CN113981670B - Flexible stretchable electromagnetic shielding fiber film and preparation method thereof - Google Patents
Flexible stretchable electromagnetic shielding fiber film and preparation method thereof Download PDFInfo
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- 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
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- D01F6/58—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolycondensation products
- D01F6/70—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolycondensation products from polyurethanes
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- D01F6/78—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from copolycondensation products
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- D04H1/70—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres
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- D04H1/728—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged by electro-spinning
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- H05K9/0073—Shielding materials
- H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
- H05K9/0083—Electromagnetic shielding materials, e.g. EMI, RFI shielding comprising electro-conductive non-fibrous particles embedded in an electrically insulating supporting structure, e.g. powder, flakes, whiskers
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- D06M2101/16—Synthetic fibres, other than mineral fibres
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Abstract
The invention discloses a flexible stretchable electromagnetic shielding fiber film and a preparation method thereof, wherein the method comprises the following steps: firstly, preparing a PU fiber film by an electrostatic spinning technology; secondly, taking the PU fiber film as a substrate, embedding and crosslinking carbon nanotubes on the surface of the PU fiber film through an ultrasonic cavitation loading process to obtain the PU/CNTs fiber film; finally, the PU/CNTs fiber film is subjected to a post-treatment process of reducing silver nano particles by a solution method to prepare the PU/CNTs/AgNPs composite fiber film, so that the electromagnetic shielding effectiveness of the composite fiber film is improved. The flexible stretchable electromagnetic shielding fiber film prepared by the invention utilizes the carbon nano tube and the nano silver to modify and modify the electrostatic spinning PU fiber film, can effectively shield electromagnetic interference, and has the outstanding advantages of high stretching rate, good conductivity, light weight and the like. Has wide application prospect in electromagnetic shielding in the fields of flexible electronics, wearable devices and the like.
Description
Technical Field
The invention relates to the field of electromagnetic protection of wearable devices and electronic communication equipment, in particular to a flexible stretchable electromagnetic shielding fiber film and a preparation method thereof.
Background
With the advent of the 5G age, pollution caused by electromagnetic radiation is also receiving more and more attention. At present, the main way to eliminate the negative influence of electromagnetic waves is to prepare an electromagnetic shielding material to protect a protected object, and the metal electromagnetic shielding material widely used at present based on the electromagnetic wave reflection principle has the defects of large size and heavy module of electronic information equipment due to the defects of high self density, high cost, low specific efficiency and the like, so that the requirements of light weight, intelligence, flexibility and microminiaturization of modern electronic equipment can not be met. Thus, development of a novel electromagnetic shielding material with light weight, flexibility and high performance has become an urgent need in the field of modern electronic technology.
The polymer micro-nano fiber film prepared based on the electrostatic spinning technology has the advantages of light weight, flexibility, large specific surface area, high porosity and the like, and is an ideal template for developing a new generation of electromagnetic shielding film. In order to provide the electrospun polymer fibers with excellent electrical conductivity, thereby improving electromagnetic shielding effectiveness, conventionally, high temperature processes are often used to carbonize the polymer fibers. However, the high-temperature treatment method has the defects of complex process, high cost and the like, reduces the flexibility characteristic of the polymer fiber, and severely restricts the application and popularization of the process method.
Disclosure of Invention
The invention aims to overcome the defects and shortcomings of the prior art and the process, and provides a flexible and stretchable electromagnetic shielding fiber film and a preparation method thereof, so as to solve the problem that the conventional polymer micro-nano fiber film is difficult to have high flexibility and excellent conductivity.
The object of the invention is achieved by at least one of the following technical solutions.
A flexible and stretchable electromagnetic shielding fiber film comprises a Polyurethane (PU) fiber film, wherein Carbon Nanotubes (CNTs) are loaded in the PU fiber film, and the PU fiber film is an electrostatic spinning film.
Preferably, the PU fiber film loaded with carbon nanotubes is covered with silver nanoparticles (AgNPs).
The invention also provides a method for preparing the flexible stretchable electromagnetic shielding fiber film, which comprises the following steps:
preparing a PU fiber film by an electrostatic spinning method;
the PU fiber film is used as a flexible stretchable substrate, carbon nanotubes are embedded and crosslinked on the surface of the PU fiber through an ultrasonic cavitation loading process, so that the PU/CNTs fiber film is obtained, and the PU/CNTs fiber film is a flexible stretchable electromagnetic shielding fiber film.
Preferably, when the PU fiber film is prepared by an electrostatic spinning method, the electrostatic spinning precursor solution adopts a PU solution with the mass fraction of 25-35%, and the solvent of the electrostatic spinning precursor solution adopts a mixed solution of dimethylformamide and acetone.
Preferably, when the PU fiber film is prepared by an electrostatic spinning method, the electrostatic spinning working voltage is 10-15 kV, the distance from a spinning nozzle to a fiber receiving device is 10-20 cm, and the feeding rate of an injector is 0.1-100 mL/h.
Preferably, when the PU/CNTs fiber film is obtained by embedding and crosslinking carbon nanotubes on the surface of the PU fiber through an ultrasonic cavitation loading process, the power of an ultrasonic vibrator is 320-350W, the frequency of ultrasonic waves is 20kHz, the single ultrasonic cavitation loading time is 5min, the ultrasonic action duty ratio is 1:2, wherein the ultrasonic action time and the interruption time are 5s and 10s respectively.
Preferably, when the PU/CNTs fiber film is obtained by embedding and crosslinking carbon nanotubes on the surface of the PU fiber through an ultrasonic cavitation loading process, 40-60 mg of sodium dodecyl benzene sulfonate and 40-60 mg of carbon nanotubes are added into every 100mL of deionized water in the carbon nanotube suspension, and the length of the carbon nanotubes is 5-30 mu m.
Preferably, silver nano particles are attached to the PU/CNTs fiber film by a solution reduction method, so that the PU/CNTs/AgNPs composite fiber film is obtained, and the PU/CNTs/AgNPs composite fiber film is a flexible stretchable electromagnetic shielding fiber film.
Preferably, the process of attaching silver nanoparticles to the PU/CNTs film by solution reduction method includes:
primary soaking: soaking the PU/CNTs fiber film in silver precursor solution for 40-80 min, and then drying in vacuum environment;
and (3) secondary soaking: soaking the dried PU/CNTs fiber film in silver reducing agent solution for 20-40 min, washing the reducing agent on the PU/CNTs fiber film by deionized water, and drying in a vacuum environment;
repeating the process from one soaking to two soaking for several times to obtain the PU/CNTs/AgNPs composite fiber film.
Preferably:
when in one-time soaking, the adopted silver precursor solution is ethanol solution of silver trifluoroacetate with the solute mass fraction of 10-20%, the drying temperature is 40-50 ℃ and the drying time is 10-20min;
during the secondary soaking, the adopted silver reducing agent solution is L-ascorbic acid deionized water solution with the concentration of 15-25 mg/mL, the drying temperature is 40-50 ℃, and the drying time is 10-20min;
the times of repeating the soaking process from one time to the second time are 3 to 8 times.
The invention has the following beneficial effects:
the flexible and stretchable electromagnetic shielding fiber film takes the PU fiber film prepared by electrostatic spinning as a flexible and stretchable substrate, and the substrate has the characteristics of light weight, flexible and stretchable property and high porosity, and can provide multiple reflection interfaces for electromagnetic shielding. The carbon nanotubes are loaded in the PU fiber film, the conductivity of the PU fibers in the PU fiber film is directly endowed by the aid of the carbon nanotubes, the flexibility of the PU fiber film is enhanced, the breaking strength is greatly improved, and the flexibility and the high-efficiency functionalization are both considered. In conclusion, the flexible and stretchable electromagnetic shielding fiber film has the characteristics of high flexibility, strong stretchability and excellent conductivity.
Drawings
FIG. 1 is a schematic diagram of the preparation of a PU fiber film by an electrostatic spinning technology, wherein E is a high-voltage electrostatic field, and F is an electrostatic field stretching force.
FIG. 2 is a schematic diagram of an ultrasonic cavitation load-bearing process platform employed in the present invention.
FIG. 3 is an SEM image of an electrospun PU fiber film prepared according to an embodiment of the invention.
FIG. 4 is an SEM image of a PU/CNTs fiber film prepared according to an embodiment of the invention.
Fig. 5 (a) and fig. 5 (b) are a schematic structural view and an SEM view of a flexible and stretchable PU/CNTs/AgNPs composite fiber film prepared in the embodiment of the present invention, respectively.
Fig. 6 is a schematic flow chart of preparing a flexible stretchable electromagnetic shielding fiber film according to an embodiment of the present invention.
FIG. 7 is a graph showing the electrical conductivity of flexible and stretchable PU/CNTs/AgNPs composite fiber films prepared in accordance with the present invention as a function of mechanical bending action.
FIG. 8 is an electromagnetic shielding effectiveness chart of a PU/CNTs/AgNPs composite fiber film prepared by the embodiment of the invention, wherein PU/CNTs/AgNPs-2, PU/CNTs/AgNPs-4 and PU/CNTs/AgNPs-6 are respectively samples for reducing and loading silver nano particles for 2 times, 4 times and 6 times.
The device comprises a 1-electrostatic spinning precursor liquid, a 2-spinneret, a 3-fiber receiving device, a 4-injection pump, a 5-injector, a 6-high-voltage power supply, a 7-computer, an 8-signal acquisition system, a 9-temperature sensor, a 10-sound pressure sensor, an 11-ultrasonic generator, a 12-ultrasonic vibrator, a 13-water bath device, a 14-precise displacement platform, a 15-PU fiber film, 16-fiber surface embedded and crosslinked CNTs and 17-reduced AgNPs.
Detailed Description
The invention is described in further detail below with reference to the attached drawing figures and to specific embodiments:
the invention provides a preparation method of a flexible stretchable electromagnetic shielding fiber film, which comprises the following steps:
firstly, preparing a precursor liquid by using a PU polymer, and preparing a PU fiber film by using an electrostatic spinning technology;
secondly, taking the prepared PU fiber film as a substrate, embedding and crosslinking CNTs on the surface of the PU fiber through an ultrasonic cavitation loading process, and preparing the PU/CNTs fiber film;
finally, the PU/CNTs/AgNPs composite fiber film is prepared by a post-treatment process of reducing AgNPs by a solution method, so that the electromagnetic shielding effectiveness of the PU/CNTs/AgNPs composite fiber film is further improved.
Referring to fig. 1, the device adopted in the preparation of the PU fiber film by the electrostatic spinning technology of the invention mainly comprises a spinneret 2, a fiber receiving device 3, an injection pump 4, an injector 5 and a high-voltage power supply 6;
wherein the injection pump 4 is connected with the injector 5, the spinneret 2 is connected with the injector 5, and the electrostatic spinning precursor liquid 1 is arranged in the injector 5; the positive electrode of the high-voltage power supply 6 is connected with the spinneret 2, and the negative electrode of the high-voltage power supply 6 is connected with the fiber receiving device 3; the spinneret 2 is arranged at the left side of the fiber receiving device 3, and an electrostatic field is formed between the spinneret 2 and the fiber receiving device 3; by adjusting the flow rate of the syringe pump 4, the precursor liquid 1 can be ejected from the spinneret 2 by electrostatic force to form nanofibers.
As a preferred embodiment of the invention, the PU electrostatic spinning fiber film is prepared by adopting an electrostatic spinning process. Under the action of a strong electric field and electrostatic stretching in the electrostatic spinning process, PU is made into a highly stretchable fiber mat, in addition, the diameter of a spinning fiber and the thickness of a fiber film can be regulated and controlled by regulating the working voltage of a high-voltage power supply 6 and the distance from a spinneret 2 to a fiber receiving device 3 and the feeding rate of an injector 5, and electrostatic spinning parameters are as follows: the working voltage of the high-voltage power supply 6 is 10-15 kV, the distance from the spinneret 2 to the fiber receiving device 3 is 10-20 cm, the electric field formed between the spinneret 2 and the fiber receiving device 3 can enable the electrostatic spinning precursor liquid to be sprayed out from the spinneret 2, and the feeding rate of the injector 5 is set to be 0.1-100 mL/h.
As a preferred embodiment of the invention, PU is adopted to prepare the electrostatic spinning precursor liquid, the material has good flexibility characteristic and thermoplastic property, and the electrostatic spinning fiber structure with high ductility can be prepared. The method for preparing the electrostatic spinning precursor liquid by using PU comprises the following steps: and (3) taking a mixed solution of dimethylformamide and acetone in a mass ratio of 1:1 as a solvent, and dissolving PU particles in the solvent to obtain the electrostatic spinning precursor solution with the PU mass fraction of 25% -35%.
Referring to fig. 2, the device adopted when embedding and crosslinking CNTs into a PU electrostatic spinning fiber film through an ultrasonic cavitation loading process mainly comprises a computer 7, a signal acquisition system 8, a temperature sensor 9, a sound pressure sensor 10, an ultrasonic generator 11, an ultrasonic vibrator 12, a water bath device 13 and a precision displacement platform 14;
wherein the ultrasonic generator 11 is connected with the ultrasonic vibrator 12, CNTs suspension is filled in the water bath device 13, and the ultrasonic vibrator 12 is arranged in the CNTs suspension to realize power input; the temperature sensor 10 and the sound pressure sensor 11 are used for detecting temperature and sound pressure signals in the ultrasonic cavitation load process; the signal acquisition system 8 is connected with the computer 7 and is used for acquiring and displaying sensing signals in real time; in the ultrasonic cavitation load process, in order to conveniently adjust the intensity of ultrasonic cavitation load action, a sample is placed on the precise displacement platform 14, the distance between the sample and the ultrasonic vibrator 12 is adjusted by adjusting the height of the precise displacement platform 14, and the effective distance between the ultrasonic vibrator 12 and the sample is adjusted to be 0.5-50 mm; by adjusting the parameters and processing time of the ultrasonic generator 11, CNTs can be anchored on the PU fiber film under the actions of transient high temperature (more than 5000K), high pressure (100 MPa), shock wave and microjet generated by ultrasonic cavitation effect.
As a preferred embodiment of the invention, when the PU/CNTs fiber film is prepared by an ultrasonic cavitation CNTs loading process, CNTs suspension is used as a raw material, cavitation bubbles are generated in the CNTs suspension under the action of high-power ultrasonic waves, and the cavitation bubbles are accompanied with the actions of microjet and shock waves when collapsing in an ultrasonic field. These microfluidics and shockwaves generate high temperatures and pressures that cause sintering of the CNTs, thereby pushing the CNTs at very high velocities towards the surface of the nanofibers. When the fast moving CNTs strike the surface of the nanofiber, interfacial collision between CNTs and the nanofiber occurs, the electrospun PU nanofiber may be partially softened or even melted at the impact part, and then CNTs may be uniformly anchored on the electrospun PU fiber film. The electrostatic spinning PU fiber film has excellent conductivity, the recoverable elongation reaches 250%, the breaking strength is enhanced by 4 times, and the flexibility is enhanced by 20% due to the excellent physical properties of CNTs, in addition, the number, depth and uniformity of the CNTs embedded and crosslinked on the surface of the electrostatic spinning PU nanofiber can be regulated and controlled by setting the power of the ultrasonic vibrator 12, the frequency of ultrasonic waves, the single ultrasonic cavitation time and the number of ultrasonic cavitation loads, so that the high-efficiency load of CNTs is realized, and a conductive network channel is formed. The ultrasonic cavitation load CNTs process parameters are as follows: the power of the ultrasonic vibrator 12 is 320-350 w, the frequency of ultrasonic waves is 20kHz, the duration of single ultrasonic cavitation is 5min, and the ultrasonic cavitation loading process is repeated for 6 times, so that the high-efficiency load of CNTs is realized. In order to inhibit ultrasonic cavitation-induced high-temperature melting of PU fibers, the duty cycle of ultrasonic action is set to be 1:2, namely the ultrasonic action time and the interruption time are respectively 5s and 10s, and meanwhile, the temperature of the water bath device 13 is set to be 50 ℃. The preparation method of the CNTs suspension liquid comprises the following steps: adding a proper amount of sodium dodecyl benzene sulfonate as a solvent into a certain amount of deionized water, weighing a certain amount of long CNTs powder with the carbon nano tube length of 5-30 mu m, and dispersing the long CNTs powder into the solvent through low-power ultrasonic treatment. Wherein, the ultrasonic power for dispersing the suspension is 120W, 40-60 mg of sodium dodecyl benzene sulfonate and 40-60 mg of CNTs powder are added into every 100mL of deionized water.
As a preferred embodiment of the invention, the post-treatment process of the PU/CNTs fiber film adopts a solution reduction method to uniformly attach AgNPs to the PU/CNTs fiber film, so as to prepare the PU/CNTs/AgNPs composite fiber film, thereby achieving the purpose of reducing resistance and enhancing conductivity, and retaining high flexibility, light weight and excellent electromechanical properties.
The key process steps of the AgNPs loading process by the solution reduction method are as follows:
firstly, putting a PU/CNTs fiber film into silver precursor solution for soaking, and then putting into an oven for drying in a vacuum environment;
secondly, soaking the dried film in silver reducing agent solution for a period of time, washing the residual reducing agent on the film by deionized water, and then drying the film in a vacuum environment in an oven;
finally, repeating the steps for 3-8 times to uniformly cover more AgNPs on the surface of the PU/CNTs fiber film, thereby obtaining the PU/CNTs/AgNPs composite fiber film.
The adopted silver reducing agent solution is L-ascorbic acid with the concentration of 15-25 mg/mL, and deionized water is adopted as the solvent; the soaking time of the step is 20-40 min; the temperature of the oven is controlled to be 40 ℃; the drying time was 30min.
As a preferred embodiment of the invention, when the PU/CNTs/AgNPs composite fiber film is prepared by a silver reduction process, the PU/CNTs fiber film is soaked in silver precursor solution for 40-80 min, taken out and dried for 10min in a vacuum environment at 40 ℃. And then, soaking the dried film in a silver reducing agent solution for 30min, and reducing the silver precursor absorbed in the PU/CNTs fiber film into silver simple substance to be attached to the fiber film. Finally, the residual reducing agent on the film is washed by deionized water, and the film is dried for 30min under the vacuum environment at 40 ℃. The silver simple substance is uniformly fixed on the PU/CNTs fiber film through the continuous repeated adsorption-drying process. In the process of increasing the number of times of restoring the load AgNPs from 0 to 6, the sheet resistance is rapidly reduced from 200Ω/∈ly to 25Ω/∈ly, and the conductivity and electromagnetic shielding performance of the sheet resistance are well enhanced. The preparation method of the silver precursor solution comprises the following steps: ethanol is used as a solvent, and silver trifluoroacetate crystal powder with certain mass is dissolved in the solvent to obtain silver precursor solution with 15% of silver trifluoroacetate mass fraction. The preparation method of the silver reducing agent solution comprises the following steps: deionized water is used as a solvent, and a certain mass of L-ascorbic acid is dissolved in the solvent to obtain a reducer solution with the concentration of 20 mg/mL.
From the above scheme, the invention has the following advantages and effects:
(1) When the flexible stretchable electromagnetic shielding fiber film is prepared, the light, flexible stretchable and high-porosity PU fiber film is successfully prepared by utilizing an electrostatic spinning process, and a multiple reflection interface is provided for electromagnetic shielding.
(2) When the flexible stretchable electromagnetic shielding fiber film is prepared, an ultrasonic cavitation loading process is provided, the softened fiber surface material is damaged based on cavitation, and in-situ embedding and crosslinking of CNTs on the PU fiber surface are realized. The CNTs are used for directly endowing the PU fiber with conductivity, enhancing the flexibility of the PU fiber film, greatly improving the breaking strength and combining flexibility and high-efficiency functionalization. Compared with the traditional process, the high-temperature carbonization method has the advantages that the high-temperature carbonization is adopted to obtain the conductivity, the complexity and the cost of the process are reduced, the material utilization rate is high, the large-area manufacturing can be realized, the simplicity and the high efficiency are realized, the low-temperature environment-friendly performance is realized, the reliability and the controllability are realized, and the like.
(3) When the flexible stretchable electromagnetic shielding fiber film is prepared, the post-treatment process of reducing AgNPs by a solution method is adopted, so that the conductivity of the film is further improved, and the composite fiber film with high conductivity, excellent mechanical stretching performance, excellent electromechanical comprehensive performance and good shielding performance is obtained.
(4) The technical means for preparing the flexible stretchable electromagnetic shielding fiber film is simple and easy to implement, and is convenient to popularize and apply.
Examples:
weighing 3gPU particles as raw materials, placing the raw materials into a mixed solution of 5g of dimethylformamide and 5g of acetone, fully stirring until PU is completely dissolved to obtain 30wt% PU electrostatic spinning precursor solution, and transferring the prepared electrostatic spinning precursor solution 1 to a syringe 5;
fixing an injector 5 on a stage of an injection pump 4, installing a spinneret 2 on the injector 5, pushing a piston of the injector 5 to convey electrostatic spinning precursor liquid to the spinneret 2 through the injection pump 4, and setting the output rate of the injection pump 4 to be 1mL/h;
the positive electrode and the negative electrode of the high-voltage power supply 6 are respectively connected with the spinneret 2 and the fiber receiving device 3, and the fiber receiving device 3 is grounded;
adjusting the position of the fiber receiving device 3 to enable the distance between the fiber receiving device 3 and the spinneret 2 to be 15cm, enabling the center of the fiber receiving device 3 to face the spinneret 2, and enabling the spinning jet to be completely collected in the fiber receiving device 3;
setting the output voltage of the high-voltage power supply 6 to be 12kV, opening the high-voltage power supply 6 and the injection pump 4, and carrying out electrostatic spinning for 2 hours;
after spinning is completed, the high-voltage power supply 6 and the injection pump 4 are closed, the PU electrostatic spinning fiber film is peeled off from the fiber receiving device 3, the fiber film is dried for more than 12 hours on a hot plate at 50 ℃, the solvent which is not completely volatilized is removed, and finally the fiber film is stored in a drying oven, as shown in figure 3, the diameter of the PU fiber is about 800nm;
adding 50mg of sodium dodecyl benzene sulfonate into 100mL of deionized water, fully stirring to obtain a solvent, weighing 50mg of long CNTs powder with the carbon nanotube length of 5-30 mu m, dispersing in the solvent, performing 120W low-power ultrasonic treatment for 1 hour, standing to obtain CNTs suspension, and transferring the prepared CNTs suspension into a water bath device 13;
the ultrasonic generator 11 is connected with the ultrasonic vibrator 12, the ultrasonic vibrator 12 is arranged in CNTs suspension, the ultrasonic generator 11 is used for controlling ultrasonic parameters in the ultrasonic cavitation load process, the power of the ultrasonic vibrator 12 is set to be 350W, the frequency of ultrasonic waves is 20kHz, the time of single ultrasonic cavitation load CNTs is 5min, the ultrasonic action duty ratio is 1:2, namely, the ultrasonic action time and the interruption time are respectively 5s and 10s, and meanwhile, the temperature of the water bath device 13 is controlled to be 50 ℃;
placing the prepared PU electrostatic spinning fiber film on a precise displacement platform 14, and adjusting the height of the precise displacement platform 14 to enable the effective distance between the placing position of the PU electrostatic spinning fiber film and an ultrasonic vibrator to be 1mm;
the temperature sensor 9 and the sound pressure sensor 10 are connected with the signal acquisition system 8, the temperature and sound signal acquisition system 8 is connected with the computer 7, and the state parameters of the ultrasonic cavitation effect are detected in real time, in situ and on line;
starting an ultrasonic generator 11, carrying out an ultrasonic cavitation loading process, and repeating the ultrasonic cavitation loading process for 6 times, wherein the total ultrasonic cavitation time is 30min;
after the ultrasonic cavitation loading process is completed, the ultrasonic generator is turned off, the PU/CNTs fiber film is taken out from the CNTs suspension liquid, and is dried, as shown in figure 4, CNTs are successfully anchored on the surface of the PU fiber, and a corresponding conductive path is formed;
preparing a silver precursor solution by adopting silver trifluoroacetate, and dissolving 3g of silver trifluoroacetate crystal powder into 20g of ethanol to obtain 15wt% silver precursor solution;
soaking the prepared PU/CNTs fiber film in silver precursor solution for 60min, and then vacuum drying in an oven at 40 ℃ for 10min;
preparing a silver reducing agent solution by adopting L-ascorbic acid, and dissolving 2g of L-ascorbic acid in 100mL of deionized water to obtain the silver reducing agent solution with the concentration of 20mg/mL of L-ascorbic acid;
the dried film is put into silver reducing agent solution for soaking for 30min, silver precursor absorbed in the fiber film is reduced into silver simple substance to be attached to micro-nano fiber, then the residual reducing agent on the film is washed by deionized water, the film is put into an oven for vacuum drying for 30min at 40 ℃, the adsorption-reduction process is repeated for 6 times, reduced AgNPs 17 are uniformly covered on the PU fiber film 15 and the CNTs 16 embedded and crosslinked on the fiber surface, as shown in fig. 5 (a), and the flexible stretchable electromagnetic shielding fiber film is prepared, as shown in fig. 5 (b).
In the above scheme of the embodiment, the preparation process of the flexible and stretchable electromagnetic shielding fiber film firstly utilizes the electrostatic spinning technology to successfully prepare the light, flexible and stretchable PU fiber film with high porosity, and the electrostatic spinning PU fiber film has a larger specific surface area and a three-dimensional network structure, and electromagnetic waves can be reflected in the electrostatic spinning PU fiber film for multiple times, so that the electromagnetic shielding effectiveness (EMI SE) is improved. The electromagnetic shielding effectiveness of the conductive polymer composite material depends on the conductivity of the conductive polymer composite material to a great extent, so that an ultrasonic cavitation loading process is developed, the embedding and crosslinking of CNTs on the surface of PU fibers are realized, and the conductivity of the PU fibers is directly endowed by the CNTs. Finally, agNPs are uniformly covered on the surface of the PU/CNTs fiber film by a process of loading the AgNPs by a solution reduction method, so that the conductivity and electromagnetic shielding performance of the film are further improved, and the whole preparation flow of the PU/CNTs/AgNPs composite fiber film is shown in figure 6. The prepared PU/CNTs/AgNPs composite fiber film shows excellent conductivity, mechanical stretching performance and excellent dynamic tolerance, as shown in figure 7, after 1000 times of mechanical bending action, the conductivity of the sheet is reduced by about 3 percent, and long-term electromagnetic shielding guarantee can be provided. In addition, the prepared flexible stretchable electromagnetic shielding film shows good electromagnetic shielding effectiveness (EMI SE). In the process of loading AgNPs by a solution reduction method, the average EMI SE of the PU/CNTs/AgNPs-6 composite fiber film prepared after 6 times of silver nano particles are reduced and exceeds 13.9dB at the bandwidth of 8.2-12.4GHz, as shown in figure 8.
In conclusion, the flexible stretchable electromagnetic shielding fiber film prepared by the invention utilizes the carbon nano tube and the nano silver to modify and modify the electrostatic spinning PU fiber film, can effectively shield electromagnetic interference, and has the outstanding advantages of high stretching rate, good conductivity, light weight and the like. Has wide application prospect in electromagnetic shielding in the fields of flexible electronics, wearable devices and the like.
The above embodiments are only for illustrating the technical solution of the present invention, and it should be understood by those skilled in the art that although the present invention has been described in detail with reference to the above embodiments: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention, which is intended to be encompassed by the claims.
Claims (4)
1. A method for preparing a flexible and stretchable electromagnetic shielding fiber film, which is characterized by comprising the following steps:
preparing a PU fiber film by an electrostatic spinning method;
embedding and crosslinking carbon nanotubes on the surface of PU fibers by using the PU fiber film as a flexible and stretchable substrate through an ultrasonic cavitation loading process to obtain a PU/CNTs fiber film, wherein the PU/CNTs fiber film is a flexible and stretchable electromagnetic shielding fiber film;
embedding and crosslinking carbon nanotubes on the surface of PU fiber by an ultrasonic cavitation loading process, wherein when the PU/CNTs fiber film is obtained, the power of an ultrasonic vibrator is 320-350W, the frequency of ultrasonic waves is 20kHz, the single ultrasonic cavitation loading time is 5min, the ultrasonic action duty ratio is 1:2, and the ultrasonic action time and the interruption time are 5s and 10s respectively;
embedding and crosslinking carbon nanotubes on the surface of PU fiber by an ultrasonic cavitation loading process, wherein 40-60 mg of sodium dodecyl benzene sulfonate and 40-60 mg of carbon nanotubes are added into every 100mL of deionized water in a carbon nanotube suspension when the PU/CNTs fiber film is obtained, and the length of the carbon nanotubes is 5-30 mu m;
attaching silver nano particles on the PU/CNTs fiber film by a solution reduction method to obtain a PU/CNTs/AgNPs composite fiber film, wherein the PU/CNTs/AgNPs composite fiber film is a flexible stretchable electromagnetic shielding fiber film;
the process for attaching silver nano particles on the PU/CNTs fiber film by a solution reduction method comprises the following steps:
primary soaking: soaking the PU/CNTs fiber film in silver precursor solution for 40-80 min, and then drying in vacuum environment;
and (3) secondary soaking: soaking the dried PU/CNTs fiber film in silver reducing agent solution for 20-40 min, washing the reducing agent on the PU/CNTs fiber film by deionized water, and drying in a vacuum environment;
repeating the process from primary soaking to secondary soaking for a plurality of times to obtain the PU/CNTs/AgNPs composite fiber film;
when in one-time soaking, the adopted silver precursor solution is ethanol solution of silver trifluoroacetate with the solute mass fraction of 10-20%, the drying temperature is 40-50 ℃, and the drying time is 10-20min;
during the secondary soaking, the adopted silver reducing agent solution is L-ascorbic acid deionized water solution with the concentration of 15-25 mg/mL, the drying temperature is 40-50 ℃, and the drying time is 10-20min;
the times of repeating the soaking process from one time to the second time are 3 to 8 times.
2. The method for preparing the flexible and stretchable electromagnetic shielding fiber film according to claim 1, wherein when the PU fiber film is prepared by an electrostatic spinning method, a PU solution with the mass fraction of 25% -35% is adopted as an electrostatic spinning precursor solution, and a mixed solution of dimethylformamide and acetone is adopted as a solvent of the electrostatic spinning precursor solution.
3. The method for preparing a flexible and stretchable electromagnetic shielding fiber film according to claim 1 or 2, wherein when the PU fiber film is prepared by an electrostatic spinning method, the electrostatic spinning working voltage is 10-15 kV, the distance from a spinning nozzle to a fiber receiving device is 10-20 cm, and the feeding rate of an injector is 0.1-100 mL/h.
4. A flexible and stretchable electromagnetic shielding fiber film, which is characterized in that the flexible and stretchable electromagnetic shielding fiber film is prepared by the preparation method of any one of claims 1-3, the flexible and stretchable electromagnetic shielding fiber film comprises a PU fiber film, carbon nanotubes are loaded in the PU fiber film, and the PU fiber film is an electrostatic spinning film;
the PU fiber film loaded with carbon nanotubes is covered with silver nanoparticles.
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