                                  Lenzinger Berichte, 86 (2006) 154-161


                          CELLULOSE PROCESSING WITH
                         CHLORIDE-BASED IONIC LIQUIDS

       Gino Bentivoglio1,2, Thomas Röder3, Mario Fasching1, Mario Buchberger3,
                          Herwig Schottenberger2, and Herbert Sixta3.
                  1
                     Kompetenzzentrum Holz GmbH, St.-Peter-Str. 25, 4021 Linz, Austria;
          Phone: +43 512 507 5117; Fax: +43 512 507 2934; E-mail: g.bentivoglio@kplus-wood.at
     2
       Faculty of Chemistry and Pharmacy, University of Innsbruck, Innrain 52a, 6020 Innsbruck, Austria
              3
                Lenzing AG, Department of Pulp Research, Werkstrasse 1, 4860 Lenzing, Austria


Ionic liquids (ILs, salts with a melting    imidazolium chloride and 1,3-diallyl-
point below 100 °C) are discussed as        imidazolium chloride the temperature
solvents for cellulose with a potential for effect on degradation was studied. Fibres
industrial applications. Several chloride   could be obtained by spinning the IL
containing ILs have been tested for their   solutions into water; fibre characteristics
cellulose dissolving properties. Partly,    are presented. The experimental cellulose
strong    cellulose    degradation     was  spinning process with chloride containing
observed, but could be prevented in some    ILs is compared to the well-known
cases by addition of stabilisers. Cellulose NMMO-based Lyocell process.
degradation was compared for five
chloride ILs.                               Keywords:       cellulose,   ionic   liquids,
For three solvents, 1-butyl-3-methyl-       degradation, fibres, Lyocell process
imidazolium chloride, 1-allyl-3-methyl-
              __________________________________________________

Introduction
Ionic liquids [1a,b]
Liquids consisting only of ions are called                characteristics of ionic liquids are their
ionic liquids (ILs). In the broader sense,                non-measurable vapor pressure, thermal
this term includes all kind of salt melts,                stability, wide liquid range, electric
like sodium chloride at temperatures above                conductivity and solvating properties for
its melting point of 800 °C. Today, the                   diverse kinds of materials. Another
term “ionic liquid” refers particularly to                important feature of ionic liquids is their
salts with a melting point below 100 °C.                  designability: miscibility with water or
Salts with a melting point below 25 °C are                organic solvents can be tuned through
called “room-temperature ionic liquids”                   sidechain lengths on the cation and choice
(RTILs).                                                  of anion. Furthermore, their properties can
Usually, ionic liquids consist of a bulky,                be varied by introduction of functional
asymmetric organic cation, like 1-alkyl-3-                groups.
methylimidazolium, 1-alkylpyridinium, 1-                  Because of their specific properties, ionic
methyl-1-alkylpyrrolidinium             or                liquids have found to be useful in many
ammonium ions. A wide range of anions is                  fields, like as reaction media in organic
employed, from simple halides which                       synthesis      or      electrolytes     for
inflect high melting points, to inorganic                 electrochemical applications. In addition,
anions such as tetrafluoroborate and                      their non-volatility results in low impact
hexafluorophosphate and to large organic                  on the environment and human health
anions like bis(trifluorosulfonyl)amide,                  advantaging them in comparison to
triflate or tosylate. The notable                         conventional organic solvents, and they


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                                 Lenzinger Berichte, 86 (2006) 154-161


are recognized as “green solvents”.                      the context of cellulose. Rogers &
However, this term is misleading, as many                coworkers investigated the cellulose
ILs show aquatic toxicity [2] and spilling               dissolving      ability      of       several
into waterways should be avoided.                        dialkylimidazolium-based ILs. [5] With 1-
Ionic liquids as solvents and reaction                   butyl-3-methylimidazolium           chloride
media for biomacromolecules                              (BMIM-Cl, Figure 2), using a pulp with
The search for suitable cellulose solvents               polymerisation degree of ~ 1000, cellulose
was and is still of great importance in                  solutions up to 10 % could be obtained.
cellulose research, as shaping of cellulose              The dissolved cellulose was subsequently
can only be achieved by dissolution and                  precipitated in water or organic solvents
regeneration. The fact that cellulose is                 like ethanol or acetone. Water in
earth’s     most      abundant      renewable            concentrations above 1 % prevents the
biomacromolecular          resource       will           cellulose from being dissolved. By
encourage further development of                         microwave irradiation solutions with 25 %
cellulose-based        materials,       whose            cellulose were prepared. This high
production will require suited solvents.                 solubility under microwave irradiation
Today, only one solvent                                  suggests that decomposition takes place;
system with structural                                   unfortunately, no information regarding
analogies to ionic liquids                               the degradation of the cellulose was given
is used commercially on                                  by the authors.
large scale, namely N- Figure 1. NMMO-                   Since then, a number of cellulose
methylmorpholine-N-                 monohydrate.         dissolving ionic liquids based on
oxide monohydrate (NMMO, Figure 1).                      imidazolium cations have been found. In
The cellulose is dissolved without                       1-allyl-3-methylimidazolium         chloride
derivatisation and subsequently spun                     (AMIM-Cl) cellulose concentrations of
(Lyocell-process). This system has already               14.5 % (DP of dissolving pulp of ~ 650)
been extensively described in the                        and 8 % (DP ~ 1600) could be achieved.
literature. [3] As many ILs, NMMO                        [6] 1-Allyl-3-butylimidazolium chloride
possesses a quaternized nitrogen atom.                   (ABIM-Cl) and 1,3-diallylimidazolium
Contrarily to ionic liquids, introduction of             chloride (AAIM-Cl) are solvents for
alkyl substituents into the heterocyclic ring            cellulose as well. [1a]
of NMMO decreases the solubility of                      Among the multitude of tested ILs,
cellulose.                                               especially the chlorides have shown
The       application     of      low-melting            outstanding cellulose dissolving abilities.
quaternised nitrogen bases as solvents for               The exact dissolution mechanism is still
cellulose was first proposed by Graenacher               unknown; however, it is assumed that the
in 1934. [4] In his patent, he describes the             unhydratised chloride anions present in the
preparation of cellulose solutions in benzyl             ionic liquid are able to disrupt the strong
pyridinium chloride in the presence of                   intra- and intermolecular hydrogen bonds
nitrogen bases, possibly derivatisation and              between the cellulose chains. This
subsequent regeneration of the cellulose                 assumption is supported by the fact that
(e.g. as threads or films) by precipitation in           the dissolving ability increases with the
water or alcohols. However, these results                chloride ion concentration. [7]
were thought to be of little practical value             A number of publications deal with the
and the invention found no application.                  derivatisation of cellulose in ionic liquids.
In 2002, the                                             Cellulose acetate with a substitution
term “ionic                                              degree of 0.9 – 2.7 can be produced in a
liquid” was                                              homogeneous reaction with AMIM-Cl as
first                                                    solvent. [8] In ionic liquids, acylations
mentioned in               Figure 2. BMIM-Cl.            with various acid chlorides and


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                                Lenzinger Berichte, 86 (2006) 154-161


carbanilations are possible under mild                 peroxide solution, metal ions are removed
conditions without the need of a catalyst              with the aid of an ion exchanger and the
and in short reaction times. [9] Cellulose             water is finally removed by distillation.
ethers can be synthesised in ionic liquids             According to the Bisfa-Definition, this
with slight excess of reagents under mild              process is a Lyocell-process. [16] Fibres
conditions in a water free environment.                obtained by this procedure are very similar
[10]                                                   to Lyocell fibres obtained by the NMMO-
Besides cellulose, other biopolymers can               process, due to the comparable dissolution
be dissolved in ionic liquids, as it is known          step, the similar solution structure, and the
from NMMO. Lignocellulosic material                    same regeneration conditions. The so
like straw or wood in the form of chips or             called working capacity (tenacity*
sawdust can be dissolved in BMIM-Cl                    elongation) in dry conditions is the same.
under microwave irradiation. This opens                The tendency to fibrillation is comparable,
an easy way to isolate individual wood                 too.
components, for instance by fractional                 Other patents concerning the production of
precipitation. [11] Wool (keratin) could be            cellulose fibres from ionic liquids have
dissolved in BMIM-Cl with concentrations               been applied by Chinese groups. [17, 18]
up to 11 % and regenerated by
precipitation into water or alcohols. By               Experimental
adding a solution of cellulose in BMIM-Cl              Ionic liquids
prior to precipitation, wool-cellulose                 Ionic liquids were synthesised according to
composites in form of fibres or membranes              known procedures. [1a, 19, 20, 21]
were obtained. [12] Ionic liquids have also
proven to be good solvents for silk. For               Synthesis of 1-Allyl-2-methylpyridinium
instance, the saturation concentration of              chloride
silk       fibroin       in         1-ethyl-3-         To 20.0 ml of 2-picoline (18.9 g, 0.20 mol,
methylimidazolium chloride (EMIM-Cl) at                1 eq.) was added an excess of allyl
100 °C is about 23 %. [13] By spinning 10              chloride (20.0 ml, 18.6 g, 0.24 mol, 1.2
% solutions into methanol regenerated silk             eq.). The reaction mixture was refluxed for
fibres were obtained. [14]                             48 h. After 1 h, a dark brown, heavier
                                                       phase began to separate. TLC analysis
Ionic liquids as solvents in the spinning              (Merck silica gel, ethyl acetate) showed
process                                                traces of starting material. After refluxing
A method for the production of cellulosic              for additional 24 h, excess allyl chloride
moulds like fibres or films from ionic                 was removed by means of an oil pump
liquids was described by the Thuringian                leaving behind a brown solid. The crude
Institute of Textile and Plastics Research.            product was washed with 50 ml of diethyl
[15] After dispersion in water, the moist              ether and finally dried on a high vacuum
cellulose is mixed with aqueous BMIM-Cl                line giving 17.4 g of 1-allyl-2-
solution under addition of stabilizers like            methylpyridinium       chloride      (brown
sodium hydroxide and propyl gallate.                   powder, 51 % of theory). Analytical data:
Under shear strain, temperature, and                   1
                                                         H NMR (CDCl3): δ 2.93 (3H, s), 5.10
vacuum the suspension is transformed into              (1H, d, J 17.2 Hz), 5.35 (1H, d, J 10.6 Hz),
a homogeneous, nearly water free dope.                 5.66 (2H, d, J 5.6 Hz), 6.00 (1H, m), 7.92
By passing through a spinneret and an air              (1H, t, J 6.8 Hz), 8.00 (1H, d, J 7.9 Hz),
gap, the solution is shaped into fibres or             8.41 (1H, t, J 7.6 Hz), 9.70 ppm (1H, d, J
foils. The cellulose is regenerated by                 5.9). 13C NMR (CDCl3): δ 20.5, 60.0,
precipitation in an aqueous spinning bath.             120.9, 126.2, 130.0, 130.1, 145.5, 146.9,
To regenerate the solvent, the spinning                155.0 ppm. IR (neat, ATR): 3009, 2921,
bath is treated with alkaline hydrogen                 2438, 1622, 1573, 1503, 1478, 1455, 1421,


                                                 156
                               Lenzinger Berichte, 86 (2006) 154-161


1296, 1158, 1141, 1053, 1004, 930, 829,               dissolve cellulose as well.
794, 770, 710, 663 cm-1. Mp.: 91-94 °C.
                                                      Table 1. Solubility of 3% cellulose in ILs
                                                      (chlorides).
Dissolution experiments
                                                      Ionic liquid
Chloride based ionic liquids have been                1-Butyl-3-methylimidazolium chloride (BMIM-Cl)    +
tested in the face of their cellulose-                1-Allyl-3-methylimidazolium chloride (AMIM-Cl)    +
                                                      1-Allyl-3-butylimidazolium chloride (ABIM-Cl)     +
dissolving ability. For this, the preparation         1,3-Diallylimidazolium chloride (AAIM-Cl)         +
of 3 % solutions of cellulose in the ionic            1-Allyl-2-methylpyridinium chloride (A2Pic-Cl)    +
                                                      1-Butyl-2,3-dimethylimidazolium chloride          +
liquid was attempted. Beech sulfite pulp              1-Allyl-3-propargylimidazolium chloride          reacts
was hackled in a kitchen blender, mixed               1-Allyloxy-3-methylimidazolium chloride           –
                                                      1-Allyl-3-Hydroxyethylimidazolium chloride        –
with the ionic liquid, and stirred                    1-Methyl-3-Hydroxyethylimidazolium chloride       –
magnetically in a teflon coated reaction
vessel at 100 °C for 2 h. If no dissolution           Degradation behaviour
took place under these conditions, stirring           The degradation of the dissolved polymer
was continued for another 2 h at 110 °C.              is of great importance to determine the
Then, the solution was examined under a               suitability of a solvent system. Rogers &
light microscope to reveal undissolved                coworkers describe the dissolution of 25 %
fibres. To determine the degradation, 3 %             cellulose in BMIM-Cl with the aid of
cellulose solutions were prepared and the             microwave irradiation. By means of a
dissolved cellulose reconstituted by                  vertical kneader, 25 % solutions are
contacting with water. The molecular mass             feasible, too. However, the cellulose is
distribution of the reconstituted cellulose           subjected to strong degradation (Figure 7).
samples was determined by gel permeation              These results point out the need of a
chromatography using DMA/LiCl as                      stabiliser to prevent cellulose degradation.
eluent. The method was described in detail            With conventional dissolving pulps,
earlier. [22]                                         cellulose concentrations in the spinning
                                                      dope of more than 15 % are not within
Spinning experiments                                  reach due to the high viscosity of such
Spinning dopes with concentrations over               solutions. Higher temperatures lead to
10 % were prepared in a vertical kneader.             stronger degradation; therefore it has no
For this, the dry pulp was added to the               advantage to the NMMO-process.
solvent under optional addition of propyl             It was found, that the stability of the
gallate and/or sodium hydroxide as                    cellulose depends clearly on the used
stabilisers and transformed into a                    cation (Table 2). All of the tested solvents
homogenous solution under shear strain,               based on chloride showed conspicuous
temperature, and vacuum.                              degradation of the cellulose at 100 °C. The
                                                      degradation was exceptionally strong in
Results and discussion [23]                           AMIM-Cl and A2Pic-Cl, whereas
                                                      cellulose regenerated from ABIM-Cl and
Besides the well-known cellulose solvents             AAIM-Cl showed relatively high molar
AMIM-Cl and BMIM-Cl, new solvents                     masses.
with imidazolium- and methylpyridinium-
                                                      Table 2. Molecular masses of cellulose after
cations were found (Table 1).                         dissolution in various ILs.
The assumption, that a N-O-bond in the
                                                      Solvent                    Mn (x 103)      Mw (x 103)
cation would be favorable for cellulose
                                                      pulp: Euca-PHK (1)           68.8           200.2
dissolution (structural analogy to N-                 BMIM-Cl                      37.9           100.8
methylmorpholine-N-oxide), proved to be               AMIM-Cl                       19             31.4
false. Cellulose was insoluble in the tested          A2Pic-Cl                     14.8             24
N-alkyloxyimidazolium salts. Ionic liquids            AAIM-Cl                      43.1           117.2
functionalised with hydroxyl groups didn’t            ABIM-Cl                      48.2           150.5



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                                                                                            Lenzinger Berichte, 86 (2006) 154-161



            Differential Weight Fraction
                                                                                                ABIM-Cl                    pronounced even at 80 °C. Propyl gallate
                                                                                                AAIM-Cl
                                                                                                BMIM-Cl                    showed no significant influence on the
                                                                                                A2Pic-Cl                   degradation behaviour.
                                                                                                AMIM-Cl
                                            1                                                   Euca-PHK (1)               Table 4. Molecular masses in AMIM-Cl at various
                                                                                                                           temperatures, with/without propyl gallate.
                                                                                                                                                                  Not stabilised                  Propyl gallate
                                                                                                                                                                        Mn               Mw            Mn                Mw
                                                                                                                                                                    ( x 1000 )      ( x 1000 )     ( x 1000 )         ( x 1000 )
                                            0
                                                 3,5        4,0      4,5       5,0    5,5         6,0     6,5                80 °C                                      38.7             98.8         38.5               100
                                                                  log Molar Mass                                             90 °C                                      28.3             57.3         29.2              62.2
Figure 3. Molecular mass distribution of cellulose
                                                                                                                             100 °C                                     19.4             32.9             19            31.7
after regeneration from ILs.
                                                                                                                                                                                                               Euca-PHK (1)
The effect of the temperature on                                                                                                                            1,6   AMIM-Cl                                      80°C, no stab.




                                                                                                                             Differential Weight Fraction
degradation was examined on the well-                                                                                                                       1,4                                                90°C, no stab.
                                                                                                                                                                                                               100°C, no stab.
known solvents BMIM-Cl and AMIM-Cl                                                                                                                          1,2                                                80°C, stab.
and on the new solvent AAIM-Cl. At the                                                                                                                      1,0                                                90°C, stab.
                                                                                                                                                                                                               100°C, stab.
same time, the effect of propyl gallate, a                                                                                                                  0,8
stabiliser with antioxidative action used in                                                                                                                0,6
the NMMO-process, was investigated.                                                                                                                         0,4
                                                                                                                                                            0,2
BMIM-Cl: As expected, the extent of                                                                                                                         0,0
degradation    increased    with     the                                                                                                                          3,5     4,0      4,5      5,0     5,5         6,0     6,5
temperature. Above 90 °C, drastic                                                                                                                                               log Molar Mass
degradation occurred. Propyl gallate had                                                                                   Figure 5. AMIM-Cl at various temperatures,
no stabilising effect under these                                                                                          with/without propyl gallate.
conditions.                                                                                                                AAIM-Cl:        This   solvent    showed
Table 3. Molecular masses in BMIM-Cl at various                                                                            temperature dependent degradation, too.
temperatures, with/without propyl gallate.                                                                                 However, compared to the other two
                                                          Not stabilised                    propyl gallate                 solvents, the degradation occurred to a
                                                       Mn                 Mw               Mn              Mw              much lesser extent. Propyl gallate had no
                                                 ( x 1000 )          ( x 1000 )      ( x 1000 )         ( x 1000 )         stabilizing effect.
80 °C                                              48.2               160.3            49.7               164.4                                                                                                 Euca-PHK (1)
                                                                                                                           Differential Weight Fraction




                                                                                                                                                            1,2                                                 80°C, no stab.
90 °C                                              48.1                149.6               46.7           148.6                                                   AAIM-Cl
                                                                                                                                                                                                                90°C, no stab.
100 °C                                             37.9                100.8               39             98.2                                              1,0                                                 100°C, no stab.
                                                                                                                                                                                                                80°C, stab.
                                                                                                  no stab. 80°C                                             0,8                                                 90°C, stab.
Differential Weight Fraction




                                           1,2   BMIM-Cl                                          no stab. 90°C                                                                                                 100°C, stab.
                                                                                                  no stab. 100°C                                            0,6
                                           1,0                                                    stab. 80°C
                                                                                                  stab. 90°C                                                0,4
                                           0,8                                                    stab. 100°C
                                                                                                  Euca-PHK (1)                                              0,2
                                           0,6
                                                                                                                                                            0,0
                                                                                                                                                                  3,5    4,0       4,5      5,0     5,5        6,0     6,5
                                           0,4
                                                                                                                                                                                 log Molar Mass
                                           0,2
                                                                                                                           Figure 6. AAIM-Cl at various temperatures,
                                           0,0                                                                             with/without propyl gallate.
                                                 3,5        4,0     4,5        5,0   5,5        6,0     6,5
                                                                  log Molar Mass
                                                                                                                           The experiments showed clearly, that the
Figure 4. BMIM-Cl at various temperatures,
with/without propyl gallate.                                                                                               substituents on the cation have an effect on
                                                                                                                           the stability of the dissolved cellulose.
AMIM-Cl: A distinct temperature effect                                                                                     Propyl gallate was useless under these
could be observed. The degradation was                                                                                     conditions.


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                                                                           Lenzinger Berichte, 86 (2006) 154-161


Table 5. AAIM-Cl at various temperatures,                                                         Table 7. Temperature effect on molecular mass of
with/without propyl gallate.                                                                      cellulose in AMIM-Cl dopes.
                                         Not stabilised              Propyl gallate                                                                 Mn (x1000)     Mw (x1000)
                                         Mn           Mw            Mn              Mw
                                                                                                       Euca-PHK (2)                                     67            170
                                                                                                          70 °C                                        45.6          127.6
                                      ( x 1000 ) ( x 1000 ) ( x 1000 ) ( x 1000 )                         100 °C                                        8.5          14.5
80 °C                                   49.5         174.4          50.6           182.2
                                                                                                                                                                        Euca-PHK
90 °C                                   49.5         152.9          47.6           145.5                                          1.2
                                                                                                                                                                        solution (100°C)




                                                                                                   Differential Weight Fraction
100 °C                                  43.1         117.2          45.2           114.2                                          1.0                                   solution (70°C)

                                                                                                                                  0.8
Spinning experiments
                                                                                                                                  0.6
BMIM-Cl: The addition of propyl gallate
                                                                                                                                  0.4
in conjunction with sodium hydroxide has
a stabilising effect. [15] Fibres could be                                                                                        0.2

spun from 11 % stabilised solutions.                                                                                              0.0
                                                                                                                                        3.5   4.0     4.5   5.0   5.5     6.0   6.5

Table 6. Stabiliser effect on the molecular masses                                                                                                   log Molar Mass
of cellulose in BMIM-Cl.                                                                           Figure 8. Molecular mass distribution of
                     Mn [103        Mw [103                                                       reconstituted cellulose out of 15 % solution (red,
                      g/mol]         g/mol]                                                       100 °C, stirring time 2 h) and 11 % solution (blue,
                                                                                                  70 °C, stirring time 5 h) in AMIM-Cl.
    Euca-PHK (2)                                        67                 170
                                stabilised             52.3                148.9
                                                                                                  Fibre characteristics
           not stabilised                               10                  27
                                                                                                  The     spinning    conditions    in    our
                                1,2                                                               experiments are similar to the spinning
                                                                            Euca-PHK (2)
 Differential Weight Fraction




                                1,0                                         stab.                 conditions in the NMMO-process. The
                                                                            n. stab.              resulting    fibres   show     comparable
                                0,8
                                                                                                  characteristics, like a round profile,
                                0,6                                                               smooth surface, similar fibrillation
                                0,4
                                                                                                  behaviour and the same “working
                                                                                                  capacity”. The observed, somewhat higher
                                0,2
                                                                                                  tenacities are compensated by lower
                                0,0                                                               elongation values. Advantages of IL-
                                        3,5    4,0     4,5    5,0    5,5      6,0     6,5
                                                     Log Molar Mass
                                                                                                  Lyocell-fibres over NMMO-Lyocell-fibres
                                                                                                  could not be observed. From our point of
 Figure 7. Molecular mass distribution of                                                         view, there is no significant difference in
reconstituted cellulose out of stabilised 11 %
solution (red) and not stabilised 25 % solution                                                   the physical and chemical characteristics.
(green) in BMIM-Cl. 100 °C, stirring time 3-4 h.                                                  Cellulose dissolution: Chloride containing
                                                                                                  ionic liquids compared to NMMO
AMIM-Cl: 15 % solutions could be
obtained at 100 °C within 2 h. However,                                                           A comparison with the NMMO-process
the cellulose was strongly degraded by this                                                       shows no improvement of the fibre
procedure to an extent which affected the                                                         characteristics, especially of the fibrillation
spinnability of the solution. By stirring for                                                     tendency. The similar processes lead to
5 h at a temperature of 70 °C, 11 %                                                               similar fibre properties. ILs have a lower
solutions were obtained. Due to the lower                                                         melting point than NMMO, which
temperature, the degradation remained on                                                          simplifies handling of the solvents.
a reasonable scale and spinning was                                                               However,      the    required      processing
possible.                                                                                         temperatures are the same in both cases.



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                                            Lenzinger Berichte, 86 (2006) 154-161



Table 8. Comparison of fibre data for the solvents BMIM-Cl, AMIM-Cl, and NMMO

                                         Tenac.      Elong.         Tenac.   Elong.        Working
       Fibre              Titre
                                         (cond)      (cond)         (wet)    (wet)      capacity (cond)
                          dtex           cN/tex        %            cN/tex     %           %cN/tex
  BMIM-Cl*                0.9             51.2        8.5            45.3     11.6          435
  BMIM-Cl*                2.1              45         7.5            32.8     8.1           338
  AMIM-Cl*                2.2             41.6        12.2           33.4     17.6          508
   TENCEL
                           0.9            38           14            31        18            532
  (NMMO)**
   TENCEL
                           1.3            37           13            30        15            481
  (NMMO)**
* experimental fibre; **standard fibre


Stabilisers are required in both cases. The                          modifiability, and low melting points are
preparation of the spinning dopes is more                            countervailed     by     their   numerous
expensive than in the NMMO-process,                                  disadvantages: the need for stabiliser use,
because of the required nearly complete                              potential (aquatic) toxicity, corrosivity,
removal of water. An advantage is the                                and a higher energy input for dope
thermal stability of the system, no auto-                            preparation and solvent recovery due to
catalytically initiated exothermic run-                              the required complete removal of water.
away-events      were      observed.     The                         In their textile quality, IL-fibres are
degradation of the cellulose is higher than                          virtually      indistinguishable      from
in NMMO. Little is known about the                                   conventional Lyocell-fibres on NMMO-
reaction mechanisms, except that they                                basis.
differ from those in the NMMO-system.                                Up to now, an industrial application of the
As for the solution process, the recovery of                         tested IL-systems for the production of
the solvent from the aqueous spinning bath                           man-made cellulosic fibres is not useful.
is more energy-consuming because of the                              Firstly, none of these systems showed
need for complete water removal. For                                 significant advantages in comparison to
industrial processes, the high corrosivity of                        already used technologies; secondly, the
chloride melts to steel may be of further                            recovery of the solvent is more expensive
concern. The potential toxicity of the ILs                           than in the NMMO process.
is also a disadvantage. For this reasons, we
don’t consider the tested chloride-based                             Acknowledgement
ILs to be an alternative to the NMMO
system.                                                              Financial support was provided by the
                                                                     Austrian government, the provinces of
Conclusions                                                          Lower Austria, Upper Austria and
                                                                     Carinthia as well as by the Lenzing AG.
Chloride-based ionic liquids are suitable                            We also express our gratitude to the
solvents for cellulose dissolution and for                           Johannes Kepler University, Linz, the
fibre spinning. The resulting fibres belong                          University of Natural Resources and
to the class of Lyocell-fibres and show                              Applied Life Sciences, Vienna, and the
comparable or same characteristics as                                Lenzing AG for their in kind contributions.
fibres obtained from NMMO solutions.
The advantages of ionic liquids, like their
non-volatility, thermal stability, chemical



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                              Lenzinger Berichte, 86 (2006) 154-161


References
[1]    a) Laus, G.; Bentivoglio, G;                  [14]   Phillips, D. M.; Drummy, L. F.;
       Schottenberger, H; Kahlenberg, V.;                   Naik, R. R.; De Long, H. C.; Fox,
       Kopacka, H.; Röder, T.; Sixta, H.;                   D. M.; Trulove; P. C.; Mantz, R. A.
       Lenzinger Berichte, 2005, 84, 71-                    J. Mater. Chem. 2005, 15, 4206–
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