The invention relates to a method of electrostatic spinning of polymer melt, at which prepared polymer melt is supplied into an electric field induced between a spinning electrode and a collecting electrode.

Background art

At present for production of polymer nanofibres mostly the process of electrostatic spinning of polymer solutions is being used. Upon usage of spinning electrode formed of rotating elongated body according to EP patent 1673493, or body according to EP application 2059630, this method is able to produce nanofibres in sufficient quantity and quality for majority of industrial applications. Nevertheless its shortcoming is that, it enables production of nanofibres only of polymers that easily form solutions in common solvents. On the contrary, the most important polymers, like e.g. polyethylene or polypropylene, which are worldwide produced in largest quantities, dissolve in these solvents only reluctantly or not at all, and for creation of solutions usable for electrostatic spinning, they require using of specific solvents, like e.g. xylene or toluene. Nevertheless these are not suitable for industrial applicability.

Another disadvantage of electrostatic spinning of polymer solutions is necessity of continual removal of vapours of the solvent, which evaporate from produced nanofibres, and in some cases also from free surface of polymer solution in a reservoir, from the space in which electrostatic spinning is performed. Even slightly increased concentration of these vapours negatively influences output of electrostatic spinning and also quality and morphology of nanofibres being produced. At higher concentrations of vapours of some solvents there even exists danger of their ignition or explosion. Usually it is necessary to neutralise and/or to recycle removed vapours due to their nature, and so there is an increase in acquisition costs as well as in operational costs of the device on which the process of electrostatic spinning of polymer solutions is performed.

An alternative to electrostatic spinning of polymer solutions, that remedies both mentioned disadvantages, is electrostatic spinning of polymer melts, because the melt can be prepared from many known polymers, while no solvent evaporates from it. From experiments realised to date it is nevertheless obvious, that even at creating the same conditions in the electric field at which from polymer solutions the nanofibres are created, from melts of these polymers only microfibres having diameter in range from c. 10 to 50 micrometers are created. Obviously it is caused by different properties of solvents and melts of polymers, especially of their different viscosity. In this sense describes article of Paul D. Dalton, Dirk Grafahrend, Kristina Klinkhammer, Doris Klee and Martin Moller: „Electrospinning of Polymer Melts: Phenomenological Observations", Polymer 48 (2007) 6823-6833, a possibility to produce nanofibres having diameter 650 to 1030 nanometers through electrostatic spinning of polypropylene melt by means of spinning electrode formed of nozzle, in case when the viscosity of the melt is reduced by suitable additive. In the mentioned case the additive designated by trademark„lrgatec" is used. Simultaneously application of special type of collecting electrode with two elongated segments arranged into the shape of V letter contributes to production of nanofibres. This procedure is nevertheless due to its technological demand and low output suitable only to be carried out in laboratory conditions, and is in no case applicable for industrial production of nanofibres.

The goal of the invention is to remedy or at least to minimise the disadvantages of the background art and to propose a method of electrostatic spinning of polymer melts, especially of polyethylene, polypropylene, polycaprolactone and copolymer of polyethylene-acrylic acid with 5% content of acrylic acid, which could be applicable in industrial scale.

Principle of the invention

The goal of the invention is achieved by a method of electrostatic spinning of polymer melt in an electric field induced between a spinning electrode and a collecting electrode, whose principle consists in that, before and/or during and/or after preparation of the polymer melt 1 to 25% by weight of a conducting agent is added to the polymer, by which electrical conductivity of the polymer melt is increased.

If there is a need, the polymer melt is before supplying into the electric field homogenised by mixing.

The most suitable conducting agent for spinning of polyethylene melt is tetraalkylammonium halogenide with four identical alkyls and temperature of melting up to 250°C, like e.g. tetrabutylammonium iodide or tetrabutylammonium bromide, in quantity of 3 to 25% by weight, or tetraalkylammonium halogenide with three identical alkyls and temperature of melting up to 250°C, like for example triethylhexylammonium bromide in quantity of 3 to 25% by weight, or their mixture.

At another polymers the same conducting agents may be used, whose quantity varies in case of copolymer of ethylene-acrylic acid with 5% content of acrylic acid in the range from 5 to 20% by weight, in case of polycaprolactone in the range from 1 to 10% by weight, and in the case of polypropylene in the range from 3 to 15% by weight.

To get smaller diameter of nanofibres of polypropylene tetraalkylphosphonium salt with four identical alkyls, where the anion is halogenide, tosylate or bistriflamide, or tetraalkylphosphonium salt with three identical alkyls, where the anion is halogenide, tosylate or bistriflamide, or their mixture in quantity of 1 to 5% by weight can be used as the conducting agent. Suitable and verified tetraalkylphosphonium salt with four identical alkyles is tetraoctylphosphonium bromide or tetraoctylphosphonium iodide, in case of tetraalkylphosphonium salt with three identical alkyls it is then tributhylhexadecylphosphonium bromide, tributhylhexadecylphosphonium chloride, trihexyltetradecylphosphonium chloride, tributhylhexadecylphosphonium tosylate or triisobuthyl(methyl)phosphonium tosylate. For the same purpose also sodium salt of higher fatty acid or mixture of sodium salts of higher fatty acid in quantity from 5 to 15% by weight may be used. For example sodium stearate or sodium octanoate is suitable salt.

Description of the drawing

Principle of the invention will be explained referring to enclosed drawing, where Fig. 1 shows a cross-section of one of variants of a device for electrostatic spinning of polymer melt, Fig. 1a a SEM picture of fibres produced through electrostatic spinning of polyethylene melt according to the invention, Fig. 1b shows distribution of diameters of these fibres, Fig. 2a a SEM picture of fibres produced through electrostatic spinning of polyethylene melt of another composition, Fig. 2b shows distribution of diameters of these fibres, Fig. 3a a SEM picture of fibres produced through electrostatic spinning of copolymer melt of ethylene-acrylic acid with 5% content of acrylic acid, Fig. 3b shows distribution of diameters of these fibres, Fig. 4a a SEM picture of fibres produced through electrostatic spinning of polycaprolactone melt according to the invention, Fig. 4b shows distribution of diameters of these fibres, Fig. 5a, 6a, 7a, 8a, 9a, 10a, 11a SEM pictures of fibres produced through electrostatic spinning of polypropylene melt of various compositions according to the invention, and Fig. 5b, 6b, 7b, 8b, 9b, 10b, 11b shows distribution of diameters of these fibres.

Examples embodiment

A method of electrostatic spinning of polymer melt according to the invention will be explained on examples of electrostatic spinning of melt of polyethylene, melt of copolymer of polyethylene-acrylic acid with 5% content of acrylic acid, melt of polycaprolactone and melt of polypropylene performed on the device represented in Fig. 1. This device comprises in its spinning chamber static cylindric collecting electrode 2 according to the international patent application WO 2008011840, and against it rotatably arranged spinning electrode 3 according to EP patent application 2059630 or CZ PV 2009-525 with electrically conducting faces 31 , between which the spinning elements 32 formed of electrically conducting wire are led. The spinning electrode 3 is coupled with not represented drive for rotating motion around its longitudinal axis 30, which is parallel with longitudinal axis 20 of collecting electrode 2, while extends by its lower section and respective spinning elements 32 into the polymer melt 4 contained in the reservoir 5.

Spinning elements 32 of the spinning electrode 3 and the collecting electrode 2 are connected with opposite poles of source 6 of high direct voltage positioned outside the spinning chamber Λ , by which an electric field of high intensity is induced between them. In other variants of embodiment this electric field may be induced also by grounding the spinning electrode 3 or the collecting electrode 2, while to the second of electrodes high voltage of positive or negative polarity is supplied.

In the space between the spinning electrode 3 and the collecting electrode 2 in vicinity of the collecting electrode 2 by means of not represented guiding elementsa substrate 7, which in the represented example of embodiment is polypropylene spunbond with antistatic finish, is guided moveably. In other examples of embodiment different type of substrate 7 may be used, which may be according to the considered application both electrically conducting as well as electrically non-conducting, while most frequently planar or linear textile formations of various types, plastic or metallic foils, various types of paper, filtration paper etc., are used. If an electrically non-conducting substrate 7 is used, it may be advantageous to use a corona discharger according to the international patent application WO 2008098526, which deposits an electric charge on the substrate 7, so that it behaves thanks to this as the collecting electrode. The substrate 7 is coupled with not represented drive, and according to the requirements moves in the spinning chamber 1 either in an interrupted manner, or non-interrupted manner in direction of arrow A, thus in direction from the picture plane of Fig. 1. In other variants of embodiment the substrate 7 may in the spinning chamber Λ move, if there is such a need, also reversibly. The device for performance the method according to the invention is in the spinning chamber 1 and/or outside it provided with not represented elements to increase temperature in the spinning chamber 1 and/or to maintain it on the required value. Their construction, principle, number and positioning may be at the same time totally individual, depending on inner arrangement of other elements of this device, and/or on the polymer being subject to spinning, and due to the fact, that they do not influence principle of the invention, will not be further described.

During operation the spinning elements 32 of the rotating spinning electrode 3 carry out on their surface the polymer melt 4 from reservoir 5 into the electric field, which is induced between the given spinning element 32 and the collecting electrode 2, and in which due to its action of force this melt 4 is transformed into nanofibres. These nanofibres move after their creation towards the collecting electrode 2 and are caught on the impact side 71 of the substrate 7, where they deposit into a layer. The layer of nanofibres is after then used according to the requirements and type of application either in combination with the substrate 7, at the same time it may be, if required, in some of the known methods additionally attached to it, or adhesion of the nanofibre layer to the substrate 7 may be increased, e.g. using the method according to CZ 2009-148 or CZ 2009-149, or it is detached from it and is used independently, possibly in combination with other layers of material.

The method for production of nanofibres through electrostatic spinning of polymer melt 4 according to the invention is nevertheless not bound only to the construction of the device represented in Fig. 1. The same or very similar results may be achieved also at usage of not represented modified variants of this device, which utilise any other types of collecting electrodes 2 and/or spinning electrodes 3, including the spinning electrodes 3 formed of full cylinder or any other elongated body rotating around its longitudinal axis, a needle or system of needles, a capillary or system of capillaries, etc., possibly variants which in the spinning chamber 1 comprise other number of spinning electrodes 3 and/or collecting electrodes 2. Next to this, these devices may be of different mutual space arrangement of the spinning electrode 3 (spinning electrodes) and the collecting electrode 2 (collecting electrodes), while e.g. the spinning electrode 3 according to CZ PV 2010-21 1 may be positioned in the space above the collecting electrode 2 (collecting electrodes), so that spinning is performed in direction downwards or askew downwards, eventually other types of spinning electrode 3 may be positioned beside the collecting electrode 2 (collecting electrodes), so that spinning is performed to the side or askew to the side.

In other not represented variants the substrate 7 is guided outside the space between the spinning electrode 3 and the collecting electrode 2, while the nanofibres being produced are brought to its impact side 71 by means of stream of air or any other gas, or by other suitable manner.

Polymer melt 4 for electrostatic spinning according to the invention is prepared by melting the respective polymer, to which before melting and/or during and/or after melting suitable quantity of conducting agent is added. This conducting agent increases electrical conductivity of the polymer melt 4, and due to this increases output of electrostatic spinning as it facilitates transfer of electric charge between the spinning electrode 3 and the collecting electrode 2, and simultaneously facilitates separating of polymeric chains, by which it reduces diameter of fibres being produced and enables creating of nanofibres instead of to date common microfibres. In this manner prepared melt 4 is subsequently mixed, preferably in double screw extruder, through which homogeneity is achieved in its whole volume, and after that it is positioned into the reservoir 5, from which it is through the above mentioned method carried out into the electric field and transformed into nanofibres. If sufficient mixing of polymer and conducting agent is secured already during preparation of the melt 4, there is no need to mix the melt 4 additionally.

Preparation and concrete composition of the melts 4 of polyethylene, copolymer of polyethylene-acrylic acid with 5% content of acrylic acid, polycaprolactone and polypropylene are as well as conditions under which their electrostatic spinning was performed and achieved results shown in the following examples. The principle of the invention is nevertheless, next to the mentioned polymers and conducting agents, usable also for number of other polymers and conducting agents with similar character. On the basis of experiments it was revealed, that the most suitable conducting agent for electrostatic spinning of melt 4 of polyethylene are tetraalkylammonium halogenides with four identical alkyls (e.g. tetrabutylammonium iodide or tetrabutylammonioum bromide), or with three identical and one different alkyl (e.g. triethylhexylammonium bromide), with temperature of melting up to 250°C. Only one of the above mentioned tetraalkylammonium halogenides, or mixture of several of them may be used, while total part of conducting agent in the melt 4 varies in the range from 3 to 25% by weight, preferably from 10 to 15% by weight.

Examplel

The melt 4 was prepared by melting of 28,5 g of polyethylene with Mn ( number average molar mass) 1800 and 1 ,5 g of tetrabutylammonium iodide - i.e. 5% by weight, at temperature of 180°C. After homogenisation in double screw extruder, which was running for period of 10 minutes, the melt 4 was positioned into reservoir 5 of the device for electrostatic spinning in variant represented in Fig. 1 and subjected to spinning at temperature of 180°C. The difference of electric voltage brought to spinning elements 32 of the spinning electrode 3 and to the collecting electrode 2 was 120 kV, distance between the nearest spinning element 32 of the spinning electrode 3 and the collecting electrode 2 was 30 cm. The spinning electrode 3 was rotating around its longitudinal axis 30 at speed of 20 rpm.

Through electrostatic spinning a layer of fibres represented in the SEM picture in Fig. 1a was produced.. Fig. 1b represents distribution of diameters of polyethylene fibres in this layer, from which it is obvious that diameter of 95% of produced fibres varied in the range from 200 to 1000 nanometers, so that these were nanofibres, and at only 5% of fibres it exceeded value of 1000 nanometers.

Example 2 The melt 4 was prepared by melting of 27 g of polyethylene with Mn 1800 and 3 g of tetrabutylammonium iodide - i.e. 10% by weight, at temperature of 180°C. After homogenisation in double screw extruder, which was running for period of 10 minutes, the melt 4 was positioned into reservoir 5 of the device for electrostatic spinning in variant represented in Fig. 1 and subjected to spinning at temperature of 180°C. The difference of electric voltage brought to spinning elements 32 of the spinning electrode 3 and to the collecting electrode 2 was 120 kV, distance between the nearest spinning element 32 of the spinning electrode 3 and the collecting electrode 2 was 30 cm. The spinning electrode 3 was rotating around its longitudinal axis 30 at speed of 15 rpm.

Through electrostatic spinning a layer of fibres that is represented in the SEM picture in Fig. 2a was produced. Fig. 2b represents distribution of diameters of polyethylene fibres in this layer, from which it is obvious that diameter of 95% of produced fibres varied in the range from 100 to 800 nanometers, so that these were nanofibres, and only at 5% of fibres it exceeded value of 1000 nanometers. The greatest recorded diameter was then 1500 nanometers.

In further examples the melt 4 of polyethylene contained 15% by weight or 20% by weight of tetrabutylammonium iodide. The fibre layer prepared by its electrostatic spinning under the same conditions as in examples 1 and 2 then contained 91 to 97% of fibres having diameter up to 1000 nanometers, thus nanofibres, and 3% to 9% of fibres having diameter above 1000 nanometers, thus microfibres.

Thanks to the same or similar physical properties the same or similar results may be achieved even at usage of other tetraalkylammonium halogenides with four identical alkyls (e.g. tetrabutylammonioum bromide), or with three identical and one different alkyl (e.g. triethylhexylammonium bromide), and with temperature of melting up to 250°C, or of their mixtures.

The same tetraalkylammonium halogenides with four identical alkyls or tetraalkylammonium halogenide with three identical and one different alkyl and temperature of melting up to 250°C, possibly their mixtures, may be used as conducting agent also at electrostatic spinning of the melt 4 of copolymer of ethylen-acrylic acid with 5% content of acrylic acid. The total part of conducting agent in the melt 4 thus varies from 5 to 20% by weight, preferably from 8 to 12% by weight.

Example 3

The melt 4 was prepared by melting of 27 g of copolymer of ethylene- acrylic acid with 5% content of acrylic acid with Mn 1800 and 3 g of tetrabutylammonium iodide - i.e. 10% by weight at temperature of 180°C. After homogenisation in double screw extruder, which was running for period of 10 minutes, the melt 4 was positioned into reservoir 5 of the device for electrostatic spinning in variant represented in Fig. 1 and subjected to spinning at temperature of 180°C. The difference of electric voltage brought to spinning elements 32 of the spinning electrode 3 and to the collecting electrode 2 was 120 kV, distance between the nearest spinning element 32 of the spinning electrode 3 and the collecting electrode 2 was 30 cm. The spinning electrode 3 was rotating around its longitudinal axis 30 at speed of 15 rpm.

Through electrostatic spinning a layer of fibres that is represented in the SEM picture in Fig. 3a was produced. Fig. 3b represents distribution of diameters of fibres of copolymer of ethylene-acrylic acid in this layer, from which it is obvious that diameter of more than 95% of produced fibres varied in the range from 100 to 700 nanometers, so these were nanofibres, only at 5% of fibres their diameter exceeded value of 1000 nanometers. The greatest recorded diameter was 1300 nanometers.

In further examples the melt 4 of copolymer of ethylene-acrylic acid with 5% content of acrylic acid gradually contained 5% by weight, 15% by weight and 20% by weight of tetrabutylammonium iodide. The layer of fibres produced through its electrostatic spinning under the same conditions as in example 3 then contained 90 to 97% of fibres of diameter up to 1000 nanometers, thus nanofibres, and 3 to 10% fibres having diameter above 1000 nanometers, thus microfibres. Thanks to the same or similar physical properties the same or similar results may be achieved even at usage of other tetraalkylammonium halogenides with four identical alkyls (e.g. tetrabutylammonioum bromide), or with three identical and one different alkyl (e.g. triethylhexylammonium bromide), and with temperature of melting up to 250°C, or of their mixtures.

The same tetraalkylammonium halogenides with four identical alkyls or tetraalkylammonium halogenide with three identical and one different alkyl and temperature of melting up to 250°C, possibly their mixtures, may be used as conducting agent also at electrostatic spinning of the melt 4 of polycaprolactone. The total part of conducting agent in the melt 4 thus varies from 1 to 10% by weight, preferably from 3 to 6% by weight.

Example 4

The melt 4 was prepared by melting of 28,5 g of polycaprolactone with Mn 10000, Mw (weight average molar mass) 14000 and 1 ,5 g of tetrabutylammonium iodide - i.e. 5% by weight, at temperature of 180°C. After homogenisation in double screw extruder, which was running for period of 10 minutes, the melt 4 was positioned into reservoir 5 of the device for electrostatic spinning in variant represented in Fig. 1 and subjected to spinning at temperature of 180°C. The difference of electric voltage brought to spinning elements 32 of the spinning electrode 3 and to the collecting electrode 2 was 120 kV, distance between the nearest spinning element 32 of the spinning electrode 3 and the collecting electrode 2 was 30 cm. The spinning electrode 3 was rotating around its longitudinal axis 30 at speed of 12,5 rpm.

Through electrostatic spinning a layer of fibres that is represented in the

SEM picture in Fig. 4a was produced. Fig. 4b represents distribution of diameters of polycaprolactone fibres in this layer, from which it is obvious that diameter of all produced fibres varied in the range from 100 to 300 nanometers, so that these were exclusively nanofibres. The smallest recorded diameter was 64 nanometers, the greatest was 300 nanometers. In further examples the melt 4 of polycaprolactone contained 1% by weight, or 10% by weight of tetrabutylammonium iodide. The layer of fibres prepared through its electrostatic spinning under the same conditions as in example 4 then contained exclusively nanofibres having diameter up to 1000 nanometers.

Thanks to the same or similar physical properties the same or similar results may be achieved even at usage of other tetraalkylammonium halogenides with four identical alkyls (e.g. tetrabutylammonium bromide), or with three identical and one different alkyl (e.g. triethylhexylammonium bromide), and with temperature of melting up to 250°C, or of their mixtures.

For preparation of the melt 4 of polypropylene and its subsequent electrostatic spinning as conducting agent the same tetraalkylammonium halogenides with four identical alkyls or tetraalkylammonium halogenides with three identical and one different alkyl and temperature of melting up to 250°C, possible their mixtures are also usable. The part of such conducting agent in the melt 4 thus varies from 3 to 15% by weight, preferably from 5 to 10% by weight.

Example 5

The melt 4 was prepared by melting of 27,9 g of polypropylene with Mn 5000, Mw 14000 and 2,1 g of tetrabutylammonium iodide - i.e. 7% by weight, at temperature of 180°C. After homogenisation in double screw extruder, which was running for period of 10 minutes, the melt 4 was positioned into reservoir 5 of the device for electrostatic spinning in variant represented in Fig. 1 and subjected to spinning at temperature of 210°C. The difference of electric voltage brought to spinning elements 32 of the spinning electrode 3 and to the collecting electrode 2 was 120 kV, distance between the nearest spinning element 32 of the spinning electrode 3 and the collecting electrode 2 was 30 cm. The spinning electrode 3 was rotating around its longitudinal axis 30 at speed of 15 rpm.

Through electrostatic spinning a layer of fibres that is represented in the SEM picture in Fig. 5a was produced. Fig. 5b represents distribution of diameters of polypropylene fibres in this layer, from which it is obvious that diameter of 97% of produced fibres varied in the range from 200 to 900 nanometers, so that these were nanofibres, and only at less than 3% of fibres their diameter exceeded 1000 nanometers.

Example 6

The melt 4 was prepared by melting of 27g of polypropylene with Mn 5000, Mw 14000 and 3 g of tetrabutylammonium iodide - i.e. 10% by weight, at temperature of 180°C. After homogenisation in double screw extruder, which was running for period of 10 minutes, the melt 4 was positioned into reservoir 5 of the device for electrostatic spinning in variant represented in Fig. 1 and subjected to spinning at temperature of 210°C. The difference of electric voltage brought to spinning elements 32 of the spinning electrode 3 and to the collecting electrode 2 was 120 kV, distance between the nearest spinning element 32 of the spinning electrode 3 and the collecting electrode 2 was 30 cm. The spinning electrode 3 was rotating around its longitudinal axis 30 at speed of 15 rpm.

Through electrostatic spinning a layer of fibres that is represented in the SEM picture in Fig. 6a was produced. Fig. 6b represents distribution of diameters of polypropylene fibres in this layer, from which it is obvious that diameter of 97% of produced fibres varied in the range from 100 to 900 nanometers, so that these were nanofibres, and only at less than 3% of fibres their diameter exceeded value of 1000 nanometers.

In further examples the melt 4 of polyethylene contained 5% by weight or 15% by weight of tetrabutylammonium iodide. The fibre layer prepared by its electrostatic spinning under the same conditions as in example 6 then contained 94 to 98% of fibres having diameter up to 1000 nanometers, thus nanofibres, and 2% to 6% of fibres having diameter above 1000 nanometers, thus microfibres.

Thanks to the same or similar physical properties the same or similar results may be achieved even at usage of other tetraalkylammonium halogenides with four identical alkyls (e.g. tetrabutylammonioum bromide), or with three identical and one different alkyl (e.g. triethylhexylammonium bromide), and with temperature of melting up to 250°C, or of their mixtures

During experiments it was further revealed, that as conducting agent for preparation of the melt 4 of polypropylene and its subsequent electrostatic spinning further also tetraalkylphosphonium salt with four identical alkyls (e.g. tetraoctylphosphonium bromide or tetraoctylphosphonium iodide, etc.), tetraalkylphosphonium salts with three identical and one different alkyl (e.g. tributylhexadecylphosphonium bromide, tributylhexadecylphosphonium chloride, trihexyltetradecylphosphonium chloride, tributylhexadecylphosphonium tosylate, triisobutyl(methyl)phosphonium tosylate, etc.) where the anion is halogenide, tosylate or bistriflamide, or mixture of such tetraalkylphosphonium salts are usable, regardless their temperature of melting. The part of this conducting agent in the melt 4 of polypropylene varies in the interval from 1 to 5% by weight, preferably from 3 to 4% by weight.

Example 7

The melt 4 was prepared by melting of 29, 1g of polypropylene with Mn 5000, Mw 12000 and 0,9g of tributylhexadecylphosphonium bromide - i.e. 3% by weight, at temperature of 180°C. After homogenisation in double screw extruder, which was running for period of 10 minutes, the melt 4 was positioned into reservoir 5 of the device for electrostatic spanning in variant represented in Fig. 1 and subjected to spinning at temperature of 180°C. The difference of electric voltage brought to spinning elements 32 of the spinning electrode 3 and to the collecting electrode 2 was 120 kV, distance between the nearest spinning element 32 of the spinning electrode 3 and the collecting electrode 2 was 30 cm. The spinning electrode 3 was rotating around its longitudinal axis 30 at speed of 15 rpm.

Through electrostatic spinning a layer of fibres that is represented in the SEM picture in Fig. 7a was produced. Fig. 7b represents distribution of diameters of polypropylene fibres in this layer, from which it is obvious that diameter of all produced fibres varied in the range from 100 to 900 nanometers, so that these were exclusively nanofibres. The smallest recorded diameter was 60 nanometers.

In further examples the melt 4 of polypropylene contained 1% by weight, or 5 % by weight of tributylhexadecylphosphonium bromide. The layer of fibres prepared through its electrostatic spinning under the same conditions as in example 7 then contained exclusively nanofibres having diameter in the range from 100 to 900 nanometers.

Example 8

The melt 4 was prepared by melting of 29, 1g of polypropylene with Mn

5000, Mw 12000 and 0,9g of trihexyltetradecylphfosphonium chloride - i.e. 3% by weight at temperature of 180°C. After homogenisation in double screw extruder, which was running for period of 10 minutes, the melt 4 was positioned into reservoir 5 of the device for electrostatic spinning in variant represented in Fig. 1 and subjected to spinning at temperature of 180°C. The difference of electric voltage brought to spinning elements 32 of the spinning electrode 3 and to the collecting electrode 2 was 120 kV, distance between the nearest spinning element 32 of the spinning electrode 3 and the collecting electrode 2 was 30 cm. The spinning electrode 3 was rotating around its longitudinal axis 30 at speed of 15 rpm.

Through electrostatic spinning a layer of fibres that is represented in the SEM picture in Fig. 8a was produced. Fig. 8b represents distribution of diameters of polypropylene fibres in this layer, from which it is obvious that diameter of all produced fibres varied in the range from 100 to 550 nanometers, so that these were exclusively nanofibres. The smallest recorded diameter was 80 nanometers.

In further examples the melt 4 of polypropylene contained 1% by weight, or 5 % by weight of trihexyltetradecylphosphonium chloride. The layer of fibres prepared through its electrostatic spinning under the same conditions as in example 8 then contained exclusively nanofibres having diameter in the range from 80 to 800 nanometers. Example 9

The melt 4 was prepared by melting of 29, g of polypropylene with Mn 5000, Mw 12000 and 0,9g of triisobutyl(methyl)phosphonium tosylate - i.e. 3% by weight at temperature of 180°C. After homogenisation in double screw extruder, which was running for period of 10 minutes, the melt 4 was positioned into reservoir 5 of the device for electrostatic spinning in variant represented in Fig. 1 and subjected to spinning at temperature of 180°C. The difference of electric voltage brought to spinning elements 32 of the spinning electrode 3 and to the collecting electrode 2 was 120 kV, distance between the nearest spinning element 32 of the spinning electrode 3 and the collecting electrode 2 was 30 cm. The spinning electrode 3 was rotating around its longitudinal axis 30 at speed of 15 rpm.

Through electrostatic spinning a layer of fibres that is represented in the SEM picture in Fig. 9a was produced. Fig. 9b represents distribution of diameters of polypropylene fibres in this layer, from which it is obvious that diameter of all produced fibres varied in the range from 250 to 900 nanometers, so that these were exclusively nanofibres. The smallest recorded diameter was 200 nanometers.

In further examples the melt 4 of polypropylene contained 1% by weight, or 5 % by weight of triisobutyl(methyl)phosphonium tosylate. The layer of fibres prepared through its electrostatic spinning under the same conditions as in example 9 then contained exclusively nanofibres having diameter in the range from 200 to 1000 nanometers.

Thanks to the same or similar physical properties the same or similar results may be achieved even at usage of tetraalkylphosphonium salts with four identical alkyls where anion is halogenide, tosylate or bistriflamide (e.g. tetraoctylphosphonium bromide, tetraoctylphosphonium iodide, etc.), of other tetraalkyphosophonium salts with three identical and one different alkyl, where the anion is halogenide, tosylate or bistriflamide, or their mixtures (e.g. tributylhexadecylphosphonium chloride, tributylhexadecylphosphonium tosylate, etc.). Next to this, for electrostatic spinning of the melt 4 of polypropylene as conducting agent also sodium salts of higher fatty acids, like e.g. sodium stearate or sodium octanoate, etc., or their mixtures may be used, while the part of this conducting agent in the melt 4 varies in the interval from 5 to 15% by weight, preferably from 8 to 12% by weight.

Example 10

The melt 4 was prepared by melting of 27g of polypropylene with Mn 5000, Mw 12000 and 3g of sodium stearate - i.e. 10% by weight, at temperature of 260°C. After homogenisation in double screw extruder, which was running for period of 10 minutes, the melt 4 was positioned into reservoir 5 of the device for electrostatic spinning in variant represented in Fig. 1 and subjected to spinning at temperature of 240°C. The difference of electric voltage brought to spinning elements 32 of the spinning electrode 3 and to the collecting electrode 2 was 120 kV, distance between the nearest spinning element 32 of the spinning electrode 3 and the collecting electrode 2 was 30 cm. The spinning electrode 3 was rotating around its longitudinal axis 30 at speed of 15 rpm.

At this process a layer of fibres that is represented in the SEM picture in Fig. 10a was produced. Fig. 10b represents distribution of diameters of polypropylene fibres in this layer, from which it is obvious that diameter of all produced fibres varied in the range from 100 to 700 nanometers, so that these were exclusively nanofibres.

In further examples the melt 4 of polypropylene contained 5% by weight, or 15% by weight of sodium stearate. The layer of fibres prepared through its electrostatic spinning under the same conditions as in example 10 then contained exclusively nanofibres having diameter in the range from 100 to 900 nanometers.

Example 11

The melt 4 was prepared by melting of 28, 5g of polypropylene with Mn

5000, Mw 12000 and 1 ,5g of sodium octanoate - i.e. 5% by weight at temperature of 250°C. After homogenisation in double screw extruder, which was running for period of 10 minutes, the melt 4 was positioned into reservoir 5 of the device for electrostatic spinning in variant represented in Fig. 1 , and subjected to spinning at temperature of 240°C. The difference of electric voltage brought to spinning elements 32 of the spinning electrode 3 and to the collecting electrode 2 was 120 kV, distance between the nearest spinning element 32 of the spinning electrode 3 and the collecting electrode 2 was 30 cm. The spinning electrode 3 was rotating around its longitudinal axis 30 at speed of 15 rpm.

At this process a layer of fibres that is represented in the SEM picture in Fig. 11a was produced. Fig. 1 1b represents distribution of diameters of polypropylene fibres in this layer, from which it is obvious that diameter of all produced fibres varied in the range from 100 to 700 nanometers, so that these were exclusively nanofibres.

In further examples the melt 4 of polypropylene contained 10% by weight, or 15% by weight of sodium octanoate. The layer of fibres prepared through its electrostatic spinning under the same conditions as in example 11 then contained exclusively nanofibres having diameter in the range from 100 to 1000 nanometers.

Thanks to the same or similar physical properties the same or similar results may be achieved even at usage of other sodium salts of higher fatty acids or their mixtures.

Presence of relatively small quantity of microfibres among the nanofibres in examples 1 , 2, 3, 5 and 6 in no manner reduces the advantageous properties of produced layer of fibres, because it in an advantageous manner increases its strength and abrasion resistance, thus also its applicability.

During performance of experiments, the above mentioned quantities of individual conducting agents were specified to be optimum. If greater quantity of them was used, thanks to increased electrical conductivity of the melt 4 bunches of nanofibres were created instead of required uniform layer, by which total output of electrostatic spinning was considerably reduced. At lower content of the conducting agent in the melt 4, output of electrostatic spinning was also reduced at simultaneous increasing of diameter of the fibres being produced, when in the prepared layer prevailed fibres having diameter above 1000 nanometers, thus microfibres.

Also the specified temperatures are optimum for the given combination of polymer and conducting agent, because at higher temperatures thermal decomposition of the conducting agent occurs relatively quickly, so that it does not fulfil the required task, and at lower temperatures viscosity of resultant melt 4 is too high and the melt 4 is not capable of electrostatic spinning.