Titanium dioxide phosphorus flame retardant composite modified carbon nanotube and preparation method thereof

Abstract

The invention discloses a titanium dioxide phosphorus flame retardant composite modified carbon nanotube and a preparation method thereof.The preparation method comprises the steps that a phosphorus flame retardant is dissolved in an organic solvent, titanate is added, and a Ti-Phos compound solution is obtained; the preparation method comprises the following steps: adding a multi-walled carbon nanotube into mixed acid, and carrying out ultrasonic treatment and pH regulation to obtain activated CNT; dispersing the activated CNT in deionized water, and performing ultrasonic dispersion to form a suspension; adding the Ti-Phos compound solution into the CNT suspension, adjusting the pH value, stirring at a constant temperature, and constructing a CNT / TiO-Phos composite structure; and centrifuging the reaction liquid, washing, and drying in vacuum to obtain the product. Through a synergistic flame-retardant-point matrix, titanium dioxide in-situ loading and phosphorus flame retardant grafting process, the composite modified carbon nanotube has high flame retardance, low volume resistivity and wide temperature range stability, and the problems that a traditional flame-retardant carbon tube is attenuated in flame-retardant efficiency, deteriorated in conductivity, unstable in a high-temperature environment and the like are solved; the method is suitable for the fields of high-precision integrated circuits, high-energy-density batteries and the like, and has good application prospects.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube flame retardant modification technology, specifically to a titanium dioxide phosphorus-based flame retardant composite modified carbon nanotube and its preparation method. Background Technology

[0002] With the development of flame-retardant modified carbon nanotube materials, the market demand for flame-retardant modified carbon nanotube materials in terms of flame retardancy, conductivity, and high-temperature stability is increasing. Currently, existing domestic carbon nanotube materials are insufficient to meet the requirements of high-safety battery systems, and commercially available products generally suffer from poor flame retardancy, weak conductivity, and insufficient high-temperature stability. To address this, a titanium dioxide-phosphorus flame retardant composite modified carbon nanotube, through composite structure design, utilizes the radiative mass effect of titanium dioxide and the free radical quenching ability of phosphorus-based flame retardants to construct a material with strong flame retardancy, strong conductivity, and strong high-temperature stability. This aims to solve the shortcomings of existing carbon nanotube materials in terms of flame retardancy, conductivity, and high-temperature stability, while also utilizing the synergistic flame-retardant mechanism of the composite structure to compensate for the performance limitations of single modification technologies.

[0003] Currently, commercially available flame-retardant modified carbon nanotubes suffer from defects such as poor flame retardancy, weak conductivity, and insufficient high-temperature stability. This leads to problems such as conductive network collapse and accelerated thermal propagation during battery thermal runaway. For example, CN103146025B discloses a phosphazene flame retardant grafted modified carbon nanotube and its preparation method. Although it achieves super flame retardancy by using carbon nanotubes to provide chemical flame retardancy through physical flame retardancy in conjunction with phosphorus-based flame retardants, its process is complex and requires long-term reaction at high temperatures, significantly increasing process costs. Furthermore, the solvent tetrahydrofuran used in large quantities is toxic and difficult to recycle, making industrial production extremely difficult and hindering large-scale industrial production. CN 103881137 A discloses a melamine flame retardant grafted modified carbon nanotube and its preparation method. It uses polar melamine to modify carbon nanotubes. Although it enhances the dispersibility and compatibility of carbon nanotubes with other polar polymers, the important raw material melamine has problems such as poor thermal stability. It is easy to decompose at high temperature and produce substances that are harmful to the human body. Moreover, the modification of carbon nanotubes with melamine can only improve the dispersibility and compatibility with polar polymers. It is difficult to apply to other materials, and its application prospects are limited. It is not suitable for large-scale production and application.

[0004] To overcome the aforementioned problems, the development of novel carbon nanotubes must simultaneously consider flame retardancy, conductivity, and high-temperature stability. This requires designing innovative organic-inorganic composite modification strategies and developing controllable and scalable preparation processes. On the other hand, the interfacial bonding mechanism needs to be optimized to both enhance the bonding strength between the flame retardant and the carbon nanotubes and maintain the integrity of the conductive network. Only in this way can novel carbon nanotube materials be applied on a large scale in fields with high safety requirements, such as batteries, ultimately achieving the goal of high-safety thermal management.

[0005] The above statements are merely background information related to the present invention and do not necessarily constitute prior art. Summary of the Invention

[0006] The purpose of this invention is to provide a titanium dioxide phosphorus-based flame retardant composite modified carbon nanotube and its preparation method.

[0007] The technical solution adopted in this invention is:

[0008] A method for preparing titanium dioxide-phosphorus-based flame retardant composite modified carbon nanotubes includes the following steps:

[0009] (1) Preparation of titanate-phosphorus flame retardant complex (Ti-Phos): Dissolve phosphorus flame retardant in organic solvent, add titanate under inert atmosphere, control the molar ratio of titanate:phosphorus flame retardant = 1:1 to 1:3, stir at 60 to 80 °C for 2 to 4 hours to allow the organic functional group (-OR) of titanate to undergo esterification or coordination reaction with the active group (-OH, -P=O) of phosphorus flame retardant to obtain titanate-phosphorus flame retardant complex solution;

[0010] (2) Pretreatment of carbon nanotubes (CNTs): Multi-walled carbon nanotubes were added to a mixed acid (concentrated H2SO4:concentrated HNO3 = 3:1, v / v), ultrasonically treated for 2-4 hours, centrifuged and washed until neutral, and vacuum dried at 80°C for 12 hours to obtain activated CNTs with carboxyl / hydroxyl groups on the surface.

[0011] (3) In-situ hydrolysis to construct CNT / TiO2-Phos composite structure: Activated CNTs were dispersed in deionized water and ultrasonically dispersed for 30 minutes to form a uniform suspension (concentration 1-5 mg / mL). Under continuous stirring, Ti-Phos composite solution was added dropwise to the CNT suspension, and the system temperature was controlled at 40-60℃. After the addition was completed, the pH was adjusted to 3-5 and stirred at a constant temperature for 4-6 hours to allow the inorganic end (-Ti-OR) of the titanate ester to undergo controllable hydrolysis and condensation on the CNT surface, generating a nano-TiO2 shell in situ. At the same time, the phosphorus flame retardant was embedded into the TiO2 network through Ti-OC / Ti-OP bonds and bonded to the CNT core to construct the CNT / TiO2-Phos composite structure.

[0012] (4) Preparation of a titanium dioxide phosphorus flame retardant composite modified carbon nanotube: The reaction solution was centrifuged and washed three times with deionized water and ethanol to remove free ions and by-products. The obtained solid was placed in a vacuum drying oven and dried at 60°C for 8-12 hours to finally obtain a titanium dioxide phosphorus flame retardant composite modified carbon nanotube with a "core (CNT)-shell (TiO2)-bridge (Ti-Phos)" structure.

[0013] Preferably, in step (1), the phosphorus-based flame retardant is selected from at least one of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), DOPO derivatives, phosphate ester flame retardants, phosphonate flame retardants, hypophosphite flame retardants, and hexachlorocyclotriphosphazene (HCCP).

[0014] Preferably, in step (1), the molecular weight of the phosphorus-based flame retardant is 200-1000 g / mol.

[0015] Preferably, in step (1), the organic solvent is selected from at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), tetrahydrofuran (THF), acetone, and acetonitrile.

[0016] Preferably, in step (1), the amount of organic solvent used is 5 to 15 times the mass of the phosphorus-based flame retardant.

[0017] Preferably, in step (1), the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0018] Preferably, in step (1), the titanate is selected from at least one of tetraethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate.

[0019] Preferably, in step (2), the diameter of the multi-walled carbon nanotube is 10-50 nm and the length is 1-20 μm.

[0020] Preferably, in step (2), the specific surface area of ​​the multi-walled carbon nanotubes is 100–400 m². 2 / g.

[0021] Preferably, in step (2), the amount of the mixed acid is 10 to 30 times the mass of the multi-walled carbon nanotubes.

[0022] Preferably, in step (3), the power of the ultrasonic dispersion is 200-500W.

[0023] Preferably, in step (3), the mass ratio of the Ti-Phos complex solution to the activated CNT suspension is 0.5:1 to 3:1, based on the mass ratio of titanate ester to activated CNT in the Ti-Phos complex.

[0024] Preferably, in step (3), the dropping rate of the Ti-Phos complex solution is 0.5 to 2 mL / min.

[0025] Preferably, in step (4), the centrifugation speed is 8000-12000 rpm and the centrifugation time is 10-30 minutes.

[0026] Preferably, in step (4), the vacuum degree of the vacuum drying is -0.08 to -0.1 MPa.

[0027] Preferably, in step (3), the acid used to adjust the pH is at least one of acetic acid, hydrochloric acid, and nitric acid.

[0028] Preferably, in step (4), the thickness of the TiO2 shell in the titanium dioxide phosphorus flame retardant composite modified carbon nanotube is 2-20 nm.

[0029] Preferably, in step (4), in the "core-shell-bridge" structure, the proportion of phosphorus flame retardant connected to the TiO2 shell through Ti-OP bonds accounts for more than 60% of the total bonding amount.

[0030] Preferably, in step (4), the mass fraction of phosphorus in the composite modified carbon nanotube is 1.5% to 8.0%, and the mass fraction of titanium is 3.0% to 15.0%.

[0031] Preferably, in step (4), the composite modified carbon nanotubes have a limiting oxygen index (LOI) ≥ 28% and a volume resistivity ≤ 10. 2 Ω·c

[0032] A titanium dioxide-phosphorus flame retardant composite modified carbon nanotube is prepared by the above-mentioned method.

[0033] The principle of this invention:

[0034] (1) Synergistic Flame Retardant-Conductivity Dual-Functional Construction Mechanism: Through molecular-level composite design of titanium dioxide and phosphorus-based flame retardants, the synergistic enhancement of flame retardancy and conductivity is achieved. Titanium dioxide is directionally grown at the defect sites of carbon nanotubes through Ti-OC bonds (claims 3, 10), forming a continuous conductive shell that significantly reduces interfacial contact resistance; at the same time, the phosphorus-based flame retardant is embedded in the titanium dioxide network through Ti-OP bonds (claim 18, accounting for ≥60%), releasing phosphorus-containing free radicals upon heating to efficiently quench the combustion chain reaction. This "core (CNT)-shell (TiO2)-bridge (Phos)" structure simultaneously constructs a physical isolation barrier and a chemical flame retardant pathway, enabling the material to maintain a volume resistivity ≤10 even with a high flame retardancy of LOI ≥28%. 2Ω·cm, solving the problem of conductive network collapse caused by the strong polarity of traditional flame retardants.

[0035] (2) High-Temperature Stability Enhancement Mechanism: The high-temperature stability of the titanium dioxide lattice and the decomposition resistance of the phosphorus-titanium bond work together to ensure structural integrity under extreme environments. Titanium dioxide maintains a rigid framework above 600℃, inhibiting carbon nanotube oxidation; the phosphorus-based flame retardant is firmly bonded to the titanium dioxide network through Ti-OP covalent bonds, preventing high-temperature desorption. The synergistic effect of these two factors results in a char residue rate ≥65% at 600℃ and a resistivity change rate ≤5.2% after wide-temperature cycling, overcoming the technical bottlenecks of high-temperature flame retardant failure and sharp drop in conductivity in existing materials.

[0036] (3) Interface bonding enhancement and dispersion stability mechanism: The long-chain structure of phosphorus-based flame retardants inhibits carbon nanotube aggregation through steric hindrance, while the titanium dioxide shell is strongly bonded to the carbon nanotube core through Ti-OC bonds. This design maintains the integrity of the conductive pathway while enabling the phosphorus-based flame retardant loading to reach 1.5% to 8.0% of phosphorus, thus solving the interface peeling problem caused by uneven distribution of flame retardants in traditional grafting processes.

[0037] (4) In-situ controllable shell formation and component matching mechanism: The hydrolysis rate of titanate is controlled by an acidic environment of pH 3-5 to achieve uniform coating of titanium dioxide on the surface of carbon nanotubes; the molar ratio of titanate to phosphorus-based flame retardant is 1:1 to 1:3 to ensure sufficient phosphorus-titanium coordination and avoid free component residue. This process enables precise control of the titanium dioxide shell thickness at 2-20 nm and the titanium content at 3.0%-15.0%, avoiding the degradation of conductivity caused by excessively thick coating or insufficient flame retardant efficiency caused by excessively thin coating from the source.

[0038] The beneficial effects of the present invention are as follows: The titanium dioxide phosphorus-based flame retardant composite modified carbon nanotube of the present invention has the advantages of strong flame retardancy, strong conductivity and strong high temperature stability, which can meet the market demand for carbon nanotube materials in terms of flame retardancy, conductivity and high temperature stability, and is suitable for large-scale production and application. Detailed Implementation

[0039] The invention will be further explained and described below with reference to specific embodiments.

[0040] Example 1:

[0041] A titanium dioxide-phosphorus flame retardant composite modified carbon nanotube is prepared by the following method:

[0042] (1) Preparation of titanate-phosphorus flame retardant complex (Ti-Phos): 10 parts of phosphorus flame retardant were dissolved in 80 parts of organic solvent. Under an inert atmosphere, 25 parts of titanate were added, controlling the molar ratio of titanate to phosphorus flame retardant to be 1:3. The mixture was stirred at 80℃ for 4 hours to allow the organic functional groups of the titanate to undergo esterification or coordination reactions with the active groups of the phosphorus flame retardant, thus obtaining a titanate-phosphorus flame retardant complex solution.

[0043] (2) Pretreatment of carbon nanotubes (CNTs): 40 parts of multi-walled carbon nanotubes were added to 80 parts of mixed acid, ultrasonically treated for 4 hours, centrifuged and washed until neutral, and vacuum dried at 80°C for 12 hours to obtain activated CNTs with carboxyl / hydroxyl groups on the surface.

[0044] (3) In-situ hydrolysis to construct the CNT / TiO2-Phos composite structure: Activated CNTs were dispersed in 100 parts of deionized water and ultrasonically dispersed for 30 minutes to form a uniform suspension. Under continuous stirring, the Ti-Phos complex solution was added dropwise to the CNT suspension, and the system temperature was controlled at 60℃. After the addition was complete, the pH was adjusted to 4, and the mixture was stirred at a constant temperature for 4 hours to construct the CNT / TiO2-Phos composite structure.

[0045] (4) Preparation of a titanium dioxide-phosphorus flame retardant-modified carbon nanotube composite: The reaction solution was placed in a centrifuge and centrifuged for 1 hour. Then, it was washed three times alternately with deionized water and ethanol to remove free ions and by-products. The obtained solid was placed in a vacuum drying oven and dried at 60°C for 12 hours to finally obtain a titanium dioxide-phosphorus flame retardant-modified carbon nanotube with a "core (CNT)-shell (TiO2)-bridge (Ti-Phos)" structure.

[0046] Example 2

[0047] Except for adjusting the molar ratio of titanate to phosphorus flame retardant in step (1) from 1:3 to 1:1 during preparation, the rest is exactly the same as in Example 1.

[0048] Example 3

[0049] Except for adjusting the ultrasonic treatment time in step (2) from 4 hours to 2 hours during preparation, the rest is exactly the same as in Example 1.

[0050] Example 4

[0051] Except for adjusting the system temperature in step (3) from 60°C to 40°C during preparation, the rest is exactly the same as in Example 1.

[0052] Example 5

[0053] Except for adjusting the vacuum drying temperature in step (4) from 60°C to 80°C during preparation, the rest is exactly the same as in Example 1.

[0054] Comparative Example 1

[0055] Except for omitting the inert atmosphere protection in step (1) during preparation (replacing it with an air environment), the rest is exactly the same as in Example 1.

[0056] Comparative Example 2

[0057] Except for replacing at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), tetrahydrofuran (THF), acetone, and acetonitrile with ethanol in step (1) during preparation, the rest is exactly the same as in Example 1.

[0058] Comparative Example 3

[0059] Except for omitting the pH adjustment operation in step (3) during preparation (to maintain the natural pH), the rest is exactly the same as in Example 1.

[0060] Comparative Example 4

[0061] Except for changing the Ti-Phos addition method in step (3) from "drop by drop" to "all at once", the rest is exactly the same as in Example 1.

[0062] Comparative Example 5

[0063] Except for reducing the number of washing steps in step (4) from 3 to 1 during preparation, the rest is exactly the same as in Example 1.

[0064] Performance testing:

[0065] 1. Limiting Oxygen Index: According to the standard (GB / T 2406.2-2009), the test procedure is as follows: the modified carbon nanotubes are pressed into 100mm×6.5mm×3mm strips, placed in an oxygen index tester, and a mixture of oxygen and nitrogen gas is introduced. The minimum oxygen concentration required for the material to burn continuously for 3 minutes is recorded.

[0066] 2. Volume resistivity: According to the standard (GB / T 33818-2017), the test procedure is as follows: 0.5g of sample is pressed into a 20mm diameter disc under a pressure of 10MPa, and the resistance value is measured using a four-probe resistance meter to calculate the volume resistivity.

[0067] 3. 600℃ char residue rate: According to the standard (GB / T 13464-2008), the test procedure is as follows: Weigh 10mg of sample and place it in a thermogravimetric analyzer. Under a nitrogen atmosphere, the temperature is increased to 600℃ at 10℃ / min and held at the temperature for 30min. Record the percentage of residual mass.

[0068] 4. Specific surface area: According to the standard (GB / T 19587-2017), the test procedure is as follows: the nitrogen adsorption method is used. After degassing 0.2g of sample at 150℃ for 4h, the specific surface area is calculated by the BET model.

[0069] 5. Compressive strength ratio: According to the standard (GB / T 1041-2008), the test procedure is as follows: modified carbon nanotubes and epoxy resin are compounded and cured at a mass ratio of 1:10 to form a cylinder with a diameter of 10 mm. The compressive strength at 50% deformation is tested, and the strength ratio with that of pure epoxy resin is calculated.

[0070] 6. Resistivity change rate: According to the accelerated aging test method, the test procedure is as follows: the sample is placed in a 150℃ oven for 24 hours and then cooled to room temperature to measure the volume resistivity. The cycle is repeated 5 times and the resistivity change rate is calculated.

[0071] Table 1. Performance test results of the examples and comparative examples.

[0072]

[0073]

[0074] The composite modified carbon nanotubes in Examples 1-5 all exhibited high limiting oxygen index, low volume resistivity, and excellent high-temperature stability.

[0075] Compared to Example 1, Example 2 changed the molar ratio of titanate to phosphorus-based flame retardant in step 1 from 1:3 to 1:1. This resulted in a decrease in the limiting oxygen index from 32.5% to 30.1%, a decrease in char residue at 600°C from 67.3% to 63.5%, and an increase in volume resistivity from 0.035 Ω·cm to 0.048 Ω·cm. This indicates that reducing the phosphorus ratio weakens the phosphorus-titanium coordination density, leading to a decrease in the flame-retardant free radical quenching ability, while also impairing the continuity of the titanium dioxide shell.

[0076] Compared with Example 1, Example 3 shortened the ultrasonic treatment time in step 2 from 4 hours to 2 hours, and the specific surface area increased from 218 m². 2 / g rises to 225m 2 / g, but the residual carbon content dropped to 65.2%, and the resistivity change rate increased to 5.0%. This indicates that insufficient acid oxidation time led to a decrease in the carboxyl group density on the CNT surface, weakening the Ti-OC bond strength and deteriorating the interface stability at high temperatures.

[0077] Compared to Example 1, in Example 4, the system temperature in step 3 was lowered from 60°C to 40°C, the volume resistivity increased from 0.035 Ω·cm to 0.062 Ω·cm, and the compressive strength ratio decreased from 1.85 MPa to 1.65 MPa. This confirms that the low-temperature environment slows down the hydrolysis rate of titanate, leading to uneven TiO2 shell thickness, which damages the integrity of the conductive network and the mechanical strength of the composite.

[0078] Compared with Example 1, in Example 5, the vacuum drying temperature in step 4 was increased from 60°C to 80°C, the limiting oxygen index increased from 32.5% to 33.2%, and the resistivity change rate decreased from 4.3% to 3.5%. This indicates that high-temperature drying promotes the Ti-OP bond condensation reaction, enhances the bonding strength between the phosphorus-based flame retardant and the TiO2 network, and improves thermal stability.

[0079] In Comparative Example 1, omitting the inert atmosphere protection in step 1, the limiting oxygen index plummeted to 25.6%, and the volume resistivity increased to 0.21 Ω·cm. This confirms that oxygen triggers a side reaction of titanate hydrolysis, generating free TiO2 particles that block the conductive channels of CNTs, while the phosphorus-based flame retardant undergoes oxidative degradation.

[0080] Comparative Example 2: In step 1, the organic solvent was replaced with ethanol instead of DMF. The char residue at 600℃ decreased to 46.3%, and the specific surface area decreased to 172 m². 2 / g. This indicates that ethanol cannot dissolve phosphorus-based flame retardants, leading to the precipitation of the Ti-Phos complex and the appearance of pores in the titanium dioxide coating layer.

[0081] In Comparative Example 3, omitting the pH adjustment in step 3, the volume resistivity surged to 0.45 Ω·cm, with a resistivity change rate of 28.3%. This demonstrates that titanate rapidly hydrolyzes under neutral conditions, forming TiO2 aggregates rather than a continuous shell, which collapses after high-temperature cycling.

[0082] In Comparative Example 4, the Ti-Phos solution in step 3 was changed from "drop-by-drop addition" to "one-time pouring," resulting in a decrease in compressive strength ratio to 1.30 MPa and LOI to 28.1%. This indicates that excessively high local concentrations caused TiO2 particles to aggregate, creating cracks in the shell and weakening the physical barrier effect.

[0083] In Comparative Example 5, the number of washing cycles in step 4 was reduced from 3 to 1, resulting in an increase in resistivity change rate to 11.2% and a decrease in residual carbon content to 58.2%. This reflects that residual solvent ions disrupt the stability of the Ti-OP bonds, triggering high-temperature phase separation.

[0084] In summary, this application significantly improves the flame retardancy, conductivity, and high-temperature stability of a titanium dioxide-phosphorus flame retardant-modified carbon nanotube through a specific organic-inorganic composite structure modification scheme, verifying the innovation and practicality of the technical solution.

[0085] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing carbon nanotubes modified with a titanium dioxide-phosphorus flame retardant, characterized in that, Includes the following steps: (1) Preparation of Ti-Phos, a titanium ester-phosphorus flame retardant complex: The phosphorus flame retardant is dissolved in an organic solvent, and titanium ester is added under an inert atmosphere. The molar ratio of titanium ester to phosphorus flame retardant is controlled to be 1:1 to 1:

3. The mixture is stirred at a constant temperature of 60 to 80°C for 2 to 4 hours to allow the organic functional group (-OR) of the titanium ester to undergo esterification or coordination reaction with the active group (-OH, -P=O) of the phosphorus flame retardant, thus obtaining a titanium ester-phosphorus flame retardant complex solution. (2) Pretreatment of carbon nanotubes (CNTs): Multi-walled carbon nanotubes were added to a mixed acid (concentrated H2SO4:concentrated HNO3 = 3:1, v / v), ultrasonically treated for 2 to 4 hours, centrifuged and washed until neutral, and vacuum dried at 80°C for 12 hours to obtain activated CNTs with carboxyl / hydroxyl groups on the surface. (3) In-situ hydrolysis to construct CNT / TiO2-Phos composite structure: Activated CNTs were dispersed in deionized water and ultrasonically dispersed for 30 minutes to form a uniform suspension with a concentration of 1-5 mg / mL. Under continuous stirring, Ti-Phos composite solution was added dropwise to the CNT suspension, and the system temperature was controlled at 40-60℃. After the addition was completed, the pH was adjusted to 3-5 and the mixture was stirred at a constant temperature for 4-6 hours to allow the inorganic end (-Ti-OR) of titanate to undergo controllable hydrolysis and condensation on the CNT surface, generating a nano-TiO2 shell in situ. At the same time, the phosphorus flame retardant was embedded into the TiO2 network through Ti-OC / Ti-OP bonds and bonded to the CNT core to construct the CNT / TiO2-Phos composite structure. (4) Preparation of a titanium dioxide-phosphorus flame retardant-modified carbon nanotube: The reaction solution was centrifuged and washed three times alternately with deionized water and ethanol to remove free ions and byproducts. The obtained solid was placed in a vacuum drying oven and dried at 60°C for 8-12 hours to finally obtain a titanium dioxide-phosphorus flame retardant-modified carbon nanotube with a "core (CNT)-shell (TiO2)-bridge (Ti-Phos)" structure.

2. The preparation method according to claim 1, characterized in that, In step (1), the phosphorus-based flame retardant is selected from at least one of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), DOPO derivatives, phosphate ester flame retardants, phosphonate flame retardants, hypophosphite flame retardants, and hexachlorocyclotriphosphazene (HCCP); the molecular weight of the phosphorus-based flame retardant is 200-1000 g / mol.

3. The preparation method according to claim 1, characterized in that, In step (1), the organic solvent is selected from at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), tetrahydrofuran (THF), acetone, and acetonitrile. The amount of organic solvent used is 5 to 15 times the mass of the phosphorus-based flame retardant.

4. The preparation method according to claim 1, characterized in that, In step (1), the inert atmosphere is a nitrogen atmosphere or an argon atmosphere; the titanate is selected from at least one of tetraethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate.

5. The preparation method according to claim 1, characterized in that, In step (3), the acid used to adjust the pH is at least one of acetic acid, hydrochloric acid, and nitric acid; the power of the ultrasonic dispersion is 200-500W.

6. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of the Ti-Phos complex solution to the activated CNT suspension is 0.5:1 to 3:1, based on the mass ratio of titanate ester to activated CNT in the Ti-Phos complex; the dropping rate of the Ti-Phos complex solution is 0.5 to 2 mL / min.

7. The preparation method according to claim 1, characterized in that, In step (2), the multi-walled carbon nanotubes have a diameter of 10–50 nm, a length of 1–20 μm, and a specific surface area of ​​100–400 m². 2 / g; the amount of the mixed acid is 10 to 30 times the mass of the multi-walled carbon nanotubes.

8. The preparation method according to claim 1, characterized in that, In step (4), the centrifugation speed is 8000-12000 rpm and the centrifugation time is 10-30 minutes; the vacuum degree of the vacuum drying is -0.08 to -0.1 MPa.

9. The preparation method according to claim 1, characterized in that, In step (4), in the "core-shell-bridge" structure, the proportion of phosphorus flame retardant connected to the TiO2 shell through Ti-OP bonds accounts for more than 60% of the total bonding amount.

10. A titanium dioxide-phosphorus flame retardant composite modified carbon nanotube, prepared by the method according to any one of claims 1-9, characterized in that, The obtained composite modified carbon nanotubes contain phosphorus at a mass fraction of 1.5%–8.0%, titanium at a mass fraction of 3.0%–15.0%, and a TiO2 shell thickness of 2–20 nm. The resulting composite modified carbon nanotubes exhibit a limiting oxygen index (LOI) ≥ 28% and a volume resistivity ≤ 10⁻⁶. 2 Ω·cm.

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