Flexible conductive fibers with multi-level porous structure and their preparation method

Abstract

This invention discloses a flexible conductive fiber with a multi-level porous structure and its preparation method. A spinning solution is obtained by dissolving polyurethane and graphene in a predetermined proportion in a first solvent prepared with N,N-dimethylformamide and toluene in a predetermined proportion. Then, using a pyrrole-water solution as the first coagulation bath, pyrrole-polyurethane fibers are prepared by wet spinning. Finally, a ferric chloride solution is used as the second coagulation bath to prepare the flexible conductive fiber with a multi-level porous structure. Through phase replacement during wet spinning, pyrrole fills the surface and interior of the fiber material, achieving a superposition of internal and external conductivity, increasing the fiber's sensing performance. Thus, while ensuring the elasticity of the polyurethane by constructing a multi-level porous structure, the phase replacement process deeply bonds the conductive layer to the fiber matrix, ensuring synchronous tensile change sensing between the conductive layer and the elastic matrix.

Description

Technical Field

[0001] This invention relates to the field of flexible conductive fiber technology, and in particular to a flexible conductive fiber with a multi-level pore structure and its preparation method. Background Technology

[0002] Traditional electronic systems are typically composed of rigid components such as metal fibers and integrated circuit boards. With the increasing demand for wearable devices, the high mechanical rigidity of traditional electronic systems makes them unsuitable for skin contact, thus limiting their application in wearable smart devices. In recent years, intelligent flexible electronic materials have received widespread attention in areas such as smart displays, sustainable energy, wearable sensing, healthcare, energy management, and human-computer interaction. Flexible electronic devices are those that possess flexibility and can adapt to different working environments (stretching, compression, etc.). Their flexibility, stretchability, and portability allow them to meet various deformation requirements, thus adapting to diverse working conditions.

[0003] Currently, the building materials used for sensors are mainly solid or fibrous materials. Among them, flexible fiber fabrics have a foundation for application in wearable smart applications due to their flexibility, light weight, low cost, and good biocompatibility. Furthermore, they are attracting more market attention because they can be woven into fabric sensing materials.

[0004] Polyurethane fiber is a fiber with excellent elasticity and resilience, making it an excellent matrix material for designing high-strain sensors. However, its conductivity is poor, so strain sensors can only be fabricated by combining it with other highly conductive materials, such as graphene, carbon nanotubes, polyaniline, and polypyrrole. Common methods for imparting conductivity to polyurethane fibers include uniform mixing, coating, and in-situ polymerization. In the manufacturing of wearable smart devices, common polyurethane-based elastic conductive fibers require a strong bond between the conductive layer and the polyurethane layer to meet the performance requirements of flexible electronic sensors that can deform under external stimuli and effectively recover. This is often achieved by filling conductive materials into the elastomer or modifying the surface of the conductive filler to enhance the adhesion between the two. Increasing the amount of conductive filler can effectively improve the conductivity of the composite material, but it will reduce the flexibility and tensile strength of the composite material. Furthermore, the conductive fibers prepared by existing technologies are prone to separation from the elastic matrix due to the difference in elastic properties between the conductive layer and the elastic matrix, thus affecting conductivity. Conductive fibers prepared by blending methods lead to a decrease in the elastic properties of the elastic matrix itself. If the properties of the elastic matrix are maintained, the conductivity will decrease. Improving conductivity while maintaining the properties of the elastic matrix requires too many preparation steps and is too complex to be widely used. In addition, during the blending process, some conductive material is wrapped by the elastic matrix, which reduces the conductivity of the conductive fiber.

[0005] In the prior art, patent CN 108385201 A discloses a graphene / polyurethane composite stretchable conductive fiber and its preparation method. The fiber includes polyurethane fibers with pores, and graphene is doped into the pores of the polyurethane fibers to form a composite conductive fiber with stretchable properties. The graphene / polyurethane composite stretchable conductive fiber prepared by the above method has good stretchability. However, the method of physically fixing graphene into the polyurethane can cause slippage between the graphene sheets when the conductive fiber deforms due to the difference in elastic properties between graphene and polyurethane, thus affecting the sensing stability of the conductive fiber.

[0006] In view of this, it is necessary to design a flexible conductive fiber with a multi-level porous structure and its preparation method to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide a flexible conductive fiber with a multi-level porous structure and its preparation method. A two-step molding method is used, namely, the preparation of pyrrole-polyurethane fibers using a binary system and induced polymerization, to obtain a flexible conductive fiber with conductive properties. This reduces the content of blended materials to minimize their impact on the tensile strength of the conductive fiber. Simultaneously, the mechanism of polyurethane molding in a multi-component system achieves a network connection within the fiber, and conductive pathways are formed within the fiber using pyrrole polymerization. The conductive layer synthesis steps are optimized, and the conductive layer is deeply bonded to the fiber matrix, ensuring synchronous tensile change sensing between the conductive layer and the elastic matrix.

[0008] To achieve the above-mentioned objective, this invention provides a method for preparing a flexible conductive fiber with a multi-level porous structure, comprising the following steps:

[0009] S1. Add polyurethane (hereinafter referred to as PU) and graphene in a predetermined ratio to the first solvent and mix well to obtain the spinning solution;

[0010] S2. Using a pyrrole-water solution of a certain concentration as the first coagulation bath, pyrrole-polyurethane fibers with pyrrole on the surface and inside are prepared by wet spinning.

[0011] S3. Using a ferric chloride solution of a certain concentration as the second coagulation bath, the pyrrole-polyurethane fiber prepared in step S2 is left to stand for a certain time at a certain temperature to obtain a flexible conductive fiber with a multi-level porous structure.

[0012] As a further improvement of the present invention, in step S1, the mass ratio of the polyurethane to the graphene is 50:2 to 50:4.

[0013] As a further improvement of the present invention, the first solvent is prepared by N,N-dimethylformamide (hereinafter referred to as DMF) and toluene (hereinafter referred to as TOL).

[0014] As a further improvement of the present invention, the mass ratio of the DMF to the TOL is 6:4 to 9:1.

[0015] As a further improvement of the present invention, the mass fraction of polyurethane in the spinning solution is 15% to 25%.

[0016] As a further improvement of the present invention, the mass ratio of the pyrrole to the polyurethane is 4.2:5 to 10:5.

[0017] As a further improvement of the present invention, in step S3, the mass concentration of the ferric chloride solution is 20-30 g / L.

[0018] As a further improvement of the present invention, in step S3, the certain temperature is 0 to 4°C and the certain time is 10 to 18 hours.

[0019] As a further improvement of the present invention, in step S1, the mixing operation is to stir at room temperature for 0.5 to 2 hours.

[0020] The present invention also provides a flexible conductive fiber with a multi-level pore structure, wherein the flexible conductive fiber is prepared according to the preparation method of the flexible conductive fiber with a multi-level pore structure described in any of the above technical solutions.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention involves preparing a first solvent by mixing DMF and TOL in a predetermined ratio, then dissolving polyurethane and graphene in the first solvent in a predetermined ratio to obtain a spinning solution. A pyrrole-water solution of a certain concentration is used as the first coagulation bath. By utilizing the phase displacement molding principle of wet spinning, different displacement rates are achieved in the multi-solvent system due to varying solvent compatibility, thereby preparing graphene / pyrrole / polyurethane conductive fibers with pyrrole on the surface and inside. The conductive fibers exhibit obvious pore stratification. The large pores are mainly due to the faster diffusion of solvent into the coagulation bath during wet spinning of the DMF system, as the compatibility between TOL and DMF is greater than that between DMF and the polymer. This results in an instantaneous phase separation process, where the non-solvent of polyurethane rapidly diffuses into the polymer, accelerating polyurethane molding and forming a large-pore structure. The small pores are mainly due to the uniform dispersion of pyrrole in the coagulation bath. During the diffusion of the non-solvent into the fiber, pyrrole preferentially adheres to the outer layer of the fiber. Because the pyrrole dispersed in the non-solvent affects the rate of the dual diffusion process to some extent, the molding speed of the outer polymer slows down, gradually forming a small-pore structure. As the non-solvent gradually diffuses inward, the pyrrole content gradually decreases, and normal phase replacement occurs inside the fiber, thus forming a hierarchical porous structure with small pores on the outside and large pores on the inside. Based on this, ferric chloride solution is used as a second coagulation bath to induce the polymerization of pyrrole on the surface and inside of the pyrrole-polyurethane fiber, thereby constructing a flexible conductive fiber (G-PPY-PU) with a hierarchical porous structure based on a multi-component system.

[0023] 2. This invention uses polyurethane as the matrix material and adds a certain amount of graphene to prepare the spinning solution. During the subsequent coagulation bath with a pyrrole-water solution, the π-π conjugated bonds between pyrrole and graphene induce pyrrole to arrange itself regularly on the surface of the polyurethane fiber, with pyrrole preferentially adhering to the outer layer of the fiber. Simultaneously, using a predetermined ratio of DMF and TOL as the first solvent, the double diffusion phenomenon during the phase displacement process between the solvent (DMF) and the non-solvent (water) in the polyurethane molding process diffuses the pyrrole dispersed in the non-solvent into the polyurethane fiber. This allows pyrrole to not only be distributed on the fiber surface but also penetrate into the fiber interior, thereby preparing conductive fibers with higher strength and interconnected pores. The first coagulation bath allows pyrrole to diffuse into the fiber interior through bidirectional diffusion during the phase displacement process. Furthermore, ferric chloride simultaneously induces the polymerization of pyrrole inside and outside the fiber, forming polypyrrole conductive layers on the surface and inside the conductive fiber, effectively enhancing the conductivity of the pyrrole / graphene / polyurethane fiber.

[0024] 3. This invention uses phase substitution to fill the surface and interior of the fiber material with pyrrole, and forms polypyrrole through in-situ polymerization of ferric chloride, thereby achieving the superposition of internal and external conductivity and increasing the sensing performance of the fiber. In this way, while constructing a multi-level porous structure to ensure the elastic properties of polyurethane, the conductive layer is deeply bonded to the fiber matrix through the phase substitution process, ensuring the synchronous tensile change sensing of the conductive layer of the fiber and the elastic matrix.

[0025] 4. In this invention, due to the higher polyurethane content and lower displacement rate at the fiber center during the displacement process, and the more complete and faster displacement between the surface and the coagulation bath, more pyrrole is adsorbed onto the fiber surface and the outer layer of the fiber during the initial molding process. Compared with traditional fiber sensing materials, the flexible conductive fiber with a multi-level porous structure of this invention can form conductive pathways internally using the fiber molding structure, thus enhancing electrical performance. Simultaneously, by utilizing the gas sensing properties of polypyrrole and the multi-level porous structure generated during fiber molding, the specific surface area of ​​the fiber can be increased, enabling the construction of a multifunctional sensing material for both motion and gas sensing.

[0026] 5. This invention reduces the content of blended materials to minimize the impact on the tensile strength of conductive fibers. At the same time, it achieves network connections within the fibers through the molding mechanism of multi-component polyurethane systems and utilizes pyrrole to form conductive pathways within the fibers, thus optimizing the conductive layer synthesis steps and effectively reducing production costs.

[0027] 6. The flexible conductive fiber with a multi-level porous structure of the present invention provides high comfort to the human body. The fiber has a three-dimensional porous structure, and the pores formed through the phase displacement process can create internal connection channels with a certain degree of connectivity within the fiber, and can support a large amount of conductive polymer. Simultaneously, the porous structure contributes to heat insulation. During the stretching process, the resistance of the flexible conductive fiber changes due to the splitting of the conductive layer itself, resulting in excellent and stable conductivity. It is also reusable and can be cut to the desired length, allowing for free adjustment of dimensions to meet the needs of different situations. Attached Figure Description

[0028] Figure 1 The resistance sensing signal and sensitivity test results of the multi-level porous flexible conductive fiber prepared in Example 1;

[0029] Figure 2 SEM images of the conductive fiber surfaces prepared in Comparative Examples 1-3 (ac) and Examples 1-3 (df);

[0030] Figure 3 Thermal properties (DTG) of the conductive fibers prepared in Examples 1-3 and Comparative Examples 1-3;

[0031] Figure 4 The stress-strain curves and bar charts of Young's modulus of the conductive fibers prepared in Examples 1-3 and Comparative Examples 1-3 are shown.

[0032] Figure 5 SEM image of the cross-section of the conductive fiber prepared in Comparative Example 4;

[0033] Figure 6 The results are the conductivity measurement results for Comparative Example 5;

[0034] Figure 7 These are the mechanical performance test results for Comparative Example 6. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0037] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0038] This invention provides a method for preparing flexible conductive fibers with a multi-level porous structure, comprising the following steps:

[0039] S1. Add polyurethane and graphene in a predetermined ratio to the first solvent and stir at room temperature for 0.5-2 hours to obtain the spinning solution;

[0040] S2. Using a certain concentration of pyrrole-water solution as the first coagulation bath, the wet spinning machine is operated by setting the push rate of the push pump to 50 μL / h and the winding speed to 2 r / min. The spinning head is placed in the pyrrole-water solution to prepare polyurethane fibers with pyrrole on the surface and inside.

[0041] S3. Using a ferric chloride solution with a mass concentration of 20-30 g / L as the second coagulation bath, the polyurethane fiber prepared in step S2 is left to stand for 10-18 h at 0-4 °C to obtain a flexible conductive fiber with a multi-level pore structure.

[0042] Specifically, in step S1, the mass ratio of polyurethane to graphene is preferably 50:2 to 50:4, more preferably 50:3; the mass fraction of polyurethane in the spinning solution is 15% to 25%.

[0043] Specifically, in step S1, the first solvent is prepared by DMF and TOL, wherein the mass ratio of DMF to TOL is 0.8:1 to 1.2:1.

[0044] Specifically, the mass ratio of pyridine to polyurethane is preferably 4.2:5 to 10:5, and more preferably 8.4:5.

[0045] The present invention also provides a flexible conductive fiber with a multi-level pore structure, wherein the flexible conductive fiber is prepared according to any of the above technical solutions.

[0046] The preparation method of the flexible conductive fiber with multi-level pore structure provided by the present invention will be described below with reference to specific embodiments.

[0047] Example 1

[0048] This embodiment provides a method for preparing flexible conductive fibers with a multi-level porous structure, including the following steps:

[0049] S1. Prepare a first solvent by mixing DMF and TOL in a mass ratio of 8:2. Add polyurethane and graphene to the first solvent so that the mass fraction of polyurethane in the first solvent is 25% and the mass fraction of graphene is 1.5%. Stir at room temperature for 1 hour to obtain a spinning solution.

[0050] S2. A pyrrole-water solution with a mass concentration of 1.2 g / 100 mL was used as the first coagulation bath, and the mass ratio of pyrrole in the first coagulation bath to polyurethane in the spinning solution was controlled at 8.4:5. By wet spinning, the feed rate of the wet spinning machine push pump was set to 50 μL / h, the winding speed was set to 2 r / min, the spinning head was placed in the uniformly dispersed pyrrole-water solution, and the spinning solution was sprayed out through the spinning head to prepare polyurethane fibers with pyrrole on the surface and inside.

[0051] S3. Using a ferric chloride solution with a mass concentration of 24 g / L as the second coagulation bath, the polyurethane fiber prepared in step S2 was allowed to stand for 12 h at 0 °C to obtain a flexible conductive fiber with a multi-level porous structure (named 1.5G-PPy-PU). Its conductive sensing signal is as follows: Figure 1 As shown.

[0052] Depend on Figure 1It can be seen that when the strain range is 0-20%, the sensor has the ability to respond to strain and realize real-time changes. Furthermore, the sensing capability steadily increases with increasing strain. An inflection point appears at 10% strain, where the sensitivity coefficient for 0-10% is 11.4. When the strain reaches 20%, ΔR / R0 reaches 290%, and the sensitivity coefficient for 10-20% strain reaches 17.8, exhibiting excellent sensing response and good repeatability. This is mainly due to the in-situ polymerization of the polyurethane fiber matrix surface, forming a polypyrrole conductive layer sufficient to create a crack sensing effect.

[0053] Examples 2-3

[0054] Examples 2 and 3 respectively provide a method for preparing flexible conductive fibers with multi-level porous structures. Compared with Example 1, the only difference is that the mass fraction of graphene in the spinning solution is changed. The other steps are the same as in Example 1, and will not be repeated here.

[0055] In Example 2, the mass fraction of graphene was 1%, and the resulting conductive fiber was named 1G-PPy-PU; in Example 3, the mass fraction of graphene was 2%, and the resulting conductive fiber was named 2G-PPy-PU.

[0056] Comparative Examples 1-3

[0057] Comparative Examples 1-3 provide methods for preparing flexible conductive fibers with a multi-level porous structure. Compared with Example 1, no pyrrole was added to the first coagulation bath of Comparative Examples 1-3, and the mass fraction of graphene in the spinning solutions prepared in Comparative Examples 1-3 was 1%, 1.5%, and 2%, respectively. The conductive fibers obtained were named 1G-PU, 1.5G-PU, and 2G-PU, respectively. Other preparation methods and parameters in Comparative Examples 1-3 were consistent with those in Example 1 and will not be repeated here.

[0058] The morphology, thermal properties, and mechanical properties of Examples 1-3 and Comparative Examples 1-3 are as follows: Figure 2-4 As shown. By Figure 2 It can be seen that the conductive fibers prepared in Comparative Examples 1-3 have relatively smooth surfaces, and the porous channels on the fiber surface are due to the diffusion of solvent and non-solvent during the phase displacement process. In contrast, the conductive fibers prepared in Examples 1-3 have formed a wrinkled layer on their surface. This structure demonstrates that the in-situ polymerization of polypyrrole successfully constructed a conductive layer on the polyurethane surface. Figure 3 It can be seen that 1.5G-PPy-Pu has the best thermal performance. (From...) Figure 4 It can be seen that, under the same polymerization conditions, the fiber has the best tensile properties when the mass fraction of graphene is 1.5%; at the same time, compared with comparative examples 1 to 3, the Young's modulus of the conductive fibers prepared in examples 1 to 3 is significantly increased.

[0059] Comparative Example 4

[0060] This comparative example provides a method for preparing flexible conductive fibers with a multi-level porous structure. Compared with Example 1, the only difference is that the first solvent is N,N-dimethylformamide. All other steps are the same as in Example 1 and will not be repeated here.

[0061] The cross-sectional porous structure of the conductive fiber prepared in this comparative example was characterized by SEM, and the results are as follows: Figure 5 As shown, by Figure 5 It can be seen that the conductive fibers formed by wet spinning of a single-component solvent component have larger pores inside. Compared with the conductive fibers formed in Example 1, the pores supported by non-solvent water are formed rapidly inside. When the conductive filler is physically blended into the fiber, the pores are too large and cannot form conductive pathways, resulting in unstable conductivity of the flexible polyurethane fiber. In Example 1, DMF has stronger compatibility with water than with polyurethane and TOL. Therefore, during the replacement process, water preferentially diffuses with DMF. TOL, which is originally compatible with polyurethane, has lower compatibility with water and diffuses slowly. The slow diffusion rate results in smaller pores slowly forming inside the polyurethane, which is more conducive to the formation of conductive pathways by the conductive filler.

[0062] Comparative Examples 5-6

[0063] Comparative Examples 5 and 6 respectively provide a method for preparing flexible conductive fibers with multi-level porous structures. Compared with Example 1, the only difference is that the mass fraction of graphene in the spinning solution is changed. The other steps are the same as those in Example 1, and will not be repeated here.

[0064] In Comparative Example 5, the graphene content in the spinning solution was 0.5%, resulting in conductive fibers with poor conductivity. Testing with a digital multimeter showed excessively high resistance (e.g., ...). Figure 6 (As shown). In Comparative Example 6, the graphene content in the spinning solution was 2.5%, and the tensile strain of the resulting conductive fiber could only reach about 600% (e.g., Figure 7 As shown in the figure, excessive graphene content leads to a decrease in flexible tensile strain.

[0065] In summary, the flexible conductive fiber with a multi-level porous structure and its preparation method disclosed in this invention achieve the superposition of internal and external conductivity by filling the surface and interior of the fiber material with pyrrole through phase substitution, thereby increasing the sensing performance of the fiber. In this way, while ensuring the elastic properties of polyurethane by constructing a multi-level porous structure, the conductive layer is deeply bonded to the fiber matrix by the phase substitution process, ensuring the synchronous tensile change sensing of the conductive layer of the fiber and the elastic matrix. By preparing a spinning solution using polyurethane as the matrix material and adding a certain amount of graphene, a conductive layer is formed on the surface of the conductive fiber through the π-π conjugated bonds between pyrrole and graphene during the subsequent coagulation bath using a pyrrole-water solution. Simultaneously, using a predetermined ratio of DMF and TOL as the first solvent, pyrrole preferentially adheres to the outer layer of the fiber. Utilizing the double diffusion phenomenon during the phase displacement process between the solvent (DMF and TOL) and the non-solvent (water) in the polyurethane molding process, the pyrrole dispersed in the non-solvent diffuses into the polyurethane fiber, allowing it to not only be distributed on the fiber surface but also penetrate into the fiber interior, thus producing a conductive fiber with higher strength and interconnected pores. Furthermore, ferric chloride simultaneously induces the polymerization of pyrrole inside and outside the fiber, forming polypyrrole conductive layers on both the surface and inside of the conductive fiber, effectively enhancing the conductivity of the pyrrole / graphene / polyurethane fiber.

[0066] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a flexible conductive fiber with a multi-level porous structure, characterized in that, Includes the following steps: S1. Add polyurethane and graphene in a predetermined ratio to a first solvent and mix well to obtain a spinning solution; the first solvent is prepared by N,N-dimethylformamide and toluene; the mass ratio of polyurethane to graphene is 50:3~50:

4. S2. Using a pyrrole-water solution of a certain concentration as the first coagulation bath, pyrrole-polyurethane fibers with pyrrole on the surface and inside are prepared by wet spinning. S3. Using a ferric chloride solution of a certain concentration as the second coagulation bath, the pyrrole-polyurethane fiber prepared in step S2 is left to stand for a certain time at a certain temperature to obtain a flexible conductive fiber with a multi-level porous structure.

2. The method for preparing flexible conductive fibers with a multi-level porous structure according to claim 1, characterized in that: The mass ratio of N,N-dimethylformamide to toluene is 6:4 to 9:

1.

3. The method for preparing flexible conductive fibers with a multi-level porous structure according to claim 1, characterized in that: The mass fraction of polyurethane in the spinning solution is 15%~25%.

4. The method for preparing flexible conductive fibers with a multi-level porous structure according to claim 1, characterized in that: The mass ratio of pyrrole to polyurethane is 4.2:5 to 10:

5.

5. The method for preparing flexible conductive fiber with multi-level porous structure according to claim 1, characterized in that: In step S3, the mass concentration of the ferric chloride solution is 20~30 g / L.

6. The method for preparing flexible conductive fibers with a multi-level porous structure according to claim 4, characterized in that: In step S3, the specified temperature is 0~4℃ and the specified time is 10~18h.

7. The method for preparing flexible conductive fiber with multi-level porous structure according to claim 1, characterized in that: In step S1, the mixing operation is to stir at room temperature for 0.5 to 2 hours.

8. A flexible conductive fiber with a multi-level porous structure, characterized in that, The flexible conductive fiber is prepared by the method for preparing a flexible conductive fiber with a multi-level pore structure according to any one of claims 1-7.

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