U.S. patent application number 10/438307 was filed with the patent office on 2004-05-06 for multiple passage extrusion apparatus.
Invention is credited to Knight, David P., Vollrath, Friedrich W. L..
Application Number | 20040086591 10/438307 |
Document ID | / |
Family ID | 29252498 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040086591 |
Kind Code |
A1 |
Vollrath, Friedrich W. L. ;
et al. |
May 6, 2004 |
Multiple passage extrusion apparatus
Abstract
The application relates to an extrusion apparatus which
comprises at least one first reservoir connected at a first end to
a first opening of a plurality of regulatory modules. The
regulatory modules or spinnerets contain tubular passages through
which dope material is extrudable. The extrusion apparatus has at
least 1,000 of the tubular passages per square metre
cross-section.
Inventors: |
Vollrath, Friedrich W. L.;
(Oxford, GB) ; Knight, David P.; (Winchester,
GB) |
Correspondence
Address: |
DANN, DORFMAN, HERRELL & SKILLMAN
1601 MARKET STREET
SUITE 2400
PHILADELPHIA
PA
19103-2307
US
|
Family ID: |
29252498 |
Appl. No.: |
10/438307 |
Filed: |
May 14, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10438307 |
May 14, 2003 |
|
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10148101 |
May 22, 2002 |
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10148101 |
May 22, 2002 |
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PCT/GB00/04489 |
Nov 24, 2000 |
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Current U.S.
Class: |
425/143 ;
425/149; 425/225; 425/382.2; 425/464 |
Current CPC
Class: |
D01D 5/00 20130101; D01D
5/06 20130101; D01F 4/00 20130101; D01D 4/02 20130101; D01D 5/0069
20130101 |
Class at
Publication: |
425/143 ;
425/149; 425/382.2; 425/464; 425/225 |
International
Class: |
D01D 004/08; D01D
005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 1999 |
GB |
9927950.7 |
Claims
What is claimed is:
1. Extrusion apparatus comprising at least one first reservoir
fluidly connected at a first end to a first opening of a plurality
of regulatory modules having passages, through which material is
extrudable, wherein the extrusion apparatus has at least 1,000
passages per square meter cross-section.
2. Extrusion apparatus according to claim 1, wherein the extrusion
apparatus is a spinning apparatus.
3. Extrusion apparatus according to claim 2 wherein said apparatus
is an electrospinning apparatus.
4. Extrusion apparatus according to claim 1, wherein said passages
are tubular.
5. Extrusion apparatus according to claim 1, wherein at least one
second reservoir is connected to the plurality of regulatory
modules
6. Extrusion apparatus according to claim 5, wherein the second
reservoir is fluidly connected to at least one opening in at least
one of the passages.
7. Extrusion apparatus according to claim 1, further comprising one
or more sensors.
8. Extrusion apparatus according to claim 7, comprising at least
one sensor selected from the following group of sensors: pressure
sensors, temperature sensors, thermal conductivity sensors, thermal
absorption sensors, molecular size sensors, viscosity sensors,
rheology sensors, anisotropy sensors, mechanical modulus sensors,
mechanical toughness sensors, ultrasound sensors, chemical sensors,
pH sensors, electrical conductivity sensors, light-absorption
sensors, refractive index sensors, sensors for measuring
light-scattering, morphological sensors, infra-red absorption
sensors and rapid Fourier Transform Infra Red sensors.
9. Extrusion apparatus according to claim 7, wherein one or more of
said regulatory modules comprise at least one sensor.
10. Extrusion apparatus according to claim 9, wherein said sensor
is integral to said one or more of said regulatory modules.
11. Extrusion apparatus according to claim 1, wherein the
regulatory modules additionally comprise one or more pumps.
12. Extrusion apparatus according to claim 11, wherein said one or
more pumps comprise a pump selected from the group of pumps
consisting of piezo-electric pumps, peristaltic pumps and vibration
pumps.
13. Extrusion apparatus according to claim 1, wherein said passages
further comprise flow inlets.
14. Extrusion apparatus according to claim 13, said one or more
flow inlets comprise at least one concentrically arranged flow
inlet.
15. Extrusion apparatus according to claim 1, wherein at least part
of one wall of each of said passages is permeable.
16. Extrusion apparatus according to claim 1, wherein at least part
of one wall of each of said passages is semipermeable.
17. Extrusion apparatus according to claim 1, wherein the
regulatory modules are at least partly formed by injection
molding.
18. Extrusion apparatus according to claim 1, wherein the
regulatory modules are at least partly formed by ablasion.
19. Extrusion apparatus according to claim 1, wherein the
regulatory modules are at least partly formed by a lost wax
process.
20. Extrusion apparatus according to claim 1, wherein, in
operation, said material is drawn down within the individual
passages at a first distance that is at least 0.05 mm from an outer
exit opening.
21. Extrusion apparatus according to claim 20, wherein said first
distance is at least 0.5 mm from an outer exit opening.
22. Extrusion apparatus according to claim 1, wherein a component
of said material in an initial zone of one of the said passages
forms rod-shaped units that are substantially perpendicular to at
least one wall of said one of the passages.
23. Extrusion apparatus according to claim 1, wherein a component
of said material in a subsequent zone of one of the said passages
has rod-shaped units which tumble as said material flows within the
one of the said passages.
24. Extrusion apparatus according to claim 1, further comprising a
ridged surface having a plurality of ridges on at least one wall of
one of the passages.
25. Extrusion apparatus according to claim 24, wherein the height
of the ridges is less than 10% of the broadest cross-sectional
dimension of said one of the passages.
26. Extrusion apparatus according to claim 24, wherein the surface
energy of the ridged surface is lower than the surface energy of
said material.
27. Extrusion apparatus according to claim 24, wherein said ridges
are substantially oriented along a long axis of said one of the
passages.
28. Extrusion apparatus according to claim 24, wherein said ridges
comprise hydrophobic material.
29. Extrusion apparatus according to claim 24, wherein said ridges
are coated with hydrophobic material.
30. Extrusion apparatus according to claim 24, wherein, in
operation, said material is drawn down substantially adjacent to
the ridged surface.
31. Extrusion apparatus according to claim 1, wherein said material
is a liquid crystalline polymer.
32. Extrusion apparatus according to claim 1, further comprising
cleaning apparatus.
33. Extrusion apparatus according to claim 32, wherein said
cleaning apparatus comprises a permeable wall of the passage,
through which cleaning agents are introduced.
34. Extrusion apparatus according to claim 33, wherein the cleaning
agents are alkaline fluids.
35. Extrusion apparatus according to claim 1, wherein said first
reservoir is capable of containing a dope that provides material to
be extruded.
36. Extrusion apparatus according to claim 35, wherein said dope
comprises a protein solution.
37. Extrusion apparatus according to claim 36, wherein the protein
of said protein solution is selected from the following group: (a)
recombinant spider silk proteins; (b) analogs of recombinant spider
silk proteins; (c) recombinant silk-worm silk proteins; (d) analogs
of recombinant silk-worm silk proteins; (e) regenerated silk
solution from silk-worm silk; and (f) mixtures of (a) to (e).
38. Extrusion apparatus according to claim 37, wherein said dope in
said first reservoir is stored in said first reservoir at a pH
value above the gelling pH of said protein.
39. Extrusion apparatus according to claim 7, further comprising a
microprocessor connected to said sensor.
40. Extrusion apparatus according to claim 39, wherein the
microprocessor has an output for sending signals to regulate at
least one parameter of the extrusion apparatus.
41. Extrusion apparatus according to claim 39, wherein said
microprocessor is integral to the plurality regulatory modules.
42. Extrusion apparatus according to claim 1, wherein said
apparatus is produced by a process comprising the following steps:
(a) covering an electrically-conductive base plate with a layer of
resist; (b) forming a resist pattern in the resist by means
selected from lithographic processes and radiation ablation
processes; (c) placing a layer of metal over the resist pattern
using an electroformation means; (d) removing said base plate and
dissolving the remaining resist pattern to produce a mold insert;
and (e) filling the mold insert with plastic molding compound to
mold the extrusion apparatus.
43. Object formed from the material extruded by the extrusion
apparatus according to claim 1.
Description
PRIORITY APPLICATION
[0001] The present application is a continuation-in-part of
co-pending U.S. patent application Ser. No. 10/148,101 filed May
22, 2002 which is a .sctn.371 filing of International Patent
Application No. PCT/GB00/04489, which was filed on Nov. 24, 2000,
which claims priority to U.K. Patent Application No. 9927950.7,
which was filed on Nov. 27, 1999. Each of the foregoing
applications is hereby incorporated by reference.
TECHNICAL FIELD
[0002] This invention relates to an apparatus and method for
forming extruded material, such as filaments, fibers, ribbons,
sheets or other solid products, from a liquid solution, such as a
polymer solution (which term includes a protein solution or
cellulose solution).
BACKGROUND ART
[0003] Methods of producing filaments or fibers have been known in
the art for a long time. For example, spinning techniques are used
to produce fibers from polymer solutions. British patent
specification GB-A-441 440 (Ziegner, 1936) discloses one technique
in which filaments are produced by passing a liquid raw material to
be solidified through a rigid, highly porous porcelain tube. The
filaments emerge from the end of the porous porcelain tube in this
disclosure. An operative fluid medium is introduced into the porous
porcelain tube by being passed through the pores of the tube under
relatively high pressure. However, this document fails to teach
treatment of the liquid by passage of material through a
semipermeable and/or porous membrane, or through a passage having
flexible walls.
[0004] U.S. Pat. No. 2,450,457 (Te Grotenhuis, 1948) discloses a
process and apparatus for coagulating a coagulable fluid, which is
fed into a forming chamber of a die. The forming chamber walls are
of a material that is completely porous, such as unglazed porcelain
or microporous rubber, and which contains within its pores an
electrolyte so that the walls conduct an electric current that
heat-coagulates a spinning solution. This document fails to teach
both the passing of a liquid raw material to be solidified through
a passage having flexible walls, and the treatment of a spinning
solution with components passing through semipermeable and/or
porous walls of a forming chamber.
[0005] There is currently considerable interest in the development
of improved processes and apparatus to enable the manufacture of
polymer filaments, fibers, ribbons or sheets. It is theoretically
possible to obtain materials with high tensile strength and
toughness by engineering the orientation of the polymer molecules
and the way in which they interact with one another. Cheng et al,
in "Characteristics and Design Procedure of Hyperbolic Dies" (J
Polymer Sci, B: Polymer Phys, 30:557-561 (1992)) discuss the design
of hyperbolic dies in general, without teaching the passing of
spinning material through a tubular passage having walls of a
semipermeable and/or porous membrane.
[0006] Strong, tough filaments, fibers or ribbons are useful in
their own right for the manufacture, for example, of sutures,
threads, cords, ropes, wound or woven materials. They can also be
incorporated into a matrix with or without other filler particles
to produce tough and resilient composite materials. Sheets, whether
formed from fibers or ribbons, can be stuck together to form tough
laminated composites.
[0007] Natural silks are fine, lustrous filaments produced by the
silk-worm Bombyx mori and other invertebrate species. They offer
advantages compared with the synthetic polymers currently used for
the manufacture of materials. The tensile strength and toughness of
the dragline silks of certain spiders can exceed that of
Kevlar.TM., the toughest and strongest man-made fiber. Spider
dragline silks also possess high thermal stability. Many silks are
also biodegradable and do not persist in the environment. They are
recyclable and are produced by a highly efficient low pressure and
low temperature process using only water as a solvent. The natural
spinning process is remarkable in that an aqueous solution of
protein is concerted into a tough and highly insoluble
material.
[0008] According to an article by J. Magoshi, Y. Magoshi, M. A.
Becker and S. Nakamura entitled "Biospinning (Silk Fiber Formation,
Multiple Spinning Mechanisms)" published in Polymeric Materials
Encyclopedia, by the Chemical Rubber Company, it is reported that
natural silks are produced by sophisticated spinning techniques
which cannot yet be duplicated by man-made spinning
technologies.
[0009] Fibers produced by existing technological processes and
apparatus suffer from the following disadvantages. Many show "die
swell" which leads to some loss of molecular orientation with a
consequent degradation of mechanical properties. Furthermore,
existing processes are not energy efficient, requiring high
temperatures and pressures to reduce the viscosity of the feedstock
so that it can be forced through a die. Separate stages are often
required, for example for further "draw-down", to anneal the fiber
with heat, and to process it through separate acid or alkaline
treatment baths.
[0010] One example of an improved method for producing fibers is
known from European Patent Application EP-A-0 656 433 (Filtration
Systems, Inc. and Japan Steel Works, Ltd.) which teaches a nozzle
plate with a plurality of spinning holes. This document fails,
however, to address the problem of die swell which occurs when the
spun fiber or filament emerges from the exit of the nozzle
plate.
[0011] A system for producing a multi-ingredient composite fiber is
known from European patent application EP-A-0 104 081 (Toray
Industries). This application discloses a spinneret assembly for
producing "island-in-sea" type fibers using multiple feedstocks.
The spinneret assembly can have more than one nozzle for
concurrently producing more than one fiber. This document fails,
however, to teach the size of the fibers and the dimensions of the
apparatus.
SUMMARY OF THE INVENTION
[0012] There remains a need to rapidly produce a large number of
high-strength fibers.
[0013] These and other objects of the invention are solved by
providing an extrusion apparatus with at least one first reservoir
fluidly connected at a first end to a first opening of a plurality
of regulatory modules having passages, through which material is
extrudable. The extrusion apparatus has at least 1,000 passages per
square metre cross-section. Using this apparatus a large number of
fibers can be rapidly produced. The passages can be, for example,
tubular or ribbon-shaped. The extrusion apparatus can be, or can be
incorporated into, a spinning apparatus or an electrospinning
apparatus.
[0014] In one advantageous embodiment of the extrusion apparatus at
least one second reservoir is connected to the plurality of
regulatory modules, preferably through at least one opening in at
least one of the passages. The use of a second reservoir allows a
multi-component fiber to be produced.
[0015] Preferably, the extrusion apparatus further comprises one or
more sensors, such as pressure sensors, temperature sensors,
thermal conductivity sensors, thermal absorption sensors, molecular
size sensors, viscosity sensors, rheology sensors, anisotropy
sensors, mechanical modulus sensors, mechanical toughness sensors,
ultrasound sensors, chemical sensors, pH sensors, electrical
conductivity sensors, light-absorption sensors, refractive index
sensors, sensors for measuring light-scattering, morphological
sensors, infra-red absorption sensors and/or rapid Fourier
Transform Infra Red sensors. These sensors measure the parameters
of the extrusion process and allow rapid adjustment of the
extrusion conditions, if required. Preferably one or more of the
regulatory modules comprise these sensors and more preferably the
sensors are integral to the one or more regulatory modules. In this
latter embodiment, the sensors are not constructed as separate
entities, but are formed as part of the regulatory modules.
[0016] The extrusion apparatus comprising one or more sensors
preferably comprises a microprocessor connected to at least one of
the sensors, the microprocessor preferably having an output for
sending signals to regulate at least one parameter of the extrusion
apparatus. The microprocessor is preferably integral to the
plurality of regulatory modules.
[0017] The extrusion apparatus can also have pumps in the
regulatory modules for pumping feedstocks through the extrusion
apparatus. Such pumps can be Piero-electric, peristaltic, vibration
pumps or other known pumps.
[0018] The passages may have flow inlets. These flow inlets allow
the addition of further material to the feedstock during the
extrusion process. Such further material could include dopants
which alter the properties of the final extruded material. The
further material can also modify the extrusion process in
advantageous manner. One or more flow inlets may be concentrically
arranged, allowing for co-extrusion of a polymer mixture or for
coating of the extrusion.
[0019] In one aspect of the invention, the interior walls of the
tubular passages are made of a permeable material. This allows
further material to diffuse through the interior walls to be
incorporated into the final extruded materials. The regulatory
modules can be made, for example, by injection molding, laser
ablation, or a lost wax process.
[0020] In order to avoid problems of die swell, which may lead to a
reduction of mechanical strength of the application in operation
the material is drawn down at a first distance at least 0.05 mm
from an outer exit opening within the tubular passages, and
preferably 0.5 mm from such outer exit opening.
[0021] Internal draw-down is aided by providing a ridged surface on
the internal surface of at least one of the tubular passages. The
height of the ridges on the ridged surface are typically less than
10% of the broadest cross-sectional dimension of the tubular
passage. The ridges on the ridged surface are substantially
continuous and are substantially oriented parallel to the long axis
of the tubular passages. Preferably the ridges are constructed
from, at least in part, a hydrophobic material, or they at least
partially coated with a hydrophobic material. The surface energy of
the ridged surface is preferably lower than the surface energy of
the extrudable material, the material preferably being drawn down
adjacent to the ridged surface.
[0022] The extrusion apparatus may further comprise cleaning
apparatus, which preferably comprises a permeable wall of the
passage, through which cleaning agents, such as alkaline fluids,
are introduced.
[0023] The first reservoir of the extrusion apparatus is preferably
capable of containing a dope that provides material to be extruded,
said material preferably being a liquid crystalline polymer, and
preferably comprising a protein solution. Storage of a dope
comprising a protein solution in the first reservoir is preferably
at a pH value above the gelling point of the protein. Preferred
protein solutions which the dope may comprise are recombinant
spider silk proteins and their analogs, recombinant silk-worm
proteins and their analogs, regenerated silk from silk-worm silk,
and mixtures of these protein solutions.
[0024] A component of the material in an initial zone of one or
more of the passages preferably forms rod-shaped units that are
substantially perpendicular to at least one wall of one of the
passages, and these rod-shaped units may tumble in a subsequent
zone of one of the passages as the material flows within the
passage.
[0025] The extrusion apparatus of the invention is preferably
produced by a process comprising covering an
electrically-conductive base-plate with a layer of resist, forming
a resist pattern in the resist by means selected from lithographic
processes and radiation ablation processes, placing a layer of
metal over the resist pattern using an electroformation means,
removing the base-plate and dissolving the remaining resist pattern
to produce a mold insert, and filling the mold insert with plastic
molding compound to mold the extrusion apparatus.
DESCRIPTION OF THE FIGURES
[0026] FIG. 1 is a generalized schematic representation of
apparatus for the formation of extruded materials form a spinning
solution;
[0027] FIG. 2 is a schematic cross-sectional view along the
longitudinal axis of a die assembly of the apparatus shown in FIG.
1;
[0028] FIG. 3 is a schematic perspective view of the die assembly
shown in FIG. 2;
[0029] FIG. 4 is a schematic exploded view illustrating another
embodiment of a die assembly of apparatus according to the
invention; and
[0030] FIG. 5 is a view showing a number of die assemblies of FIG.
4 assembled together in a unit to enable a plurality of fibers to
be extruded.
[0031] FIG. 6 is a view illustrating tumbling of rod-shaped
elements in the tubular passage.
[0032] FIG. 7 is a cross-sectional view of the tubular passage.
DETAILED DESCRIPTION OF THE INVENTION
[0033] The discovery of the way in which spiders produce dragline
silk provides the basis for the invention. We have found that by
making the walls of the or each tubular passage at least partly
permeable or porous, preferably selectively permeable along the
length of the tubular passage, which is preferably tapered, it is
possible to control properties such as the pH, water content, ionic
composition and shear regime of the spinning solution in different
regions of the tubular passage of the die. Ideally this enables the
phase diagram of the spinning solution to be controlled allowing
for pre-orientation of the fiber-forming molecules followed by a
shear-induced phase separation and allowing the formation of
insoluble fibers containing well-orientated fiber, forming
molecules.
[0034] Conveniently the walls defining the tubular passage(s) are
surrounded by said enclosure means to provide one or more
compartments. These compartments act as jackets around the tubular
passage(s). The or each tubular passage suitably has an inlet at
one end to receive the spinning solution and an outlet at the other
for the formed or extruded material and is typically divided into
three parts arranged consecutively, the first part or initial zone
allowing for the pre-treatment and pre-orientation of the
fiber-forming polymer molecules in the liquid feedstock prior to
forming the material by draw down, the second region or subsequent
zone in which draw down of the "thread" takes place and which
functions as a treatment and coating bath, and the third part or
final zone has an outlet or opening of restricted cross-section
which serves to prevent the loss of the contents of the "treatment
bath" with the emerging fiber and to provide for the commencement
of an optional air drawing stage.
[0035] It will be appreciated that any solution or solvent or other
phase or phases surrounding the fiber in the second part of the or
each tubular passage also serves to lubricate the fiber as it moves
through and out of the tubular passage.
[0036] In a further aspect of the invention, the walls of the or
each tubular passage may contain flow inlets through which further
material can be introduced into the tubular passage. The further
material can either alter the conditions under which the extrusion
process is performed or can be incorporated as dopant in the final
extruded material.
[0037] In an embodiment of the invention, an opening into and
surrounding the first zone or second zone of the tubular passage
allows the introduction of a coating onto the surface of the fiber
or extruded material. One or more concentrically arranged flow
inlets allow for co-extrusion of polymer mixtures or for coating
the material to be extruded.
[0038] All or part of the length of each tubular passage typically
has a convergent geometry typically with the diameter decreasing in
a substantially hyperbolic fashion. According to G. Y. Chen, J. A.
Cuculo and P. A. Tucker in an article entitled "Characteristic and
Design Procedure of Hyperbolic Dies" in the Journal of Polymer
Sciences: Part B: Polymer Physics, Vol 30, 557-561 in 1992, it is
reported that the orientation of molecules in a fiber can be
improved by using a die with a convergent hyperbolic geometry
instead of the more usual parallel capillary or conical dies.
[0039] The geometry of substantially all or part of the or each
tubular passage may be varied to optimize the rate of elongational
flow in the spinning solution (dope) and to vary the
cross-sectional shape of the formed material produced from it. The
preferred substantially hyperbolic taper for part or all of the or
each tubular passage maintains a slow and substantially constant
elongational flow rate thus preventing unwanted disorientation of
the fiber-forming molecules resulting from variation in the
elongational flow rate or from premature formation of insoluble
material before the dope has been appropriately reoriented. A
convergent taper to the tubular passage of the die will induce
elongational flow which will tend to induce a substantially axial
alignment in the fiber-forming molecules, short fibers or filler
particles contained in the dope by exploiting the well known
principle of elongational flow. Alternatively, the principle of
elongational flow through a divergent part of a die instead of the
convergent die can be used to induce orientation in the hoop
direction that is substantially transverse to the direction of flow
through the divergent part of the die.
[0040] The diameter of the or each tubular passage may be varied to
produce fibers of the desired diameter. In the embodiment of the
invention disclosed herewith, the diameter of the or each tubular
passage has to be chosen such that at least 1000 fibers are
produced per square meter.
[0041] The rheology of the liquid feedstock in the tubular passage
of the die is largely independent of scale, thus enabling the size
of the apparatus to be scaled up or down. The convergence of the
tubular passage allows a wide range of drawing rates to be used
typically ranging from 0.01 to 1000 mm sec.sup.-1. If fibers are
being extruded they may typically have a diameter of from 0.1 to
100 .mu.m. Typically the outlet of the tubular passage has a
diameter of from 1 to 100 .mu.m with the diameter of the inlet of
the tubular passage being from 25 to 150 times greater depending on
the extensional flow it is desired to produce. Tubular passages of
alternative cross-sectional shapes can be used to produce fibers,
flat ribbons or sheets of extruded materials with other
cross-sectional shapes.
[0042] All or part or parts of the walls of the or each tubular
passage of the die assembly are constructed from or formed or
molded from selectively permeable and/or porous material, such as
cellulose acetate-based membrane sheets. The membrane can be
substituted with diethylaminoethyl or carboxyl or carboxymethyl
groups to help maintain protein-containing dopes in a state
suitable for spinning. The membrane can also be rendered
substantially hydrophobic with a siliconizing or silanizing
solution or with polytetrafluoroethylene particles. Other examples
of permeable and/or porous material are hollow-fiber membranes,
such as hollow fibers constructed from polysulfone,
polyethyleneoxide-polysulfone blends, silicone or
polyacrylonitrile. The exclusion limit selected for the
semipermeable membrane will depend on the size of the small
molecular weight constituents of the dope but is typically less
than 12 kDa.
[0043] All or part of the walls of the or each tubular passage can
be constructed from selectively permeable and/or porous material in
a number of different ways. By way of example only a selectively
permeable and/or porous sheet can be held in place over a groove
with suitable geometry cut into a piece of material to form the
tubular passage. Alternatively two sheets of selectively permeable
and/or porous material can be held in place on either side of a
separator to construct the tubular passage. Alternatively a single
sheet can be bent round to form a tubular passage. A hollow tube of
selectively permeable and/or porous material can also be used to
construct all or part of the tubular passage. By way of example
only, a variety of methods are available to shape the tube into a
die as is commonly known to a craftsman skilled in the art.
[0044] The interior walls may furthermore be substantially smooth
or may be provided with "ridges" or bumps on at least part of the
wall. The presence of such modifications in the walls aids in the
draw-down process. Such ridges or bumps are typically less than 10%
of the diameter of the tubular passage.
[0045] The use of selectively permeable and/or porous walls of
substantially all or part or parts of the tubular passage(s)
enables the proper control within desired limits of, for example,
the concentration of fiber-forming material; solute composition;
ionic composition; pH; dielectric properties; osmotic potential and
other physico chemical properties of the dope within the tubular
passage by applying the well-known principles of dialysis, reverse
dialysis, ultrafiltration and pre-evaporation. Electro-osmosis can
also be used to control the composition of the dope within the
tubular passage. It will be appreciated that a control mechanism
receiving inputs relating to the product being formed, for example
the diameter of the extruded product and/or the resistance
countered in the tubular passage, such as during extrusion through
the outlet of the tubular passage, can be used to control, for
example, polymer concentration, solute composition, ionic
composition, pH, dielectric properties, osmotic potential and/or
other physicochemical properties of the dope within the tubular
passage.
[0046] The selective permeability and/or porosity of the walls of
the or each tubular passage may also allow for the diffusion
through the walls of further substances into the tubular passage(s)
provided that these have a molecular weight lower than the
exclusion limit of the selectively permeable material from which
the walls of the tubular passage(s) are constructed. By way of
example only the additional substances added to the dope in this
manner may include surfactants; dopants; coating agents;
cross-linking agents; hardeners; and plasticizers. Larger sized
aggregates can be passed through the walls of the tubular passage
if it is porous rather than being simply semipermeable.
[0047] The compartments surrounding the walls of the tubular
passage or passages may act as one or more treatment zones or baths
for conditioning the fiber as it passes through the tubular
passage(s). Additional treatment can occur after the material has
exited the outlet of the tubular passage.
[0048] One or more regions of the or each tubular passage may be
surrounded by one or more compartments arranged consecutively so as
to act as a jacket or jackets to hold solution, solvent, gas or
vapour in contact with the outer surface of the selectively
permeable walls of the tubular passage(s). Typically solution,
solvent, gar or vapour is circulated through the compartment or
compartments. The walls of the compartment or compartments are
sealed to the outer surface of the wall or walls of the tubular
passage(s) by methods that will be understood by a person skilled
in the art. The compartment or compartments serve to control the
chemical and physical conditions within the or each tubular
passage. Thus the compartments surrounding the tubular passage(s)
serve to define the correct processing conditions within the dope
at any point along the tubular passage(s). In this way parameters
such as the temperature; hydrostatic pressure; concentration of
fiber-forming material; pH; solute; ionic composition; dielectric
constant; osmolarity or other physical or chemical parameter can be
controlled in different regions of the tubular passage as the dope
moves down the length of the die. By way of example only,
continuously graded or stepped changes in the processing
environment can be obtained.
[0049] Conveniently a selectively permeable/porous membrane can be
used to treat one side of a forming extrusion in a different way to
the other side. This can be used, for example, to coat the
extrusion or remove solvent from it asymmetrically in such a way
that the extrusion can be made to curl or twist.
[0050] Sensors can be included in the tubular passage in order to
measure parameters such as pressure, temperature, thermal
conductivity, thermal absorption, molecular size, viscosity,
rheology, anisotropy, mechanical modulus, mechanical toughness,
ultrasound, chemical composition, pH, electrical conductivity,
light-absorption, refractive index, light-scattering, morphology,
surface topography, and/or infra-red absorption. Additional
radiation absorption sensors may be used, and the sensor results
may be further processed as in, for example, Fourier Transform
Infra Red (FTIR) spectroscopic analysis. SAMMS thermal analysis may
be used to screen for thermal properties to determine, inter alia,
the transition temperature of a polymer in the extrudable material,
and thereby to indicate additional properties of the polymer, such
as its flexible resilience and/or elasticity and whether the
polymer is a glassy brittle plastic, a tough yielding plastic or a
rubber. Measurement of optical properties may provide information
regarding the phase morphology and/or microstructure of a polymer
in the extrudable material: for example, sharp spectral
delineations in optical micrographs of the material may result from
microphase separation, which may also be detected by birefringence
measurements indicating optical anisoptropy, or (for example) by
Theological measurements, electron microscopy or x-ray scattering.
Molecular size distribution may be determined by a variety of
methods, including amongst others, gel permeation chromatography.
Rapid, high-throughput and/or microscopic variants of each of the
analytical techniques known to those of skill in the art may be
incorporated in the employment of the sensors and analysis of the
data obtained from them.
[0051] Properties that may be screened for by means of such sensors
include, but are not limited to, the following. Electrical
properties may comprise, inter alia, conductivity, dielectric
constant, dialectric strength, stability under bias, polarization
and/or piezoelectricity. Thermal properties may comprise, inter
alia, thermal conductivity, vapor pressure, and/or thermal
absorption. Mechanical properties may comprise, inter alia, stress,
anisotropy, adhesion, hardness, density, ductility, elasticity or
porosity. Morphological properties may comprise, inter alia,
crystallinity, liquid-crystallinity, microstructural
characteristics, surface topography and/or crystallite orientation.
Optical properties may comprise, inter alia, refraction, light
scattering absorption, fluorescence, birefringence, spectral
characteristics of absorption and/or fluorescence, dispersion,
circular dichroism, polarization and/or frequency modulation.
Chemical properties may comprise, inter alia, composition, content
and/or composition of impurities, acidity-basicity, reactivity,
catalysis, corrosion resistance and/or erosion resistance. Both the
absolute value of the property may be evaluated, and its variance
over time, or between one part of the apparatus and another (for
example, before and after the anticipated draw-down location in one
or more of the passages).
[0052] Using the results of the sensors, the process parameters of
the extrusion process can be dynamically altered. An example of the
employment of such sensors includes the use of light-scattering
sensors to detect the presence, size and distribution of particles
within the dope and, with appropriate software, to determine
whether the dope is in a sol or gel state. Further examples include
high-throughput Theological analysis for determination of
viscosity,
[0053] All or part of the draw down process may typically occur
within the tubular passage of the die rather than at the outer face
of the die assembly as occurs in existing spinning apparatus. The
former arrangement offers advantage over existing spinning
apparatus. The distortion of molecular alignment due to die swell
is avoided. The region of the die assembly after the internal
commencement of the draw down taper can be used to apply coatings
or treatments to the extrusion. Further, the last part of the die
assembly is water lubricated by the solvent-rich phase surrounding
the extrusion.
[0054] By way of example only the apparatus can be used for forming
fibers from dopes containing solutions of recombinant spider silk
proteins or analogues or recombinant silk-worm silk proteins or
analogues or mixtures of such proteins or protein analogues or
regenerated silk solution from silk-worm silk. When these dopes are
used it is necessary to store the dope at a pH above a critical
value to prevent the premature formation of insoluble material. It
will be appreciated that other constituents may be added to the
dope to keep the proteins or protein analogues in solution. These
constituents may then be removed through the semipermeable and/or
porous walls when the dope has reached the appropriate portion of
the tubular passage in which it is desired to induce the transition
from liquid dope to solid product, e.g. thread or fiber. The dope
within the tubular passage can then be brought by dialysis against
an appropriate acid or base or buffer solution to a pH value at or
close to the critical value to induce the aggregation or
conformation change in one or more of the constituent proteins of
the dope. Such a pH change will promote the formation of an
insoluble material. A volatile base or acid or buffer can also be
diffused through the walls of the or each tubular passage from a
vapour phase in the surrounding compartment or jacket to adjust the
pH of the dope to the desired value. Vapour phase treatment to
adjust the pH can also occur after the extruded material has left
the outlet of the die assembly.
[0055] The draw rate and length, wall thickness, geometry and
material composition of the or each tubular passage may be varied
along its length to provide different retention times and treatment
conditions to optimize the process.
[0056] One or more regions of the walls defining the or each
tubular passage can be made impermeable by coating their inner or
outer surfaces with a suitable material to modify the internal
environment in a length of the tubular passage using any coating
method as will be understood by a person skilled in the art.
[0057] The inner surface of the walls of the or each tubular
passage can be coated with suitable materials to reduce the
friction between the walls of the tubular passage and the dope or
fiber. Such a coating can also be used to induce appropriate
interfacial molecular alignment at the walls of the tubular passage
in liquid crystalline polymers when these are included in the
dope.
[0058] A further embodiment allows for one or more additional
components to be fed to the start of the or each tubular passage
via concentric openings (flow inlets) to allow two or more
different dopes to be co-extruded through the same tubular passage
allowing for the formation of one or more coats or layers to the
fiber or fibers.
[0059] A further embodiment utilizes a dope prepared from a phase
separating mixture containing two or more components which, for
example, may be different proteins. The removal or addition of
components through the selectively permeable and/or porous material
can be used to control the phase separation process to produce
droplets of one or more components typically with a diameter of 100
to 1000 nm within the bulk phase in the final extrusion. These can
be used to enhance the toughness and other mechanical properties of
the extrusion. The use of a convergent or divergent die
conveniently induces elongational flow in the droplets to produce
orientated and elongated filler particles or voids within the bulk
phase. A convergent die will orientate and elongate such droplets
in a direction parallel to that of the formed product whereas a
divergent die will tend to orientate the droplets in hoops
transverse to the direction of flow of each particle within the
tubular passage of the dope. Both types of arrangement can be used
to enhance the properties of the formed product. Further it will be
understood that the selectively permeable and/or porous walls of
the or each tubular passage can be used to diffuse in or out
chemicals to initiate the polymerisation of filler particles.
[0060] The extrusion apparatus with one or more tubular passages
surrounded by a compartment or compartments to act as jackets can
be constructed by one or two stage molding or other methods known
to a person skilled in the art. The jackets do not have to
completely surround the tubular passage. The jackets can be of
different shape as appropriate. It will be appreciated that a
molding process can be used to create simple or complex profiles
for the or each tubular passage and the outlet of the die assembly.
Very small flexible lips can be formed, e.g. molded, at the outlet
to prevent the escape of the contents of the treatment bath and act
as a restriction to enable an optional additional air drawing stage
or wet drawing after the material has left the outlet of the die
assembly should this be required. The microscopic profile of the
inner surface of the lips at the outlet can be used to modify the
texture of the surface coating of the extruded material.
[0061] In one embodiment of the invention, the extrusion apparatus
is manufactured using the so-called LIGA process. The principles of
the LIGA process are described in the book "Angewandte
Mikrotechnik. LIGA--Laser--Feinwerktechnik" by Rainer Bruck and
Andreas Schmidt (Herausgeber). Munich: Hanser Fachbuch, 2001.
[0062] In the LIGA prcess, an electrically-conductive base plate is
covered with a layer of resist. The resist is typically a poly
(methyl methacrylate) (termed PMMA) based resist, but may also be a
poly-(lacitde-coglycolide) resist, a polyimide resist or another
suitable resist. A resist pattern is formed in the resist by
lithographic thechniques. The lithographic techniques used include
photolithographic, UV-lithographic or X-ray lithographic process.
The smallest structures are created using synchrotron radiation.
Alternatively, the resist pattern could be formed by laser or
electron ablation.
[0063] A layer of metal, typically nickel, copper, gold, NiFe or
NiP, is subsequently placed over the resist pattern using an
electroformation process. The electrically-conductive base plate is
removed and the remaining resist pattern dissolved to produce a
mold insert. The mold insert is then filled with a plastic molding
compound from which the extrusion apparatus is molded.
[0064] By way of further example only, the jackets and supports for
the tubular passages can also be constructed from two or more
components, by laser ablation or constructed in other ways as will
be understood by a person skilled in the arts. It will be
appreciated that this method of construction is modular and that a
number of such modules can be assembled in parallel to produce
simultaneously a number of fibers or other shaped products. Sheet
materials can be produced by a row or rows of such modules. Such a
modular arrangement allows for the use of manifolds to supply dope
to the inlet of the tubular passage(s) and to supply and remove
processing solvents, solutions, gases or vapours to and from the
jacket or jackets surrounding the tubular passages. Additional
components may be added if desired. Potential modifications to the
arrangements shown will be apparent to persons skilled in the
art.
[0065] Other methods of constructing spinning apparatus in which
the walls of the tubular passages are substantially or partially
constructed from semipermeable and/or porous material or materials
will be known by a person skilled in the art. By way of example
only these include micro-machining techniques, laser ablation
techniques and lithography techniques. In addition it will be
appreciated that walls of the tubular passages substantially or
partially constructed from semipermeable/porous material can be
incorporated into other types of spinning apparatus, such as
electrospinning apparatus.
[0066] The or each tubular passage may be made self-starting and
self-cleaning. It will be appreciated that blockage of spinning
dies during the commercial production of extruded materials is
time-consuming and costly. To overcome this difficulty, the walls
of the tubular passage may be constructed by two or more jackets
arranged in sequence. The pressure in each of these jackets can be
varied independently by methods that will be understood by a
craftsman skilled in the art. Pressure changes in the jackets can
be used to change the diameter of different regions of the tubular
passage in a manner analogous to a peristaltic pump to pump the
dope to the outlet to commence the drawing of fibers or to clear a
blockage. Thus a decrease in pressure in a jacket towards the
outlet end of the tubular passage will dilate the elastic walls of
the tubular passage within the jacket. If the pressure is now
raised in a second jacket closer to the input end of the tubular
passage a region of the walls of the tubular passage running
through this jacket will tend to collapse forcing the dope towards
the outlet. Alternatively, the pressure in the dope fed to the
tubular passage could be increased causing the diameter of the
elastic tubular passage walls to increase. It will be appreciated
that both methods could be used together or consecutively. With
both methods, the elasticity of the passage walls enables the
diameter of the tubular passage to be increased reducing the
resistance to flow. With both methods it is to be noted that
increasing the pressure of the dope will also assist in start up
and in clearing blockages in the tubular passage. It will also be
appreciated by way of example only that the use of rollers such as
are used in peristaltic pumps can be used as an alternative means
of applying pressure to pump dope to the outlet to commence
spinning or to clear a blockage.
[0067] The pressure in the sealed compartments surrounding the
tubular passage(s) may be controlled to define and modify the
geometry of the tubular passage to optimize spinning conditions. It
will be also appreciated that the semipermeable or porous membrane
can be used to introduce agents to help clean blocked dies. Such
agents include ammonia vapour or solutions, including-dilute
solutions, of alkalis or alkaline buffers.
[0068] If the or each tubular passage has a convergent or divergent
geometry along all or part of its length, filler particles or short
fibers included in the dope may be orientated as they flow through
the tubular passage by exploiting the well understood principle of
elongational flow. It will be understood that the substantially
axial orientation of such filler particles or short fibers will be
produced by a convergent tubular passage while a divergent one will
produce orientation in the hoop direction that is approximately
transverse to the long axis of the extruded material. Both patterns
of orientation confer additional useful properties on the fiber. It
will be appreciated that a convergent or divergent geometry of all
or part of the or each tubular passage will also serve to elongate
and orientate small fluid droplets of an additional solvent or
solution or other phase or phases or additional unpolymerized
polymer or polymers present in the dope as supplied to the tubular
passage or arising by a process of phase separation within the
dope. The presence of elongated and well orientated narrow
inclusions formed by either a convergent or divergent tubular
passage can be used to confer additional useful properties to the
extruded material.
[0069] The apparatus my be arranged in such a way that two or more
fibers are formed in parallel and twisted around each other or
crimped or wound onto a former or coated or left uncoated as
desired. The fibers can be drawn through a coating bath and
subsequently through a convergent die to give rise to a "sea and
island" composite material as will be understood by a person
skilled in the art. One or more rows of dies or one or more dies
with slit or annular opening can be used to form sheet
materials.
BEST MODE FOR CARRYING OUT THE INVENTION
[0070] FIG. 1 shows a schematic apparatus for the formation of
extruded materials from a extrusion solution such as liquid
crystalline polymer or other polymers or polymer mixtures. The
apparatus comprises a dope reservoir 1 containing dope 25; a
pressure regulating valve or pump means 2 which maintains a
constant output pressure under normal operating conditions; a
connecting pipe 3; and a spinning die assembly 4 comprising at
least one spinning tube or die further described in FIGS. 2 to 5. A
take-up drum 5 of any known construction draws out at a draw rate
and reels up extruded material at a constant uptake tension exiting
from the outlet of the die assembly 3. The pressure regulating
valve or pump means 2 may be any device normally producing a
constant pressure commonly known to a person skilled in the
art.
[0071] The arrangement shown in FIG. 1 is purely exemplary and
additional components to the arrangement shown in FIG. 1 will be
apparent to persons skilled in the art. In use dope 25 is passed
from the feedstock reservoir 1 at a constant low pressure by means
of the regulating valve or pump means 2 via the connecting pipe 3
to the inlet of the spinning die assembly 4.
[0072] The apparatus may further comprise one or more sensors,
shown schematically at 70. The one or more sensors 70 are connected
to a microprocessor 75 which receives the output from the one or
more sensors 70. The sensors 70 are preferably integral to the die
assembly 4, i.e. they are constructed at the same time and in the
same manufacturing step. An output of the microprocessor 75 can be
used to regulate the parameters of the extrusion process such as
the extrusion rate, uptake tension draw rate and pH. It will be
furthermore understood that components of the microprocessor 75 can
be made integral to the apparatus. In particular the components can
be fabricated with the other parts of the apparatus.
[0073] The die assembly 4 is shown in greater detail in FIGS. 2 and
3 and comprises a first spinning tube or die 8 upstream of a second
spinning tube or die 12, the dies together defining a tubular
passage 17 for spinning solution 25 through thee die assembly 4.
The die 12 has an interior wall 18 and is divided into an initial
zone 60 and a subsequent zone 62. The dies 8 and 12 are made of
semipermeable and/or porous material, such as cellulose acetate
membranes or sheets. Other examples of suitable semipermeable
and/or porous materials are diethylaminoethyl or carboxyl or
carboxymethyl groups which help to maintain protein-containing
dopes in a state suitable for spinning. Hollow-fiber membranes
material, such hollow-fiber membranes being made from polysulfone,
polythyleneoyide-polysulfone blends, silicone or polyacrylonitrile
can also be used. The exclusion limit selected for the
semipermeable membrane will depend on the size of the small
molecular weight constituents of the spinning dope 25 but is
typically less than 12 kDa.
[0074] The die 8 is held at its upstream end by a tapered adaptor 6
positioned at the inlet end of the die assembly 4 and at its
downstream end by a tapered adaptor 7 positioned internally in the
die assembly 4. The die 8 is held at its upstream end by the
adaptor 7 and at its downstream end by a spigot 13 at the outlet of
the die assembly 4. The die 8 has a convergent, preferably
hyperbolic, internal passage and the geometrical taper is
preferably continued with the internal passage of the die 12. This
can be achieved during construction by softening a semipermeable
tube or die an a warmed suitably tapered mandrel, or by other
methods as will be appreciated by a craftsman skilled in the art
before fitting the spinning tube or die into the apparatus. The
internal passages of the dies 8 and 12 together provide the tubular
passage 17 for spinning solution from the inlet to the outlet of
the die assembly 4.
[0075] A jacket 9 surrounds the die 8 and may contain a fluid, e.g.
a solvent, solution, gas or vapour to control the processing
conditions within the spinning tube or die 8. The jacket 9 is
fitted with an inlet 10 and an outlet 11 to control flow of fluid
into and out of the jacket. A further jacket 14 surrounds the tube
or die 12 and is fitted with a fluid inlet 15 and a fluid outlet 16
to enable fluid, e.g. solvent, solution or gas, to be passed into
and out of the jacket 14 in contact with the semipermeable/porous
walls of the die 12.
[0076] As an alternative to the die 8 shown having semipermeable
walls, a die 8 may be constructed from material which is not
semipermeable or porous but which is preferably tapered, e.g.
convergently, and may be temperature-controlled by circulation
fluid at a predetermined temperature through the jacket 9.
[0077] In operation spinning solution or dope 25, e.g. a polymer
solution, is fed to the inlet of the die 8, as the dope passes
along the tubular passage 17 it is treated firstly as it passes
through the die 8 and secondly as it passes trough the die 12. The
fluid passing through the jacket 9 may merely serve to heat or
maintain the dope 25 at the correct temperature or provide the
correct external pressure to the walls of the die 8. in this case
it is not essential for the walls of the die to be made of
semipermeable and/or material. The temperature of the dies 8 and 12
for the extrusion of protein-containing dopes 25 should typically
be maintained at a temperature of about 20.degree. C. but spinning
may be carried out at temperatures as low as 2.degree. C. and as
high as 40.degree. C. The temperature of the dies 8 and 12 for the
extrusion of dopes can more generally be as high as 100.degree. C.
providing that the material is not destroyed at this temperature.
The pressure of the fluid, liquid or gas, in the jackets
surrounding the walls of the tubular passage 17 is typically
maintained at a pressure close to that at which the dope 25 is
supplied to the die assembly 4. However the pressure can be
somewhat higher or lower depending on the geometry of the dies and
the strength of the generally flexible semipermeable and/or porous
membrane. "Chemical" treatment of the dope 25 occurs during "draw
down" as the dope 25 passes through the die 12 although chemical
treatment may also occur as the dope 25 passes through the die 8 if
the walls of the latter are at least partly made of semipermeable
material. In FIGS. 2 and 3, the abrupt pulling away of the dope 25
from the walls of the die 12 at 12A indicates the internal draw
down of the "fiber". This occurs at the boundary of the initial
zone 60 and the subsequent zone 62. This is a feature of the
invention as draw down in existing processes always start at the
outer opening 13 of a die (i.e. the extrusion orifice) and not
before. The pulling away of the "fiber" from the die walls at 12A
occurs at a place in the tubular die 12 where the force required to
produce extensional flow to create a new surface just falls below
the force required to flow the dope through the die 12 in contact
with the die walls. This is the position at which the surface
energy of the interior wall 18 becomes lower than the surface
energy of the dope 25. The position of 12A will depend on: the
changing Theological properties of the dope; the rate and force of
drawing; the surface properties of the die 12; the surface
properties of the lining of the die 12; and the properties of the
dope and the aqueous phase surrounding the dope. The position of
12A should be at least 0.05 mm from the outer opening or spigot 13,
and preferably 0.5 mm from the outer opening or spigot 13.
[0078] In one embodiment of the invention, a surface 66 of the
interior wall 18 of the die 12 is provided with ridges 68 to
facilitate the draw down of the fiber at position 12A. This is
shown in FIGS. 6 and 7. These ridges 68 have a height of typically
less than 10% of the diameter of the die 12. Typically the diameter
of the die 12 at this position is 20 .mu.m and the ridges 68 are
0.5 .mu.m high. The ridges 68 could be between 100 nm and 20 .mu.m
high. It is believed that draw-down of the fiber occurs because in
the die 8 and the initial zone 60 of the die 12, rod-shaped units
64 in the dope 25 are arranged substantially perpendicular to the
interior wall 18. At position 12A, these rod-shaped units start to
"tumble" within the dope 25 and thus increase the viscosity and
decrease the surface energy of the dope 25. This produces changes
in the rheology of the dope which, when aided by the presence of
the ridges 68 on the interior wall 18, helps to initiate the
drawing down of the fiber.
[0079] It will be appreciated that the temperature, pH, osmotic
potential, colloid osmotic potential, solute composition, ionic
composition, hydrostatic pressure or other physical or chemical
factors of the solution, solvent gas or vapour supplied to the
jacket(s) control or regulate the conditions inside the tubular
passage 17 and thus the extrusion process as is commonly understood
by a craftsman skilled in the art. Chemicals in the fluid supplied
to the jacket(s) 9 are able to pass through the semipermeable
and/or porous walls of the tubular passage 17 to "treat" the dope
25 passing therethrough. It is also possible for chemicals in the
dope 25 to pass outwardly through the semipermeable and/or porous
walls of the tubular passage 17. The fluids supplied to the dope 17
will obviously depend on the type of dope 25 used and the
semipermeable and/or porous membranes used. However, by way of
example only, for the spinning of concentrated spider major
ampullate gland protein solutions, the jacket 9 may contain 100 mM
Tris or PIPES buffer solution, typically at a pH of 7.4, and 400 mM
sodium chloride to help maintain the folded state of the protein.
The jacket 14 may contain 100 mM ammonium acetate buffer solution
at al lower pH, typically less than 5.0, and 250 mM potassium
chloride to encourage the unfolding/refolding of the protein. High
molecular weight polyethylene glycol can be added to the solution
in both jackets to maintain or reduce the concentration of water in
the dope 25.
[0080] It will be realized that the spinning tube or die 12 can be
hanked or coiled or arranged in other ways between the tapered
collar 7 and the spigot 13. The diameter and cross-sectional shape
or the exit 13 can be varied or adjusted to suit the diameter and
cross sectional shape of the formed material. For a formed product
having a circular cross-sectional, the typical diameter of the
outlet is from 1 to 100 .mu.m and the typical diameter of the inlet
to the tubular passage 17 would be from 25 to 150 times greater
than the outlet diameter depending on the extent of the extensional
flow. It will be appreciated that the arrangements and proportions
shown in FIG. 2 are purely exemplary and thus that additionally
components may be added if desired. Potential modifications to the
arrangements shown in FIG. 2 will be apparent to persons skilled in
the art.
[0081] FIG. 4 shows a module containing three spinning tubes or
dies 12 mounted within a housing defining three "jackets" 14, the
same numbering being used as in the previous embodiments to
identify the same or similar parts. The arrangements and
proportions shown in FIG. 2 are purely exemplary and thus
additional components may be added if desired. Potential
modifications to the arrangements shown in FIG. 4 will be apparent
to persons skilled in the art, including the provision of fewer or
more dies 12 or jackets 14.
[0082] FIG. 5 shows how two or more modular units constructed from
the apparatus shown in FIG. 4 can be held together to enable a
plurality of extruded fibers to be produced. It will be appreciated
that the arrangements and proportions shown in FIG. 5 are purely
exemplary and thus additional components may be added if desired.
Potential modifications to the arrangements shown in FIG. 5 will be
apparent to persons skilled in the art.
[0083] The permeability or porosity of the walls of the tubular
passage may be the same throughout the length of the latter.
Alternatively, however, if the tubular passage 17 passes through
more than one treatment zone the permeability/porosity of the walls
of the tubular passage may change from treatment zone to treatment
zone by using different semipermeable or porous materials for the
walls of the tubular passage. Thus the walls of the tubular passage
17 may comprise: semipermeable material of the same permeability
throughout the length of the tubular passage; semipermeable
material of different permeability for different portions of the
tubular passage; porous material of the same porosity throughout
the length of the tubular passage 17; porous material of different
porosity for different portions of the passage; or semipermeable
material for one or more portions of the length of the tubular
passage and porous material for one or more other portions of the
tubular passage. As mentioned above, some portions of the walls of
the tubular passage may be non-permeable. By way of example only,
suitable semipermeable materials are: cellulose derivatives,
expanded PTFE, polysulfone, polyethylenoxide-polysulfone blends,
and silicone polyacrylonitrile blends. By way of example only, the
suitable porous materials are: polyacrylate, poly
(lactide-co-glycolide), porous PTFE, porous silicon, porous
polyethylene, cellulose derivatives and chitosan.
[0084] It will be appreciated that the apparatus is suitable for
the information of fibers of sheets from all solutions of lyotropic
liquid crystal polymers whether synthetic or man-made or natural or
modified or copolymer mixtures or solutions of recombinant proteins
or analogues derived from them or mixtures of these. By way of
example only these include collagens; certain cellulose
derivatives; spidroins; fibroins; recombinant protein analogues
based on spidroins, or fibroins, and poly (p-phenylene
terephthalates). The method is also suitable for use with other
polymers or polymer mixtures provided that they are dissolved in
solvents, whether aqueous or non-aqueous, protein solutions,
cellulose or chitin solutions. It will also be appreciated that the
use of one or more semipermeable and/or porous treatment zones can
be used for dies or die assemblies having essentially annular or
elongated slit openings used for the formation of sheet
materials.
[0085] Although the present invention has been described in terms
of specific exemplary embodiments, it will be appreciated that
various modifications and alterations might be made by those
skilled in the art without departing from the spirit and scope of
the invention as set forth in the following claims.
* * * * *