Graphene oxide grafted polyurethane coating as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of preparation of electric insulating materials, and particularly relates to a graphene oxide grafted polyurethane coating as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) adding diisocyanate into dispersion liquid containing graphene oxide, and carrying out first reaction to obtain isocyanate grafted graphene oxide; the diisocyanate is of a symmetrical structure and has an aromatic ring; (2) mixing the isocyanate grafted graphene oxide with polyether glycol, and stirring for second reaction to form a prepolymer; and (3) mixing the prepolymer with linear micromolecular dihydric alcohol, and carrying out a third reaction. The graphene oxide grafted polyurethane coating prepared by the method disclosed by the invention shows good nonlinear electrical behavior, high photo-thermal conversion rate and repeated self-repairing function, can have the properties of self-repairing, deicing, lightning protection and the like, and can be used for packaging of high-power-density power electronic devices, tensile conductor insulating coatings, dielectric layers of energy collection devices and the like.

Description

Technical Field

[0001] This invention belongs to the field of electrical insulation material preparation technology, and particularly relates to a graphene oxide-grafted polyurethane coating, its preparation method and application. Background Technology

[0002] The rapid development of the Global Energy Interconnection has presented new challenges to critical power and power electronic equipment, driving an urgent need for high-performance functional coatings. One of the most prominent issues is the insulation synergy between continuously increasing system operating voltages and the increasing miniaturization and lightweighting of equipment. The highly concentrated electric fields within more compact equipment necessitate more sophisticated coating designs to suppress partial discharge and surface flashover. This requirement is widespread in high-voltage cable terminations, capacitor insulation sleeves, and power module packaging. Meanwhile, coating degradation is unavoidable during long-term operation, especially under extreme climatic conditions such as icing disasters, which can lead to ice buildup on the coating surface, causing electric field distortion, ice spike discharge, and even ice flashover breakdown, accelerating the decline in insulation performance.

[0003] While traditional protective coatings strive for physicochemical stability to extend service life, performance degradation under complex operating conditions can still accumulate gradually, eventually leading to functional failure. Inspired by the self-repairing capabilities of most organisms in nature to maintain morphological integrity and functional stability, the development of coatings with adaptive, effective anti-icing, de-icing, and self-healing properties, capable of responding to changes in electric fields and resisting environmental influences such as icing, is of great significance for improving the reliability and service life of power equipment in complex environments. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a graphene oxide-grafted polyurethane coating, its preparation method, and its application.

[0005] In a first aspect, the present invention provides a method for preparing a graphene oxide-grafted polyurethane coating, comprising the following steps: (1) Prepare a dispersion containing graphene oxide; add diisocyanate to the dispersion and carry out a first reaction to obtain isocyanate-grafted graphene oxide; the diisocyanate has a symmetrical structure and has an aromatic ring; (2) The isocyanate-grafted graphene oxide is mixed with polyether diol and stirred to carry out a second reaction to form a prepolymer; (3) The prepolymer is mixed with a linear small molecule diol to carry out a third reaction; The graphene oxide accounts for 1-2% of the total mass of the graphene oxide, diisocyanate, polyether glycol and linear small molecule diol.

[0006] As an optional implementation, the hard segment content in the polyurethane is 33-37 wt%; As an optional implementation, the polyether diol is polypropylene glycol and / or polyethylene glycol; As an optional implementation, the diisocyanate includes 4,4'-methylene diphenyl diisocyanate.

[0007] As an optional implementation, the linear small molecule diol includes 1,4-butanediol.

[0008] As an optional implementation, the graphene oxide accounts for 1.3% of the total mass of the graphene oxide, diisocyanate, polyether glycol, and linear small molecule diol.

[0009] As an optional implementation, the temperature of the first reaction is 65-70°C and the time is 3-4 hours; As an optional implementation, the temperature of the second reaction is 65-70°C, and the time is 2-3 hours; As an optional implementation, the stirring speed is 390-400 rpm; As an optional implementation, the temperature of the third reaction is 65-70°C and the time is 2-3 hours.

[0010] As an optional implementation, graphene oxide is mixed with a solvent, and then stirred and ultrasonically dispersed to obtain a dispersion containing graphene oxide. Preferably, the ultrasound duration is 2-2.5 hours; Preferably, the ultrasound duration is 1-1.2 hours.

[0011] Secondly, the present invention provides a coating prepared by the above-described preparation method.

[0012] Thirdly, the present invention provides an apparatus comprising a substrate and a coating disposed on the surface of the substrate, wherein the raw material of the coating comprises a coating material prepared by the above-described preparation method; Preferably, the substrate includes an insulator, a cable, or a transformer bushing.

[0013] Fourthly, the present invention provides a method for preparing the above-mentioned device, wherein the coating is applied to the surface of the substrate and left to stand.

[0014] As an optional implementation, the settling temperature is 70°C and the time is 24-30 hours.

[0015] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art: 1. The preparation method of graphene oxide-grafted polyurethane coating provided by the present invention includes the following steps: (1) preparing a dispersion containing graphene oxide; adding diisocyanate to the dispersion and carrying out a first reaction to obtain isocyanate-grafted graphene oxide; the diisocyanate has a symmetrical structure and has an aromatic ring; (2) mixing the isocyanate-grafted graphene oxide with polyether diol and stirring to carry out a second reaction to form a prepolymer; (3) mixing the prepolymer with a linear small molecule diol and carrying out a third reaction. The present invention uses diisocyanate with an aromatic ring and a symmetrical structure. The aromatic ring gives the hard segment of polyurethane rigidity and strength, which helps to form a microphase separation structure and improve the mechanical properties and dielectric strength of the material; adding a linear small molecule diol to the prepolymer and carrying out a chain extension reaction, through regular linear chain extension, constructing a strong and tough polyurethane structure that can be microphase separated, while ensuring the strength of the material, providing the ability of molecular chain movement, which is conducive to realizing dynamic functions such as self-repair. The graphene oxide-grafted polyurethane coating prepared by the method of this invention exhibits excellent nonlinear electrical behavior, high photothermal conversion efficiency, and repeatable self-healing function. It combines self-healing, de-icing, and lightning protection properties, and can be used for high-power-density power electronic device packaging, tensile conductor insulating coatings, and dielectric layers in energy harvesting devices. Furthermore, this preparation method has advantages such as simple operation, operability, and high repeatability. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This invention illustrates the connection relationships between molecular chains during the preparation of graphene oxide-grafted polyurethane coatings. Detailed Implementation

[0019] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0020] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0021] In a first aspect, embodiments of the present invention provide a method for preparing a graphene oxide-grafted polyurethane coating, comprising the following steps: (1) Prepare a dispersion containing graphene oxide; add diisocyanate to the dispersion and carry out a first reaction to obtain isocyanate-grafted graphene oxide; the diisocyanate has a symmetrical structure and has an aromatic ring; (2) The isocyanate-grafted graphene oxide is mixed with polyether diol and stirred to carry out a second reaction to form a prepolymer; (3) The prepolymer is mixed with a linear small molecule diol to carry out a third reaction; The graphene oxide accounts for 1-2% of the total mass of the graphene oxide, diisocyanate, polyether glycol and linear small molecule diol.

[0022] Graphene oxide (GO), as a functional two-dimensional carbon-based filler, exhibits significantly higher photothermal conversion efficiency, larger specific surface area, lower density, and superior mechanical strength compared to traditional nanoparticles. This allows GO to form infiltrated structures with a volume fraction of approximately 3% within polymers. The abundant oxygen-containing functional groups at the bottom and edges of GO, such as epoxy, hydroxyl, carboxyl, and carbonyl groups, disrupt the sp2 hybridization of graphene and act as energy barriers for electron transfer in olefin conjugated structures, resulting in significant semiconductor properties. Furthermore, these oxygen-containing functional groups demonstrate good compatibility with the polymer matrix, serving as active centers for polymerization and grafting reactions. Simultaneously, GO possesses broad-spectrum, high-efficiency absorption characteristics in the visible to near-infrared band, enabling rapid conversion of light energy into heat energy under external illumination, achieving rapid temperature rise at the interface. This photothermal property makes it a promising candidate for anti-icing and de-icing coatings: on the one hand, the photothermal effect can actively increase the surface temperature of the coating, delaying the icing process and reducing ice adhesion; on the other hand, after ice formation, local heat generation can be achieved through photothermal conversion, enabling non-destructive and low-energy removal of the ice layer, providing a new active protection path for the reliable operation of power equipment in extreme cold and icing environments. Therefore, GO is a potential option for organically integrating autonomous functions, including adaptive, anti-icing, and self-healing capabilities, into the same medium.

[0023] The connection relationship between molecular chains in the preparation of graphene oxide-grafted polyurethane coatings in this invention is referenced. Figure 1This invention utilizes a diisocyanate with an aromatic ring and a symmetrical structure to provide hydrogen bonding sites, forming hard segment microregions. This provides reversible physical crosslinking points and microphase separation structures for self-healing, and offers a highly polar environment, enhancing interfacial polarization and improving lightning protection performance. Furthermore, the aromatic ring imparts rigidity and strength to the polyurethane hard segments, improving the material's mechanical and dielectric properties. Adding a linear small-molecule diol to the prepolymer initiates a chain extension reaction. Through regular linear chain extension, a strong and tough polyurethane structure with microphase separation is constructed, balancing the material's strength and chain mobility—that is, balancing mechanical strength and self-healing performance. This facilitates the connection of adjacent graphene oxide segments, and hydrogen bonding can form between adjacent polyurethane links, thus providing molecular chain mobility while ensuring material strength, which is beneficial for achieving dynamic functions such as self-healing. Compared to existing technologies that only utilize polyether diols reacted with isocyanates to generate polyurethane, this invention better balances self-healing performance and adaptive electrical properties.

[0024] The graphene oxide-grafted polyurethane coating prepared by the method of this invention exhibits excellent nonlinear electrical behavior, high photothermal conversion efficiency, and repeatable self-healing capabilities. It combines self-healing, de-icing, and lightning protection properties, making it suitable for high-power-density power electronic device packaging, tensile conductor insulation coatings, and dielectric layers in energy harvesting devices. During long-term operation, it can mitigate the effects of extreme weather conditions, such as icing disasters leading to ice accumulation on the coating surface, causing electric field distortion, ice discharge, and accelerated insulation performance degradation. Furthermore, this preparation method is simple to operate, highly operable, and reproducible.

[0025] As an optional implementation, the hard segment content in the polyurethane is 33-37 wt%; in this invention, the hard segment content HS% is calculated using the following formula:

[0026] Wherein, W1 refers to the mass of the added linear small molecule diol, W2 refers to the mass of the added diisocyanate, and W3 refers to the mass of the added polyether diol. As an example, the hard segment content HS% in the polyurethane is 33%, 34%, 35%, 36%, 37%, or any value within the above range.

[0027] As an optional implementation, the polyether diol is polypropylene glycol and / or polyethylene glycol; optionally, the molecular weight of polypropylene glycol is 1100 and the molecular weight of polyethylene glycol is 450. As an optional implementation, the diisocyanate includes 4,4'-methylene diphenyl diisocyanate.

[0028] As an optional implementation, the linear small molecule diol includes 1,4-butanediol. It should be noted that the proportions of the polyether diol, linear small molecule diol, and diisocyanate can be determined by the hard segment content in the polyurethane.

[0029] As an optional implementation, the graphene oxide accounts for 1.3% of the total mass of the graphene oxide, diisocyanate, and linear small molecule diol; the present invention regulates the amount of graphene oxide to better balance self-healing performance and nonlinear electrical properties. As an optional implementation, the temperature of the first reaction is 65-70℃, and the time is 3-4 hours. As an optional implementation, the temperature of the second reaction is 65-70°C, and the time is 2-3 hours; As an optional implementation, the stirring speed is 390-400 rpm; As an optional implementation, the temperature of the third reaction is 65-70°C and the time is 2-3 hours.

[0030] As an optional implementation, graphene oxide is mixed with a solvent, and then dispersed by stirring and ultrasonication to obtain a dispersion containing graphene oxide; wherein the solvent is a type of solvent known in the art, including but not limited to DMF.

[0031] Preferably, the ultrasound duration is 2-2.5 hours; Preferably, the ultrasound duration is 1-1.2 hours. Secondly, embodiments of the present invention provide coatings prepared by the above method.

[0032] Thirdly, embodiments of the present invention provide an apparatus comprising a substrate and a coating disposed on the surface of the substrate, wherein the raw material of the coating comprises a paint prepared by the above-described preparation method.

[0033] As an alternative implementation, the substrate includes an insulator, a cable, or a transformer bushing; wherein, when the substrate includes a cable, the coating is located at the cable terminal or joint.

[0034] Fourthly, embodiments of the present invention provide a method for preparing the above-mentioned device, comprising coating the coating on the surface of the substrate and allowing it to stand; wherein the purpose of standing is to allow the crosslinking reaction to proceed completely.

[0035] As an optional implementation method, the settling temperature is 70°C and the time is 24-30 hours. Adjusting the settling temperature and time is beneficial for complete curing.

[0036] The raw materials used in the following examples and comparative examples are all conventional raw materials that can be obtained commercially.

[0037] Example 1 This embodiment provides a method for preparing graphene oxide-grafted polyurethane coatings, including the following steps: (1) Weigh 38 ml of dimethylformamide (DMF) and 0.005 g of graphene oxide, mix and stir for 2 h, then sonicate for 2 h to obtain a dispersion; inject the dispersion into a three-necked round-bottom flask with an anchored propeller stirrer, funnel and nitrogen inlet, heat in a water bath to 70 °C, and then slowly add 0.11252 g of 4,4'-methylene diphenyl diisocyanate during stirring. After the addition is completed, stir and react for 3 h under a nitrogen atmosphere to obtain isocyanate-grafted graphene oxide (IGO).

[0038] (2) 0.24663 g of polypropylene glycol was added to the above isocyanate-grafted graphene oxide and heated and stirred at 70°C and 400 rpm for 2 hours to form a prepolymer; 0.02031 g of 1,4-butanediol was added to the prepolymer to carry out chain extension reaction to obtain the product graphene oxide-grafted polyurethane (GGO-5).

[0039] The obtained graphene oxide-grafted polyurethane was injected into a tetrafluoroethylene mold and placed in an oven at 70°C for 48 hours to allow the solvent DMF to evaporate and the crosslinking reaction to proceed completely, thus obtaining the test sample.

[0040] Comparative Example 1 This comparative example provides a method for preparing a polyurethane coating, comprising the following steps: (1) Weigh 0.2466g of polypropylene glycol and 0.1125g of 4,4'-methylene diphenyl diisocyanate into a flask, mix them, and stir at 70℃ and 400rpm for 2h to prepare NCO end-group prepolymer. Then take 0.0203g of 1,4-butanediol and add it dropwise to the above flask and stir for 2h to prepare PU solution.

[0041] (2) Weigh 0.005g of graphene oxide and 38ml of dimethylformamide (DMF), mix them, stir for 2h and then ultrasonically disperse for 2h to obtain a dispersion. Add the dispersion to the above PU solution, stir for 1h and then ultrasonically disperse for 30min to obtain a mixture. Pour the mixture into a covered Teflon mold and evaporate at 70°C for 48h to obtain polyurethane.

[0042] Comparative Example 2 This comparative example provides a method for preparing a polyurethane coating, comprising the following steps: Weigh 0.23458 g of polypropylene glycol and 0.1 g of 4,4'-methylene diphenyl diisocyanate into a flask, mix them, and stir at 70 °C and 400 rpm for 2 h to prepare an NCO-terminated prepolymer. Then, add 0.0449 g of 1,4-butanediol dropwise to the above flask and stir for 2 h to prepare a PU solution.

[0043] Comparative Example 3 This comparative example provides a method for preparing a polyurethane coating, which is basically the same as that in Example 1. The main difference is that isophorone diisocyanate (IPDI) is used instead of 4,4'-methylene diphenyl diisocyanate. The hard segment content (HS%) in this comparative example is the same as that in Example 1. The amount of IPDI used in this comparative example is 0.1089 g, the amount of polypropylene glycol is 0.2467 g, and the amount of BDO is 0.0239 g.

[0044] Comparative Example 4 This comparative example provides a method for preparing a polyurethane coating, which is basically the same as that in Example 1, except that diethyltoluene diamine (DETDA) is used instead of 1,4-butanediol. The hard segment content (HS%) in this comparative example is the same as that in Example 1. The amount of polypropylene glycol used in this comparative example is 0.2467 g, the amount of MDI is 0.1009 g, and the amount of DETDA is 0.0319 g.

[0045] Comparative Example 5 This comparative example provides a method for preparing a graphene oxide-grafted polyurethane coating, which is basically the same as that in Example 1. In this example, IPDI is used instead of MDI, and DETDA is used instead of 1,4-butanediol. The hard segment content (HS%) in this comparative example is the same as in Example 1. The amounts of polypropylene glycol, IPDI, DETDA, and graphene oxide used in this comparative example are 0.2467 g, 0.0959 g, 0.0369 g, and 0.005 g, respectively.

[0046] Comparative Example 6 This comparative example provides a method for preparing a graphene oxide-grafted polyurethane coating, which is basically the same as that in Example 1, except that 0.001g of graphene oxide is used instead of 0.005g of graphene oxide.

[0047] Test case This test example provides the performance of the polyurethane coatings provided in the various embodiments and comparative examples, as detailed below: Test method for self-healing performance: The test samples for the examples and comparative examples were obtained according to the method described in Example 1. The sample size was 1cm × 1cm. The tensile strength of the test samples was tested. A crack was cut into the surface of the test sample using a knife, ensuring consistency in all tests; the knife size was not limited. A strength of 1W / cm² was used. 2The above cracks were repaired by irradiation with 808 nm NIR light for 30 min. After self-healing, the tensile strength was tested again. The healing efficiency = tensile strength after healing / tensile strength before healing × 100%.

[0048] The tensile strength test method includes the following steps according to GB / T 528-2009: First, prepare a dumbbell-shaped standard specimen and accurately measure its dimensions; then, condition the specimen in a standard temperature and humidity environment (e.g., 23℃, 50% humidity) for at least 16 hours; then, use a universal testing machine to stretch the specimen at a specified speed (e.g., 500 mm / min is commonly used for elastomers) until it breaks; finally, calculate the tensile strength (maximum tensile force / cross-sectional area) based on the recorded force-displacement curve.

[0049] Test method for anti-icing performance: The test samples of the examples and comparative examples were obtained according to the method of Example 1; under a light intensity of 1kW / m 2 Under a xenon lamp at a temperature of -15°C, the time required for a fixed-size ice block to form on the surface of all samples was recorded; at the same time, the time required for this ice block to melt at 0°C under the same specified illumination was also recorded.

[0050] The testing method for lightning protection performance mainly involves comparing nonlinear electrical characteristics (nonlinear coefficient, switching field strength, and saturation current density). These nonlinear electrical characteristics are evaluated through DC volume conductivity measurements. Using a three-electrode system and a digital electrometer, a stepped DC electric field ranging from 0.5 to 15 kV / mm is applied to a 200 μm thick sample. This field is maintained for 30 minutes at each voltage level to measure the steady-state conduction current, thus obtaining the current density-electric field strength (JE) relationship curve. Key parameters such as switching field strength, saturation current density, and nonlinear coefficient are directly extracted from this curve.

[0051] Table 1 Test Results

[0052] The test results above show that the present invention uses diisocyanates with symmetrical structures and containing aromatic rings, linear small molecule diols, and controls the amount of graphene oxide to enable the material to take into account self-healing properties, anti-icing properties and good nonlinear electrical properties, such as high saturation current density, low switching field strength and high nonlinear coefficient.

[0053] As seen in Comparative Examples 1-2, compared to directly blending graphene oxide with polyurethane or polyurethane, the polyurethane of this invention can take into account self-healing properties, anti-icing properties, and adaptive electrical properties.

[0054] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0055] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a graphene oxide-grafted polyurethane coating, characterized in that, Includes the following steps: (1) Prepare a dispersion containing graphene oxide; add diisocyanate to the dispersion and carry out a first reaction to obtain isocyanate-grafted graphene oxide; the diisocyanate has a symmetrical structure and has an aromatic ring; (2) The isocyanate-grafted graphene oxide is mixed with polyether diol and stirred to carry out a second reaction to form a prepolymer; (3) The prepolymer is mixed with a linear small molecule diol to carry out a third reaction; The graphene oxide accounts for 1-2% of the total mass of the graphene oxide, diisocyanate, polyether glycol and linear small molecule diol.

2. The preparation method according to claim 1, characterized in that, The hard segment content in the polyurethane is 33-37 wt%; And / or, the polyether diol is polypropylene glycol and / or polyethylene glycol; And / or, the diisocyanate includes 4,4'-methylene diphenyl diisocyanate.

3. The preparation method according to claim 1 or 2, characterized in that, The linear small molecule diols include 1,4-butanediol.

4. The preparation method according to any one of claims 1-3, characterized in that, The graphene oxide accounts for 1.3% of the total mass of the graphene oxide, diisocyanate, polyether glycol, and linear small molecule diol.

5. The preparation method according to any one of claims 1-4, characterized in that, The temperature of the first reaction is 65-70℃, and the time is 3-4 hours; And / or, the temperature of the second reaction is 65-70°C, and the time is 2-3 hours; And / or, the stirring speed is 390-400 rpm; And / or, the temperature of the third reaction is 65-70°C, and the time is 2-3 hours.

6. The preparation method according to any one of claims 1-5, characterized in that, Graphene oxide is mixed with a solvent, and then dispersed by stirring and ultrasonication to obtain a dispersion containing graphene oxide. Preferably, the ultrasound duration is 2-2.5 hours; Preferably, the ultrasound duration is 1-1.2 hours.

7. The coating prepared by the method according to any one of claims 1-6.

8. An apparatus, characterized in that, It includes a substrate and a coating disposed on the surface of the substrate, wherein the raw material of the coating includes a coating prepared by the preparation method according to any one of claims 1-6; Preferably, the substrate includes an insulator, a cable, or a transformer bushing.

9. The method for preparing the device according to claim 8, characterized in that, The coating is applied to the surface of the substrate and left to stand.

10. The preparation method according to claim 9, characterized in that, The settling temperature is 70℃, and the time is 24-30h.

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