Linear Fibrous Formation with a Coating of Polymeric Nanofibers Enveloping a Supporting Linear Formation Constituting a Core, a Method and a Device for Producing It

Abstract

A method, system, and resulting linear fibrous formation are provided wherein a supporting linear formation defines a core that is transported through a spinning chamber. A coating of polymeric nanofibers enveloping the supporting linear formation in the spinning chamber. The coating of polymeric nanofibers comprises a flat stripe wound around the core into a helical form, the flat stripe created from a hollow electrically neutral nanofibrous plume generated in a spinning space above a spinning electrode during spinning by AC electric voltage in the spinning chamber.

Claims

1-16. (canceled)

17. A linear fibrous formation, comprising: a supporting linear formation defining a core; a coating of polymeric nanofibers enveloping the supporting linear formation; and wherein the coating of polymeric nanofibers comprises a flat stripe wound around the core into a helical form, the flat stripe created from a hollow electrically neutral nanofibrous plume generated above a spinning electrode during spinning by AC electric voltage.

18. The linear fibrous formation according to claim 17, wherein the coating of polymeric nanofibers comprises at least two layers of the flat nanofibrous stripes, each stripe comprising an organized structure of nanofibers created from the nanofibrous plumes during spinning by the AC voltage, whereby the first layer is wound around the supporting linear formation and the second layer is wound around the first layer.

19. The linear fibrous formation according to claim 18, wherein the first layer of the flat nanofibrous stripes is formed from a first polymeric nanofibers and the second layer of the flat nanofibers is formed from a second polymeric fibers having different properties than the first polymeric nanofibers.

20. The linear fibrous formation according to claim 19, wherein the first polymeric nanofibers comprise an adhesive material or a heat-shrinkable material.

21. The linear fibrous formation according to claim 19, wherein one of the layers of the flat nanofibrous stripes defines an outer cover material layer that protects inner ones of the layers of the flat nanofibrous stripes from damage.

22. The linear fibrous formation according to claim 17, wherein the core is removable from the resulting linear fibrous formation to produce a hollow tubular formation defined by the coating of polymeric nanofibers.

23. A method for production of a linear fibrous formation, comprising: conveying a supporting linear formation in the form of a core through a spinning chamber wherein the core is enveloped with a coating of polymeric nanofibers, the spinning chamber having a spinning electrode powered by AC voltage; in the spinning chamber, forming a hollow electrically neutral plume of nanofibers in a spinning space above the spinning electrode from a polymeric material fed to the spinning chamber, the plume changing into a flat stripe having an organized structure of the nanofibers; guiding the flat stripe onto a circumference of the core while rotating the core around its axis or while ballooning the core in the spinning space; and wherein the stripe is wound around the core in a manner to form a helix winding around the core.

24. The method according to claim 23, wherein the ballooning of the core is formed by rotation of an eccentric member of a twisting device through which the core passes before entering the spinning space.

25. The method according to claim 23, wherein the ballooning of the core is formed by blowing a pulsed airflow onto the core as the core is rotated around is axis.

26. The method according to claim 23, wherein the stripe is dried and fixed on the core in the helical form.

27. A system for production of a linear fibrous formation, comprising: a spinning chamber; a feeding device disposed so as to feed a supporting linear formation to the spinning chamber; a spinning electrode arranged in the spinning chamber and connected to a source of AC electric voltage, wherein a plume of polymeric nanofibers is formed in a sinning space above the spinning electrode in the spinning chamber; a draw-off device disposed to withdraw the linear fibrous formation from the spinning chamber; a twisting device disposed in a path of the supporting linear formation, the twisting device configured to create a false twist in or a rotating balloon from the supporting linear formation in the spinning chamber; and wherein, as a result of the false twist or ballooning of the supporting linear formation moving through the spinning chamber, the plume of polymeric nanofibers is wound around the supporting linear formation in a form a flat stripe having an organized structure the nanofibers.

28. The system according to claim 27, further comprising a drying and fixing device downstream of the spinning chamber in the path of the supporting linear formation to dry and fix the stripe wound around the supporting linear formation in a helix.

29. The system according to claim 27, wherein the twisting device is arranged upstream of the spinning chamber.

30. The system according to claim 27, wherein the twisting device is arranged downstream of the drying and fixing device.

31. The system according to claim 27, wherein the twisting device comprises a rotating eccentric member.

32. The system according to claim 27, further comprising an additional spinning electrode arranged in the spinning chamber along the path of the supporting linear formation downstream of the spinning electrode.

Description

DESCRIPTION OF DRAWINGS

[0020] Other advantages and features of the method and device according to the invention are illustrated in the enclosed drawings, wherein:

[0021] FIG. 1, FIG. 2 and FIG. 4 schematically represent examples of an embodiment for performing the method for the production of a linear fibrous formation according to the invention and the principle of this method;

[0022] FIG. 3 shows the principle of ballooning or rotation of a supporting linear formation (silk, staple yarns, monofilament) by means of a twisting device with a twisting tube;

[0023] FIGS. 5a, 5b, 5c and 5d show the linear fibrous formation according to the invention at different magnifications of a scanning electron microscope (SEM);

[0024] FIG. 6 is a SEM picture of a cross-section of the linear fibrous formation according to the invention with a coating of polymeric nanofibers and with a supporting linear formation formed by polyester yarn;

[0025] FIG. 7A shows a SEM image of a cross-section of the linear fibrous formation according to the invention with a supporting linear formation formed by monofilament;

[0026] FIG. 7B is a SEM image of a cross-section of a linear fibrous formation with a core composed of yarn and a coating of nanofibers and a cross-section of a nanofibrous tube formed after the removal of the core; and

[0027] FIGS. 8A, B provide a detailed representation of a cross-section of a nanofibrous tube formed after the removal of the core.

DETAILED DESCRIPTION

[0028] Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein.

[0029] In the embodiment according to FIG. 1, in the direction of the movement of the supporting linear formation 3 are arranged behind one another a feeding device 1, which serves to unwind the supporting linear formation 3 in a known manner from an unillustrated supply package, a twisting device 2, which can form a balloon with at least one antinode loop or at least false twist on the supporting linear formation 3, and a spinning chamber 4. Behind the spinning chamber 4 is arranged a drying and fixing device 7 for drying and fixing a nanofibrous coating 32, preferably in the shape of a tube or a channel, and a draw-off mechanism 8, behind which the stabilized resulting linear fibrous formation 30 with a nanofibrous coating 32 according to the invention is wound on an unillustrated bobbin in a known manner. Optionally, the drawing-off of the resulting linear formation can be performed directly by a winding device.

[0030] Spinning takes place due to the effect of alternating current voltage according to CZ 304 137.

[0031] In the spinning chamber 4 is arranged a spinning electrode 5, which is connected to an unillustrated adjustable source of AC high voltage, for example having a voltage of 35 kV and a frequency of 50 Hz, and to an unillustrated inlet for supply of a polymeric solution for spinning. The polymeric solution is dispensed into the spinning chamber 4, for example by means of an unillustrated linear pump. In the vicinity of the front face 51 of the spinning electrode 5 and above it in the spinning chamber 4, there is spinning space 41. In case of need, the impact of electric winding is enhanced by airflow in a required direction. The nanofibrous plume 6 is electrically neutral, since during its movement through the spinning space 41, mutual recombination of opposite electric charges of the individual nanofibers or their segments occurs. The polymeric nanofibers in the nanofibrous plume 6 are arranged in an irregular grid structure, in which the individual nanofibers in short segments change their direction.

[0032] As is shown in FIG. 3, the supporting linear formation 3, as a result of the rotation of the eccentric member 23 of the twisting device 2 through which it passes, for example the rotation of an opening located off the axis of the rotation of the twisting device 2, forms a balloon having several antinode loops passing through the spinning chamber 4, and in the spinning space 41, a nanofibrous plume 6 is deposited on the surface of the supporting linear formation 3 rotating in the balloon. The nanofibrous plume 6 is drifted to this space due to the effect of electric winding and wraps around the supporting linear formation 3, forming a stripe, that is, a flat formation created from the nanofibrous plume 6, which during ballooning winds around the core 31 (FIGS. 6-7) composed of a supporting linear formation 3, forming a nanofibrous coating 32 (FIGS. 6-7) on it, formed by helix-shaped windings. The antinode loops of the balloon are illustrated in FIGS. 1, 3 and 4, whereby FIG. 3 shows the twisting device and the antinodes of the supporting linear formation 3 constituting a core 31 of the resulting linear fibrous formation in the spinning chamber. The supporting linear formation 3 is fed from an unillustrated supply package by the feeding device 1 with a defined bias. The twisting device 2 is in the exemplary embodiment provided with an inlet 20, which is situated in its axis 22 of rotation. The supporting linear formation 3 is guided from the inlet 20 over a pin 21 to an eccentric member 23, which is in the illustrated embodiment formed by an axial orifice located off the axis 22 of the rotation of the twisting device 2. Due to the rotation of the twisting device 2 ballooning of the supporting linear formation 3 occurs, whereby onto the supporting linear formation 3 the nanofibrous plume 6 in the shape of a stripe is deposited in the spinning chamber 4.

[0033] If the winding speed of the nanofibrous plume 6 is the same as that of the process of its formation, the arrangement of nanofibers in the nanofibrous plume 6 remains the same even after it is wound around the core, as is apparent also on the coating 32 of the resulting linear fibrous formation 30, shown in FIGS. 5a-d. If the winding speed of the nanofibrous plume 6 is greater than the speed of its formation, the nanofibrous plume 6 becomes longer and, as a result, a certain orientation of the nanofibers in the structure of the nanofibrous plume 6 may occur after the nanofibrous plume 6 is wound onto the core 31.

[0034] From the spinning chamber 4, the produced resulting linear fibrous formation 30 with the nanofibrous coating 32 is withdrawn by the drawing-off mechanism 8 through the drying and fixing device 7, in which the nanofibrous coating 32 is dried and fixed at temperatures (for example, in the range from 60? C. to 250? C.) corresponding to the kind of the polymer being spun and the material of the supporting linear formation 3. The resulting linear fibrous formation 30 with the nanofibrous coating 32, usually called nanofibrous core yarn, is wound in a known manner onto an unillustrated bobbin behind the drawing-off mechanism 8.

[0035] In a series of verification experiments, AC high voltage of ?36 kV with a frequency of 50 Hz was supplied to the spinning electrode. Polyester multifilament having a fineness of 150 Tex was used as a core. The twisting device 2 rotated at a frequency of between 5,000 and 20,000 rpm, and the draw-off speed was set at 10 to 60 meters per minute. The material used for spinning was a solution of polyvinyl butyral (PVB) or polyacrylonitrile (PAN). Dispensing of the solution for the spinning electrode was set in the range of 80 to 250 ml per hour. The values of fiber diameters for the core yarn of PVB were in the range of 682?280 nm. During the spinning of the solutions of PAN, the mean value of the fiber diameter measured was 1805 nm with a large value of standard deviation of ?1322 nm and therefore with a significant proportion of nanofibers.

[0036] In the exemplary embodiment according to FIG. 2, the arrangement of the device is very similar to FIG. 1, only the twisting device 2 is disposed between the drying and fixing device 7 and the drawing-off device 8. In this arrangement, during the rotation of the twisting device 2, false twist is formed on the supporting linear formation 3 and on the resulting linear fibrous formation 31 between the twisting device 2 and the feeding device 1. Due to the location of the twisting device 2, ballooning does not occur in the spinning chamber 4 or its antinode loops are very small. Therefore, in the spinning chamber 4, the supporting fibrous formation 3 rotates around its axis and the nanofibrous plume 6, whose path is intersected by the supporting fibrous material 3, winds on it in the form of a stripe, which forms a layer in the form of a helix on the core 31. In this embodiment, ballooning can be achieved by blowing a pulsed airflow on the mechanically rotated supporting linear formation.

[0037] In the exemplary embodiment according to FIG. 4, two twisting devices 2 are used. The first twisting device is located in front of the spinning chamber 4, as in example 1, and ensures the ballooning of the supporting linear formation 3 in the spinning chamber 4 and the second twisting device 2 is located behind the drying and fixing device 7, as in example 2, and imparts false twist to the passing resulting linear fibrous formation 30, which is transmitted as far as to the supporting linear formation 3, constituting a core 31.

[0038] The revolutions of the second twisting device 2 implement false twist. It should be taken into account that real revolutions implementing false twist are lower than the revolutions of the second twisting device 2, since instead of pure rolling of the resulting linear fibrous formation 30 being twisted in cases when friction forces in the axial opening are exceeded, slippage and loss of twists occur. If the revolutions of the second twisting device 2 are greater than those of the first twisting device 2, during the winding of nanofibrous plume 6 onto the supporting linear formation 3 composed of a core 31, the nanofibrous stripe is twisted by the false twist, which leads to improving the strength of the connection of the nanofibrous coating 32 and the core 31 in the resulting linear fibrous formation 30, which has been experimentally verified. Having passed through the drying and fixing device 7 the nanofibrous coating is fixed on the core, apparently after the cancellation of the false twist behind the second twisting device 2.

[0039] If a nanofibrous coating 32 consisting of two or more layers of nanofibers is required, it appears to be advantageous to place two or more spinning electrodes 5 behind each other into the spinning chamber 4, so that from the spinning electrode 5, the first flat formation consisting of a hollow nanofibrous plume 6 is deposited on the supporting linear formation 3 during its ballooning and/or during the false-twisting operation, thereby creating the first nanofibrous layer. Subsequently, from the second spinning electrode 5, the second flat formation composed of a hollow nanofibrous plume 6 is deposited on the first layer of nanofibers in the same manner. Optionally, another flat formation consisting of a hollow nanofibrous plume 6 created by another spinning electrode 5 is deposited on the second layer of nanofibers. The individual layers of the nanofibrous coating can be composed of materials with different properties. For example, the first layer enveloping the supporting linear formation 3 constituting a core 31 of the resulting nanofibrous formation 30 is made of an adhesive material or a heat shrinkable material, such as PVB or polycaprolactone (PCL). In a preferred embodiment, the outer nanofibrous layer of the nanofibrous coating 32 is composed of a cover material capable of protecting the inner layers from damage, for example of polyvinylidene fluoride (PVDF) or polyurethane (PU).

[0040] A multi-layer nanofibrous coating 32 can be also produced by repeated applications of another layer to the preceding layer, whereby each layer is dried and fixed after being applied.

[0041] By means of a strong or tight wind of the core yarn of a suitable thickness/fineness or monofilament having a suitable diameter, or a firm core of another material of a suitable shape and cross-section, the resulting linear formation 30 with a nanofibrous coating 32 is formed, as is shown in FIGS. 6 and 7. The supporting core is removed from the resulting linear formation 30 by pulling out, dissolving, washing out, or by using another appropriate method. The preserved nanofibrous coating 32, which covered the core 31, will create a tubular formation shown in FIGS. 7 and 8, which can serve, for example, as a nanofibrous synthetic blood vessel having a suitable diameter.

[0042] The formation of a tubular formation can be performed by a continuous or discontinuous methodaccording to requirements. Preferably, for the production of a tubular formation it is possible to use the device and the method according to FIG. 1 or 4.

INDUSTRIAL APPLICABILITY

[0043] Linear fibrous formations according to the invention can be processed as core yarn by subsequent textile technologies into flat or three-dimensional textile formations, or it is possible to remove a core from them and produce hollow nanofibrous tubular formations.

[0044] Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims.

LIST OF REFERENCES

[0045] 1 feeding device

[0046] 2 twisting device

[0047] 20 inlet

[0048] 21 pin

[0049] 22 axis of rotation of twisting device

[0050] 23 eccentric member

[0051] 3 supporting linear formation

[0052] 30 resulting linear fibrous formation with a nanofibrous coating

[0053] 31 core of the resulting linear fibrous formation

[0054] 32 nanofibrous coating

[0055] 4 spinning chamber

[0056] 41 spinning space

[0057] 5 the spinning electrode

[0058] 51 front face of spinning electrode

[0059] 6 nanofibrous plume

[0060] 7 a drying and fixing device

[0061] 8 draw-off mechanism