WO2008049397A2

WO2008049397A2 - Method for producing nano- and mesopolymer fibers by electrospinning polyelectrolytes of opposite charge

Info

Publication number: WO2008049397A2
Application number: PCT/DE2007/001880
Authority: WO
Inventors: Andreas Greiner; Lisa Hamel
Original assignee: Philipps-Universität Marburg
Priority date: 2006-10-23
Filing date: 2007-10-22
Publication date: 2008-05-02
Also published as: EP2084312A2; DE102006050279A1; WO2008049397A3; EP2084312B1

Abstract

The invention relates to a method for producing polymer fibers, especially nano- and mesofibers, according to the electrospinning technique, wherein an aqueous solution including polyelectrolytes of opposite charge is electrospun. The fibers obtained according to said technique are stable in water. The solution to be spun can optionally contain at least one nonionic surfactant and/or at least one water-soluble polymer. The invention also relates to the fibers that can be obtained by said method.

Description

Process for the preparation of nano- and mesopolymer fibers by electrospinning polyelectrolytes of opposite charge

The present invention relates to a process for the preparation of polymer fibers, in particular of nano- and mesofasem, wherein an aqueous solution of oppositely charged polyelectrolytes is electro-spun, and fibers obtainable by this process. After subsequent contact with water there is no disintegration of the fibers according to the invention.

Description and introduction of the general field of the invention

The present invention relates to the fields of macromolecular chemistry, process engineering and materials science.

State of the art

For the production of nanofibres and mesofasems, the skilled worker is familiar with a large number of processes, of which the electrospinning process is of greatest importance at present.This process, which is described, for example, by DH Reneker, HD Chun in Nanotechn. , Page 216 f, a polymer melt or a polymer solution is usually exposed to a high electric field at an edge serving as an electrode, which can be achieved, for example, by subjecting the polymer melt or polymer solution in an electric field under low pressure to a pole Due to the resulting electrostatic charging of the polymer melt or polymer solution, a material flow directed onto the counterelectrode, which solidifies on the way to the counterelectrode, is produced with this method depending on the electrode geometries called nonwovens or ensembles of ordered fibers.

DE 101 33 393 A1 discloses a process for producing hollow fibers having an inner diameter of 1 to 100 nm, in which a solution of a water-insoluble polymer-for example a poly-L-lactide solution in dichloromethane or a polyamide-46 Solution in pyridine - is electrospun. A similar method is also known from WO 01/09414 A1 and DE 103 55 665 A1. DE 196 00 162 A1 discloses a process for producing lawn mower wire or textile fabrics in which polyamide, polyester or polypropylene as a thread-forming polymer, a maleic anhydride-modified polyethylene / polypropylene rubber and one or more aging stabilizers are combined, melted together and melted together are mixed before this melt is melt-spun.

DE 10 2004 009 887 A1 relates to a process for the production of fibers with a diameter of <50 μm by electrostatic spinning or spraying of a melt of at least one thermoplastic polymer.

The electrospinning of polymer melts allows only fibers with diameters greater than 1 μm to be produced. For a variety of applications, e.g. Filtration applications, however, nano- and / or mesofasem are required with a diameter of less than 1 micron, which can be prepared by the known electrospinning process only by using polymer solutions.

However, these methods have the disadvantage that the polymers to be spun first have to be brought into solution. For water-insoluble polymers, such as polyamides, polyolefins, polyesters and polyurethanes, it is therefore necessary to use nonaqueous solvents - regularly organic solvents - which are generally toxic, flammable, irritant, explosive and / or corrosive. In the case of water-soluble polymers, such as polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone or hydroxypropylcellulose, although the use of nonaqueous solvents can be dispensed with, the fibers obtained in this way are naturally soluble in water, which is why their technical application is severely restricted. For this reason, after electrospinning, these fibers must be stabilized against water by at least one further processing step, for example by chemical crosslinking, which represents a considerable technical expense and increases the manufacturing costs of the fibers.

WO 2004/080681 A1 relates to devices and methods for the electrostatic processing of polymer formulations. The polymer formulations may be solutions, dispersions, suspensions, emulsions, mixtures thereof or polymer melts. As a method of electrostatic processing, among others, electrospinning is mentioned. In WO 2004/080681 A1, however, no concrete polymer formulations are mentioned which are suitable for electrospinning.

WO 2004/048644 A2 discloses the electrosynthesis of nanofibers and nano-composite films. For Elektroverspinnen solutions of suitable starting materials are used. According to the description, the term "solutions" also encompasses heterogeneous mixtures such as suspensions or dispersions, inter alia, fibers from electrically conductive polymers can be produced according to WO 2004/048644 A2 2004/046644 A2 preferably obtained from the solutions containing the corresponding monomers.

DE 10 2005 008 926 A1, "Process for the Production of Nanofibres and Mesofibers by Electrospinning of Colloidal Dispersions" relates to a process for producing polymer fibers, wherein a colloidal dispersion of at least one substantially water-insoluble polymer is electrospun in an aqueous medium In this process, it has been possible for the first time to spin aqueous polymer dispersions by means of an electrospinning process, with polymer fibers, in particular nano- and mesofasem, being obtained.

With the aid of the process described in DE 10 2005 008 926 A1, it has been possible to avoid the above-mentioned disadvantages of the prior art and to provide a process for producing water-stable polymer fibers, in particular nano- and mesofibres, by the electrospinning process can be dispensed with the use of non-aqueous solvents for the preparation of a polymer solution and a post-treatment of the electro-spun fibers to stabilize the same with respect to water.

EP 06119248.0 dated 21.08.2006, which has priority over prior unpublished applications, describes a process optimized for the electrospinning of aqueous polymer dispersions which is optimized with respect to DE 10 2005 008 926 A1 and with which polymer fibers having optimized structural and / or mechanical properties can be obtained. In this case, a colloidal dispersion of at least one substantially water-insoluble polymer in an aqueous medium electrospun. The process according to EP 06119248.0 is characterized in that the colloidal dispersion contains at least one nonionic surfactant.

With the method according to EP 06119248.0 fibers with a high water resistance can be obtained, which are characterized by a good mechanical stability. It is possible with the method according to EP 06119248.0 to produce nano- and mesofasem with a diameter of less than 1 μm from aqueous dispersions, so that the use of non-aqueous, toxic, combustible, irritating, explosive and / or corrosive solvents can be avoided , Since the fibers produced according to the process according to EP 06119248.0 are composed of essentially water-insoluble polymers, a subsequent process step for water stabilization of the fibers is not required.

So far, however, there is no method that allows aqueous solutions comprising oppositely charged polyelectrolytes to be processed into fibers, thereby obtaining fibers which are not water-soluble.

task

The object of the present invention is to provide a process for electrospinning aqueous polymer systems which can be used to obtain water-stable polymer fibers in which there is no disintegration of the fibers after subsequent contact with water.

Solution of the task

This object is achieved according to the invention by a process in which aqueous solutions comprising oppositely charged polyelectrolytes are electrospun.

Surprisingly, it has been found that aqueous solutions of oppositely charged polyelectrolytes are insoluble in water after electrospinning. Upon subsequent water treatment, no disintegration of the electrospun fibers is observed.

Compared to the prior art, water-soluble polymers can now also be spun with the aid of polyelectrolytes from aqueous systems, without any further after-treatment, eg. As thermal or photochemical crosslinking is necessary. Thus, the use of corrosive, toxic, combustible, irritating, explosive, etc. solvents is obsolete. The often necessary use of water-soluble polymers with subsequent crosslinking step becomes unnecessary, resulting in significant technical advantages.

Polyelectrolytes are polymers that carry ionic groups at each repeat unit. In order for the electrolyte properties to emerge, dissociation must occur, but this may be limited even in water. By appropriate additives, for. As acids or bases, the dissociation ability and thus the Polyektrolytstärke can be increased. If oppositely charged posi- When electrolytes are used, charge balance can lead to the formation of polyelectrolyte complexes, which are generally difficult to rehydrolysable.

There are a number of technically available polyelectrolytes or polymers which assume the character of an electrolyte by means of acid or base treatment. For example, but not exhaustive, may be mentioned:

Positively charged polyelectrolytes: polyvinylamine, poly (diallyldimethylammonium chloride), polypyridine, polyethylenimine.

Negatively charged polyelectrolytes: polyacrylic acid, polyalcohol, polystyrenesulfonic acid.

Numerous other polyelectrolytes are known to the person skilled in the art. He can use them without departing from the scope of the claims.

Suitable bases by means of which the polyelectrolyte strength of the negatively charged polyelectrolytes to be used according to the invention can be adjusted, for example, but not exhaustively, LiOH, NaOH, KOH, Ca (OH) ₂ , Mg (OH) ₂ and Ba (OH) ₂ .

According to the invention, charge-carrying groups of the polyacids used are neutralized to from 0.01 to 99.99% before electrospinning, preferably from 0.1 to 10% and particularly preferably from 0.1 to 1%.

Suitable acids, with the aid of which the polyelectrolyte strength of the positively charged polyelectrolytes to be used according to the invention can be adjusted, are, for example but not exhaustive, HCl, HBr, Hl, H ₂ SO ₄ .

In a preferred embodiment, impurity additives are removed before the solution is electrospun. The person skilled in the art knows how to remove foreign ions, for example with the aid of ion exchangers.

In a preferred embodiment, the molar ratio of the negatively charged to the positively charged polyelectrolytes is 6: 4 to 4: 6, more preferably 1: 1.

The aqueous medium in which the polyelectrolytes are present is generally water. The aqueous medium can in addition to water more Contain additives, such as additives for the neutralization of charge-carrying groups or for changing the conductivity and surface tension of the solution to be spun. Suitable additives are known in the art. Optionally, the aqueous solution of polyelectrolyte used for electrospinning may contain at least one nonionic surfactant.

With the help of nonionic surfactants, physical properties of the aqueous polyelectrolyte solutions to be spun can be specifically changed, for example viscosity, surface tension and conductivity. Furthermore, nonionic surfactants influence the process conditions of electrospinning and the stability and morphology of the resulting fibers, especially in the case of meso- and nanofibers.

In principle, any surfactants known to the person skilled in the art can be used in the process according to the invention.

Without being bound by theory, it is believed that the use of nonionic surfactants provides steric stabilization of the polyelectrolytes. Thereby, the mechanical stability of the fibers obtained by the method according to the invention can be improved. Furthermore, it has been found that the use of nonionic surfactants can improve the formation of fibers by electrospinning compared with spraying the aqueous polyelectrolyte solution. Furthermore, it has been found that by the presence of ionic surfactants, a decrease in the viscosity of the colloidal dispersion can be achieved, whereby the production of thinner and more compact fibers than without addition of nonionic surfactants is possible. Furthermore, an increase in the conductivity of the dispersions and a decrease in the surface tension can be detected.

Suitable nonionic surfactants are known to those skilled in the art and are e.g. selected from the group consisting of (oligo) oxyalkylene-containing surfactants, carbohydrate-containing surfactants and amine oxides.

By "(oligo) oxyalkylene" - (OR ¹ ) _n - is to be understood that the (OH go) oxyalkylene groups containing surfactants one or more Oxyalkylengrup- may have pen. In the general formula - (OR ¹ ) _n -, R ^{1 is} an alkylene group, preferably an alkylene group having 2 to 4 carbon atoms and n is a natural number greater than or equal to 1, preferably 3 to 30. In this case, n is usually a When n is greater than 1, the radicals R ¹ in the oxalkylene groups may be the same or different.

Suitable (oligo) oxalkylene group-containing surfactants are e.g. selected from the group consisting of (oligo) oxyethylene groups (= polyethylene glycol groups) surfactants, (oligo) oxypropylene group-containing surfactants, (oligo) oxybutylene group-containing surfactants, and surfactants containing two or more different oxyalkylene groups, e.g. (Oligo) oxyethylene groups and (oligo) oxypropylene groups, in random order or in the form of blocks (block copolymer), e.g. Block copolymers based on polypropylene oxide and ethylene oxide. The surfactants containing (oligo) oxyalkylene groups are preferably selected from the group consisting of fatty alcohol alkoxylates, alkoxylated triglycerides and polyalkylene glycol ethers alkylated on both sides. Suitable alkoxylates or alkoxylated compounds are e.g. Ethoxylates, propoxylates, butoxylates, or random or block copolymers (or oligomers) composed of two or more different alkoxylates, e.g. Ethoxylates and propoxylates.

Suitable carbohydrate group-containing surfactants are e.g. selected from the group consisting of alkyl polyglycosides, sucrose esters, sorbitan esters (sorbitans), e.g. Polyoxyethylene sorbitan trioleate, and fatty acid N-methylglucamides (fatty acid glucamides).

As can be seen from the above-mentioned group of surfactants, the nonionic surfactants suitable according to the invention may contain either (ON-go) oxyalkylene groups or carbohydrate groups or both (OH) oxyalkylene groups and carbohydrate groups. Suitable amine oxides are, in particular, alkyldimethylamine oxides.

It is possible to use individual surfactants or mixtures of two or more surfactants in the process according to the invention.

The abovementioned nonionic surfactants are known to the person skilled in the art and are commercially available or can be prepared by processes known to the person skilled in the art.

The nonionic surfactants according to the invention can in principle be present in amounts in the aqueous solutions which do not lead to coagulation. The optimum quantities depend, among other things, on the surfactant used and the application temperature. The at least one nonionic surfactant is preferably present in the aqueous solutions in an amount of from 0.5 to 10% by weight, particularly preferably from 0.3 to 5% by weight, based on the total weight of the polyelectrolyte used. It has been found that particularly good process results - both in terms of the formation of polymer fibers and in terms of quality, e.g. the mechanical stability of the polymer fibers is achieved when 0.3 to 1% by weight, preferably 0.5 to 1% by weight, based on the total weight of the aqueous solution, of the nonionic surfactant, e.g. a block copolymer based on various alkylene oxides, e.g. based on propylene oxide and ethylene oxide.

The at least one nonionic surfactant contained in the aqueous polyelectrolyte solutions according to the process of the invention can either be added during the preparation of the aqueous polyelectrolyte solutions or subsequently after the preparation of the aqueous polyelectrolyte solutions. In a preferred embodiment, the at least one nonionic surfactant is added subsequently to the final aqueous polyelectrolyte solution prior to the start of the electrospinning process.

A particular advantage of the present invention is that the polyelectrolytes to be spun do not necessarily have to be crosslinked and crosslinking after electrospinning is not absolutely necessary. Optionally, however, it is also possible to electrospun solutions of crosslinked polyelectrolytes or solutions of mixtures of crosslinked and unvarnished polyelectrolytes, and / or it is optionally possible to carry out additional crosslinking after electrospinning.

According to a further preferred embodiment of the present invention, the solution comprising reversely charged polyelectrolytes in addition to the oppositely charged polyelectrolyte and the at least one nonionic surfactant additionally at least one water-soluble polymer, wherein water-soluble polymer according to the present invention, a polymer having a solubility in water of at least 0.1 wt .-% is understood.

Without being bound by theory, it is preferred that at least one water-soluble polymer be used as the so-called template polymer in addition to the solutions comprising oppositely charged polyelectrolytes. With the help of the template polymer, the fiber formation from the solution comprising oppositely charged polyelectrolytes (electrospinning) is further favored over spraying (electrospraying). The template polymer serves as a kind of "glue" for the polyelectrolytes in the spinning solution.

The water-soluble polymer may be a homopolymer, copolymer, block copolymer, graft copolymer, star polymer, hyperbranched polymer, dendrimer, or a mixture of two or more of the foregoing types of polymers. According to the findings of the present invention, the addition of at least one water-soluble polymer not only accelerates / promotes fiber formation. Rather, the quality of the resulting fibers is significantly improved.

In principle, the solution comprising oppositely charged polyelectrolytes in an aqueous medium may be admixed with all the water-soluble polymers known to the person skilled in the art, in particular with those of polyvinyl alcohol; Polyalkylene oxides, eg polyethylene oxides; Poly-N-vinylpyrrolidone; Hydroxymethylcelluloses; hydroxyethylcelluloses; hydroxypropyl; Carboxymethylcelluloses; maleic; alginates; collagens; Combinations made up of two or more of the above-mentioned polymer-forming monomer units, copolymers composed of two or more of the above-mentioned polymer-forming monomer units, graft copolymers composed of two or more of the above-mentioned polymers forming monomer units, star polymers formed from two or more of the above-mentioned polymers Monomer units and dendrimers composed of two or more of the aforementioned polymer-forming monomer units existing group selected water-soluble polymers particularly good results can be achieved.

In a preferred embodiment of the present invention, the water-soluble polymer is selected from polyvinyl alcohol, polyethylene oxides and poly-N-vinylpyrrolidone. The abovementioned water-soluble polymers are commercially available or can be prepared according to processes known to those skilled in the art.

Regardless of the embodiment, the solids content of the solution to be used according to the invention comprising oppositely charged polyelectrolytes - based on the total weight of the solution - preferably 5 to 60 wt .-%, more preferably 10 to 50 wt .-% and most preferably 10 to 40 wt. -%.

In a further embodiment of the present invention, the solution comprising oppositely charged polyelectrolytes in the process according to the invention contains at least one nonionic surfactant and optionally at least one water-soluble polymer in an aqueous medium, based on the total weight of the solution, from 0 to 25% by weight preferably 0.5 to 20 wt .-% and most preferably 1 to 15 wt .-%, of at least one water-soluble polymer. Thus, the solutions used according to the invention comprise oppositely charged polyelectrolytes in a preferred embodiment, in each case based on the total amount of the solution,

i. 5 to 60 wt .-%, preferably 10 to 50 wt .-%, particularly preferably 10 bis

40% by weight of oppositely charged polyelectrolytes, ii. 0 to 10 wt .-%, preferably 0.3 to 5 wt .-%, particularly preferably 0.3 to

1% by weight of at least one nonionic surfactant,

Hi. 0 to 25 wt .-%, preferably 0.5 to 20 wt .-%, particularly preferably 1 to 15 wt .-% of at least one water-soluble polymer, and iv. 5 to 94.9 wt .-%, preferably 10 to 89.2 wt .-%, particularly preferably 15 to 88.5 wt .-% water.

The weight ratio of oppositely charged polyelectrolytes to the water-soluble polymer preferably present in the aqueous solutions depends on the polymers used. For example, the oppositely charged polyelectrolytes and the water-soluble polymer preferably used in a weight ratio of 10: 1, preferably 9: 1, more preferably 8: 2 to 2: 8 are used.

The solution to be used according to the invention, comprising oppositely charged polyelectrolytes, can be electrospun in any manner known to the person skilled in the art, for example by extruding the solution under low pressure through a cannula connected to one pole of a voltage source to a counter electrode arranged at a distance from the cannula outlet. Preferably, the distance between the cannula and the counterelectrode acting as a collector and the voltage between the electrodes is set such that between the electrodes an electric field of preferably 0.5 to 2 kV / cm, particularly preferably 0.75 to 1.5 kV / cm and very particularly preferably 0.8 to 1 kV / cm is formed.

In particular, good results are obtained when the inner diameter of the cannula is 50 to 500 μm.

Depending on the intended use of the fibers obtained, it may be expedient to subsequently chemically bond them together or, for example, through a chemical intermediary to network with each other. As a result, for example, the stability of a fiber layer formed by the fibers can be further improved, in particular with regard to water and temperature resistance.

Another object of the present invention are fibers, in particular nano- and mesofibers, which are obtainable by the method according to the invention. The fibers according to the invention are distinguished by the fact that the addition of the nonionic surfactant according to the invention to fibers prepared without addition of the nonionic surfactant has optimized structural and / or mechanical properties, in particular uniformity, compactness and stability.

The diameter of the fibers according to the invention is preferably 10 nm to 50 μm, particularly preferably 50 nm to 2 μm and very particularly preferably 100 nm to 1 μm. The length of the fibers depends on the purpose and is usually 50 microns to several kilometers. Furthermore, the present invention relates to solutions comprising oppositely charged polyelectrolytes in an aqueous medium, which also contain at least 0.5 wt .-% of a water-soluble polymer having a solubility in water of at least 0.1 wt .-% and at least one nonionic surfactant.

In a preferred embodiment, the solutions according to the invention comprise comprehensively charged polyelectrolytes, in each case based on the total weight of the solution, i. 5 to 60 wt .-%, preferably 10 to 50 wt .-%, particularly preferably 10 to 40 wt .-% oppositely charged polyelectrolytes, ii. 0 to 10 wt .-%, preferably 0.3 to 5 wt .-%, particularly preferably 0.3 to

1% by weight of at least one nonionic surfactant, iii. 0 to 25 wt .-%, preferably 0.5 to 20 wt .-%, particularly preferably 1 to

15% by weight of at least one water-soluble polymer, and iv. 5 to 94.9 wt .-%, preferably 10 to 89.2 wt .-%, particularly preferably 15 to 88.5 wt .-% water.

Suitable oppositely charged polyelectrolytes, aqueous media, water-soluble polymers and nonionic surfactants and suitable amounts of these components in the solutions comprising oppositely charged polyelectrolytes are mentioned above. The solutions according to the invention comprising oppositely charged polyelectrolytes are preferably used in the process according to the invention. Furthermore, the present invention relates to the use of nonionic surfactants in a process for producing polymer fibers by an electrospinning process.

A preferred electrospinning process and suitable surfactants for this purpose are mentioned above.

By using the nonionic surfactants in the electrospinning process, on the one hand, an improvement in the electrospinning process can be achieved with a view to favoring fiber formation (electrospinning) over spraying the colloidal dispersion preferably used in the electrospinning process. On the other hand, the structural and mechanical properties of the polymer fibers produced according to the electrospinning process can be improved, in particular with regard to the fiber quality, uniformity and stability and the spinnability of the fibers.

Other objects, features, advantages and applications of the invention will become apparent from the following description of exemplary embodiments and the drawings. All described and / or illustrated features alone or in any combination form the subject matter of the invention, regardless of their combination in the claims or their dependency. embodiments

Two technically available polyelectrolytes were used: polyacrylic acid (PAS) and poly (diallyldimethylammonium chloride) (poly (DADMAC)).

A 25% by weight solution of PAS and a solution containing 20% by weight of poly (DADMAC) were prepared.

Furthermore, an aqueous NaOH solution with 4 wt .-% NaOH was prepared. 1 g of this solution was taken and made up to 20 g with H ₂ O.

PAS / poly (DADMAC) solutions were prepared in the ratio 1: 1, i. 1 g

Each PAS solution was mixed with 1.25 g of poly (DADMAC) solution and electrospun.

A part of the acrylic acid groups was neutralized with the above NaOH solution

(Experiments 2 to 5). In the control experiment (experiment 1), no neutralization of the acrylic acid groups took place.

The fibers were each treated with water after electrospinning for 1 h at 20 ° C to determine the extent of possible disintegration of the electrospun fibers.

The fibers of the control experiment were after the water treatment under the

Digital microscope examined and photographed.

Those fibers in which the acrylic acid groups had been partially neutralized with NaOH prior to electrospinning were used both immediately after Spinning (ie before water treatment) and after 1 h water treatment at 20 ¹ C under the scanning electron microscope examined t and photographed.

The electrospinning conditions are shown in Tab. 1:

Table 1: Electrospinning conditions for the PAS / poly (DADMAC) fibers

An overview of the experiments 1 to 5 is given in Table 2:

Tab. 2: Neutralization and post-treatment of the fibers

LIST OF REFERENCE NUMBERS

1 voltage source

2 capillary nozzle 3 syringe

4 polyelectrolyte solution

5 counter electrode

6 fiber formation

7 fiber mat

Figure legends

Fiq. 1 shows a schematic representation of a device suitable for carrying out the electrospinning process according to the invention.

The device comprises a syringe 3, at the tip of which is a capillary nozzle 2. This capillary nozzle 2 is connected to a pole of a voltage source 1. The syringe 3 receives the polyelectrolyte solutions 4 to be spun. Opposite the outlet of the capillary nozzle 2, a counterelectrode 5 connected to the other pole of the voltage source 1 is arranged at a distance of about 20 cm, which acts as a collector for the fibers formed. During operation of the device, a voltage between 18 kV and 35 kV is set at the electrodes 2 and 5, and the polyelectrolyte solution 4 is discharged through the capillary nozzle 2 of the syringe 3 at a low pressure. Due to the electrostatic charge of the polyelectrolytes in the solution due to the strong electric field of 0.9 to 2 kV / cm, a material flow directed towards the counterelectrode 5 is formed, which on the way to the opposite Electrode 5 solidifies with fiber formation 6, as a result of which 5 fibers 7 with diameters in the micron and nanometer range are deposited on the counterelectrode.

Fig. 2:

Digital micrograph of electrospun polyelectrolyte complex fibers (PEKOF) with polyacrylic acid (PAS): poly (DADMAC) = 1: 1. In the preparation of these fibers, the polyacrylic acid was not neutralized (0% neutralized) prior to spinning. The fibers were subjected to water treatment at 20 ° C for one hour after spinning. Fig. 2 shows the fibers after this one-hour water treatment at 20 ° C.

Fig. 3

Scanning electron micrograph of electrospun PEKOF with polyacrylic acid (PAS): poly (DADMAC) = 1: 1. Prior to spinning, 0.1% of the acrylic acid groups were neutralized with a 0.2% by weight NaOH solution. Fig. 3 shows these fibers immediately after spinning and before water treatment.

Fig. 4 Scanning electron micrograph of electrospun PEKOF with polyacrylic acid (PAS): poly (DADMAC) = 1: 1. Prior to spinning, 0.1% of the acrylic acid groups were neutralized with a 0.2 wt% NaOH solution. After spinning, the fibers were subjected to a one hour water treatment at 20 ° C. Fig. 4. shows the fibers after one hour of water treatment at 20 O. Fig. 5

Scanning electron micrograph of electrospun PEKOF with polyacrylic acid (PAS): poly (DADMAC) = 1: 1. Prior to spinning, 1% of the acrylic acid groups were neutralized with a 0.2% by weight NaOH solution. Fig. 5 shows these fibers immediately after spinning and before water treatment.

Fig. 6

Scanning electron micrograph of electrospun PEKOF with polyacrylic acid (PAS): poly (DADMAC) = 1: 1. Prior to spinning, 1% of the acrylic acid groups were neutralized with a 0.2% by weight NaOH solution. After spinning, the fibers were subjected to a one hour water treatment at 20 ° C. Fig. 6. shows the fibers after 1 hour of water treatment at 20 O.

Claims

claims

1. A process for producing polymer fibers, wherein an aqueous solution comprising oppositely charged polyelectrolytes is electrospun.

2. The method according to claim 1, characterized in that positively charged polyelectrolytes selected from the group polyvinylamine, poly (diallyldimethylammoniumchlorid), polypyridine and polyethyleneimine are used.

3. The method according to any one of claims 1 or 2, characterized in that negatively charged polyelectrolytes selected from the group polyacrylic acid, polyalcohol and polystyrene sulfonic acid are used.

4. The method according to claim 3, characterized in that the charge-carrying groups of the polyacids used before electrospinning are neutralized to 0.01 to 99.99%, preferably 0.1 to 10%, particularly preferably 0.1 to 1% ,

5. The method according to any one of claims 1 to 4, characterized in that foreign ion additives are removed prior to electrospinning.

6. The method according to any one of claims 1 to 5, characterized in that the molar ratio of the negatively charged to the positively charged polyelectrolyte is 6: 4 to 4: 6, preferably 1: 1.

7. The method according to any one of claims 1 to 6, characterized in that the aqueous solution comprising oppositely charged polyelectrolytes further contains at least one nonionic surfactant.

8. The method according to claim 7, characterized in that the at least one nonionic surfactant in an amount of 0.1 to 10 wt .-%, preferably 0.3 to 5 wt .-%, particularly preferably 0.3 to 1 wt. -%, quite more preferably 0.5 to 1 wt .-%, based on the total weight of the aqueous solution, is used.

9. The method according to any one of claims 1 to 8, characterized. in that the aqueous solution comprising in opposite directions charged polyelectrolytes additionally contains at least one water-soluble polymer having a solubility in water of at least 01,% by weight.

10. The method according to claim 9, characterized in that the water-soluble polymer is selected from the group consisting of homopolymers, copolymers, graft copolymers, star polymers, highly branched polymers and dendrimers.

11. The method according to claim 9 or 10, characterized in that the water-soluble polymer composed of the polyvinyl alcohol, polyalkylene oxides, poly-N-vinylpyrrolidone, hydroxymethylcelluloses, hydroxyethylcelluloses, hydroxypropylcelluloses, carboxymethylcelluloses, maleic acids, alginates, collagen, combinations of two or more the monomeric units constituting the above-mentioned polymers, copolymers composed of two or more monomer units constituting the above-mentioned polymers, graft copolymers composed of two or more monomer units constituting the above-mentioned polymers, star polymers composed of two or more monomer units constituting the above-mentioned polymers, highly branched polymers is selected from two or more of the above-mentioned polymer-forming monomer units and dendrimers composed of two or more of the above-mentioned polymer-forming monomer units existing groups.

12. The method according to any one of claims 1 to 11, characterized in that the solids content of the aqueous solution, based on the total weight of the solution, 5 to 60 wt .-%, preferably 10 to 50 wt .-%, particularly preferably 10 to 40 Wt .-% is.

13. The method according to any one of claims 1 to 12, characterized in that the solution, based on the total weight of the solution, 0 to 25 wt .-%, preferably 0.5 to 20 wt .-% and particularly preferably 1 to 15 wt .-% of a water-soluble polymer.

14. Fiber obtainable by a process according to one of claims 1 to 13.

15. A fiber according to claim 14, characterized in that it has a diameter of 10 nm to 50 microns, preferably 50 nm to 2 microns and more preferably from 100 nm to 1 micron.

16. A fiber according to claim 14 or 15, characterized in that it has a length of at least 50 microns.

17. An aqueous solution comprising oppositely charged polyelectrolytes, further comprising at least 0.5%, based on the total weight of the solution, of a water-soluble polymer having a solubility in water of at least 0.1 wt .-% and at least one nonionic surfactant.

18. Use of nonionic surfactants in a process for producing polyelectrolyte complex fibers by electrospinning.