Elastic piezoresistive material and environment-friendly preparation method thereof

Abstract

The invention discloses an elastic piezoresistive material and an environment-friendly preparation method thereof, and belongs to the technical field of flexible electronics. The elastic piezoresistive material is prepared from an elastic matrix and a conductive filler dispersed in the elastic matrix; wherein the elastic matrix is composed of polyurethane, polyacrylic acid and polyethylene glycol, and the conductive filler is a carbon nanotube. The preparation method comprises the following steps: adding a carbon nanotube aqueous dispersion into a polyacrylic acid aqueous emulsion, and uniformly stirring to obtain a dispersion A; dissolving polyethylene glycol in deionized water to obtain a solution B; adding a polyurethane water-based emulsion into the solution B, and uniformly stirring to obtain a mixed solution C; uniformly mixing the dispersion liquid A and the mixed liquid C to obtain a mixed liquid D; and carrying out molding and drying treatment on the mixed solution D to obtain the elastic piezoresistive material. The mechanical and electrical properties of the elastic piezoresistive material provided by the invention can be regulated and controlled according to specific application requirements, the whole process can be operated in a room-temperature air environment, no organic solvent is used, and the preparation method is environment-friendly, economical, simple and feasible, and has very high practical value.

Description

Technical Field

[0001] The present invention belongs to the field of flexible electronic technology, and in particular relates to an elastic piezoresistive material and an environmentally friendly preparation method thereof. Background Art

[0002] Elastic piezoresistive materials combine elastic and piezoresistive properties. Stress and strain sensors constructed with elastic piezoresistive materials as sensitive elements have the characteristics of fast response speed, simple signal processing, and easy large-scale array sensing. Elastic piezoresistive materials with superior performance are required to have high sensitivity, large response range, and fast response speed. At the same time, they are required to have good anti-fatigue properties to improve long-term working stability. How to improve the anti-fatigue properties of elastic piezoresistive materials is currently the focus and difficulty in this field. To improve the anti-fatigue properties, it is generally necessary to cross-link the elastic matrix. The more common method is to use cross-linkable silicone elastomers as elastic matrix materials. However, the cost of such materials is generally high, and the conductive filler needs to be surface treated to improve its dispersibility in the silicone elastomer, which further increases the cost of preparation. Another option is to use a subsequent vulcanization and cross-linking method to treat natural rubber or other elastomeric materials, but this method will cause certain environmental pollution and is not environmentally friendly. Summary of the Invention

[0003] In response to the above technical problems, the present invention proposes an elastic piezoresistive material and an environmentally friendly preparation method thereof.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] One of the objectives of the present invention is to provide an elastic piezoresistive material, which is prepared by an elastic matrix and a conductive filler dispersed therein; wherein the elastic matrix is ​​composed of polyurethane (PU), polyacrylic acid (PAA) and polyethylene glycol (PEG), and the conductive filler is carbon nanotubes (CNTs).

[0006] The present invention provides an elastic piezoresistive material with adjustable mechanical and electrical properties and excellent fatigue resistance. PAA ensures excellent dispersion of CNTs within the elastic piezoresistive material, allowing for flexible control of the material's conductivity, sensitivity, and stress response range by adjusting the CNT content to suit diverse sensing applications. PEG forms strong hydrogen bonds within the elastic matrix, enhancing the elasticity, fatigue resistance, and stability of the piezoresistive material, ultimately improving the overall performance of stress and strain sensors.

[0007] Furthermore, the carbon nanotubes are selected from one or both of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).

[0008] Furthermore, the elastic piezoresistive material comprises, by volume percentage, 60-90% polyurethane, 4-20% polyacrylic acid, 3-20% polyethylene glycol, and 3-15% carbon nanotubes.

[0009] A second object of the present invention is to provide a method for preparing an elastic piezoresistive material, comprising the following steps:

[0010] Adding the carbon nanotube aqueous dispersion to the polyacrylic acid aqueous emulsion and stirring evenly to obtain dispersion A;

[0011] Dissolving polyethylene glycol in deionized water to obtain solution B; adding polyurethane aqueous emulsion to solution B and stirring evenly to obtain mixed solution C;

[0012] Mixing the dispersion A and the mixed solution C to obtain a mixed solution D;

[0013] The mixed solution D is subjected to a molding and drying process to obtain an elastic piezoresistive material.

[0014] Furthermore, the solid content of the carbon nanotube aqueous dispersion is 5-12 wt %.

[0015] Furthermore, the solid content of the polyacrylic acid aqueous emulsion is 10-50 wt%.

[0016] Furthermore, the molecular weight of the polyethylene glycol is 200-2000.

[0017] Furthermore, the concentration of the solution B is 5-50 wt%.

[0018] Furthermore, the solid content of the polyurethane aqueous emulsion is 10-40 wt%.

[0019] A third object of the present invention is to provide an application of elastic piezoresistive material in the field of sensors.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] The preparation method of the elastic piezoresistive material provided by the present invention can be carried out in an air environment at room temperature throughout the entire process without using any organic solvents. Therefore, it is energy-saving, economical, and environmentally friendly, and is suitable for large-scale batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0023] Figure 1 A schematic diagram of the environmentally friendly preparation method of the elastic piezoresistive material provided by the present invention;

[0024] Figure 2 This is the stress-strain curve of the elastic piezoresistive material prepared in Example 1;

[0025] Figure 3 The resistance change curve of the elastic piezoresistive material prepared in Example 1 when repeatedly pressed under a pressure of 12N;

[0026] Figure 4 The resistance change curve of the elastic piezoresistive material prepared in Example 1 as the resistance changes with the applied pressure;

[0027] Figure 5 This is the resistance change curve of the elastic piezoresistive material prepared in Example 1 when repeatedly stretched under 30% strain. DETAILED DESCRIPTION

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0029] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0030] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0031] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0032] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0033] The mechanical and electrical properties of the elastic piezoresistive material provided by the present invention can be controlled according to specific application requirements, and the above-mentioned properties of the material can be flexibly controlled by adjusting the content of CNTs. The PAA introduced into the matrix can not only improve the stability of the dispersion of CNTs in the material, but also improve the interfacial bonding strength between the elastic piezoresistive material and other materials. After being mixed with PU, PEG can form a strong hydrogen bond, which significantly improves the elasticity, fatigue resistance and stability of the elastic matrix, thereby improving the overall performance of the stress sensor. The preparation method of the elastic piezoresistive material disclosed in the present invention can be operated in an air environment at room temperature throughout the process without using any organic solvents. It is an environmentally friendly, economical and simple preparation method with high practical value.

[0034] An embodiment of the present invention provides an elastic piezoresistive material, which is composed of an elastic matrix and a conductive filler dispersed therein. The conductive filler is uniformly dispersed in the insulating elastic matrix to form a conductive network; wherein the elastic matrix is ​​prepared from a polyurethane (PU) aqueous emulsion, a polyacrylic acid (PAA) aqueous emulsion and polyethylene glycol (PEG), and the conductive filler is an aqueous dispersion of carbon nanotubes (CNTs).

[0035] Based on 100% of the total amount of the elastic piezoresistive material, in a preferred embodiment, the volume percentage of the polyurethane (PU) in the elastic piezoresistive material is 60-90%, more preferably 79.4%, 80.3% or 81.1%.

[0036] Based on 100% of the total amount of the elastic piezoresistive material, in a preferred embodiment, the volume percentage of the polyacrylic acid (PAA) in the elastic piezoresistive material is 2-20%, and more preferably 4%.

[0037] Based on 100% of the total amount of the elastic piezoresistive material, in a preferred embodiment, the volume percentage of the polyethylene glycol (PEG) in the elastic piezoresistive material is 3-20%, more preferably 8.6%, 8.7% or 8.9%.

[0038] Based on 100% of the total amount of the elastic piezoresistive material, in a preferred embodiment, the volume percentage of the carbon nanotubes (CNTs) in the elastic piezoresistive material is 3-15%, more preferably 6%, 7% or 8%.

[0039] That is, in the elastic piezoresistive material, the volume ratio of polyurethane (PU), polyacrylic acid (PAA), polyethylene glycol (PEG) and carbon nanotubes (CNTs) is (60-90):(2-20):(3-20):(3-15), preferably (79.4-81.1):4:(8.6-8.9):(6-8), such as 80.3:4:8.7:7, 81.1:4:8.9:6 or 79.4:4:8.6:8.

[0040] In some optional embodiments, the carbon nanotubes are selected from one or both of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).

[0041] An embodiment of the present invention further provides a method for preparing an elastic piezoresistive material, comprising the following steps:

[0042] (1) adding the carbon nanotube aqueous dispersion to the polyacrylic acid aqueous emulsion and stirring to obtain dispersion A;

[0043] (2) dissolving polyethylene glycol in deionized water to obtain solution B; adding polyurethane aqueous emulsion to solution B and stirring well to obtain mixed solution C;

[0044] (3) mixing the dispersion A and the mixed solution C to obtain a mixed solution D;

[0045] (4) The mixed liquid D is subjected to a molding and drying process to obtain an elastic piezoresistive material.

[0046] In the present invention, the carbon nanotube aqueous dispersion is obtained by adding a defined amount of carbon nanotubes to water. For example, 7% MWCNTs refers to adding 7% MWCNTs to water to obtain the MWCNT aqueous dispersion. The specific ratio of water to MWCNTs is determined by defining the solid content of MWCNTs in water. In the present invention, the specific carbon nanotube aqueous dispersion is purchased, so its solid content is fixed. The same applies to other raw materials (polyurethane (PU) aqueous emulsion, polyacrylic acid (PAA) aqueous emulsion) and is not described in detail here.

[0047] In an optional embodiment, the solid content of the carbon nanotube aqueous dispersion is 5-12 wt %, preferably 10 wt %.

[0048] In an optional embodiment, the solid content of the polyacrylic acid aqueous emulsion is 10-50 wt %, preferably 40-50 wt %, and more preferably 45 wt %.

[0049] In an optional embodiment, the molecular weight of the polyethylene glycol is 200-2000, preferably 800.

[0050] In an optional embodiment, the concentration of solution B is 5-50 wt%, preferably 10-50 wt%, and more preferably 20 wt%.

[0051] In an optional embodiment, the solid content of the polyurethane aqueous emulsion is 10-40 wt%, preferably 35 wt%.

[0052] In the present invention, the molding and drying process can be conventional methods such as casting + drying, spin coating + drying, screen printing + drying, etc. In the following embodiments of the present invention, the casting + drying method is selected to verify the effect.

[0053] Unless otherwise specified, the "room temperature" in the present invention refers to 20-30°C.

[0054] The raw materials used in the present invention are all purchased from the market.

[0055] The "polyurethane (PU) aqueous emulsion" described in the present invention refers to "aqueous polyurethane emulsion" purchased from Shenzhen Jitian Chemical Co., Ltd.; the "polyacrylic acid (PAA) aqueous emulsion" refers to "polyacrylic acid emulsion" purchased from Shenzhen Jitian Chemical Co., Ltd.; the "single-walled carbon nanotubes (SWCNTs) aqueous dispersion" and "multi-walled carbon nanotubes (MWCNTs) aqueous dispersion" are purchased from Jiaxing Naco New Materials Co., Ltd.

[0056] The technical solution of the present invention is further illustrated by the following examples.

[0057] Figure 1 Schematic diagram of the environmentally friendly preparation method of elastic piezoresistive material of the present invention.

[0058] Example 1

[0059] An elastic piezoresistive material comprises an elastic matrix and a conductive filler. The elastic matrix is ​​made of polyurethane (PU), polyacrylic acid (PAA), and polyethylene glycol (PEG), and the conductive filler is multi-walled carbon nanotubes (MWCNTs). The conductive filler is dispersed in the elastic matrix. The volume percentages of PU, PAA, PEG, and MWCNTs are 80.3%, 4%, 8.7%, and 7%, respectively.

[0060] A method for preparing an elastic piezoresistive material comprises the following steps:

[0061] (1) A commercial multi-walled carbon nanotube (MWCNT) aqueous dispersion (MWCNTs having a diameter of 8-15 nm, a length of 10-30 μm, and a solid content of 10 wt%) was added to a commercial polyacrylic acid (PAA) aqueous emulsion (PAA solid content of 35 wt%), and the MWCNTs were uniformly dispersed by mechanical stirring to obtain dispersion A;

[0062] (2) adding PEG800 to deionized water and stirring to fully dissolve the PEG to obtain solution B, wherein the concentration of PEG in solution B is 20 wt%;

[0063] (3) adding a commercial polyurethane (PU) aqueous emulsion (PU solid content of 35 wt%) to the solution B described in step (2), and uniformly mixing by mechanical stirring to obtain a mixed solution C;

[0064] (4) mixing the dispersion A described in step (1) with the mixed solution C described in step (3) and stirring them uniformly to obtain a mixed solution D;

[0065] (5) Pour the mixed solution D described in step (4) into a mold, bake it in an oven at 80° C. for 1 hour to fully dry it, and obtain an elastic piezoresistive material.

[0066] Figure 2 This is the stress-strain curve of the elastic piezoresistive material prepared in Example 1. Figure 3 This is the resistance change curve of the elastic piezoresistive material prepared in Example 1 when repeatedly pressed under a pressure of 12N. Figure 4 The resistance curve of the elastic piezoresistive material prepared in Example 1 as the resistance changes with the applied pressure. After testing, the conductivity of the elastic piezoresistive material prepared by the method provided in Example 1 is 2.3×10 -5 S / cm, the elastic modulus is 82MPa, the response sensitivity to compressive stress is 1.7% / MPa, and the pressure threshold reaches 800MPa.

[0067] Figure 5 The resistance change curve of the elastic piezoresistive material prepared in Example 1 under 30% strain and repeated stretching. Figure 5 As can be seen in the figure, after repeated stretching 40,000 times at 30% strain, its resistance only increased to 37%, and there was no significant change in sensitivity or pressure response threshold. Compared with the elastic piezoresistive materials of the prior art, the elastic piezoresistive materials disclosed in the present invention have significant advantages in fatigue resistance. The preparation method of the elastic piezoresistive materials disclosed in the present invention is more energy-efficient, economical, and environmentally friendly than the preparation methods of elastic piezoresistive materials in the prior art.

[0068] Example 2

[0069] The same as Example 1, except that the volume percentage of MWCNTs is 6%, that is, the volume percentages of PU, PAA, PEG, and MWCNTs are 81.1%, 4%, 8.9%, and 6%, respectively.

[0070] After testing, it was found that after reducing the volume fraction of MWCNTs, the conductivity and elastic modulus of the elastic piezoresistive material decreased to 5.8×10 -7 S / cm and 65MPa. The compressive stress sensitivity increased to 21% / MPa, and the pressure threshold dropped to 300MPa. Fatigue resistance also improved somewhat, with resistance increasing by 25% after 40,000 cycles of repeated stretching at 30% strain.

[0071] Example 3

[0072] The same as Example 1, except that the mass percentage of MWCNTs is 8 wt %, that is, the volume percentages of PU, PAA, PEG, and SWCNTs are 79.4%, 4%, 8.6%, and 8%, respectively.

[0073] After testing, it was found that after increasing the volume fraction of MWCNTs, the conductivity and elastic modulus of the elastic piezoresistive material increased to 4.6×10 -4 S / cm and 94MPa. The compressive stress sensitivity dropped to 1.3% / MPa, and the pressure threshold increased to 930MPa. Fatigue resistance decreased somewhat, with resistance increasing by 60% after 40,000 cycles of repeated stretching at 30% strain.

[0074] Example 4

[0075] Same as Example 1, except that MWCNTs are replaced by single-walled carbon nanotubes (SWCNTs) in equal volume percentage.

[0076] The test results show that the conductivity of the prepared elastic piezoresistive material has increased, the elastic modulus has decreased, the sensitivity and pressure threshold have decreased, and the fatigue resistance has not changed much, that is, the conductivity is 1.3×10 -4 S / cm, an elastic modulus of 57 MPa, a compressive stress sensitivity of 3.1% / MPa, and a pressure threshold reduced to 560 MPa. Fatigue resistance has also been improved to a certain extent, with resistance increasing by 25% after 40,000 cycles of repeated stretching at 30% strain.

[0077] Comparative Example 1

[0078] The same as Example 1, except that PAA is omitted from the material, that is, the volume percentages of PU, PEG, and MWCNTs are 83.6%, 9.1%, and 7.3%, respectively.

[0079] The conductivity of the prepared elastic piezoresistive material is 8.7×10 -6 S / cm, an elastic modulus of 27 MPa, a compressive stress sensitivity of 5.2% / MPa, and a pressure threshold reduced to 130 MPa. Fatigue resistance has also been improved to a certain extent, with resistance increasing by 30% after 40,000 cycles of repeated stretching at 30% strain.

[0080] Comparative Example 2

[0081] The same as Example 1, except that PEG is omitted from the material, that is, the volume percentages of PU, PAA, and MWCNTs are 88%, 4.3%, and 7.7%, respectively. The conductivity of the prepared elastic piezoresistive material is 5.1×10-5 S / cm, an elastic modulus of 22 MPa, a compressive stress response sensitivity of 3.5% / MPa, and a pressure threshold dropped to 210 MPa. Fatigue resistance was severely degraded, and after 40,000 repeated stretches at 30% strain, the resistance increased by 1600%, and the sample showed obvious cracks.

[0082] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. An elastic piezoresistive material, characterized in that: It consists of an elastic matrix and conductive fillers dispersed inside it; wherein the elastic matrix is ​​made of polyurethane, polyacrylic acid and polyethylene glycol, and the conductive fillers are carbon nanotubes.

2. The elastic piezoresistive material according to claim 1, characterized in that: The carbon nanotubes are selected from one or both of single-walled carbon nanotubes and multi-walled carbon nanotubes.

3. The elastic piezoresistive material according to claim 1, characterized in that: Calculated by volume percentage, the elastic piezoresistive material comprises: 60-90% polyurethane, 4-20% polyacrylic acid, 3-20% polyethylene glycol and 3-15% carbon nanotubes.

4. An environmentally friendly preparation method for the elastic piezoresistive material according to any one of claims 1 to 3, characterized in that: The following steps are involved: Adding the carbon nanotube aqueous dispersion to the polyacrylic acid aqueous emulsion and stirring evenly to obtain dispersion A; Dissolve polyethylene glycol in deionized water to obtain solution B; Adding polyurethane aqueous emulsion to the solution B and stirring evenly to obtain a mixed solution C; Mixing the dispersion A and the mixed solution C to obtain a mixed solution D; The mixed solution D is shaped and dried to obtain an elastic piezoresistive material.

5. The environmentally friendly preparation method according to claim 4, characterized in that: The solid content of the carbon nanotube aqueous dispersion is 5-12 wt %.

6. The environmentally friendly preparation method according to claim 4, characterized in that: The solid content of the polyacrylic acid aqueous emulsion is 10-50 wt %.

7. The environmentally friendly preparation method according to claim 4, characterized in that: The molecular weight of the polyethylene glycol is 200-2000.

8. The environmentally friendly preparation method according to claim 4, characterized in that: The concentration of the solution B is 5-50 wt%.

9. The environmentally friendly preparation method according to claim 4, characterized in that: The solid content of the polyurethane aqueous emulsion is 10-40 wt %.

10. Use of the elastic piezoresistive material according to any one of claims 1 to 3 in the field of sensors.

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