EP3191631B1

EP3191631B1 - Device and method for preparing continuous nanofibrous yarns and bundles from electrospun fibers and fibrils

Info

Publication number: EP3191631B1
Application number: EP15774983.9A
Authority: EP
Inventors: Mihkel VIIRSALU; Teet KIVIRAND; Andres KRUMME
Original assignee: Tallinn University of Technology
Current assignee: Tallinn University of Technology
Priority date: 2014-09-08
Filing date: 2015-09-08
Publication date: 2022-08-31
Anticipated expiration: 2035-09-08
Also published as: GB201415820D0; WO2016038539A1; GB2529894A; EP3191631A1

Description

Technical field

The present invention generally relates to devices and methods for electro spinning of nanofibrous yarns including bundles from electrospinned fibers and fibrils, and more specifically, to high production rate electrospinning devices and methods.

Background

Electrospinning apparatuses have become increasingly wider spread because of the variety of uses provided by electrospinned fibers. Electrospinned fibres are used, but not limited to fields such as medical, chemical separation, chemical protection, textiles, piezo-active materials, porous materials, high reactive surface zone textiles and many more. The main reason why these electrospinned fibres are not used in commercial products is due to the fact that the production rate of yarns made of such fibers is very low. By the year 2014 the highest estimated production rate was 63 cm/min [1].
Due to small dimensions, the mechanical properties of single fibers are very low. However, by twisting and orientating the fiber along the same axis it is possible to make nanofibrous yarns with high mechanical properties.
Conventional electrospinning apparatuses rely on physically collecting the fibers or the fibrils and then forming either mats or yarns from them. This approach is difficult to upscale due to fact the fibers have different properties when they are not completely dry. This means that during the process of drying the fibers will stiffen and start to break. If the apparatus is collecting the fibres first and then pulling them to form a structure then there will inevitably be difficulties with continuous production.
Therefore the main purpose of this invention is to provide continuous production of electrospinned yarn including nanofibre bundles with drastically increased output rate and quality of such yarns and bundles made of electrospinned fibers and fibrils.
Conventional yarn spinning methods can be ring spinning, rotor spinning, friction spinning, air-jet spinning and vortex spinning. GB1427373 [2] describes an aerodynamic composite macro scale yarn spinning. Using a circularly moving air flow to twist two fibers together gives a slightly twisted yarn. This invention uses compressed air and the air flow is so powerful that it would damage or even destroy fibers in nano-scale. Beside that, vortex chamber is too small to apply an electrospinning system to that invention.
CN102703998 [3] discloses a jet yarn spinning device for an electrostatically spun nano fiber, which contains mainly two oppositely charged nozzles, collecting device such as rotating funnel- or disc-shaped collector, air-twisting unit and take-up roller. Electrostatic forces between oppositely charged nozzles will pull out fibres from the polymer solution. Due to existing electrical field, the fiber will be pulled to the rotating collector. The fibers are attached to the collector surface and mechanically pulled downwards through the air-twisting unit. Between the collector and air-twisting unit light twist will be given to the fibers forming a yarn. Air-twisting unit increases the twist and orientation of fibers in the yarn and final product will be collected to the take-up roller (bobbin). This invention gives good alignment for the yarn but due to mechanical contact between the fibers and collector the productivity of the system is low. For higher industrialization possibilities the mechanical contacts between fibers and any mechanical objects must be avoided.
In US6308509 [4] the composite yarn is produced containing nanostructured fibrils. Idea of this invention is to cover carrier or strengthening yarns with nano-fibrils for achieving special desired properties for the yarn. Electrospinned fibril bundle will be fed in an air vortex apparatus to form a linear fibrous assembly. The fibril bundle itself is well oriented but not twisted which could give additional strength to yarn. Also this invention is using core material in the yarn production and in some applications it can reduce the effect of nanofibrous material advantages.
Document CN200981905Y discloses a device for preparing a continuous nanofibrous yarn comprising vortex tube with slits similar to the present ones. A vortex can be created from a gas flow, that twists the nanofibers together.

Summary of the invention

The goal of the invention therefore is to provide industrial production process based on electrospinning for production twisted yarns consisting of continuous nanofibers and fibrils, i.e. fibres with diameter less than 1 µm.
The present invention permits high speed production of yarns made of electrospun fibers. The formation of the yarns is achieved by using a fast rotating column of gas (so-called gas vortex) to capture and twist the fibers produced by electrospinning. The fibers will be formed directly in the gas vortex field. This guarantees high alignment and collection of all nanofibers and fibrils created by electrospinning process (no material losses will be presented). This allows increasing the speed of twisting the fibers to one continuous yarn. This type of fiber collection allows more control over the process and the quality of the yarn because none of the fibers are collected on to a surface and having contact to any object before being twisted into yarn formation.
A device for preparing a continuous nanofibrous yarn comprises an electrospinning chamber, comprising at least one first opening in the upper region of said chamber for receiving gas and a second opening in the bottom region of said chamber for discharging gas and (in some embodiments, this second opening is also used for discharging said yarn while in another embodiments, there is another opening for discharging said yarn); means for creating helical movement of gas within said electrospinning chamber; electrospinning means for forming a plurality of nanofibres directly into said helical movement of gas in said electrospinning chamber, wherein said nanofibres are twisted together by said helical movement of gas; and means for continuously removing said yarn from said chamber through said second opening or through yet another opening in the bottom region of said chamber. Said means do not have any mechanical contact with the yarn within said chamber during the normal operation of the device. The means for creating helical movement of gas comprises means for creating a negative pressure within said chamber, the pressure inside the chamber is lower compared to ambient pressure so that the gas is sucked into said chamber through said first opening and said elongated slits.
The device preferably comprises means for controlling the linear speed of the air flow through the chamber, e.g., a fan attached to the top of the chamber, wherein by controlling the linear speed of the air flow, these means effectively control also the properties of the gas vortex within said chamber.
Said chamber may have different shapes, e.g., an upside down oriented cone, a bicone, a cylinder, a cube or a cuboid, etc. Different means for generating and controlling gas vortexes may be applied here, e.g., as described in US5096467 . Said means for creating helical movement of gas comprises means for creating a negative pressure within said chamber, e.g., a vacuum pump, a fan near the second and/or the third opening, said fan adapted to draw gas out of said chamber through said second opening (or, the third opening), or means for generating a horizontal gas flow below the second (and/or the third) opening.
Means to remove said yarn from said chamber may include number of alternatives. For example, the enough fibres or fibrils are twisted together into a yarn or bundle in said gas vortex and said yarn or bundle is pulled out of the chamber and attached to a pulling and collecting means such as a cylindrical roller or a conveyor belt. The cylindrical roller helps to pull the yarn out of the chamber once the yarn has made contact with the cylinder. The conveyor belt is collecting the yarn that falls onto it due to gravity. Preferably, the fibres or fibrils does not have contact with any mechanical object within said chamber until sufficiently strong yarn is twisted.
The means for forming nanofibres preferably comprises oppositely charged nozzles.
Another aspect of the invention is a method for preparing a continuous nanofibrous yarn, comprising generating a helical movement of gas in an electrospinning chamber, forming by electrospinning a plurality of nanofibres into said electrospinning chamber directly into said helically moving gas, and twisting together said plurality of nanofibres into said nanofibrous yarn by said helical movement of gas; and continuously collecting and removing said yarn from said chamber. The helical movement of gas is generated by creating negative pressure within said chamber, preferably by withdrawing gas out of the electrospinning chamber. The point where said plurality of nanofibres are joined together is controlled by adjusting the speed of the gasflow, a polymer solution used for preparing the nanofibres, the humidity inside the chamber, or the voltage applied to electrospinning nozzles (spinnerets).
The device allows to produce yarns at speed 100 m/min approximately, which is 200 times faster than the second best method known up to now. Therefore, it has high industrial potential for producing nanofibrous yarns by electrospinning. Moreover, this speed is not a limit but can evidently be increased if more productive method for creating fibres can be used instead of the nozzles used up to now.
Also, compact design of the yarn electrospinning device allows using it for modular production, installing such devices in series, in parallel, or in any such combination.

Brief description of drawings

Fig 1 is a side view of one embodiment of the device according to this invention.
Fig 2 is a cross-sectional view G-G of the device shown on Fig 1.
Fig 3 (a) is a cross-sectional view E-E of the device shown on Fig 1 and Fig 3(b) is a cross sectional view E-E of a modified embodiment of the device shown on Fig 1.
Fig 4 (a)-(d) are few possible shapes of electrospinning chambers.
Fig 5 is a side view of another embodiment of the device according to this invention.
Fig 6 is a cross-sectional view B-B of the device shown on Fig 5.
Fig 7 is a cross-sectional view E-E of the device shown on Fig 5.
Fig 8 is a enlarged side view of the spinning device shown on Fig 6.
Fig 9A to 9D show possible combinations of the devices according to the invention in parallel and/or in series.

Modes for carrying out the invention

As seen on Figs 1 to 3 (a), the device according to one embodiment comprises an electrospinning chamber 1 shaped as upside down oriented cone, where the helical movement of gas, e.g., air, is created and where the fibers are introduced. Yarn 7 is aligned and twisted by the helical movement of the gas 6. The chamber has negative pressure, i.e., the relative pressure inside the chamber compared to ambient pressure is lower and therefore, gas is sucked into the chamber through the first openings 3 in the sides of the chamber 1 to create a helically moving column of gas 6. The negative pressure may be created with a fan 2 located near the second opening 14 at the bottom of the chamber 1. There can be for example, two to six, preferably four first openings 3. Gas guiders 4 are used to provide counter-clockwise movement in the electrospinning chamber 1. Both counter or -clockwise movement of gas can be used. The oppositely charged nozzles 5 generate the fibres from the polymer solution which are then twisted into yarn 7 at a certain point inside the chamber 1. The location of the point can be regulated by adjusting the speed of the gas flow, the polymer solution feed rate used, the humidity inside the chamber and the voltage applied to the nozzles 5. The slightly twisted yarn is then removed from the chamber 1, e.g., by pulling it through the tube 11 opening 8 by the gas movement created by the lower pressure zone 12 on the other end of the tube 11. The lower pressure zone compared to ambient atmosphere can be created either by vacuum pumps or using fast moving compressed gas around the bottom of the tube 11 to create venturi effect. The compressed gas is provided by the tube 9 and guided into the fixture 10. Roller 13 is used to collect the yarn that is received at the bottom of the tube 11.
The core yarn 16 (shown on Fig. 3 (b)) is used to help starting the process of electrospinning yarns but once the production has started the feeding of core yarn 16 will be discontinued. The core yarn 16 is pulled through the electrospinning chamber 1 and the fibres are collected onto the core yarn 16. The core yarn 16 is feed into the system by the input roller 17 and pulled out using an output roller 14. When the yarn is collected it could be used with the core yarn or the electrospun fibers could be extracted by removing the core yarn with chemicals.
Gas flow rotational speed can be increased with upper openings 15 (shown on Fig 4A to Fig 4D) located at the top of electrospinning chamber.
The chamber may have different shapes such as rectangular cuboid 1' (see Fig 4 (a)), cylinder 1" (Fig 4 (b)), cone 1 (Fig 4 (c)), or bicone 1‴ (Fig 4 (d)), etc. The helical movement of gas can be also created in an open space, or also the collecting means can be located within the chamber.
As seen on Figs 5 to 7, the device according to another embodiment comprises an electrospinning chamber 1" shaped as cylinder, where the helical movement of gas, e.g., air, is created and where the fibers are introduced. Yarn 7 is aligned and twisted by the helical movement of gas. The chamber has negative pressure, i.e., the relative pressure inside the chamber compared to ambient pressure is lower and therefore, gas is sucked into the chamber through the first openings 3 in the sides of the chamber 1 to create a helically moving column of gas 6. The negative pressure may be created with a fan 2 located near the opening 18 behind the lower pressure zone at the bottom of the chamber 1. There can be for example, two to six, preferably four first openings 3. Gas guiders 4' are used to provide counter-clockwise movement in the electrospinning chamber 1. Both counter or -clockwise movement of gas can be used. A compression fan 19 is used to increase the helical gas movement in the chamber 1' and/or to control the speed of the gas in linear (vertical) direction. To achive optimal working conditions sensors can be used to regulate the speed of the air vortex to guarantee the required twistment and production speed of the nanofibre yarn.
The oppositely charged nozzles (spinnerets) 5 generate fibril and fibres from the polymer solution which are then twisted into yarn 7 at a certain point inside the chamber 1'. The location of the point can be regulated by adjusting the speed of the gas flow, the polymer solution feed rate used, the humidity inside the chamber and the voltage applied to the spinnerets 5.
It is apparent to a person skilled in the art that different means can be used to generate fibres from the polymer solution, e.g., using one or more needles as spinnerets, creating nanofibres from a surface of liquid polymer, using the SNC BEST^™ ball electrospinning technology or using a conveyour type feeding to supply the polymer liquid surface from where the nanofibres are created.
Similarly to cone shaped electrospinning chamber, the core yarn 16 is used to help starting the process of electrospinning yarns but once the production has started the feeding of core yarn 16 will be discontinued.
The slightly twisted yarn is then removed from the chamber 1, e.g., by pulling it through the opening 14 by the gas movement created by the lower pressure zone 12'. The lower pressure zone compared to ambient atmosphere can be created either by vacuum pumps or fans.
As shown on Fig.6 and Fig 8, yarn is pulled into the twisting device 20 through the funnel 21 by the bobbin 22. The flyer 24 revolves around its axis and twists the yarns 7. It is powered by motor 23. To add twistment to the yarn 7 and to guide it on the bobbin eccentric channel 25 is used. Bobbin 22 is fixed to shaft 26 and tightened by screw 27 to bearing 28. This enables to adjust bobbin 22 speed due to increase friction in the bearing. For yarn collection, bobbin 22 rotational speed has to be smaller than flyer 24 speed. To control the bobbin 22 speed more precisely, the shaft 26 could be attached also to separate motor.
Gas flow rotational speed can be increased with upper openings 15 (shown on Fig 4 (a-d)) located at the top of electrospinning chamber or with the fan 9 on top of the chamber 1.
To create a sufficiently fast moving gas vortex large volume of the electrospinning chamber should be extracted. This gas flow creates enough fast moving gas at the inlets of the chamber to start the process of twisting electrospun fibres into yarn.
The yarn production is directly related to the amount of polymer solution being pumped into the chamber and the speed of the gas flow from the electrospinning chamber. Different configurations of said invention have used variety of speeds. For the cone shape example, the gas outflow speed of 1 m/s proved to be sufficient. Polymer feed rate was 0.9 ml/h. Under those conditions the fibers were twisted together into yarn on the center line at the point located 20-25 cm above the bottom opening of the electrospinning chamber. Using the multineedle spinnerets in cylinder example, polymer feed rate reached to 4 ml/min. Changing the configurations with different type of nozzles, the fiber production rate could be increased. This leads to overall yarn production growth at the same yarn diameter if the gas outflow speed will be increased and yarn diameter growth if the gas outflow speed will remain same.
The produced yarn comprises of nanofibres that are intertwined. The level of intertwinement is controlled by the parameters set on to the spinning device.
The yarn bundle could be produced at the maximum speed of 230 m per minute. The yarn production reached to the speed of approximately 100 m per minute. Yarn production rate is strongly affected by twist level given to it - the lower it is, the bigger is production rate.
To improve or enhance the properties of the nanofibre yarn or bundle this spinning setup could be used in parallel or series with identical devices to coat an existing yarn with polymer be it the same as the yarn's or another polymer. In series production several yarns could be twisted into bigger yarns with improved mechanical properties.
Figure 9A to D show modular production concepts: Fig 9A: serial arrangement of the electrospinning devices, Fig 9B: serial arrangement of the electrospinning devices alternating with supporting units as electro spraying, Fig 9C: serial arrangement of the electrospinning devices with core yarn passing through the process, Fig 9D: parallel arrangement of the electrospinning devices leading to multiplied rope.
Modular design allows creating mini-factories for specific needs for tailor-made production in cleanrooms or bigger hospitals. Several layers of nanofibers of different chemical composition can be combined using the modules in parallel. Moreover, the production line can be accompanied with nanosprayed intermediate layers as adhesives, insulators, catalysts or bioactive components. Pre-produced core yarns or fibres, which cannot be prepared by electrospinning, can be feed into the production line. Electrospinning units of yarns can be also arranged in parallel producing thicker ropes if necessary.
Formed yarns or ropes can be also knitted or weaved in situ to 3D products of specific shape, used for producing fibre-reinforced composites by filament winding or pultrusion. More advanced 3D production technologies can be developed.
Electrospinned yarns have the following general benefits: broad range of polymers and composites available, multi-layered fibres and yarns available, high specific surface and unlimited length of constituent fibres, exceptional mechanical properties, broad range of functional properties such as conductive (shielding), energy storage / capacitors, piezoactive, stimuli responsible, sensing, light emitting, ion exchange, biocompatible, etc.
Therefore, four main zones of utilisation of such yarns can be proposed: electronics, energetics, biomedical and purification.
The field of smart textiles and wearable electronics is broadly discussed but the number of commercialised smart 3D textile products is still limited. The limiting problem, lack of durable conductors, capacitors and sensors which can be knitted or weaved into textile structures can be efficiently solved with above described multi-layered yarns and wearable electronics can become part of everyday life.
Supercapacitor yarns can be produced by process in FIG 9B for example, where a conductive carbon electrode fibre core is coated in series with a layer of conductive polymer/high porosity carbon allotrope /electrolyte composite fibres, separator PAN fibres, another layer of the composite fibres, electrode layer and finally a protective layer of PAN fibres.
For space application smart textiles can be proposed by above described electrospinned yarns, where conductors, capacitors, sensors, heating or energy harvesting devices have all real fibrous form. Up to now this is achieved only partly having some components of smart textiles still in traditional form of electronics having low flexibility. The electrospinned yarns will open new routes for functionality, flexibility, durability and comfort of such smart textiles for space applications.

References

[1] Chengwei Yang, Guoying Deng, Weiming Chen, Xiajian Ye, XiumeiMo. "A novel electrospun-aligned nanoyarn-reinforced nanofibrous scaffold for tendon tissue engineering". - Colloids and Surfaces B: Biointerfaces 2014 Vol. 122, 270-276
[2] Bobkowicz Andrew J, Bobkowicz E. "Aerodynamic spinning of composite yarn". GB Patent, No. 1427373(A), 1976 .
[3] Jianxin He, Shizhong Cui, Kejing Li, Congcong Pu. "Jet yarn spinning device for electrostatic spun nano fiber and preparing method". Chinese patent, No. 102703998A .
[4] Frank L. Scardino, Richard J. Balonis. "Fibrous structures containing nanofibrils and other textile fibers". US patent, No. 6308509B1

List of reference signs

1, 1', 1", 1‴-chamber
2, 2' - fan near the second opening between the chamber and the lower pressure zone
3 - first openings for gas in
4, 4' - gas guiders
5, 5' - oppositely charged nozzles
6 - helically moving column of gas
7 - yarn
8 - tube opening (yarn in)
9 - tube for providing compressed air
10 - fixture
11 - tube (for yarn out)
12, 12' - lower pressure zone
13 - roller
14 - secornd opening at the bottom of the chamber
15 - upper openings for additional air intake
16 - core yarn
17 - feeding roller for core yarn
18 - opening into the lower pessure zone
19 - fan at the top to controll the linear (vertical) speed of the gas
20 - twisting device
21 - yarn inlet funnel
22 - bobbin
23 - motor
24 - flyer
25 - yarn guiding channel
26 - shaft
27 - adjustment screw
28 - adjustment bearing

Claims

A device for preparing a continuous nanofibrous yarn, comprising:
an electrospinning chamber, comprising at least one first opening in the upper region of said chamber for receiving gas and a second opening in the bottom region of said chamber into a lower pressure zone for discharging gas from said electrospinning chamber;

means for creating helical movement of gas within said electrospinning chamber, said means comprising a set of elongated slits through the walls of said chamber, said slits extending in parallel to the general direction of the air flow in said chamber;

electrospinning means for forming a plurality of nanofibres directly into said helical movement of gas in said electrospinning chamber, wherein said nanofibres are twisted together by said helical movement of gas; and

means for continuously removing said yarn from said chamber through said second opening or a third opening located at the bottom region of said chamber, wherein said means do not have any mechanical contact with the yarn within said chamber during normal operation of the device; wherein

said means for creating helical movement of gas comprises means for creating a negative pressure within said chamber, the pressure inside the chamber is lower compared to ambient pressure so that the gas is sucked into said chamber through said first opening and said elongated slits.
A device as in claim 1, wherein said chamber is shaped as cylinder.
A device as in claim 1, wherein said chamber is shaped as bicone.
A device as in claim 1, wherein said chamber is shaped as upside down oriented cone.
A device as in claim 1 to 4, wherein said means for creating negative pressure comprises a fan near the second opening, said fan adapted to draw gas out of said chamber through said second opening.
A device as in claims 1 to 4, wherein said means for creating negative pressure comprises a vacuum pump.
A device as in claims 1 to 4, wherein said means for creating negative pressure comprises means for generating a horizontal gas flow below the second opening.
A device as in claims 1 to 7, wherein said means for forming nanofibres comprises oppositely charged nozzles.
A device as in claims 1 to 8, comprising means for controlling the linear speed of the gas flow through the chamber, wherein by said controlling said linear speed the shape and parameters of the gas vortex are controlled.
A device as in claim 9, wherein said means for controlling the linear speed of the gas flow comprises a fan pneumatically connected to said first opening and controlling the airflow from outside into the chamber.
A method for preparing a continuous nanofibrous yarn or bundles comprising nanofibers and fibrils in an electrospinning chamber, the method comprising:
generating a helical movement of gas in said electrospinning chamber, said gas moving in one general linear direction while simultaneously controlling the speed of said gas in said general linear direction;

forming by electrospinning a plurality of nanofibres and fibrils into said electrospinning chamber directly into said helically moving gas, and twisting together said plurality of nanofibres into said nanofibrous yarn by said helical movement of gas; and

continuously removing said yarn from said electrospinning chamber without having any mechanical contact with said yarn within said electrospinning chamber, and collecting said yarn outside the electrospinning chamber.
A method as in claim 11, wherein said helical movement of gas is generated by creating a negative pressure within said electropsinning chamber.
A method as in claim 12, wherein said helical movement of gas is generated by withdrawing gas out of said room.
A method as in claim 11, wherein a point where said plurality of nanofibres are joined together is controlled by adjusting the speed of the gasflow, a polymer solution used for preparing the nanofibres, the humidity inside the chamber, or the voltage applied to electrospinning nozzles.