Functionalized aluminum oxide as well as preparation method and application thereof

Abstract

The invention provides functionalized aluminum oxide as well as a preparation method and application thereof. The functionalized aluminum oxide comprises aluminum oxide and an organic modifier grafted on the surface of the aluminum oxide, the organic modifier is isocyanate covalently modified by an interface reinforcing agent, and the interface reinforcing agent comprises a sulfydryl-terminated polymer. The surface of aluminum oxide is sequentially grafted and coated with isocyanate and an interface reinforcing agent, green and efficient preparation of highly-functionalized aluminum oxide is achieved, the highly-functionalized aluminum oxide is added into a cable matrix, and the heat-conducting property and the mechanical property of the cable intermediate joint filling material are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, in particular to functionalized aluminum oxide and a preparation method and application thereof. Background Art

[0002] With the rapid development of the power industry, high-voltage cables are increasingly used in power transmission. Cable joints play a crucial role in high-voltage power transmission systems, connecting cable segments to facilitate power transmission. However, existing cable joint filling materials lack sufficient heat dissipation, making them prone to overheating, impacting the joint's current-carrying capacity and even causing fires, severely impacting the cable's service life and safety.

[0003] Cable intermediate joint filling materials are prepared from a polymer matrix material, a curing agent, and a filler. Adding a thermally conductive filler to the matrix material is the simplest and most effective method for improving its thermal conductivity. Alumina (Al2O3) has significant advantages, including high thermal conductivity (approximately 30 W / mK), good insulation, low cost, and easy processing, making it a promising material for improving the thermal conductivity of cable intermediate joint filling materials. However, the surface of unmodified Al2O3 is chemically inert and poorly dispersed in the polymer matrix. Furthermore, the poor interfacial compatibility between Al2O3 and the polymer matrix results in severe scattering of hot carriers (phonons) at the interface between Al2O3 and the matrix, leading to high interfacial thermal resistance. This significantly limits improvements in the thermal conductivity of polymer composites and limits the mechanical properties of the composites required for cable intermediate joint filling materials. Therefore, there is an urgent need to surface modify Al2O3 to enhance the interfacial affinity between Al2O3 and the polymer matrix and effectively improve the thermal and mechanical properties of cable intermediate joint filling materials.

[0004] Currently, Al2O3 surface modification methods primarily include high-temperature calcination and chemical modification. For example, invention patent CN117658186A proposes first hydrothermally reacting an aluminum-containing compound with a modifier and a pore-enlarging agent, followed by staged high-temperature calcination to obtain hydroxyl-modified alumina. Invention patent CN 118930976 A proposes reacting Al2O3 in a modification solution of a strong acid, ethanol, and the strong oxidizer potassium permanganate to obtain carboxyl-modified alumina. However, existing Al2O3 surface modification methods suffer from low surface functionalization rates, environmental concerns, and cumbersome procedures.

[0005] How to achieve the preparation of highly functionalized Al2O3 through simple and effective strategies still faces severe challenges. Summary of the Invention

[0006] The present invention aims to address the aforementioned deficiencies in the prior art by providing a functionalized alumina. By sequentially grafting an isocyanate and an interfacial enhancer onto the alumina surface, the present invention achieves the environmentally friendly and efficient preparation of highly functionalized alumina. Adding this to a cable matrix effectively improves the thermal conductivity and mechanical properties of the cable intermediate joint filler.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a functionalized alumina comprising alumina and an organic modifier grafted onto the surface of the alumina, wherein the organic modifier is an isocyanate covalently modified with an interfacial enhancer, wherein the interfacial enhancer comprises a terminal thiol polymer.

[0009] As an embodiment of the present invention, the mass ratio of the aluminum oxide to the organic modifier is 1:(0.1-2).

[0010] As an embodiment of the present invention, the mercapto-terminated polymer includes at least one of mercapto-terminated polysiloxane, mercapto-terminated polyether, and mercapto-terminated polyester.

[0011] As an embodiment of the present invention, the interface enhancer further includes amino-terminated polyether and polyester polyol, and the mass ratio of the thiol-terminated polymer, amino-terminated polyether and polyester polyol in the interface enhancer is 1: (0.1-0.5): (0.2-0.3).

[0012] As an embodiment of the present invention, the isocyanate in the isocyanate covalently modified with an interfacial enhancer includes at least one of toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl isocyanate, isophorone diisocyanate, and naphthalene diisocyanate.

[0013] The second aspect of the present invention provides a method for preparing the functionalized alumina according to the first aspect of the present invention, comprising the following steps:

[0014] S1: Alumina and isocyanate are mixed and dispersed in a polar solvent to obtain a first reaction solution, and the aluminum oxide undergoes a hydrolysis and condensation reaction to obtain primary aluminum oxide;

[0015] S2: The primary alumina and the interfacial enhancer obtained in step S1 are mixed and dispersed in a polar solvent to obtain a second reaction solution, and the functionalized alumina is obtained through a covalent polymerization reaction.

[0016] As an embodiment of the present invention, the polar solvent includes at least one of acetone, toluene, ethyl acetate, dimethylformamide, and dimethyl sulfoxide.

[0017] As an embodiment of the present invention, the temperature of the hydrolysis condensation reaction in step S1 is 40 to 90° C. and the time is 2 to 16 hours.

[0018] As an embodiment of the present invention, in the first reaction solution in step S1, the total mass concentration of aluminum oxide and isocyanate is 0.1-0.2 kg / L.

[0019] As an embodiment of the present invention, the temperature of the covalent polymerization reaction in step S2 is 60 to 95° C. and the time is 5 to 48 hours.

[0020] As an embodiment of the present invention, in the second reaction solution in step S2, the total mass concentration of the primary alumina and the interface enhancer is 0.125-0.5 kg / L.

[0021] The third aspect of the present invention provides a use of the functionalized alumina described in the first aspect of the present invention, wherein the functionalized alumina is used to prepare a filling material for an intermediate joint of a thermally conductive cable.

[0022] As an embodiment of the present invention, the thermal cable intermediate joint filling material includes the following components in parts by weight: 100 parts of cable matrix, 10 to 50 parts of the functionalized alumina described in the first aspect of the present invention, 0.1 to 2 parts of antioxidant, and 1 to 5 parts of curing agent; the cable matrix includes at least one of polyurethane resin, epoxy resin, and silicone rubber.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The modified functionalized alumina of the present invention has good dispersion stability and does not precipitate in a dimethylformamide dispersion for 72 hours. The thermal diffusion coefficient of the heat-conducting cable intermediate joint filling material prepared by applying the functionalized alumina to an organic matrix is ​​0.147 mm 2 / s and above, up to 0.178mm 2 / s; the thermal conductivity is above 0.48W / mK and can be as high as 0.71W / mK; the tensile strength is also above 14MPa and can be as high as 25MPa, indicating that it can be well dispersed in the organic matrix and can simultaneously improve the thermal conductivity and mechanical strength of the cable. DETAILED DESCRIPTION

[0025] For better explanation of the purpose, technical scheme and advantage of the present invention, the present invention will be further described below in conjunction with specific embodiment, but embodiment does not limit the present invention in any form.Unless otherwise stated, the reagent, method and equipment adopted in the present invention are conventional reagents, methods and equipment in the art.Unless otherwise stated, the reagents and materials used in the present invention are commercially available.

[0026] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0027] In the present invention, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0028] The reagents and instruments used in the present invention without indicating the manufacturer are all conventional products that can be purchased from the market.

[0029] In a first aspect of the present invention, an embodiment of the present invention provides a functionalized alumina, comprising alumina and an organic modifier grafted onto the surface of the alumina, wherein the organic modifier is an isocyanate covalently modified with an interfacial enhancer, wherein the interfacial enhancer comprises a terminal thiol polymer.

[0030] The invention uses a specific organic modifier to carry out surface graft modification on aluminum oxide, and fixes and coats the interface enhancer on the surface of aluminum oxide through covalent grafting reaction between isocyanate groups and hydroxyl groups on the surface of aluminum oxide and covalent reaction between isocyanate groups and mercapto groups.

[0031] Among the organic modifiers on the surface of alumina: 1) the isocyanate chain segment and the interface enhancer chain segment are connected by a thiourea bond. Through the combined action of covalent polarity, electrostatic interaction between molecular chains, and van der Waals force, the entanglement distribution state between the isocyanate chain segment and the interface enhancer chain segment can be improved, forming a specific thermal conductive network, and effectively improving the thermal conductivity; 2) the presence of the thiourea bond can also increase the interaction between phonons and intermolecular forces, thereby improving the thermal conductivity of alumina; 3) under the action of the isocyanate and thiourea bonds, the interface enhancer can also improve the interaction with the organic matrix, improve the dispersion performance of alumina in the organic matrix, and improve the thermal conductivity of the cable.

[0032] In some embodiments of the present invention, the mass ratio of alumina to organic modifier is 1:(0.1-2). Since the thermal conductivity of organic modifiers is significantly lower than that of inorganic alumina, and alumina is poorly compatible with organic matrices, resulting in easy agglomeration, when the mass ratio of alumina to organic modifier is controlled within this appropriate range, the dispersion of alumina can be improved while maintaining the thermal conductivity of alumina, thereby preventing agglomeration.

[0033] In some embodiments of the present invention, the thiol-terminated polymer includes at least one of thiol-terminated polysiloxane, thiol-terminated polyether, and thiol-terminated polyester. The thiol-terminated polysiloxane includes but is not limited to thiol-terminated polymethylphenylsiloxane; the thiol-terminated polyether includes but is not limited to thiol-terminated polyoxyethylene ether (structural formula H-(OCH2CH2) n -SH, polyoxyethylene ether (also known as polyethylene glycol) or its derivatives; terminal mercapto polyesters include but are not limited to terminal mercapto polycarbonate.

[0034] In some embodiments of the present invention, the interface enhancer further includes amino-terminated polyether and polyester polyol, and the mass ratio of the thiol-terminated polymer, amino-terminated polyether, and polyester polyol in the interface enhancer is 1:(0.1-0.5):(0.2-0.3). Among them, the thiol group can form a thiourea group (-NHC(O)-S-) with the isocyanate group, the amino group can form a urea group (-NH-C(O)-NH-) with the isocyanate group, and the alcoholic hydroxyl group can form a carbamate group (-NH-C(O)-O-) with the isocyanate group. Through the above groups, the reinforcing segment of the interface enhancer (such as: polyether segment, polyester segment, polysiloxane segment) is covalently grafted onto the isocyanate segment, and together with the isocyanate, it forms an organic modifier of aluminum oxide. In the organic modifier, the presence of the above-mentioned groups and the control of the proportion of each group within the above-mentioned appropriate range can further improve the mobility and orientation of the molecular chains between the isocyanate segment and the reinforcing segment in the interfacial enhancer through the mutual influence of covalent polarity and other effects, thereby further improving the thermal conductivity of the functionalized alumina in the polymer matrix.

[0035] In some embodiments of the present invention, the amino-terminated polyether includes but is not limited to amino-terminated polyoxyethylene ether (PEA); the polyester polyol includes but is not limited to polycarbonate diol (PCDL).

[0036] In some embodiments of the present invention, the isocyanate in the isocyanate covalently modified with an interface enhancer comprises at least one of toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI), polymethylene polyphenyl isocyanate (PAPI), isophorone diisocyanate (IPDI), and naphthalene diisocyanate (NDI). The isocyanate selected in the present invention contains unit structures such as alkyl, benzene, or alicyclic rings, which directly bind to the hydroxyl groups on the surface of the alumina, thereby increasing the activity of the active sites and facilitating further bonding of the isocyanate with the interface enhancer.

[0037] In a second aspect of the present invention, an embodiment of the present invention further provides a method for preparing the functionalized alumina described in the first aspect of the present invention, comprising the following steps:

[0038] S1: Alumina and isocyanate are mixed and dispersed in a polar solvent to obtain a first reaction solution, and the aluminum oxide undergoes a hydrolysis and condensation reaction to obtain primary aluminum oxide;

[0039] S2: The primary alumina and the interfacial enhancer obtained in step S1 are mixed and dispersed in a polar solvent to obtain a second reaction solution, and the functionalized alumina is obtained through a covalent polymerization reaction.

[0040] In the present invention, alumina undergoes surface hydrolysis to release hydroxyl reactive groups, which can undergo a condensation reaction with isocyanate groups. This covalent action imparts abundant reactive isocyanate groups to the alumina surface. These reactive isocyanate groups then covalently react with the end groups in the interfacial enhancer, securing a reinforcing layer containing a long-chain polymer to the alumina surface. This ultimately yields functionalized alumina with high thermal conductivity and high dispersibility. Furthermore, the present invention employs mild reaction conditions, eliminates the need for complex equipment and processes, offers low production costs, and is environmentally friendly, suitable for large-scale industrial production, and conducive to widespread application.

[0041] In some embodiments of the present invention, the polar solvent includes at least one of acetone, toluene, ethyl acetate (MEE), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).

[0042] In some embodiments of the present invention, the hydrolysis condensation reaction in step S1 is carried out at a temperature of 40 to 90° C. and for a time of 2 to 16 hours.

[0043] In some embodiments of the present invention, in step S1 , the total mass concentration of aluminum oxide and isocyanate in the first reaction solution is 0.1-0.2 kg / L.

[0044] In some embodiments of the present invention, the temperature of the covalent polymerization reaction in step S2 is 60-95° C. and the time is 5-48 hours.

[0045] In some embodiments of the present invention, in the second reaction solution in step S2, the total mass concentration of the primary alumina and the interface enhancer is 0.125-0.5 kg / L.

[0046] In some embodiments of the present invention, the particle size D of the aluminum oxide is V 50 is 0.5~50μm.

[0047] In a third aspect of the present invention, embodiments of the present invention further provide applications of the functionalized alumina described in the first aspect of the present invention. Specifically, the functionalized alumina is used to prepare a filling material for an intermediate joint of a thermally conductive cable.

[0048] In some embodiments of the present invention, the thermal cable intermediate joint filling material includes the following components in parts by weight:

[0049] 100 parts of cable matrix, 10 to 50 parts of the functionalized alumina according to any one of claims 1 to 5, 0.1 to 2 parts of an antioxidant, and 1 to 5 parts of a curing agent; the cable matrix comprises at least one of polyurethane resin, epoxy resin, and silicone rubber.

[0050] The present invention further combines functionalized alumina with a polymer matrix, an antioxidant, and a curing agent to produce a high-thermal-conductivity cable intermediate joint filler. Compared to the pre-modified material, the functionalized alumina is more evenly dispersed within the polymer matrix, reducing interfacial thermal resistance and creating a more efficient heat conduction path. Furthermore, the polymer reinforcement layer of the functionalized alumina interpenetrates with the polymer matrix, forming abundant molecular chain entanglements, enhancing interfacial bonding strength without debonding, and significantly improving mechanical properties.

[0051] The following are specific embodiments of the present invention.

[0052] Examples 1 to 28, Comparative Examples 1 to 3

[0053] A series of functionalized aluminas are provided, which are prepared according to a method comprising the following steps, wherein the specific preparation process parameters are detailed in Tables 1 and 2:

[0054] S1: Alumina and isocyanate are mixed and dispersed in a polar solvent to obtain a first reaction solution, and the aluminum oxide undergoes a hydrolysis and condensation reaction to obtain primary aluminum oxide;

[0055] S2: The primary alumina and the interfacial enhancer obtained in step S1 are mixed and dispersed in a polar solvent to obtain a second reaction solution, and the functionalized alumina is obtained through a covalent polymerization reaction.

[0056] It should be noted that in Table 1, the particle size of aluminum oxide refers to D V 50 particle size, obtained by testing with a particle size tester.

[0057] Wherein, the interface enhancer is selected from the following raw materials:

[0058] Thiol-modified polycarbonate (PMAC-Thiol): average molecular weight 2000 g / mol, purchased from Xi'an Qiyue Biotechnology Co., Ltd.

[0059] Amino-terminated polyether: CAM-2070, average molecular weight 2000 g / mol, purchased from Chenhua Co., Ltd.

[0060] Polycarbonate diol (PCDL): T6002, average molecular weight 2000 g / mol, purchased from Asahi Chemical Industry Co., Ltd.

[0061] Table 1

[0062]

[0063] Table 2

[0064]

[0065] In Table 2, 1) the parameters not listed are the same as those in Example 3; 2) the alumina modified with the silane coupling agent KH550 in Comparative Example 3 was prepared by immersing 1 kg of alumina having an average particle size of 20 μm in a 5 wt% KH550 aqueous solution and reacting at 60° C. for 5 h.

[0066] Performance Testing

[0067] The dispersion stability and application performance of the functionalized alumina prepared in the above examples and comparative examples were tested, wherein alumina without any modification (average particle size of 20 μm) was used as a blank control group:

[0068] 1. Dispersion Stability: The functionalized alumina prepared in the above examples and comparative examples, as well as unmodified alumina, were added to dimethylformamide to prepare a 3 wt% dispersion. The time (in hours) for the alumina to precipitate was observed and recorded. The test results are shown in Table 3.

[0069] 2. The functionalized alumina prepared in the above examples and comparative examples, as well as unmodified alumina, were added to an organic matrix to prepare a thermal cable intermediate joint filling material. The thermal conductivity and mechanical properties of the thermal cable intermediate joint filling material were tested. The thermal cable intermediate joint filling material was prepared according to a method comprising the following steps:

[0070] By weight, 100 parts of silicone rubber (Q-5000, viscosity of 5000 mPa·s at 25° C., vinyl content of 0.4 mol%, purchased from Guangdong Qianfu New Materials Co., Ltd.), 20 parts of functionalized alumina prepared in the above embodiments and comparative examples, 0.5 parts of antioxidant 1010, 0.5 parts of antioxidant 168, and 5 parts of curing agent (platinum curing agent DM-660, purchased from Dongguan Zhongzhan Silicone Materials Co., Ltd.) were thoroughly stirred and mixed, and then poured into a customized mold and vacuum degassed at 40° C. for 10 hours to obtain a thermal cable intermediate joint filling material.

[0071] 2.1 Thermal conductivity test

[0072] Use a laser thermal conductivity meter to test the thermal diffusivity and thermal conductivity (also known as thermal conductivity) of the filling material of the intermediate joint of the thermal cable according to the GB / T42919.4-2023 standard;

[0073] 2.2 Mechanical properties test

[0074] A universal testing machine was used to test the tensile strength and elongation at break of the filling material of the intermediate joint of the thermal cable according to the GB / T1040.1-2018 standard. The test temperature was 25°C and the tensile rate was 50 mm / min.

[0075] The test results are shown in Table 3.

[0076] Table 3

[0077]

[0078]

[0079] From the above results we can see that:

[0080] The results of the examples and comparative examples show that the present invention achieves the green and efficient preparation of highly functionalized alumina by sequentially grafting and coating isocyanate and interfacial enhancer on the surface of alumina, and adding it to the cable matrix effectively improves the thermal conductivity and mechanical properties of the cable intermediate joint filling material.

[0081] The modified functionalized alumina has good dispersion stability and does not precipitate in dimethylformamide dispersion for 72 hours. The thermal diffusion coefficient of the thermal conductive cable intermediate joint filling material prepared by applying it to an organic matrix is ​​0.147 mm 2 / s and above, up to 0.178mm 2 / s; the thermal conductivity is above 0.48W / mK and can be as high as 0.71W / mK; the tensile strength is also above 14MPa and can be as high as 25MPa, indicating that it can be well dispersed in the organic matrix and can simultaneously improve the thermal conductivity and mechanical strength of the cable.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A functionalized alumina, characterized in that The invention comprises aluminum oxide and an organic modifier grafted on the surface of the aluminum oxide, wherein the organic modifier is isocyanate covalently modified by an interface enhancer, wherein the interface enhancer comprises a terminal mercapto polymer.

2. The functionalized alumina according to claim 1, characterized in that The mass ratio of the aluminum oxide to the organic modifier is 1:(0.1-2).

3. The functionalized alumina according to claim 1, characterized in that The mercapto-terminated polymer includes at least one of mercapto-terminated polysiloxane, mercapto-terminated polyether, and mercapto-terminated polyester.

4. The functionalized alumina according to claim 1, characterized in that The interface enhancer further comprises amino-terminated polyether and polyester polyol, and the mass ratio of the thiol-terminated polymer, amino-terminated polyether and polyester polyol in the interface enhancer is 1:(0.1-0.5):(0.2-0.3).

5. The functionalized alumina according to claim 1, characterized in that The isocyanate in the isocyanate covalently modified with an interfacial enhancer includes at least one of toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl isocyanate, isophorone diisocyanate, and naphthalene diisocyanate.

6. The method for preparing functionalized alumina according to any one of claims 1 to 5, characterized in that: The steps include: S1: Alumina and isocyanate are mixed and dispersed in a polar solvent to obtain a first reaction solution, and the aluminum oxide undergoes a hydrolysis and condensation reaction to obtain primary aluminum oxide; S2: The primary alumina and the interfacial enhancer obtained in step S1 are mixed and dispersed in a polar solvent to obtain a second reaction solution, and the functionalized alumina is obtained through a covalent polymerization reaction.

7. The method for preparing functionalized alumina according to claim 6, wherein: The polar solvent includes at least one of acetone, toluene, ethyl acetate, dimethylformamide, and dimethyl sulfoxide.

8. The method for preparing functionalized alumina according to claim 6, wherein: Satisfy at least one of the following characteristics: (1) The hydrolysis condensation reaction in step S1 is carried out at a temperature of 40 to 90° C. and for a time of 2 to 16 hours; (2) In the first reaction solution in step S1, the total mass concentration of aluminum oxide and isocyanate is 0.1 to 0.2 kg / L; (3) The covalent polymerization reaction in step S2 is carried out at a temperature of 60 to 95° C. and for a time of 5 to 48 hours; (4) In the second reaction solution in step S2, the total mass concentration of the primary alumina and the interface enhancer is 0.125-0.5 kg / L.

9. Use of the functionalized alumina according to any one of claims 1 to 5, characterized in that: The functionalized alumina is used for preparing a filling material for a middle joint of a heat-conducting cable.

10. The use of the functionalized alumina according to claim 9, characterized in that: The thermal cable intermediate joint filling material comprises the following components in parts by weight: 100 parts of cable matrix, 10 to 50 parts of the functionalized alumina according to any one of claims 1 to 5, 0.1 to 2 parts of an antioxidant, and 1 to 5 parts of a curing agent; the cable matrix comprises at least one of polyurethane resin, epoxy resin, and silicone rubber.

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