Halloysite-loaded titanium dioxide composite modified polyurea as well as preparation method and application thereof

Abstract

The invention discloses halloysite-loaded titanium dioxide composite modified polyurea as well as a preparation method and application thereof, and belongs to the technical field of insulating paints.The preparation method comprises the steps that titanium dioxide nanoparticles grow on the surfaces of halloysite nanotubes in situ through a controllable hydrolysis reaction of tetrabutyl titanate and glacial acetic acid in an ethanol system, and TiO2-HNTs powder is prepared; the preparation method comprises the following steps: copolymerizing polydimethylsiloxane and isophorone diisocyanate to form an isocyanate-terminated prepolymer, and further carrying out chain extension reaction on the isocyanate-terminated prepolymer and 1, 6-hexamethylenediamine to synthesize a polyurea copolymer; the TiO2-HNTs powder is dispersed in the polyurea copolymer and cured to obtain halloysite loaded titanium dioxide composite modified polyurea, and the material has excellent ultraviolet aging resistance and electrical stability and can meet long-period reliable operation of power transmission lines.

Description

Technical Field

[0001] The present invention belongs to the technical field of insulating coatings, and particularly relates to halloysite-supported titanium dioxide composite modified polyurea and its preparation method and application. Background Art

[0002] As an important part of the power system, transmission lines are long-term exposed to the outdoor environment and are vulnerable to various factors. In recent years, with the coordinated advancement of ecological restoration and power grid construction, the intersection between the bird activity area and the transmission line has been continuously increasing. Line tripping caused by bird body short-circuit and bird droppings flashover has become the third largest line fault factor after lightning strike and external force damage. In addition, faults such as line wind deviation and foreign object hanging caused by extreme strong wind weather occur frequently. The root cause is that the air insulation margin between the cross-arm and the conductor is insufficient: when a conductive foreign object invades the gap and causes electric field distortion, the short-circuit current may bypass the insulator and break down the air gap, resulting in line tripping.

[0003] The local insulation spraying technology provides a feasible solution to the above-mentioned faults. By spraying an insulating material on the metal exposed points such as the cross-arm and foot studs of the tower, the gap between the cross-arm and the conductor is changed from the original air insulation to a combined insulation mode of "insulating material + air", effectively increasing the insulation margin of the tower gap and reducing the short-circuit faults caused by foreign objects invading the tower gap.

[0004] Currently, the research and application of local insulation spraying materials mainly focus on the following three types: (1) Room temperature vulcanized silicone rubber (RTV). However, RTV materials have problems such as uneven coating quality and long curing time in actual application, resulting in the coating thickness being difficult to meet the insulation requirements of high-voltage towers. In addition, the hydrophobic performance of RTV materials under long-term ultraviolet aging conditions also fails to reach the actual application standard. (2) Room temperature curing epoxy resin. However, the three-dimensional cross-linked network structure formed during the curing process of this material leads to insufficient toughness and the coating is prone to brittle fracture. Its bonding strength also decreases significantly with the increase of the curing degree. (3) Spraying type polyurea resin (PU). Due to its characteristics such as rapid curing and high mechanical strength, it can shorten the line power outage time caused by material spraying construction and form a coating with a controllable thickness, and at the same time can also meet the strength requirements for operation and maintenance personnel to step on the tower. In recent years, it has gradually become a research hotspot in the field of local insulation spraying materials.

[0005] Polyurea (PU) is a block copolymer formed by the cross-linking polymerization reaction of an isocyanate semi-prepolymer (Component A) and an amine compound (Component B). In its molecular structure, polar urea groups form hard segment microdomains, while the flexible macromolecular main chain constitutes soft segment microdomains. This microphase separation structure endows the material with excellent thermodynamic properties. In the application of overhead transmission line projects, the insulating material needs to withstand the multi-factor coupling effect of the outdoor environment for a long time. In addition to the basic mechanical strength and thermal stability, the electrical aging characteristics and ultraviolet radiation (UV) resistance of the local insulating material are the core indicators affecting the insulation reliability of the line. However, the ultraviolet stability defect of PU materials limits their application: the mechanical property loss rate of pure PU exceeds 50% after 72 hours of ultraviolet (UV) irradiation. In addition, the evolution law of its electrical properties under ultraviolet light aging conditions is not clear, resulting in a blind area in the evaluation of insulation reliability.

[0006] To improve the ultraviolet stability of PU materials, existing technologies mostly use nano-metal oxides (such as TiO2) for modification. However, the dispersion state of nano-fillers will directly affect the modification effect, and their agglomeration phenomenon will lead to the deterioration of the key properties of the material. Existing modification strategies (such as acid / alkali treatment, multi-step processes) have problems such as complex processes and the need for strongly corrosive reagents, and it is difficult to meet the requirements of green chemistry. Research shows that silicate clay minerals with tubular and other structures can effectively solve the agglomeration problem of nano-metal oxides as negative carriers. Silicate clay minerals represented by halloysite nanotubes (HNTs) have a crystal structure in which silicon-oxygen tetrahedral sheets and aluminum-oxygen octahedral sheets form a layered stacking structure by sharing oxygen atoms. This special configuration makes the adjacent layers mainly form weak interactions through hydrogen bonds and van der Waals forces, showing good dispersion performance in the organic polymer matrix. More importantly, such natural nano-clays not only have the economic advantages of rich reserves and low cost, but their unique structural stability and surface modifiability also make them ideal fillers for functional PU composites. However, the influence of HNTs loaded with nano-TiO2 on the ultraviolet aging performance of PU has not been systematically studied, especially the evolution of the electrical properties, hydrophobic characteristics and interface regulation mechanism of the composite coating still lack scientific basis. Therefore, it is urgent to develop a PU composite coating based on green dispersion technology and interface regulation optimization to improve its anti-ultraviolet aging ability and electrical stability, so as to meet the requirements of long-term reliable operation of transmission lines. Summary of the Invention

[0007] To solve the above technical problems, the present invention proposes a halloysite-supported titanium dioxide composite modified polyurea and its preparation method and application. This material has excellent anti-ultraviolet aging performance and electrical stability, and can meet the long-term reliable operation of transmission lines.

[0008] To achieve the above object, the present invention provides a preparation method of halloysite-supported titanium dioxide composite modified polyurea. Through the controllable hydrolysis reaction of tetrabutyl titanate and glacial acetic acid in an ethanol system, titanium dioxide nanoparticles are in-situ grown on the surface of halloysite nanotubes to prepare TiO2-HNTs powder; An isocyanate-terminated prepolymer is formed by copolymerizing polydimethylsiloxane and isophorone diisocyanate, and further chain-extended with 1,6-hexanediamine to synthesize a polyurea copolymer; The TiO2-HNTs powder is dispersed in the polyurea copolymer and cured to obtain halloysite-supported titanium dioxide composite modified polyurea.

[0009] Further, the mass ratio of the TiO2-HNTs powder to the polyurea copolymer is 2-10:100.

[0010] Even further, the mass ratio of the TiO2-HNTs powder to the polyurea copolymer is 4:100.

[0011] Further, the method for in-situ growing titanium dioxide nanoparticles on the surface of halloysite nanotubes through the controllable hydrolysis reaction of tetrabutyl titanate and glacial acetic acid in an ethanol system includes: At room temperature, tetrabutyl titanate, glacial acetic acid and absolute ethanol are mixed and stirred until a transparent sol is formed; halloysite nanotubes are added to the sol system and stirring is continued; a mixed solution composed of deionized water and absolute ethanol is slowly added dropwise, stirred and aged, and then filtered; the filtered product is washed with excess absolute ethanol and deionized water and dried to obtain the TiO2-HNTs powder.

[0012] Further, the mass ratio of tetrabutyl titanate to halloysite nanotubes is 102:250.

[0013] Further, the method for forming an isocyanate-terminated prepolymer by copolymerizing polydimethylsiloxane and isophorone diisocyanate and further chain-extending with 1,6-hexanediamine to synthesize a polyurea copolymer includes: Polydimethylsiloxane and isophorone diisocyanate are dissolved in tetrahydrofuran and stirred for a pre-reaction under a nitrogen atmosphere to obtain a pre-reaction solution; 1,6-hexanediamine is dissolved in isopropanol and slowly added dropwise to the pre-reaction solution, and the reaction gives a polyurea copolymer.

[0014] Further, the mass ratio of polydimethylsiloxane, isophorone diisocyanate and 1,6-hexanediamine is 300:444:220.

[0015] Further, the method for dispersing the TiO2-HNTs powder in the polyurea copolymer and curing to obtain halloysite-supported titanium dioxide composite modified polyurea includes: Disperse the TiO2-HNTs powder ultrasonically in a solution composed of isopropanol and tetrahydrofuran, add it to the polyurea copolymer system, stir, and then dry it under vacuum to obtain the halloysite-supported titanium dioxide composite modified polyurea.

[0016] The present invention also provides a halloysite-supported titanium dioxide composite modified polyurea, which is prepared by the preparation method of the halloysite-supported titanium dioxide composite modified polyurea described above.

[0017] The present invention also provides an application of the halloysite-supported titanium dioxide composite modified polyurea, which is applied to local insulation spraying of transmission lines.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects: The present invention has carried out research on the performance influence of polyurea composite coatings before and after ultraviolet aging with different contents of halloysite nanotubes supported titanium dioxide. The structure and element distribution of TiO2-HNTs were analyzed by X-ray polycrystalline diffraction, scanning transmission electron microscopy and energy dispersive spectroscopy. Combining with the ultraviolet degradation effect, the ultraviolet shielding effect of TiO2-HNTs / PU was analyzed. The changes in the molecular structure and surface morphology of TiO2-HNTs / PU composite materials before and after ultraviolet aging were tested by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, scanning electron microscopy and differential scanning calorimetry, and the hydrophobic and electrical properties of the materials were evaluated.

[0019] The present invention first proposes to use halloysite nanotubes as a carrier to load titanium dioxide to form a TiO2-HNTs composite filler. The tubular structure and surface characteristics of HNTs effectively solve the agglomeration problem of nano-TiO2, and at the same time utilize its high specific surface area and ultraviolet reflection / scattering effect to improve the ultraviolet shielding performance of polyurea.

[0020] The present invention determines through systematic experiments that the optimal addition ratio of TiO2-HNTs is 4 wt%, achieving a balance among ultraviolet shielding, dielectric properties, thermal stability and hydrophobicity. At low addition amounts, the ultraviolet shielding effect of the filler dominates, delaying the photo-degradation of the polyurea molecular chain; at high addition amounts, the photocatalytic effect of TiO2 is inhibited, avoiding performance deterioration.

[0021] The present invention develops a mild preparation method without strong acids and bases, and realizes the uniform distribution of TiO2-HNTs in the polyurea matrix through ultrasonic dispersion and planetary stirring technology. The process is simple and environmentally friendly.

[0022] After 300 hours of ultraviolet aging, the breakdown strength reduction (16.1%) of the 4 wt% THPU composite material prepared by the present invention is significantly lower than that of pure PU (23.9%), the dielectric constant increases by 76.4%, and the hydrophobic angle remains > 110°. The thermal stability (melting peak > 370 °C) and dielectric properties (low loss increment) of the material are superior to those of RTV, epoxy resin, and pure PU in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 are the microscopic morphology diagrams of TiO2, HNTs, and TiO2-HNTs; among them, Figure 1 in (a) are the XRD patterns of TiO2, HNTs, and TiO2-HNTs; Figure 1 in (b) is the EDS pattern of TiO2-HNTs; Figure 2 is the microscopic morphology characterization diagram of TiO2-HNTs; among them, Figure 2 in (a) and (b) are the STEM images of TiO2-HNTs; Figure 2 in (c) is the HAADF-STEM image of TiO2-HNTs; Figure 2 in (d), (e), (f), and (g) are the energy spectrum diagrams of TiO2-HNTs (Al, Cyan); Figure 3 are the FTIR spectra of PU and THPU materials at different aging times; among them, Figure 3 in (a), (b), (c), (d), (e), and (f) are the FTIR spectra of PU, THPU2, THPU4, THPU6, THPU8, and THPU10 in sequence; Figure 4 are the ultraviolet aging performance characterization diagrams of PU and THPU materials; among them, Figure 4 in (a) is the UV-VIS spectrum before ultraviolet aging, Figure 4 in (b) is the UV-VIS spectrum after 300 h of ultraviolet aging, Figure 4 in (c) is the band gap energy spectrum diagram before ultraviolet aging, Figure 4 in (d) is the band gap energy spectrum diagram after 300 h of ultraviolet aging; Figure 5DSC spectra of PU and THPU materials; among them, Figure 5 in (a) is the DSC spectrum before ultraviolet aging, Figure 5 in (b) is the DSC spectrum after 300 h of ultraviolet aging; Figure 6 SEM spectra of PU and THPU materials under different ultraviolet aging times; Figure 7 Contact angle diagrams of PU and THPU materials under different ultraviolet aging times; among them, Figure 7 in (a) is the contact angle diagram before ultraviolet aging, Figure 7 in (b) is the contact angle diagram after 100 h of ultraviolet aging, Figure 7 in (c) is the contact angle diagram after 200 h of ultraviolet aging, Figure 7 in (d) is the contact angle diagram after 300 h of ultraviolet aging; Figure 8 Dielectric constant and dielectric loss spectra of PU and THPU materials under different aging times; among them, Figure 8 in (a) is the dielectric constant spectrum before ultraviolet aging, Figure 8 in (b) is the dielectric constant spectrum after 300 h of ultraviolet aging, Figure 8 in (c) is the dielectric loss spectrum before and after ultraviolet aging; Figure 9 Weibull distribution curves of breakdown strength under different aging times; among them, Figure 9 in (a) is the Weibull distribution curve of breakdown strength before ultraviolet aging, Figure 9 in (b) is the Weibull distribution curve of breakdown strength after 100 h of ultraviolet aging, Figure 9 in (c) is the Weibull distribution curve of breakdown strength after 200 h of ultraviolet aging, Figure 9 in (d) is the Weibull distribution curve of breakdown strength after 300 h of ultraviolet aging. Detailed implementation mode

[0025] Now, various exemplary implementation modes of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0026] It should be understood that the terms described in the present invention are only for describing specific implementation modes and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0027] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although only preferred methods and materials are described in this invention, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0028] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the specification of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of this invention are obvious to those skilled in the art. The specification and examples of this invention are merely exemplary.

[0029] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0030] Parameters and sources of specific chemical substances are used.

[0031] Isophorone diisocyanate (IPDI), purity 99%; isopropyl alcohol (IPA), purity 99.5%; tetrahydrofuran (THF), purity 99%; tetrabutyl titanate (TBT), purity 99%; glacial acetic acid, purity 99.5%; absolute ethanol, purity 99.5%; the above reagents were all purchased from Shanghai Macklin Biochemical Co., Ltd.; deionized water, self-made in the laboratory; poly(dimethylsiloxane), bis(3-aminopropyl) terminated (PDMS), number-average molecular weight (Mn) 3000, purchased from Tianjin Xiensi Biochemical Technology Co., Ltd.; 1,6-hexanediamine (HDMA), purity 99%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; halloysite nanotubes (HNTs), purity 97%, particle size 2 - 3 μm, purchased from Jiangxi Dishi Mineral Fiber Technology Co., Ltd.

[0032] Example 1 (1) Preparation of TiO2-HNTs Under room temperature conditions, 1.02 g of TBT, 5 mL of glacial acetic acid and 20 mL of absolute ethanol solution were mixed and stirred for 10 min to form a transparent sol; 2.5 g of HNTs was added to the sol system and stirring was continued for 1 h; 30 mL of a mixed solution with a volume ratio (deionized water: absolute ethanol) = 1:2 was slowly added dropwise (the dropping rate was 1 mL / min), stirred and aged for 24 h, and then filtered; the filtered product was washed with excessive absolute ethanol and deionized water, transferred to an oven and dried at 60 °C to obtain HNTs-supported TiO2 powder (TiO2-HNTs).

[0033] (2)Preparation of TiO2-HNTs / PU 3 g of PDMS and 4.44 g of IPDI were dissolved in 30 mL of THF, and pre-reacted under a nitrogen atmosphere (30 °C) with stirring for 0.5 h to obtain a pre-reaction solution; 2.2 g of HDMA was dissolved in 30 mL of IPA and slowly added dropwise to the above pre-reaction solution; the reaction was carried out at 80 °C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0034] Based on the mass of PU, 2 wt% of TiO2-HNTs powder was weighed, ultrasonically dispersed in 10 mL of a solution with a volume ratio (IPA: THF) = 1:1, the TiO2-HNTs dispersion was added to the polyurea copolymer system, and stirred with a planetary stirrer at 600 r / min for 10 min. Finally, it was poured into a polytetrafluoroethylene mold and vacuum dried (50 °C) to obtain a TiO2-HNTs / PU sample sheet with a thickness of 0.2 mm, where the wt% of TiO2-HNTs in TiO2-HNTs / PU was 2%, denoted as THPU2.

[0035] Example 2 (1)Preparation of TiO2-HNTs Under room temperature conditions, 1.02 g of TBT, 5 mL of glacial acetic acid and 20 mL of absolute ethanol solution were mixed and stirred for 10 min to form a transparent sol; 2.5 g of HNTs was added to the sol system and stirring was continued for 1 h; 30 mL of a mixed solution with a volume ratio (deionized water: absolute ethanol) = 1:2 was slowly added dropwise (the dropping rate was 1 mL / min), stirred and aged for 24 h, and then filtered; the filtered product was washed with excessive absolute ethanol and deionized water, transferred to an oven and dried at 60 °C to obtain HNTs-supported TiO2 powder (TiO2-HNTs).

[0036] (2)Preparation of TiO2-HNTs / PU Dissolve 3 g of PDMS and 4.44 g of IPDI in 30 mL of THF, stir and pre-react for 0.5 h under a nitrogen atmosphere (30 °C) to obtain a pre-reaction solution; dissolve 2.2 g of HDMA in 30 mL of IPA and slowly add it dropwise to the above pre-reaction solution; react at 80 °C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0037] Weigh 4 wt% of TiO₂-HNTs powder based on the mass of PU, ultrasonically disperse it in 10 mL of a solution with a volume ratio of (IPA:THF) = 1:1, add the TiO₂-HNTs dispersion to the polyurea copolymer system, stir with a planetary stirrer at 600 r / min for 10 min, and finally pour it into a polytetrafluoroethylene mold and vacuum dry it (50 °C) to obtain a TiO₂-HNTs / PU sample sheet with a thickness of 0.2 mm, where the wt% of TiO₂-HNTs in TiO₂-HNTs / PU is 4%, denoted as THPU4.

[0038] Example 3 (1) Preparation of TiO₂-HNTs At room temperature, mix 1.02 g of TBT, 5 mL of glacial acetic acid, and 20 mL of absolute ethanol solution, stir for 10 min to form a transparent sol; add 2.5 g of HNTs to the sol system and continue stirring for 1 h; slowly dropwise add (dropwise addition rate of 1 mL / min) 30 mL of a mixed solution with a volume ratio of (deionized water:absolute ethanol) = 1:2, stir and age for 24 h, and filter; wash the filtered product with excessive absolute ethanol and deionized water, transfer it to an oven and dry at 60 °C to obtain TiO₂ powder supported on HNTs (TiO₂-HNTs).

[0039] (2) Preparation of TiO₂-HNTs / PU Dissolve 3 g of PDMS and 4.44 g of IPDI in 30 mL of THF, stir and pre-react for 0.5 h under a nitrogen atmosphere (30 °C) to obtain a pre-reaction solution; dissolve 2.2 g of HDMA in 30 mL of IPA and slowly add it dropwise to the above pre-reaction solution; react at 80 °C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0040] Weigh 6 wt% of TiO₂-HNTs powder based on the mass of PU, ultrasonically disperse it in 10 mL of a solution with a volume ratio of (IPA:THF) = 1:1, add the TiO₂-HNTs dispersion to the polyurea copolymer system, stir with a planetary stirrer at 600 r / min for 10 min, and finally pour it into a polytetrafluoroethylene mold and vacuum dry it (50 °C) to obtain a TiO₂-HNTs / PU sample sheet with a thickness of 0.2 mm, where the wt% of TiO₂-HNTs in TiO₂-HNTs / PU is 6%, denoted as THPU6.

[0041] Example 4 (1) Preparation of TiO2-HNTs Under room temperature conditions, 1.02 g of TBT, 5 mL of glacial acetic acid and 20 mL of absolute ethanol solution were mixed and stirred for 10 min to form a transparent sol; 2.5 g of HNTs was added to the sol system and continuously stirred for 1 h; 30 mL of a mixed solution with a volume ratio (deionized water: absolute ethanol) = 1:2 was slowly added dropwise (the dropping rate was 1 mL / min), stirred and aged for 24 h, and then filtered; the filtered product was washed with excessive absolute ethanol and deionized water, transferred to an oven and dried at 60 °C to obtain TiO2-HNTs powder supported on HNTs (TiO2-HNTs).

[0042] (2) Preparation of TiO2-HNTs / PU 3 g of PDMS and 4.44 g of IPDI were dissolved in 30 mL of THF, and pre-reacted under nitrogen atmosphere (30 °C) for 0.5 h to obtain a pre-reacted solution; 2.2 g of HDMA was dissolved in 30 mL of IPA and slowly added dropwise to the above pre-reacted solution; reacted at 80 °C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0043] Based on the mass of PU, 8 wt% of TiO2-HNTs powder was weighed, ultrasonically dispersed in 10 mL of a solution with a volume ratio (IPA: THF) = 1:1, the TiO2-HNTs dispersion was added to the polyurea copolymer system, and stirred with a planetary stirrer at 600 r / min for 10 min, and finally poured into a polytetrafluoroethylene mold and vacuum dried (50 °C) to obtain a TiO2-HNTs / PU sample sheet with a thickness of 0.2 mm, where the wt% of TiO2-HNTs in TiO2-HNTs / PU was 8%, denoted as THPU8.

[0044] Example 5 (1) Preparation of TiO2-HNTs Under room temperature conditions, 1.02 g of TBT, 5 mL of glacial acetic acid and 20 mL of absolute ethanol solution were mixed and stirred for 10 min to form a transparent sol; 2.5 g of HNTs was added to the sol system and continuously stirred for 1 h; 30 mL of a mixed solution with a volume ratio (deionized water: absolute ethanol) = 1:2 was slowly added dropwise (the dropping rate was 1 mL / min), stirred and aged for 24 h, and then filtered; the filtered product was washed with excessive absolute ethanol and deionized water, transferred to an oven and dried at 60 °C to obtain TiO2-HNTs powder supported on HNTs (TiO2-HNTs).

[0045] (2) Preparation of TiO2-HNTs / PU Dissolve 3 g of PDMS and 4.44 g of IPDI in 30 mL of THF, and stir and pre-react for 0.5 h under a nitrogen atmosphere (30 °C) to obtain a pre-reaction solution; dissolve 2.2 g of HDMA in 30 mL of IPA and slowly add it dropwise to the above pre-reaction solution; react at 80 °C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0046] Weigh 10 wt% of TiO₂-HNTs powder based on the mass of PU, ultrasonically disperse it in 10 mL of a solution with a volume ratio of (IPA:THF) = 1:1, add the TiO₂-HNTs dispersion to the polyurea copolymer system, stir with a planetary stirrer at 600 r / min for 10 min, and finally pour it into a polytetrafluoroethylene mold and vacuum dry (50 °C) to obtain a TiO₂-HNTs / PU sample sheet with a thickness of 0.2 mm, where the wt% of TiO₂-HNTs in TiO₂-HNTs / PU is 10%, denoted as THPU10.

[0047] Comparative Example 1 Preparation of PU Dissolve 3 g of PDMS and 4.44 g of IPDI in 30 mL of THF, and stir and pre-react for 0.5 h under a nitrogen atmosphere (30 °C) to obtain a pre-reaction solution; dissolve 2.2 g of HDMA in 30 mL of IPA and slowly add it dropwise to the above pre-reaction solution; react at 80 °C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0048] Weigh and ultrasonically disperse 10 mL of a solution with a volume ratio of (IPA:THF) = 1:1, add it to the polyurea copolymer system, stir with a planetary stirrer at 600 r / min for 10 min, and finally pour it into a polytetrafluoroethylene mold and vacuum dry (50 °C) to obtain a PU sample sheet with a thickness of 0.2 mm, where the wt% of TiO₂-HNTs in PU is 0%, denoted as PU.

[0049] Comparative Example 2 Preparation of a sample without adding HNTs as a pure TiO₂ control group At room temperature, mix 1.02 g of TBT, 5 mL of glacial acetic acid, and 20 mL of absolute ethanol solution, stir for 10 min to form a transparent sol; continuously stir the sol system for 1 h; slowly add dropwise (dropwise addition rate of 1 mL / min) 30 mL of a mixed solution with a volume ratio of (deionized water:absolute ethanol) = 1:2, stir and age for 24 h, and filter; wash the filtered product with excess absolute ethanol and deionized water, transfer it to an oven and dry at 60 °C to obtain pure TiO₂ powder.

[0050] Test Example The X-ray powder diffraction (XRD) Bruker D8 Advance (Germany) was used to determine the phase composition of the TiO2-HNTs samples. The comparative samples were untreated HNTs and pure TiO2. The test angle range was 5 - 90°, and the scanning rate was 2° / min. The scanning transmission electron microscopy (STEM) JEOL JEM-F200 (Japan) was used to observe the nanoscale morphology of TiO2-HNTs. The TiO2-HNTs samples were ultrasonically dispersed in absolute ethanol for 10 min and then dropped onto a copper mesh microgrid for observation. The energy-dispersive spectroscopy (EDS) was used to analyze the elemental distribution.

[0051] The Fourier transform infrared spectroscopy (FT-IR) Thermo Fisher Nicolet Summit (US) was used to analyze the chemical structure of the polyurea composite materials. The number of scans was 32, and the resolution was 4. The ultraviolet-visible spectroscopy (UV-VIS) UV-3600plus (Japan) was used to test the absorbance of the materials, and the test wavelength range was 200 - 400 nm. The differential scanning calorimetry (DSC) NETZSCH 3500 Siruis (Germany) was used to test the thermal stability of the polyurea composite materials, and the heating rate was 20℃ / min. The scanning electron microscopy (SEM) FEI Nova NanoSEM 450 (US) was used to characterize the surface morphology of the polyurea samples.

[0052] Referring to the ISO 4892-3 standard, the polyurea samples were subjected to ultraviolet aging experiments. They were continuously irradiated with a UVA-340 ultraviolet radiation lamp for 300 hours, and the radiation intensity was 0.69W / (m 2 ×nm). According to IEC 60243-1: 2013, the power frequency breakdown strength of the polyurea composite materials was tested. The positive and negative electrodes of the electrodes were spherical electrodes, and the voltage rising rate was 1 kV / s. The breakdown data was analyzed by the Weibull distribution function. The dielectric constant tester (Agilent-E4980A, US) was used to test the dielectric constant and dielectric loss angle of the materials at 40Hz - 2MHz. The test temperature was 21.6℃, and the reference standard was IEC 60250 : 1969. According to the ISO 15989:2004 test standard, a contact angle tester (SZ-CAMD33, Sunzern China) was used to test the contact angle of the samples, and the test liquid was deionized water.

[0053] The XRD characterization is as Figure 1As shown in (a), by comparing with the standard card, it can be seen that TiO2 belongs to the anatase type (JCPDS No. 29-1360), and the untreated HNTs are halloysite-7Å (JCPDS No. 09-0453). Figure 1 The energy spectrum in (b) shows that characteristic X-ray peaks corresponding to the electron transitions from the L shell to the K shell (Kα) and from the M shell to the K shell (Kβ) of titanium element appear at 4.51 keV and 4.93 keV respectively. Quantitative analysis shows that the mass fraction and atomic fraction of titanium element reach 7.93% and 3.33% respectively, confirming the presence of titanium element distribution in the prepared sample.

[0054] The microscopic morphology of TiO2-HNTs was characterized by transmission electron microscopy, as Figure 2 shown in (a). TiO2 nanoparticles with different shapes are attached to the surface of the halloysite tubular structure, showing a uniform distribution as a whole. The lattice fringes under high-resolution images show ( Figure 2 shown in (b)) that the interplanar spacings of the exposed crystal planes of TiO2 are 0.351 and 0.237 nm, corresponding to the (101) and (004) crystal planes of anatase respectively. Through Figure 2 the elements in (d), (e), (f), and (g), it is proved that the method for preparing TiO2-HNTs in the present invention is stable and feasible.

[0055] Figure 3 The Fourier transform infrared spectra of pure PU and PU composites containing different contents of TiO2-HNTs before and after the ultraviolet aging process in the whole wavelength range are shown. The characteristic absorption peaks of PU before aging are shown in Table 1 in detail. Among them, the formation of the urea C=O bond at 1635 cm -1 proves the successful preparation of PU ( Figure 3 shown in (a)).

[0056] After adding different contents of TiO2-HNTs, it is found that there is no -NCO absorption peak at 2770 cm -1 , indicating that TiO2-HNTs have no restrictive effect on the synthesis of PU. After ultraviolet light irradiation aging, the shift of the N-H bond of THPU is significantly weakened compared with that of PU, indicating that the ultraviolet shielding effect of the filler delays the partial photodegradation of the polymer.

[0057] Table 1 Characteristic absorption peaks of PU before aging

[0058] As Figure 4In (a), unmodified PU exhibits significant absorption characteristics in the ultraviolet region of 200 - 350 nm, confirming that ultraviolet radiation is the main wavelength band involved in the photodegradation of PU. In the low addition amount stage (<4 wt%), the unique cylindrical morphology (aspect ratio >20) and high specific surface area (40 - 70 m² / g) of halloysite endow the system with significant ultraviolet reflection / scattering effects, thus reducing the absorption of ultraviolet rays by the matrix; when the filler content exceeds the critical value, the inherent ultraviolet absorption characteristics of TiO2 nanoparticles gradually dominate, and its wide bandgap semiconductor characteristics (Eg = 3.2 eV) produce strong intrinsic absorption in the ultraviolet region (λ < 387 nm), resulting in an increase in the overall absorbance of the system. After 300 h of accelerated aging ( Figure 4 in (b)), the absorbance of all specimens increases in the ultraviolet light band of 200 - 400 nm, which is mainly due to the photo-dimerization and photo-cleavage effects of the materials. In addition, the characteristic absorption peaks in the short-wave region of 200 - 250 nm also show attenuation.

[0059] Estimate the bandgap energy of each composite material before and after aging through UV-VIS spectra. As can be seen from Figure 4 in (c), the bandgap energy (Eg) of PU before aging is 3.87 eV, and the initial Eg values of THPU with different TiO2-HNTs contents are distributed in the range of 3.75 - 3.99 eV. After ultraviolet aging, the energy band structure of the materials shows significant differentiation. The Eg values of PU and low-content THPU (≤6 wt%) increase by 0.02 - 0.09 eV, while the Eg values of high-content systems (THPU8, THPU10) decrease by 0.04 - 0.1 eV.

[0060] Evaluate the thermal stability of the composite materials by DSC. As can be seen from Figure 5 in (a), pure PU presents a characteristic melting peak at 380.8 °C, while the peak temperature of PU after adding TiO2-HNTs is 4.3 - 9.9 °C lower than that of pure PU. Although the introduction of TiO2-HNTs leads to detectable changes in the parameters of the endothermic peak of PU, the overall thermal performance still maintains good stability (>365 °C), confirming the applicability of TiO2-HNTs as a functional filler. The changes in the DSC curves after ultraviolet aging are shown in Figure 5 in (b). After treatment at 300 °C, all samples show a phenomenon that the endothermic peak migrates to a lower temperature, and the endothermic peak shows obvious broadening, which corresponds to the decrease in purity caused by the accumulation of degradation products inside the material. It should be noted that the peak temperature of pure PU decreases significantly by 7.3 °C, while the decrease in THPU composite materials is only 0.6 - 3.6 °C. The smaller change in the endothermic peak value of THPU indicates that the absorption and shielding of ultraviolet light by TiO2-HNTs may inhibit the photo-oxidation reaction of some carbonyl groups.

[0061] As shown inFigure 6 As shown, with the increase of the addition amount of TiO2-HNTs, rod-like structures are distributed on the material surface, and their size characteristics are consistent with the inherent particle size of HNTs. On the surfaces of THPU8 and THPU10 where TiO2-HNTs distribution can be observed, it shows that TiO2-HNTs are effectively dispersed in the PU matrix, and no significant agglomeration phenomenon is found. In addition, the surface roughness of the material before aging shows a gradual change trend of "rough-smooth-rough" with the addition of fillers.

[0062] The surface hydrophobic properties of the materials were analyzed by water contact angle. As shown in (a) of Figure 7 , the surface hydrophobic angles of PU before and after adding TiO2-HNTs are both greater than 90°. Among them, the hydrophobic angle of pure PU is 100.5°. Compared with pure PU, the change in the contact angle of the PU composite material is within ±8°. With the progress of ultraviolet aging, the hydrophobic angles of the materials increased to varying degrees at 100 h in the initial stage of aging ( Figure 7 in (b)). In this stage, the contact angle of THPU10 increased the most, from 103.7° to 124.9°, indicating a significant increase in its surface roughness. In the aging stage of 200 h ( Figure 7 in (c)), the hydrophobic angles of PU and PU composite materials (2-8 wt%) still showed an upward trend, and the increase range was between 4-9°. In addition, the hydrophobic angle of THPU10 decreased by 8.9° in the 200 h aging stage, and a similar decrease in the contact angle also occurred after 300 h of aging ( Figure 7 in (d)). Different from this, the contact angles of THPU2, THPU4 and THPU6 showed a continuous upward trend, and the change in the contact angle of THPU2 was the largest, rising from 103.1° measured in the 200 h aging stage to 121.9°. This increase in the contact angle means that the absorption and shielding of ultraviolet light by the fillers slow down the degradation rate of the materials, and still can maintain the Cassie state of the materials after 300 h, making the surface more hydrophobic.

[0063] Figure 8 In (a) of

[0064] shows the evolution law of the dielectric constant of the composite material with frequency before aging. All materials showed a two-stage change trend of dielectric constant fluctuation in the low-frequency electric field (<1 kHz) and stability and gradual decrease in the medium-high frequency region (>1 kHz).

[0065] After 300 h of ultraviolet aging, the dielectric constants of all samples showed a downward trend ( Figure 8 as shown in (b) of

[0066] Figure 8 ). It is worth noting that the dielectric constant of THPU10 decreased by 50% in the frequency band >1 kHz (from 4 to 2). In contrast, the dielectric constant of THPU6 decreased less, and it was still higher than that of pure PU after aging, indicating that an appropriate amount of TiO2-HNTs can delay the deterioration of the matrix through ultraviolet shielding, and its own high dielectricity also has a positive effect on the dielectric properties of PU.

[0067] Table 2 lists the dielectric loss tangent values of PU and THPU before and after aging at 50 Hz. The increase in dielectric loss of THPU6 after aging was the smallest, with an increase of only 0.00329, while the dielectric loss of THPU2 increased sharply by 263.7% after aging.

[0068] Table 2 Dielectric Loss of PU and PU Composites at 50 Hz

[0069] In the actual operating environment of transmission lines, extreme conditions such as tip discharge may occur. Therefore, a sphere-sphere electrode system was used to simulate extremely non-uniform electric field conditions to evaluate the insulation reliability of polyurea and its composites under power frequency alternating current fields. As Figure 9 shown in (a) of

[0070] Before aging, the breakdown voltage of the composite material was stable between 80 - 92 kV / mm, and the overall trend was similar to that of the dielectric constant. When the addition amount of TiO2-HNTs was 2 wt%, the breakdown voltage of the PU composite material decreased from 88.8 kV / mm to 81.8 kV / mm, and it maintained at around 90 kV / mm when the addition amount was 4 - 8 wt% and then decreased to 88.4 kV / mm (10 wt%). The uneven distribution of 2 wt% filler led to the formation of thermal breakdown. While the PU composite material showed a relatively high breakdown strength at the addition amount of 4 - 8 wt%.

[0071] The experimental results show that TiO2-HNTs / PU with a content below 6 wt% delays the degradation of the PU molecular chain due to the ultraviolet shielding of the filler and negligible photocatalytic effect, while maintaining the thermal stability (melting peak > 370 °C) and hydrophobicity (contact angle > 110 °) of the material. Among them, the best performance is shown at an addition amount of 4 wt%, with the dielectric constant increased by 76.4%, the breakdown strength decreased by 16.1% after 300 hours of ultraviolet aging, lower than 23.9% of PU, and the increase in dielectric loss is only 0.01332.

[0072] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of halloysite-supported titanium dioxide composite modified polyurea, characterized in that, TiO2-HNTs powder was prepared by in-situ growth of titanium dioxide nanoparticles on the surface of halloysite nanotubes through a controllable hydrolysis reaction of tetrabutyl titanate and glacial acetic acid in an ethanol system. A polyurea copolymer was synthesized by copolymerizing polydimethylsiloxane and isophorone diisocyanate to form an isocyanate-terminated prepolymer, and further performing a chain extension reaction with 1,6-hexanediamine. The TiO2-HNTs powder was dispersed in the polyurea copolymer and cured to obtain halloysite-supported titanium dioxide composite modified polyurea.

2. The preparation method of halloysite-supported titanium dioxide composite modified polyurea according to claim 1, characterized in that, The mass ratio of the TiO2-HNTs powder to the polyurea copolymer is 2-10:

100.

3. The preparation method of halloysite-supported titanium dioxide composite modified polyurea according to claim 2, characterized in that, The mass ratio of the TiO2-HNTs powder to the polyurea copolymer is 4:

100.

4. The preparation method of halloysite-supported titanium dioxide composite modified polyurea according to any one of claims 1 to 3, characterized in that, The method for in-situ growth of titanium dioxide nanoparticles on the surface of halloysite nanotubes through a controllable hydrolysis reaction of tetrabutyl titanate and glacial acetic acid in an ethanol system includes: At room temperature, tetrabutyl titanate, glacial acetic acid and absolute ethanol were mixed and stirred until a transparent sol was formed; halloysite nanotubes were added to the sol system and stirring was continued; a mixed solution composed of deionized water and absolute ethanol was slowly added dropwise, stirred and aged, and then filtered; the filtered product was washed with excessive absolute ethanol and deionized water and dried to obtain the TiO2-HNTs powder.

5. The preparation method of halloysite-supported titanium dioxide composite modified polyurea according to claim 4, characterized in that, The mass ratio of tetrabutyl titanate to halloysite nanotubes is 102:

250.

6. The preparation method of halloysite-supported titanium dioxide composite modified polyurea according to any one of claims 1 to 3, characterized in that, The method for synthesizing a polyurea copolymer by copolymerizing polydimethylsiloxane and isophorone diisocyanate to form an isocyanate-terminated prepolymer and further performing a chain extension reaction with 1,6-hexanediamine includes: Polydimethylsiloxane and isophorone diisocyanate were dissolved in tetrahydrofuran and stirred for a pre-reaction under a nitrogen atmosphere to obtain a pre-reaction solution; 1,6-hexanediamine was dissolved in isopropanol and slowly added dropwise to the pre-reaction solution, and the polyurea copolymer was obtained by reaction.

7. The preparation method of halloysite-supported titanium dioxide composite modified polyurea according to claim 6, characterized in that, The mass ratio of polydimethylsiloxane, isophorone diisocyanate and 1,6-hexanediamine is 300:444:

220.

8. The preparation method of halloysite-supported titanium dioxide composite modified polyurea according to any one of claims 1 to 3, characterized in that, The method for dispersing the TiO2-HNTs powder in the polyurea copolymer and curing to obtain halloysite-supported titanium dioxide composite modified polyurea includes: The TiO2-HNTs powder was ultrasonically dispersed in a solution composed of isopropanol and tetrahydrofuran, added to the polyurea copolymer system, stirred and then dried under vacuum to obtain the halloysite-supported titanium dioxide composite modified polyurea.

9. A halloysite-supported titanium dioxide composite modified polyurea, characterized in that, Prepared by the preparation method of the halloysite-supported titanium dioxide composite modified polyurea according to any one of claims 1 to 8.

10. An application of halloysite-supported titanium dioxide composite modified polyurea, characterized in that, Applied to local insulation spraying of transmission lines.

Images