Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD FOR FORMING MATERIALS
Related Application and Technical Field
This application is a division of co-pending Canadian
Patent Application No. 2,396,360 filed on November 24, 2000.
The invention described and claimed in the present application
relates to apparatus for the formation of extruded materials
from a solution in particular a solution of silk proteins. A
description of the invention and the drawings included herein
are directed not only to the apparatus and method for forming
extruded materials from a solution, which are the subject of
the present divisional application, but also to the spitting
apparatus for forming spun material from a liquid spinning
solution and the method of forming spun material from liquids
spinning solution which are claimed in the aforementioned co-
pending Canadian Patent Application 2,396,360, of which the
present application is a division.
Background Art
There is currently considerable interest in the
development of processes and apparatus to enable the
manufacture of polymer filaments, fibres, 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. Strong, tough filaments, fibres 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
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or without other filler particles to produce tough and
resilient composite materials. Sheets whether formed from
fibres or ribbons can be stuck together to form tough
laminated composites.
Natural silks are fine, lustrous filaments product the
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 KevlarTM, the toughest
and strongest man-made fibre. 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
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an aqueous solution of protein is converted into a tough and
highly insoluble material.
,w
According to an article by J. Magoshi, Y. Magoshi, M.
A. Be~cker and S . Nakamura entitled "Biospirming (Silk Fiber
Formation, Multiple Spinning Mechanisms)" published in
Polymeric Materials Encyclopedia, by the Chemical Rubber
Company, it is.reported that watural silks are produced by
sophisticated spinning techniques whichcannot yet be
duplicated by man-made spinning technologies.
Fibres 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. This is not seen in natvxal silks which show
strongly uniaxial orientation. 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 fibre with heat, and to 'process
it through separate acid or alkaline treatment baths.
Disclosure of the Invention
I t is an aim of the present invention to provide an
improved method and apparatus for spinning a liquid spinning
solution or "dope".
' According to a first aspect of the invention there is
provided spinning apparatus for forming spun material from
a liquid spinning solution, the apparatus including a die
assembly having, at least one tubular passage through which
the liquid spinning solution is passed, wherein walls
defining the or each tubular passage are formed at least
partly of semigermeable and/or porous material. Preferably
enclosure means suxround the walls. The provision of
enclosure means allows components of fluerit material
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aontained in the enclosure means and-in contact with the
walls to pass through the semipermeable and/or porous
material. Alternatively components of the li quid spinning
solution passing through the or each~tubular passage zaay
pass outwardly through. the walls of semiperzneable and%or
porous material. In addition, since the semipermeable. .
and/or poxous material is generally flexibly, it will be
aecessary to fill the enclosure mesas with a pressurised
fluent material to maintaia the shape of the walls defining
the tubular passage during passage of the-spinning solution
through the tubular passage.
According to a second aspect of the-inveation there
is provided a method of forming material by passing liquid,
spinning solution through at least one tubular passage of a
die assembly, wherein the or each tubular passage has walls.
formed at least partly of semipermeable and/or porous
material and in that the liquid spinning solution is
treated,. as it passes~along the or each tubular passage; by
componex~ts . permeating through the semipermeable and/or
porous material of said walls. In this way fluent material
may passinwardly into, or outwardly from, the or each
tubular passage through their semipermeable and/or porous
wal l s .
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
3 0 control properties 'such as the pH, . water content. ionic
composition and shear regime of the spinning solution is
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 fibre-forming molecules followed by a shear-induced
phase separation and allowing the forutation of insoluble
fibres containing well-orientated fibre-foaming molecules.
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Conveniently the walls defining the tubular
passage (s) are surrounded by said enclosure means to provide
one 'or more compartments . These compartments act as j aekets
around the tubular passage(s). The o= each tubular passage
S 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 allowing for the
pre-treatment and pre-orientation of the fibre-forming
polymer molecules in the liquid feedstock prior to forming
the material by draw down, the second region in -which drav~
.down of the "thread" takes place sad which functions-as a
treatment and coating bath, and the third part has. an outlet
or opening of restricted cross-section which serves to
prevent the loss of the contents of the "treatment bathe
with the emerging fibre and to provide far the commencement
of an optional air drawing stage.
It will be appzeciated that any solution or solvent
or other phase or phases surrounding the fibre in the second
part of the or each tubular passage also serves to lubricate
the f fibre as i t move s through and out o f the tubul ar
passage.
All or part of the length of each tubular passage
typically has a convergent geometry typical ly 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, 557-56I. in 1992, it is reported
that the orientation of molecules in a fibre can be improved
by using a die with a conve=gent hyperbolic geome..try instead
of the store usual parallel capillary or conical dies.
The geometry of substantially , all or part . of the or
each tubular passage may be varied to optimise the rate of
elongational flow in the spinning solution (dope) and to
vary the cross-sectional shape of the formed . material
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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
f low rate . thus preventing- unwanted disorientation of ~ the.
fibre-forming molecules ~ resulting from variation . in the
elongational flow rate or from premature formation of
ixisoluble material before the dope has been appropriately
preoriented. A convergent taper to the tubular passage of
the die will induce. elongatioaal flow which will tend to
induce a substantially axial alignment in the fibre-forming
molecules, short fibres or filler particles contained in the .
dope by exploiting the well known principle o~ elongational
flow. Alternatively,.the principle of elongational flow
through a divergent instead of convergent die can be used to
induce orientation in the hoop direction that is
approximately transverse to the longitudinal axis of the
extruded material.
The diameter of the or each tubular passage may be
varied to produce fibres of the desired diameter.
The Theology of the liquid feedstock in the tubular
passage of the die is largely independent of scale enabling
the site 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 O.Ol to 100 0
nmn ~se'1. 2f fibres are being extruded they may typically
have a diameter of from 0.1 to 100 ~cm. Typically the outlet
of the _ tubular . passage has a diameter of from . 1 to 100 ~.un
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 with a
circular cross-section are used to produce fibres with
circular cross sections. Tubular passages of alternative
cross-sectional shapes can be used to produce fibres, flat
ribbons or sheets of extruded materials with other
cross-sectional shapes.
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6
A31 or part or parts of the. walls of the or each
tubular passage of the die assembly are constructed from or
formed or moulded front selectively permeable and/or' porous
material, such as cellulose acetate-based membrane sheets:
The membrane can be substituted with diethylaminoethyl or
carboxyl ar carboxymethyl groups to help maintain protein
containing dopes in.a state suitable for spinning. other
' examples of pez~aaeable and/or porous material are hollow
fibre membranes, such as 'hollow fibres constructed from
polysulfone. polyethyleneoxide-polysulfone blends. silicone
or polyacrylonitrile. The exclusion limit selected for the
semipermeable membrane will depex~d on the size of the small
molecular-weight constituents of the dope but is typically
less than 12 kDa.
All or part of the walls of the or each tubular
passage can he 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 he7.d in place ~ over a groove with - suitable . geometry cut -
-28 into a piece of material to form the tubular passage.
Alteraatively two sheets of .selectively permeable.aad/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 i s
commonly known to a craftsman skilled is the art.
' The use of selectively permeable and/or porous wall s
of substantially all or part or parts of~ the tubular
passages) enables the proper control within desired limits
of, for example, the concentration of . fibre-forming
material; solute composition; ioi~ic 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
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dialysis, ultrafiltration and preevaporation.
Flectro-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, fox example the
diameter of the extruded product and/or the resistance
countered in the tubular passage, such as during extrusion
t~cough .the outlet of the tubular passages can be used to
control, for example, polymer concentration, solute .
composition, ionic compositions pH, dielectric properties,
osmotic potential and/or other physicochemical properties of
the dope within the tvibular passage.
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
tubule.r passage (s) provided that - these have a molecular
weighty 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 meaner may
include surfactants; dopants; coating agents; cross-linking
agents; hardeners; and plasticisers. Larger sized
aggregates can be passed through the walls of the tubular
passage ~ if it is porous rather than being simply
semipermeable.
The compartments surrounding the walls of the .tubular
passage .or passages may act as one or more treatment zones
or baths for conditioning the fibre as it passes through the
tubular passage (s) . Additional treatment can occur after
the material has exited the outlet of the tubular passage.
One or more regions of the or each tubular passage
may .be surrounded by one or more compartmea,ts arranged
consecutively so as- to act as a j acket or j aclsets to hold
solution, solvent. gas or vapour is contact with the outer .
surface of the selectively pex~tneable walls of the tubular
Passage ( s ) : Typically solution, solvent, gae or vapour is
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circulated through the compartment or compartments. The
walls of the compartment or compartments are sealed to the
outer surface of the walls of the tubular, gassage(s) by
methods that will be understood by a person skilled in the
art. The compartmeat or compartments serve to control the
chemical and physical cot~ditioas within the or each tubular
passage: Thus the compartments surrounding the tubular
passages) serve'to define the correct processing, conditions
within the dope at any poiat along the tubular passage(s).
In this way parameters such as the temperature; hydrostatic
pressure; conceatration of fibre-formi.ag material; pHt
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. Hy'way of example only,
continuously graded or stepped changes in the processing
environment can~be obtained.
Conveniently a selectively permeable/porous membrane
can he 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 i t
asymmetrically in such.a way that the extrusion can be made
to curl or twist.
All or part of the draw down process may typically
occur within the die rather thaw at the outer face of the
die asseanbly as occurs is 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 coatiags,or treatments to the extrusion. Further, the
last' part of the die assembly is water lubricated by the
solvent-rich phase surrounding the extrusion.
By way of example only the apparatus can be used for
forming fibres from dopes containing solutions of
recombinant spider silk proteins or analogues or recombinant
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silk- worm silk proteins or analogues or miXtures of such ,
proteins or protein analogues or regenerated silk solution
from silkwoxm silk. When these dopes are used it .is
necessary to store the dope at a pH value above or below the
isoelectric point of the protein to prevent the premature ,
formation of insoluble material. T.t 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 fibre. The dope Within the tubular
passage can then be brought by dialysis against an
appropriate acid or base or buf f er solution to a pH value at
or close to the pR value~of 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 ,
~~ 20 each tubular passage from a vagour phase in the surrounding
y 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 lef t the outlet
of the die assembly.
The -draw rate and length wall thickness. geometry
anc~ material composition of the or each tubular passage may
be varied along its length to provide different retention
times and treatment conditions to optimise the process.
One or more regions of the walls defining the or each
tubular passage can be made impermeable by coating .their
saner 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.
The inner surface of the walls of the or each tubular
passage can be~coated with suitable materials to reduce the
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friction between the walls of the tubular passage and the
dope , or f fibre . Such a coating can also be us ed to induce
appropriate interfacial molecular alignment at the walls of
the tubular passage in lyotropic liquid'crystalline polymers
When these are included in the dope.
A further embodiment allows for one or more
additional components to be fed to the start -o-f the. or each
tubular passage via concentric openings to allo'v 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 fibre or fibres.
A further embodiment utilises.-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 persaeable
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
2d 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 void~.within the bulk phase. A convergent die
wilh 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 iii hoops transverse
to the direction of flow within the tubular passage. Hoth
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.
The spinning apparatus with one or more tubular
passages surrounded by a compartment or compartments to act
as jackets can be constructed by one or two s Cage moulding
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or other methods known to a person skilled in the art. It w
will be appreciated that a moulding process can be used to
create. simple or complete profiles for the or each tubular
passage and the outlet of the die assembly.. Very small
flexible lips can be formed, e.g. moulded, 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 s tage or wet drawing of ter the material has lef t the
outlet of the die assembly should this .be required. The
mi.croscopic.grofile 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.
By way of examgle only, the jackets and supports for
the tubular passages can be constructed from two-or more
components formed by injection iaoulding 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. fibres -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:arxangemeats shown
will be apparent.to persons skilled in the art.
' Other methods of constructing spinning apparatus in
which the walls of the tubular passages are substantially os
partially constructed from semipermeable . and/or porous
material or materials will be known by a person skilled in
the art. 8y way of . example only these include
micro-machining techniques . In addition it will be
appreciated that walls of the tubular passages substantially
or partially constructed from .semipermeable/porous material
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can be incorporated into other types of spinning apparatus,
such as electrospinning apparatus.
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 thi s
difficulty', the walls of the tubular passage may be
constructed from an elastic material sealed into and
surrounded 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 fibres 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 j acket. If the pressure : is now .
raised iw 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
inezease . ~ It will be appreciated that both methods could. be _
used together or consecutively. With both methods the
elasticity of the passage walls enables the d3.ameter of the
tubular passage to be increased reducing the resistance to
flow. With both methods it is to be noted the't 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
altersative means of applying pressure to pump-dope to the
outlet to commence spinning or to clear a blockage.
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The-pressure in the sealed compartments surrounding
the tubular passages) may be -controlled to define and
modify the geometry of the tubular passage to optimise
spinning conditions.
If the or each tubular passage has a convergent or
divergent geometry along all or part of its length, filler,
particles or short fibres included in the dope may be
orientated as they flow through the tubular passage by
exploiting the well-understood principle'~of elongatioaal
flow. It will be understood that the substantially axial
orientation of such filler particles or short fibres 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
usefulproperties on the fibre. It will be appreciated that
a coa~re~rgent 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
impolymerised 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
conrter additional useful properties to the extruded
material.
It Will be appreciated that the direct drawing down
of a fibre or other formed product from liquid spinning
solution within a region of a tubular passage greatly
improves the molecular orientation in the final material
avoiding. the disorientation produced by die swell produced
by other methods of forming the final material. It also
greatly reduces the pressure required to form material
compared with the extrusion of fibre from~a conventional
restriction die.
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The present invention seeks to alleviate some or all
of the problems associated with the prior ar.t by providing
. a reliable apparatus and method for manufactur-ing materials
with a highly defined and typically uaiaxi al molecular
orientation from spinn:i.ng solutions. The use of
pernaeable/porous tubing, preferably selectively
permeable/porous tubing, for the construction .of the-walls
of the tubular passage enables a precise control of all
parameters of the processing environment. This enables the
processing environment to be precisely defined down the
length of the.tubular passage. Precise control of the
processing environment in the tubular passage,- enables the
polymer concentration, molecular configuration and viscosity
and other physical properties of the spinning solution to be
kept at optimum values at all points along the tubular
passage. The convergent geometry with cross-sectional area
decreasing' non-linearly and preferably hyperbolically -in-
substantially all or the first,.. part .of . the .tubular passage-
serves to align the molecules axially before the drag down
process thus improving the quality of alignment in the final
formed product.
The apparatus may be arranged in such a way.that two
or more fibres are formed in parallel and twisted around
each- other or crimped or mound onto a former or coated or
left uacoated as desired. The fibres can be, drawn through
a cpating 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 sli t or annular
openings can be used to form sheet materials.
Brief description of the drawings
An embodiment of the invention will. now he described,
by way of example only, with particular ref erence to the
accompanying drawings in which:
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Figure 1 is a generalised schematic representation of
apparatus: for the formation of extruded materials
from a.spinning solution=
Figure 2 is a schematic cross-sectional view along
the longitudinal axis of a die assembly of the
apparatus shown in Figure 1,;
Figure 3 is a schematic perspective view.of the die
assembly shows in Figure 2; '
Figure 4 is a schematic exploded view illustrating
another embodiment of a die assembly of apparatus
according to the invention; and
Figure.5 is a view showing -a number of die assemblies
of-:Figure 4 assembled together in a unit to enable a
plurality of fibres to be extruded. .
;.15 Best Mode.:: for Carrying out the Invention
Figure 1 shows apparatus for the formation of
extruded materials from a spinning solution- such as
lyotropic liquid crystalline polymer or other polymers or
polymer~mixtures. The apparatus comprises a dope reservoir
13 a pressure . regulating valve or pump means 2 which
maitrtains a constant output pressure under normal operating
conditions: a connecting pipe 3; and a spinning die assembly
3 comprising at least one spinning tube or die further
described. in Figures 2 to 5. A take-up drum 5 of any known
construction draws out and reels up extruded ataterial at a
constant tension exiting from the outlet of the die assembly
3. The pressure regulating valve or pump mesas 2 may be any
device normally producing a constant pressure commonly knows
to a person. skilled in the art.
The arrangement shown is Figure 1. is purely exemplary
sad additional components may be added if desired.
Potential modificatioas~to the arrangement shoaru in Figure
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1 will be apparent . to persons skilled in the art. In use
dope 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.
The die assembly 4 is shown in greater detail in
Figures 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
through the die assembly 4. The dies 8 and 12 are made of
semipermeable aadJor 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 storte suitable for spinning.
Hollow-fibre membranes may also be used ~ as the
semipernaeableJporous membrane material, such ho~.low-fibre
membranes being made from polysulfone. polyethyleneoxide-
.polysulfone blends, silicone or polyacryloaitrile. The
exclusion limit selected for the semipermeable membrane v~rill
depend on the s i z a o f the smal l mol a cul ar weight
constituents of the spinning dope but is typica3ly ~.ess than
12 kDa.
. The die 8 is held at its upstream end by a tapered
Z5 ada~ltor 6 positioned at the inlet end of the die. assembly 4
cad at its ~ downstream end by a tapered adaptor '~ positioned
internally is the die assembly 4. The die 8 a.s held at its
upstream end by the, adaptor 7 and at its downstream end by
a spigot 13 at the outlet of the d,ie 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 on 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
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- 17 -
tubular passage 17 for spinning solution from the inlet to
the outlet o~ the die assembly 4.
A j acket 9 surrounds the die 8 and is intended to
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 flour -of fluid into and out of the
jacket. ~A further jacket 14 surrounds the tube or die l2
and is fitted with a fluid inlet ~ 15 and a fluid outlet 16 to
enable fluid, e.g, sol~rent, solution or gas, to be~ passed
into and out of the j acket - 14 in ~ contact With the
semipermeable/porous walls of the die 12.
As- an alternative to the die 8 shown having
semipermeabie walls a die may be constructed from material
which is not semipermeable but which is preferably tapered,
e.g. convergently, and may be temperature-controlled by
- circulating f Iuid at a predetermined temperature through the
- jacket'-.9.
In operation spinning solution or dope, 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 through the die 12. The fluid passing - through the
j aek'et 9 may merely serve to heat or maintain the dope at
the correct temperature or provide the correct external -
pressure . to the' walls 'of the die 8 . Ia this case it is not
essential for the walls of the die to be made of
semipermeable aadJor material: The temperature of the die s
8 and 12 for the extrusion of protein-containing dope s
should typically be maintained at a temperature of about.
20°C but-spinning may be ca=ried out at temperatures as low
as 2°C and as .high as 40°C.~ The pressure of the fluid,
liquid or gas, in the jackets surrounding the walls of the
tubular passage 17 istypically maintained at a pressure
close to that at which the dope is supplied to . the die
assembly 4-. -However -the pressure can be ~somev~ihat higher or
CA 02546933 2000-11-24
Z8
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. occurs during
"draw down" as the- dope passes through the die . 12 although
cheiaical treatment.may also occur as the dope passes through
'the die 8 if the walls of the - latter are at least partly
made of semipermeable material. In Figures 2.aad 3, the
abxupt pulling away of the dope from the walls of the die 12
at 12A indicates the internal draw down of the "fibre".
This-is a unique feature of the invention as draw down in
existing processes always start at the outer opening of a
die (i.e,. the extrusion orifice) and not before. The
pulling away of the "fibre~ from the. die walls at 12A occurs
at a place in the,tubular die 12 where the force required to
produce exteasional flow to create a new surface just fall s
below the force required to f low the dope through the die 12
is caatact with the die Walls. The position of 12A wil l
depend on: the changing rheological properties of the dope
the rate and force of drawings the -surface properties of the
die 12; the.surface properties of.the lining of the die 12;
sad the properties of the dope and the aqueous ghas a
surrauadiag the dope.
2t 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 j acket ( s ) control or regulate
the conditions inside the tubular passage 17 as is conanonly
understood by a craftsman skilled is the art. Chemicals in
the fluid .supplied to the jacket (s) . are able to pass through -
the semipermeable and/or porous walls of the tubular passage
to "treat" the dope passing therethrough. . It is also
possible for chemicals is the dope. to pass .outwardly through
the semipermeable and/or porous walls of the tubular passage
1~. The fluids supplied to the dope will obviously depend
oa the type of dope used and the semipermeable and/or porous
membranes used. However, by way .of example only, for the
spinning of concentrated protein solutions, the j acket 9 may
CA 02546933 2000-11-24
_ 19 _
contain 100 mM Tris or PIPES buffer solution; typic°ally at
a pH of 7.4, azid 400 mM sodium chloride to-help maintain the
folded. state .of the proteiri. The jacket 14 may contain 100
mM Tri s or PIPES buffer solution at a lower pH, typicahly
6.3. and 250 mM potassium chloride to encourage the
unfolding/refolding of the protein. High molecular areight
polyethylene glycol can be added to the solution in both
. jackets to maintain.or reduce the concentration of water in ~-
the dope.
It will be realised that the spinning tube or die 12
can be banked or coiled or arranged in other ways between
the tapered collar 7 and the spigot 13. The diameter and '
crass-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-section, the typical diameter of the outlet is from l
..,
to 100 ~ ;~Zm and the typical diameter of the inlet to the
tubular~passage would be from 25 tov150 times greater than
,~.~s:~:.. the outlet diameter depending on the extent of the
.: 20 extensional flow. It Will be appreciated that the
arrangements and proportions shown in Figure 2 are purely
exemplary and thus that additional components may be added
if desired. Potential modifications to the arrangements
shown in Figure . 2 :will be apparent to persons skilled in the
art.
Figure 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 Figure 2 are
purely exemplary and thus additional comgonents may be added
if desired. . Potential modifications to the arrangements
shown in Figure 4 will be apparent to persons skilled in the
art, including . the provision of fewer or more dies 12 or
jackets, l4.
CA 02546933 2000-11-24
- 20
Figure- 5 shows how two or mere modular units
constructed from the apparatus shown in Figure 4 can be held
together to enable a plurality of extruded fibres to be
produced. It will be appreciated that the arrangements. cad
proportions. shown in Figure 5 are purely exemplary and thus
additional components may be added if desired. Potent~.al
modifications to the arrangements shown. in Figure 5 will. be
apparent to persons skilled in the art.
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
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 seanipermeable or porous materials for the walls of
the tubular passage. Thus the walls of the tubular passage
may comprise:. semipermeable material of the same
permeability throughout the length of the passages.
semipermeable material of different permeability for
different portions of the passages porous material of the
same porosity throughout the length of the pas sages porous
material of dif f erect porosity f or dif fereat portions of the
passage f 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
meabioned 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,
Goretex {Registered Trade Mark), polysulfoae,
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 sill con, porous
polyethylene, cellulose derivatives and chitosan.
It grill be appreciated that the apparatus is suitable
fos the formation of fibres or sheets from all solutions of
lyotropic liquid crystal polymers whether synthetic or maa-
CA 02546933 2000-11-24
_.ZZ
~ta.de or ~aatural oW codified or copolymer mixtures . or
~olutiong of recombinant.~proteins or analogues derived from
then or mixtures of these. By way of example only these
irialude collageas; certain cellulose derivatives; spidroins; ' '
fibroias; recombinant protein analogues based~on spidroins..
or fibroins, and poly (p-phenylene terepi~thalates) . The
method is also suitable for use v~tith other polymers or
polymer mixtures provided that they are dissolved in
solvents, whether aqueous or non-aqueous protein solutions
or cellulosevsolutions. It will .also be appreciated that,
the use of one or more semi:permeable and/or porous~treatment
zones, can- be used for dies or die assemblies having
essentially annular or elongated slit openings used for the
foirmation of sheet materials .
=adustr3al~Applicability
w The invention has industrial application ia,the
spinning of products.
