U.S. patent application number 12/677619 was filed with the patent office on 2010-08-05 for continuous method for obtaining composite fibres containing colloidal particles and resulting fibre.
This patent application is currently assigned to Arkema France. Invention is credited to Alain Derre, Antoine Lucas, Philippe Poulin.
Application Number | 20100196250 12/677619 |
Document ID | / |
Family ID | 39495671 |
Filed Date | 2010-08-05 |
United States Patent
Application |
20100196250 |
Kind Code |
A1 |
Derre; Alain ; et
al. |
August 5, 2010 |
CONTINUOUS METHOD FOR OBTAINING COMPOSITE FIBRES CONTAINING
COLLOIDAL PARTICLES AND RESULTING FIBRE
Abstract
The invention relates to a method for obtaining composite
fibers, that comprises dispersing colloidal particles in a solvent,
injecting the dispersion into a co-flow of a polymer coagulation
solution for forming a pre-fiber, circulating the pre-fiber in a
duct, extracting, optionally washing and drying the pre-fiber in
order to obtain a fiber, and winding the fiber thus obtained,
characterized in that the minimum retention time of the fiber
within the duct is adjusted so that it has a mechanical strength
sufficient to be extracted from the duct, and in that its
extraction is vertical and continuous. The invention also relates
to composite fibers that can be made according to said method.
Inventors: |
Derre; Alain; (Balizac,
FR) ; Lucas; Antoine; (Bordeaux, FR) ; Poulin;
Philippe; (Talence, FR) |
Correspondence
Address: |
ARKEMA INC.;PATENT DEPARTMENT - 26TH FLOOR
2000 MARKET STREET
PHILADELPHIA
PA
19103-3222
US
|
Assignee: |
Arkema France
Colombes
FR
|
Family ID: |
39495671 |
Appl. No.: |
12/677619 |
Filed: |
March 18, 2008 |
PCT Filed: |
March 18, 2008 |
PCT NO: |
PCT/FR08/51679 |
371 Date: |
March 11, 2010 |
Current U.S.
Class: |
423/447.2 ;
156/184; 977/742; 977/750; 977/752 |
Current CPC
Class: |
C04B 35/62281 20130101;
D01F 9/08 20130101; C04B 35/62245 20130101; C04B 35/62272 20130101;
D01D 5/06 20130101; C04B 35/63416 20130101; C04B 35/6229 20130101;
C04B 2235/5264 20130101; C04B 35/62231 20130101; C04B 35/636
20130101; C04B 35/6365 20130101; D01F 2/00 20130101; D01F 9/12
20130101 |
Class at
Publication: |
423/447.2 ;
156/184; 977/742; 977/750; 977/752 |
International
Class: |
D01F 9/12 20060101
D01F009/12; D01F 1/00 20060101 D01F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2007 |
FR |
07 06542 |
Claims
1. A continuous process for producing composite fibers, said
process comprising: dispersing colloidal particles in a solvent
optionally with the help of a surface-active agent, injecting the
dispersion of colloidal particles into a coflow of a coagulation
solution comprising a polymer as coagulating agent, in order to
form a prefiber, circulating said prefiber in a duct, extracting
said prefiber, optional washing said prefiber, drying said
prefiber, in order to obtain a fiber, and winding the fiber thus
obtained, characterized in that the minimum residence time of the
prefiber in said duct is adjusted so that the prefiber has a
sufficient mechanical strength to be extracted from said duct and
in that the extraction of said prefiber is a continuous vertical
extraction.
2. The process as claimed in claim 1, characterized in that the
colloidal particles are chosen from nanotubes, tungsten sulfide,
molybdenum sulfide, boron nitride, vanadium oxide, cellulose
whiskers, silicon carbide whiskers or clay platelets.
3. The process as claimed in claim 2, characterized in that the
nanotubes are carbon nanotubes.
4. The process as claimed in claim 3, characterized in that the
carbon nanotubes have a length from 0.1 to 20 .mu.m.
5. The process as claimed in claim 3, characterized in that the
carbon nanotubes have a diameter ranging from 0.1 to 100 nm.
6. The process as claimed in claim 1, characterized in that the
polymer is a chosen from polyalcohol, alginate or cellulose.
7. The process as claimed in claim 6, characterized in that the
polyalcohol is polyvinyl alcohol.
8. The process as claimed in claim 1, characterized in that the
rate of flow of the coagulation solution measured at the center of
the duct is from 1 m/min to 100 m/min.
9. The process as claimed in claim 1, characterized in that the
extraction of said prefiber is a continuous extraction by
overflowing of the coagulation solution.
10. A composite fiber obtained according to the process as claimed
in claim 1.
11. The process as claimed in claim 3, characterized in that the
carbon nanotubes have a diameter ranging from 0.4 to 50 nm.
12. The process as claimed in claim 3, characterized in that the
carbon nanotubes have a diameter ranging from 1 to 30 nm.
13. The process as claimed in claim 1, characterized in that the
rate of flow of the coagulation solution measured at the center of
the duct is from 2 m/min to 50 m/min.
14. The process as claimed in claim 1, characterized in that the
rate of flow of the coagulation solution measured at the center of
the duct is from 5 m/min to 25 m/min.
Description
[0001] The present invention relates to a continuous process for
producing composite fibers based on colloidal particles and in
particular on carbon nanotubes. The invention also relates to the
composite fibers capable of being obtained according to this
process.
[0002] Carbon nanotubes (or CNTs) are known and have specific
crystalline structures, of hollow and closed tubular form, composed
of atoms regularly arranged as pentagons, hexagons and/or
heptagons, obtained from carbon. CNTs are generally composed of one
or more wound graphite sheets. A distinction is thus made between
Single Wall Nanotubes (SWNTs) and Multi-Wall Nanotubes (MWNTs).
[0003] CNTs are commercially available or can be prepared by known
methods. Several processes exist for the synthesis of CNTs, in
particular electrical discharge, laser ablation and Chemical Vapor
Deposition (CVD), which makes it possible to provide for the
manufacture of a large amount of carbon nanotubes and thus their
production at a cost price compatible with their large-scale use.
This process consists specifically in injecting a carbon source at
relatively high temperature onto a catalyst which can itself be
composed of a metal, such as iron, cobalt, nickel or molybdenum,
supported on an inorganic solid, such as alumina, silica or
magnesia. The carbon sources can comprise methane, ethane,
ethylene, acetylene, ethanol, methanol, indeed even a mixture of
carbon monoxide and hydrogen (HIPCO process).
[0004] Thus, application WO 86/03455A1 from Hyperion Catalysis
International Inc. describes in particular the synthesis of CNTs.
More particularly, the process comprises bringing into contact a
particle based on a metal, such as in particular iron, cobalt or
nickel, with a gaseous carbon-based compound at a temperature of
between 850.degree. C. and 1200.degree. C., the proportion by dry
weight of the carbon-based compound with respect to the metal-based
particle being at least approximately 100:1.
[0005] CNTs have numerous outstanding properties, namely
electronic, thermal, chemical and mechanical properties. Mention
may in particular be made, among the applications, of composite
materials intended in particular for the automobile and aeronautics
industries, electromechanical actuators, cables, resisting wires,
chemical detectors, the storage and conversion of energy, electron
emission displays, electronic components and functional
textiles.
[0006] Generally, when they are synthesized, CNTs are in the form
of a disorganized powder which makes them difficult to employ in
making use of their properties. In particular for the manufacture
of composite systems, it is necessary for the CNTs to be present in
large amounts and oriented in a favored direction. Thus, the
concentration and the orientation of the CNTs are important
parameters to be taken into consideration in making use of their
properties on the macroscopic scale.
[0007] One of the solutions in overcoming this problem consists in
preparing composite fibers. For this, the nanotubes can be
incorporated in a matrix, such as an organic polymer. Spinning can
then be carried out according to conventional technologies, which
makes it possible, by drawing and/or shearing operations, to
orientate the CNTs along the axis of the fiber. However, this
technique does not make it possible to obtain high fractions of
CNTs in the fibers and the presence of aggregates, due to the high
amount of CNT dispersed in the matrix, weakens the fibers, which
may then break.
[0008] Another solution, provided in patent applications WO
01/63028 and WO 2007/101936, consists in dispersing colloidal
particles, in particular CNTs, in an aqueous or organic solvent,
optionally with the help of a surfactant, and in injecting this
dispersion into another liquid, known as coagulation solution,
which flows in a duct around the dispersion, in order to obtain a
prefiber. The prefiber thus obtained is dried in order to form a
fiber. This process makes it possible to obtain fibers, the
fraction by weight of nanotubes of which can vary between 10% and
100%.
[0009] However, this process is slow since it consists of two
separate stages (formation of the prefiber and then recovery in an
intermediate vat; and extraction of the prefiber for final drying
and winding) and limits the production of the fibers, which makes
it unsuitable for the industrial scale. This is because, once the
recovery vat is filled, the process has to be halted and it is then
also necessary to extract the prefibers formed and stored in the
intermediate recovery vat.
[0010] Another disadvantage is the absence of control of the
residence time of the prefibers in the coagulation solution. This
is because the prefiber parts formed in the first instance remain
for an extended time in the presence of the coagulation solution
while they remain in the recovery vat, in contrast to the prefiber
portions formed at the end of the operation, which have stayed
there for a shorter period of time. In point of fact, the residence
time is capable of affecting the structure and the properties of
the fibers. This process thus does not make it possible to
continuously prepare homogeneous fibers.
[0011] Finally, the process described in application WO 2007/101936
does not result in composite fibers in which the colloidal
particles are aligned in the polymer, insofar as the polymer is
premixed with the colloidal particles and with their solvent before
introduction into the coagulating agent, which is composed of a
nonsolvent for the polymer.
[0012] The need thus remains to provide a simple, fast and economic
process suited to the industrial scale which makes it possible to
prepare, starting from colloidal particles, composite fibers in
which the colloidal particles are positioned homogeneously and
optionally aligned.
[0013] The Applicant Company has discovered that this need could be
met by employing a continuous process which uses a polymer as
coagulating agent and which makes it possible to control the
residence time of a prefiber in the flow of a coagulation solution
by adjusting the length of the duct and by using a system for
extracting said prefiber in vertical configuration.
[0014] A subject matter of the present invention is thus a
continuous process for producing composite fibers, said process
comprising: [0015] the dispersion of colloidal particles in a
solvent optionally with the help of a surface-active agent, [0016]
the injection of the dispersion of colloidal particles into a
coflow of a coagulation solution comprising a polymer as
coagulating agent, in order to form a prefiber, [0017] the
circulation of said prefiber in a duct, [0018] the extraction of
said prefiber, [0019] the optional washing of said prefiber, [0020]
the drying of said prefiber, in order to obtain a fiber, and [0021]
the winding of the fiber thus obtained, characterized in that the
minimum residence time of the prefiber in said duct is adjusted so
that the prefiber has a sufficient mechanical strength to be
extracted from said duct and in that the extraction of said
prefiber is a continuous vertical extraction.
[0022] The process according to the invention can be applied to
colloidal particles in general and more particularly to anisotropic
particles, such as nanotubes, such as, for example, carbon
nanotubes, tungsten sulfide, molybdenum sulfide, boron nitride,
vanadium oxide, cellulose whiskers, silicon carbide whiskers and
clay platelets. It is preferable to use carbon nanotubes.
[0023] The carbon nanotubes which can be used according to the
invention can be of the single wall, double wall or multi-wall
type. The double wall nanotubes can in particular be prepared as
described by Flahaut et al. in Chem. Comm. (2003), 1442. The
multi-wall nanotubes can for their part be prepared as described in
the document WO 03/02456.
[0024] The nanotubes employed according to the invention usually
have a mean diameter ranging from 0.1 to 200 nm, preferably from
0.1 to 100 nm, more preferably from 0.4 to 50 nm and better still
from 1 to 30 nm and advantageously a length of more than 0.1 .mu.m
and advantageously from 0.1 to 20 .mu.m, for example of
approximately 6 .mu.m. Their length/diameter ratio is
advantageously greater than 10 and generally greater than 100.
These nanotubes thus comprise in particular the Vapor Grown Carbon
Fibers (VGCFs). Their specific surface is, for example, between 100
and 300 m.sup.2/g and their bulk density can in particular be
between 0.05 and 0.5 g/cm.sup.3 and more preferably between 0.1 and
0.2 g/m.sup.3. The multi-wall carbon nanotubes can, for example,
comprise from 5 to 15 sheets and more preferably from 7 to 10
sheets.
[0025] An example of crude carbon nanotubes is in particular
commercially available from Arkema under the trade name
Graphistrength.RTM. C100.
[0026] The nanotubes can be purified and/treated (in particular
oxidized) and/or milled before they are employed in the process
according to the invention. They can also be functionalized by
chemical methods in solution, such as amination or the reaction
with coupling agents.
[0027] The milling of the nanotubes can in particular be carried
out under cold conditions or under hot conditions and can be
carried out according to the known techniques employed in devices
such as ball, hammer, buhr, knife or gas jet mills or any other
milling system capable of reducing the size of the entangled
network of nanotubes. It is preferable for this milling stage to be
carried out according to a gas jet milling technique, in particular
in an air jet mill, or in a ball or bead mill.
[0028] The nanotubes can be purified by washing with a solution of
sulfuric acid or of another acid, so as to free them from possible
residual inorganic and metallic impurities originating from the
process for the preparation thereof. The ratio by weight of the
nanotubes to the sulfuric acid can in particular be between 1:2 and
1:3. The purification operation can furthermore be carried out at a
temperature ranging from 90 to 120.degree. C., for example for a
time of 5 to 10 hours. This operation can advantageously be
followed by stages of rinsing with water and of drying the purified
nanotubes.
[0029] The oxidation of the nanotubes is advantageously carried out
by bringing the latter into contact with a sodium hypochlorite
solution including from 0.5 to 15% by weight of NaOCl and
preferably from 1 to 10% by weight of NaOCl, for example in a ratio
by weight of the nanotubes to the sodium hypochlorite ranging from
1:0.1 to 1:1. The oxidation is advantageously carried out at a
temperature of less than 60.degree. C. and preferably at ambient
temperature, for a time ranging from a few minutes to 24 hours.
This oxidation operation can advantageously be followed by stages
of filtering and/or centrifuging, washing and drying the oxidized
nanotubes.
[0030] The first stage of the process according to the invention
can in particular be such as described in application WO 01/63028.
It thus consists in dispersing colloidal particles (of hydrophobic
nature) in an aqueous or organic solvent, such as water or an
alcohol, for example ethanol, optionally with the help of a
surface-active agent conventionally used to disperse hydrophobic
particles in such a solvent. In the case where the solvent used is
water, such a dispersion can be obtained with different molecular
or polymeric and anionic, cationic or neutral surfactants, such as,
in particular, sodium dodecyl sulfate (SDS), alkylaryl esters or
tetradecyltrimethylammonium bromide. According to the
characteristics of the agents used, their concentration varies from
a few thousandths of a % to several %.
[0031] As regards the amount colloidal particles in the dispersion,
it is preferable to use the most concentrated possible suspensions
while attempting to keep the suspensions homogeneous. For example,
when the solvent is water, it is advantageous to use a
concentration by weight of nanotubes of between 0.1% and 2% and a
concentration by weight of SDS of between 0.5% and 2%.
[0032] The second stage of the process according to the invention
consists in injecting the dispersion obtained after the first stage
through at least one orifice emerging in the coflow, advantageously
laminar coflow, of a coagulation solution, the viscosity of which
should preferably be greater than that of said dispersion, the
viscosities being measured under the same temperature and pressure
conditions, in order to bring about, due to the shear forces, the
alignment of the colloidal particles in the direction initially
imposed by the flow of said coagulation solution.
[0033] The coagulation solution is also referred to as flocculation
solution, indeed even also coagulating solution. Use is made, as
coagulant, of a polymer, such as a polyol or a polyalcohol
(polyvinyl alcohol (PVA) which also has a viscosifying role),
alginate or cellulose, as described in application WO 01/63028.
Mention may be made, as solvents, of in particular water or DMSO
(dimethyl sulfoxide). Preferably, the solution is a solution of
polyvinyl alcohol. Use may in particular be made of solutions of
the polyvinyl alcohol in water or DMSO (dimethyl sulfoxide) at
concentrations by weight of between 1% by weight and 10% by weight,
with respect to the total weight of the coagulation solution, with
varied molecular weights.
[0034] The rate of flow of the coagulation solution measured at the
center of the duct is from 1 m/min to 100 m/min, preferably from 2
m/min to 50 m/min and more preferably still from 5 m/min to 25
m/min.
[0035] The viscosity, measured at 20.degree. C. in a Couette cell,
of the coagulation solution is between 1 mPas and 1000 mPas,
preferably between 30 mPas and 300 mPas.
[0036] Advantageously, the dispersion of colloidal particles is
injected through a needle and/or a cylindrical or conical nozzle
which is nonporous into the coflow of the coagulation solution. The
mean rate of injection of the dispersion is between 0.1 m/min and
50 m/min, preferably between 0.5 m/min and 20 m/min and more
preferably still between 1 m/min and 6 m/min. The coagulating
solution brings about the coagulation in the form of a prefiber by
destabilization of the dispersion of colloidal particles. In order
for the particles to become orientated, it is preferable for the
rate of injection of the dispersion to be less than the rate of
flow of the coagulation solution. This difference in rates causes,
at the needle or nozzle outlet, a shearing which brings about the
preferential orientation of the particles in the axis of the
prefiber which is formed. The viscosity of the injected dispersion
is, at 20.degree. C., between 1 mPas and 100 mPas, preferably
between 1 mPas and 10 mPas.
[0037] In a specific embodiment, the coagulation is provided by the
adsorption of the polymer chains of the coagulant on the colloidal
particles.
[0038] The prefiber thus formed and the coagulation solution
subsequently flow in an advantageously cylindrical duct having a
length L defined by the following equation L=T.sub.min*R in which R
is the rate of circulation of the prefiber in the duct, this rate
being measured at the center of the flow of the coagulation
solution, that is to say at the center of the duct, and T.sub.min
is the minimum residence time.
[0039] In the above equation, "minimum residence time T.sub.min,"
of the prefiber in the coagulation solution is understood to mean,
in the context of the present invention, the minimum residence time
of the prefiber in the duct which is necessary in order to confer,
on the prefiber, a strength sufficient to allow it to be extracted
from the duct. This time corresponds to the time during which the
prefiber will interact with the coagulation solution. This
parameter governs the sturdiness of said prefiber.
[0040] This is because, on the macroscopic scale, if the residence
time is too short, the prefiber will be too brittle to be extracted
from the coagulation solution and may break at any moment.
[0041] On the other hand, from a certain value of the residence
time known as minimum residence time, the prefiber will have a
satisfactory strength and can be extracted from the coagulation
solution without breaking.
[0042] A person skilled in the art will know how to determine, by
simple routine operations, the minimum residence time. By way of
indication, it can be from a few seconds to several tens of
seconds.
[0043] It is understood from the above that the residence time, and
consequently the length of the duct, is an important parameter for
the continuous production of homogeneous fibers since the residence
time is capable of affecting the structure and the property of the
fibers.
[0044] It is clearly understood that it is advantageous
industrially to use a duct of minimum length in order to reduce the
space required. The rate of circulation of the prefiber in the duct
should then be reduced as much as possible if it is desired to
observe the minimum residence time.
[0045] In the process according to the invention, it is thus
possible to adjust the length of the duct via a series of tubes as
a function of the rate of flow of the coagulation solution in order
to achieve a given residence time before the extraction of the
prefiber.
[0046] The minimum residence time depends on the kinetics of
diffusion of the chains of the polymer in the prefiber. In order to
reduce this minimum residence time, it is thus possible to use
solutions of polymers with lower molecular weights, or mixtures
with different molecular weights, which will then diffuse more
rapidly in the prefiber.
[0047] Another solution in order to reduce the minimum residence
time consists in using the chemical route, agents which promote the
coagulation being added to the coagulating solution.
[0048] The following stage of the process according to the
invention consists in continuously extracting the prefiber from the
coagulation solution.
[0049] This extraction can be carried out independently of the
configuration initially chosen for the device in which the process
is carried out, provided that it is carried out vertically.
[0050] This is because, in vertical configuration, the continuous
extraction is carried out by overflowing of the coagulation
solution into a chamber placed around the duct in which the
prefiber and the coagulation solution flow. The prefiber is
subsequently carried off continuously by virtue of a roller placed
above the duct, at a linear rate of between 1 m/min and 100 m/min,
preferably of between 2 m/min and 50 m/min and more preferably
still of between 5 m/min and 25 m/min.
[0051] This configuration exhibits some major advantages for the
production of fibers on the industrial scale.
[0052] Specifically, the first advantage is that it is possible to
redirect the coagulation solution to an external tank or chamber in
order to subsequently keep it recirculated. In a specific
embodiment where a surfactant has been incorporated in the
dispersion of colloidal particles, this tank can make it possible
to easily change the polymer solution in order to prevent the
possible aging thereof due to the surfactant employed or to
possible chemical decompositions.
[0053] Another advantage of the vertical configuration is that it
makes possible precise adjustment of the residence time. This is
because, as the prefiber is not stored in an intermediate bath, its
residence time in the coagulation solution is precise and identical
at the beginning or the end of the experiment. A homogeneous
prefiber is then obtained.
[0054] However, the extraction of the prefiber during the
overflowing of the coagulation solution into the external chamber
may be rendered difficult when the rate of flow R of the
coagulation solution in the tube is high. This is because the
coagulation solution then has a tendency to carry the prefiber
along into the external chamber. It is then possible to adapt
geometries at the duct outlet, such as a conical component or a
component with successive flarings, in order to slow down the
prefiber and facilitate the handling and extraction thereof.
[0055] Yet another advantage of the vertical configuration is the
freeing from the effects of gravity during the flowing of the
prefiber in the duct.
[0056] This is because, in horizontal configuration, the prefiber
does not always remain at the center of the flow in the duct, its
density being different from that of the coagulation solution. It
may then be necessary to incorporate a 90.degree. elbow at the end
of the duct in order to make possible the extraction by vertical
overflowing.
[0057] When the duct conveying the prefiber is in the horizontal
configuration, it is possible to produce one or more 180.degree.
bends in order to link more tubes together. If the experiment takes
place in a reduced space, it is possible, by this means, to adjust
the length of the duct in order to achieve a given residence time.
The prefiber is not damaged by these bends if a low radius of
curvature is chosen. If the radius of curvature is high, the
prefiber travels a large distance and spends a long time in these
bends. There is then a risk of it gradually moving away from the
axis of the tube under the action of the centrifugal force until it
rubs against the walls of the tube, becomes entangled and/or
breaks.
[0058] However, it is probable that, beyond a certain radius of
curvature, it should again be possible to cause the prefiber to
make a half turn without damaging it. This is because the
centrifugal force increases when the difference in density between
the prefiber and the coagulation solution increases. It also
increases when the radius of curvature decreases or when the rate
of flow of the coagulation solution and of the prefiber increases.
Likewise, the passage time in the bend is reduced when the radius
of curvature is reduced or when the rate of flow of the coagulating
solution and of the prefiber increases. The success of this half
turn thus requires a compromise between the strength of the
centrifugal force applied to the prefiber and the passage time in
this bend.
[0059] After the continuous extraction of the prefiber from the
duct, the prefiber can be carried along to a washing vat comprising
water. The washing stage makes it possible to remove a portion of
the peripheral polymer from the prefiber and thus to enrich the
composition of the prefiber in colloidal particles. In addition,
the washing bath can comprise agents which make it possible to
modify the composition of the prefiber or which interact chemically
with the latter. In particular, agents for chemical or physical
crosslinking can be added to the bath in order to strengthen the
prefiber.
[0060] The prefiber is advantageously carried along to the washing
bath via at least one roller. The prefiber might also be carried by
a conveyor belt composed of multiple rollers driven by gears. The
use of a conveyor belt during the washing stage makes it possible
to prevent any uncontrolled lengthening of the prefiber.
[0061] A drying stage is also included in the process according to
the invention. This stage can take place either directly after the
extraction or consecutively to the washing.
[0062] In particular, if it is desired to obtain a fiber enriched
in polymer, it is desirable to dry the prefiber directly after the
extraction.
[0063] When the drying is consecutive to the washing, the presence
of a second roller at the outlet of the washing bath allows it to
be carried along continuously to an oven which will dry the
prefiber by virtue of hot air circulating in a duct inside the
oven. It is necessary to increase the speed of rotation of this
second roller with respect to the speed of that situated at the
inlet of the bath in order to prevent an accumulation of prefiber
in the bath.
[0064] The prefiber is advantageously carried along to the oven by
at least one roller. It might also be carried by a conveyor belt
composed of multiple rollers driven by gears.
[0065] The final stage of the process, which is well known to a
person skilled in the art, comprises the winding of the fiber thus
obtained via a conventional winder situated at the end of the
spinning line.
[0066] The process according to the invention can also comprise a
stage of hot drawing which would be carried out between the drying
stage and the winding stage.
[0067] The diameter of the fibers obtained is between 0.005 mm and
0.100 mm and preferably between 0.02 mm and 0.04 mm. The length of
the fibers is undefined since, while the plant operates, fiber
production is continuous.
[0068] The process described above is advantageously carried out in
a device comprising at least one tank containing a coagulation
solution, at least one tank containing a dispersion of colloidal
particles, at least one means for conveying said coagulation
solution, at least one means for conveying said dispersion, at
least one means for injecting said dispersion into said coagulation
solution, at least one means for circulating a prefiber in a coflow
of said coagulation solution, at least one means for extracting the
prefiber, optionally at least one washing means, optionally at
least one drying means, at least one winding means and at least one
means for carrying along the prefiber or the fiber. Said
circulating means is a duct, the length L of which is defined by
the equation L=T.sub.min.times.R, where T.sub.min is the minimum
residence time of the prefiber in the coagulation solution in order
to confer on the prefiber a stiffness sufficient to allow it to be
extracted and R is the rate of flow of said coagulation solution
measured at the center of said duct, and the said extraction means
is in the vertical configuration.
[0069] The plant for carrying out the process according to the
invention can adopt either a vertical configuration or a horizontal
configuration, as described above.
[0070] The tanks which can be used in the device according to the
invention are any type of tank known to a person skilled in the
art.
[0071] The conveying means are any type of means known to a person
skilled in the art, such as pipes, ducts, and tubes or tubular
conduits.
[0072] The injection means is in particular an injector which can
coupled to two pumps, the first pump being used for the flow of the
coagulating solution and the second being used for the injection of
the dispersion of colloidal particles, such as, in particular, a
positive displacement pump, for example a gear pump. In the case of
the use of a needle for the injection and of a glass tube for the
coflow, the injector makes it possible to adjust the coaxiality of
the needle in the glass tube. Specifically, it can center the
needle by the tightening of adjusting screws situated at the rear
of the injector.
[0073] The means for circulating a prefiber can be any means known
to a person skilled in the art and advantageously a cylindrical
duct. This duct can in particular be composed of a series of
cylindrical glass tubes or of a single tube of appropriate length.
Tubes with different cross sections can be used, such as, for
example, tubes with an internal diameter of 2 mm and 4 mm.
Advantageously, tubes with small diameters, namely with an internal
diameter of between 0.5 mm and 15 mm and preferably of 2 mm, are
favored in order to prevent differences due to the presence of air
bubbles.
[0074] It is clearly understood that, the smaller the internal
diameter of the tube or tubes, the more powerful must be the pump
necessary for bringing about flow.
[0075] In a preferred embodiment, the means for extracting in the
vertical configuration comprises, at the outlet of the duct, a
conical component or a component with successive flarings.
[0076] The means for carrying along the prefiber or the fiber can
be at least one roller or a conveyor belt composed of multiple
rollers driven by gears.
[0077] The device according to the invention can also comprise
additional equipment on the spinning line, such as in particular
hot drawing rollers situated between the oven and the winder.
[0078] Another subject matter of the invention is a composite fiber
capable of being obtained according to the process of the
invention.
[0079] Other characteristics and advantages of the invention will
become apparent on reading the description which will follow. Forms
and embodiments of the invention are given as nonlimiting examples
illustrated by the appended drawings, in which:
[0080] the single FIGURE illustrates a general view of the plant
making possible implementation of the process according to the
invention.
EXAMPLE
Example 1
Continuous Process for the Manufacture of a Composite Fiber
[0081] This example is illustrated by the appended FIGURE, which
represents a general view of a plant for the implementation of the
process according to the invention in a preferred embodiment.
[0082] The FIGURE represents a plant 1 for the continuous
production of homogeneous fibers based on CNTs. This plant 1
comprises two tanks 2 and 3 connected to an injector 4 via pipes 5
and 6 respectively. The injector comprises, at the outlet, a needle
7 which passes longitudinally and centrally through a cylindrical
glass duct 8. An extraction region 9, in the vertical
configuration, is situated at the outlet of the duct 8 and
comprises an external chamber 10 connected to the tank 3 via a pipe
12 and a conical component 11 surmounting the duct 8. Rollers 13,
14 and 15 make it possible to carry along the prefiber 16 thus
obtained to a washing unit 17, a drying unit (or oven) 18 and a
winding unit (or winder) 19 respectively.
[0083] 0.3% by weight of Elicarb.RTM. single wall nanotubes from
Thomas Swan were dispersed using ultrasound in a solution
comprising water and 1% by weight of sodium dodecyl sulfate (SDS).
The dispersion is placed in the tank 2. Use is made, in the tank 3,
as coagulating solution, of a 5% by weight solution of Mowiol.RTM.
56-98 polyvinyl alcohol (PVA) from Clariant with a molecular weight
of 195 kDa.
[0084] The CNT dispersion of the tank 2 is conveyed via the pipe 5
to the injector 4 while the coagulating polymer solution of the
tank 3 is conveyed via the pipe 6 to the injector 4. The dispersion
is injected into the cylindrical duct 8 via the needle 7 with a
diameter of 0.3 mm, at a mean injection rate of 4.2 m/min. The mean
rate of flow of the coagulating polymer solution in the duct is
R'=4.4 m/min, which corresponds to a rate at the center of the duct
of 8.8 m/min. A prefiber 16 is thus formed in the duct 8.
[0085] The duct 8 is composed of a plurality of tubes, the diameter
of which is 6 mm. The length of the duct 8 is adjusted in order for
the residence time to be minimal, according to the equation
L=T.sub.min.times.(2*R'), where 2*R' is the rate of flow at the
center of the duct.
[0086] At the outlet of the duct 8, the continuous extraction of
the prefiber is carried out in the vertical configuration by
overflowing with the help of the conical component 11 situated at
the top of the duct. The coagulating polymer solution is redirected
to the external chamber 10 and is then returned to the tank 3 via
the pipe 12. Simultaneously, the prefiber 16 is carried along
continuously by the roller 13 as far as the washing bath 17, in
order to remove a portion of the peripheral polymer and thus to
enrich the composition of the prefiber in CNT. The prefiber 16 is
subsequently carried along by the roller 14 to the oven 18, where
it is dried by virtue of hot air. Once dried, a fiber 20 thus
obtained is carried along by a roller as far as a winder 19 in
order to be wound off around a reel and easily stored.
Example 2
Evaluation of T.sub.min
[0087] The steadiness of the fibers obtained as described in
example 1 and their strength was studied while varying the length L
of the duct 8 in order to be able to evaluate the minimum residence
time under these highly specific conditions. The results are
combined in table I below.
TABLE-US-00001 Mean Rate at the center of Theoretical Length rate
the duct (m/min) residence L.sub.n (m) (m/min) (=2*mean Rate) time
(s) L.sub.1 = 10.6 4.4 8.8 75 L.sub.2 = 7.6 4.4 8.8 52 L.sub.3 =
4.6 4.4 8.8 32 L.sub.4 = 2.5 4.4 8.8 17
[0088] It is found that, on using a duct with the length L.sub.1
(4.5 m going+0.6 m bend+4.5 m coming+1 m vertical extraction) and
L.sub.2 (3 m going+0.6 m bend+3 m coming+1 m vertical extraction),
the prefibers obtained are strong and able to be handled. They can
be continuously extracted with a roller at a rate of approximately
11 m/min.
[0089] With the length L.sub.3 (1.5 m going+0.6 m bend+1.5 m
coming+1 m vertical extraction), the prefiber has strength but is
difficult to handle. Continuous extraction is achieved, but with
difficulty.
[0090] With the length L.sub.4 (1.5 m going+1 m vertical
extraction), the prefiber is not sufficiently strong and cannot be
continuously extracted.
[0091] In the light of these results and under the specified
conditions, the minimum residence time is evaluated at T.sub.min=30
s.
* * * * *