U.S. patent application number 14/325554 was filed with the patent office on 2014-10-30 for cellulose suspension and processes for its production.
This patent application is currently assigned to LENZING AG. The applicant listed for this patent is LENZING AG. Invention is credited to Heinrich Firgo, Josef Innerlohinger, Helmut Schkorwaga.
Application Number | 20140318415 14/325554 |
Document ID | / |
Family ID | 40158631 |
Filed Date | 2014-10-30 |
United States Patent
Application |
20140318415 |
Kind Code |
A1 |
Innerlohinger; Josef ; et
al. |
October 30, 2014 |
CELLULOSE SUSPENSION AND PROCESSES FOR ITS PRODUCTION
Abstract
The present invention relates to cellulosic particles, a
suspension of cellulosic particles and a process for the production
of a suspension of cellulosic particles, whereby the cellulosic
material is never dried between the dissolution of the cellulose
and the disintegration of the suspended cellulose fibers.
Inventors: |
Innerlohinger; Josef; (Berg
i.A., AT) ; Firgo; Heinrich; (Vocklabruck, AT)
; Schkorwaga; Helmut; (Attersee, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LENZING AG |
Lenzing |
|
AT |
|
|
Assignee: |
LENZING AG
Lenzing
AT
|
Family ID: |
40158631 |
Appl. No.: |
14/325554 |
Filed: |
July 8, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12679227 |
Sep 9, 2010 |
8827192 |
|
|
PCT/AT2008/000323 |
Sep 12, 2008 |
|
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14325554 |
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Current U.S.
Class: |
106/447 ;
106/471; 106/476; 106/501.1; 524/35 |
Current CPC
Class: |
C08L 101/00 20130101;
C08L 67/00 20130101; C08K 3/30 20130101; C08K 3/04 20130101; C08L
1/02 20130101; C08L 1/02 20130101; C08B 16/00 20130101; C08L 23/12
20130101; C08K 3/22 20130101; D01F 2/00 20130101; C08L 23/06
20130101; C08K 2003/3045 20130101; C08L 101/00 20130101; C08K 3/04
20130101 |
Class at
Publication: |
106/447 ;
106/471; 106/476; 106/501.1; 524/35 |
International
Class: |
C08L 1/02 20060101
C08L001/02; C08K 3/30 20060101 C08K003/30; C08L 67/00 20060101
C08L067/00; C08L 23/06 20060101 C08L023/06; C08L 23/12 20060101
C08L023/12; C08K 3/22 20060101 C08K003/22; C08K 3/04 20060101
C08K003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2007 |
AT |
A1497/2007 |
Claims
1.-10. (canceled)
11. A suspension comprising from about 0.1 to about 20 weight
percentage, preferably from about 0.1 to about 10 weight percentage
of cellulosic particles, wherein the cellulosic particles were
never dried during their production.
12. The suspension according to claim 11, wherein the cellulosic
particles of the suspension comprise a large share of
additives.
13. The suspension according to claim 11, wherein the cellulosic
particles of the suspension comprise from about 1 to about 200
weight percentage, in relation to the cellulose amount, of
incorporated additives selected from the group consisting of
pigments, titanium oxide, barium sulphate, ion-exchangers,
polyethylene, polypropylene, polyester, activated carbon, polymer
superabsorbers and flame-retardant agents.
14. Cellulosic particles having a water content of about 80 to
about 99.9 weight percentage wherein the cellulosic particles are
not dried during production.
15. The particles in accordance with claim 14, wherein the
particles contain a large share of additives.
16. The particles according to claim 14, wherein the particles
comprise from about 1 to about 200 weight percentage, in relation
to the cellulose amount, of incorporated additives, selected from
the group consisting of pigments, titanium oxide, barium sulphate,
ion-exchangers, polyethylene, polypropylene, polyester, activated
carbon, polymer superabsorbers and flame-retardant agent.
17. The particles according to claim 13, wherein the titanium oxide
is substoichiometric titanium oxide.
18. The particles according to claim 16, wherein the titanium oxide
is substoichiometric titanium oxide.
Description
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
[0001] The present invention relates to cellulosic particles, a
suspension of cellulosic particles and a process for the production
of a suspension of cellulosic particles, whereby the cellulosic
material is never dried between the dissolution of the cellulose
and the disintegration of the suspended cellulose fibers.
DESCRIPTION OF RELATED ART
[0002] Dry cellulose powders are commercially available in various
sizes and are used in a number of different applications, such as
for example as auxiliary filter materials, additives and auxiliary
materials in food stuffs and pharmaceutical products,
chromatography materials as well as in the form of additives in the
building material trade. The greater part, which is extracted from
pulp, wood or one-year plants, is accounted for by fibrous
cellulose-I-powder. In this respect the lower limit of the fiber
length of this fibrous cellulose powder is limited to 10-20 .mu.m.
In the upper range fiber lengths are used in the mm range whereby
there is already some overlapping with short-cut fibers.
[0003] In smaller quantities cellulose-II-powder can also be found
whereby spherical powder can be found in addition to fibrous
powder. These powders are mainly made by the precipitation of
dissolved cellulose in suitable precipitants. Spherical cellulose
powders in the size range below 10 .mu.m can only be made with much
more effort and are thus difficult to find on the market.
[0004] For example WO 02/57319 describes the production of
cellulose pearls using the NMMO-process whereby large amounts of
various additives are added to the cellulose solution prior to
forming, such as for example titanium dioxide or barium sulphate as
well as materials which provoke ion exchange. The products obtained
can be used as ion exchangers or catalysts.
[0005] The production of a titanium oxide suitable as an ion
exchange material, for example for waste water purification, is
described in U.S. Pat. No. 6,919,029. Particularly high absorption
capacities and speeds are attained with this material by means of
the fact that the titanium oxide material is activated by a special
treatment on the surface. This titanium oxide material can be
described as a "substoichiometric titanium oxide". This means that
the ratio of the oxygen atoms to the titanium atoms in the material
is smaller than 2. For a more detailed description of this surface
activation, reference is made to the description in U.S. Pat. No.
6,919,029.
[0006] Other possibilities for the production of particular
functionalized titanium oxides can be found in the so-called
"doping" of titanium oxide with iron and sulphur atoms. These
compounds display a photocatalytic activity.
[0007] Cellulosic materials in the mm range are likewise being
given greater attention recently. In this respect one can
differentiate between the rigid crystalline Whiskers (de Souza
Lima, M. M. and R. Borsali, Macromolecular Rapid Communications,
2004. 25: p. 771-787) and the flexible MFC (Microfibrillated
Cellulose) (Herrick, F. W. et al, Journal of Applied Polymer
Science; Applied Polymer Symposium, 1983. 37: p. 797-813) and also
(Turbak, A. F. F. W. Snyder and K. R. Sandberg, Journal of Applied
Polymer Science; Applied Polymer Symposium, 1983. 37: p. 815-827).
Both particle types are smaller in the size range of around 1 .mu.m
and are in the form of suspensions or gels with only a slight
cellulose content due to their production process. Production is
done largely via one or several mechanical disintegration steps
(ultrasound, homogenizer, etc.) in combination with a strong
degradation of the cellulosic starting material via enzymes or
strong acids.
[0008] Likewise, cryo processes are described in the literature
with the help of liquid nitrogen to release micro-fibrils of
cellulosic materials (Chakraborty, A. M. Sain, and M. Kortschot,
Holzforschung, 2005. 59: p. 102-107).
[0009] An alternative method for the production of cellulose
nano-fibers is the electro spinning process (Kulpinski, P., Journal
of Applied Polymer Science, 2005. 98 (4): p. 1855-1859) which also
demands a great deal of effort.
[0010] The main field of application for these nano-structured
materials is currently above all the reinforcement of compound
materials (Favier, V., H. Chanzy and J. Y. Cavaille,
Macromolecules, 1999. 28: p. 6365-6357).
[0011] In the literature, films or membranes are described as
another special application of the cellulose particles described
above. Often the cellulosic materials used in combination with
other substances and/or the production of the films demands a great
deal of effort. Examples can be found in (Fendler, A., et al.
Characterization of barrier properties of composites of HDPE and
purified cellulose fibers. Cellulose, 2007. In press. Doi.
10.1007/s10570-007-9136-x), Liu, H. and Y.-L Hsieh, Ultrafine
Fibrous Cellulose Membranes from the Electrospinning of Cellulose
Acetate. Journal of Polymer Science: part B: Polymer Physics,
2002.40:p. 2119-2129) or (Sanchez-Garcia, M.D. E. Gimenez and J. M.
Lagaron, Morphology and barrier properties of solvent cast
composites of thermoplastic biopolymers and purified cellulose
fibers, Carbohydrate Polymers, 2007 in press. doi:
10.1016/j.carbpol.2007.05.041).
SUMMARY OF THE INVENTION
[0012] Compared to the known state of the art, the task of the
present invention was, therefore, to produce cellulose fibrids
which fill the gap in the available particle sizes between the
nano-materials suspended in a suspension medium such as for example
Whiskers of MFC in the range smaller than 1 .mu.m and the
conventional dry powders in the range between 10 .mu.m to some mm
(is this right???) and thereby demonstrate an enhanced economic
efficiency.
[0013] Moreover, the production process should be characterized by
its simple execution and preferably should work without the strong
degradation of the cellulosic material via enzymatic or chemical
treatment (above all strong acids) of the starting material since
this would involve the elaborate cleaning of the product. Likewise
it should be possible to produce more highly concentrated
(.about.10% solid substance) suspensions of the fibrids produced
which can moreover also be readily processed.
[0014] It was possible to solve this task via a process for the
production of a suspension of cellulosic particles involving the
following steps:
[0015] Dissolving cellulose to obtain a spinning solution
comprising cellulose,
[0016] Extruding the solution containing the cellulose,
[0017] Precipitating the cellulose wherein cellulose fibers are
obtained,
[0018] Cutting the precipitated cellulose fibers,
[0019] Suspending the cut cellulose fibers and
[0020] Disintegrating the suspended cellulose fibers, [0021]
wherein the cellulosic material is never dried between the
dissolving of the cellulose and the disintegrating of the suspended
cellulose fibers.
[0022] With this process, cellulosic particles with excellent
properties can be obtained with a reduced number of process steps,
shorter overall retention times in the process and a reduced need
for energy compared to the present state of the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 shows a film which was made of commercially available
dry cellulose powder by suspending, spreading the suspension onto
an object slide and finally drying it. The film is very
coarse-grained and inhomogeneous as can be readily seen with the
naked eye.
[0024] FIG. 2 shows a film which is produced by spreading a
suspension in accordance with the invention onto an object plate of
glass and subsequent drying. This film is very homogeneous as can
be seen with the naked eye.
[0025] FIG. 3 shows the film of FIG. 2 produced from the suspension
in accordance with the invention under the electron microscope. In
this magnification it can also be seen that the film is very
homogeneous.
DETAILED DESCRIPTION OF THE INVENTION
[0026] In a preferred embodiment, the cellulosic material has a
moistness of about at least 50% and preferably of about at least
100% and most preferably of about at least 150%. For this reason
care has to be taken that the cellulose does not dry out even
during further processing, particularly during disintegration, and
the process steps in between i.e., always has a sufficiently
aqueous phase.
[0027] Compared to the state of the art, cellulose particles and
suspensions which contain these particles can be produced with the
process according to the invention, which have comparable
properties and fields of application to the well-known smaller
nano-particles but which can be produced at a more favorable price.
An additional economic advantage is that the suspensions made in
accordance with the invention can display much higher cellulose
contents, namely up to about 20 weight percentage instead of only
about 2 weight percentage as is the case with the nano-materials.
In this way, the packaging and transportation costs drop and
likewise the use of the suspensions become more favorably priced
because, for example, less suspension medium has to be removed to
obtain a film of the cellulose particles.
[0028] The production of cellulose fibers on the basis of Lyocell
technology is well known and state of the art. It is fundamental
for the production of fibrids of fibers in accordance with the
invention, that the fibers are not dried during the process and
display a correspondingly high moisture content (at least 50%,
preferably at least 100% and most preferably at least 150%).
[0029] The best known solvent already being used on a commercial
scale in Lyocell technology is aqueous N-methyl morpholine-N-oxide
(NMMO). However other well-known solvents, in which cellulose is
physically dissolved without chemical derivatization, are both
suitable and economical for the production of cellulosic fibers in
accordance with the present invention. In particular the
dissolution in so-called "ionic liquids" or in other amine oxide
containing solvents should be named. In the same way the well known
viscose processes are suitable and economical for the
implementation of the present invention in which the cellulose is
xanthated in a medium containing caustic soda and thereby
dissolved, the spinning solution containing cellulose produced in
this way is then extruded and finally precipitated in a
precipitation bath and regenerated.
[0030] Auxiliary materials can be applied to the moist fibers
(e.g., stearic acid-PEG-ester, partly sulphated fatty alcohols and
fatty alkyl ethophosphate) which alleviate further processing, for
example, to improve the grinding ability.
[0031] The moist fiber cables are cut by conventional means to a
staple length of about 2-60 mm. Starting with these initially moist
(short-cut) fibers, further processing takes place. When producing
the fibers, the properties of the fibrids obtained at the end can
be determined in part. To this end the measurements known to
specialists, for example, are suitable which would lead to an
influencing of the fiber titer, fiber tenacity, elongation or loop
strength if conventional textile fibers were to be produced.
Measurements of this kind are among other things the corresponding
selection of pulp with respect to the spinning conditions. While
the fiber titer particularly has an effect on the particle size,
the brittleness and fibril tendency can be influenced by the fiber
tenacity. More brittle fibers which fibrillate more easily can be
ground more readily since the duration of grinding is shorter, less
energy has to be used for grinding and the thermal load of the
particles when grinding is also reduced.
[0032] The fibers are suspended in water or in a suitable other
medium whereby this suspension is homogeneous and should be
free-flowing and pumpable. A fiber content in a range of about 4-6%
abs.dry, i.e., in relation to absolutely dry cellulose, has proved
to be best suited. The suspending is performed via suitable
mechanical aggregates whereby in addition a fibrillation of the
fibers can also occur. A fibrillation, i.e., the separation of
individual fibrils from the fiber surface leads to a higher share
of smaller cellulose particles in the suspension due to the fine
fractions which are produced in this way. A fine-grain fraction of
this kind can be either desired or undesired depending on the
properties targeted in the end product. For this reason, the
suspending aggregate must be selected accordingly.
[0033] Several variants are possible for the further process
steps:
[0034] In the first variant, the fibers are first of all only
suspended wherein their size remains largely unchanged. Finally
they are broken down in a disintegration step to the desired final
size.
[0035] In a second variant, the fibers are already disintegrated
during suspending and then finally broken down to the final size
desired in a concluding disintegration step. In a third variant,
the fibers are already broken down to the desired final size during
suspending.
[0036] In a fourth variant it is possible to separate the water
from the fibers after cutting and to disintegrate these moist
fibers without any surrounding liquid in a cutting mill, a high
consistency mill or a shredder and then suspending them and
breaking them down to the desired final size.
[0037] In general it can be said that most devices, which are used
in pulp disintegration during preparation, are also suitable for
the production of a fiber suspension in accordance with this
invention. The following devices have proved to be suitable for the
suspension of the fibers: Ultra Turax with a cutting head, a Jokro
mill, a Valley Beater and a Refiner.
[0038] In a preferred embodiment of the process in accordance with
the invention, the fibers are disintegrated at the same time as
being suspended. In this respect suspending devices are suitable of
the kind which break the fibers down to a length in the range of
between about 100 .mu.m and about 600 .mu.m at the same time as
suspending. This length is particularly well suited to further
disintegration.
[0039] In another preferred embodiment of the process in accordance
with the invention, disintegration to a particle size of about 1 to
about 5 .mu.m takes place following suspending. The disintegration
is preferably a wet grinding.
[0040] Disintegration is preferably performed with a cellulose
content of between about 0.1 and about 5.0 weight percentage in the
suspension. With lower cellulose contents, in relation to the
quantity of cellulose particles, the mills required are too big and
consequently too high an amount of suspension medium may have to be
removed after disintegration. When the cellulose content is too
high, the viscosity of the suspension becomes too high and too much
shearing energy is introduced through the grinding movement.
[0041] Here, as well, it is possible to add additives to support
the disintegration and/or stabilization of the fibrids in the
surrounding medium. Wet grinding takes place in mills with which
the desired final fineness (about 1-5 .mu.m) can be obtained. These
are preferably different agitator bead mills (impeller stirrers,
pin stirrers, etc.). Other mills such as (double) conus mills can
also be used but may be less preferable.
[0042] To achieve the desired particle properties, in particular
the final fineness, it is in general necessary to circulate the
suspension in a closed loop during the wet grinding so that the
ground stock can pass through the mill several times. The fineness
can thus be controlled via the duration of grinding and at the same
time it is possible to influence the particle size via other
parameters. Thus, the size of the grinding media or the speed of
the mill can be adjusted.
[0043] Following grinding, a classification of the fibrids is
required using a wet classifier for example of the type
Hosokawa-Alpine Hydroplex when a very narrow distribution is
desired.
[0044] At the end of grinding, the fibrids are in the suspended
medium with a length of about 1-5 .mu.m and a diameter of about
100-500 nm in a concentration of about 1.1-5 weight percentage. In
this respect both individual fibrids as well as interconnected
fibrid-bonds can be found. The fibrids sediment depending on their
size and the type of stabilization.
[0045] To stabilize the suspension, if this is desired, measures
can be used which cause the suspension to thicken. This can either
be done by removing a small share of the suspension medium, for
example via centrifuging, evaporation at gentle temperatures or
membrane separation processes or by adding thickening agents.
Suitable thickening agents are known to the expert, for example
commercially available carboxymethylcellulose or gylcerin. The use
of dispersion agents or tensides as surface-active substances may
also stabilize the suspension. This is not, however, a preference
because it introduces another class of substance to the suspension
in contrast to the polymer or polymer-like thickening agents.
[0046] But even if the cellulose particles in accordance with the
invention sediment in the suspension, no aggregation generally
occurs and the fibrid deposition can be easily shaken out again. As
a result of this sedimenting in connection with decanting the
excess, the concentration of the fibrids in the suspensions can
also be increased. Other methods to increase the concentration of
solids are to centrifuge and evaporate the liquid phase. In this
respect, however, care should be taken that the suspensions are not
thickened too much otherwise this will lead to irreversible
aggregations of the fibrids. The upper limit of the solid content
in the suspension depends on the fibrid size and, for fibrids, this
equals around several .mu.m with 15-20% of dry substance in the
suspension.
[0047] The particles can be obtained from suspensions in accordance
with the invention as a result of spray drying. Processes and
devices for spray drying are basically known to experts. It is,
however, surprising that the suspensions in accordance with the
invention can still be sprayed without any difficulty even with
exceptionally high particle contents. Suspensions with particles
which are state of the art with contents of a maximum of 2 weight
percentage cannot be readily sprayed because they display high
viscosities and a non-Newtonian flow behavior which can be
problematic in the spraying ducts.
[0048] In spray drying the individual fibrids do in fact remain
intact but they lose their characteristic properties. Spray drying
would, however, be interesting to obtain very fine cellulose
powders which are not accessible via dry grinding.
[0049] In accordance with the invention additives which remain on
or in the cellulosic particle can be included in the process. In
this way additional functional properties can be conveyed on the
particles whereby, surprisingly, the good processing properties of
the suspension remain intact. These additives are not removed
during the treatment in the wet state in accordance with the
invention such as for example washing out, suspending and
disintegration, but rather they remain in the cellulose particles.
The additives can be contained in quantities of between about 1 and
about 200 weight percentage in relation to the cellulose amount on
or in the particle.
[0050] These additives can be already added to the cellulosic
spinning solution before it is precipitated. They can for example
be selected from the group consisting of pigments, inorganic
substances such as for example titanium oxide, such as
substoichiometric titanium oxide, barium sulphate, ion exchangers,
polyethylene, polypropylene, polyester, activated carbon, soot,
zeolites, polymer superabsorbers and flame-retardant agents.
[0051] In the same way additives can be applied to the precipitated
cellulose fibers before or after cutting. Suitable devices for this
are known to the expert.
[0052] Additives can also be included before, during or after the
disintegration procedure in the suspension in accordance with the
invention. In this case these are mainly distributed on the surface
such as in the outer layers of the cellulosic particles. In this
case additives can for example be finishings, dyestuffs or
cyclodextrins. In this way, the processing properties in the
process in accordance with the invention are influenced or,
accordingly, the functional properties of the particles such as,
for example, a higher absorption capacity for certain substances
are achieved.
[0053] The subject matter of the present invention is also a
suspension comprising from about 0.01 to about 20 weight percentage
and preferably from about 0.1 to about 10 weight percentage of
cellulosic particles produced according to the invention whereby
the cellulosic particles were never dried during their production.
They form a homogeneous film when drying from the mother
suspension. The production of this suspension can take place
according to the process described above in accordance with the
invention. Until now it has not been possible to find a physical
characterization method which records the unique properties of this
suspension and the particles contained in it. The suspension in
accordance with the invention can, however, clearly be recognized
by the film formation behavior described here which is unique for a
suspension of cellulosic particles. Cellulosic particles known
until now form homogeneous films only when deliberately applying
elevated temperatures, pressures or additional solvents (see for
example Endo et al., Polymer Journal (32) 2, 182-185 (2000).
[0054] The basic characteristic of the fibrids described is that
they are extracted from the cellulose solution and are sufficiently
moist throughout the entire production process. Therefore we are
dealing with so-called never-dried particles. Without being bound
by any theory, it is believed that the process in accordance with
the invention avoids or reduces irreversible hydrogen bridges
between the OH groups of the cellulose molecules. For this reason
the suspensions described tend to form a homogeneous, dense film
when drying up since the OH groups can still freely arrange
themselves.
[0055] If one dries the fibrids, introduces them to the suspension
again and then dries them, this results in a film which is in fact
not so homogeneous but clearly more coarse-grained and which has a
higher tendency to form cracks. The dried up fibrids behave like
commercially available dry cellulose powder when one uses them to
form film from the suspension.
[0056] Cellulosic particles with a water content of 80 to 99.9
weight percentage are also the subject matter of the present
invention. These are characterized in that they are not dried
during their production. They form a homogeneous film when drying
up from the mother suspension.
[0057] The particles described herein can, as has already been
described above, contain a large share of additives. The additives
can be included in a quantity of between about 1 and about 200
weight percentage in relation to the cellulose amount in the
particles whereby they can be distributed either in the overall
particle or mainly on the surface of the particle such as in the
outer layers of the particle.
[0058] Another object of the invention is the use of cellulosic
particles with a water content of about 80 to about 99.9 weight
percentage produced using the process described above to produce
homogeneous films.
[0059] An advantage of the use of the fibrids according to the
invention for film formation is, in comparison to the process
described above from the state of the art, its very simple
execution. The production of films is done simply via the gentle
drying of the fibrid suspension. In addition, pressure and
temperature can also be applied when forming the films. A higher
temperature accelerates the drying. This is done, for example, by
blowing with heated gas, radiant heat or direct contact with heated
surfaces.
[0060] The application of a higher pressure produces, in
particular, a denser film and is, for example, attained by pressing
between flat surfaces or rolls.
[0061] In the following, preferred embodiments of the invention are
described using examples. The invention is, however, not restricted
to these embodiments but rather also encompasses other embodiments
which are based on the same inventive concept.
[0062] The size of the particle was determined using a laser
diffraction measuring apparatus.
EXAMPLE 1
[0063] According to what is basically a well known process using
NMMO, 6 mm long Lyocell fibers with an individual fiber titer of
1.3 dtex were produced. In this respect the spinning solution was
extruded in a dry-wet spinning process first of all through an air
gap into a precipitation bath, the gel threads formed were drawn
out of the precipitation bath and then cut following a washing step
in a wet condition. After cutting, the fibers suspended in the
water were ground in a Valley Beater (Lorentzen & Wettre). The
suspension thereby contained 2.5% cellulose and the grinding
duration equalled 150 min. The second grinding took place in a
agitator bead mill from Drais Werke manufacturers with a 1000 ml
milling space volume and with zirconium oxide balls with a diameter
of 0.9-1.1 mm for three hours at 2000 rpm and then for another hour
at 3000 rpm. The suspension obtained in this way was finally
thickened for 15 hours at 60.degree. C. in the drying cabinet to 7%
cellulose. The suspension was viscous and there was no phase
separation even after a long period of standing. It was possible to
dilute the suspension again with water without any problems to a
lower cellulose content. As a result of thickening (and diluting)
the suspension, no noticeable (irreversible) aggregation of the
fibrids occurred. The length of the fibrids was in the range of 1-8
.mu.m (laser diffraction, microscopy).
EXAMPLE 2
[0064] 8 g of cut, moist fibers (cellulose content 30% abs.dry)
from example 1 (6 mm, 1.3 dtex) was mixed into 60 ml of water using
a glass stirrer. This suspension was emptied together with 300 g of
zirconium oxide balls (1, 1-1.4 mm diameter) into a stainless steel
glass. With an impeller stirrer (IKA RE 166) the suspension was
ground for 2 hours at 300 rpm. The grinding balls were separated
from the fibrid suspension using a sieve. The fibrids were longer
than those in example 1. There were indeed also fibrids with a
length of 1 .mu.m, however, the mean value of the length was at
around 10 .mu.m and fibrids with a length of up to 40 .mu.m could
be found.
EXAMPLE 3
[0065] 15 g of non-finished, non-dried viscose fibers (1.3 dtex, 38
mm cut length) from a commercial production line with a cellulose
content of 35% (abs.dry) were pre-disintegrated and broken into a
fibrous state in a laboratory mixer with a Stern knife. 2 g of
fibers were dispersed from the sample pre-treated in this way by
stirring into 80 ml of water using a glass stirrer. This suspension
was mixed with 300 g of zirconium oxide balls (0.9-1.1 mm diameter)
in a stainless steel beaker glass and finally ground for a long
time with an impeller stirrer (IKA RE 166) at 3000 rpm for 3 hours.
The separation of the grinding balls from the fibrid suspension was
performed by a sieve. The fibrids obtained were of a size
comparable to those in example 1 with lengths in the range of 2-12
.mu.m (laser diffraction).
* * * * *