CA2546933A1 - Apparatus and method for forming materials - Google Patents

Abstract

An apparatus and method for forming liquid spinning solution into a solid formed product whereby the solution is passed through at least one tubular passage (17) having walls formed at least partly of semipermeable and/or porous material. The semipermeable and/or porous material allows parameters, such as the concentration of hydrogen ions, water, salts and low molecular weight, of the liquid spinning solution to be altered as the spinning solution passes through the tubular passage(s).

Description

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 - la -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 - ~ -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 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.

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 _ .5 _ 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.

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 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 _ 8 _ 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 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 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 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 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.

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.

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:

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 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 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 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 _ 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.

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-_.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.

Claims (36)

1. Apparatus for the formation of extruded materials from a solution, the apparatus comprising a die assembly (4) that includes at least one extrusion orifice (13) as an outlet from said die assembly (4) for said extruded materials; wherein in operation draw down of the solution (12A) is performed at least partially within said die assembly (14).

2. The apparatus according to claim 1, wherein in operation draw down of the solution (12A) is performed entirely within said die assembly (4).

3. The apparatus according to one of claims 1 or 2, further comprising a dope reservoir (1) connected to said die assembly (4), wherein said dope reservoir (1) is capable of containing said solution and capable of supplying said solution to said die assembly (4).

4. The apparatus according to any of the above claims, wherein said solution comprises a protein solution.

5. The apparatus according to claim 4, wherein the protein of said protein solution is selected from the following group:

(a) recombinant spider silk proteins;
(b) analogues of recombinant spider silk proteins;
(c) recombinant silk-worm sills proteins;
(d) analogues of recombinant silk-worm silk proteins;
(e) regenerated silk solution from silk-worm silk; and (f) mixtures of (a) to (e).

6. The apparatus according to one of claims 4 or 5, wherein said protein solution is stored in said dope reservoir (1) at a pH value above the isoelectric point of said protein.

7. The apparatus according any of the above claims, wherein said die assembly (4) comprises at least one tubular passage (17), wherein said at least one tubular passage (17) delivers said solution to said at least one extrusion orifice (13), and wherein in operation draw down of the solution (13A) commences within said tubular passage at a first distance from said extrusion orifice (13).

8. The apparatus according to claim 7, wherein the at least one tubular passage ( 17) is defined by one or more walls (8, 12) to form an internal surface and wherein in operation said solution detaches from said internal surface of said tubular passage (17) at a second distance from said extrusion orifice (13).

9. The apparatus according to claim 8, wherein said first distance is substantially equal to said second distance.

10. The apparatus according to any one of the above claims, wherein concentrically arranged feed means (3) are positioned at an inlet end of said tubular passage (13) to supply said solution and one or more additional components to the tubular passage (17).

11. The apparatus according to any one of the above claims, wherein a solvent-rich phase surrounds the extrusion and lubricates a region of the die assembly (4) after the draw down of said solution within said die assembly (4).

12. The apparatus according to claim 11, wherein solvent in the solvent-rich phase comprises water.

13. The apparatus according to any one of claims 7 to 12, wherein said tubular passage (17) exhibits a tapered geometry for part or all of said tubular passage (17), and wherein said tapered geometry is selected from the group consisting of:
(a) a divergent tapered geometry; and (b) a convergent tapered geometry.

14. The apparatus according to claim 13, wherein said tapered geometry is a substantially hyperbolic tapered geometry.

15. The apparatus according to claim 13 or 14, wherein a region of the die assembly (4) after the internal commencement of the tapered geometry is capable of being used to apply a coating to the extruded material.

16. The apparatus according to one of claims 13 or 14, wherein the region of the die assembly (4) after internal commencement of the tapered geometry is capable of being used to apply a treatment to the extruded material.

17. The apparatus according to any one of claims 8 to 16 wherein said one or more walls (8, 12) are at least partly formed of material selected from the group of semipermeable materials and porous materials.

18. The apparatus according to claim 17, wherein said material selected from the group of semipermeable materials and porous materials comprises a component selected from the group consisting of cellulose acetate based materials, cellulose acetate based materials substituted with diethylaminoethyl groups, cellulose acetate based materials substituted with carboxyl groups, and cellulose acetate based materials substituted with carboxymethyl groups.

19. The apparatus according to claim 17, wherein said material selected from the group of semipermeable materials and porous materials comprises a hollow-fibre membrane selected from the group consisting of polysulfone membranes, polyethyleneoxide-polysulfone . blend membranes, silicone membranes and polyacrylonitrile membranes.

20. The apparatus according to any one of claims 8 to 19, wherein said one or more walls are at least partly coated with a material selected from the following group:
(a) friction reducing material; and (b) impermeable material.

21. The apparatus according to any one of claims 8 to 20, wherein said one or more walls are elastic.

22. The apparatus according to any one of claims 8 to 21 wherein said one or more walls (8, 12) are formed at least partly of flexible material, wherein enclosure means (9, 14) surround said one or more walls (8, 12) to provide at least one pressurisable compartments surrounding said one or more walls (8, 12), wherein the shape of said tubular passage (17) can be controlled by pressurisation of said at least one pressurisable compartment.

23. The apparatus according to claim 22 wherein each of said at least one pressurisable compartment has a supply means (10, 15) for supplying fluent material to said at least one pressurisable compartment, and a removal means (11, 16) for removing fluent material from said at least one pressurisable compartment.

24. The apparatus according to any one of claims 7 to 23, wherein said apparatus comprises a plurality of said tubular passages (17), each having an independent extrusion orifice (13) and delivering said solution to the independent extrusion orifice (13).

25. The apparatus according to any one of the above claims, wherein a plurality of said die assemblies (4) is assembled together in a unit.

26. The apparatus according to any one of the above claims wherein said apparatus is incorporated into an electrospinning apparatus.

27. A method of forming an extruded material from a solution using a die assembly (4), wherein at least part of a draw down process of said solution (12A) is performed within the die assembly (4).

28. The method of claim 27, wherein all of said draw down process occurs within the die assembly (4).

29. The method of claim 27 or 28, wherein said die assembly (4) comprises at least one extrusion orifice (13) as an outlet from said die assembly (4) for said extruded material, wherein said die assembly (4) further comprises at least one tubular passage (17) within the die assembly (4) that delivers said solution to said extrusion orifice (13), and wherein at least part of said draw down process of said solution is performed within said tubular passage (17).

30. The method of any one of claims 27 to 30, wherein said extruded material is formed from a dope comprising a protein solution.

31. The method of claim 30, wherein the protein of said protein solution is selected from the following group:
(a) recombinant spider silk proteins;
(b) analogues of recombinant spider silk proteins;
(c) recombinant silk-worm silk proteins;
(d) analogues of recombinant sills-worm silk proteins;
(e) regenerated silk solution from silk-worm sills; and (f) mixtures of (a) to (e).

32. The method of one of claims 29 to 31, wherein said tubular passage (17) is defined by one or more walls (8, 12) formed at least partly of semipermeable and/or porous material and wherein said solution is treated, as it passes through said tubular passage (17) to form the extruded material, by a component permeating through the semipermeable and/or porous material of said one or more walls (8, 12).

33. The method of claim 32, wherein said component is a fluid material.

34. The method of one of claim 32 or 33, wherein at least two compartments (9, 14) surround said tubular passage (17), and different components are supplied to each of said at least two compartments (9, 14) for treating said solution.

35. The method of one of claims 32 to 34 wherein said solution is a treatment selected from the group of treatments consisting of diffusion, dialysis, reverse dialysis, ultrafiltration, electro-osmosis, pre-evaporation and a combination of these treatments.

36. The method of one of claims 32 to 35, wherein said solution comprises a phase separating mixture and wherein said component regulates a phase separation and polymerization process.