Preparation method and application of halogen-free flame retardant

Abstract

The invention discloses a preparation method and application of a halogen-free flame retardant, and the preparation method comprises the following steps: S1, mixing 3, 5-diamino triazole with thiophene-2-formaldehyde, adding a DOPO solution, and reacting to obtain a phosphaphenanthrene flame retardant; s2, mixing the phosphaphenanthrene flame retardant with copper molybdate, and performing ultrasonic oscillation to obtain a phosphaphenanthrene-copper molybdate compound; s3, reacting the CNTs with an oxidizing agent to obtain F-CNTs of which the surface contains carboxyl or hydroxyl; s4, the phosphaphenanthrene-copper molybdate compound, F-CNTs and titanium dioxide are subjected to ultrasonic mixing, and a halogen-free flame retardant is obtained; according to the invention, the phosphaphenanthrene flame retardant is generated through reaction of the phosphaphenanthrene flame retardant and DOPO, and the flame retardant property is improved through gas-phase flame retardance and carbon layer formation; the copper molybdate loaded phosphaphenanthrene flame retardant can improve the synergistic flame retardant effect of the material; the functionalized CNTs can enhance the hydrophilicity, dispersity and mechanical property of the composite material; the flame retardant has the beneficial effects of high thermal stability, good flame retardant effect and the like.

Description

Technical Field

[0001] The present invention relates to the field of flame retardants, and in particular to a preparation method and application of a halogen-free flame retardant. Background Art

[0002] With the increasing demand for flame retardant materials in industry and daily life, especially in the fields of electronics, automobiles and construction, traditional halogen flame retardants have been gradually eliminated because they produce toxic gases during combustion, thereby polluting the environment. Therefore, environmentally friendly halogen-free flame retardants have become the focus of current research and application. Halogen-free flame retardants can not only improve the flame retardant properties of materials, but also will not release halogen compounds that are harmful to humans and the environment during combustion.

[0003] At present, the common halogen-free flame retardants on the market mainly include phosphorus-containing, nitrogen-containing and other types of compounds. These flame retardants not only provide flame retardant effects, but also improve the thermal stability and mechanical properties of materials. However, existing halogen-free flame retardants still face problems such as insufficient flame retardant effect, limited thermal stability and poor processing performance, especially in some composite materials with high performance requirements. Therefore, how to achieve efficient flame retardancy, improve heat resistance and improve the mechanical properties of materials remains a technical problem that needs to be solved urgently. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a preparation method and application of a halogen-free flame retardant with good flame retardant effect and high heat resistance.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] A method for preparing a halogen-free flame retardant comprises the following steps:

[0007] S1. 3,5-diaminotriazole and thiophene-2-carboxaldehyde are mixed in a mass ratio of 1:1 to form a reactant, a solvent is added to dissolve the reactant, and a 10-20 wt% DOPO solution is added in a mass ratio of 0.7-1.2:1 to the reactant. The mixture is stirred continuously and the reaction temperature is controlled at 50-80°C for 2-3 hours. After the reaction is completed, the solvent is removed by rotary evaporation to obtain a phosphaphenanthrene flame retardant.

[0008] S2. Adding a phosphaphenanthrene flame retardant and copper molybdate in a mass ratio of 4-5:1 to deionized water, stirring at 80-100° C. for 1-2 hours after ultrasonic oscillation, and centrifuging, washing, and drying the resulting product to obtain a phosphaphenanthrene-copper molybdate complex;

[0009] S3, mixing CNTs and an oxidant in a volume ratio of 1:2-3, reacting at 60-80° C. for 1-2 hours, washing to neutrality, and then drying to obtain F-CNTs containing carboxyl groups and / or hydroxyl groups on the surface;

[0010] S4. Ultrasonic mixing is performed on the phosphaphenanthrene-copper molybdate complex, F-CNTs and titanium dioxide in a mass ratio of 1.2-1.3:0.1-0.2:0.1-0.2, the ultrasonic frequency is 40-50 kHz, and the ultrasonic treatment is performed for 30-60 minutes to obtain a phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant.

[0011] According to the above technical solution, in step S1, the stirring rate of the reactant is 200-300 r / min, the solvent is tetrahydrofuran solvent, and the mass ratio between the reactant and tetrahydrofuran solvent is 1:10-20 g / mL.

[0012] Using the above technical solution, in step S2, the ultrasonic frequency is 40-50 kHz, and the ultrasonic treatment is performed for 20-30 minutes.

[0013] According to the above technical solution, in step S3, the oxidant is concentrated nitric acid and / or hydrogen peroxide, the concentration of the concentrated nitric acid is 60-70 wt%, and the concentration of the hydrogen peroxide is 25-35 wt%.

[0014] According to the above technical solution, magnesium hydroxide is further added in step S2, and the mass ratio of the phosphaphenanthrene flame retardant, copper molybdate and magnesium hydroxide is 4-5:1:0.2.

[0015] According to the above technical solution, in step S4, an organosilicon coupling agent is further added, and the amount of the organosilicon coupling agent added is 1-3 wt % of the total mass of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant.

[0016] According to the above technical solution, the organic silicon coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-propylenetriethoxysilane or phenyltriethoxysilane.

[0017] Using the above technical solution, in step S4, a nano-silicate mineral filler is further added, and the addition amount of the nano-silicate mineral filler is 0.5-1wt% of the total mass of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant. The nano-silicate mineral filler is montmorillonite or bentonite.

[0018] This technical solution also provides an application of a halogen-free flame retardant, wherein the application of the halogen-free flame retardant is to fill the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant into a polymer, and the filling amount of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant is controlled to be 6-30wt%. The polymer is thermoplastic polyurethane, polyethylene or nylon.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention generates a phosphaphenanthrene flame retardant by reacting a phosphaphenanthrene flame retardant with a DOPO solution. The phosphaphenanthrene flame retardant can not only suppress the spread of flames through the release of gases such as phosphoric acid through a gas-phase flame retardant mechanism, but also further slow down thermal decomposition by forming a carbon layer, thereby improving the flame retardant properties of the material. The phosphaphenanthrene flame retardant is loaded in copper molybdate, and copper molybdate acts as a synergistic flame retardant to provide an additional flame retardant effect. The addition of CNTs and functionalization of their surfaces can not only enhance the hydrophilicity and dispersibility of the CNTs, but also improve the mechanical properties, thermal stability and flame retardant properties of the composite material. Titanium dioxide is used as an inorganic filler to enhance the thermal stability and synergistic flame retardant effect of the composite material. Magnesium hydroxide has excellent heat absorption and can further enhance the flame retardant properties of the material. The organosilicon coupling agent can enhance the interfacial bonding between the components and promote molecular-level crosslinking, thereby improving the overall performance of the composite material. Filling the composite flame retardant into a polymer can improve the mechanical properties, high-temperature resistance and long-term durability of the polymer while ensuring good flame retardant properties. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the descriptions of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" described below mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0022] The present invention provides a method for preparing a halogen-free flame retardant, comprising the following steps:

[0023] S1. Mix 3,5-diaminotriazole and thiophene-2-carboxaldehyde in a mass ratio of 1:1 to form a reactant. After adding a solvent to dissolve, add a DOPO solution with a concentration of 10-20wt% in a ratio of 0.7-1.2:1 to the reactant. Continue stirring and control the reaction temperature at 50-80°C. The reaction time is 2-3h. After the reaction is completed, remove the solvent by rotary evaporation to obtain a phosphaphenanthrene flame retardant. Mix 3,5-diaminotriazole and thiophene-2-carboxaldehyde in a mass ratio of 1:1 to form a reactant. This ensures that the two raw materials react completely to form a phosphaphenanthrene structure. Then, Adding a solvent for dissolution can ensure that the reactants are fully dissolved and increase the contact opportunities between the reactants. Then, a DOPO solution with a concentration of 10-20wt% is added, and the mass ratio to the reactants is set to 0.7-1.2:1. In this way, sufficient DOPO molecular weight can be provided to generate phosphorus-containing flame retardant groups. As a phosphorus-containing flame retardant, DOPO can release gases such as phosphoric acid during the combustion of the material, thereby inhibiting the spread of flames and further slowing down thermal decomposition by forming a carbon layer. After the reaction is completed, the solvent is removed by rotary evaporation to effectively separate the reaction products and prevent residual solvent from affecting the performance of the product.

[0024] S2. Add phosphaphenanthrene flame retardant and copper molybdate into deionized water in a mass ratio of 4-5:1, and after ultrasonic oscillation, stir at 80-100°C for 1-2 hours. The obtained product is centrifuged, washed and dried to obtain a phosphaphenanthrene-copper molybdate complex. Copper molybdate acts as a synergistic flame retardant and works together with the phosphaphenanthrene flame retardant to provide an additional flame retardant effect during the combustion process. Ultrasonic oscillation is performed for 10-20 minutes, mainly through the effect of high-frequency oscillation, so that copper molybdate can be evenly dispersed on the surface of the phosphaphenanthrene flame retardant, promoting contact and reaction between the two. The effect of ultrasonic oscillation can effectively break up the agglomerated copper molybdate particles and improve its dispersibility in the solution, thereby accelerating the formation of the complex. Thereafter, stirring is performed at 80-100°C for 1-2 hours, and the chemical reaction can be promoted by heating, so that the interaction between the phosphaphenanthrene and copper molybdate is more sufficient, and the stability of the complex is ensured.

[0025] S3. CNTs are mixed with an oxidant in a volume ratio of 1:2-3, reacted at 60-80°C for 1-2 hours, washed to neutrality and then dried to obtain F-CNTs containing carboxyl and / or hydroxyl groups on the surface; the oxidant can functionalize the surface of CNTs through oxidation reaction to generate hydrophilic functional groups containing carboxyl and hydroxyl groups, thereby improving the dispersibility, hydrophilicity and binding properties of CNTs with respect to the substrate; specifically, the carboxyl group has strong polarity and water solubility, and can provide good compatibility with other hydrophilic substances, thereby improving the dispersion of CNTs in aqueous solutions or other polar substrates. The hydrophilic functional groups can increase the hydrophilicity of the material, prevent the aggregation of CNTs in the matrix, and thus improve the uniformity and performance of the composite material. In addition, the hydroxyl group also has a strong polarity, which can increase the hydrophilicity of the material, so that the CNTs form a stronger adhesion between the substrate and enhance their dispersion in the matrix material. In addition, the hydroxyl group can also participate in the formation of hydrogen bonds, thereby increasing the bonding strength of the composite material and improving the mechanical properties. By introducing these hydrophilic functional groups, F-CNTs can be more evenly dispersed in the composite material, avoiding agglomeration, thereby forming a stronger bond with other materials, and improving the mechanical properties, thermal stability and flame retardancy of the composite material.

[0026] S4. Ultrasonic mixing of a phosphaphenanthrene-copper molybdate complex, F-CNTs, and titanium dioxide in a mass ratio of 1.2-1.3:0.1-0.2:0.1-0.2 is performed at an ultrasonic frequency of 40-50 kHz for 30-60 minutes to obtain a phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant. The phosphaphenanthrene-copper molybdate complex, as the primary flame retardant component, provides effective flame retardancy; F-CNTs improve the mechanical properties of the composite; and titanium dioxide, as an inorganic filler, not only improves the thermal stability of the composite but also exhibits a certain flame retardant synergistic effect. Due to the strong hydrophobicity and surface aggregation of F-CNTs, ultrasonic mixing can break up aggregates in the composite, preventing agglomeration from affecting the performance of the composite.

[0027] Furthermore, in step S1, the stirring rate of the reactants is 200-300 r / min, the solvent is tetrahydrofuran, and the mass ratio of the reactants to the tetrahydrofuran is 1:10-20 g / mL. Tetrahydrofuran has good solubility and can effectively dissolve the two raw materials, 3,5-diaminotriazole and thiophene-2-carboxaldehyde.

[0028] Furthermore, in step S2, the ultrasonic frequency is 40-50 kHz, and the ultrasonic treatment is performed for 20-30 minutes. Setting the ultrasonic frequency to 40-50 kHz can provide sufficient energy to break up the agglomeration of copper molybdate particles in the phosphaphenanthrene-copper molybdate composite without excessively damaging the structure of the composite.

[0029] Furthermore, in step S3, the oxidant is concentrated nitric acid and / or hydrogen peroxide, with the concentrated nitric acid at a concentration of 60-70 wt% and the hydrogen peroxide at a concentration of 25-35 wt%. The oxidant can introduce oxygen functional groups during the oxidation process, thereby enhancing the hydrophilicity and dispersibility of the CNTs. Concentrated nitric acid, as a strong oxidant, can introduce oxygen groups, particularly carboxyl groups, onto the surface of the CNTs through oxidation, making the CNT surface more hydrophilic and reducing its hydrophobicity. Hydrogen peroxide, as a milder oxidant, can oxidize the CNT surface to generate hydroxyl functional groups.

[0030] Furthermore, in step S2, magnesium hydroxide is added, with the mass ratio of the phosphaphenanthrene flame retardant, copper molybdate, and magnesium hydroxide being 4-5:1:0.2. As a halogen-free synergistic flame retardant, magnesium hydroxide has excellent heat absorption properties and can release water vapor at high temperatures, thereby absorbing large amounts of heat and inhibiting the spread of flames. Its high melting point and excellent thermal stability provide additional protection for the flame retardant. Furthermore, magnesium hydroxide promotes the formation of a protective carbonized layer on the material surface, thereby reducing the diffusion of heat and gases and improving the material's fire resistance in fires.

[0031] Furthermore, in step S4, an organosilicon coupling agent is added in an amount of 1-3 wt% of the total mass of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant. The organosilicon coupling agent can enhance the interfacial bonding between the components of the composite material, thereby promoting molecular-level crosslinking and improving the overall performance of the material.

[0032] Furthermore, the organic silicon coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-propylenetriethoxysilane or phenyltriethoxysilane.

[0033] Furthermore, in step S4, a nano-silicate mineral filler is added, the amount of the nano-silicate mineral filler being 0.5-1 wt% of the total mass of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant. The nano-silicate mineral filler is montmorillonite or bentonite. As nano-silicate mineral fillers, montmorillonite and bentonite have very fine layered structures and high specific surface areas, thereby forming an effective barrier structure in the composite material to reduce heat transfer. At the same time, they can produce a good carbonized layer under high temperature conditions to inhibit oxygen ingress, thereby improving the flame retardant effect. Furthermore, montmorillonite and bentonite can be evenly dispersed in the composite material, thereby enhancing the mechanical properties of the material, allowing the material to have high strength and toughness while maintaining good flame retardant properties.

[0034] The present invention also provides an application of a halogen-free flame retardant, which comprises adding a phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant to a polymer, wherein the amount of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant is controlled to be between 6 and 30 wt%. The polymer is thermoplastic polyurethane, polyethylene, or nylon. Thermoplastic polyurethane has good elasticity and wear resistance, polyethylene has excellent flexibility in low-temperature environments, and nylon has significant advantages in high strength and wear resistance. By adding the composite flame retardant, the stability of the polymer in high-temperature or fire environments is enhanced, and its overall mechanical properties and long-term durability are also improved.

[0035] Example 1

[0036] Example 1 of the present invention provides a preparation method and application of a halogen-free flame retardant, comprising the following steps:

[0037] S1. 3,5-diaminotriazole and thiophene-2-carboxaldehyde are mixed in a mass ratio of 1:1 to form a reactant, tetrahydrofuran solvent is added to dissolve the reactant, and a 10 wt% DOPO solution is added in a ratio of 0.7:1 to the reactant mass, and the reaction temperature is continuously stirred at 50°C, the stirring rate is 200 r / min, and the reaction time is 2 h. After the reaction is completed, the solvent is removed by rotary evaporation to obtain a phosphaphenanthrene flame retardant; wherein the mass ratio between the reactant and the tetrahydrofuran solvent is 1:10 g / mL;

[0038] S2, adding phosphaphenanthrene flame retardant, copper molybdate and magnesium hydroxide in a mass ratio of 4:1:0.2 to deionized water, subjecting to ultrasonic oscillation at an ultrasonic frequency of 40 kHz for 20 min, stirring at 80° C. for 1 h, and centrifuging, washing and drying the resulting product to obtain a phosphaphenanthrene-copper molybdate complex;

[0039] S3, mixing CNTs with concentrated nitric acid at a volume ratio of 1:2, with a concentration of 60 wt%, reacting at 60°C for 1 hour, washing to neutrality, and then drying to obtain F-CNTs with carboxyl groups on the surface;

[0040] S4. After mixing the phosphaphenanthrene-copper molybdate complex, F-CNTs and titanium dioxide in a mass ratio of 1.2:0.1:0.1, an organosilicon coupling agent and a nano-silicate mineral filler are added, and the mixture is subjected to ultrasonic oscillation treatment at an ultrasonic frequency of 40 kHz for 30 minutes to obtain a phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant; wherein the amount of the organosilicon coupling agent added is 1wt% of the total mass of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant, and the organosilicon coupling agent is γ-aminopropyltriethoxysilane; the amount of the nano-silicate mineral filler added is 0.5wt% of the total mass of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant, and the nano-silicate mineral filler is montmorillonite.

[0041] S5. Filling the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant into the thermoplastic polyurethane polymer, and controlling the filling amount of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant to be 10 wt %.

[0042] Example 2

[0043] Embodiment 2 of the present invention provides a preparation method and application of a halogen-free flame retardant, comprising the following steps:

[0044] S1. 3,5-diaminotriazole and thiophene-2-carboxaldehyde are mixed in a mass ratio of 1:1 to form a reactant, tetrahydrofuran solvent is added to dissolve the reactant, and a 20 wt% DOPO solution is added in a mass ratio of 1.2:1 to the reactant, and the reaction temperature is continuously stirred at 80°C, the stirring rate is 300 r / min, and the reaction time is 3 h. After the reaction is completed, the solvent is removed by rotary evaporation to obtain a phosphaphenanthrene flame retardant; wherein the mass ratio between the reactant and the tetrahydrofuran solvent is 1:20 g / mL;

[0045] S2. Add phosphaphenanthrene flame retardant, copper molybdate and magnesium hydroxide in a mass ratio of 5:1:0.2 into deionized water, subject the mixture to ultrasonic oscillation at a frequency of 50 kHz for 30 min, stir the mixture at 100° C. for 2 h, and centrifuge, wash and dry the resulting product to obtain a phosphaphenanthrene-copper molybdate complex;

[0046] S3, mixing CNTs with concentrated nitric acid at a volume ratio of 1:3, with a concentration of 70 wt%, reacting at 80°C for 2 h, washing to neutrality, and then drying to obtain F-CNTs with carboxyl groups on the surface;

[0047] S4. After mixing the phosphaphenanthrene-copper molybdate complex, F-CNTs and titanium dioxide in a mass ratio of 1.3:0.2:0.2, an organosilicon coupling agent and a nano-scale silicate mineral filler are added, and the mixture is subjected to ultrasonic oscillation treatment with an ultrasonic frequency of 50 kHz and ultrasonic treatment for 60 minutes to obtain a phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant; wherein the amount of the organosilicon coupling agent added is 3wt% of the total mass of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant, and the organosilicon coupling agent is γ-propylenetriethoxysilane; the amount of the nano-scale silicate mineral filler added is 1wt% of the total mass of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant, and the nano-scale silicate mineral filler is bentonite.

[0048] S5. Filling the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant into the nylon polymer, and controlling the filling amount of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant to be 20 wt %.

[0049] Comparative Example 1

[0050] The preparation method and application of the halogen-free flame retardant of Comparative Example 1 are different from those of Example 1 in that in step S1 , no DOPO solution is added to react with the reactants.

[0051] Comparative Example 2

[0052] The preparation method and application of the halogen-free flame retardant of Comparative Example 2 are different from those of Example 1 in that: in step S2, the phosphaphenanthrene flame retardant is not loaded on copper molybdate.

[0053] Comparative Example 3

[0054] The preparation method and application of the halogen-free flame retardant of Comparative Example 3 are different from those of Example 1 in that: in step S3, the CNTs do not undergo an oxidation reaction with the oxidant.

[0055] Comparative Example 4

[0056] The preparation method and application of the halogen-free flame retardant of Comparative Example 4 are different from those of Example 1 in that: in step S2, magnesium hydroxide is not added.

[0057] Comparative Example 5

[0058] The preparation method and application of the halogen-free flame retardant of Comparative Example 5 are different from those of Example 1 in that: in step S4, no organosilicon coupling agent is added.

[0059] The following experiments were conducted on the above Examples 1-2 and Comparative Examples 1-5 to verify or understand their performance. In the thermoplastic polyurethane polymer filled with phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant prepared in the above Examples 1-2 and Comparative Examples 1-5,

[0060]

[0061] Table 1 Comparison of halogen-free flame retardant performance test data

[0062] Table 1 above shows that in the application of the halogen-free flame retardants prepared in Examples 1 and 2, the phosphaphenanthrene flame retardant produced by reacting the phosphaphenanthrene flame retardant with a DOPO solution not only releases gases such as phosphoric acid through a vapor-phase flame retardant mechanism to inhibit flame spread, but also further slows thermal decomposition by forming a char layer, thereby improving the flame retardancy of the material. The phosphaphenanthrene flame retardant is loaded into copper molybdate, which acts as a synergistic flame retardant and provides additional flame retardancy. The addition of CNTs and surface functionalization not only enhances the hydrophilicity and dispersibility of the CNTs but also improves the mechanical properties, thermal stability, and flame retardancy of the composite material. Titanium dioxide, as an inorganic filler, improves the thermal stability and synergistic flame retardancy of the composite material. Magnesium hydroxide, with its excellent heat absorption properties, further enhances the flame retardancy of the material. The organosilicon coupling agent improves the interfacial bonding between the components and promotes molecular-level crosslinking, thereby enhancing the overall performance of the composite material. Filling the composite flame retardant into a polymer improves the mechanical properties, high-temperature resistance, and long-term durability of the polymer while maintaining good flame retardancy.

[0063] In Comparative Example 1, DOPO, as a phosphorus-containing flame retardant, can provide phosphorus to release gases such as phosphoric acid when a fire occurs, suppressing the spread of flames through gas-phase flame retardancy, while forming a char layer to further slow down thermal decomposition. Without the participation of DOPO, the phosphorus content in the phosphaphenanthrene structure will be significantly reduced, resulting in a decrease in flame retardancy, and it will not be able to effectively suppress the spread of flames and slow down the thermal degradation process.

[0064] In Comparative Example 2, the phosphaphenanthrene flame retardant was not loaded on copper molybdate, which resulted in a significant reduction in the performance and thermal stability of the composite flame retardant. Copper molybdate, as a synergistic flame retardant, can provide additional flame retardant effects during the combustion of the material, especially at high temperatures, by releasing molybdenum compounds to inhibit the spread of flames, thereby reducing the release of harmful gases. If the phosphaphenanthrene flame retardant did not form a complex with the copper molybdate load, the synergistic flame retardant effect of copper molybdate would not be fully exerted, resulting in a significant reduction in flame retardant performance. Secondly, copper molybdate can improve the stability of the composite material at high temperatures and reduce thermal degradation.

[0065] In Comparative Example 3, the CNTs did not undergo an oxidation reaction with the oxidant, and the CNT surface maintained its original hydrophobicity, resulting in poor dispersion in the composite material and easy agglomeration. In addition, the bonding force between the CNTs and the substrate was also weak, and a good interface bonding with the polymer could not be formed, resulting in reduced mechanical properties of the composite material.

[0066] In Comparative Example 4, magnesium hydroxide was not added, which would result in a significant reduction in the flame retardant effect and thermal stability of the composite flame retardant. Magnesium hydroxide, as a halogen-free synergistic flame retardant, has excellent heat absorption and a high melting point. It can absorb a large amount of heat during the combustion process to reduce the flame temperature, thereby effectively inhibiting the spread of flames. In addition, magnesium hydroxide can release water vapor at high temperatures, and the evaporation heat absorption effect of water vapor is used to reduce the local temperature. At the same time, a protective carbonized layer is formed to reduce the diffusion of heat and gas, thereby improving the fire resistance of the material. Without magnesium hydroxide, the composite material will lack an effective heat absorption mechanism and carbonized layer for protection in a high temperature environment, thereby affecting the thermal stability and flame retardant properties of the material.

[0067] In Comparative Example 5, no organosilicon coupling agent was added, which would lead to deterioration of the interfacial bonding and compatibility between the components in the composite material, thereby affecting the mechanical properties, thermal stability and flame retardant effect of the composite material; the organosilicon coupling agent forms chemical bonds with inorganic substances such as copper molybdate, titanium dioxide and organic substrates through its silane group, thereby enhancing the bonding strength of the components in the composite material; if no coupling agent is added, these inorganic and organic components are difficult to effectively combine, resulting in weak interfacial bonding, which in turn affects the uniformity and stability of the composite material.

[0068] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a halogen-free flame retardant, characterized in that: The following steps are involved: S1. 3,5-diaminotriazole and thiophene-2-carboxaldehyde are mixed in a mass ratio of 1:1 to form a reactant, a solvent is added to dissolve the reactant, and a 10-20 wt% DOPO solution is added in a mass ratio of 0.7-1.2:1 to the reactant. The mixture is stirred continuously and the reaction temperature is controlled at 50-80°C for 2-3 hours. After the reaction is completed, the solvent is removed by rotary evaporation to obtain a phosphaphenanthrene flame retardant. S2. Adding a phosphaphenanthrene flame retardant and copper molybdate in a mass ratio of 4-5:1 to deionized water, stirring at 80-100° C. for 1-2 hours after ultrasonic oscillation, and centrifuging, washing, and drying the resulting product to obtain a phosphaphenanthrene-copper molybdate complex; S3, mixing CNTs and an oxidant in a volume ratio of 1:2-3, reacting at 60-80° C. for 1-2 hours, washing to neutrality, and then drying to obtain F-CNTs containing carboxyl groups and / or hydroxyl groups on the surface; S4. Ultrasonic mixing is performed on the phosphaphenanthrene-copper molybdate complex, F-CNTs and titanium dioxide in a mass ratio of 1.2-1.3:0.1-0.2:0.1-0.2, the ultrasonic frequency is 40-50 kHz, and the ultrasonic treatment is performed for 30-60 minutes to obtain a phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant.

2. The method for preparing a halogen-free flame retardant according to claim 1, wherein: In step S1, the stirring rate of the reactant is 200-300 r / min, the solvent is tetrahydrofuran solvent, and the mass ratio between the reactant and tetrahydrofuran solvent is 1:10-20 g / mL.

3. The method for preparing a halogen-free flame retardant according to claim 1, wherein: In step S2, the ultrasonic frequency is 40-50 kHz, and the ultrasonic treatment is performed for 20-30 min.

4. The method for preparing a halogen-free flame retardant according to claim 1, wherein: In step S3, the oxidant is concentrated nitric acid and / or hydrogen peroxide, the concentration of the concentrated nitric acid is 60-70 wt%, and the concentration of the hydrogen peroxide is 25-35 wt%.

5. The method for preparing a halogen-free flame retardant according to claim 1, wherein: In step S2, magnesium hydroxide is further added, and the mass ratio of the phosphaphenanthrene flame retardant, copper molybdate and magnesium hydroxide is 4-5:1:0.

2.

6. The method for preparing a halogen-free flame retardant according to claim 1, wherein: In step S4, an organosilicon coupling agent is further added, and the amount of the organosilicon coupling agent added is 1-3 wt % of the total mass of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant.

7. The method for preparing a halogen-free flame retardant according to claim 6, wherein: The organic silicon coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-propylenetriethoxysilane or phenyltriethoxysilane.

8. The method for preparing a halogen-free flame retardant according to claim 7, wherein: In step S4, a nano-silicate mineral filler is further added. The amount of the nano-silicate mineral filler added is 0.5-1 wt% of the total mass of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant. The nano-silicate mineral filler is montmorillonite or bentonite.

9. Use of a halogen-free flame retardant obtained as claimed in any one of claims 1 to 8, characterized in that: The phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant is filled into the polymer, and the filling amount of the phosphaphenanthrene-copper molybdate / carbon nanotube composite flame retardant is controlled to be 6-30wt%.

10. The use of the halogen-free flame retardant according to claim 9, characterized in that: The polymer is thermoplastic polyurethane, polyethylene or nylon.

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