A halloysite-loaded titanium dioxide composite modified polyurea and its preparation method and application

Abstract

The invention discloses a halloysite-loaded titanium dioxide composite modified polyurea and a preparation method and application thereof, belonging to the technical field of insulating coatings. Titanium dioxide nanoparticles are in-situ grown on the surface of halloysite nanotubes through a controlled hydrolysis reaction of tetrabutyl titanate and glacial acetic acid in an ethanol system to prepare TiO2-HNTs powder. An isocyanate-terminated prepolymer is formed by copolymerizing polydimethylsiloxane and isophorone diisocyanate, and a chain extension reaction is further carried out with 1,6-hexamethylenediamine to synthesize a polyurea copolymer. The TiO2-HNTs powder is dispersed in the polyurea copolymer and cured to obtain the halloysite-loaded titanium dioxide composite modified polyurea. The material has excellent UV aging resistance and electrical stability, and can meet the long-term reliable operation requirements of power transmission lines.

Description

Technical Field

[0001] The invention belongs to the technical field of insulating coatings, and in particular relates to a halloysite-loaded titanium dioxide composite modified polyurea and a preparation method and application thereof. Background Art

[0002] As a critical component of the power system, transmission lines are exposed to the outdoors for extended periods, making them susceptible to a variety of factors. In recent years, with the coordinated advancement of ecological restoration and power grid construction, the intersection between bird activity areas and transmission lines has continued to increase. Line tripping due to bird short circuits and flashovers from bird droppings has become the third-leading cause of line failures, after lightning strikes and external damage. Furthermore, extreme winds, such as line deflection and foreign objects hanging from the air, are frequent faults. The root cause is insufficient air insulation margin between the crossarm and the conductor. When conductive foreign objects intrude into the gap, causing electric field distortion, short-circuit currents can bypass the insulators and penetrate the air gap, causing line tripping.

[0003] Local insulation spraying technology provides a feasible solution to the above-mentioned faults. This technology sprays a layer of insulating material on the exposed metal points such as the crossarms and foot nails of the pole tower, so that the gap between the crossarms and the conductors is transformed from the original air insulation to a combined insulation method of "insulating material + air", effectively increasing the insulation margin of the pole tower gap and reducing short-circuit faults caused by foreign objects invading the pole tower gap.

[0004] At present, the research and application of local insulation spray coating materials are mainly concentrated in 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, which makes it difficult for the coating thickness to meet the insulation requirements of high-voltage towers. In addition, the hydrophobicity of RTV materials under long-term UV aging conditions is also difficult to meet the actual application standards. (2) Room temperature curing epoxy resin. However, the three-dimensional cross-linked network structure formed by this material during the curing process will lead to insufficient toughness and easy brittle fracture of the coating. Its bonding strength also decreases significantly with the increase of curing degree. (3) Sprayable polyurea resin (PU). Due to its characteristics such as fast curing and high mechanical strength, it can shorten the line power outage time caused by material spray coating construction and form a coating with controllable thickness. At the same time, it can also meet the strength requirements of operation and maintenance personnel when climbing the tower. In recent years, it has gradually become a research hotspot in the field of local insulation spray coating materials.

[0005] Polyurea (PU) is a block copolymer produced through the cross-linking polymerization of an isocyanate semi-prepolymer (component A) and an amine compound (component B). In its molecular structure, polar urea groups form hard segments, while the flexible macromolecular backbone constitutes soft segments. This microphase separation imparts excellent thermodynamic properties to the material. In overhead transmission line applications, insulation materials must withstand the multi-factor coupling of long-term outdoor environments. In addition to basic mechanical strength and thermal stability, the electrical aging properties and ultraviolet (UV) resistance of local insulation materials are key indicators of line insulation reliability. However, PU's limited UV stability limits its application: pure PU exhibits a mechanical property loss exceeding 50% after 72 hours of UV irradiation. Furthermore, the evolution of its electrical properties under UV aging conditions remains unclear, creating a blind spot in insulation reliability assessment.

[0006] To improve the UV stability of polyurethane (PU) materials, existing technologies often utilize nano-metal oxides (such as TiO2) for modification. However, the dispersion of the nanofillers directly affects the modification results, and nanofiller agglomeration can lead to degradation of key material properties. Existing modification strategies (such as acid / base treatment and multi-step processes) are complex and require highly corrosive reagents, making them difficult to meet green manufacturing requirements. Research has shown that tubular silicate clay minerals can effectively address the agglomeration problem of nano-metal oxides as a support. Silicate clay minerals, such as halloysite nanotubes (HNTs), have a crystal structure composed of layers of silicon-oxygen tetrahedral sheets and aluminum-oxygen octahedral sheets, stacked by shared oxygen atoms. This unique configuration allows weak interactions between adjacent layers, primarily through hydrogen bonds and van der Waals forces, resulting in excellent dispersion in organic polymer matrices. Importantly, these natural nanoclays not only offer the economic advantages of abundant reserves and low cost, but also possess unique structural stability and surface modifiability, making them ideal fillers for functional PU composites. However, the impact of HNTs-loaded nano-TiO2 on the UV aging performance of PU has not been systematically studied. In particular, the evolution of the electrical properties, hydrophobicity, and interface regulation mechanisms of the composite coatings remain largely unresolved. Therefore, there is an urgent need to develop a PU composite coating based on green dispersion technology and optimized interface regulation to enhance its UV aging resistance and electrical stability, thereby meeting the requirements for long-term reliable operation of transmission lines. Summary of the Invention

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

[0008] To achieve the above object, the present invention provides a method for preparing a halloysite-loaded titanium dioxide composite modified polyurea.

[0009] TiO2-HNTs powder was prepared by in situ growth of titanium dioxide nanoparticles on the surface of halloysite nanotubes through the controlled hydrolysis reaction of tetrabutyl titanate and glacial acetic acid in an ethanol system.

[0010] Polyurea copolymer was synthesized by copolymerizing polydimethylsiloxane with isophorone diisocyanate to form an isocyanate-terminated prepolymer, which was then chain-extended with 1,6-hexanediamine.

[0011] The TiO2-HNTs powder is dispersed in the polyurea copolymer and cured to obtain the halloysite-loaded titanium dioxide composite modified polyurea.

[0012] Furthermore, the mass ratio of the TiO2-HNTs powder to the polyurea copolymer is 2-10:100.

[0013] Furthermore, the mass ratio of the TiO2-HNTs powder to the polyurea copolymer is 4:100.

[0014] Furthermore, the method for in-situ growing titanium dioxide nanoparticles on the surface of halloysite nanotubes through the controlled hydrolysis reaction of tetrabutyl titanate and glacial acetic acid in an ethanol system comprises:

[0015] Under room temperature, tetrabutyl titanate, glacial acetic acid and anhydrous ethanol are mixed and stirred until a transparent sol is formed; halloysite nanotubes are added to the sol system and stirred continuously; a mixed solution consisting of deionized water and anhydrous ethanol is slowly added dropwise, stirred and aged, and filtered; the filtered product is washed with excess anhydrous ethanol and deionized water, and dried to obtain the TiO2-HNTs powder.

[0016] Furthermore, the mass ratio of tetrabutyl titanate to halloysite nanotubes is 102:250.

[0017] Furthermore, the method for synthesizing a polyurea copolymer by copolymerizing polydimethylsiloxane with isophorone diisocyanate to form an isocyanate-terminated prepolymer, and then further performing a chain extension reaction with 1,6-hexanediamine comprises:

[0018] Polydimethylsiloxane and isophorone diisocyanate are dissolved in tetrahydrofuran and stirred under a nitrogen atmosphere for pre-reaction to obtain a pre-reaction liquid; 1,6-hexanediamine is dissolved in isopropanol and slowly added dropwise to the pre-reaction liquid to react and obtain a polyurea copolymer.

[0019] Furthermore, the mass ratio of the polydimethylsiloxane, isophorone diisocyanate and 1,6-hexanediamine is 300:444:220.

[0020] Furthermore, the method of dispersing the TiO2-HNTs powder in the polyurea copolymer and curing to obtain the halloysite-loaded titanium dioxide composite modified polyurea comprises:

[0021] The TiO2-HNTs powder is ultrasonically dispersed in a solution consisting of isopropyl alcohol and tetrahydrofuran, and then added into the polyurea copolymer system. After stirring, vacuum drying is performed to obtain the halloysite-loaded titanium dioxide composite modified polyurea.

[0022] The present invention also provides a halloysite-loaded titanium dioxide composite modified polyurea, which is prepared by the above-mentioned preparation method of the halloysite-loaded titanium dioxide composite modified polyurea.

[0023] The present invention also provides an application of halloysite-loaded titanium dioxide composite modified polyurea, which is applied to local insulation spraying of power transmission lines.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] This study investigated the effects of varying halloysite nanotube-loaded titanium dioxide content on the performance of polyurea composite coatings before and after UV aging. The structure and elemental distribution of the TiO2-HNTs were analyzed using X-ray polycrystal diffraction, scanning transmission electron microscopy, and energy dispersive spectroscopy. The UV shielding effect of the TiO2-HNTs / PU composite was analyzed in conjunction with UV degradation. Fourier transform infrared spectroscopy, UV-visible spectroscopy, scanning electron microscopy, and differential scanning calorimetry were used to measure changes in the molecular structure and surface morphology of the TiO2-HNTs / PU composite before and after UV aging, and the hydrophobic and electrical properties of the material were evaluated.

[0026] This invention proposes, for the first time, using halloysite nanotubes as a carrier to load titanium dioxide, forming a TiO2-HNT composite filler. The tubular structure and surface properties of HNTs effectively address the agglomeration problem of nano-TiO2. Furthermore, their high specific surface area and UV reflection / scattering properties enhance the UV shielding properties of polyurea.

[0027] Through systematic experiments, the present invention determined that the optimal TiO2-HNT addition ratio is 4 wt%, achieving a balance between UV shielding, dielectric properties, thermal stability, and hydrophobicity. At low addition levels, the filler's UV shielding effect dominates, slowing the photodegradation of the polyurea molecular chains. At higher addition levels, the TiO2's photocatalytic effect is suppressed, preventing performance degradation.

[0028] The present invention develops a mild preparation method that does not require strong acids or bases. Ultrasonic dispersion and planetary stirring technology are used to achieve uniform distribution of TiO2-HNTs in a polyurea matrix. The process is simple and environmentally friendly.

[0029] After 300 hours of UV aging, the composite modified polyurea prepared by this invention exhibited a significantly lower breakdown strength drop (16.1%) than pure polyurethane (23.9%) for a 4 wt% THPU composite. The dielectric constant increased by 76.4%, and the hydrophobic angle remained above 110°. The material also exhibited superior thermal stability (melting peak > 370°C) and dielectric properties (low loss increment) to existing RTV, epoxy resin, and pure polyurethane. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 The microscopic morphology of TiO2, HNTs and TiO2-HNTs; Figure 1 (a) is the XRD pattern of TiO2, HNTs and TiO2-HNTs; Figure 1 (b) is the EDS spectrum of TiO2-HNTs;

[0032] Figure 2 is a microscopic morphology characterization diagram of TiO2-HNTs; Figure 2 (a) and (b) are STEM images of TiO2-HNTs; Figure 2 (c) is the HAADF-STEM image of TiO2-HNTs; Figure 2 (d), (e), (f) and (g) are the energy spectra of TiO2-HNTs (Al, Cyan);

[0033] Figure 3 FTIR spectra of PU and THPU materials at different aging times; Figure 3 (a), (b), (c), (d), (e), and (f) are the FTIR spectra of PU, THPU2, THPU4, THPU6, THPU8, and THPU10, respectively;

[0034] Figure 4 It is the UV aging performance characterization diagram of PU and THPU materials; Among them, Figure 4 (a) is the UV-VIS spectrum before UV aging. Figure 4 (b) is the UV-VIS spectrum after 300h of UV aging. Figure 4 (c) is the band gap energy spectrum before UV aging. Figure 4(d) is the band gap energy spectrum after UV aging for 300h;

[0035] Figure 5 It is the DSC spectrum of PU and THPU materials; Among them, Figure 5 (a) is the DSC spectrum before UV aging. Figure 5 (b) is the DSC spectrum after UV aging for 300 h;

[0036] Figure 6 The SEM spectra of PU and THPU materials under different UV aging times;

[0037] Figure 7 The contact angle diagrams of PU and THPU materials under different UV aging times are shown below. Figure 7 (a) is the contact angle diagram before UV aging. Figure 7 (b) is the contact angle diagram after UV aging for 100 hours. Figure 7 (c) is the contact angle diagram after UV aging for 200 hours. Figure 7 (d) is the contact angle diagram after UV aging for 300h;

[0038] Figure 8 The dielectric constant and dielectric loss spectra of PU and THPU materials under different aging times are shown in Figure 2. Figure 8 (a) is the dielectric constant spectrum before UV aging. Figure 8 (b) is the dielectric constant spectrum after UV aging for 300 hours. Figure 8 (c) is the dielectric loss spectrum before and after UV aging;

[0039] Figure 9 is the Weibull distribution curve of breakdown strength at different aging times; Figure 9 (a) is the Weibull distribution curve of breakdown strength before UV aging. Figure 9 (b) is the Weibull distribution curve of the breakdown strength after 100 hours of UV aging. Figure 9 (c) is the Weibull distribution curve of the breakdown strength after 200h of UV aging. Figure 9 (d) is the Weibull distribution curve of the breakdown strength after 300h of UV aging. DETAILED DESCRIPTION

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0041] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0042] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0043] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0044] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0045] Parameters for specific chemical substances used, sources.

[0046] 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%; and anhydrous ethanol, purity 99.5% were all purchased from Shanghai MacLean Biochemical Technology Co., Ltd. Deionized water was homemade; poly(dimethylsiloxane), bis(3-aminopropyl)-terminated (PDMS), number-average molecular weight (Mn) 3000, was purchased from Tianjin Xiens Biochemical Technology Co., Ltd.; 1,6-hexanediamine (HDMA), purity 99%, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; and halloysite nanotubes (HNTs), purity 97%, particle size 2–3 μm, were purchased from Jiangxi Dishi Mineral Fiber Technology Co., Ltd.

[0047] Example 1

[0048] (1) Preparation of TiO2-HNTs

[0049] At room temperature, 1.02 g of TBT, 5 mL of glacial acetic acid, and 20 mL of anhydrous ethanol solution were mixed and stirred for 10 min to form a transparent sol. 2.5 g of HNTs were added to the sol system and stirred for 1 h. 30 mL of a mixed solution with a volume ratio of (deionized water: anhydrous ethanol) = 1:2 was slowly added dropwise (dropping speed of 1 mL / min), stirred and aged for 24 h, and filtered. The filtered product was washed with excess anhydrous ethanol and deionized water, and dried in an oven at 60°C to obtain HNTs-loaded TiO2 powder (TiO2-HNTs).

[0050] (2) Preparation of TiO2-HNTs / PU

[0051] 3 g of PDMS and 4.44 g of IPDI were dissolved in 30 mL of THF and stirred for a pre-reaction for 0.5 h under a nitrogen atmosphere (30°C) to obtain a pre-reaction liquid. 2.2 g of HDMA was dissolved in 30 mL of IPA and slowly added dropwise to the pre-reaction liquid. The mixture was reacted at 80°C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0052] Based on the mass of PU, 2 wt% TiO2-HNTs powder was weighed and ultrasonically dispersed in 10 mL of a solution with a volume ratio of (IPA:THF) = 1:1. The TiO2-HNTs dispersion was added to the polyurea copolymer system and stirred at 600 r / min using a planetary stirrer for 10 min. Finally, the mixture was poured into a polytetrafluoroethylene mold and vacuum dried (50°C) to obtain a TiO2-HNTs / PU sample with a thickness of 0.2 mm. The wt% of TiO2-HNTs in the TiO2-HNTs / PU was 2%, which was recorded as THPU2.

[0053] Example 2

[0054] (1) Preparation of TiO2-HNTs

[0055] At room temperature, 1.02 g of TBT, 5 mL of glacial acetic acid, and 20 mL of anhydrous ethanol solution were mixed and stirred for 10 min to form a transparent sol. 2.5 g of HNTs were added to the sol system and stirred for 1 h. 30 mL of a mixed solution with a volume ratio of (deionized water: anhydrous ethanol) = 1:2 was slowly added dropwise (dropping speed of 1 mL / min), stirred and aged for 24 h, and filtered. The filtered product was washed with excess anhydrous ethanol and deionized water, and dried in an oven at 60°C to obtain HNTs-loaded TiO2 powder (TiO2-HNTs).

[0056] (2) Preparation of TiO2-HNTs / PU

[0057] 3 g of PDMS and 4.44 g of IPDI were dissolved in 30 mL of THF and stirred for a pre-reaction for 0.5 h under a nitrogen atmosphere (30°C) to obtain a pre-reaction liquid. 2.2 g of HDMA was dissolved in 30 mL of IPA and slowly added dropwise to the pre-reaction liquid. The mixture was reacted at 80°C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0058] Based on the mass of PU, 4 wt% TiO2-HNTs powder was weighed and ultrasonically dispersed in 10 mL of a solution with a volume ratio of (IPA:THF) = 1:1. The TiO2-HNTs dispersion was added to the polyurea copolymer system and stirred at 600 r / min using a planetary stirrer for 10 min. Finally, the mixture was poured into a polytetrafluoroethylene mold and vacuum dried (50°C) to obtain a TiO2-HNTs / PU sample with a thickness of 0.2 mm. The wt% of TiO2-HNTs in the TiO2-HNTs / PU was 4%, which was recorded as THPU4.

[0059] Example 3

[0060] (1) Preparation of TiO2-HNTs

[0061] At room temperature, 1.02 g of TBT, 5 mL of glacial acetic acid, and 20 mL of anhydrous ethanol solution were mixed and stirred for 10 min to form a transparent sol. 2.5 g of HNTs were added to the sol system and stirred for 1 h. 30 mL of a mixed solution with a volume ratio of (deionized water: anhydrous ethanol) = 1:2 was slowly added dropwise (dropping speed of 1 mL / min), stirred and aged for 24 h, and filtered. The filtered product was washed with excess anhydrous ethanol and deionized water, and dried in an oven at 60°C to obtain HNTs-loaded TiO2 powder (TiO2-HNTs).

[0062] (2) Preparation of TiO2-HNTs / PU

[0063] 3 g of PDMS and 4.44 g of IPDI were dissolved in 30 mL of THF and stirred for a pre-reaction for 0.5 h under a nitrogen atmosphere (30°C) to obtain a pre-reaction liquid. 2.2 g of HDMA was dissolved in 30 mL of IPA and slowly added dropwise to the pre-reaction liquid. The mixture was reacted at 80°C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0064] Based on the mass of PU, 6 wt% TiO2-HNTs powder was weighed and ultrasonically dispersed in 10 mL of a solution with a volume ratio of (IPA:THF) = 1:1. The TiO2-HNTs dispersion was added to the polyurea copolymer system and stirred at 600 r / min using a planetary stirrer for 10 min. Finally, the mixture was poured into a polytetrafluoroethylene mold and vacuum dried (50°C) to obtain a TiO2-HNTs / PU sample with a thickness of 0.2 mm. The wt% of TiO2-HNTs in the TiO2-HNTs / PU was 6%, which was recorded as THPU6.

[0065] Example 4

[0066] (1) Preparation of TiO2-HNTs

[0067] At room temperature, 1.02 g of TBT, 5 mL of glacial acetic acid, and 20 mL of anhydrous ethanol solution were mixed and stirred for 10 min to form a transparent sol. 2.5 g of HNTs were added to the sol system and stirred for 1 h. 30 mL of a mixed solution with a volume ratio of (deionized water: anhydrous ethanol) = 1:2 was slowly added dropwise (dropping speed of 1 mL / min), stirred and aged for 24 h, and filtered. The filtered product was washed with excess anhydrous ethanol and deionized water, and dried in an oven at 60°C to obtain HNTs-loaded TiO2 powder (TiO2-HNTs).

[0068] (2) Preparation of TiO2-HNTs / PU

[0069] 3 g of PDMS and 4.44 g of IPDI were dissolved in 30 mL of THF and stirred for a pre-reaction for 0.5 h under a nitrogen atmosphere (30°C) to obtain a pre-reaction liquid. 2.2 g of HDMA was dissolved in 30 mL of IPA and slowly added dropwise to the pre-reaction liquid. The mixture was reacted at 80°C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0070] Based on the mass of PU, 8wt% TiO2-HNTs powder was weighed and ultrasonically dispersed in 10mL of a solution with a volume ratio of (IPA:THF) = 1:1. The TiO2-HNTs dispersion was added to the polyurea copolymer system and stirred at 600r / min using a planetary stirrer for 10min. Finally, the mixture was poured into a polytetrafluoroethylene mold and vacuum dried (50℃) to obtain a TiO2-HNTs / PU sample with a thickness of 0.2mm. The wt% of TiO2-HNTs in the TiO2-HNTs / PU was 8%, which was recorded as THPU8.

[0071] Example 5

[0072] (1) Preparation of TiO2-HNTs

[0073] At room temperature, 1.02 g of TBT, 5 mL of glacial acetic acid, and 20 mL of anhydrous ethanol solution were mixed and stirred for 10 min to form a transparent sol. 2.5 g of HNTs were added to the sol system and stirred for 1 h. 30 mL of a mixed solution with a volume ratio of (deionized water: anhydrous ethanol) = 1:2 was slowly added dropwise (dropping speed of 1 mL / min), stirred and aged for 24 h, and filtered. The filtered product was washed with excess anhydrous ethanol and deionized water, and dried in an oven at 60°C to obtain HNTs-loaded TiO2 powder (TiO2-HNTs).

[0074] (2) Preparation of TiO2-HNTs / PU

[0075] 3 g of PDMS and 4.44 g of IPDI were dissolved in 30 mL of THF and stirred for a pre-reaction for 0.5 h under a nitrogen atmosphere (30°C) to obtain a pre-reaction liquid. 2.2 g of HDMA was dissolved in 30 mL of IPA and slowly added dropwise to the pre-reaction liquid. The mixture was reacted at 80°C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0076] 10 wt% of TiO2-HNTs powder, based on the mass of PU, was weighed and ultrasonically dispersed in 10 mL of a solution with a volume ratio of (IPA:THF) = 1:1. The TiO2-HNTs dispersion was added to the polyurea copolymer system and stirred at 600 r / min using a planetary stirrer for 10 min. Finally, the mixture was poured into a polytetrafluoroethylene mold and vacuum dried (50°C) to obtain a TiO2-HNTs / PU sample with a thickness of 0.2 mm. The wt% of TiO2-HNTs in the TiO2-HNTs / PU was 10%, which was recorded as THPU10.

[0077] Comparative Example 1

[0078] Preparation of PU

[0079] 3 g of PDMS and 4.44 g of IPDI were dissolved in 30 mL of THF and stirred for a pre-reaction for 0.5 h under a nitrogen atmosphere (30°C) to obtain a pre-reaction liquid. 2.2 g of HDMA was dissolved in 30 mL of IPA and slowly added dropwise to the pre-reaction liquid. The mixture was reacted at 80°C for 2.5 h to obtain a milky white polyurea copolymer (PU).

[0080] 10 mL of a solution with a volume ratio of (IPA:THF) = 1:1 was weighed and ultrasonically dispersed, added to the polyurea copolymer system, stirred at 600 r / min using a planetary stirrer for 10 min, and finally poured into a polytetrafluoroethylene mold and vacuum dried (50°C) to obtain a PU sample with a thickness of 0.2 mm, in which the wt% of TiO2-HNTs in the PU was 0%, recorded as PU.

[0081] Comparative Example 2

[0082] Preparation of the sample without HNTs as the pure TiO2 control group

[0083] At room temperature, mix 1.02g TBT, 5mL glacial acetic acid and 20mL anhydrous ethanol solution, stir for 10 minutes to form a transparent sol; continue to stir the sol system for 1 hour; slowly add (dropping speed of 1 mL / min) 30mL of a mixed solution with a volume ratio of (deionized water: anhydrous ethanol) = 1:2, stir and age for 24 hours, and filter; use excess anhydrous ethanol and deionized water to wash the filtered product, transfer it to an oven at 60°C to dry, and obtain pure TiO2 powder.

[0084] Test example

[0085] The phase composition of the TiO2-HNTs sample was determined using X-ray polycrystal diffraction (XRD) using a Bruker D8 Advance (Germany). Untreated HNTs and pure TiO2 were used as comparison samples. The test angle range was 5-90°, and the scanning rate was 2° / min. The nanoscale morphology of the TiO2-HNTs was observed using a scanning transmission electron microscope (STEM) using a JEOL JEM-F200 (Japan). The TiO2-HNTs sample was ultrasonically dispersed in anhydrous ethanol for 10 minutes and then dropped onto a copper mesh microgrid for observation. The elemental distribution was analyzed using energy dispersive spectroscopy (EDS).

[0086] The chemical structure of the polyurea composites was analyzed using Fourier transform infrared spectroscopy (FT-IR) using a Thermo Fisher Nicolet Summit (US) with 32 scans and a resolution of 4. The absorbance of the materials was measured using an ultraviolet-visible spectroscopy (UV-VIS) UV-3600plus (Japan) in the 200-400 nm range. The thermal stability of the polyurea composites was tested using a differential scanning calorimetry (DSC) NETZSCH 3500 Siruis (Germany) at a heating rate of 20°C / min. The surface morphology of the polyurea samples was characterized using a scanning electron microscope (SEM) FEI Nova NanoSEM 450 (US).

[0087] According to ISO 4892-3 standard, the polyurea samples were subjected to UV aging test, and the UVA-340 UV radiation lamp was used to continuously irradiate for 300 hours with a radiation intensity of 0.69W / (m 2The polyurea composites were subjected to power frequency breakdown strength testing according to IEC 60243-1:2013, with spherical electrodes at a voltage ramp rate of 1 kV / s. The breakdown data were analyzed using the Weibull distribution function. The dielectric constant and dielectric loss factor of the materials were measured at 40 Hz to 2 MHz using a dielectric constant meter (Agilent-E4980A, US) at a temperature of 21.6°C, according to IEC 60250:1969. The contact angle of the samples was measured using a contact angle meter (SZ-CAMD33, Sunzern, China) in accordance with ISO 15989:2004, using deionized water as the test fluid.

[0088] XRD characterization Figure 1 As shown in (a), compared with the standard card, it can be seen that TiO2 belongs to anatase type (JCPDS No.29-1360), and the untreated HNTs are halloysite-7Å (JCPDS No. 09-0453). Figure 1 The energy spectrum (b) in Figure 2 shows characteristic X-ray peaks at 4.51 keV and 4.93 keV, corresponding to titanium's L-to-K (Kα) and M-to-K (Kβ) electron transitions, respectively. Quantitative analysis reveals that the mass and atomic fractions of titanium reach 7.93% and 3.33%, respectively, confirming the presence of titanium in the prepared sample.

[0089] The micromorphology of TiO2-HNTs was characterized by transmission electron microscopy. Figure 2 As shown in (a), TiO2 nanoparticles of different shapes are attached to the surface of the halloysite tubular structure and are evenly distributed. The lattice fringes in the high-resolution image show ( Figure 2 In (b), the interplanar spacing of TiO2 exposed is 0.351 and 0.237 nm, corresponding to the (101) and (004) planes of anatase, respectively. Figure 2 The elements in (d), (e), (f) and (g) respectively prove that the method of preparing TiO2-HNTs of the present invention is stable and feasible.

[0090] Figure 3 The Fourier transform infrared spectra of pure PU and PU composites containing different amounts of TiO2-HNTs before and after UV aging are shown in the entire wavelength range. The characteristic absorption peaks of PU before aging are detailed in Table 1. -1 The formation of the urea C=O bond at the end of the reaction demonstrates the successful preparation of PU ( Figure 3 (a) in the text.

[0091] After adding different contents of TiO2-HNTs, it was found that 2770 cm-1 The absence of an -NCO absorption peak indicates that TiO2-HNTs do not restrict the synthesis of PU. After UV aging, the shift of the NH bond in THPU is significantly reduced compared to PU, indicating that the filler's UV shielding effect delays the partial photodegradation of the polymer.

[0092] Table 1 Characteristic absorption peaks of PU before aging

[0093]

[0094] like Figure 4 In (a), the unmodified PU exhibits significant absorption characteristics in the ultraviolet region of 200-350 nm, confirming that ultraviolet radiation is the main wavelength involved in the photodegradation of PU. At the low addition stage (<4wt%), the unique cylindrical morphology of halloysite (aspect ratio>20) and its high specific surface area (40~70 m² / g) give the system a significant ultraviolet reflection / scattering effect, thereby reducing the matrix's absorption of ultraviolet rays; and when the filler content exceeds the critical value, the inherent ultraviolet absorption characteristics of TiO2 nanoparticles gradually dominate, and their wide bandgap semiconductor characteristics (Eg=3.2 eV) produce strong intrinsic absorption in the ultraviolet region (λ<387 nm), resulting in a rebound in the overall absorbance of the system. After 300 h of accelerated aging ( Figure 4 As shown in (b) of Figure 2, all samples exhibit enhanced absorbance in the 200-400 nm UV range, primarily due to the photodimerization and photolysis effects of the materials. Furthermore, the characteristic absorption peak in the short-wavelength region of 200-250 nm also exhibits attenuation.

[0095] The band gap energy of each composite material before and after aging was estimated by UV-VIS spectrum. Figure 4 As shown in (c), the band gap energy (Eg) of unaged PU is 3.87 eV, while the initial Eg values of THPU with different TiO2-HNTs contents range from 3.75 to 3.99 eV. After UV aging, the material band structure shows significant differentiation, with the Eg values of PU and low-content THPU (≤6 wt%) increasing by 0.02-0.09 eV, while the Eg values of high-content systems (THPU8, THPU10) decrease by 0.04-0.1 eV.

[0096] The thermal stability of the composites was evaluated by DSC. Figure 5As shown in (a), pure PU exhibits a characteristic melting peak at 380.8°C, while the corresponding 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 causes detectable changes in the PU endothermic peak parameters, the overall thermal properties remain well stable (>365°C), confirming the applicability of TiO2-HNTs as a functional filler. Changes in the DSC curve after UV aging are shown in Figure 2. Figure 5 As shown in (b), after treatment at 300°C, all samples exhibit a shift in their endothermic peaks to lower temperatures and a significant broadening of the peaks, corresponding to a decrease in purity caused by the accumulation of degradation products within the material. Notably, the peak temperature of pure PU decreased significantly by 7.3°C, while the decrease for the THPU composite was only 0.6-3.6°C. The smaller shift in the THPU endothermic peak suggests that the absorption and shielding of UV light by TiO2-HNTs may inhibit the photooxidation of some carbonyl groups.

[0097] like Figure 6 As shown, with increasing TiO2-HNT addition, rod-like structures appear on the material surface, with size characteristics consistent with the intrinsic HNT particle size. The presence of TiO2-HNTs on the surfaces of THPU8 and THPU10 indicates effective dispersion of the TiO2-HNTs within the PU matrix, with no significant agglomeration observed. Furthermore, the surface roughness of the pre-aging material exhibits a gradual "rough-smooth-rough" transition with the addition of filler.

[0098] The surface hydrophobicity of the material was analyzed by water contact angle. Figure 7 As shown in (a), the surface hydrophobic angle of PU before and after the addition of TiO2-HNTs is greater than 90°, of which the hydrophobic angle of pure PU is 100.5°. Compared with pure PU, the contact angle change of PU composite materials is within ±8°. As UV aging progresses, the hydrophobic angle of the material increases to varying degrees in the initial 100 hours of aging ( Figure 7 (b) in the figure). During this stage, the contact angle of THPU10 increased the most, from 103.7° to 124.9°, indicating a significant improvement in its surface roughness. Figure 7 In (c), the hydrophobic angles of PU and PU composites (2-8wt%) still show an upward trend, with an increase of 4-9°. In addition, the hydrophobic angle of THPU10 decreased by 8.9° during the 200h aging period, and a similar decrease in contact angle also occurred after 300h aging ( Figure 7(d)). In contrast, the contact angles of THPU2, THPU4, and THPU6 show a continuous upward trend, with THPU2 showing the largest change, rising from 103.1° to 121.9° after 200 hours of aging. This increase in contact angle indicates that the filler's absorption and shielding of UV light slows the material's degradation, maintaining its Cassie state even after 300 hours, making the surface more hydrophobic.

[0099] Figure 8 Panel (a) shows the frequency evolution of the dielectric constant of the composite materials before aging. All materials exhibit a two-stage trend: a fluctuation in dielectric constant at low frequencies (less than 1 kHz) and a stable and gradually decreasing dielectric constant in the mid- to high-frequency range (greater than 1 kHz).

[0100] The dielectric response of the material changes significantly after the addition of TiO2-HNTs. When the filler content reaches 2wt%, the dielectric constant of the composite material decreases by approximately 14% compared to pure PU (from 3.5 to 3). However, when the filler content is increased to 4wt%, the dielectric constant of THPU4 rises to around 6.0. As the filler content continues to increase, the dielectric constant begins to gradually decrease.

[0101] After 300h of UV aging, the dielectric constants of all samples showed a downward trend ( Figure 8 (b) in the figure). Notably, the dielectric constant of THPU10 decreases by 50% (from 4 to 2) in the frequency band above 1 kHz. In contrast, the dielectric constant of THPU6 decreases less significantly and remains higher than that of pure PU after aging, indicating that an appropriate amount of TiO2-HNTs can delay matrix degradation through UV shielding, and their inherent high dielectric properties also have a positive effect on the dielectric properties of PU.

[0102] Figure 8 (c) shows the dielectric loss tangent before and after aging. The dielectric loss increases after aging.

[0103] Table 2 lists the dielectric loss tangent values of PU and THPU before and after aging at 50 Hz. THPU6 has the smallest dielectric loss increase after aging, at only 0.00329, while THPU2's dielectric loss increases by 263.7%.

[0104] Table 2 Dielectric loss of PU and PU composites at 50 Hz frequency

[0105]

[0106] In the actual transmission line operation environment, extreme conditions such as tip discharge may occur, so a ball-ball electrode system is used to simulate extreme non-uniform electric field conditions to evaluate the insulation reliability of polyurea and its composite materials under power frequency AC electric field. Figure 9 As shown in (a), before aging, the breakdown voltage of the composite material is stable between 80 and 92 kV / mm, and the overall trend is similar to that of the dielectric constant. When the TiO2-HNTs addition is 2 wt%, the breakdown voltage of the PU composite decreases from 88.8 kV / mm to 81.8 kV / mm. At 4-8 wt%, it remains around 90 kV / mm before decreasing again to 88.4 kV / mm (10 wt%). The uneven distribution of the 2 wt% filler leads to thermal breakdown. However, the PU composite exhibits higher breakdown strength at 4-8 wt% addition.

[0107] As the composite material ages, the UV absorption and shielding of low-content TiO2 and HNTs delay the photodegradation of PU to a certain extent, and the degree of breakdown decreases to a small extent.

[0108] Experimental results show that TiO2-HNTs / PU with a TiO2-HNTs content below 6 wt% slows the degradation of the PU molecular chain due to the filler's UV shielding and negligible photocatalytic effect, while maintaining the material's thermal stability (melting peak > 370°C) and hydrophobicity (contact angle > 110°). The 4 wt% addition achieved the best performance, with a 76.4% increase in dielectric constant and a 16.1% decrease in breakdown strength after 300 hours of UV aging, lower than the 23.9% decrease in PU. The dielectric loss increase was only 0.01332.

[0109] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a halloysite-loaded titanium dioxide composite modified polyurea, characterized in that: At room temperature, tetrabutyl titanate, glacial acetic acid, and anhydrous ethanol were mixed and stirred until a transparent sol was formed; halloysite nanotubes were added to the sol system and stirred continuously; a mixed solution consisting of deionized water and anhydrous ethanol was slowly added dropwise, stirred, aged, and filtered; The filtered product was washed with excess anhydrous ethanol and deionized water, and dried to obtain the TiO2-HNTs powder; Dissolving polydimethylsiloxane and isophorone diisocyanate in tetrahydrofuran, stirring and pre-reacting under a nitrogen atmosphere to obtain a pre-reaction liquid; Dissolving 1,6-hexanediamine in isopropyl alcohol and slowly adding the solution dropwise to the pre-reaction solution to obtain a polyurea copolymer; The TiO2-HNTs powder is ultrasonically dispersed in a solution consisting of isopropyl alcohol and tetrahydrofuran, and then added to the polyurea copolymer system. After stirring, vacuum drying is performed to obtain the halloysite-loaded titanium dioxide composite modified polyurea; The mass ratio of the TiO2-HNTs powder to the polyurea copolymer is 4:100; The mass ratio of tetrabutyl titanate to halloysite nanotubes is 102:250; The mass ratio of the polydimethylsiloxane, isophorone diisocyanate and 1,6-hexanediamine is 300:444:

220.

2. A halloysite-loaded titanium dioxide composite modified polyurea, characterized in that: The polyurea is prepared by the preparation method of the halloysite-loaded titanium dioxide composite modified polyurea according to claim 1.

3. An application of the halloysite-loaded titanium dioxide composite modified polyurea according to claim 1, characterized in that: Used for local insulation spraying of transmission lines.

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