A bio-based strain sensor and its preparation method

Abstract

The present invention belongs to the field of new materials and discloses a bio-based strain sensor, which includes a bio-based polyurethane film and a graphene fabric attached to the surface of the film. This strain sensor uses the bio-based polyurethane film as an elastic matrix and can exhibit more excellent response time, recovery time, and resistance stability under different working conditions compared to strain sensors with petroleum-based polyurethane or polyurethane-urea as the matrix. At the same time, the present invention also discloses a preparation method for this strain sensor.

Description

Technical Field

[0001] The present invention belongs to the field of new materials, and more specifically, relates to a strain sensor and a preparation method thereof. Background Art

[0002] Flexible strain sensors are devices used to measure the deformation or strain generated in an object when it is subjected to a force. Their working principles are diverse, including resistive, capacitive, and piezoelectric types, etc. In resistive strain sensors, deformation or strain causes a change in the internal resistance value of the sensor, which is then reflected as a change in voltage or current in the circuit. These sensors are widely used in engineering, science, and medicine for monitoring the health status of structures, the mechanical properties of materials, and the movement of organisms. In engineering, strain sensors can be used to monitor the deformation of structures such as bridges, buildings, and aircraft wings, while in the medical field, they are commonly used to monitor human movement, muscle activity, and the movement of prosthetics. Generally speaking, strain sensors play an important role in multiple fields, and their wide applications and diverse working principles make them one of the indispensable tools in the fields of engineering, science, and medicine.

[0003] Resistive strain sensors usually consist of a flexible matrix material and conductive fillers: the flexible matrix material provides structural support and flexibility, and the conductive fillers form a conductive path and generate an electrical response to external loads. Although a great deal of effort has been made to optimize the role of these composite materials by developing various conductive materials (such as graphene, carbon nanotubes, carbon black, metal nanoparticles / nanowires, conductive polymers, ionic fluids, and liquid metals) and nano / microstructures (such as thin films, fibers, textiles, foams, aerogels, serpentine, woven fabrics, islands, and hierarchical structures), the role of the flexible polymer matrix has been overlooked for a long time.

[0004] For example, CN112853743A discloses a preparation method and application of a fabric strain sensor that can be used to monitor human physiological information. The flexible strain sensor uses common polyurethane (PU) fibers and polyamide (PA) fibers as the matrix material, and a cross-stretching dip-coating method is used to adsorb multi-walled carbon nanotubes and reduced graphene oxide on the fabric surface to form a conductive layer to obtain a conductive fabric, thereby completing the preparation of the strain sensor.

[0005] Thermoplastic polyurethane is an excellent elastomer material with good flexibility, wear resistance and chemical resistance. There have been many reports on the preparation of strain sensors / flexible sensors based on thermoplastic polyurethane through appropriate processing and modification. At present, most of the research mainly focuses on the improvement of performance and the realization of functional diversification (authorized announcement number: CN112980178B; application publication number: CN 112374490 A, CN 117260814 A, CN 117426901 A). There is little research on the elastic matrix of strain sensors. In fact, the selection of the substrate material has a very important impact on flexible strain sensors. The substrate material with good tensile ability and good flexibility endows the flexible strain sensor with a corresponding wide sensing detection range and the ability to be bent and folded at will.

[0006] Among them, CN112113497B discloses a self-healing resistive strain sensor and its preparation method and application. The preparation method is to first soak, purge and dry the nickel sponge in the graphene oxide dispersion solution for multiple cycles to obtain nickel sponge coated with graphene oxide; use hydrogen bromide and thiourea to etch and reduce the nickel sponge coated with graphene oxide, wash and dry it to obtain a three-dimensional hollow mercapto-functionalized graphene framework; soak and dry the graphene framework in the dispersion solution of silver nanowires for multiple cycles to obtain a highly conductive silver nanowire-loaded graphene framework, connect the electrodes, and place it in a solution of self-healing functionalized polyurethane, and dry it to obtain a self-healing resistive strain sensor.

[0007] This solution is based on an etched graphene-wrapped nickel sponge as the framework, covered with polyurethane, to obtain a strain sensor; the specification of this solution states that its response time / recovery time is 40 / 84 ms. However, after further research on this solution, we found that there is still room for improvement in terms of response time, recovery time, resistance stability under large strain, long-cycle stability, and resistance stability under rapid strain. Summary of the Invention

[0008] The main object of the present invention is to provide a bio-based strain sensor. After the bio-based polyurethane film acts on the fabric framework, this strain sensor can exhibit more excellent response time, recovery time, and resistance stability under different working conditions compared with the strain sensor prepared from petroleum-based polyurethane.

[0009] At the same time, the present invention also discloses a preparation method of this strain sensor.

[0010] According to the first aspect of the present invention, a strain sensor is provided, which includes a graphene fabric and a bio-based polyurethane film attached to the surface of the fabric.

[0011] This bio-based polyurethane film can exhibit more excellent response time, recovery time, and resistance stability under different working conditions compared to the strain sensors prepared from petroleum-based polyurethanes; this shows that the use of bio-based and petroleum-based raw materials is very important for the products in the application scenarios of the present invention.

[0012] During the experiment, we expected that the bio-based polyurethane-urea film should exhibit the same pattern as the bio-based polyurethane film. However, it was found that the bio-based polyurethane-urea film did not exhibit similar excellent properties, indicating that the selection and use of chain extenders are also very important in the application scenarios of the present invention.

[0013] In the above-mentioned bio-based strain sensor, the bio-based polyurethane film comprises the following structural units:

[0014] 60-80 parts by weight of bio-based polyglycol;

[0015] 20-35 parts by weight of diisocyanate;

[0016] 2-10 parts by weight of glycol chain extender;

[0017] In the above-mentioned bio-based strain sensor, the hard segment ratio in the bio-based polyurethane film is 20-40 wt%, preferably, the hard segment ratio in the bio-based polyurethane is 23-40 wt%.

[0018] In the above-mentioned bio-based strain sensor, the molecular weight of the bio-based polyglycol is 1000-2700, preferably, the molecular weight of the bio-based polyglycol is 2000-2700.

[0019] In the above-mentioned bio-based strain sensor, the structural units of the bio-based polyglycol are one or more combinations of propylene glycol, butylene glycol, and hexylene glycol.

[0020] In the above-mentioned strain sensor, the bio-based polyurethane film is attached to the upper and lower surfaces of the graphene fabric; the thickness of the bio-based polyurethane film is 0.05-1 mm.

[0021] In the above-mentioned bio-based strain sensor, the framework of the fabric is a nickel mesh, and graphene is deposited on the surface of the nickel mesh; the mesh number of the nickel mesh is 100-200 meshes; the wire diameter of the nickel mesh is 50-100 μm.

[0022] In the above-mentioned bio-based strain sensor, the nickel mesh with graphene grown on it is etched to remove the nickel mesh.

[0023] Meanwhile, the present invention also discloses a preparation method of the strain sensor as described above. The fabric is adhered to the bio-based polyurethane film, and wires are connected to the fabric.

[0024] In the above preparation method, the preparation method of the fabric is as follows: Put a clean nickel mesh into a tube furnace and go through four steps: heating, heat preservation, deposition, and cooling. Argon and hydrogen are introduced during the heating process, and methane is introduced after heat preservation for a period of time. Graphene grown on the nickel mesh skeleton is obtained by deposition; the nickel mesh attached with graphene is etched with an FeCl3·HCl solution to obtain a fabric with graphene on the surface.

[0025] More specifically, the argon flow rate is 200 sccm, the hydrogen flow rate is 100 sccm, and the methane flow rate is 27 sccm.

[0026] The heating rate of temperature rise is 17 °C / min, the temperature is raised to 1000 °C, heat preservation is for 10 min, the deposition time is 20 min, and then it is air-cooled to room temperature. In the FeCl3·HCl solution used for etching, the FeCl3 content is 3 - 4 g, 4 - 5 ml of 12 mol / L hydrochloric acid, and 40 - 50 ml of deionized water.

[0027] One of the technical solutions in the above technical solutions of the present invention has at least the following advantages or beneficial effects:

[0028] The present invention prepares a strain sensor with a bio-based polyurethane film as the matrix, solving the problems of resource consumption and environmental protection caused by the use of non-bio-based polyurethanes. At the same time, compared with the commercially available BASF 60A polyurethane, the bio-based polyurethane film still has excellent mechanical properties such as excellent resilience. The bio-based polyurethane film strain sensor prepared has more stable strain sensing performance, more excellent long-cycle stability, better fast response performance, etc. Description of the Drawings

[0029] Figure 1 It is the uniaxial sensing performance test result of the bio-based polyurethane strain sensor 2 and the petroleum-based polyurethane strain sensor 7;

[0030] Figure 2 It is the response performance test result of the bio-based polyurethane strain sensor 1;

[0031] Figure 3 It is the response performance test result of the bio-based polyurethane strain sensor 2;

[0032] Figure 4 It is the response performance test result of the petroleum-based polyurethane strain sensor 7;

[0033] Figure 5 It is the strain resistance stability test result of the bio-based polyurethane strain sensor 2 and the petroleum-based polyurethane strain sensor 7;

[0034] Figure 6 It is the long-cycle resistance stability test result of the bio-based polyurethane strain sensor 1;

[0035] Figure 7 Results of long - cycle resistance stability test for biobased polyurethane strain sensor 2;

[0036] Figure 8 Results of long - cycle resistance stability test for biobased polyurethane - urea strain sensor 5;

[0037] Figure 9 Results of long - cycle resistance stability test for petroleum - based polyurethane strain sensor 7;

[0038] Figure 10 Results of resistance stability test for biobased polyurethane strain sensor 1 at different strain rates;

[0039] Figure 11 Results of resistance stability test for biobased polyurethane strain sensor 2 at different strain rates;

[0040] Figure 12 Results of resistance stability test for petroleum - based polyurethane strain sensor 7 at different strain rates;

[0041] Figure 13 Results of resistance stability test for biobased polyurethane strain sensor 1 under different strain tensions;

[0042] Figure 14 Results of resistance stability test for biobased polyurethane strain sensor 2 under different strain tensions;

[0043] Figure 15 Results of resistance stability test for biobased polyurethane - urea strain sensor 5 under different strain tensions;

[0044] Figure 16 Results of resistance stability test for petroleum - based polyurethane strain sensor 7 under different strain tensions. Detailed implementation manners

[0045] The following details the implementation manners of the present invention. The described implementation manners are exemplary and are only used to explain the present invention, and should not be construed as a limitation of the present invention.

[0046] First part: Preparation of biobased polyurethane

[0047] Example 1

[0048] Step 1: Put biobased poly - diester with a molecular weight of 2000 and BDO chain extender into a vacuum oven, and dry at 90 °C for 1 h to remove water.

[0049] Step 2: Conduct the synthesis of bio-based polyurethane by a one-step method. The proportion of the soft-segment bio-based poly-diester is 60 wt%, and the proportion of the hard-segment diisocyanate and chain extender is 40 wt%. There are 60 parts by weight of bio-based polyglycol, 31 parts by weight of diisocyanate, and 9 parts by weight of chain extender. React at 55 °C for 4 h.

[0050] Step 3: Dry the bio-based polyurethane formed by the reaction.

[0051] Obtain bio-based polyurethane 1.

[0052] Example 2

[0053] Step 1: Place the bio-based poly-diester with a molecular weight of 2000 and the PDO chain extender into a vacuum oven and dry at 90 °C for 1 h to remove water.

[0054] Step 2: Conduct the synthesis of bio-based polyurethane by a one-step method. The proportion of the soft-segment bio-based poly-diester is 70 wt%, and the proportion of the hard-segment diisocyanate and chain extender is 30 wt%. There are 70 parts by weight of bio-based polyglycol, 25 parts by weight of diisocyanate, and 5 parts by weight of chain extender. React at 55 °C for 4 h.

[0055] Step 3: Dry the bio-based polyurethane formed by the reaction.

[0056] Obtain bio-based polyurethane 2.

[0057] Example 3

[0058] Step 1: Place the bio-based poly-diester with a molecular weight of 2700 and the HDO chain extender into a vacuum oven and dry at 90 °C for 1 h to remove water.

[0059] Step 2: Conduct the synthesis of bio-based polyurethane by a one-step method. The proportion of the soft-segment bio-based poly-diester is 77 wt%, and the proportion of the hard-segment diisocyanate and chain extender is 23 wt%. There are 80 parts by weight of bio-based polyglycol, 20 parts by weight of diisocyanate, and 4 parts by weight of chain extender. React at 55 °C for 4 h.

[0060] Step 3: Dry the bio-based polyurethane formed by the reaction.

[0061] Obtain bio-based polyurethane 3.

[0062] Example 4

[0063] Step 1: Place the bio-based poly-diester with a molecular weight of 2000 and the ADH adipic dihydrazide into a vacuum oven and dry at 90 °C for 1 h to remove water.

[0064] Step 2: The synthesis of bio-based polyurethane-urea is carried out by a two-step method. The proportion of the soft segment bio-based polyester is 80 wt%, and the proportion of the hard segment diisocyanate and chain extender is 23 wt%. 80 parts by weight of bio-based polyglycol, 13 parts by weight of diisocyanate, and 7 parts by weight of chain extender. In the first step, bio-based polyester and diisocyanate are added and reacted at 55 °C for 4 h. In the second step, adipic dihydrazide dissolved in a solvent is added to the product of the first step and reacted at 40 °C for 10 h.

[0065] Step 3: Dry the bio-based polyurethane-urea produced by the reaction.

[0066] Obtain bio-based polyurethane-urea 4.

[0067] The second part: Preparation of fabric

[0068] Example 5

[0069] Step 1: Ultrasonically clean and dry 100-mesh nickel mesh with acetone, ethanol, and deionized water respectively for standby. The diameter of the nickel wire is 50 μm.

[0070] Step 2: Put the clean nickel mesh into a tube furnace, pass a mixed protective gas (argon with a flow rate of 200 sccm and hydrogen with a flow rate of 100 sccm), and start heating at 17 °C / min. After heating to 1000 °C, keep it warm for 10 min;

[0071] Step 3: Introduce methane gas (flow rate 27 sccm, methane concentration 8%) and deposit for 20 min. After the reaction, air-cool to room temperature to obtain graphene nickel mesh.

[0072] Step 4: Cut the graphene nickel mesh prepared in Step 3 into sample strips with a size of 6 mm × 15 mm.

[0073] Step 5: Etch the nickel mesh with FeCl3·HCl solution at 60 °C for 2 h. In the FeCl3·HCl solution used for etching, the content of FeCl3 is 3 - 4 g, 4 - 5 ml of 12 mol / L hydrochloric acid, and 40 - 50 ml of deionized water.

[0074] Step 6: Soak the graphene fabric in deionized water at 60 °C for 10 min, wash several times, and dry at 60 °C for standby to obtain fabric 1.

[0075] Example 6

[0076] Step 1: Ultrasonically clean and dry 200-mesh nickel mesh with acetone, ethanol, and deionized water respectively for standby. The diameter of the nickel wire is 100 μm.

[0077] Step 2: Place the clean nickel mesh into a tubular furnace. After passing a mixed protective gas (argon with a flow rate of 200 sccm and hydrogen with a flow rate of 100 sccm), start heating at a rate of 17 °C / min. After heating to 1000 °C, hold the temperature for 10 min;

[0078] Step 3: Introduce methane gas (flow rate of 27 sccm and methane concentration of 8%) and deposit for 20 min. After the reaction ends, air-cool to room temperature to obtain the graphene nickel mesh.

[0079] Step 4: Cut the graphene nickel mesh prepared in Step 3 into sample strips with a size of 6 mm × 15 mm.

[0080] Step 5: Etch the nickel mesh with FeCl3·HCl solution at 60 °C for 2 h. In the FeCl3·HCl solution used for etching, the content of FeCl3 is 3 - 4 g, 4 - 5 ml of 12 mol / L hydrochloric acid, and 40 - 50 ml of deionized water.

[0081] Step 6: Immerse the graphene fabric in deionized water at 60 °C for 10 min, wash several times, and dry at 60 °C for standby to obtain Fabric 2.

[0082] Part Three: Preparation of Strain Sensors

[0083] Strain Sensor 1

[0084] Step 1: Dissolve the bio-based polyurethane in DMF at a mass ratio of TPU (bio-based polyurethane 1 of Example 1): DMF = 1:5 to prepare a bio-based polyurethane solution for standby.

[0085] Step 2: Pour the bio-based polyurethane solution into a polytetrafluoroethylene mold with a length of 60 mm, a width of 40 mm, and a depth of 2 mm, and dry at 60 °C for 4 h.

[0086] Step 3: Use a small amount of DBSA solution to stick Fabric 1 on the TPU film. After natural drying, use conductive silver paste to stick copper wires with a length of about 3 cm at both ends of Fabric 1, and let the silver paste dry naturally.

[0087] Step 4: Fill the mold with the bio-based polyurethane solution again, and dry at 60 °C for 4 h. Take out the film and cut to obtain the bio-based polyurethane strain sensor 1.

[0088] Strain Sensor 2

[0089] Step 1: Dissolve the bio-based polyurethane in DMF at a mass ratio of TPU (bio-based polyurethane 2 of Example 2): DMF = 1:5 to prepare a bio-based polyurethane solution for standby.

[0090] Step 2: Fill a polytetrafluoroethylene mold with dimensions of 60 mm in length, 40 mm in width, and 2 mm in depth with the bio-based polyurethane solution, and dry it at 60 °C for 4 h.

[0091] Step 3: Use a small amount of DBSA solution to stick Fabric 2 onto the TPU film. After natural air drying, attach copper wires with a length of approximately 3 cm to both ends of Fabric 2 using conductive silver glue, and let the silver glue dry naturally.

[0092] Step 4: Fill the mold again with the bio-based polyurethane solution, and dry it at 60 °C for 4 h. Take out the film and cut to obtain the bio-based polyurethane strain sensor 2.

[0093] Strain sensor 3

[0094] Step 1: Prepare a bio-based polyurethane solution for later use by dissolving bio-based polyurethane in DMF at a mass ratio of TPU (bio-based polyurethane 3 of Example 3): DMF = 1:5.

[0095] Step 2: Fill a polytetrafluoroethylene mold with dimensions of 60 mm in length, 40 mm in width, and 2 mm in depth with the bio-based polyurethane solution, and dry it at 60 °C for 4 h.

[0096] Step 3: Use a small amount of DBSA solution to stick Fabric 2 onto the TPU film. After natural air drying, attach copper wires with a length of approximately 3 cm to both ends of Fabric 2 using conductive silver glue, and let the silver glue dry naturally.

[0097] Step 4: Fill the mold again with the bio-based polyurethane solution, and dry it at 60 °C for 4 h. Take out the film and cut to obtain the bio-based polyurethane strain sensor 3.

[0098] Strain sensor 4

[0099] Step 1: Prepare a bio-based polyurethane-urea solution for later use by dissolving bio-based polyurethane-urea in DMF at a mass ratio of TPU (bio-based polyurethane-urea 4 of Example 4): DMF = 1:5.

[0100] Step 2: Fill a polytetrafluoroethylene mold with dimensions of 60 mm in length, 40 mm in width, and 2 mm in depth with the bio-based polyurethane-urea solution, and dry it at 60 °C for 4 h.

[0101] Step 3: Use a small amount of DBSA solution to stick Fabric 1 onto the TPU film. After natural air drying, attach copper wires with a length of approximately 3 cm to both ends of Fabric 1 using conductive silver glue, and let the silver glue dry naturally.

[0102] Step 4: Fill the mold again with the bio-based polyurethane-urea solution, and dry it at 60 °C for 4 h. Take out the film and cut to obtain the bio-based polyurethane-urea strain sensor 4

[0103] Strain sensor 5

[0104] Step 1: Prepare a bio-based polyurethane-urea solution for standby by dissolving the bio-based polyurethane-urea in DMF at a mass ratio of TPU (bio-based polyurethane-urea 4 of Example 4): DMF = 1:5.

[0105] Step 2: Pour the bio-based polyurethane-urea solution into a polytetrafluoroethylene mold with a length of 60 mm, a width of 40 mm, and a depth of 2 mm, and dry it at 60 °C for 4 h.

[0106] Step 3: Use a small amount of DBSA solution to stick Fabric 2 onto the TPU film. After natural air drying, stick copper wires with a length of about 3 cm onto both ends of Fabric 2 with conductive silver glue, and let the silver glue dry naturally.

[0107] Step 4: Fill the mold with the bio-based polyurethane-urea solution again, and dry it at 60 °C for 4 h. Take out the film and cut to obtain the bio-based polyurethane-urea strain sensor 5

[0108] Strain sensor 6

[0109] Step 1: Prepare a petroleum-based polyurethane solution for standby by dissolving the petroleum-based polyurethane in DMF at a mass ratio of TPU (BASF-60A): DMF = 1:5.

[0110] Step 2: Pour the petroleum-based polyurethane solution into a polytetrafluoroethylene mold with a length of 60 mm, a width of 40 mm, and a depth of 2 mm, and dry it at 60 °C for 4 h.

[0111] Step 3: Use a small amount of DBSA solution to stick Fabric 1 onto the TPU film. After natural air drying, stick copper wires with a length of about 3 cm onto both ends of Fabric 1 with conductive silver glue, and let the silver glue dry naturally.

[0112] Step 4: Fill the mold with the petroleum-based polyurethane solution again, and dry it at 60 °C for 4 h. Take out the film and cut to obtain the petroleum-based polyurethane strain sensor 6.

[0113] Strain sensor 7

[0114] Step 1: Prepare a petroleum-based polyurethane solution for standby by dissolving the petroleum-based polyurethane in DMF at a mass ratio of TPU (BASF-60A): DMF = 1:5.

[0115] Step 2: Pour the petroleum-based polyurethane solution into a polytetrafluoroethylene mold with a length of 60 mm, a width of 40 mm, and a depth of 2 mm, and dry it at 60 °C for 4 h.

[0116] Step 3: Use a small amount of DBSA solution to stick Fabric 2 onto the TPU film. After natural air drying, stick copper wires with a length of about 3 cm onto both ends of Fabric 2 with conductive silver glue, and let the silver glue dry naturally.

[0117] Step 4: Fill the mold with the petroleum-based polyurethane solution again and dry it at 60 °C for 4 h. Take out the film and cut to obtain the petroleum-based polyurethane strain sensor 7.

[0118] Performance Test

[0119] Uniaxial sensing performance test: Test the uniaxial sensing performance of the bio-based polyurethane strain sensor through a tensile testing machine and a resistance recorder, with a tensile speed of 12 mm / min and a tensile strain of 50%;

[0120] Response performance test: Test the responsiveness of the bio-based polyurethane strain sensor through a tensile testing machine and a resistance recorder, with a tensile speed of 50 mm / min, a tensile strain of 2%, and a dwell time of 2 s;

[0121] Strain resistance stability test: Test the stability of the bio-based polyurethane strain sensor under a certain strain through a tensile testing machine and a resistance recorder, with a tensile speed of 12 mm / min and a tensile strain of 20%;

[0122] Long-cycle resistance stability test: Test the long-cycle stability of the bio-based polyurethane strain sensor through a tensile testing machine and a resistance recorder, with a tensile speed of 12 mm / min, a tensile strain of 20%, and 100 cycles;

[0123] Resistance stability test at different strain rates: Test the adaptability of the bio-based polyurethane strain sensor to different strain rates through a tensile testing machine and a resistance recorder. The tensile speeds are 12 mm / min, 24 mm / min, and 48 mm / min in sequence, the tensile strain is 20%, and the number of cycles for each tensile speed is 5 times;

[0124] Resistance stability test under different strain tensions: Test the stability of the bio-based polyurethane strain sensor under different strain tensions through a tensile testing machine and a resistance recorder, with a tensile speed of 12 mm / min and tensile strains of 5%, 10%, 15%, 20%, and 25% in sequence, and the number of cycles for each tensile speed is 10 times.

[0125] Use the bio-based polyurethane strain sensor 1, bio-based polyurethane strain sensor 2, bio-based polyurethane-urea strain sensor 5, and petroleum-based polyurethane strain sensor 7 as the test objects to conduct the above tests;

[0126] Figure 1It is a comparison curve of the uniaxial tensile sensing performance of the bio-based polyurethane strain sensor 2 and the petroleum-based polyurethane strain sensor 7. At the same strain, the sensitivity of the resistance change of the petroleum-based polyurethane strain sensor 7 is better than that of the bio-based polyurethane strain sensor 2. The sensitivity of the resistance change is close within the strain range of 0% - 20%; at 30% strain, the sensitivity of the resistance change of the bio-based polyurethane strain sensor 2 is 6.5, and the sensitivity of the resistance change of the petroleum-based polyurethane strain sensor 7 is 22.1; at 40% strain, the sensitivity of the resistance change of the bio-based polyurethane strain sensor 2 is 10.6, and the sensitivity of the resistance change of the petroleum-based polyurethane strain sensor 7 is 58.0; at 50% strain, the sensitivity of the resistance change of the bio-based polyurethane strain sensor 2 is 18.2, and the sensitivity of the resistance change of the petroleum-based polyurethane strain sensor 7 is 211.1.

[0127] Figure 2 , 3 , 4 is the response and recovery time test curve of the bio-based polyurethane strain sensor 1, the bio-based polyurethane strain sensor 2, and the petroleum-based polyurethane strain sensor 7. The tensile strain is 2%, the holding time is 2 s, and the tensile and recovery rates are both 50 mm / min. The response time of the bio-based polyurethane strain sensor 1 is 98 ms, and the recovery time is 106 ms; the response time of the bio-based polyurethane strain sensor 2 is 87 ms, and the recovery time is 89 ms; the response time of the petroleum-based polyurethane strain sensor 7 is 94 ms, and the recovery time is 216 ms. The rapid response performance of the bio-based polyurethane strain sensor under small strain conditions is significantly better than that of the petroleum-based polyurethane strain sensor 7.

[0128] Figure 5 It is the resistance change rate curve of the bio-based polyurethane strain sensor 2 and the petroleum-based polyurethane strain sensor 7 under 20% strain holding. The bio-based polyurethane strain sensor 2 reaches stability at about 25 min under 20% strain holding, and the resistance change rate decays by 10.2%; the petroleum-based polyurethane strain sensor 7 does not reach stability at 225 min under 20% strain holding, and the resistance change rate decays as high as 53.8%. It can be seen from this that the sensing signal of the bio-based polyurethane strain sensor is more stable and has an obvious advantage in signal accuracy.

[0129] Figure 6 , 7, 8, and 9 are the 100 - cycle sensing curves at 20% strain of bio - based polyurethane strain sensor 1, bio - based polyurethane strain sensor 2, bio - based polyurethane - urea strain sensor 5, and petroleum - based polyurethane strain sensor 7. The resistance change sensitivity of bio - based polyurethane strain sensor 1 is about 13.75, that of bio - based polyurethane strain sensor 2 is about 11, that of bio - based polyurethane - urea strain sensor 5 is about 3, and that of petroleum - based polyurethane strain sensor 7 is about 22.5. The resistance change rate of bio - based polyurethane strain sensor 1 and bio - based polyurethane strain sensor 2 remains basically unchanged during the cycle; the resistance change rate of bio - based polyurethane - urea strain sensor 5 and petroleum - based polyurethane strain sensor 7 shows an increasing trend. Thus, it can be seen that bio - based polyurethane strain sensors have obvious advantages in long - cycle stability.

[0130] Figure 10 , 11 , 12 are the variable - speed sensing test curves at 20% strain of bio - based polyurethane strain sensor 1, bio - based polyurethane strain sensor 2, and petroleum - based polyurethane strain sensor 7, with the tensile speeds of 12 mm / min, 24 mm / min, and 48 mm / min. The resistance change rate of bio - based polyurethane strain sensors remains basically unchanged at different speeds; the resistance change rate of petroleum - based polyurethane strain sensor 7 shows an increasing trend, and the faster the strain speed of the strain sensor, the more unstable its sensing signal, and the larger the peak resistance and the resistance offset at the end of a single cycle. Thus, it can be seen that bio - based polyurethane strain sensors have obvious advantages in adaptability to different strain speeds.

[0131] Figure 13 , 14 , 15, and 16 are the different - strain cycle test curves of bio - based polyurethane strain sensor 1, bio - based polyurethane strain sensor 2, bio - based polyurethane - urea strain sensor 5, and petroleum - based polyurethane strain sensor 7. The resistance change rate of bio - based polyurethane strain sensors remains basically stable at different strains; the resistance at the end of a single tensile cycle of petroleum - based polyurethane strain sensor 7 shows an increasing trend during the cycle, and the corresponding resistance change rate is unstable. Moreover, the larger the strain of the strain sensor, the more unstable its sensing signal, and the larger the resistance offset at the end of a single cycle. The strain - sensing performance of bio - based polyurethane - urea strain sensor 5 is comparable to that of petroleum - based polyurethane strain sensor 7. Thus, it can be seen that bio - based polyurethane strain sensors have obvious advantages in stability to different strain stretches.

[0132] Generally speaking, using bio - based materials and petroleum - based materials only has advantages in terms of environmental protection and renewable raw materials, and generally there is no obvious performance difference between petroleum - based and bio - based materials in terms of performance.

[0133] Experiments of the present invention can confirm that on the strain sensor, using bio-based raw materials not only has significant advantages in terms of cost and environmental protection, but also has obvious advantages in terms of strain sensing performance, long-term cycling stability, rapid responsiveness, etc.

Claims

1. A bio-based strain sensor, characterized in that: It comprises a bio-based polyurethane film and a graphene fabric attached to the surface of the film; the bio-based polyurethane film is composed of the following structural units: 60 to 80 parts by weight of bio-based polyglycol; 20 to 35 parts by weight of diisocyanate; 2 to 10 parts by weight of diol chain extender; The molecular weight of the bio-based polyglycol is 2000 to 2700; The hard segment ratio in the bio-based polyurethane is 23 to 40 wt%; The structural unit of the bio-based polyglycol is one or more combinations of propylene glycol, butanediol and hexanediol; The bio-based polyurethane film is attached to the upper and lower surfaces of the fabric; the thickness of the bio-based polyurethane film is 0.05 to 1 mm; The skeleton of the grown graphene is a nickel mesh; the mesh number of the nickel mesh is 100 to 200 meshes; and the wire diameter of the nickel mesh is 50 to 100 μm.

2. The bio-based strain sensor according to claim 1, characterized in that: The nickel mesh with graphene is etched to remove the nickel mesh.

3. The method for preparing a bio-based strain sensor according to claim 1 or 2, characterized in that: Stick the graphene fabric to the bio-based polyurethane film, connect the wires to the fabric, and then attach another layer of bio-based polyurethane film.

4. The preparation method according to claim 3, characterized in that: The preparation method of the fabric comprises the following steps: placing a clean nickel mesh in a tubular furnace and undergoing four steps of heating, heat preservation, deposition and cooling, introducing argon and hydrogen during the heating process, introducing methane after heat preservation for a period of time, and depositing graphene grown on the nickel mesh skeleton; and etching the nickel mesh with graphene attached by using a FeCl3·HCl solution to obtain a fabric with graphene on the surface.

Images