CN113005535A - Polyvinyl alcohol nanofiber with controllable diameter and preparation method thereof - Google Patents

Polyvinyl alcohol nanofiber with controllable diameter and preparation method thereof Download PDF

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Publication number
CN113005535A
CN113005535A CN201911321915.1A CN201911321915A CN113005535A CN 113005535 A CN113005535 A CN 113005535A CN 201911321915 A CN201911321915 A CN 201911321915A CN 113005535 A CN113005535 A CN 113005535A
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polyvinyl alcohol
solution
diameter
nanofibers
fiber
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李双武
曹春
朱建军
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Sinochem Ningbo Runwo Membrane Technology Co Ltd
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Sinochem Ningbo Runwo Membrane Technology Co Ltd
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    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/0007—Electro-spinning
    • D01D5/0015—Electro-spinning characterised by the initial state of the material
    • D01D5/003—Electro-spinning characterised by the initial state of the material the material being a polymer solution or dispersion
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/0007—Electro-spinning
    • D01D5/0061—Electro-spinning characterised by the electro-spinning apparatus
    • D01D5/0069—Electro-spinning characterised by the electro-spinning apparatus characterised by the spinning section, e.g. capillary tube, protrusion or pin
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/0007—Electro-spinning
    • D01D5/0061—Electro-spinning characterised by the electro-spinning apparatus
    • D01D5/0076—Electro-spinning characterised by the electro-spinning apparatus characterised by the collecting device, e.g. drum, wheel, endless belt, plate or grid
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/0007—Electro-spinning
    • D01D5/0061—Electro-spinning characterised by the electro-spinning apparatus
    • D01D5/0092—Electro-spinning characterised by the electro-spinning apparatus characterised by the electrical field, e.g. combined with a magnetic fields, using biased or alternating fields
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
    • D01F6/02—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D01F6/14—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polymers of unsaturated alcohols, e.g. polyvinyl alcohol, or of their acetals or ketals

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  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • Spinning Methods And Devices For Manufacturing Artificial Fibers (AREA)
  • Artificial Filaments (AREA)
  • Nonwoven Fabrics (AREA)

Abstract

The invention discloses polyvinyl alcohol nanofiber electrostatic spinning with a controllable uniform diameter and a preparation method thereof. The method of the invention does not need to add any filler, the solvent is environment-friendly and nontoxic, and the prepared fiber has smooth surface and no pearl shape or branch shape. The method of the invention can obtain the uniform fiber with the diameter of the nanofiber between 100-400 nanometers by only singly controlling the electrostatic spinning process parameters. The preparation method is suitable for the application fields of various biological medicines and filtering protection products.

Description

Polyvinyl alcohol nanofiber with controllable diameter and preparation method thereof
Technical Field
The invention belongs to the field of electrostatic spinning nanofibers, and particularly relates to a polyvinyl alcohol nanofiber with a controllable diameter and a preparation method thereof.
Background
There are various methods for preparing nanofibers including stretching, phase separation, template synthesis, self-assembly, electrospinning, etc. Stretching is carried out by dipping a micropipette of a few micrometers in diameter into a liquid droplet using a micromanipulator, withdrawing the micropipette from the liquid and applying the micropipette at about 1X 10-4m·s-1After moving at the speed of (2), the nanofibers will be drawn. The drawing of the nanofibers can be repeated on one droplet to produce many fibers, which has the disadvantage of a discontinuous process. The template synthesis process is to use a mold to produce the desired nanofibers. The principle of template synthesis is to add a polymer solution into the pores of the membrane. For nanofiber production, the template is an aluminum oxide film with nanoscale pore sizes of uniform thickness. Polymer solutionThe liquid will be subjected to water pressure on one side and will be confined by the porous membrane, squeezing and contact with the curing solution. In this process, the diameter of the nanofibers will be determined by the porosity and this method cannot produce continuous fibers. Phase separation is a common concept in polymer science and is applied to the production of polymer nanofibers. The concept of phase separation relies on a mixture of two or more mobile components that separate into different phases due to their different surface tensions. The polymer is first mixed with a solvent to give a gel network and a solvent phase, which is extracted leaving a solid phase. Polylactic acid (PLLA) nanofibers can be prepared using this method, the main steps of which include polymer dissolution, gelation and solvent extraction, which is only suitable for specific polymers. Self-assembly is a common method of construction that is composed of molecular control. Thus, this self-assembly can be used to produce nanofibers from smaller molecules. The mechanism of self-assembly is that small molecules are gathered together by intermolecular force, the shape of the small molecules determines the shape of the macromolecular nano-fiber, and the process of the method is complex.
The first example of electrospinning, which occurred in the 20 th century, was electrospinning fibers from molten sealing wax. Electrospinning is a process for producing polymer filaments using electrostatic forces. The mechanism is mainly liquid jet produced by electric field, usually electrostatic spinning produces nanofibers by charged jet of polymer melt or polymer solution. The polymer is dissolved in a suitable solvent for electrospinning while a sufficiently fast evaporation rate is required. The surface tension and viscosity of the solution must be within a certain range to form electrospun fibers. The polymer needs to be dissolved in some suitable solvent before electrospinning, and polymers that can be melted at high temperature can also be electrospun into nanofibers. Among all the above nanofiber processing techniques, electrospinning is the only successful process that can be further developed and can be used for large-scale production of continuous nanofibers from a variety of polymers. Due to the high electric field force applied to the polymer solution, the diameter of the generated fiber is small, so that the nanofiber structure has a very large surface area-to-volume ratio and is suitable for application fields of biomedicine, filtration protection products and the like.
The polymer solution is influenced by the electrostatic spinning process parameters in the process of electrostatic spinning and conversion into the nano-fibers, so that the morphology of the nano-fibers is influenced and determined. These parameters include: (a) solution properties such as concentration, viscosity, surface tension, conductivity, etc.; (b) setting parameters of the experiment, such as solution flow rate, voltage applied to the needle tip, and distance between the needle tip and a collection target; (c) environmental parameters such as solution temperature, humidity, and air velocity in the electrospinning chamber. It is noted that the effects of the above parameters on the electrospinning process and fiber morphology are interdependent, rather than independent.
For example, electrostatic spinning polyethylene oxide (PEO) can only be carried out from a corresponding solution with the viscosity of 1-20 poise, the surface tension is 35-55 dyne/cm, and the method is suitable for forming fine nano fibers. When the viscosity exceeds 20 poise, the electrostatic force generated by the applied voltage is insufficient to perform electrostatic stretching. When the viscosity is below 1 poise, the rotating jet breaks down rapidly into spherical droplets to reduce the surface area of the liquid, thereby forming droplets. Another example is the effect of viscosity demonstrated in electrospinning of Cellulose Acetate (CA) dissolved in a 2:1 acetone/DMAc (dimethylacetamide) solvent, with viscosities between 1.2 and 10.2 poise found suitable for electrospinning. If outside this range, the solution cannot be electrospun into fibers at room temperature, and very few fibers can be processed from the more viscous solution. Or the liquid jet breaks into droplets due to the solution viscosity being below 1.2 poise. The formation of microbeads favors the formation of nanofibers of finer diameter. In studying the effect of voltage on the diameter of electrospun fibers of Polystyrene (PS) solution, the diameter of PS fibers decreased from 20 μm to 10 μm when the voltage was increased from 5kV to 12kV, a phenomenon also observed in other polymers such as synthetic filaments. However, higher applied voltages have been shown to eject more solution in the jet, resulting in larger fiber diameters. This complexity can be explained by considering the electric field strength applied to the spinneret rather than the electric potential, since the electric field strength is high, resulting in a large amount of solution sprayed. The polymer solution flow rate is an important process parameter because it affects the spray rate and solution delivery rate. The volume of polymer solution spun determines the fiber diameter, so higher feed rates result in coarser fibers, and the flow rate of the solution exiting the spinneret follows the same principle. For example, when electrospinning polystyrene fibers, it was found that as the flow rate of the polymer solution increased, the fiber diameter and pore size increased. The fibers have a pronounced beaded morphology with increasing flow rate while increasing the average pore size from 90 nm to 150 nm. Generally, low flow rates produce fibers with smaller diameters. Too high a flow rate can result in beaded nanofibers since the fibers do not have an opportunity to dry before reaching the collector.
Polyvinyl alcohol (PVA) is a semi-crystalline water-soluble polymer with good chemical and thermal stability. The polyvinyl alcohol has excellent grease resistance, solvent resistance, film forming, emulsifying and bonding properties. The melting point of the fully hydrolyzed polyvinyl alcohol was 230 ℃ and the melting point of the partially hydrolyzed polyvinyl alcohol was 180 ℃ and 190 ℃. PVA is non-toxic and biodegradable, and can be used as an environment-friendly polymer.
Patent CN106012047B discloses a method for preparing polyvinyl alcohol composite fiber with controllable morphology by using filler (layered double hydroxide nanorods), and the fiber diameter is large, rather than preparing polyvinyl alcohol fiber with controllable diameter by controlling electrospinning process parameters alone. Patent application CN105413654A discloses a method for preparing LDHs/PVA composite fiber membrane based on electrostatic spinning method and application thereof. Patent CN105088377B provides polyvinyl alcohol nanofibers prepared by electrospinning and an ion exchange membrane formed by the polyvinyl alcohol nanofibers. The preparation methods can not obtain the polyvinyl alcohol nano-fiber with controllable diameter by singly controlling the process parameters.
Therefore, there is a lack in the art of a method for obtaining polyvinyl alcohol nanofibers with controlled diameters by a single control of the process parameters of electrospinning.
Disclosure of Invention
In order to solve the problems, the invention discloses polyvinyl alcohol nanofiber electrostatic spinning with a controllable uniform diameter and a preparation method thereof. The method of the invention does not need to add any filler, the solvent is environment-friendly and nontoxic, and the prepared fiber has smooth surface and no pearl shape or branch shape. The method of the invention can obtain the uniform fiber with the diameter of the nanofiber between 100-400 nanometers by only singly controlling the electrostatic spinning process parameters. The preparation method is suitable for the application fields of various biological medicines and filtering protection products.
Specifically, the invention provides a polyvinyl alcohol nanofiber, wherein the diameter of the polyvinyl alcohol nanofiber is between 100 nanometers and 400 nanometers.
In one or more embodiments, the polyvinyl alcohol nanofibers have a diameter between 100 nanometers and 300 nanometers.
In one or more embodiments, the polyvinyl alcohol nanofibers have a diameter between 100 nanometers and 200 nanometers.
In one or more embodiments, the polyvinyl alcohol nanofibers have a diameter between 200 nanometers and 400 nanometers.
In one or more embodiments, the polyvinyl alcohol nanofibers have a diameter between 200 nanometers and 300 nanometers.
In one or more embodiments, the polyvinyl alcohol nanofibers comprise polyvinyl alcohol having a number average molecular weight of 98000-143000 g-mol-1。
In one or more embodiments, the polyvinyl alcohol nanofibers comprise polyvinyl alcohol having a hydrolysis rate of 97% to 99%.
The invention also provides a method for preparing the polyvinyl alcohol nano fiber, which adopts an electrostatic spinning method to prepare the polyvinyl alcohol nano fiber, and the polyvinyl alcohol aqueous solution with the polyvinyl alcohol concentration of 5-15 wt/v% is used in the electrostatic spinning.
The invention also provides a method for preparing the polyvinyl alcohol nano fiber by adopting an electrostatic spinning method, wherein the voltage applied to a needle head during electrostatic spinning is between 11.2 and 17.2 kilovolts, and the flow rate of the polyvinyl alcohol solution is 1 mul.min-1To 10. mu.l.min-1In the meantime.
In one or more embodiments, the polyvinyl alcohol has a number average molecular weight of 98000-143000 g.mol-1And & -Or the hydrolysis rate of the polyvinyl alcohol is 97-99%.
In one or more embodiments, the flow rate of the polyvinyl alcohol solution during electrospinning is 1. mu.l.min-1To 10. mu.l.min-1In the meantime.
In one or more embodiments, the flow rate of the polyvinyl alcohol solution during electrospinning is 1. mu.l.min-1To 9. mu.l.min-1In the meantime.
In one or more embodiments, the distance from the tip of the needle to the collector in electrospinning is 8-20 cm.
In one or more embodiments, the distance from the tip of the needle to the collector in electrospinning is from 13 to 20 cm.
In one or more embodiments, the voltage applied to the needle during electrospinning is between 10.5 and 17.2 kilovolts.
In one or more embodiments, the voltage applied to the needle during electrospinning is between 11.2 and 17.2 kilovolts.
In one or more embodiments, the voltage applied to the needle during electrospinning is between 13.5 and 17.2 kilovolts.
In one or more embodiments, the voltage applied to the needle during electrospinning is between 15.8 and 17.2 kilovolts.
The invention provides polyvinyl alcohol nano-fibers prepared by the method according to any one embodiment of the invention.
In one or more embodiments, the polyvinyl alcohol nanofibers produced by the method of any of the embodiments of the present invention have a diameter of between 100 nanometers and 1 micron, preferably between 100 nanometers and 400 nanometers, between 100 nanometers and 300 nanometers, between 100 nanometers and 200 nanometers, between 200 nanometers and 400 nanometers, and between 200 nanometers and 300 nanometers.
Drawings
FIG. 1 is an electron micrograph of polyvinyl alcohol nanofibers fabricated in example 1, wherein FIGS. 1(a), 1(b), 1(c) and 1(d) are nanofibers fabricated from polyvinyl alcohol solutions having concentrations of 6 wt/v%, 7 wt/v%, 8 wt/v% and 13 wt/v%, respectively.
FIG. 2 is an electron micrograph of the polyvinyl alcohol nanofibers obtained in example 2, wherein FIG. 2(a), FIG. 2(b), FIG. 2(c) and FIG. 2(d) are each performed at 1.0. mu.l.min-1Flow rate of (2), Distance (DTC) of a tip of 15cm from the collector, 9.0. mu.l.min-1Flow rate of (2), DTC of 15cm, 1.0. mu.l.min-1Flow rate of (3), DTC of 13cm, and 1.0. mu.l.min-1And a DTC of 20cm to produce the resulting nanofibers.
Fig. 3 is an electron microscope image of the polyvinyl alcohol nanofibers fabricated in example 3, wherein fig. 3(a), fig. 3(b), fig. 3(c), and fig. 3(d) are nanofibers fabricated using voltages of 11.2 kv, 13.5 kv, 15.8 kv, and 17.2 kv, respectively.
Detailed Description
To make the features and effects of the present invention comprehensible to those skilled in the art, general description and definitions are made below with reference to terms and expressions mentioned in the specification and claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The theory or mechanism described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.
The numerical ranges described herein should be considered to have covered and specifically disclosed all possible subranges and any individual numerical value within the range.
Herein, when embodiments or examples are described, it is to be understood that they are not intended to limit the invention to these embodiments or examples. On the contrary, all alternatives, modifications, and equivalents of the methods and materials described herein are intended to be included within the scope of the invention as defined by the appended claims.
In this context, for the sake of brevity, not all possible combinations of features in the various embodiments or examples are described. Therefore, the respective features in the respective embodiments or examples may be arbitrarily combined as long as there is no contradiction between the combinations of the features, and all the possible combinations should be considered as the scope of the present specification.
The invention aims to provide a preparation method for obtaining electrostatic spinning polyvinyl alcohol (PVA) nano-fibers with controllable uniform diameters by singly controlling process parameters. The preparation method in the prior art can not obtain the polyvinyl alcohol nano-fiber with controllable diameter by singly controlling the process parameters. The invention carries out deep research on the influence of solution properties and process parameters on the appearance of the electrospun fiber, and obtains the optimal controllable uniform-diameter electrospun polyvinyl alcohol nanofiber by determining the optimal process parameters such as the concentration of the polymer solution, the applied voltage, the flow rate, the Distance (DTC) between the needle point and the grounding electrode and the like.
The diameter of the polyvinyl alcohol nanofiber is between 100 nanometers and 1 micron, preferably between 100-500 nanometers, 100-400 nanometers, 100-300 nanometers, 200-400 nanometers, 200-300 nanometers and 100-200 nanometers.
Preferably, the polyvinyl alcohol nanofibers of the present invention are uniform in diameter, smooth in fiber surface, and free of beaded and branched morphology.
Preferably, the polyvinyl alcohol nanofibers of the present invention are free of fillers; such fillers include, but are not limited to, layered double hydroxide nanorods as used in CN 106012047B. More preferably, the polyvinyl alcohol nanofibers of the present invention contain only polyvinyl alcohol.
The polyvinyl alcohol suitable for use in the present invention may be polyvinyl alcohol conventionally used in the art for producing polyvinyl alcohol nanofibers. Preferably, the polyvinyl alcohol used in the present invention has a number average molecular weight of 98000-143000 g.mol-1. Preferably, the polyvinyl alcohol used in the present invention has a hydrolysis rate of 97 to 99%, for example, about 98%. Polyvinyl alcohols suitable for use in the present invention are commercially available.
The polyvinyl alcohol nanofibers according to the present invention can be prepared using an electrospinning apparatus for producing nanofibers, which is conventional in the art. Generally, an electrospinning apparatus for producing nanofibers includes: the device comprises a pump, an injector, a pipeline, a needle, a heat collector and a high-voltage power supply, wherein the pump, the injector, the pipeline and the needle are sequentially connected, the heat collector and the needle are spaced at a certain distance, and the high-voltage power supply generates an electric field between the needle and the heat collector. The material of the heat collector can be conventional, and can be aluminum foil or silicon chip, for example. The placement of the heat collector and pins may be conventional, for example, the heat collector may be placed at a height less than or equal to the height at which the pins are placed. In certain embodiments, the heat collector is placed directly below the pins. In certain embodiments, the pins are positioned such that the pin holes are oriented vertically toward the heat collector.
The basic process for preparing the polyvinyl alcohol nano-fiber by adopting the electrostatic spinning method is conventional in the field, and mainly comprises the following steps: pumping the polymer solution into a syringe by adopting a pump to control the flow rate; the polymer solution in the syringe flows to the needle through the pipeline, and a small drop of the polymer solution is stably suspended on the needle under the action of constant pressure; the high-voltage power supply generates an electric field, liquid drops form a cone under the action of the electric field, when the applied voltage reaches a critical potential Vc, the charged polymer solution is ejected from the cone in the jet flow, and in the process of moving towards the heat collector, the solvent is evaporated, and finally the polymer fibers are deposited on the heat collector.
In the present invention, the polyvinyl alcohol solution for electrostatic spinning is an aqueous solution of polyvinyl alcohol. The invention creatively adopts water as a nontoxic environment-friendly solvent. And (3) dissolving the polyvinyl alcohol in water (preferably distilled water) to prepare the polyvinyl alcohol solution for the subsequent electrostatic spinning. In certain embodiments, the polyvinyl alcohol solution is heated to 80-90 ℃, stirred uniformly for 2-3 hours, and the uniform solution is obtained using a magnetic heating stirrer and then used for electrostatic spinning. The concentration of the polyvinyl alcohol solution used in the present invention is preferably between 5 and 15 wt/v%, such as between 6 and 13 wt/v%, between 7 and 13 wt/v%, between 8 and 13 wt/v%, between 7 and 8 wt/v%, between 7.5 and 8.5 wt/v%.
In the present invention, the flow rate of the polyvinyl alcohol solution is preferably 1. mu.l.min-1To 10. mu.l.min-1E.g. 0.5. mu.l.min-1To 9. mu.l.min -11 μ l/min-1To 9. mu.l.min-1In the meantime.
In the present invention, the Distance (DTC) from the needlepoint to the heat collector is preferably 8 to 20cm, for example, 10 to 20cm, 13 to 20 cm.
In the present invention, the critical potential Vc is about 10.5 kv. In the present invention, the voltage applied to the needle at the time of electrospinning is preferably 11.2 to 17.2 kv, more preferably 13.5 to 17.2 kv and 15.8 to 17.2 kv. The invention finds that when the voltage applied to the needle during electrostatic spinning is between 10.5 and 11.2 kilovolts, the diameter of the fiber increases with the increase of the voltage. The voltage is between 11.2 and 17.2 kilovolts, and the diameter of the fiber is reduced along with the increase of the voltage; if the flow rate of the polyvinyl alcohol solution is controlled to be 1 mul min-1To 10. mu.l.min-1Preferably 1. mu.l.min-1To 9. mu.l.min-1The obtained nano-fiber has small and uniform diameter, smooth fiber surface and no pearl shape or branch shape.
The beneficial effects of the invention include: when the electrostatic spinning polyvinyl alcohol nanofiber with the controllable uniform diameter is prepared, no filler is needed to be added, the solvent is environment-friendly and nontoxic, and the industrial production is easy to realize; the nano-fiber prepared by the method has small and uniform diameter, smooth fiber surface and no pearl and branch morphology, and can obtain the uniform nano-fiber with the diameter between 100 plus 400 nanometers, even between 100 plus 300 nanometers and between 100 plus 200 nanometers by simply controlling the electrostatic spinning process parameters such as applied voltage and the distance from the needle point to the heat collector; the preparation method is suitable for the application fields of biological medicines, filtering and protecting products and the like.
The invention is described below by way of specific examples, which are intended to better understand the content of the invention. It is to be understood that these examples are illustrative only and not limiting. The reagents used in the examples are, unless otherwise indicated, commercially available. The methods used in the examples are conventional methods unless otherwise specified.
In the following examples, the electrospinning was carried out as follows: injecting a polyvinyl alcohol solution into the injector, and controlling the flow rate of the polyvinyl alcohol solution by using a pump; the polymer solution in the syringe flows to the needle through the pipeline, and a small drop of the polymer solution is stably suspended on the needle under the action of constant pressure; providing voltage by using a high-voltage direct-current power supply; under the action of an external electric field, the liquid drops form a cone, and when the applied voltage exceeds a critical potential Vc, the charged polymer solution jet is ejected from the cone; the heat collector is arranged right below the needle, and the needle hole vertically faces the heat collector; in this process, the solvent is rapidly evaporated, so that the ultra fine polymer fiber is deposited on the heat collector.
The polyvinyl alcohol used in the following examples had a number average molecular weight of 98000-143000 g.mol-1The hydrolysis rate was 97%, and the scanning electron micrograph shows the nanofiber diameter of the electrospun polyvinyl alcohol.
Example 1
Respectively adopting polyvinyl alcohol solutions with the concentrations of 6 wt/v%, 7 wt/v%, 8 wt/v% and 13 wt/v% to carry out electrostatic spinning, and applying an external voltage of 15.0kV and 1.0 mul min in the experiment-1And the distance of the tip of the 15cm needle from the collector (DTC). The morphologies of nanofibers prepared from polyvinyl alcohol solutions at concentrations of 6 wt/v%, 7 wt/v%, 8 wt/v% and 13 wt/v% were characterized by electron microscopy, and the results are shown in FIG. 1(a), FIG. 1(b), FIG. 1(c) and FIG. 1(d), respectively.
Fibers made from a polyvinyl alcohol solution at a concentration of 6 wt/v% had many large spherical beads present therein as shown in FIG. 1 (a). Increasing the PVA solution concentration to 7 wt/v% reduced the number of beads in the electrospun fiber, and the bead structure changed from spherical to fusiform, as shown in FIG. 1 (b). Further increasing the PVA solution concentration to 8 wt/v%, the nanofiber morphology was changed from a bead-like structure to a uniform fiber structure with an average fiber diameter of about 200nm, as shown in FIG. 1 (c). For the PVA solution with a concentration of 13 wt/v%, the inventors thought that the electrospun nanofibers obtained increased in diameter due to the decrease in the solvent evaporation rate in the liquid jet as the solution viscosity increased, and thus the average fiber diameter of the fibers produced increased to 1 μm, as shown in FIG. 1 (d).
Example 2
Adopting PVA solution with the concentration of 8 wt/v% to carry out electrostatic spinning, and adopting different solutions in experimentsSolution flow rate of (1.0. mu.l.min)-1And 9.0. mu.l.min-1) And DTC (13cm to 20cm), the voltage applied to the PVA solution being kept constant at 15 kV. The characterization by a galvanometer adopts 1.0 mul.min-1Flow rate of (2), DTC of 15cm, 9.0. mu.l.min-1Flow rate of (2), DTC of 15cm, 1.0. mu.l.min-1Flow rate of (3), DTC of 13cm, and 1.0. mu.l.min-1Flow rate of (a) and DTC of 20cm, the results are shown in FIG. 2(a), FIG. 2(b), FIG. 2(c) and FIG. 2(d), respectively.
When the flow rate is from 1.0. mu.l.min, as shown in FIGS. 2(a) and 2(b)-1Increased to 9.0. mu.l.min-1When the electrospun PVA fiber diameter was observed to increase slightly. In the electrospinning process, the solution jet is considered to be rapidly elongated and then deposited due to the high conductivity of the fully hydrolyzed PVA used. As the DTC increases, the diameter of the electrospun fiber increases slightly. When the distance between the needle and the collector (DTC) was increased from 13cm to 20cm, the morphology of the fibers in fig. 2(d) was dry fibers, rather than the ribbon-like wet fiber morphology in fig. 2 (c).
Example 3
Adopting PVA solution with the concentration of 8 wt/v% to carry out electrostatic spinning, and keeping the flow rate of the solution at 1.0 mul.min-1The distance between the needle and the collector (DTC) was controlled to be 15cm, and different voltages (10.5 kv, 11.2 kv, 13.5 kv, 15.8 kv, 17.2 kv) were used. This example found that when the applied voltage exceeded the critical value of 10.5 kilovolts, the charged liquid was ejected from the tip of the cone, forming a conical spray pattern; the application voltage is between 10.5 and 17.2 kilovolts, and the stable cone-shaped injection mode of the whole electron spinning process can be maintained. The morphology of the nanofibers prepared using voltages of 11.2 kv, 13.5 kv, 15.8 kv, and 17.2 kv was characterized by using a galvanometer, and the results are shown in fig. 3(a), fig. 3(b), fig. 3(c), and fig. 3(d), respectively.
The results show that when the applied voltage is increased from 11.2 kv to 17.2 kv, the average fiber diameter decreases from 400 nm to 200nm, as shown in fig. 3(a) - (d). The inventors believe that this is because the high electric field strength induces finer liquid jets and forms finer PVA nanofibers in the conical jet zone.

Claims (10)

1. Polyvinyl alcohol nanofibres, characterised in that the diameter of the polyvinyl alcohol nanofibres is between 100 and 400 nanometres, preferably between 100 and 300 nanometres.
2. The polyvinyl alcohol nanofiber as claimed in claim 1, wherein the polyvinyl alcohol has a number average molecular weight of 98000-143000 g-mol-1。
3. The polyvinyl alcohol nanofiber according to claim 1, wherein the hydrolysis rate of polyvinyl alcohol is 97% to 99%.
4. A method for preparing polyvinyl alcohol nano fiber is characterized in that the polyvinyl alcohol nano fiber is prepared by adopting an electrostatic spinning method, wherein the voltage applied to a needle head during electrostatic spinning is 11.2-17.2 kilovolts, and the flow rate of a polyvinyl alcohol solution is 1 mul.min-1To 10. mu.l.min-1In the meantime.
5. The method of claim 4, wherein the concentration of the polyvinyl alcohol solution is between 5 and 15 wt/v%.
6. The process as claimed in claim 4, wherein the polyvinyl alcohol has a number-average molecular weight of 98000-143000 g-mol-1And/or the hydrolysis rate of the polyvinyl alcohol is 97-99%.
7. The method of claim 4, wherein the flow rate of the polyvinyl alcohol solution is 1 μ l-min during electrospinning-1To 9. mu.l.min-1In the meantime.
8. The method of claim 4, wherein the distance from the needle tip to the heat collector in the electrospinning is 8-20 cm.
9. The method of claim 4, wherein the voltage applied to the needle during electrospinning is between 13.5 and 17.2 kilovolts.
10. Polyvinyl alcohol nanofibres obtainable by the method according to any of claims 4-9.
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