Preparation method of double-channel self-repairing waterborne polyurethane composite material with adjustable mechanical property

Abstract

The invention discloses a preparation method of a double-channel self-repairing waterborne polyurethane composite material with adjustable and controllable mechanical properties. According to the invention, polycarbonate diol and polypropylene glycol are adopted as a mixed soft segment, and a DA bond is introduced into a polyurethane main chain to endow the polyurethane with self-repairing performance. The mechanical property of the water-based self-repairing polyurethane can be regulated and controlled by adjusting the proportion of the mixed soft segments. When the molar ratio of the polycarbonate diol to the polypropylene glycol is 1: 1, the tensile strength of the waterborne polyurethane film is 20.4 MPa, and the elongation at break reaches 1143%. On the basis, graphene (GNP) is added to serve as photo-thermal filler, and the waterborne polyurethane composite material which is adjustable and controllable in mechanical property and capable of achieving self-repairing through two channels is prepared. When the GNP content is 5 wt%, the composite film realizes crack repair under 808 nm near-infrared irradiation for 12 min, and the composite film can be recycled through a shearing hot-pressing method.

Description

Technical Field

[0001] This invention belongs to the field of self-healing polymer composite materials technology, specifically relating to a method for preparing a dual-channel self-healing waterborne polyurethane composite material with adjustable mechanical properties. Background Technology

[0002] Polyurethane (PU) is widely used in various fields such as biomedicine, coatings, adhesives, foams, and construction. Depending on the dispersion medium, it can be divided into solvent-based polyurethane and waterborne polyurethane. The use of organic solvents (tetrahydrofuran, DMF, etc.) in the preparation of solvent-based polyurethane generates a large amount of volatile organic compounds, which can easily harm human health and cause serious environmental pollution. Compared with traditional polyurethane, waterborne polyurethane (WPU) uses water as a dispersion system, reducing the use of organic solvents in production and use, making it more environmentally friendly than solvent-based polyurethane.

[0003] During the use of polyurethane materials, damage such as cracks is inevitable due to working conditions. This not only affects aesthetics but may also impair the material's mechanical properties, reduce its service life, and create safety hazards. Currently, an effective approach to address this problem is to introduce dynamic reversible bonds into the material. Reversible bonds can be classified into reversible covalent bonds and reversible non-covalent bonds. Examples of reversible covalent bonds include disulfide bonds, diselenide bonds, borate ester bonds, DA bonds, and imine bonds, while examples of reversible non-covalent bonds include hydrogen bonds, metal coordination bonds, host-guest interactions, and π-π interactions. The Diels-Alder reaction, with its mild conditions, few side reactions, and the ability to break and recombine chemical bonds through temperature control, is widely used in self-healing materials. However, waterborne polyurethanes currently prepared using DA bonds as repair units exhibit poor mechanical properties, limiting their wide range of applications. For example, in the literature, waterborne polyurethane with polydimethylsiloxane as the soft segment and DA bonds introduced into the main chain exhibits tensile strength and elongation at break of 2.4 MPa and 88%, respectively (Applied Surface Science, 2018, 429, 128-133). Introducing DA units with rigid benzene ring structures into castor oil-based waterborne polyurethane allows the material to repair cracks after heating at 100 °C for 50 min, but its mechanical properties are only 5.96 MPa and elongation at break is 115% (Materials TodayChemistry, 2024, 42, 102354). Chinese Patent 201910355028.X discloses a self-healing waterborne polyurethane material and its preparation method. This material is prepared by introducing furan groups into the main chain and / or end groups of waterborne polyurethane using a DA reaction, achieving a maximum tensile strength and elongation at break of 17.92 MPa and 487.92%, respectively. Therefore, developing high-strength and tunable waterborne polyurethane self-healing materials based on DA bonds as self-healing units is of great significance for expanding their application scenarios.

[0004] On the other hand, traditional self-healing materials rely on thermal stimulation to break and rebuild chemical bonds. While this method can repair damage, the overall temperature increase inevitably affects the structure and properties of the undamaged areas of the material. Photothermal conversion materials can absorb light energy and efficiently convert it into heat, transferring it to the polymer for localized, targeted irradiation of the damaged area. This provides a solution for achieving a more precise, remote, controllable, and clean self-healing process. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing a dual-channel self-healing waterborne polyurethane composite material with controllable mechanical properties. This invention allows for the control of the mechanical properties of the waterborne self-healing polyurethane by adjusting the proportion of soft segments in the mixture, while simultaneously introducing DA bonds into the polyurethane backbone to impart self-healing properties. Further mixing with graphene yields a dual-channel self-healing, recyclable composite membrane. The addition of graphene enables the conversion of light energy into heat energy, allowing the material to achieve rapid, long-range, efficient, and clean self-healing under near-infrared irradiation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In the synthesis of waterborne polyurethane, polycarbonate has a rigid structure, which can improve the modulus and heat resistance of the material; polypropylene glycol has flexible segments, which can enhance the elasticity and flexibility of the material. Based on the above raw materials, this invention adds graphene as a photothermal filler to prepare a waterborne polyurethane composite material with adjustable mechanical properties and dual-channel self-healing capability.

[0008] Specifically, the steps include the following:

[0009] Step 1: Preparation of waterborne polyurethane with isocyanate-terminated groups

[0010] Weigh the dehydrated polycarbonate diol and polypropylene glycol into a three-necked flask, add 4.80 g of isophorone diisocyanate, 1.68 g of 2,2-hydroxymethylpropionic acid, an appropriate amount of dibutyltin dilaurate and solvent, and react at 90℃ for 3 h. After the reaction is completed, cool down to below 50℃ and add 1.27 g of triethylamine to neutralize for 10 min. This solution is recorded as solution A.

[0011] In step 1, the molar ratio of isocyanate to hydroxyl groups in the system is controlled at 1.08:1. The excess -NCO ensures that terminal isocyanate polyurethane can be generated after reacting with -OH, which can then react with furfuryl alcohol, enabling the next step of successfully reacting with bismaleimide to introduce dynamic DA bonds into the molecular chain.

[0012] Step 2: Preparation of self-healing waterborne polyurethane WPU-DA-X

[0013] 0.32 g of furfuryl alcohol was weighed and added to solution A, and the temperature was raised to 75 ℃ and reacted for 3 h. Then, 1.15 g of bismaleimide was weighed and reacted at 60 ℃ for 36 h. Finally, deionized water was added at a solid content of 30% for emulsification for 30 min. The reaction solvent was removed by rotary evaporation to obtain an aqueous polyurethane emulsion, denoted as WPU-DA-X, where X represents an aqueous polyurethane emulsion synthesized with different soft segment ratios.

[0014] In step 2, the rotary evaporation temperature is 40 ℃, the rotation speed is 80 rpm, and the rotary evaporation time is 1 h.

[0015] Step 3: Preparation of dual-channel self-healing composite material (GNP / WPU-DA)

[0016] A certain amount of graphene was weighed and ultrasonically dispersed in anhydrous tetrahydrofuran for 12 h to obtain a dispersion. The graphene dispersion was added to the aqueous polyurethane emulsion obtained in step 2 and mechanically stirred for 24 h until it was uniformly mixed. The mixture was placed in a vacuum drying oven for 0.5~1 h to remove air bubbles. The resulting GNP / WPU-DA emulsion was poured onto a clean polytetrafluoroethylene template and placed on a hot table at 70℃ for 48 h to obtain a dual-channel self-healing GNP / WPU-DA composite film.

[0017] The solvent is acetone. Acetone is added intermittently during the reaction to dilute the viscosity and keep the viscosity of the system within a range that is easy to mechanically stir.

[0018] In step 1, the total amount of polycarbonate diol and polypropylene glycol added is 0.015 mol.

[0019] The hydroxyl value of the polycarbonate diol is 56 mg KOH / g, and the hydroxyl value of the polypropylene glycol is 54~58 mg KOH / g.

[0020] Furthermore, the polycarbonate diol is polycarbonate diol-2000; the polypropylene diol is polypropylene diol-2000.

[0021] The molar ratio of polycarbonate diol to polypropylene diol is 0:1, 1:3, 1:1, or 1:0, preferably 1:1, because it ensures mechanical properties while possessing self-healing properties.

[0022] The amount of graphene added is 5-20% of the total solid content of the system. A graphene addition amount of 5 wt% is preferred because it ensures self-healing properties while exhibiting good photothermal performance.

[0023] The beneficial effects of this invention are reflected in:

[0024] This invention employs a two-step chemical synthesis process (waterborne polyurethane reaction and Diels-Alder reaction), achieving adjustable mechanical properties of the waterborne polyurethane by controlling the proportion of the mixed soft segments. Furthermore, the addition of graphene endows the material with photothermal conversion properties, and the synergistic effect of hydrogen bonds and dynamic DA bonds in the molecular chain results in excellent self-healing properties, preparing a waterborne polyurethane composite material with adjustable mechanical properties that can self-heal through photo and thermal responses. When the molar ratio of polycarbonate diol to polypropylene glycol in the mixed soft segments is 1:1, the tensile strength of the material reaches 20.4 MPa, and the elongation at break reaches 1143%. Under repair conditions of 110 °C, the WPU-DA pure film can complete crack repair within 10 minutes. When the graphene content is 5 wt%, the average surface temperature of the material reaches 112 °C within 3 minutes under 600 mW near-infrared irradiation, and crack self-healing can be completed within 12 minutes. The composite film can be recycled through shearing-hot pressing reshaping. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the synthetic route of WPU-DA-X with synergistic hydrogen and DA bond effects obtained in the embodiments of the present invention.

[0026] Figure 2 This is a schematic diagram of the self-healing mechanism of WPU-DA-X with synergistic effects of hydrogen bonds and DA bonds obtained in an embodiment of the present invention.

[0027] Figure 3 The images show the Zeta potential diagrams of the WPU-DA-X emulsions obtained in Examples 1, 2, 3, and 4 of this invention and Comparative Example 1.

[0028] Figure 4 The mechanical properties of the WPU-DA-X emulsions obtained in Examples 1, 2, 3, and 4 of this invention and Comparative Example 1 are shown in the diagram.

[0029] Figure 5 This is a self-healing optical image of the aqueous polyurethane film obtained in Example 3 of the present invention under heating conditions.

[0030] Figure 6 The above are the near-infrared temperature rise curves of the composite materials obtained in Examples 5, 6, 7, and 8 of this invention.

[0031] Figure 7 This is an optical image of the crack repair of the 5wt% GNP / WPU-DA composite material obtained in Example 7 of the present invention under 600 mw near-infrared light irradiation.

[0032] Figure 8 This is a diagram showing the remodeling and recycling of 5 wt% GNP / WPU-DA composite material obtained in Example 7 of the present invention. Detailed Implementation

[0033] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0034] In the following embodiments, the test method for crack repair is as follows: a crack of uniform width is made on the film with a sharp blade, irradiated with an 808 nm laser, and then the repair is observed under a polarizing microscope; the method for material reshaping and recycling is as follows: after the composite film is cut into pieces, it is hot-pressed at 40 ℃ and 5 MPa pressure for 10 min to reform a uniform and complete composite film.

[0035] Example 1:

[0036] This embodiment prepares WPU-DA self-healing waterborne polyurethane with synergistic effects of hydrogen bonding and dynamic DA bonds according to the following steps:

[0037] Step 1: Preparation of waterborne polyurethane with isocyanate-terminated groups

[0038] Weigh 15 g (0.015 mol) of dehydrated polypropylene glycol into a 250 ml three-necked flask, add 4.80 g (0.043 mol) of isophorone diisocyanate, 1.68 g (0.025 mol) of 2,2-hydroxymethylpropionic acid, an appropriate amount of dibutyltin dilaurate, and solvent. React at 90 °C for 3 h. After the reaction is complete, cool to below 50 °C and add 1.27 g (0.025 mol) of triethylamine for 10 min to neutralize. This solution is labeled as solution A.

[0039] Step 2: Preparation of self-healing waterborne polyurethane WPU-DA

[0040] Weigh 0.32 g (0.0032 mol) of furfuryl alcohol and add it to solution A. Heat the solution to 75 °C and react for 3 h. Then weigh 1.15 g (0.0032 mol) of bismaleimide and react at 60 °C for 36 h. Finally, add deionized water at a solid content of 30% to emulsify the solution. Remove the reaction solvent by rotary evaporation to obtain an aqueous polyurethane emulsion, denoted as WPU-DA-1.

[0041] Example 2:

[0042] This embodiment prepares WPU-DA self-healing waterborne polyurethane using the same method as in Example 1, except that step 1 is as follows: 3.75 g (0.00375 mol) of dehydrated polycarbonate diol and 11.25 g (0.01125 mol) of polypropylene glycol are weighed into a 250 ml three-necked flask. 4.80 g (0.0432 mol) of isophorone diisocyanate, 1.68 g (0.025 mol) of 2,2-hydroxymethylpropionic acid, an appropriate amount of dibutyltin dilaurate, and solvent are added. The mixture is reacted at 90°C for 3 h. After the reaction is complete, the temperature is lowered to below 50°C, and 1.27 g (0.025 mol) of triethylamine is added for neutralization for 10 min. This is designated WPU-DA-2.

[0043] Example 3:

[0044] This embodiment prepares WPU-DA self-healing waterborne polyurethane using the same method as in Example 1, except that step 1 is as follows: 7.5 g (0.0075 mol) of dehydrated polycarbonate diol and 7.5 g (0.0075 mol) of polypropylene glycol are weighed into a 250 ml three-necked flask. 4.801 g (0.0432 mol) of isophorone diisocyanate, 1.68 g (0.025 mol) of 2,2-hydroxymethylpropionic acid, an appropriate amount of dibutyltin dilaurate, and solvent are added. The mixture is reacted at 90 °C for 3 h. After the reaction is complete, the temperature is lowered to below 50 °C, and 1.27 g (0.025 mol) of triethylamine is added for neutralization for 10 min. This is designated WPU-DA-3.

[0045] Example 4:

[0046] This embodiment prepares WPU-DA self-healing waterborne polyurethane using the same method as in Example 1, except that step 1 is as follows: 15 g (0.015 mol) of dehydrated polycarbonate diol is weighed into a 250 ml three-necked flask, and 4.80 g (0.0432 mol) of isophorone diisocyanate, 1.68 g (0.025 mol) of 2,2-hydroxymethylpropionic acid, an appropriate amount of dibutyltin dilaurate, and solvent are added. The mixture is reacted at 90 °C for 3 h. After the reaction is complete, the temperature is lowered to below 50 °C, and 1.27 g (0.025 mol) of triethylamine is added for neutralization for 10 min. This is designated as WPU-DA-4.

[0047] Example 5:

[0048] In this embodiment, a GNP / WPU-DA dual-channel self-healing composite material with synergistic effects of hydrogen bonding and dynamic DA bonding is prepared according to the following steps:

[0049] Step 1: Preparation of waterborne polyurethane with isocyanate-terminated groups

[0050] Weigh 7.5 g (0.0075 mol) of dehydrated polycarbonate diol and 7.5 g (0.0075 mol) of polypropylene glycol into a 250 ml three-necked flask. Add 4.80 g (0.0432 mol) of isophorone diisocyanate, 1.68 g (0.025 mol) of 2,2-hydroxymethylpropionic acid, an appropriate amount of dibutyltin dilaurate, and solvent. React at 90 °C for 3 h. After the reaction is complete, cool to below 50 °C and add 1.27 g (0.025 mol) of triethylamine to neutralize for 10 min. This solution is labeled as solution A.

[0051] Step 2: Preparation of self-healing waterborne polyurethane WPU-DA

[0052] Weigh 0.32 g (0.0032 mol) of furfuryl alcohol and add it to solution A. Heat the solution to 75 °C and react for 3 h. Then weigh 1.15 g (0.0032 mol) of bismaleimide and react at 60 °C for 36 h. Finally, add deionized water at a solid content of 30% to emulsify the solution. Remove the reaction solvent by rotary evaporation to obtain an aqueous polyurethane emulsion, denoted as WPU-DA-3.

[0053] Step 3: Preparation of dual-channel self-healing composite material (GNP / WPU-DA)

[0054] 0.53 g of graphene was weighed and ultrasonically dispersed in anhydrous tetrahydrofuran for 12 h to obtain a dispersion. The graphene dispersion was added to the aqueous polyurethane emulsion obtained in step 2 and mechanically stirred for 24 h until it was uniformly mixed. The mixture was placed in a vacuum drying oven for 0.5-1 h to remove air bubbles. The resulting GNP / WPU-DA emulsion was poured onto a clean polytetrafluoroethylene template and placed on a hot table at 70 ℃ for 48 h to obtain a GNP / WPU-DA dual-channel self-healing composite film with a filler content of 5 wt%.

[0055] Example 6:

[0056] In this embodiment, the GNP / WPU-DA dual-channel self-healing composite material was prepared using the same method as in Example 5, except that step 3 was as follows: 1.11 g of graphene was weighed and ultrasonically dispersed in anhydrous tetrahydrofuran for 12 h to obtain a dispersion. The graphene dispersion was added to the aqueous polyurethane emulsion obtained in step 2 and mechanically stirred for 24 h until uniformly mixed. The mixture was then placed in a vacuum drying oven for 0.5-1 h to remove air bubbles. The resulting GNP / WPU-DA emulsion was poured onto a clean polytetrafluoroethylene template and placed on a hot table at 70 ℃ for 48 h to obtain a GNP / WPU-DA dual-channel self-healing composite film with a filler content of 10 wt%.

[0057] Example 7:

[0058] In this embodiment, the GNP / WPU-DA dual-channel self-healing composite material was prepared using the same method as in Example 5, except that step 3 was as follows: 1.76 g of graphene was weighed and ultrasonically dispersed in anhydrous tetrahydrofuran for 12 h to obtain a dispersion. The graphene dispersion was added to the aqueous polyurethane emulsion obtained in step 2, and mechanically stirred for 24 h until uniformly mixed. The mixture was then placed in a vacuum drying oven for 0.5-1 h to remove air bubbles. The resulting GNP / WPU-DA emulsion was poured onto a clean polytetrafluoroethylene template and placed on a hot table at 70 ℃ for 48 h to obtain a GNP / WPU-DA dual-channel self-healing composite film with a filler content of 15 wt%.

[0059] Example 8:

[0060] In this embodiment, the GNP / WPU-DA dual-channel self-healing composite material was prepared using the same method as in Example 5, except that step 3 was as follows: 2.5 g of graphene was weighed and ultrasonically dispersed in anhydrous tetrahydrofuran for 12 h to obtain a dispersion. The graphene dispersion was added to the aqueous polyurethane emulsion obtained in step 2, and mechanically stirred for 24 h until uniformly mixed. The mixture was then placed in a vacuum drying oven for 0.5-1 h to remove air bubbles. The resulting GNP / WPU-DA emulsion was poured onto a clean polytetrafluoroethylene template and placed on a hot table at 70 ℃ for 48 h to obtain a GNP / WPU-DA dual-channel self-healing composite film with a filler content of 20 wt%.

[0061] Comparative Example 1:

[0062] This comparative example provides an aqueous polyurethane material that does not contain DA bonds and is not filled with GNP:

[0063] This embodiment prepares WPU-DA self-healing waterborne polyurethane using the same method as in Example 1, except that step 1 is as follows: 7.5 g (0.0075 mol) of dehydrated polycarbonate diol and 7.5 g (0.0075 mol) of polypropylene glycol are weighed into a 250 ml three-necked flask, and 4.80 g (0.0432 mol) of isophorone diisocyanate, 1.68 g (0.025 mol) of 2,2-hydroxymethylpropionic acid, an appropriate amount of dibutyltin dilaurate, and solvent are added. The mixture is reacted at 90 °C for 3 h. After the reaction is completed, the temperature is lowered to below 50 °C and 1.27 g (0.025 mol) of triethylamine is added for neutralization for 10 min. 0.29 g (0.0032 mol) of 1,4-butanediol was added and chain extension was performed at 70 °C for 3 h. Finally, water was added to emulsify the emulsion to obtain a control emulsion without DA bonds, denoted as WPU-BDO.

[0064] Figure 1 This is a schematic diagram of the synthesis route of WPU-DA-X, a self-healing waterborne polyurethane material with synergistic effects of hydrogen bonds and DA bonds obtained in the above embodiments.

[0065] Figure 2 This is a schematic diagram of the self-healing mechanism of the self-healing waterborne polyurethane composite material obtained in the above embodiments. Graphene imparts photothermal conversion properties to the material, while hydrogen bonds and dynamic DA bonds provide the self-healing properties of the composite material.

[0066] Figure 3 The figures show the Zeta potential diagrams of the emulsions obtained in Examples 1, 2, 3, and 4 of this invention, and the aqueous polyurethane emulsion obtained in Comparative Example 1. When DA bonds are introduced into the molecular chain, the absolute values ​​of the Zeta potentials of the resulting emulsions are all above 30 mV, indicating good stability.

[0067] Figure 4 The figures show the mechanical properties of the materials obtained in Examples 1, 2, 3, and 4 of this invention, and the waterborne polyurethane material obtained in Comparative Example 1. As the proportion of polycarbonate diol in the molecular chain increases, the tensile strength of the material increases, while the elongation at break decreases. When the molar ratio of polycarbonate diol to polypropylene glycol is 1:1, the tensile strength of the material reaches 20.4 MPa, and the elongation at break reaches 1143%, exhibiting mechanical properties superior to the waterborne polyurethane material obtained in Comparative Example 1.

[0068] Figure 5 This is a self-healing optical image of the waterborne polyurethane film obtained in Example 3 of the present invention under heating conditions. The material can achieve self-healing of cracks within 10 minutes at 110°C.

[0069] Figure 6 The figures show the temperature rise curves of the composite materials obtained in Examples 5, 6, 7, and 8 of this invention under different wattages in 808 nm near-infrared light. The surface temperature of the material increases with increasing light intensity wattage. When the GNP content is 5 wt%, the average surface temperature of the material rises to 112 °C within 3 minutes.

[0070] Figure 7 This is an optical image of the crack repair of the 5 wt% GNP / WPU-DA composite material obtained in Example 7 of this invention under 600 mW near-infrared light irradiation. It can be clearly seen that the cracks in the material gradually healed over time under near-infrared light irradiation.

[0071] Figure 8 This is a diagram showing the hot-pressing remodeling and recycling of the 5 wt% GNP / WPU-DA composite material obtained in Example 7 of this invention. After cutting the composite film into pieces, it can be hot-pressed at 40 °C and 5 MPa for 10 min to reform a uniform and complete film.

[0072] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a dual-channel self-healing waterborne polyurethane composite material with adjustable mechanical properties, characterized in that... Includes the following steps: Step 1: Preparation of waterborne polyurethane with isocyanate-terminated groups Weigh the dehydrated polycarbonate glycol and polypropylene glycol into a three-necked flask, add isophorone diisocyanate, 2,2-hydroxymethylpropionic acid, dibutyltin dilaurate and solvent, and react at 90℃ for 3 h. After the reaction is completed, cool down to below 50℃ and add triethylamine to neutralize. This is denoted as solution A. Step 2: Preparation of self-healing waterborne polyurethane WPU-DA-X Weigh furfuryl alcohol and add it to solution A. Heat the solution to 75 °C and react for 3 h. Then add bismaleimide and react at 60 °C for 36 h. Finally, add deionized water to emulsify the solution. Remove the reaction solvent by rotary evaporation to obtain an aqueous polyurethane emulsion, denoted as WPU-DA-X, where X represents an aqueous polyurethane emulsion synthesized with different soft segment ratios. Step 3: Preparation of dual-channel self-healing composite material Graphene was weighed and ultrasonically dispersed in anhydrous tetrahydrofuran to obtain a dispersion. The graphene dispersion was added to the aqueous polyurethane emulsion obtained in step 2 and mechanically stirred until uniformly mixed. The mixture was placed in a vacuum drying oven to remove air bubbles. The resulting GNP / WPU-DA emulsion was poured onto a clean polytetrafluoroethylene template and allowed to stand on a hot table to obtain a dual-channel self-healing GNP / WPU-DA composite film.

2. The preparation method according to claim 1, characterized in that: The hydroxyl value of the polycarbonate diol is 56 mg KOH / g, and the hydroxyl value of the polypropylene glycol is 54~58 mg KOH / g.

3. The preparation method according to claim 2, characterized in that: The molar ratio of the polycarbonate diol to the polypropylene diol is 1:3 to 1:

1.

4. The preparation method according to claim 1, characterized in that: In step 1, the molar ratio of isocyanate to hydroxyl groups in the control system is 1.08:

1.

5. The preparation method according to claim 1, characterized in that: The amount of graphene added is 5-20% of the total solid content of the system.

6. The preparation method according to claim 5, characterized in that: The amount of graphene added is 5% of the total solid content of the system.

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