Water-resistant self-repairing polyurethane elastomer, preparation method thereof and application of polyurethane elastomer in humidity sensor

Abstract

The invention belongs to the technical field of preparation of polyurethane elastomers, and discloses a water-resistant self-repairing polyurethane elastomer, a preparation method thereof and application of the water-resistant self-repairing polyurethane elastomer in a humidity sensor. The method comprises the following steps: S1, dissolving 4, 4 '-diaminodiphenylmethane and p-hydroxybenzaldehyde in absolute ethyl alcohol, and carrying out a Schiff base reaction to generate micromolecular MDOH with an imine bond structure, which is used as a chain extender of polyurethane; s2, reacting hydroxyl-terminated polybutadiene with isophorone diisocyanate at 60 DEG C to generate a prepolymer, and adding MDOH and glyceryl monostearate into the obtained prepolymer for chain extension; mDOH is introduced, so that the material has excellent self-repairing capability, and glyceryl monostearate is beneficial to further improving the self-repairing capability and water resistance. In addition, the humidity sensor based on the polyurethane elastomer can show good sensing performance.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of polyurethane elastomers, and particularly relates to a water-resistant, self-repairing polyurethane elastomer and a preparation method thereof and application in a humidity sensor. Background Art

[0002] For most flexible electronic devices, exposure to water environments is unavoidable during daily use, such as encountering different ambient humidity levels, sweat (in the case of skin sensors), and water from external sources such as rain. However, the functionality of flexible electronic devices is easily affected by water molecules, affecting normal use, while the reversible dynamic bonds used for self-healing performance are very susceptible to interference from water molecules, thereby destroying the active sites and reducing the self-healing ability. Therefore, achieving water resistance and underwater self-healing of flexible electronic devices by rationally designing the molecular structure of the elastomeric matrix is ​​an urgent problem to be solved.

[0003] Flexible humidity sensors should not only have good humidity-sensitive properties (e.g., high sensitivity, small hysteresis, and fast response / recovery speed), but also have more demanding performance: good flexibility to adapt to the wearing and bending requirements of wearable devices; stable humidity response without being disturbed by deformation (bending, torsion, elongation, etc.); light weight and breathability to ensure wearing comfort; non-toxic when in direct contact with the skin as a wearable device; good processability and low cost, etc. In order to meet such high requirements, high-performance humidity-sensitive materials and substrates should be vigorously developed, and the sensor configuration should be cleverly designed. Summary of the invention

[0004] In order to overcome the shortcomings and deficiencies in the prior art, the primary purpose of the present invention is to provide a method for preparing a water-resistant, self-healing polyurethane elastomer, which can improve the water resistance and self-healing efficiency of the polyurethane elastomer, and realize that the polyurethane elastomer can not only self-heal at room temperature, but also can self-heal underwater.

[0005] Another object of the present invention is to provide a water-resistant, self-healing polyurethane elastomer prepared by the above preparation method; it has good humidity sensitivity, high sensitivity, small hysteresis and fast response / recovery speed.

[0006] Another object of the present invention is to provide an application of the above-mentioned water-resistant, self-repairing polyurethane elastomer in the preparation of a humidity sensor.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a water-resistant, self-repairing polyurethane elastomer comprises the following steps:

[0009] S1, dissolving 4,4′-diaminodiphenylmethane and p-hydroxybenzaldehyde in anhydrous ethanol and reacting with a Schiff base to generate a small molecule MDOH with an imine bond structure;

[0010] S2. Using dibutyltin dilaurate as a catalyst, terminal hydroxy polybutadiene (HTPB) and isophorone diisocyanate (IPDI) are reacted in a solvent at 60°C to generate an isocyanate-terminated prepolymer; small molecule MDOH obtained in step S1 and glyceryl monostearate are added to the obtained isocyanate-terminated prepolymer for chain extension, and the reaction temperature is controlled to be 60-70°C for polymerization reaction. After the reaction is completed, the mixture is poured into a mold and dried at 60°C to obtain a water-resistant, self-healing polyurethane elastomer.

[0011] Step S1 specifically follows the following operating steps: at room temperature, 20 parts by mass of 4,4′-diaminodiphenylmethane and 40 parts by mass of p-hydroxybenzaldehyde are respectively dissolved in 100 ml of anhydrous ethanol to obtain a 4,4′-diaminodiphenylmethane solution and a p-hydroxybenzaldehyde solution; then the 4,4′-diaminodiphenylmethane solution and the p-hydroxybenzaldehyde solution are transferred to a 250 ml three-necked flask and mixed for reaction for 6 hours to form a precipitate, the precipitate is vacuum filtered and washed with ethanol 2-3 times to obtain a small molecule MDOH with an imine bond structure.

[0012] Step S2 specifically follows the following operating steps: 2.5 parts by mass of hydroxy-terminated polybutadiene is dried under vacuum at 110° C. for 2 hours to remove trace moisture, then dissolved in tetrahydrofuran, 7.5 parts by mass of isophorone diisocyanate and catalyst dibutyltin dilaurate are added through a syringe, and the amount of dibutyltin dilaurate added is 0.2-0.5wt% of the hydroxy-terminated polybutadiene; stirred in a nitrogen atmosphere at 60-70° C. for 2-3 hours to obtain an isocyanate-terminated prepolymer; 1.5 parts by mass of the small molecule MDOH obtained in step S1 is added to the isocyanate-terminated prepolymer, the temperature is raised to 70-80° C., the reaction is continued for 4-6 hours, and then 1.0 parts by mass of glyceryl monostearate is added thereto, the temperature is maintained at 70-80° C. and the reaction is continued for 2 hours, the solution after the reaction is poured into a polytetrafluoroethylene mold, and dried at 60° C. to obtain a water-resistant, self-healing polyurethane elastomer.

[0013] A water-resistant and self-repairing polyurethane elastomer prepared by the above preparation method.

[0014] The above-mentioned water-resistant, self-healing polyurethane elastomer is used in the preparation of humidity sensors.

[0015] A humidity sensor made of the above-mentioned water-resistant, self-repairing polyurethane elastomer, the humidity sensor is composed of the water-resistant, self-repairing polyurethane elastomer and a conductive network, and the conductive network is dripped on the water-resistant, self-repairing polyurethane elastomer.

[0016] The conductive network is carboxylated multi-walled carbon nanotubes (MWCNTs-COOH); the preparation method of the humidity sensor is as follows: 10 mg of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) are uniformly dispersed in 10 mL of a mixed solvent of anhydrous ethanol and deionized water by ultrasonic treatment, and then the obtained slurry is uniformly distributed on the above-mentioned water-resistant, self-healing polyurethane elastomer by drop coating, and dried to obtain a humidity sensor.

[0017] The ultrasonic treatment time is 30 minutes; the anhydrous ethanol and deionized water mixed solvent is composed of anhydrous ethanol and deionized water in a volume ratio of 4:1.

[0018] Principle of the present invention:

[0019] The invention mainly consists of a prepolymer composed of terminal hydroxyl polybutadiene and isophorone diisocyanate, and the prepolymer, small molecule MDOH with an imine bond structure and glyceryl monostearate constitute the final elastomer. MDOH and glyceryl monostearate are added to the prepolymer to form a network structure containing imine bonds and long side chains. Such a design not only enhances the self-healing ability and water resistance of the polyurethane elastomer, but also gives it self-healing ability underwater. The material has a wide range of applications and is suitable for complex environments in the field of elastomer technology, such as high humidity and water applications.

[0020] In the present invention, terminal hydroxyl polybutadiene provides a hydrophobic polymer skeleton; small molecule MDOH introduces an imine bond into the polyurethane chain, has a dynamic reversible characteristic, can undergo an exchange reaction under a variety of external drives, provides a dynamic self-repair mechanism, and combined with the hydrophobic terminal hydroxyl polybutadiene, can give the polyurethane elastomer the ability to self-repair underwater.

[0021] The water-resistant, self-repairing polyurethane elastomer of the present invention can be prepared into a humidity sensor, which includes a hydrophobic substrate and a carboxylated carbon nanotube layer. When the ambient humidity increases, the carboxylated carbon nanotubes will form many hydrogen bonds with water molecules, promoting the adsorption of water molecules in the response process, which helps to improve the sensitivity of the humidity sensor. When the ambient humidity decreases, the hydrophobic substrate will promote the desorption of water molecules in the recovery process, which is conducive to enhancing the reversibility and faster recovery speed of the humidity sensor.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] (1) The polyurethane elastomer prepared by the present invention has excellent water resistance and self-healing properties, and can still maintain good mechanical properties and self-healing properties underwater. It has a wide range of applications and is suitable for use in complex environments, such as high humidity and water.

[0024] (2) The water-resistant, self-healing polyurethane elastomer prepared by the present invention is used for humidity sensors, which have high sensitivity, fast response speed, good stability and self-healing function in high humidity environments.

[0025] (3) The preparation method of the present invention has the advantages of simple process, easy control, low cost, and suitability for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The synthetic route of the small molecule MDOH having an imine bond structure in the embodiment of the present invention is shown; Figure 2 It is a schematic diagram of the molecular chain design of the polyurethane elastomer prepared in the embodiment of the present invention; Figure 3 The infrared spectra of the small molecule MDOH and the polyurethane elastomer prepared in Example 1 of the present invention, wherein (a) is the infrared spectra of the small molecule MDOH prepared in the example of the present invention, and (b) is the infrared spectra of the polyurethane elastomer prepared in the example of the present invention; Figure 4 1 is a stress-strain curve diagram of the polyurethane elastomer prepared in Example 1 of the present invention and Comparative Example 1; Figure 5 The stress-strain curves of the polyurethane elastomers prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention after being treated with water for three days; Figure 6 This is a self-healing performance diagram of the polyurethane elastomer prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0028] Unless otherwise specified, the reagents used in the following examples can be purchased from the market.

[0029] The parts mentioned in the following examples and comparative examples are all molar parts, wherein "1 part" means "1 mmol".

[0030] Example 1 like Figure 1 , Figure 2 The preparation method of the water-resistant, self-repairing polyurethane elastomer shown in the figure has the following synthesis steps: S1. Synthesis of small molecule MDOH with an imine bond structure: at room temperature, 20 parts by mass of 4,4′-diaminodiphenylmethane and 40 parts by mass of p-hydroxybenzaldehyde were dissolved in 100 ml of anhydrous ethanol respectively to obtain a 4,4′-diaminodiphenylmethane solution and a p-hydroxybenzaldehyde solution; then the 4,4′-diaminodiphenylmethane solution and the p-hydroxybenzaldehyde solution were transferred to a 250 ml three-necked flask and mixed for reaction for 6 hours to form a yellow precipitate, and finally the precipitate was vacuum filtered and washed with ethanol for 3 times to obtain a small molecule MDOH with an imine bond structure.

[0031] S2. Synthesis of polyurethane elastomer: Dry 2.5 parts by mass of terminal hydroxyl polybutadiene at 110°C under vacuum for 2h to remove trace moisture, then dissolve in tetrahydrofuran, add 7.5 parts by mass of isophorone diisocyanate and catalyst dibutyltin dilaurate through a syringe, the amount of dibutyltin dilaurate added is 0.2wt% of the terminal hydroxyl polybutadiene; stir in a nitrogen atmosphere at 60°C for 2h to obtain an isocyanate-terminated prepolymer; add 1.5 parts by mass of the small molecule MDOH obtained in step S1 to the isocyanate-terminated prepolymer, heat to 70°C, continue to react for 5h, then add 1.0 parts by mass of glyceryl monostearate thereto, maintain 70-80°C and continue to react for 2h, pour the reacted solution into a polytetrafluoroethylene mold, and dry at 60°C to obtain a water-resistant, self-healing polyurethane elastomer.

[0032] S3. Preparation of humidity sensor: 10 mg of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were uniformly dispersed in 10 mL of a mixed solvent of anhydrous ethanol and deionized water (anhydrous ethanol: deionized water = 4:1 (volume ratio)) by ultrasonic treatment for 30 min, and then uniformly distributed on the above-mentioned water-resistant, self-healing polyurethane elastomer by drop coating method, and dried to obtain a humidity sensor.

[0033] Comparative Example 1

[0034] The other steps are the same as those in Example 1, except that 1,4-butanediol is used to replace glyceryl monostearate in the process of synthesizing the polyurethane elastomer in step S2. The specific steps of step S2 are as follows:

[0035] 2.5 parts by weight of terminal hydroxyl polybutadiene was dried at 110° C. under vacuum for 2 h to remove trace moisture, then dissolved in tetrahydrofuran, 7.5 parts by weight of isophorone diisocyanate and catalyst dibutyltin dilaurate were added through a syringe, and the amount of dibutyltin dilaurate added was 0.2wt% of the terminal hydroxyl polybutadiene; stirred in a nitrogen atmosphere at 60° C. for 2 h to obtain an isocyanate-terminated prepolymer; 1.5 parts by weight of the small molecule MDOH obtained in step S1 was added to the isocyanate-terminated prepolymer, the temperature was raised to 70° C., the reaction was continued for 5 h, and 1.0 parts by weight of 1,4-butanediol was added thereto, the temperature was maintained at 70-80° C. and the reaction was continued for 2 h, the solution after the reaction was poured into a polytetrafluoroethylene mold, and dried at 60° C. to obtain a water-resistant, self-healing polyurethane elastomer.

[0036] Comparative Example 2

[0037] The other steps are the same as those in Example 1, except that in the process of synthesizing the polyurethane elastomer in step S2, polytetrahydrofuran is used to replace the hydroxy-terminated polybutadiene. The specific steps of step S2 are as follows:

[0038] Synthesis of polyurethane elastomer: Dry 2.5 parts by mass of polytetrahydrofuran at 110°C under vacuum for 2h to remove trace moisture, then dissolve it in tetrahydrofuran, add 7.5 parts by mass of isophorone diisocyanate and catalyst dibutyltin dilaurate through a syringe, and the amount of dibutyltin dilaurate added is 0.2wt% of the terminal hydroxyl polybutadiene; stir in a nitrogen atmosphere at 60°C for 2h to obtain an isocyanate-terminated prepolymer; add 1.5 parts by mass of the small molecule MDOH obtained in step S1 to the isocyanate-terminated prepolymer, heat to 70°C, continue to react for 5h, then add 1.0 parts by mass of glyceryl monostearate thereto, maintain 70-80°C and continue to react for 2h, pour the reacted solution into a polytetrafluoroethylene mold, and dry at 60°C to obtain a water-resistant, self-healing polyurethane elastomer.

[0039] The methods for each performance test are as follows:

[0040] Fourier transform infrared spectroscopy was used to qualitatively analyze the chemical composition of all samples. The polyurethane elastomer was cut into standard specimens of 4 mm × 50 mm with a cutter to test the tensile properties of polyurethane (including self-healing properties and water resistance), and the tensile speed was 200 mm / min. To test the water resistance of the polyurethane elastomer, the polyurethane elastomer needs to be placed in water for 3 days. The sensing performance of the humidity sensor was tested with a desktop digital multimeter (DM 3068).

[0041] like Figure 3 As shown in (a), in the infrared spectrum of MDOH, the -1 There is an obvious intensity peak, which represents the -OH group, located at 1606cm-1 There is an intensity peak, which represents the -C=N group, located at 1581, 1515, 1446 cm -1 The intensity peaks of represent the -C=C stretching vibration on the benzene ring. Figure 3 As shown in (b), in the infrared spectrum of IPDI, the -1 There is an obvious intensity peak, which represents the -NCO group. In the HTPB spectrum, it is located at 2800-3000cm -1 , 964cm -1 and 918cm -1 The intensity peaks of represent the -CH stretching vibration on the vinyl group and the -CH out-of-plane bending vibration on the trans-butadiene component. In the spectrum curve of Example 1, the intensity peak representing the -NCO group disappeared, indicating that the -NCO group on IPDI reacted, and the results showed that polyurethane was successfully synthesized.

[0042] like Figure 4 As shown, the tensile strength, elongation at break and toughness of the polyurethane elastomer of Example 1 are 4.2 MPa, 1171% and 34.9 MJ*m respectively. -3 The tensile strength, elongation at break and toughness of the polyurethane elastomer in Comparative Example 1 were 5.0 MPa, 1314% and 37.1 MJ*m -3 .

[0043] like Figure 5 As shown, after being immersed in water for three days, the tensile strengths of the polyurethane elastomers of Example 1, Comparative Example 1 and Comparative Example 2 were 3.4 MPa, 3.4 MPa and 0.76 MPa, respectively, which were 81%, 67% and 61% of the original tensile strengths, respectively. This indicates that the polyurethane elastomer prepared by the method of the present invention has excellent water resistance, and its mechanical properties are not greatly affected by water.

[0044] like Figure 6 As shown, the self-repairing efficiencies of the polyurethane elastomers of Example 1, Comparative Example 1 and Comparative Example 2 at 35°C after 24 repair times are 95.0%, 53.5% and 94.7%, respectively, and the self-repairing efficiencies underwater are 79.1%, 51.6% and 63.8%, respectively. This indicates that the polyurethane elastomer prepared by the method of the present invention has excellent self-repairing efficiency and self-repairing performance underwater.

[0045] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a water-resistant, self-repairing polyurethane elastomer, characterized in that The steps include: S1, dissolving 4,4′-diaminodiphenylmethane and p-hydroxybenzaldehyde in anhydrous ethanol and reacting with a Schiff base to generate a small molecule MDOH with an imine bond structure; S2. Using dibutyltin dilaurate as a catalyst, terminal hydroxyl polybutadiene and isophorone diisocyanate are reacted in a solvent at 60°C to generate an isocyanate-terminated prepolymer; small molecule MDOH obtained in step S1 and glyceryl monostearate are added to the obtained isocyanate-terminated prepolymer for chain extension, and the reaction temperature is controlled to be 60-70°C for polymerization reaction. After the reaction is completed, the mixture is poured into a mold and dried at 60°C to obtain a water-resistant, self-healing polyurethane elastomer.

2. The method for preparing a water-resistant, self-repairing polyurethane elastomer according to claim 1, characterized in that: Step S1 specifically follows the following operating steps: at room temperature, 20 parts by mass of 4,4′-diaminodiphenylmethane and 40 parts by mass of p-hydroxybenzaldehyde are respectively dissolved in 100 ml of anhydrous ethanol to obtain a 4,4′-diaminodiphenylmethane solution and a p-hydroxybenzaldehyde solution; then the 4,4′-diaminodiphenylmethane solution and the p-hydroxybenzaldehyde solution are transferred to a 250 ml three-necked flask and mixed for reaction for 6 hours to form a precipitate, the precipitate is vacuum filtered and washed with ethanol 2-3 times to obtain a small molecule MDOH with an imine bond structure.

3. The method for preparing a water-resistant, self-repairing polyurethane elastomer according to claim 1, characterized in that: Step S2 specifically follows the following operating steps: 2.5 parts by mass of hydroxy-terminated polybutadiene is dried under vacuum at 110° C. for 2 hours to remove trace moisture, then dissolved in tetrahydrofuran, 7.5 parts by mass of isophorone diisocyanate and catalyst dibutyltin dilaurate are added through a syringe, and the amount of dibutyltin dilaurate added is 0.2-0.5wt% of the hydroxy-terminated polybutadiene; stirred in a nitrogen atmosphere at 60-70° C. for 2-3 hours to obtain an isocyanate-terminated prepolymer; 1.5 parts by mass of the small molecule MDOH obtained in step S1 is added to the isocyanate-terminated prepolymer, the temperature is raised to 70-80° C., the reaction is continued for 4-6 hours, and then 1.0 parts by mass of glyceryl monostearate is added thereto, the temperature is maintained at 70-80° C. and the reaction is continued for 2 hours, the solution after the reaction is poured into a polytetrafluoroethylene mold, and dried at 60° C. to obtain a water-resistant, self-healing polyurethane elastomer.

4. A water-resistant, self-repairing polyurethane elastomer prepared by the preparation method according to claim 1.

5. Use of the water-resistant, self-healing polyurethane elastomer according to claim 4 in the preparation of a humidity sensor.

6. A humidity sensor made of the water-resistant, self-healing polyurethane elastomer according to claim 4, characterized in that: The humidity sensor is composed of a water-resistant, self-repairing polyurethane elastomer and a conductive network, and the conductive network is dripped onto the water-resistant, self-repairing polyurethane elastomer.

7. The humidity sensor according to claim 6, characterized in that: The conductive network is carboxylated multi-walled carbon nanotubes; the preparation method of the humidity sensor follows the following steps: 10 mg of carboxylated multi-walled carbon nanotubes are uniformly dispersed in 10 mL of a mixed solvent of anhydrous ethanol and deionized water by ultrasonic treatment, and then the resulting slurry is uniformly distributed on the above-mentioned water-resistant, self-healing polyurethane elastomer by drop coating, and dried to obtain a humidity sensor.

8. The humidity sensor according to claim 7, characterized in that: The ultrasonic treatment time is 30 minutes; the anhydrous ethanol and deionized water mixed solvent is composed of anhydrous ethanol and deionized water in a volume ratio of 4:1.

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