U.S. patent application number 16/151536 was filed with the patent office on 2019-01-31 for method of spinning fibres or extrusion, and the products obtained.
The applicant listed for this patent is RISE INNVENTIA AB. Invention is credited to Andreas Fall, Karl Hakansson, Mathias Kvick, Fredrik Lundell, Daniel Soderberg, Lars Wagberg.
Application Number | 20190032247 16/151536 |
Document ID | / |
Family ID | 50544983 |
Filed Date | 2019-01-31 |
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United States Patent
Application |
20190032247 |
Kind Code |
A1 |
Soderberg; Daniel ; et
al. |
January 31, 2019 |
METHOD OF SPINNING FIBRES OR EXTRUSION, AND THE PRODUCTS
OBTAINED
Abstract
The invention relates to a continuous, scalable and
parallelizable method for preparing strong and stiff fibres
(filaments) or films. The fibre or film is prepared by utilizing
hydrodynamically induced alignment of the constituents of a
dispersion in combination with surface-charge controlled gel
transition to produce fibres with a high degree of alignment of the
constituents (polymer(s), fibrils etc.). The invention also relates
to the fibres or films so formed.
Inventors: |
Soderberg; Daniel; (Taby,
SE) ; Lundell; Fredrik; (Osterskar, SE) ;
Fall; Andreas; (Stockholm, SE) ; Hakansson; Karl;
(Stockholm, SE) ; Kvick; Mathias; (Stockholm,
SE) ; Wagberg; Lars; (Lidingo, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RISE INNVENTIA AB |
Stockholm |
|
SE |
|
|
Family ID: |
50544983 |
Appl. No.: |
16/151536 |
Filed: |
October 4, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14437406 |
Apr 21, 2015 |
10132005 |
|
|
PCT/SE2013/051227 |
Oct 22, 2013 |
|
|
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16151536 |
|
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|
61716905 |
Oct 22, 2012 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D01D 5/40 20130101; D01F
9/14 20130101; D01D 5/06 20130101; D01F 4/00 20130101; C01B 32/16
20170801; D01F 2/00 20130101; D01D 5/14 20130101; D10B 2101/122
20130101; D01D 5/38 20130101 |
International
Class: |
D01D 5/06 20060101
D01D005/06; D01F 4/00 20060101 D01F004/00; D01D 5/14 20060101
D01D005/14; D01D 5/40 20060101 D01D005/40; C01B 32/158 20060101
C01B032/158; D01F 2/00 20060101 D01F002/00; D01F 9/14 20060101
D01F009/14; D01D 5/38 20060101 D01D005/38; C01B 32/16 20060101
C01B032/16 |
Claims
1. An oriented fibre or oriented sheet comprising long-chained
polymer(s) or non-spherical particles, wherein the oriented fibre
or oriented sheet was manufactured by a method of spinning fibres
or extrusion comprising steps of: (a) Injection of a central flow
dispersion comprising long-chained polymer(s) or non-spherical
particles into a central flow channel of one or more reaction
chambers; (b) Acceleration of the central flow in the one or more
reaction chambers by at least two opposite, aligning flow streams,
essentially perpendicular to the central flow, whereby the
long-chained polymer(s) or non-spherical particles are aligned in
the flow direction; and (c) Gelling of the aligned long-chained
polymer(s) or non-spherical particles, through diffusion of salt,
chelating agent or acid contained in the aligning flow streams,
into the aligned long-chained polymer(s) or non-spherical
particles, followed by coagulation of the gel string obtained,
and/or (d) Polymerization of a polymerizable component contained in
the central flow dispersion; and (e) Drying of the oriented fibre
or oriented sheet obtained.
2. The oriented fibre or oriented sheet according to claim 1,
wherein the central flow is constituted by multiple streams.
3. The oriented fibre or oriented sheet according to claim 1,
wherein the one or more reaction chambers comprise at least two
reaction chambers in parallel.
4. The oriented fibre or oriented sheet according to claim 3,
wherein the number of reaction chambers in parallel is 3-30.
5. The oriented fibre or oriented sheet according to claim 1,
wherein the long chained polymer(s) or nonspherical particles in
(a) are nanocellulose, a polymeric protein, or carbon nano
tubes.
6. The oriented fibre or oriented sheet according to claim 1,
wherein the flow dispersion in (a) additionally comprises nano clay
or graphene.
7. The oriented fibre or oriented sheet according to claim 1,
wherein the flow dispersion in (a) has a concentration of 0.01-10%
(w/w) of long-chained polymer(s) or non-spherical particles.
8. The oriented fibre or oriented sheet according to claim 1,
wherein the aligning flow streams are constituted by water, and the
central flow comprises a polymerizable component.
9. The oriented fibre or oriented sheet according to claim 1,
wherein in (c) the gelling salt, chelating agent or acid is chosen
from the group consisting of organic acids, inorganic acids, water
soluble complexing agents, organic salts, and inorganic salts.
10. The oriented fibre or oriented sheet according to claim 1,
wherein the diffusion of salt, chelating agent or acid contained in
the aligning flow streams comprises diffusion of ions of the salt,
chelating agent or acid contained in the aligning flow streams.
11. The oriented fibre or oriented sheet according to claim 1,
wherein in (c) the coagulation proceeds inside the reaction chamber
by addition of a coagulating agent or outside of the reaction
chamber in a separate coagulating bath.
12. The oriented fibre or oriented sheet according to claim 1,
wherein the coagulation is effected by immersion of the gel string
into acetone or alcohol.
13. The oriented fibre or oriented sheet according to claim 1,
wherein in (d) the polymerization is effected in the reaction
chamber through light, radiation, ultrasound, or heat.
14. The oriented fibre or oriented sheet according to claim 1,
wherein the reaction chamber(s) have rectangular cross
section(s).
15. The oriented fibre or oriented sheet according to claim 1,
wherein the central flow dispersion is swirled or oscillated,
either before step (b), or in step (b) by additional, oblique
flow(s).
16. The oriented fibre or oriented sheet according to claim 15,
wherein the flow dispersion is swirled or oscillated by a change of
geometry in the reaction chamber.
17. The oriented fibre or oriented sheet according to claim 1,
wherein the fibre obtained is carbonized.
18. The oriented fibre or oriented sheet according to claim 1,
wherein the oriented fibre or oriented sheet is void free and has a
uniform orientation distribution radially.
19. The oriented fibre or oriented sheet according to claim 1,
wherein the oriented fibre or oriented sheet has different
orientations in different layers.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/437,406, filed Apr. 21, 2015, which is a national stage
application of International Application PCT/SE2013/051227, filed
Oct. 22, 2013, which claims the benefit of U.S. Provisional
Application No. 61/716,905, filed Oct. 22, 2012, all of which are
hereby incorporated by reference.
FIELD OF INVENTION
[0002] The present invention relates to the field of spinning or
extruding fibres or films, and in particular to a method of
manufacturing an oriented fibre or film. The invention also
pertains to the fibre or film manufactured.
BACKGROUND
[0003] Many biological materials show impressive and controllable
properties that are determined by their micro and nanostructure.
Cellulose fibres extracted from wood and spider silk represent two
excellent examples. The main constituent of cellulose fibres is the
nano-scale fibril, which has the prospective of being a building
block for future high-performance bio-based materials and textiles
and/or to provide a template for functional nano-materials.
However, processes that enable full utilisation of the potential of
the fibrils are yet to be developed. The fibrils in cellulose
fibres from wood are organised in a nano-scale lamellar structure
having a highly ordered spiralling orientation along the fibre
axis. The fibres demonstrate high ultimate strength and stiffness
that vary in a wide range depending on the mean fibril orientation.
In the tree, the fibril orientation also varies through the
thickness of the stem so that the mechanical performance of the
tree is maximized.
[0004] The fibrils of cellulose fibres can be separated by several
methods (1) to produce nano-fibrillated cellulose (NFC) and
recently, films and filaments have been manufactured from NFC with
promising properties (2, 3, 4). However, the properties obtained
are far from the maximum values reported for individual cellulose
fibres liberated from wood.
[0005] In order to manufacture materials such as fibre-composite
materials and textiles there is a need for manufacturing methods
for fibres (threads). Specifically, there is a need for
environmentally friendly methods using fewer chemicals that can
make fibres from bio-based polymers.
[0006] Wet spinning of fibres (filaments) is performed in an
apparatus where a raw spinning liquid is discharged from a nozzle
into a coagulation liquid where a fibre is formed. The raw spinning
liquid is commonly prepared by dissolution of constituents into a
suitable solvent. These substances typically are non-spherical,
which contributes the properties of the final fibres. The spinning
liquid is injected through a nozzle, i.e. the spinnaret, into a
bath where a coagulation liquid is contained. The injection can be
directly into the coagulation liquid by submersion of the nozzle
into the coagulation liquid or into the coagulation liquid after
passing through a gas such as air.
[0007] Typically a drawing roll is immersed at the other end in the
spinning bath. The spinning raw liquid discharged from the nozzle
(i.e. the spinnaret) is coagulated by the coagulation liquid and
thus formed into a coagulated fibre (filament), which can be drawn
out of the spinning bath using the drawing roll. The coagulated
fibres (coagulated filaments) solidified in the spinning bath are
separated from the coagulation liquid, washed, and transferred to
subsequent steps such as chemical liquid treatment, drying, and
thermal treatment. As an improvement to the process, coagulation
liquid has been applied already in the spinnaret, as disclosed in
e.g. Patents GB1087212 and U.S. Pat. No. 2,510,135. This process
can be performed for single fibres (monofilament) or a multitude of
fibres in parallel (multifilament).
[0008] In order to meet product requirements regarding fibre
mechanical properties such as strength, it has proven to be
beneficial to achieve alignment of the constituents within the spun
fibre. Furthermore, in order to achieve alignment of the
constituents (polymers, fibrils, etc.) there are two main
approaches used: [0009] 1) The constituents are stretched after
coagulating/gelling of the fibre produced has been initiated. This
causes the constituents to be elongated and the constituents
aligned in the direction of the fibre. There are two routes for
this stretching: [0010] a) Mechanically pulling the fibre in its
gelled stated; or [0011] b) Using a co-flowing liquid flowing
faster than the produced fibre, which pulls the fibre through shear
forces excerpted on the developing surface of the fibre; [0012] 2)
A nozzle designed with a specific geometry, i.e. a nozzle with a
contraction, that aligns the constituents in the direction of the
fibre produced.
[0013] These approaches typically need a sufficiently high
viscosity of the spinning liquid to function and the co-flow needs
to be significantly faster to achieve stretching. The above
approaches (1a, 1b and 2) for achieving orientation of the
constituents of the fibre can all be combined. As an example this
is disclosed in patent application WO9724476.
[0014] In order to achieve a good final product it is preferred to
achieve a uniform alignment of the constituents throughout the
diameter of the fibres, i.e. the degree of alignment in the core of
the fibre should be the same as at the surface of the fibre.
[0015] Regarding approach 1 a, high shear or strain within the
fibre, in the gelled or partly gelled state can cause local
weakening of the fibre and thus inferior performance. This effect
will be present regardless of type of constituent.
[0016] For the case of non-molecular constituents, such as fibrils,
shear gradients within the liquid before gelling will also decrease
alignment. The effect cannot be avoided and was described by
Jeffery (1922) (5). The shear gradient within the liquid will force
elongated particles such as fibrils to flip, i.e. rotate, and thus
depart from the alignment to the direction of the flow.
Furthermore, this effect of fibres forced to depart from the
alignment with the flow is significantly enhanced in the presence
of a solid surface, which was described by e.g. Holm and Soderberg
(2005) (6), which showed that close to a solid surface, elongated
particles will tend to orient perpendicular to the flow, i.e. the
opposite of the desired alignment along the extent of the
fibre.
[0017] The detrimental effects of shear gradients on alignment of
non-molecular constituents will be present in approach 1b and 2 but
not in approach 1 a. Molecular substances such as polymers will
most likely also be affected by the shear gradient albeit to a
lesser degree.
[0018] The possibility, although only at higher concentrations, to
manufacture fibres from fibrils, e.g. cellulose microfibrils, has
been previously exploited and described, e.g. in U.S. Pat. No.
6,248,267, where a process for manufacturing of fibres based on the
film-forming ability of the spinning liquid is revealed. This
process is based on having a cellulose composition of less than 30
weight percent cellulose or similar matter moulded out from a
nozzle into a reaction chamber where it is subjected to a coagulant
spray. The preferred embodiments all identify concentrations above
5 weight percent or more. Furthermore, in order to achieve the
shear needed in the described reaction chamber the coagulant spray
should be co flowing with the spinning liquid with a preferred
angle of 20.degree.-80.degree. where 0.degree. corresponds to a
coagulant spray in the same direction as the ejection of the
spinning liquid from the nozzle.
[0019] It should also be noted that all the above mentioned patents
and patent applications are characterised by having an axisymmetric
design focused on spinning a predominantly cylindrical fibre, and
can hence not be extended to form a film.
[0020] Specifically the coagulant flows are designed to reach the
ejected spinning liquid from all directions, i.e. more or less
axisymetrically. Furthermore, as mentioned above these spinning
processes all depend on high-viscosity liquids, achieved by having
high concentrations of the polymers, fibrils etc., where the
surrounding co-flowing liquid has a viscosity at least one order of
magnitude lower than the viscosity of the spinning liquid.
[0021] As is apparent from the above, there is a need for oriented
fibres and films without local weakening or shear gradient.
Moreover, there is a need for a method of manufacturing said fibres
and films being less dependent on e.g. solvents.
SUMMARY OF THE INVENTION
[0022] The present invention relates to a continuous, scalable and
parallelizable method for preparing strong and stiff fibres
(filaments) or films. The fibre or film is prepared by utilizing
hydrodynamically induced alignment of the constituents of a
dispersion in combination with surface-charge controlled gel
transition to produce fibres with a high degree of alignment of the
constituents (polymer(s), fibrils etc.).
[0023] In accordance with one embodiment, an oriented fibre or
oriented sheet comprising long-chained polymer(s) or non-spherical
particles is provided. The oriented fibre or oriented sheet was
manufactured by a method of spinning fibres or extrusion comprising
steps of:
[0024] (a) Injection of a central flow dispersion comprising
long-chained polymer(s) or non-spherical particles into a central
flow channel of one or more reaction chambers;
[0025] (b) Acceleration of the central flow in the one or more
reaction chambers by at least two opposite, aligning flow streams,
essentially perpendicular to the central flow, whereby the
long-chained polymer(s) or non-spherical particles are aligned in
the flow direction; and
[0026] (c) Gelling of the aligned long-chained polymer(s) or
non-spherical particles, through diffusion of salt, chelating agent
or acid contained in the aligning flow streams, into the aligned
long-chained polymer(s) or non-spherical particles, followed by
coagulation of the gel string obtained, and/or
[0027] (d) Polymerization of a polymerizable component contained in
the central flow dispersion; and
[0028] (e) Drying of the oriented fibre or oriented sheet
obtained.
[0029] In some examples, the central flow is constituted by
multiple streams.
[0030] In some examples, the one or more reaction chambers comprise
at least two reaction chambers in parallel. In some of these
examples, the number of reaction chambers in parallel is 3-30.
[0031] In some examples, the long chained polymer(s) or
nonspherical particles in (a) are nanocellulose, a polymeric
protein, or carbon nano tubes.
[0032] In some examples, the flow dispersion in (a) additionally
comprises nano clay or graphene.
[0033] In some examples, the flow dispersion in (a) has a
concentration of 0.01-10% (w/w) of long-chained polymer(s) or
non-spherical particles.
[0034] In some examples, the aligning flow streams are constituted
by water, and the central flow comprises a polymerizable
component.
[0035] In some examples, in (c) the gelling salt, chelating agent
or acid is chosen from the group consisting of organic acids,
inorganic acids, water soluble complexing agents, organic salts,
and inorganic salts.
[0036] In some examples, the diffusion of salt, chelating agent or
acid contained in the aligning flow streams comprises diffusion of
ions of the salt, chelating agent or acid contained in the aligning
flow streams.
[0037] In some examples, in (c) the coagulation proceeds inside the
reaction chamber by addition of a coagulating agent or outside of
the reaction chamber in a separate coagulating bath.
[0038] In some examples, the coagulation is effected by immersion
of the gel string into acetone or alcohol.
[0039] In some examples, in (d) the polymerization is effected in
the reaction chamber through light, radiation, ultrasound, or
heat.
[0040] In some examples, the reaction chamber(s) have rectangular
cross section(s).
[0041] In some examples, the central flow dispersion is swirled or
oscillated, either before step (b), or in step (b) by additional,
oblique flow(s). In some of these examples, the flow dispersion is
swirled or oscillated by a change of geometry in the reaction
chamber.
[0042] In some examples, the fibre obtained is carbonized.
[0043] In some examples, the oriented fibre or oriented sheet is
void free and has a uniform orientation distribution radially.
[0044] In some examples, the oriented fibre or oriented sheet has
different orientations in different layers.
BRIEF DESCRIPTION OF THE FIGURES
[0045] FIG. 1 shows an illustration of continually controlled
alignment followed by phase transition from liquid dispersion to
gel, induced by electrolytes or acid. The fibrils in the focused
central flow dispersion are illustrated as rods (fibril length is
exaggerated by approximately a factor of 300). The diffusion of
Na.sup.+, from addition of NaCl in the aligning flow streams, is
illustrated in shading. The rows of small images above and below
the central image illustrate the hydrodynamical, molecular and
electrochemical processes involved. (I) Brownian diffusion
(illustrated with the dashed arrows) affects the orientation of a
single fibril, (II) hydrodynamically induced alignment (illustrated
by solid arrows) occurs during the acceleration/stretching, (III)
Brownian diffusion continues to act after the stretching has
ceased, (IV) Brownian diffusion is prevented by the transition to a
gel. The lower row of small images illustrate how the electrostatic
repulsion (illustrated underneath the central figure representing
the Debye-length), decreases from (i) to (iv) as the Debye length
is decreased with increasing Na.sup.+ concentration.
[0046] FIG. 2 shows a schematic drawing of the reaction chamber
where Q.sub.1 represents the central flow dispersion and Q.sub.2
the aligning flow streams containing e.g. coagulants.
[0047] FIG. 3 shows images of the focusing region of the central
flow channel, wherein the flow is directed downwards, in images (a)
and (b). Water is focusing an ink-water mix in (a) and a NaCl
solution is focusing a NFC dispersion in (b). The channel is in (b)
placed between two crossed polarisation filters rotated 45.degree.
from the vertical axis (white arrows). To the right (c) SAXS
diffractograms from before, during and after the acceleration in
the channel, where the elliptical cloud corresponds to a constant
intensity. The locations of each of the diffractiograms are marked
with squares in figure (b).
[0048] FIG. 4 shows images and diffractograms of dried fibre. (a)
Image of a single filament placed between two crossed polarisation
filters rotated 45.degree. with respect to the vertical axis (white
arrows). (b) Image of a filament in a light microscope. (c)-(e) and
(g), (h), SEM images of a filament, where the outlined squares are
close-ups and scale-bars are given in each image. (f)
Diffractograms from a horizontal scan of the fibre shown in (b),
where the fibre has a diameter of .about.30 .mu.m, the beam size is
1.5.times.1.2 .mu.m.sup.2 (Horizontally.times.Vertically) and the
distance between two diffractograms is 6 .mu.m (the region covered
by each diffractogram is indicated with white rectangles in
(b).
[0049] FIG. 5 shows the mechanical performance of the fibres
(overview in (a) and close-up in (b)), showing specific ultimate
strength as a function of specific Young's modulus for a wide range
of fibre materials as well as steel and aluminium. The filled,
connected markers show data that have been obtained from
stress-strain curves for bleached cellulose pulp fibres extracted
from wood, from this point on denoted cellulose pulp fibres. More
recent experiments (as indicated by the legend) report lower values
and connected, filled circles and line must therefore be considered
as extremely good values. The filled circles correspond to
different mean angles between the fibrils and the fibre (nanofibril
angle); this variation occurs naturally in different parts of a
tree since the tree optimizes its structural integrity. The data
points for cellulose pulp fibres appear near a line that also
collects most other.
DETAILED DESCRIPTION OF THE INVENTION
[0050] As noted above, the present invention relates to a
continuous, scalable and parallelizable method for preparing strong
and stiff fibres (filaments) or films. The fibre or film is
prepared by utilizing hydrodynamically induced alignment of the
constituents of a dispersion in combination with surface-charge
controlled gel transition to produce fibres with a high degree of
alignment of the constituents (polymer(s), fibrils etc.).
[0051] Accordingly, in accordance with the invention there is
provided a method of spinning fibres or extrusion, comprising:
[0052] a) Injection of a central flow dispersion comprising
long-chained polymer(s) or non-spherical particles into a central
flow channel of a reaction chamber;
[0053] b) Acceleration of the central flow in the reaction chamber
by at least two opposite, aligning flow streams, essentially
perpendicular to the central flow, whereby the long-chained
polymer(s) or non-spherical particles are aligned in the flow
direction; and
[0054] c) Gelling of the aligned long-chained polymer(s) or
non-spherical particles, through
diffusion of salt, chelating agent or acid contained in the
aligning flow streams, into the aligned long-chained polymer(s) or
non-spherical particles, followed by coagulation of the gel string
obtained, and/or [0055] d) Polymerization of a polymerizable
component contained in the central flow dispersion; and [0056] e)
Drying of the fibre obtained.
[0057] The invention does not make use of any co-flowing liquid
significantly stretching the long-chained polymer(s) or
non-spherical particles.
[0058] The at least two opposite, aligning flow streams are each
located such that they have identical angles in relation to the
central flow. The at least two opposite, aligning flow streams
being essentially perpendicular to the central flow means that the
angle between the central flow and each aligning flow stream is
from 70.degree. to 90.degree.. The at least two aligning flow
streams may be located such that they have identical angles to the
central flow. Alternatively, there may be a difference of up to
10.degree. between the two aligning flow streams, in relation to
the central flow.
[0059] The person skilled in the art is well equipped to choose an
appropriate angle, based on the characteristics and concentration
of the flow dispersion.
[0060] The invention enables production of fibres from long-chained
polymer(s) or non-spherical particles from the group of
nanocellulose, polymeric protein(s), and carbon nanotubes, as
contained in the flow dispersion. The flow dispersion may
additionally comprise nano-clay or graphene.
[0061] The invention allows manufacture of strong filaments from
e.g. wood fibre raw material for subsequent production of high
performance bio-composites as well as for textile production. In
the latter context, the filaments could be a replacement product
for cotton and industrially produced viscose and Lyocell, and
thereby significantly contribute to a reduced environmental
footprint.
[0062] The principle behind the invention is shown stepwise in FIG.
1. Above and below the illustration of a flowing fibril suspension,
the mechanical (above) and electrochemical (below) processes are
illustrated. The spinning liquid is constituted of a dispersion of
the constituents into a suitable liquid such as water (I). When the
term "fibril" is used herein, it should be understood that this
encompasses any non-spherical constituent that may be used in
accordance with the invention, e.g. any long-chained polymer or
non-spherical particle such as nanocellulose, a polymeric protein,
or carbon nanotubes, unless specifically defined otherwise. The
dispersion is characterized in that the fibrils are fairly free to
rotate thanks to a sufficiently low concentration and electrostatic
repulsion.
[0063] The dispersion is accelerated, which causes the fibrils to
align in the flow direction (II). Before the alignment is lost due
to Brownian diffusion (III), the electrostatic repulsion between
the particles is reduced by an electrolyte diffusing into the
suspension (ii-iv), which causes a gel to form and thus freezes the
internal structure of the fibre (IV).
[0064] Hydrodynamical alignment can be achieved in different ways.
The cross section of the central flow channel can be increased or
decreased, imposing deceleration or acceleration, respectively, of
the flow. As a consequence, fibrils will tend to orient themselves
perpendicular (deceleration) or parallel (acceleration) to the flow
direction.
[0065] In accordance with the invention, streams are merged and the
fundamental principle of mass continuity controls the acceleration.
In this case, acceleration is achieved with a minimum amount of
shear, see FIG. 2. This figure illustrates what we define as a
reaction chamber. In the reaction chamber, the central flow is
accelerated as it is deformed by two opposite, aligning flow
streams, which are injected with an high angle to the central flow.
If the central flow contains fibrils, these will tend to align
during the acceleration. If this forcing overcomes Brownian
relaxation towards isotropy, an aligned structure will be created.
Since the acceleration is controlled by continuity, the potentially
detrimental shear is minimal.
[0066] In FIG. 3, the central flow is a NFC (nano fibrillar
cellulose) dispersion and the fibrils are aligned by the
acceleration. This alignment is visualized by polarized light
visualizations in FIG. 3b, where the birefringence of the NFC
dispersion results in higher intensity of the transmitted light in
regions were the fibrils are aligned. The alignment is further
demonstrated by small angle X-ray diffraction in FIG. 3c, wherein
the lighter contours show that the initially isotropic structure
(circle) is deformed further downstream. This deformation in small
angle diffraction is a footprint of alignment on the nano
level.
[0067] When the aligning streams contain electrolytes or an acid,
ions will diffuse into the dispersion and eventually induce a gel
transition at positions where the ion concentration has reached
values above the gelation concentration threshold. For the case of
nanocellulose this gel transition is due to a cancellation of the
electrostatic repulsion between the fibrils, which originates from
the carboxyl groups on the fibrils. As mentioned, the fibrils must
be aligned before the structure is frozen by gelation while
gelation must occur before the temporary flow-induced alignment is
lost due to Brownian rotational diffusion. Furthermore, gelation
must occur before the aligned fibre is convected out of the channel
system. Thus, the below relations between the time scales 1-4 need
to be fulfilled. The person skilled in the art is well qualified to
ensure that the time scale conditions are fulfilled, based on the
below guidance.
[0068] 1. Alignment of the fibrils due to the flow focusing. An
estimate for the time scale of this process is t.sub.align.about.2
h.sup.3/Q.sub.1, where h is the channel size and Q.sub.1 is the
volumetric flow rate as indicated in FIG. 2.
[0069] 2. Increase of ion concentration in the thread by diffusion,
with the timescale t.sub.ion.about.the time it takes for the ions
to reach the core of the fibre that is forming in the channel. An
estimate can be obtained as t.sub.ion.about.Ch.sup.2/D.sub.ion,
where D.sub.ion is the diffusivity and C is a constant that can be
calculated numerically by solving the equations controlling the
diffusion of ions into the forming fibre.
[0070] 3. Brownian rearrangement of the fibrils towards isotropy.
This is a diffussive process with a rotational diffusivity
D.sub.rot. The time scale of this process is
t.sub.rot.about..DELTA..phi..sup.2/D.sub.rot where .DELTA..phi. is
the maximum de-alignment that can be accepted (here 22.5.degree. is
chosen). The diffusivity constant D.sub.rot is difficult to
estimate from first principles; it can however be measured from a
combination of flow orientation and the use of a polarized light
setup. The fibrils of a NFC-dispersion is aligned (by water) in
e.g. the flow focusing cell. By stopping the flow and measure the
decay of the light intensity, D.sub.rot can be identified.
[0071] 4. Convective transport of the suspension out of the
channel, with the timescale
t.sub.conv.about.Lh.sub.2/(Q.sup.1+Q.sup.2), where L is the length
of the outlet channel and Q.sub.1, Q.sub.2 are the volumetric flow
rates rate as indicated in FIG. 2.
[0072] Note that the time scales are independent of the
viscosities. In the case of shear induced acceleration, t.sub.conv
would be viscosity dependent. In order to successfully form fibres
the rough conditions on these time scales are that
t.sub.align<t.sub.ion<t.sub.rot and
t.sub.ion<t.sub.conv.
[0073] After forming the fibre in the reaction chamber, the fibre
is gelled through diffusion of salt, chelating agent or acid
contained in the aligning flow streams. The gelling salt, chelating
agent or acid is chosen from the group consisting of organic acids,
inorganic acids, water soluble complexing agents, organic salts,
and inorganic salts.
[0074] After gelling, the gel string obtained is coagulated.
Coagulation may proceed inside the reaction chamber by addition of
a coagulating agent or outside of the reaction chamber in a
separate coagulating bath.
[0075] The gel string may be ejected from the central channel of
the reaction chamber for subsequent coagulation. As an example the
formed gel fibre is coagulated by either (i) passing a rinsing bath
or (ii) through solvent exchange in e.g. acetone or alcohol. After
this step the fibre may be dried in air.
[0076] Alternatively or in addition to the gelling and coagulation,
a polymerizable component of the central flow may be polymerized,
whereupon the fibre is dried. When the central flow dispersion is
polymerized without prior gelling, such polymerization is effected
in the reaction chamber. Polymerization may be effected through
light, radiation, ultrasound, or heat. When the central flow
comprises a polymerizable component, the aligning flow streams may
be constituted by water. When the central flow dispersion comprises
a polymerizable component, gelling and coagulation of the fibre
formed may be dispensed with, and the polymerized fibre may proceed
directly to drying.
[0077] In accordance with the invention, the gel string, coagulated
gel string or polymerized gel string may be mechanically pulled to
further enhance its properties. Pulling of the fibre may also make
the method more industrially suitable.
[0078] Upon coagulation or polymerization, as the case may be, the
fibre may proceed directly to a carbonization step. The fibre need
not be dried before carbonization commences.
[0079] In order to successfully spin a fibre using the inventive
method, a correct behaviour of the flow dispersion is necessary.
Compared to traditional wet spinning techniques the concentration
of the fibrils needs to be sufficiently low. Assuming that the
dispersion is in the non-coagulated state, i.e. before entering
into the reaction chamber, and if the concentration is too high
there will be no alignment of the fibrils in the accelerating flow,
due to strong mechanical interaction with surrounding fibrils. This
entanglement is generally controlling the mobility of elongated
particles, as described in e.g. Lundell, Soderberg and Alfredsson
(2012) (7), through the so-called crowding factor N, which is given
by N=2/3*Cv*(L/d).sup.2, where Cv is the volume fraction of the
elongated particle with a characteristic length L and
characteristic diameter d. Typically it is required that N<60 to
assure mobility of the elongated particles in the suspension. In
traditional spinning techniques on the other hand the viscosity and
thus rheology should be high enough to prevent the break-up of the
liquid column, formed by the spinning liquid ejected through the
nozzle, due to the shear of the surrounding fluid.
[0080] The concentration of long-chained polymer(s) or
non-spherical particles may in accordance with the invention be in
the interval of 0.01-10% (w/w), counted on the total weight of the
flow dispersion. Said concentration interval may be formed from two
end points chosen from the following concentrations, which are all
expressed as % (w/w) on the total weight of the flow dispersion:
0.01%; 0.05%; 0.1%; 0.5%; 1%; 2%; 3%; 4%; 5%; 6%; 7%; 8%; 9%;
10%.
[0081] When nanofibrillar cellulose constitutes the sole content of
the flow dispersion, its concentration should be <1% (w/w).
[0082] The person skilled in the art is able to choose a suitable
concentration, based on e.g. the constituents of the flow
dispersion and the above mentioned Crowding factor.
[0083] Moreover, the central flow of the reaction chamber must be
hydrodynamically stable. Viscous confined jet/wake flows can be
susceptible to loss of stability in certain parameter regions. This
loss of stability causes self-sustained oscillations that are
potentially detrimental for the fibre forming process.
[0084] For the example with the fibre spun from nanofibrillar
cellulose, FIG. 4 shows a photo in polarized light, SEM images and
micro-focused wide angle X-ray diffractograms of the filament. The
SEM images (c-e, g, h) show that the filament is void free and has
a fairly constant cross section, although some irregularities are
visible. Furthermore, the X-ray diffractograms in FIG. 4f, taken at
different non-overlapping positions across the full width of the
filament, reveal that the fibril orientation is distinct and does
not vary across the filament, i.e. uniform properties. Thus, there
is no skin-core effect and the data demonstrates that the filaments
have a very homogeneous structure.
[0085] In FIG. 5 (overview in a) and close-up in b)) the specific
ultimate strength as a function of specific Young's modulus for a
wide range of fibre materials as well as steel and aluminium are
shown. The filled, connected circles show data that have been
obtained from stress-strain curves for bleached cellulose pulp
fibres extracted from wood (herein also denoted cellulose pulp
fibres). More recent experiments report lower values and the filled
connected circles (and line) must therefore be considered as
extremely good values. The filled connected circles correspond to
different mean angles between the fibrils and the fibre
(microfibrillar angle); this variation occurs naturally in
different parts of a tree since the tree optimizes its structural
integrity. The data points for cellulose pulp fibres appear near a
line that also collects most of the other fibres from plastic
fibres in the lower left, via natural fibres to stronger and
stiffer synthetic fibres such as glass, Kevlar, Spectra and carbon
fibres in the upper right. Note that cellulose pulp fibres with
fully aligned fibrils can have a specific ultimate strength
comparable to glass-fibres and a specific stiffness comparable to
Kevlar.
[0086] The open connected markers (square, triangles and circles)
show properties of fibres and films made from NFC (8, 9, 10).
Filaments from NFC have been made by ejection of NFC gel from a
nozzle (syringe) followed by coagulation and the fibril alignment
is a function of the ejection speed. In these studies, the
orientation is averaged over a millimetre-sized sample consisting
of nanometre sized fibrils. It is therefore not possible to deduce
the variation of the fibril orientation across the filaments. As
for the natural cellulose fibre, the open symbols represent values
that are among the best found in literature. Our filaments are
shown with filled stars and reproduce the properties of the
cellulose pulp fibres.
[0087] NFC materials of the present invention are by far superior
to the state of the art man-made NFC based materials.
[0088] The central flow dispersion may be swirled or oscillated,
either before acceleration of the flow dispersion, or during the
acceleration, in the latter case by additional, oblique flow(s).
Swirling or oscillation may be induced by introduction of
geometrical modifications that break the symmetry of the flow
conduits in the reaction chamber. Swirling or oscillation may be
utilised to produce twisted fibres with non-circular cross
sections.
[0089] Moreover, planar geometry of the reaction chamber allows the
central flow channels to be extended in the direction perpendicular
to the cross depicted in FIG. 2, which allows manufacture of a film
instead of a fibre. The central flow channel would hence have a
rectangular cross section.
[0090] The central flow may be constituted by multiple flow
streams.
[0091] The above planar geometry also allows several reaction
chambers to be stacked close together for the production of
parallel fibres. The number of reaction chambers in parallel may be
any number from 2 to 30, e.g. 5, 10, 15, 20, or 25.
[0092] Twisted fibres and films, respectively, cannot be produced
by traditional spinnaret designs wherein the addition of coagulant
liquids has to be made more or less axisymmetrically.
[0093] Sequential addition of liquids can be obtained by having
several crosses adding to the central flow. This can be used to
pre-treat the flow dispersion as well as to post-treatments of the
gelled fibre in the flow channel of the reaction chamber. The
pre-treatment with a cross directly before the reaction chamber
allows e.g. a minor shear flow to be added before entering into the
reaction chamber where the main acceleration takes place. This
minimizes the risk of clogging the entrance channel and thus makes
the manufacturing process more efficient. Post-treatment with a
cross after the reaction chamber and gelling will allow e.g.
stretching of the gel or rinsing of the gel fibre.
[0094] The oriented fibre or oriented sheet produced in accordance
with the invention comprises long-chained polymer(s) or
non-spherical particles. Such fibre or sheet may be carbonized.
[0095] The long-chained polymer(s) contained in the fibre is chosen
from the group consisting of nanocellulose, a polymeric protein,
and carbon nanotubes.
[0096] The oriented fibre or oriented sheet in accordance with the
invention is void free and has a uniform orientation distribution
radially. The oriented fibre or oriented film may moreover be
layered and have different orientation in different layers.
[0097] The person skilled in the art realizes that alterations of
the method described herein can be made without departing from the
inventive concept.
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