Preparation method for composite foam material and use thereof

Abstract

The present application discloses a method for preparing a composite foam material and the use thereof. The preparation method comprises the following steps: S1, mixing and reacting polyurethane, a sacrificial template, carbon black, a catalyst and a curing agent, pressing same into a membrane, and then heating same to obtain an incompletely-cured modified polyurethane membrane A; S2, mixing and reacting polyurethane, a sacrificial template, a dispersant and a curing agent, pressing same into a membrane, and then heating same to obtain an incompletely-cured modified polyurethane membrane B; S3, laminating the incompletely-cured modified polyurethane membrane A and the incompletely-cured modified polyurethane membrane B together, pressing same, and then curing same to obtain a double-layer porous polyurethane membrane; and S4, impregnating the double-layer porous polyurethane membrane with an aqueous dispersion of multi-walled carbon nanotubes, and then performing membrane formation. A flexible sensor further prepared from the composite foam material of the present application still maintains good performance after long-term use and high-intensity bending tests, which not only proves the high reliability of the sensor in a dynamic environment, but also demonstrates the good sensing performance thereof.

Description

A method for preparing and applying a composite foam material Technical Field

[0001] This application belongs to the field of new materials technology, and in particular to a method for preparing and applying a composite foam material. Background Technology

[0002] Since the beginning of the 21st century, the rapid development of artificial intelligence and wireless communication has driven the demand for portable electronic devices, leading to widespread attention on the development and application of flexible sensors. Currently, different pressure sensing mechanisms, such as piezoelectric, capacitive, and piezoresistive, have been developed based on their working principles. Among these, flexible sensing technology has demonstrated enormous potential and broad application prospects in the field of orientation recognition. In orientation recognition, flexible sensors sense changes in external pressure or deformation, converting these changes into electrical signals. Through signal processing and analysis, the orientation of an object's motion is identified.

[0003] Because the traditional pure carbon-based materials such as graphene and graphene oxide reported so far all have limited humidity sensitivity, resulting in low sensitivity.

[0004] Therefore, developing a highly sensitive flexible sensor is of paramount importance.

[0005] Summary of the Invention

[0006] This application aims to solve at least one of the technical problems existing in the prior art. To this end, this application proposes a method for preparing composite foam materials.

[0007] This application also proposes the application of the above-mentioned preparation method in the preparation of flexible sensors.

[0008] According to an embodiment of the first aspect of this application, a method for preparing a composite foam material is proposed, comprising the following steps:

[0009] S1. Polyurethane, sacrificial template, carbon black, catalyst and curing agent are mixed and reacted, pressed into a film and then heated to obtain an incompletely cured modified polyurethane film A;

[0010] S2. Polyurethane, sacrificial template, dispersant and curing agent are mixed and reacted, pressed into a film and then heated to obtain an incompletely cured modified polyurethane film B;

[0011] The particle size of the sacrificial template is 50-80 mesh;

[0012] S3. After bonding the partially cured modified polyurethane film A and the partially cured modified polyurethane film B together, press and cure to obtain a double-layer polyurethane porous film.

[0013] S4. A bilayer polyurethane porous membrane is impregnated in an aqueous dispersion of multi-walled carbon nanotubes to form a film.

[0014] Steps S1 and S2 are performed simultaneously.

[0015] The embodiments according to the first aspect of this application have at least the following beneficial effects:

[0016] Polyurethane (PU), as a high-performance elastomer material, possesses excellent processability and biocompatibility, making it one of the ideal materials for preparing porous functional membranes. PU porous functional membranes based on asymmetric structures combine the advantages of porous materials and asymmetric structures, and hold promise for achieving higher sensitivity and better motion recognition in the field of pressure sensors.

[0017] The flexible sensor further prepared from the composite foam material described in this application maintained good performance under prolonged use and high-intensity bending tests, without significant performance degradation or damage. During 200 bending cycles, the sensor consistently maintained a relatively stable resistance change output, accurately reflecting the resistance changes on different surfaces. This stable data performance not only demonstrates the sensor's high reliability in dynamic environments but also reflects its excellent sensing performance.

[0018] Inspired by the tissue modulus gradient between the epidermis and dermis of human skin, this application proposes an asymmetric structure design for polyurethane porous membranes. This asymmetric structure of the composite foam material (where the raw materials for modified polyurethane membrane A include carbon black, while those for modified polyurethane membrane B do not) not only maintains the material's flexibility but also enhances its sensing performance in specific directions, providing a new direction for the development of flexible sensors. It optimizes the overall performance of the sensor and provides differential responses to stimuli from different directions, enabling applications such as orientation recognition. When carbon black and multi-walled carbon nanotubes (MWCNTs) are mixed in a certain proportion, they exhibit a synergistic effect. Carbon black (CB) and MWCNTs intertwine and contact each other in the composite material, forming a complex and well-distributed conductive network. This asymmetric structure not only maintains the material's flexibility but also enhances its sensing performance in specific directions, providing a new direction for the development of flexible sensors. The synergistic effect of carbon black and multi-walled carbon nanotubes enables the sensor to simultaneously meet the requirements of flexibility and sensitivity. In addition, this asymmetric design provides differences in response to stimuli from different directions, making it possible for applications such as orientation recognition.

[0019] The sacrificial template in this application, through its shape, size, and distribution, can leave pores during the material forming process. The sacrificial template is easy to remove and can be completely removed in a later stage of the preparation process, thus leaving the desired porous structure without affecting the properties of the final material.

[0020] In some embodiments of this application, the dispersant includes at least one of N,N-dimethylformamide and N,N-dimethylacetamide.

[0021] In some embodiments of this application, the curing agent includes HK-825.

[0022] In some embodiments of this application, the heating temperature in step S2 is 80-90°C.

[0023] In some embodiments of this application, the heating time in step S2 is 8-10 minutes.

[0024] In some embodiments of this application, step S2, by weight, includes: mixing and reacting 10-20 parts of polyurethane, 40-50 parts of sacrificial template, 1-3 parts of N,N-dimethylacetamide and 1-3 parts of curing agent, pressing them into a film and then heating them to obtain an incompletely cured modified polyurethane film B.

[0025] In some embodiments of this application, step S2, by weight, includes: mixing 10-20 parts of polyurethane and 40-50 parts of sacrificial template and mechanically stirring for 2-5 minutes; then adding 1-3 parts of N,N-dimethylacetamide and 1-3 parts of curing agent and mixing and reacting for 3-5 minutes; pouring the mixture onto a glass plate covered with PET plastic film; sequentially covering the mixture with PET plastic film and glass plate; placing a conical flask containing 500-600 ml of water on the glass plate and pressing the mixture into a film for 8-10 minutes; removing the conical flask and glass plate; and placing the film in an oven at 80-90°C for 2-5 minutes.

[0026] In some embodiments of this application, in step S1, the carbon black is 3-8 parts by weight and the polyurethane is 100 parts.

[0027] In some embodiments of this application, step S3, the pressing step includes bonding the incompletely cured modified polyurethane film A and the incompletely cured modified polyurethane film B together, pressing them with a glass plate for 10-13 minutes, drying for 10-13 minutes, and then drying at 80-90°C for 4 hours.

[0028] In some embodiments of this application, in step S4, the mass concentration of the multi-walled carbon nanotube aqueous dispersion is 0.1-0.4%.

[0029] In some embodiments of this application, in step S4, the mass concentration of the multi-walled carbon nanotube aqueous dispersion is 0.2-0.3%.

[0030] The effects of varying amounts of multi-walled carbon nanotube (MWC) aqueous dispersions on the sensitivity of asymmetric polyurethane pressure sensors under tensile conditions are significant. A 0.2-0.3% MWC aqueous dispersion exhibits the best performance in tensile tests. This concentration of MWC aqueous dispersion, after ultrasonic dispersion, demonstrates good dispersion and forms a relatively ideal conductive network within the polyurethane porous membrane. This network ensures both good conductivity and stable resistance changes during stretching. During stretching, this conductive network effectively responds to deformation, causing resistance changes through the relative displacement between the MWC nanotubes, thereby enhancing the sensor's sensitivity.

[0031] In some embodiments of this application, in step S4, the film-forming method includes at least one of drying, freeze-drying, and water bath coagulation.

[0032] In some embodiments of this application, the soaking time in step S4 is 20-30 hours.

[0033] In some embodiments of this application, step S4 further includes drying after impregnation.

[0034] In some embodiments of this application, the sacrificial template includes at least one of salt, sugar, and monosodium glutamate.

[0035] According to an embodiment of the second aspect of this application, the application of a method for preparing composite foam materials in the fabrication of flexible sensors is proposed. Attached Figure Description

[0036] Figure 1 is a flowchart of the preparation process of the composite foam material of this application;

[0037] Figure 2 is a schematic diagram of an embodiment of this application under tension;

[0038] Figure 3 shows the sensitivity test of an embodiment of this application;

[0039] Figure 4 shows a bending test according to an embodiment of this application;

[0040] Figure 5 shows the stability test of an embodiment of this application. Detailed Implementation

[0041] The terms "preferred," "more preferably," etc., used in this application refer to embodiments of this application that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this application.

[0042] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0043] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of this application.

[0044] Unless otherwise specified, the reagents, methods and equipment used in this application are all conventional reagents, methods and equipment in this technical field.

[0045] Example 1

[0046] This embodiment provides a method for preparing a composite foam material, including the following steps:

[0047] A1. Thoroughly clean the beaker with deionized water, then dry it in an oven. Weigh 12g of polyurethane (model HK-3010) into the beaker using a balance, and then weigh 42g of 50-mesh salt into the beaker using weighing paper. Mechanically stir the salt and polyurethane for 2 minutes. Next, measure 1g of N,N-dimethylacetamide and 1.5g of curing agent and add them to the beaker in sequence, mechanically stirring for 3 minutes. After thoroughly mixing, pour the mixture onto a glass plate lined with PET plastic film. Cover the mixture with the PET plastic film and the glass plate in sequence. Place a conical flask containing 500ml of water on the glass plate and press the mixture into a film for 8 minutes. After the conical flask is full for 8 minutes, remove the conical flask and the top glass plate, and place the film in an oven (oven temperature set to 80℃).

[0048] A2. The difference between the preparation method of polyurethane porous membrane containing carbon black and the preparation method of polyurethane porous membrane without carbon black is that after the salt and polyurethane are mixed evenly, carbon black with a ratio of 3:100 to polyurethane is added. Then, the mixture is mechanically stirred for 5 minutes to fully mix the salt / polyurethane / carbon black mixture evenly.

[0049] A3. After the polyurethane porous membrane containing carbon black is heated and dried in an oven for 2 minutes, the PET plastic film on the polyurethane porous membrane containing carbon black and the polyurethane porous membrane without carbon black is peeled off at a uniform speed. At this time, the two polyurethane films have not yet cured. The two polyurethane films are quickly combined together, and the double-layer film is placed on a glass plate. Another glass plate is placed on the double-layer film to make the double-layer film adhere better. After pressing with the glass plate for 10 minutes, the upper glass plate is removed, and the PET plastic film on the double-layer film is peeled off at a uniform speed. After drying for 10 minutes, the double-layer film is flipped and placed on the glass plate, and the PET plastic film is peeled off at a uniform speed. Finally, it is dried for 4 hours to obtain the double-layer polyurethane porous membrane.

[0050] A4. A 5% aqueous dispersion of multi-walled carbon nanotubes (MWCNTs) was diluted with deionized water to a mass percentage of 0.4% to form a stable black suspension. The suspension was then ultrasonicated for 30 minutes in an ultrasonic cleaner to ensure uniform dispersion of the MWCNTs. The bilayer polyurethane porous membrane was then cut into 10×40mm pieces. 2 Specifications: The material was immersed in suspensions of MWCNTs with different contents for 24 hours. After immersion, it was dried in an oven for 2 hours to obtain a composite foam material (a porous polyurethane functional membrane with an asymmetric structure).

[0051] The preparation flow chart of the composite foam material of this application is shown in Figure 1.

[0052] Example 2

[0053] This embodiment provides a method for preparing a composite foam material, including the following steps:

[0054] A1. Thoroughly clean the beaker with deionized water, then dry it in an oven. Weigh 12g of polyurethane (model HK-3010) into the beaker using a balance, and then weigh 42g of 50-mesh salt into the beaker using weighing paper. Mechanically stir the salt and polyurethane for 2 minutes. Next, measure 1g of N,N-dimethylacetamide and 1.5g of curing agent and add them to the beaker in sequence, mechanically stirring for 3 minutes. After thoroughly mixing, pour the mixture onto a glass plate lined with PET plastic film. Cover the mixture with the PET plastic film and the glass plate in sequence. Place a conical flask containing 500ml of water on the glass plate and press the mixture into a film for 8 minutes. After the conical flask is full for 8 minutes, remove the conical flask and the top glass plate, and place the film in an oven (oven temperature set to 80℃).

[0055] A2. The difference between the preparation method of polyurethane porous membrane containing carbon black and the preparation method of polyurethane porous membrane without carbon black is that after the salt and polyurethane are mixed evenly, carbon black with a ratio of 3:100 to polyurethane is added. Then, the mixture is mechanically stirred for 5 minutes to fully mix the salt / polyurethane / carbon black mixture evenly.

[0056] A3. After the polyurethane porous membrane containing carbon black is heated and dried in an oven for 2 minutes, the PET plastic film on the polyurethane porous membrane containing carbon black and the polyurethane porous membrane without carbon black is peeled off at a uniform speed. At this time, the two polyurethane films have not yet cured. The two polyurethane films are quickly combined together, and the double-layer film is placed on a glass plate. Another glass plate is placed on the double-layer film to make the double-layer film adhere better. After pressing with the glass plate for 10 minutes, the upper glass plate is removed, and the PET plastic film on the double-layer film is peeled off at a uniform speed. After drying for 10 minutes, the double-layer film is flipped and placed on the glass plate, and the PET plastic film is peeled off at a uniform speed. Finally, it is dried for 4 hours to obtain the double-layer polyurethane porous membrane.

[0057] A4. A 5% aqueous dispersion of multi-walled carbon nanotubes (MWCNTs) was diluted with deionized water to a mass percentage of 0.25% to form a stable black suspension. The suspension was then ultrasonicated for 30 minutes in an ultrasonic cleaner to ensure uniform dispersion of the MWCNTs. The bilayer polyurethane porous membrane was then cut into 10×40mm pieces. 2 Specifications: The material was immersed in suspensions of MWCNTs with different contents for 24 hours. After immersion, it was dried in an oven for 2 hours to obtain a composite foam material (a porous polyurethane functional membrane with an asymmetric structure).

[0058] Example 3

[0059] This embodiment provides a method for preparing a composite foam material, including the following steps:

[0060] A1. Thoroughly clean the beaker with deionized water, then dry it in an oven. Weigh 12g of polyurethane (model HK-3010) into the beaker using a balance, and then weigh 42g of 50-mesh salt into the beaker using weighing paper. Mechanically stir the salt and polyurethane for 2 minutes. Next, measure 1g of N,N-dimethylacetamide and 1.5g of curing agent and add them to the beaker in sequence, mechanically stirring for 3 minutes. After thoroughly mixing, pour the mixture onto a glass plate lined with PET plastic film. Cover the mixture with the PET plastic film and the glass plate in sequence. Place a conical flask containing 500ml of water on the glass plate and press the mixture into a film for 8 minutes. After the conical flask is full for 8 minutes, remove the conical flask and the top glass plate, and place the film in an oven (oven temperature set to 80℃).

[0061] A2. The difference between the preparation method of polyurethane porous membrane containing carbon black and the preparation method of polyurethane porous membrane without carbon black is that after the salt and polyurethane are mixed evenly, carbon black with a ratio of 3:100 to polyurethane is added. Then, the mixture is mechanically stirred for 5 minutes to fully mix the salt / polyurethane / carbon black mixture evenly.

[0062] A3. After the polyurethane porous membrane containing carbon black is heated and dried in an oven for 2 minutes, the PET plastic film on the polyurethane porous membrane containing carbon black and the polyurethane porous membrane without carbon black is peeled off at a uniform speed. At this time, the two polyurethane films have not yet cured. The two polyurethane films are quickly combined together, and the double-layer film is placed on a glass plate. Another glass plate is placed on the double-layer film to make the double-layer film adhere better. After pressing with the glass plate for 10 minutes, the upper glass plate is removed, and the PET plastic film on the double-layer film is peeled off at a uniform speed. After drying for 10 minutes, the double-layer film is flipped and placed on the glass plate, and the PET plastic film is peeled off at a uniform speed. Finally, it is dried for 4 hours to obtain the double-layer polyurethane porous membrane.

[0063] A4. A 5% aqueous dispersion of multi-walled carbon nanotubes (MWCNTs) was diluted with deionized water to a mass percentage of 0.1% to form a stable black suspension. The suspension was then ultrasonicated for 30 minutes in an ultrasonic cleaner to ensure uniform dispersion of the MWCNTs. The bilayer polyurethane porous membrane was then cut into 10×40mm pieces. 2 Specifications: The material was immersed in suspensions of MWCNTs with different contents for 24 hours. After immersion, it was dried in an oven for 2 hours to obtain a composite foam material (a porous polyurethane functional membrane with an asymmetric structure).

[0064] Comparative Example 1

[0065] This comparative example provides a method for preparing a composite foam material. The difference between this comparative example and Example 1 is that the composite foam material prepared is a symmetrical structure modified polyurethane film A, and the raw materials used in the preparation do not include carbon black, while the other conditions are the same.

[0066] Test Example 1

[0067] Sensitivity test:

[0068] In this test example, the composite foam material from the embodiment and comparative example is assembled into a sensor. The specific steps are as follows: copper foil is attached to the upper and lower sides of the porous membrane, and conductive silver paste is used to fill the gaps. Then, the resistance can be measured using a digital source meter.

[0069] Tensile and bending tests were conducted on polyurethane porous pressure sensors using a flexible electronic testing instrument to explore the electrical performance of pressure sensors with different mesh sizes under tensile deformation. The tensile parameters were set as follows: tensile speed 2 mm / s, tensile elongation 12.5% ​​and 25%, and tensile cycles 20 times.

[0070] In the embodiment, the asymmetric polyurethane porous membrane undergoes a change in pore size and deformation under stretching, as shown in Figure 2.

[0071] This test case uses the strain coefficient (GF) of a strain-type flexible sensor to represent the sensitivity coefficient of an asymmetric polyurethane pressure sensor. The formula for calculating GF is as follows: GF=(ΔR / R0) / ε;

[0072] in:

[0073] GF is the sensing coefficient, also known as sensitivity;

[0074] ΔR is the change in resistance of the flexible strain sensor after deformation, i.e., R-R0, where R is the resistance value after deformation and R0 is the initial resistance value. In the asymmetric polyurethane pressure sensor, the side containing carbon black is defined as side A, and the side without carbon black is defined as side B. The tensile test results (i.e., sensitivity test results) are shown in Figure 3.

[0075] Figure 3(a) shows the tensile sensitivity of pressure sensors impregnated with different CNT (carbon nanotubes, i.e., MWCNTs) contents.

[0076] Figure 3(b) shows the R / Ro diagram of an asymmetric porous membrane impregnated with 0.1% CNT (carbon nanotubes, i.e., MWCNTs) at an elongation of 10%.

[0077] Figure 3(c) shows the R / Ro diagram of an asymmetric porous membrane impregnated with 0.25% CNT (carbon nanotubes, i.e., MWCNTs).

[0078] Figure 3(d) shows the R / Ro diagram of an asymmetric porous membrane impregnated with 0.4% CNT (carbon nanotubes, i.e., MWCNTs).

[0079] As shown in the figure, the impregnation content of different amounts of MWCNTs significantly affects the sensitivity of the asymmetric polyurethane pressure sensor under tensile conditions. This result may be due to the following reasons: When the porous membrane layer A (i.e., the porous membrane containing the carbon black layer) is impregnated with 0.4% MWCNTs, although the initial conductivity of the porous membrane is good, the excessively high MWCNT content leads to insignificant changes in the conductive network during stretching, thus affecting its sensitivity under high MWCNT content. When the impregnation content of MWCNTs is 0.1%, the dispersion of MWCNTs in the porous membrane is relatively sparse, failing to form a superior conductive network. This results in a minimal change in resistance when the sensor is stretched, i.e., low sensitivity. A sparse distribution of MWCNTs means fewer conductive channels, making it difficult to induce higher resistance changes even with relative displacement between MWCNTs during stretching. MWCNTs impregnated with 0.25% content performed best in the tensile test. This content of MWCNTs, after ultrasonic dispersion, exhibited good dispersion, forming a relatively ideal conductive network within the polyurethane porous membrane. This network ensured both good conductivity and stable resistance changes during stretching. During stretching, this conductive network effectively responded to deformation, causing resistance changes through relative displacement between MWCNTs, thereby improving the sensor's sensitivity. The sensitivity of the B-layer porous membrane (i.e., the porous membrane without a carbon black layer) decreased with increasing MWCNT impregnation content. The sensitivity in the examples was around 1.9, while the sensitivity in Comparative Example 1 was around 0.8.

[0080] Carbon black and MWCNTs have a synergistic effect, which enhances the sensitivity of the sensor. Different contents of MWCNTs and carbon black in polyurethane form a complex conductive network. By optimizing the ratio of MWCNTs to carbon black, the tensile sensitivity of the sensor can be improved. Under the idea of ​​asymmetric design, pressure sensors with different tensile sensitivities can be obtained.

[0081] Test Example 2

[0082] Bending test:

[0083] This test example examines the resistance change rate of an asymmetric polyurethane pressure sensor after impregnation with different amounts of CNTs (carbon nanotubes, i.e., MWCNTs) during bending. The bending parameters were set to bend at 30°-60° and a speed of 15° / s. The bending test results are shown in Figure 4.

[0084] The possible reasons for this result are as follows: Impregnating the porous membrane with a 0.4% MWCNT dispersion resulted in relatively high MWCNT content, leading to poor dispersion of MWCNTs in the aqueous dispersion and poor adsorption of MWCNTs onto the porous membrane. This resulted in poor resistance change and a relatively low resistance change rate during membrane bending. Impregnation with a 0.1% MWCNT dispersion resulted in sparse distribution of MWCNTs on the pore walls of the porous membrane, making it difficult to form a good conductive network. Therefore, under bending deformation, the sensor's resistance change was not significant, and the resistance change rate was low; even with relative displacement between MWCNTs during bending, it was difficult to induce a significant resistance change, resulting in an unsatisfactory resistance change rate. Impregnation with a 0.25% MWCNT dispersion showed the best resistance change rate in the bending test. This content of MWCNTs formed a relatively ideal conductive network in the polyurethane, which maintained good resistance change during bending and also achieved good asymmetric differences.

[0085] Test Example 3

[0086] Stability test:

[0087] Pressure sensors need to have good durability in practical applications to ensure stable and reliable operation during long-term use or in harsh environments. The purpose of this test example is to conduct a bending durability test on an asymmetric porous polyurethane pressure sensor to evaluate its performance and lifespan under 200 bending conditions. A flexible electronic tester was used to conduct 200 bending tests with the following parameters: starting angle 30°, ending angle 60°, bending rate 15° / s, and number of bending cycles 200.

[0088] As shown in Figures 5(a) and (b), the sensor maintained good performance even after prolonged use and high-intensity bending tests, without any significant performance degradation or damage. This excellent durability demonstrates impressive data stability and outstanding resilience. During 200 bending cycles, the sensor consistently maintained a relatively stable resistance change output, accurately reflecting the resistance changes on different surfaces. This stable data performance not only proves the sensor's high reliability in dynamic environments but also reflects its excellent sensing performance.

[0089] The embodiments and descriptions above are merely illustrative of the principles and preferred embodiments of this application. Various changes and modifications may be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed.

Claims

1. A method for preparing a composite foam material, characterized in that, Includes the following steps: S1. Polyurethane, sacrificial template, carbon black, catalyst and curing agent are mixed and reacted, pressed into a film and then heated to obtain an incompletely cured modified polyurethane film A; S2. Polyurethane, sacrificial template, dispersant and curing agent are mixed and reacted, pressed into a film and then heated to obtain an incompletely cured modified polyurethane film B; The particle size of the sacrificial template is 50-80 mesh; S3. After bonding the partially cured modified polyurethane film A and the partially cured modified polyurethane film B together, press and cure to obtain a double-layer polyurethane porous film. S4. A bilayer polyurethane porous membrane is impregnated in an aqueous dispersion of multi-walled carbon nanotubes to form a film. Steps S1 and S2 are performed simultaneously.

2. The method for preparing the composite foam material according to claim 1, characterized in that, In step S1, the carbon black is 3-8 parts by weight, and the polyurethane is 100 parts.

3. The method for preparing the composite foam material according to claim 1, characterized in that, The heating temperature in step S2 is 80-90℃.

4. The method for preparing the composite foam material according to claim 1, characterized in that, The heating time in step S2 is 8-10 minutes.

5. The method for preparing the composite foam material according to claim 1, characterized in that, By weight, step S2 includes: mixing 10-20 parts of polyurethane, 40-50 parts of sacrificial template, 1-3 parts of N,N-dimethylacetamide and 1-3 parts of curing agent, reacting them, pressing them into a film and heating them to obtain an incompletely cured modified polyurethane film B.

6. The method for preparing the composite foam material according to claim 1, characterized in that, In step S4, the mass concentration of the multi-walled carbon nanotube aqueous dispersion is 0.1-0.4%.

7. The method for preparing the composite foam material according to claim 1, characterized in that, In step S4, the mass concentration of the multi-walled carbon nanotube aqueous dispersion is 0.2-0.3%.

8. The method for preparing the composite foam material according to claim 7, characterized in that, In step S4, the film-forming method includes at least one of drying, freeze-drying, and water bath coagulation.

9. The method for preparing the composite foam material according to claim 1, characterized in that, The sacrificial template includes at least one of salt, sugar, and monosodium glutamate.

10. The application of a method for preparing a composite foam material as described in any one of claims 1-9 in the preparation of flexible sensors.

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