Application of surface-modified titanium dioxide powder as additive in improving electrical properties of polypropylene high-voltage cable nanocomposite

Abstract

The invention provides an application of surface-modified titanium dioxide powder in improving the electrical aging performance of a polypropylene composite material for a cable insulation system and the dielectric strength under an alternating electric field, and is characterized in that the specific surface area (BET) range of the surface-modified titanium dioxide powder is 40-100 square meters / gram; the invention also discloses a polypropylene nano composite material which comprises the surface modified titanium dioxide powder and polypropylene.

Description

Technical Field

[0001] This invention relates to compositions for high-voltage cable applications. Background Technology

[0002] Using green and clean electricity is of paramount importance to the economic development of countries worldwide. With increasing electricity demand, the construction of long-distance power transmission systems faces greater challenges. Cross-linked polyethylene has been extensively studied and used as cable insulation material. However, in recent years, polypropylene has emerged as one of the most promising materials for next-generation cables due to its superior properties, such as recyclability, lower energy consumption, elimination of complex cross-linking processes, and higher operating temperatures.

[0003] However, some drawbacks exist, such as the reliability of polypropylene (e.g., electrical aging), which can be a problem because its molecular chains contain more tertiary carbon atoms. The composite of nanostructured particles in cross-linked polyethylene or polypropylene has become one solution for improving the electrical aging of cables, and the lifespan of AC cables has been a major concern. How to effectively disperse these nanostructured particles in the polymer system for use in cable insulation layers will be crucial.

[0004] In the cable industry, Sumitomo Electric Industries (US20240059877A1) provides a new resin formulation that offers a solution using nano-sized magnesium oxide particles. This is achieved through surface treatment of the magnesium oxide using a silane coupling agent (e.g., vinyltrimethoxysilane, VTMS), where the magnesium oxide particle size is between 50 and 500 nm. Furthermore, in US20240059864A1, Sumitomo Electric Industries also emphasizes the same concept, but uses fumed silica with a native particle size of approximately 12 nm as its key additive. Of course, this silica particle size is also treated with a silane coupling agent.

[0005] Jiangsu Shangshang Cable Group published a polypropylene resin composition for 20kV cables in CN116130156A. The composition uses surface treatment agents, including amide fatty acid esters, ethoxylated fatty acids, hexamethyldisilazane or propoxylated fatty acids, to treat silica with a native particle size between 5-18 nanometers, thereby obtaining excellent water treeing (a type of discharge at defects in cable insulation) performance.

[0006] Gao Junguo et al. disclosed commercial grades of vapor-phase titanium dioxide for hydrophilic and hydrophobic vapor-phase titanium dioxide in Polymers 2022, 14, 2762. TiO2P 90 (P90) and The impact of TiO2NKT 90 (NKT90) as a key nanostructure additive on high-voltage cable materials. The results show that hydrophilic nanostructured vapor-phase titanium dioxide tends to agglomerate at low concentrations, resulting in poor space charge suppression; charge easily penetrates certain polypropylene composites, significantly reducing AC and DC breakdown field strength. However, hydrophobic nanostructured titanium dioxide, as a key additive, exhibits better dispersibility and less space charge accumulation in polypropylene composites. However, excessive addition leads to poor properties; at a nanostructure content of 2 wt.%, charge penetration is easily achieved. The hydrophobic vapor-phase titanium dioxide material with nanostructure, at a content of 1 wt.%, shows a maximum increase of 20.8% in breakdown strength under both AC and DC electric fields. Summary of the Invention

[0007] This invention provides the use of surface-modified titanium dioxide powder in improving the electro-aging performance and dielectric strength under AC electric field of polypropylene composite materials used in cable insulation systems, characterized in that the specific surface area (BET) of the surface-modified titanium dioxide powder is in the range of 40-100 m² / g.

[0008] The specific surface area (BET) of the surface-modified titanium dioxide powder is preferably in the range of 50-100 m² / g, more preferably 50-80 m² / g, for example 50-70 m² / g.

[0009] Preferably, in the polypropylene composite material, the content of the surface-modified titanium dioxide powder is 0.2-2 wt.%, more preferably 0.5-1.5 wt.%, for example 0.8-1.2 wt.%.

[0010] BET surface area can be measured using the method described in ISO (International Organization for Standardization) 9277:2022 "Determination of specific surface area of ​​solids by gas adsorption—BET method". Examples of measuring instruments include... TriStar IIPlus Fully Automated Surface Area and Porosity Analyzer.

[0011] In this invention, "surface-modified titanium dioxide powder" refers to hydrophobically treated titanium dioxide powder, such as titanium dioxide powder treated with at least one compound selected from organosilanes, alkylsilanes, fluorinated silanes, and / or disilazanes. The surface of the titanium dioxide powder is preferably modified with an organosilane.

[0012] Other fumed titanium dioxide materials can also be modified for hydrophobicity by using hydrophobicating materials that make the surface of fumed titanium dioxide particles appropriately hydrophobic. Suitable hydrophobicating materials include all materials commonly found in the art that are compatible with titanium dioxide materials to make their surfaces appropriately hydrophobic. Suitable examples include, but are not limited to: organosilanes, alkylsilanes, fluorinated silanes, and / or disilazanes. Suitable organosilanes include, but are not limited to: alkylchlorosilanes; alkoxysilanes, such as methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, n-octyltriethoxysilane, phenyltriethoxysilane, polytriethoxysilane, etc. Silanes; trimekoxyarylsilanes; isooctyltrimethoxysilanes; N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethylcarbamate; N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethylcarbamate; polydialkylsiloxanes, including, for example, polydimethylsiloxanes; arylsilanes, including, for example, substituted and unsubstituted arylsilanes; alkylsilanes, including, for example, substituted and unsubstituted alkylsilanes, including, for example, methoxy and hydroxy-substituted alkylsilanes; and combinations thereof. Suitable alkylchlorosilanes include, for example, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, octylmethyldichlorosilane, octyltrichlorosilane, octadecylmethyldichlorosilane, and octadecyltrichlorosilane. Other suitable materials include, for example, methylmethoxysilanes such as methyltrimethoxysilane, dimethyldimethoxysilane, and trimethylmethoxysilane; methylethoxysilanes such as methyltriethoxysilane, dimethyldiethoxysilane, and trimethylethoxysilane; methylacetoxysilanes such as methyltriacetoxysilane, dimethyldiacetoxysilane, and trimethylacetoxysilane; and vinylsilanes such as vinyltrichlorosilane, vinylmethyldichlorosilane, vinyldimethylchlorosilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, and vinyldimethylethoxysilane.

[0013] Disilazanes that can be used as processing aids in this invention are well known in the art. Suitable disilazanes include, but are not limited to, for example, hexamethyldisilazane, divinyltetramethyldisilazane, and bis(3,3-trifluoropropyl)tetramethyldisilazane. Cyclosilazanes are also suitable, including, for example, octamethylcyclotetrasilazane. Therefore, these disilazanes and cyclosilazanes can be used as hydrophobic materials for hydrophobically modified fumed silica particles, and also as processing aids for forming the pre-dispersions described below.

[0014] Suitable fluorinated silanes include fluorinated alkyl-, alkoxy-, aryl-, and / or alkylaryl-silanes, as well as perfluorinated alkyl-, alkoxy-, aryl-, and / or alkylaryl-silanes. Examples of fluoroalkylsilanes include, but are not limited to, those marketed by Evonik Industries AG under the trade name "Dynasylan". An example of a suitable fluorinated alkoxy-silane is perfluorooctyltrimethoxysilane.

[0015] In some embodiments, the surface-modified titanium dioxide powder is a hydrophobic TiO2 nanoparticle treated with trimethoxy(2-methylpropyl)silane; preferably, its original particle size is 20 nm, and preferably, its density is 3.5 g / cm³. 3 The surface-modified titanium dioxide is preferably selected from commercially available products from Evonik Industries AG, Germany. TiO2 NKT 90.

[0016] Preferably, the original particle size of the surface-modified titanium dioxide powder is 10-100 nm, more preferably 15-50 nm.

[0017] The present invention also provides a polypropylene nanocomposite material comprising surface-modified titanium dioxide powder and polypropylene.

[0018] Preferably, the content of surface-modified titanium dioxide powder in the polypropylene nanocomposite material is 0.2-2 wt.%, more preferably 0.5-1.5 wt.%, for example 0.8-1.2 wt.%.

[0019] The polypropylene of this invention is a polypropylene cable material. The polypropylene cable material is a composite of a polypropylene matrix, one or more elastomers, and antioxidants, etc., and is a material suitable for cable processing and production.

[0020] In this invention, hydrophobic vapor-phase titanium dioxide particles treated with alkylsilanes are used. TiO2NKT 90 exhibited excellent electrical aging test performance. Two polypropylene composite samples obtained from nanostructured fumed oxide particles, processed using two different compounding methods—melt blending (laboratory scale) and Evonik Industries' proprietary screw extrusion compounding process (industrial scale)—demonstrated superior electrical performance.

[0021] Excellent uniform dispersion of surface-modified titanium dioxide powder in a polypropylene matrix is ​​a key factor in significantly improving the polymer's dielectric properties. Careful tuning of process design and processing parameters is required to disperse the metal oxide particles in the submicron range while preserving the inherent properties of the original polypropylene material. Figure 6Transmission electron microscopy (TEM) images show the effect of using Evonik's screw extrusion compounding process. An example of the dispersion effect achieved by TiO2 NKT 90 in a polypropylene matrix.

[0022] Evonik's screw extrusion compounding process is a special preparation process. Specifically, it uses a twin-screw extruder (screw diameter 27mm) to produce polypropylene masterbatch with nanostructured hydrophobic fumed oxide particles at a particle concentration of 10 wt.%. This polypropylene masterbatch is then diluted with pure polypropylene material using a reused single-screw extruder (screw diameter 30mm) to produce a polypropylene composite material containing 1 wt.% of nanostructured hydrophobic fumed oxide particles.

[0023] While not wishing to be limited by any theory, the inventors believe that using nanostructured particles as functional additives increases the contact points between the polymer matrix and the polypropylene composite material, thereby improving insulation performance; introduces deep traps to suppress space charge accumulation; and the uniform charge trap distribution caused by the nanostructured particles results in the excellent electrical properties of this invention.

[0024] The present invention achieves surprisingly excellent electrical aging performance and dielectric strength under alternating current, and the surface-modified titanium dioxide powder of the present invention exhibits a surprisingly significant higher electrical aging life than polypropylene samples with surface-modified silica (R974 and R504). The reason for the superior performance of surface-modified titanium dioxide is likely that under long-term electric field conditions, the Joule heating effect occurs when current passes through PP insulation, causing temperature rise that leads to the breakage of molecular chains and structural damage. Polypropylene materials with surface-modified titanium dioxide exhibit higher heat resistance, reducing the damage to the insulation material caused by the Joule heating effect, thereby enhancing electrical aging performance. Furthermore, the application of the screw extrusion compounding process disclosed in this invention achieves a surprisingly significant higher life index and electrical aging life than composite materials prepared by melt blending processes on a laboratory scale. This makes it possible to develop cable materials for specific applications and uses.

[0025] Other advantages of the present invention will be apparent to those skilled in the art upon reading the specification. Attached Figure Description

[0026] Figure 1 The inverse power law model fitting curves of (SiO2, TiO2) / polypropylene composites prepared by melt blending process are shown.

[0027] Figure 2 The inverse power law model fitting curves of (SiO2, TiO2) / polypropylene composites prepared using Evonik's screw extrusion mixing process are shown.

[0028] Figure 3 The image shows the Weber distribution of the AC breakdown field strength of the (SiO2, TiO2) / polypropylene composite material prepared by melt blending process.

[0029] Figure 4 The image shows the Weber distribution of the AC breakdown field strength of (SiO2, TiO2) / polypropylene composites prepared using Evonik's screw extrusion mixing process.

[0030] Figure 5 The diagram shows a stress pattern of gradually increasing pressure to accelerate aging.

[0031] Figure 6 The image shows a TEM image of a cross-section of the TiO2 / polypropylene composite material prepared according to Example 2 using Evonik's screw extrusion compounding process. Detailed Implementation

[0032] The present invention will now be described in detail through the following embodiments. The scope of protection of the present invention should not be limited to the embodiments described herein.

[0033] Material

[0034] In the embodiments, the following materials were used:

[0035] Polypropylene: PP-CT produced by Jiangsu Shangshang Group Cable Co., Ltd., density 0.945 g / cm³ 3 The melt flow rate is 2.20 g / 10 min.

[0036] Surface-modified vapor-phase titanium dioxide powder: Hydrophobic vapor-phase titanium dioxide powder treated with trimethoxy(2-methylpropyl)silane. TiO2NKT90, with a density of 3.5 g / cm³. 3 BET specific surface area: 50-75m² 2 / g, produced by Evonik Industries, Inc.

[0037] Hydrophobic fumed silica R 504: A hydrophobic fumed silica produced by treating hexamethyldisilazane (HMDS) and aminosilane, manufactured by Evonik Industries, Inc.

[0038] Hydrophobic fumed silica R 974: A hydrophobic fumed silica post-treated with dimethyldichlorosilane (DDS), manufactured by Evonik Industries, Inc.

[0039] Example 1 (0.5NKT 90-melt blend)

[0040] 1. Preparation of polypropylene nanocomposites using a laboratory-scale melt blending process: Polypropylene material for high-voltage cables (melt flow rate: 2.2 g / 10 min) and surface-modified titanium dioxide powder were dried in a vacuum oven at 60 °C for 24 hours; then, 39.8 g of polypropylene material and 0.2 g of nanomaterial NKT90 were added to a torque rheometer (model RM-200A, HarperElectric Technology) and mixed (melt blending) at 190 °C and 40 rpm for 20 minutes.

[0041] 2. The composite material was hot-pressed into a nanocomposite film sample using a vulcanizing machine (model XLB-350, Jinma Rubber & Plastics Machinery Technology). The vulcanizing machine was preheated to 190℃ for 5 minutes, and the pressure was increased to 15MPa in three steps, with each step increasing by 5MPa and lasting for 5 minutes. The pressed sample was cooled to room temperature, and all obtained samples were stored in vacuum bags.

[0042] 3. Electrical aging test:

[0043] Test Method: The electrodes used in the accelerated electrical aging test are plate electrodes made of brass, with polished surfaces to ensure smoothness. The plate electrodes are 50mm in diameter and 5mm thick, while the cylindrical electrodes are 25mm in diameter with a 3mm radius to avoid localized electric field concentration. The accelerated electrical aging test samples are immersed in oil for measurement; this is 45# transformer oil (Sinopec Lubricating Oil Co., Ltd., Wuhan, China). This oil is uniformly vacuum-dried for 24 hours before use. The AC transformer is pressurized at a rate of 2kV / s using a KZT series power frequency high-voltage control panel (Yingkou Special Transformer Testing Equipment Co., Ltd., Liaoning Province, China). The accelerated electrical aging test is performed on the samples using a voltage ramp method. The sample thickness is controlled at 0.18mm-0.22mm, and the diameter is 60mm. The voltage is ramped up from 0kV until the sample breaks down, and the total breakdown time t and breakdown voltage U are recorded. j The boost step size U n For each voltage level of 0.5kV, the duration T is... n The voltage durations were set to 30s, 60s, 180s, and 600s, with 9 samples for each level. The obtained breakdown field strength E and voltage duration T were substituted into the equation ln t = -n ln E + ln C. The lifetime exponent n was then fitted using least squares. Finally, the value of n, E, and T were substituted into the inverse power law t = C·E. -n Calculate C for the four voltage durations and take their average value. As a material life parameter, n and Substituting t = C·E -n An aging model is then constructed; finally, the constructed aging model is used to evaluate the long-term aging life.

[0044] Example 2 (1.0NKT 90 - Evonik's screw extrusion compounding process)

[0045] 1. Preparation of polypropylene composites using Evonik's industrial-scale twin-screw extrusion compounding process: Polypropylene masterbatch with nanostructured hydrophobic fumed oxide particles was produced using a twin-screw extruder (screw diameter 27 mm) with a particle concentration of 10 wt.%.

[0046] This polypropylene masterbatch was produced by using a recycled single-screw extruder (screw diameter 30mm) to dilute pure polypropylene material to a polypropylene composite containing 1 wt.% of nanostructured hydrophobic fumed oxide particles.

[0047] 2. The composite material was hot-pressed into nanocomposite film samples using a vulcanizing machine (model XLB-350, Haimen Jinma Rubber & Plastic Machinery Technology Co., Ltd.). The vulcanizing machine was preheated to 190℃ for 5 minutes, and the pressure was increased to 15MPa in three steps, with each step increasing by 5MPa for 5 minutes. The pressed samples were then cooled to room temperature, and all obtained samples were stored in vacuum bags.

[0048] 3. Electrical aging test:

[0049] The method is the same as in Example 1.

[0050] like Figure 6 As shown, in the TiO2 / polypropylene composite material prepared in Example 2, the surface-modified titanium dioxide powder was well uniformly dispersed in the polypropylene matrix.

[0051] Example 3 (1.0NKT 90 - melt blend)

[0052] Example 3 differs from Example 1 only in sample preparation step 1. In Example 3, 39.6g of polypropylene material and 0.4g of NKT90 nanomaterial were added to the torque rheometer. All other steps were the same.

[0053] Comparative Example 1 (Pure Polypropylene - Melt Blend)

[0054] Comparative Example 1 differs from Example 1 only in sample preparation step 1; in Comparative Example 1, 40.0 g of polypropylene material was added to the torque rheometer. All other steps were identical.

[0055] Comparative Example 2 (0.5) R 504 (melt blend)

[0056] Comparative Example 2 differs from Example 1 only in sample preparation step 1. Comparative Example 2 uses 39.8g of polypropylene material and 0.2g of nanomaterial. R 504 is added to the torque rheometer. All other steps are the same.

[0057] Comparative Example 3 (1.0) R 504 (melt blend)

[0058] Comparative Example 3 differs from Example 1 only in sample preparation step 1. Comparative Example 3 uses 39.6g of polypropylene material and 0.4g of nanomaterials. R 504 is added to the torque rheometer. All other steps are the same.

[0059] Comparative Example 4 (0.5) R 974 - Melt Blend)

[0060] Comparative Example 4 differs from Example 1 only in sample preparation step 1. Comparative Example 4 uses 39.8g of polypropylene material and 0.2g of nanomaterials. R 974 is added to the torque rheometer. All other steps are the same.

[0061] Comparative Example 5 (1.0) R 974 - Melt Blend)

[0062] Comparative Example 5 differs from Example 1 only in sample preparation step 1. Comparative Example 5 uses 39.6g of polypropylene material and 0.4g of nanomaterials. R 974 is added to the torque rheometer. All other steps are the same.

[0063] Comparative Example 6 (Pure Polypropylene - Evonik's Mixing Process)

[0064] The only difference between Example 6 and Example 2 is the sample preparation step 1; the masterbatch used is pure polypropylene. All other steps are the same.

[0065] Comparative Example 7 (0.5) R 974 - Evonik's mixing process)

[0066] Comparative Example 7 and Example 2 differ only in sample preparation step 1; the masterbatch contains the following: R974 was diluted with pure polypropylene material to a concentration of 0.5 wt.%. All other steps were the same.

[0067] Comparative Example 8 (1.0) R 974 - Evonik's mixing process)

[0068] Comparative Example 8 and Example 2 differ only in sample preparation step 1; the masterbatch contains [missing information]. R974. All other steps are the same.

[0069] Comparative Example 9 (1.0) R 504 - Evonik's mixing process)

[0070] Comparative Example 9 and Example 2 differ only in sample preparation step 1; the masterbatch contains the following: R504. All other steps are the same.

[0071] Electrical aging test results:

[0072] (SiO2, TiO2) / polypropylene composite materials prepared by melt blending process:

[0073] Based on the accelerated electrical aging test data, the breakdown field strength E and voltage duration T are substituted into the equation ln t=-n ln E+ln C. The lifetime exponent n is shown in Table 1. The breakdown field strength E and T are then substituted into the inverse power law t=C·E. -n Calculate C for the four voltage durations and take their average value. As a material life parameter, n and Substituting t = C·E -n An inverse power-law electrical aging lifetime model was constructed. The long-term aging lifetime was evaluated using this model, as shown in Table 2. Plotting the model on a double logarithmic coordinate system yielded the following results. Figure 1 .from Figure 1 The diagram shows the changes in the electrical aging lifetime of samples from Examples 1 and 3, as well as Comparative Examples 1-5, with voltage. The addition of NKT90 in both ratios increased the electrical aging lifetime of the materials. Compared with pure polypropylene, the curves for 0.5 NKT90 and 1.0 NKT90 shifted upward and the tilt angle decreased. As the aging field strength decreased, the difference in electrical aging lifetime gradually increased.

[0074] Evonik's screw extrusion compounding process for preparing (SiO2, TiO2) / polypropylene composites:

[0075] Based on the accelerated electroaging test data of twin-screw extruded composite materials, the breakdown field strength E and voltage duration T are substituted into the equation ln t=-n ln E+ln C. The lifetime exponent n can be obtained by fitting using the least squares method, as shown in Table 3. Substituting the breakdown field strength E and T into the inverse power law t=C·E -n Calculate C for the four voltage durations and take their average value. As a material life parameter, n and Substituting t = C·E -n An inverse power-law electrical aging lifetime model was constructed. The long-term aging lifetime was evaluated using this model, as shown in Table 4. Plotting the model on a double logarithmic coordinate system yielded the following results. Figure 2 .from Figure 2The results show the changes in the electrical aging lifetime of the samples from Example 2 and Comparative Examples 6-9 as a function of voltage. The addition of 1.0NKT90 increased the low-field electrical aging lifetime of the materials. Compared with pure polypropylene, the tilt angle of 1.0NKT90 is smaller, and the electrical aging lifetime of 1.0NKT90 increases rapidly as the aging field strength decreases.

[0076] Electrical aging test:

[0077] The method is the same as in Example 1.

[0078] Figure 5 The diagram illustrates the process of stress variation during accelerated aging under progressively increasing pressure, where x represents sample failure, U represents sample failure voltage, and t represents test breakdown time. From... Figure 5 As can be seen, for each material, the voltage was increased from 0kV to the point where the sample was aged to breakdown, and the total breakdown time t and breakdown voltage U were recorded. j The boost step size U n For each voltage level of 0.5kV, the duration T is... n Set to 30s, 60s, 180s, and 600s.

[0079] Electrical aging characteristics table (samples prepared by melt blending process):

[0080] Table 1. (SiO2, TiO2) / Polypropylene lifetime index n calculated using the step-up pressure method

[0081]

[0082] Table 2. Prediction results of electro-aging life of (SiO2, TiO2) / polypropylene

[0083]

[0084] As shown in Tables 1 and 2, the electrical aging test results of the polypropylene nanocomposites obtained by melt blending are as follows:

[0085] 1. According to Table 1, the polypropylene sample with 0.5 wt.% AEROXIDE TiO2 NKT 90 added: based on the inverse power law ln t=-n ln E+ln C, the lifetime index n is calculated to be 14.85 (the larger n is, the higher the lifetime), which is 19.66% higher than that of the pure polypropylene sample; and significantly higher than that of the polypropylene sample with 0.5 wt.% R974 added.

[0086] 2. According to Table 1, the polypropylene sample with 1.0 wt.% AEROXIDE TiO2 NKT 90 added had a lifetime index n of 13.76, which was 10.88% higher than that of the pure polypropylene sample; and surprisingly significantly higher than the lifetime index of the polypropylene samples with 1 wt.% R974 and 1 wt.% R504 added.

[0087] 3. According to Table 2, under an electric field of 30kV / mm,

[0088] The polypropylene sample with 0.5 wt.% AEROXIDE TiO2 NKT 90 added had an electrical aging life of 3.534 years, which was 16.6 times that of the pure polypropylene sample; and significantly higher than the electrical aging life of the polypropylene sample with 0.5 wt.% R974 added.

[0089] The polypropylene sample with 1 wt.% AEROXIDE TiO2 NKT 90 added had an electrical aging life of 1.17 years, which was 5.5 times that of the pure polypropylene sample; and surprisingly significantly higher than the electrical aging life of the polypropylene samples with 1 wt.% R974 and 1 wt.% R504 added.

[0090] Since cable materials have different application scenarios and requirements, it is important to obtain very high electrical properties at specific metal oxide addition levels, such as greater than 0.5 wt.% or 1 wt.%, which helps to develop composite materials suitable for specific performance requirements.

[0091] Electrical aging characteristics table (samples prepared using Evonik's screw extrusion compounding process):

[0092] Table 3. Lifetime Index n of (SiO2, TiO2) / Polypropylene (Evonik) calculated using the step-up pressure method.

[0093]

[0094] Table 4. Predicted Electro-Aging Life of (SiO2, TiO2) / Polypropylene (Evonik)

[0095]

[0096] Tables 3 and 4 show the electrical aging test results of the polypropylene nanocomposites obtained using Evonik's screw extrusion compounding process:

[0097] 1. According to Table 3, the polypropylene sample with 1.0 wt.% AEROXIDE TiO2 NKT 90 added had a lifetime index n of 17.48, which was 13.3% higher than that of the pure polypropylene sample; and surprisingly significantly higher than the lifetime index of the composite material prepared by melt blending process on a laboratory scale.

[0098] 2. According to Table 4, under an electric field of 32kV / mm,

[0099] The polypropylene sample with 1.0 wt.% AEROXIDE TiO2 NKT 90 added exhibited an electrical aging lifetime of 11.7 years, four times that of the pure polypropylene sample; and surprisingly significantly higher than the electrical aging lifetime of composite materials prepared by melt blending processes on a laboratory scale. Similar results were obtained under an electric field of 30 kV / mm.

[0100] Breakdown voltage test under alternating electric field:

[0101] Test Method: Samples were placed in a 60℃ drying oven for 10 hours, followed by AC breakdown strength testing to eliminate the influence of moisture. To prevent surface arcing, the entire process was conducted in an electrical breakdown chamber immersed in transformer oil (45#, Sinopec Lubricating Oil Co., Ltd., Wuhan, China) at room temperature (approximately 30℃). The AC voltage boost rate was 2kV / s. The diameter of the cylindrical electrode was 25mm, and the breakdown voltage of each sample was recorded at 18 points. After calculating the breakdown strength, the Weibull distribution method was used to process the test data.

[0102] Breakdown voltage test results under alternating current (sample prepared by melt blending process):

[0103] When analyzing and processing experimental data on breakdown field strength, Weibull distribution statistics are often used to estimate the breakdown behavior of dielectric materials. Figure 3 This is a graph showing the results of processing composite material breakdown data using a two-parameter Weibull distribution model. In the graph, α represents the breakdown strength when the breakdown failure probability is 63.2%, and n represents the number of experiments for each material. In this graph, there are 20 experimental data points for each material. Figure 3 The addition of NKT90 significantly improved the breakdown field strength of the composite material. The highest breakdown field strength of the 0.5 NKT90 (polypropylene sample with 0.5 wt.% AEROXIDE TiO2 NKT 90) was 85.42 kV / mm, which was 11.7 kV / mm higher than that of pure polypropylene. It also showed a narrow but vertical Weibull distribution.

[0104] Breakdown voltage test results under alternating current (samples prepared using Evonik's screw extrusion compounding process):

[0105] Figure 4 This is a graph showing the results of processing composite material breakdown data using a two-parameter Weibull distribution model. In the graph, α represents the breakdown strength when the breakdown failure probability is 63.2%, and n represents the number of experiments for each material. In this graph, there are 18 experimental data points for each material. Figure 4 The addition of 1.0 wt.% AEROXIDE TiO2 NKT 90 significantly improved the breakdown field strength of the composite material. The highest breakdown field strength of 1.0 wt.% NKT90 (Evonik) was 91.95 kV / mm, which is 7.31 kV / mm higher than that of pure polypropylene and significantly higher than that of composite materials prepared by melt blending. Furthermore, the improvement in breakdown field strength of the composite material with NKT90 was significantly greater than that of the composite material with R974 or R504.

[0106] Surprisingly, unlike composites prepared by melt blending, the polypropylene nanocomposite obtained using Evonik's screw extrusion compounding process showed the best breakdown field strength in samples containing 1.0 wt.% polypropylene nanocomposites. The best sample of the composite material prepared by melt blending was made with 0.5 wt.% TiO2NKT 90. Composite material of TiO2 NKT 90.

[0107] The following conclusions can be drawn from the above experimental data:

[0108] 1. Vapor-phase titanium dioxide TiO2NKT 90, as a special and key additive, provides excellent electrical aging performance for the insulation design of polypropylene cables.

[0109] 2. Gas-phase titanium dioxide TiO2NKT 90, as a special and crucial additive, provides excellent breakdown voltage withstand capability for polypropylene cables under alternating current; and

[0110] 3. By employing Evonik's screw extrusion compounding process, the electrical aging and AC breakdown performance of all polypropylene cable composite materials of this invention can be improved.

[0111] As used herein, unless otherwise specified, terms such as “include” are open-ended terms meaning “at least include”.

[0112] All references, tests, standards, documents, publications, etc., mentioned herein are incorporated herein by reference. Where numerical limits or ranges are specified, endpoints are included. Furthermore, all values ​​and subranges within numerical limits or ranges are explicitly included as if explicitly stated.

[0113] The above description is intended to enable those skilled in the art to make and use the invention, and is provided in the context of specific applications and their requirements. Various modifications to the preferred embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope of the invention. Therefore, the invention is not intended to be limited to the embodiments shown, but is to be given the broadest scope consistent with the principles and features disclosed herein. In this regard, some embodiments within the scope of the invention may not exhibit every advantage of the invention in a broad sense.

Claims

1. The use of a surface-modified titanium dioxide powder in improving the electro-aging properties and dielectric strength under alternating current of polypropylene composites used in cable insulation systems, characterized in that, The specific surface area (BET) of the surface-modified titanium dioxide powder ranges from 40 to 100 square meters per gram.

2. The use according to claim 1, characterized in that, The specific surface area (BET) of the surface-modified titanium dioxide powder is preferably in the range of 50-100 m² / g, more preferably 50-80 m² / g, for example 50-70 m² / g.

3. The use according to claim 1, characterized in that, The surface-modified titanium dioxide powder is titanium dioxide powder treated with at least one compound selected from organosilanes, alkylsilanes, fluorinated silanes and / or disilazanes, preferably titanium dioxide powder treated with alkoxysilanes.

4. The use according to claim 1, characterized in that, The original particle size of the surface-modified titanium dioxide powder is 10-100 nm, more preferably 15-50 nm.

5. The use according to claim 1, characterized in that, In the polypropylene composite material, the content of the surface-modified titanium dioxide powder is 0.2-2 wt.%, more preferably 0.5-1.5 wt.%, for example 0.8-1.2 wt.%.

6. The use according to claim 1, characterized in that, The surface-modified titanium dioxide powder was commercially purchased from Evonik Industries, Inc. TiO2 NKT 90.

7. A polypropylene nanocomposite material comprising surface-modified titanium dioxide powder and polypropylene.

8. The polypropylene nanocomposite material according to claim 7, characterized in that, The content of surface-modified titanium dioxide powder in the polypropylene nanocomposite material is 0.2-2 wt.%, more preferably 0.5-1.5 wt.%, for example 0.8-1.2 wt.%.

9. The polypropylene nanocomposite material according to claim 7, characterized in that, The specific surface area (BET) of the surface-modified titanium dioxide powder is in the range of 40-100 m² / g, preferably 50-100 m² / g, more preferably 50-80 m² / g, for example 50-70 m² / g.

10. The polypropylene nanocomposite material according to claim 7, characterized in that, The surface-modified titanium dioxide powder is titanium dioxide powder treated with at least one compound selected from organosilanes, alkylsilanes, fluorinated silanes and / or disilazanes, preferably titanium dioxide powder treated with alkoxysilanes.

11. The polypropylene nanocomposite material according to claim 7, characterized in that, The original particle size of the surface-modified titanium dioxide powder is 10-100 nm, more preferably 15-50 nm.

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