Water-resistant, self-healing polyurethane elastomers, methods of making the same, and use in humidity sensors

Abstract

The application belongs to the technical field of polyurethane elastomer preparation, and discloses a water-resistant and self-repairing polyurethane elastomer, a preparation method thereof and application of the polyurethane elastomer in a humidity sensor. The method comprises the following steps: S1, dissolving 4,4'-diaminodiphenyl methane and p-hydroxybenzaldehyde in anhydrous ethanol to generate a small molecule MDOH with an imine bond structure through Schiff base reaction, and the small molecule MDOH is used as a chain extender of polyurethane; S2, reacting hydroxyl-terminated polybutadiene and isophorone diisocyanate at 60 DEG C to generate a prepolymer, and adding MDOH and glycerol monostearate into the obtained prepolymer to extend the chain; the introduction of MDOH can make the material have excellent self-repairing capability, and the glycerol monostearate is beneficial to further improve the self-repairing capability and water resistance. In addition, the humidity sensor based on the polyurethane elastomer can exhibit good sensing performance.

Description

TECHNICAL FIELD

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

[0002] For most flexible electronic devices, they are inevitably exposed to water environment in daily use, such as encountering different environmental humidity levels, sweat (in the case of skin sensors) and water from external sources, such as rain. However, the function of the flexible electronic device is easily affected by water molecules, affecting normal use, and the reversible dynamic bond for self-repairing performance is very susceptible to water molecules, thereby destroying the active site and reducing the self-healing ability. Therefore, it is an urgent problem to be solved to achieve water resistance and underwater self-repairing of the flexible electronic device by reasonably designing the molecular structure of the elastomer matrix.

[0003] The flexible humidity sensor should not only have good humidity sensitive characteristics (for example, high sensitivity, small hysteresis and fast response / recovery speed), but also have more stringent performance: good flexibility to adapt to the wearing and bending requirements of wearable devices; stable humidity response is not disturbed by deformation (bending, twisting, stretching, etc.); light and breathable to ensure wearing comfort; non-toxic when directly contacted with the skin as a wearable device; good processability, low cost, etc. In order to meet such high requirements, high-performance humidity-sensitive materials and substrates should be developed, and the sensor configuration should be designed skillfully. SUMMARY

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

[0005] Another purpose of the present application is to provide a water-resistant and self-repairing polyurethane elastomer prepared by the above preparation method; which has good humidity sensitive characteristics, high sensitivity, small hysteresis and fast response / recovery speed.

[0006] Still another purpose of the present application is to provide an application of the above water-resistant and self-repairing polyurethane elastomer in preparing a humidity sensor.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] A preparation method of a water-resistant and self-repairing polyurethane elastomer, comprising the following operation steps:

[0009] S1, dissolving 4,4'-diaminodiphenyl methane and p-hydroxybenzaldehyde in anhydrous ethanol and Schiff base reaction to generate a small molecule MDOH with imine bond structure;

[0010] S2, using dibutyltin dilaurate as catalyst, hydroxyl-terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI) are reacted in a solvent at 60°C to generate isocyanate-terminated prepolymer; adding small molecule MDOH obtained in step S1 and glycerol monostearate chain extender to the obtained isocyanate-terminated prepolymer, controlling the reaction temperature at 60-70°C to carry out polymerization reaction, after the reaction is completed, pouring into a mold, drying at 60°C to obtain water-resistant, self-repairing polyurethane elastomer.

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

[0012] Step S2 is specifically as follows: 2.5 parts by mass of hydroxyl-terminated polybutadiene is dried at 110°C under vacuum for 2 hours to remove trace amount of water, and then is dissolved in tetrahydrofuran, 7.5 parts by mass of isophorone diisocyanate and catalyst dibutyltin dilaurate are added through a syringe, the amount of dibutyltin dilaurate added is 0.2-0.5 wt% of the hydroxyl-terminated polybutadiene; stirring at 60-70°C under nitrogen atmosphere for 2-3 hours to obtain isocyanate-terminated prepolymer; adding 1.5 parts by mass of small molecule MDOH obtained in step S1 to the isocyanate-terminated prepolymer, heating to 70-80°C, continuing to react for 4-6 hours, then adding 1.0 part by mass of glycerol monostearate, keeping at 70-80°C to continue to react for 2 hours, pouring the solution after the reaction into a polytetrafluoroethylene mold, drying at 60°C to obtain water-resistant, self-repairing polyurethane elastomer.

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

[0014] The above water-resistant, self-repairing polyurethane elastomer is used in the preparation of a humidity sensor.

[0015] A humidity sensor made of the above water-resistant, self-repairing polyurethane elastomer, the humidity sensor is composed of water-resistant, self-repairing polyurethane elastomer and conductive network, the conductive network is drop-coated 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) is uniformly dispersed in 10 mL of a mixed solvent of anhydrous ethanol and deionized water by ultrasonic treatment, then the obtained slurry is uniformly distributed on the above-mentioned water-resistant and self-repairing polyurethane elastomer by drop coating, and dried, to obtain the humidity sensor.

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

[0018] The principle of the present application is as follows:

[0019] The present application mainly comprises a pre-polymer composed of hydroxyl-terminated polybutadiene and isophorone diisocyanate, and the pre-polymer and a small molecule MDOH having an imine bond structure and glycerol monostearate to form a final elastomer. By adding MDOH and glycerol monostearate to the pre-polymer, a network structure containing an imine bond and a long side chain is formed. Such a design not only enhances the self-repairing ability and water resistance of the polyurethane elastomer, but also endows it with underwater self-repairing ability. The material has a wide range of applications and is suitable for complex environments in the elastomer technical field, such as high humidity and underwater applications.

[0020] In the present application, hydroxyl-terminated polybutadiene provides a hydrophobic polymer skeleton; the small molecule MDOH introduces an imine bond into the polyurethane chain, has a dynamic reversible feature, can undergo exchange reaction under various external driving, provides a dynamic self-repairing mechanism, and, in combination with the hydrophobic hydroxyl-terminated polybutadiene, can endow the polyurethane elastomer with the ability to perform self-repairing underwater.

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

[0022] The present application has the following advantages and beneficial effects relative to the prior art:

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

[0024] (2) The water-resistant and self-repairing polyurethane elastomer prepared by the method has high sensitivity, fast response speed, good stability and self-repairing function in a high-humidity environment.

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

[0026] Figure 1 The synthesis route of the small molecule MDOH with an imine bond structure in the embodiments of the present application is shown in the figure.

[0027] Figure 2 The molecular chain design schematic diagram of the polyurethane elastomer prepared in the embodiments of the present application is shown in the figure.

[0028] Figure 3 The infrared spectrum of the small molecule MDOH and the polyurethane elastomer prepared in Embodiment 1 of the present application is shown in the figure, wherein (a) is the infrared spectrum of the small molecule MDOH prepared in the embodiments of the present application, and (b) is the infrared spectrum of the polyurethane elastomer prepared in the embodiments of the present application.

[0029] Figure 4 The stress-strain curve diagram of the polyurethane elastomer prepared in Embodiment 1 and Comparative Example 1 of the present application is shown in the figure.

[0030] Figure 5 The stress-strain curve diagram of the polyurethane elastomer prepared in Embodiment 1, Comparative Example 1 and Comparative Example 2 of the present application after water treatment for three days is shown in the figure.

[0031] Figure 6 The self-healing performance diagram of the polyurethane elastomer prepared in Embodiment 1, Comparative Example 1 and Comparative Example 2 of the present application is shown in the figure. DETAILED DESCRIPTION

[0032] The present application will be further described in detail below in combination with embodiments and drawings, but the embodiments of the present application are not limited thereto.

[0033] The reagents used in the following embodiments can be commonly purchased from the market unless otherwise specified.

[0034] The parts mentioned in the following examples and comparative examples are all molar parts, wherein “1 part” is “1 mmol”.

[0035] Embodiment 1

[0036] The preparation method of the water-resistant and self-repairing polyurethane elastomer as shown in Figure 1 , Figure 2 is as follows:

[0037] S1, synthesis of small molecule MDOH with imine bond structure: 20 parts by mass of 4,4'-diaminodiphenyl methane and 40 parts by mass of p-hydroxybenzaldehyde were respectively dissolved in 100 ml of anhydrous ethanol at room temperature to obtain a 4,4'-diaminodiphenyl methane solution and a p-hydroxybenzaldehyde solution; then the 4,4'-diaminodiphenyl methane solution and the p-hydroxybenzaldehyde solution were transferred into a 250 ml three-necked flask for mixing reaction for 6 h to form a yellow precipitate, and finally the precipitate was vacuum filtered and washed with ethanol for 3 times to obtain the small molecule MDOH with imine bond structure.

[0038] S2, synthesis of polyurethane elastomer: 2.5 parts by mass of hydroxyl-terminated polybutadiene was dried at 110°C under vacuum for 2 h to remove trace amount of water, and then was dissolved in tetrahydrofuran, 7.5 parts by mass of isophorone diisocyanate and a catalyst dibutyltin dilaurate were added by syringe, the amount of dibutyltin dilaurate was 0.2 wt% of the hydroxyl-terminated polybutadiene; stirring at 60°C under nitrogen atmosphere for 2 h to obtain an isocyanate-terminated prepolymer; 1.5 parts by mass of the small molecule MDOH obtained in step S1 was added to the isocyanate-terminated prepolymer, and the temperature was raised to 70°C, and the reaction was continued for 5 h, then 1.0 parts by mass of glyceryl monostearate was added, and the reaction was continued for 2 h at 70-80°C, and the reaction solution was poured into a polytetrafluoroethylene mold and dried at 60°C to obtain a water-resistant and self-repairing polyurethane elastomer.

[0039] 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 were uniformly distributed on the above-mentioned water-resistant and self-repairing polyurethane elastomer by drop coating, and dried to obtain a humidity sensor.

[0040] Comparative Example 1

[0041] Other steps are the same as in Example 1, except that 1,4-butanediol is used instead of glyceryl monostearate in the process of synthesizing the polyurethane elastomer in step S2, and the specific steps of step S2 are as follows:

[0042] 2.5 parts by mass of hydroxyl-terminated polybutadiene were dried under vacuum at 110°C for 2 hours to remove trace amounts of moisture, and then dissolved in tetrahydrofuran. 7.5 parts by mass of isophorone diisocyanate and dibutyltin dilaurate catalyst were added via syringe, with the amount of dibutyltin dilaurate added being 0.2 wt% of the hydroxyl-terminated polybutadiene. The mixture was stirred at 60°C under a nitrogen atmosphere for 2 hours to obtain an isocyanate-terminated prepolymer. 1.5 parts by mass of the small molecule MDOH obtained in step S1 were added to the isocyanate-terminated prepolymer, the temperature was raised to 70°C, and the reaction was continued for 5 hours. Then, 1.0 part by mass of 1,4-butanediol was added, and the reaction was continued at 70-80°C for 2 hours. The resulting solution was poured into a polytetrafluoroethylene mold and dried at 60°C to obtain a water-resistant, self-healing polyurethane elastomer.

[0043] Comparative Example 2

[0044] The other steps are the same as in Example 1, except that in step S2, during the synthesis of the polyurethane elastomer, polytetrahydrofuran is used to replace the hydroxyl-terminated polybutadiene. The specific steps of step S2 are as follows:

[0045] Synthesis of polyurethane elastomer: 2.5 parts by mass of polytetrahydrofuran were dried under vacuum at 110℃ for 2 hours to remove trace moisture, and then dissolved in tetrahydrofuran. 7.5 parts by mass of isophorone diisocyanate and dibutyltin dilaurate catalyst were added via syringe. The amount of dibutyltin dilaurate added was 0.2 wt% of the hydroxyl-terminated polybutadiene. The mixture was stirred at 60℃ under a nitrogen atmosphere for 2 hours to obtain an isocyanate-terminated prepolymer. 1.5 parts by mass of the small molecule MDOH obtained in step S1 were added to the isocyanate-terminated prepolymer, the temperature was raised to 70℃, and the reaction was continued for 5 hours. Then, 1.0 part by mass of glyceryl monostearate was added, and the reaction was continued at 70-80℃ for 2 hours. The resulting solution was poured into a polytetrafluoroethylene mold and dried at 60℃ to obtain a water-resistant, self-healing polyurethane elastomer.

[0046] The methods for each performance test are as follows:

[0047] Fourier transform infrared spectroscopy was used for qualitative analysis of the chemical composition of all samples. Polyurethane elastomers were cut into standard specimens of 4mm × 50mm using a cutter to test the tensile properties (including self-healing properties and water resistance) of the polyurethane at a tensile speed of 200mm / min. To test the water resistance of the polyurethane elastomers, they were first immersed in water for 3 days. The sensing performance of the humidity sensor was tested using a benchtop digital multimeter (DM 3068).

[0048] like Figure 3 As shown in (a), in the infrared spectrum of MDOH, the value is located at 3452 cm⁻¹. -1 There is a distinct intensity peak, representing the -OH group, located at 1606 cm⁻¹.-1 There is an intensity peak, representing the -C=N group, located at 1581, 1515, and 1446 cm⁻¹. -1 The intensity peaks represent the -C=C stretching vibrations on the benzene ring. For example... Figure 3 As shown in (b), in the infrared spectrum of IPDI, the value is located at 2260 cm⁻¹. -1 There is a distinct intensity peak, representing the -NCO group. In the HTPB spectrum, it is located at 2800-3000 cm⁻¹. -1 964cm -1 and 918cm -1 The intensity peaks represent the -CH tensile vibration on the vinyl group and the -CH out-of-plane bending vibration on the trans-butadiene component, respectively. In the spectral curve of Example 1, the intensity peak representing the -NCO group disappeared, indicating that the -NCO group on IPDI had reacted, demonstrating the successful synthesis of polyurethane.

[0049] like Figure 4 As shown, the tensile strength, elongation at break, and toughness of the polyurethane elastomer in Example 1 were 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, respectively. -3 .

[0050] like Figure 5 As shown, after soaking in water for three days, the tensile strengths of the polyurethane elastomers in Examples 1, 1, and 2 were 3.4 MPa, 3.4 MPa, and 0.76 MPa, respectively, representing 81%, 67%, and 61% of their original tensile strengths. This indicates that the polyurethane elastomers prepared by the method of this invention have excellent water resistance, and their mechanical properties are not significantly affected by water.

[0051] like Figure 6 As shown, the self-healing efficiencies of the polyurethane elastomers in Example 1, Comparative Example 1, and Comparative Example 2 after 24 hours of repair at 35°C were 95.0%, 53.5%, and 94.7%, respectively, and their self-healing efficiencies underwater were 79.1%, 51.6%, and 63.8%, respectively. This indicates that the polyurethane elastomer prepared by the method of the present invention possesses excellent self-healing efficiency and also exhibits self-healing properties underwater.

[0052] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A process for the preparation of a water resistant, self-healing polyurethane elastomer, characterized in that The following steps are included: S1. Dissolve 4,4′-diaminodiphenylmethane and p-hydroxybenzaldehyde in anhydrous ethanol and react with a Schiff base to generate a small molecule MDOH with an imine bond structure. S2. Using dibutyltin dilaurate as a catalyst, hydroxyl-terminated polybutadiene and isophorone diisocyanate are reacted in a solvent at 60°C to generate an isocyanate-terminated prepolymer. The small molecule MDOH and glyceryl monostearate obtained in step S1 are added to the obtained isocyanate-terminated prepolymer for chain extension. The reaction temperature is controlled at 60-70°C for polymerization. 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. A process for the preparation of a water resistant, self-healing polyurethane elastomer as claimed in claim 1, wherein: Step S1 is performed as follows: At room temperature, 20 parts by mass of 4,4′-diaminodiphenylmethane and 40 parts by mass of p-hydroxybenzaldehyde are dissolved in 100 ml of anhydrous ethanol to obtain 4,4′-diaminodiphenylmethane solution and p-hydroxybenzaldehyde solution respectively; then the 4,4′-diaminodiphenylmethane solution and p-hydroxybenzaldehyde solution are transferred to a 250 ml three-necked flask and mixed and reacted for 6 h to form a precipitate. The precipitate is vacuum filtered and washed with ethanol 2-3 times to obtain small molecule MDOH with an imine bond structure.

3. A process for the preparation of a water resistant, self-healing polyurethane elastomer as claimed in claim 1, wherein: Step S2 is performed as follows: 2.5 parts by mass of hydroxyl-terminated polybutadiene is dried under vacuum at 110°C for 2 hours to remove trace amounts of moisture, then dissolved in tetrahydrofuran. 7.5 parts by mass of isophorone diisocyanate and dibutyltin dilaurate catalyst are added via syringe. The amount of dibutyltin dilaurate added is 0.2-0.5 wt% of the hydroxyl-terminated polybutadiene. The mixture is stirred for 2-3 hours under a nitrogen atmosphere at 60-70°C 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, and the reaction continues for 4-6 hours. Then, 1.0 part by mass of glyceryl monostearate is added, and the reaction continues for 2 hours at 70-80°C. The resulting solution 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-healing polyurethane elastomer prepared by the preparation method described in claim 1.

5. The application of the water-resistant, self-healing polyurethane elastomer according to claim 4 in the preparation of humidity sensors.

6. A humidity sensor made from the water resistant, self-healing polyurethane elastomer of claim 4, characterized by: The humidity sensor is composed of a water-resistant, self-healing polyurethane elastomer and a conductive network, wherein the conductive network is drop-coated onto the water-resistant, self-healing polyurethane elastomer.

7. The humidity sensor of claim 6, wherein: The conductive network is a carboxylated multi-walled carbon nanotube; the humidity sensor is prepared according to the following steps: 10 mg of carboxylated multi-walled carbon nanotubes are uniformly dispersed in a mixed solvent of 10 mL 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 the humidity sensor.

8. The humidity sensor of claim 7, wherein: 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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