A novel composite flame-retardant material and a preparation method thereof
By constructing a core-shell structure with montmorillonite as the core and LDH-CNTs as the shell, the flame retardant and mechanical properties of epoxy resin-based composite materials were synergistically improved, resolving the contradiction between flame retardancy and mechanical properties, and reducing heat and smoke release.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANDONG NON METALLIC MATERIAL RESEARCH INSTITUTE
- Filing Date
- 2026-04-14
- Publication Date
- 2026-07-10
AI Technical Summary
There is a contradiction between the flame retardancy and mechanical properties of existing epoxy resin-based composite materials. It is difficult to improve the flame retardancy rating and reduce the heat release rate at the same time. In addition, the addition of inorganic flame retardants leads to a decrease in mechanical properties.
A core-shell structure with montmorillonite as the core and LDH-CNTs as the shell was constructed using a one-pot method, achieving uniform dispersion of LDH, CNTs, and MMT in an epoxy resin substrate. LDH nanosheets were then grown in situ using an alkaline medium hot water hydrolysis method to form a ternary composite flame retardant material.
It significantly improves the flame retardant and mechanical properties of epoxy resin, reduces heat release rate and smoke release rate, and the material preparation is simple and low cost, with broad application potential.
Smart Images
Figure CN122356589A_ABST
Abstract
Description
Technical Field This invention belongs to the field of polymer flame retardant materials technology, specifically a novel composite flame retardant material and its preparation method. Background Technology Epoxy resin (EP) is widely used in aerospace structural materials, adhesives, and sealants due to its lightweight and corrosion-resistant properties. However, its inherent flammability limits its application in fields with high safety requirements. In aviation fire scenarios, the flame retardancy of epoxy resin-based composites is particularly important. Excellent flame retardant properties can effectively reduce smoke and heat release, prevent the spread of flames, and buy valuable time for emergency response.
[0001] In recent years, bimetallic hydroxides have attracted widespread attention as novel green nanomaterials. Layered bimetallic hydroxides (LDHs), with their halogen-free chemical composition and layered structure, have been used as cost-effective and environmentally friendly inorganic flame retardants. Under high-temperature combustion conditions, LDH decomposes to produce metal oxides that coat the substrate surface, forming a protective layer that isolates the external oxygen supply and the heat backflow of the combustion flame. Furthermore, LDH decomposition also generates H2O and CO2, reducing the flame temperature and diluting oxygen and combustible gases. However, LDH, as an inorganic flame retardant, has poor compatibility with organic epoxy resins, and composite materials formed by adding LDH to epoxy resins face the challenge of decreased mechanical properties.
[0002] Traditional silicon-based flame retardant montmorillonite (MMT) exhibits excellent flame retardant properties, but its poor dispersibility in EP polymer matrices leads to deterioration of the mechanical properties of composites after flame retardant treatment. Carbon nanotubes (CNTs), due to their unique tubular nanostructure and composition of sp² hybridized carbon atoms, demonstrate superior mechanical properties, including high tensile strength and elastic modulus. The interwoven network structure of carbon nanotubes provides a good mechanical support framework for flame retardant additives, and the oxygen-containing functional groups on their surface can improve the compatibility of flame retardants with organic EP matrices.
[0003] Therefore, there is an urgent need to explore composite strategies of LDH and MMT to leverage their synergistic flame-retardant advantages while maintaining the mechanical properties of flame-retardant EP composites. Summary of the Invention The technical problem to be solved by the present invention is to provide a ternary in-situ composite flame retardant material and its preparation method, which can improve the flame retardant rating of epoxy resin, significantly reduce heat release rate and smoke release rate, and alleviate mechanical property loss.
[0004] To address the aforementioned problems, this invention employs the following technical solution: a core-shell structure with montmorillonite as the core and LDH-CNTs as the shell is constructed using a one-pot method. This achieves uniform dispersion of LDH, CNTs, and MMT in the epoxy resin substrate, significantly improving the mechanical property degradation caused by the addition of inorganic flame retardants to the epoxy resin substrate. Consequently, the flame retardant and mechanical properties of the prepared ternary in-situ composite flame retardant material are significantly enhanced, thus achieving the objective of this invention.
[0005] This invention relates to a method for preparing a novel composite flame-retardant material, comprising the following steps: (a) Functionalized carbon nanotubes were dispersed in a solvent and ultrasonically dispersed to obtain a uniform dispersion of functionalized carbon nanotubes. (b) Add the precursor metal salt of the bimetallic hydroxide, montmorillonite particles and alkaline solute to the uniform dispersion of functionalized carbon nanotubes, and stir to obtain an alkaline mixture. (c) Under reflux conditions of 80~140℃, the alkaline mixture obtained is subjected to hot water hydrolysis reaction. After the reaction is completed, it is separated, washed until pH=7, and dried to obtain a new type of composite flame retardant material.
[0006] Preferably, in step (a), the functionalized carbon nanotube is one of single-walled or multi-walled carbon nanotubes functionalized with hydroxyl, carboxyl, or epoxy groups.
[0007] Preferably, in step (b), the precursor for the synthesis of the bimetallic hydroxide is a chloride, sulfate, or nitrate of a divalent metal such as magnesium, zinc, copper, or cobalt, or a chloride, sulfate, or nitrate of a trivalent metal such as aluminum, iron, or chromium, with a molar ratio of divalent to trivalent metal ranging from 3:2 to 3:1; the alkaline solute is at least one of urea, melamine, thiourea, or sodium hydroxide.
[0008] Preferably, in step (c), the hot hydrolysis reaction time is 4 to 8 hours.
[0009] Preferably, in step (a), the ultrasonic dispersion time is 30-60 minutes and the power is 100-200W; in step (b), the stirring speed is 500-800 rpm; and in step (c), centrifugation is used and the mixture is washed with water and ethanol until pH=7.
[0010] The present invention also relates to a novel composite flame retardant material prepared by the above method.
[0011] This invention employs an alkaline medium hot water hydrolysis method to construct a novel ternary in-situ composite material with montmorillonite as the core and LDH-CNTs as the shell. LDH nanosheets grow in situ on an interwoven CNT network and further coat the outer surface of larger MMT particles. The in-situ growth of LDH nanosheets inhibits the self-entanglement of CNTs. CNTs help improve the mechanical properties of the flame-retardant polymer material, and the oxygen-containing functional groups on the CNTs enhance the interfacial dispersibility and compatibility of the ternary composite flame-retardant material within the polymer matrix. Ultimately, this achieves uniform dispersion of the three flame-retardant components in the polymer, significantly improving the mechanical property degradation caused by the addition of inorganic flame retardants. The flame-retardant polymer substrate exhibits significantly improved flame-retardant and mechanical properties. The material preparation process is simple, the reaction conditions are easy to control, and the flame-retardant components are non-toxic and low-cost, possessing broad practical application potential. The novel composite flame-retardant material prepared by this invention significantly reduces heat release and smoke release rates while improving the flame-retardant rating of epoxy resin and mitigating mechanical property loss. Compared with LDH-CNTs+MMT, which is a simple physical mixture, the LDH-CNTs-MMT prepared in this invention has superior mechanical properties and flame retardant effect. Attached Figure Description
[0012] Figure 1 Images showing the structural morphology of the LDH-CNTs-MMT composite flame retardant material obtained in Example 1; Figure 2 The images and elemental distribution maps of LDH-CNTs-MMT obtained in Example 1 are shown in the high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image. Figure 3 The thermogravimetric analysis curves and thermogravimetric differential analysis curves of the specimens obtained in the comparative example; Figure 4 The cone calorimeter test curves of the samples obtained for comparison are shown. Detailed Implementation The technical solution of the present invention will be further described below with reference to specific embodiments and accompanying drawings, but this should not be construed as limiting the technical solution of the present invention.
[0013] Example 1 0.2 g of carboxyl-functionalized multi-walled carbon nanotubes were dispersed in 250 mL of deionized water and treated with sonication at 200 W for 30 minutes to achieve uniform dispersion. Then, 0.5 g of MMT, 30 mmol of AlCl3·6H2O, 70 mmol of ZnCl2, 480 mmol of urea, and 230 mmol of NaOH were added and mixed uniformly under sonication to prepare an alkaline mixture. The alkaline mixture was transferred to a round-bottom flask, magnetically stirred for 30 minutes (600 rpm), and then a reflux condenser was installed. The mixture was then subjected to hydrolysis at 100 °C for 4 hours. During the reaction, LDH nanosheets grew in situ on the interwoven CNT network and further coated the outer surface of larger MMT particles, ultimately generating a novel ternary in-situ composite material mixture of LDH-CNTs-MMT with MMT as the core and LDH-CNTs as the shell. After the reaction was completed, the reaction mixture was cooled to room temperature, the product was separated by centrifugation, the product was repeatedly washed with deionized water and ethanol until pH=7, dried at 60℃ for 12 hours, and ground to obtain LDH-CNTs-MMT ternary resetting composite flame retardant with MMT as the core and LDH-CNTs as the shell.
[0014] The scanning electron microscope image of the flame retardant LDH-CNTs-MMT prepared in this embodiment is as follows: Figure 1 As shown, the flame retardant shell contains LDH nanosheets and dispersed CNTs. Transmission electron microscopy images are shown below. Figure 2 As shown, Si elements from MMT and Zn elements from LDH can be detected in LDH-CNTs-MMT, and Zn and Al elements exist in the outer layer, while Si is wrapped in the inner layer of LDH-CNTs-MMT. This indicates that the method of this embodiment can successfully construct the LDH-CNTs-MMT ternary reset composite flame retardant composite material with MMT as the core and LDH-CNTs as the shell.
[0015] Compared with LDH-CNTs+MMT prepared by existing technology, according to the method of "GB / T 2408-2021 Determination of Burning Performance of Plastics - Horizontal and Vertical Methods", the LDH-CNTs-MMT ternary reset composite flame retardant prepared in this embodiment improves the flame retardant performance of epoxy resin to UL-94 V-1 level with a limiting oxygen index of 31.0%, and reduces the heat release rate by 35.12% and the smoke release rate by 37.58%.
[0016] Example 2 0.2 g of hydroxyl-functionalized single-walled carbon nanotubes were dispersed in 250 mL of deionized water and sonicated at 200 W for 30 minutes to ensure complete dispersion. Then, 0.5 g of MMT, 30 mmol of AlCl3·6H2O, 90 mmol of MgCl2·6H2O, 480 mmol of melamine, and 230 mmol of NaOH were added and mixed thoroughly under sonication to prepare an alkaline mixture. The alkaline mixture was transferred to a round-bottom flask, magnetically stirred for 30 minutes (600 rpm), and then refluxed at 80 °C for 10 hours. After the reaction, the reaction mixture was cooled to room temperature, centrifuged to separate the product, and washed repeatedly with deionized water and ethanol until pH=7. The product was then dried at 60 °C for 12 hours and ground to obtain the LDH-CNTs-MMT composite flame retardant.
[0017] Compared with LDH-CNTs+MMT prepared by existing technology, according to the method of "GB / T 2408-2021 Determination of Burning Performance of Plastics - Horizontal and Vertical Methods", the LDH-CNTs-MMT ternary resetting composite flame retardant prepared in this embodiment improves the flame retardant performance of epoxy resin to UL-94 V-1 level with a limiting oxygen index of 30.3%, and reduces the heat release rate by 34.81% and the smoke release rate by 35.67%.
[0018] Example 3 0.2 g of epoxy-functionalized multi-walled carbon nanotubes were dispersed in 250 mL of deionized water and sonicated at 200 W for 30 minutes to ensure complete dispersion. Then, 0.5 g of MMT, 40 mmol of CrCl3·6H2O, 60 mmol of MgCl2·6H2O, 480 mmol of thiourea, and 230 mmol of NaOH were added and mixed thoroughly under sonication to prepare an alkaline mixture. The alkaline mixture was transferred to a round-bottom flask, magnetically stirred for 30 minutes (600 rpm), and then reacted at 140 °C for 5 hours using a reflux condenser. After the reaction, the reaction mixture was cooled to room temperature, and the product was separated by centrifugation. The product was washed repeatedly with deionized water and ethanol until pH=7, dried at 60 °C for 12 hours, and ground to obtain the LDH-CNTs-MMT composite flame retardant.
[0019] Compared with LDH-CNTs+MMT prepared by existing technology, the LDH-CNTs-MMT ternary resetting composite flame retardant prepared in this embodiment improves the flame retardant performance of epoxy resin to UL-94 V-1 level with a limiting oxygen index of 30.5%, according to the method of "GB / T 2408-2021 Determination of Burning Performance of Plastics - Horizontal and Vertical Methods". The heat release rate is reduced by 34.61% and the smoke release rate is reduced by 36.29%.
[0020] Example 4 0.2 g of hydroxyl-functionalized multi-walled carbon nanotubes were dispersed in 250 mL of deionized water and sonicated at 200 W for 30 minutes to ensure complete dispersion. Then, 0.5 g of MMT, 30 mmol of Al2(SO4)3·18H2O, 90 mmol of MgSO4·7H2O, 480 mmol of melamine, and 230 mmol of NaOH were added and mixed thoroughly under sonication to prepare an alkaline mixture. The alkaline mixture was transferred to a round-bottom flask, magnetically stirred for 30 minutes (600 rpm), and then reacted at 120 °C for 10 hours using a reflux condenser. After the reaction, the reaction mixture was cooled to room temperature, and the product was separated by centrifugation. The product was washed repeatedly with deionized water and ethanol until pH=7, dried at 60 °C for 12 hours, and ground to obtain the LDH-CNTs-MMT composite flame retardant.
[0021] Compared with LDH-CNTs+MMT prepared by existing technology, according to the method of "GB / T 2408-2021 Determination of Burning Performance of Plastics - Horizontal and Vertical Methods", the LDH-CNTs-MMT ternary reset composite flame retardant prepared in this embodiment improves the flame retardant performance of epoxy resin to UL-94 V-1 level with a limiting oxygen index of 29.7%, and reduces the heat release rate by 34.52% and the smoke release rate by 35.98%.
[0022] Example 5 0.2 g of epoxy-functionalized single-walled carbon nanotubes were dispersed in 250 mL of deionized water and sonicated at 150 W for 40 minutes to ensure complete dispersion. Then, 0.5 g of MMT, 60 mmol of Co(NO3)2·6H2O, 40 mmol of Cr(NO3)3·9H2O, 480 mmol of thiourea, and 230 mmol of NaOH were added and mixed thoroughly under sonication. The alkaline mixture was transferred to a round-bottom flask, magnetically stirred for 20 minutes (800 rpm), and then refluxed at 100 °C for 6 hours. After the reaction, the mixture was cooled to room temperature, centrifuged to separate the product, and washed repeatedly with deionized water and ethanol until pH=7. The product was then dried at 60 °C for 12 hours and ground to obtain the LDH-CNTs-MMT composite flame retardant.
[0023] Compared with LDH-CNTs+MMT prepared by existing technology, according to the method of "GB / T 2408-2021 Determination of Burning Performance of Plastics - Horizontal and Vertical Methods", the LDH-CNTs-MMT ternary resetting composite flame retardant prepared in this embodiment improves the flame retardant performance of epoxy resin to UL-94 V-1 level with a limiting oxygen index of 30.6%, and reduces the heat release rate by 35.02% and the smoke release rate by 37.53%.
[0024] Comparative Example Take 3 g of the LDH-CNTs-MMT flame retardant prepared in Example 1, add 77.6 g of molten epoxy resin E44, melt in an oil bath at 100 ℃, and then mechanically stir at 900 rpm for 0.5 hours. Add 19.4 g of molten 4,4-diaminodiphenylmethane to the above mixture, mechanically stir for 5 minutes, pour into a polytetrafluoroethylene mold, cure at 120 ℃ for 2 hours, then cure at 140 ℃ for 2 hours, cool to room temperature, and demold to obtain the flame-retardant treated sample EP@LDH-CNTs-MMT.
[0025] LDH-CNTs flame retardant, LDH flame retardant, and LDH-CNTs+MMT flame retardant were prepared according to existing technology and then added to epoxy resin E44 according to the above-mentioned method for preparing test specimens to obtain flame-retardant treated test specimens EP@LDH-CNTs, EP@LDH, and EP@LDH-CNTs+MMT.
[0026] EP specimens are prepared directly without adding flame retardants according to the above method.
[0027] The thermogravimetric analysis test results of the above five types of specimens are as follows: Figure 3 As shown. During the thermal decomposition process ( Figure 3 a) The temperature at which a 5wt% mass loss is achieved is called T. 5wt% This refers to the initial decomposition temperature. In the DTG curve, the temperature at which the maximum thermal decomposition rate is reached is defined as T. max . Figure 3 In section a, thanks to the early endothermic decomposition of LDH and MMT under heating conditions and the early initiation of the coking process, the T of the flame-retardant EP composite material... 5wt% The values are all lower than those of pure EP (370.7 °C). Ta of EP@LDH-CNTs+MMT 5wt% The temperature (354.8°C) is slightly higher than that of EP@LDH-CNTs-MMT (353.8 °C), indicating that the core-shell structure of MMT and LDH-CNTs can contribute to the heat absorption and cooling properties of the material in flame retardants. According to... Figure 3 The DTG curve in b, and the T values of EP and the flame-retardant EP composite. maxThe values are in the following order: EP (392.9 °C) > EP@LDH-CNTs (382.5 °C) > EP@LDH (382.0 °C) > EP@LDH-CNTs+MMT (380.5 °C) > EP@LDH-CNTs-MMT (378.2 °C). It can be seen that the endothermic pyrolysis of LDH and MMT helps to lower the temperature of the combustion cycle, thereby lowering the temperature at which the maximum decomposition rate is reached.
[0028] The cone calorimeter test data for the above five types of splines are as follows: Figure 4 As shown, (a) heat release rate (HRR), (b) total heat release (THR), (c) smoke generation rate (SPR), and (d) total smoke production (TSP). Pure EP burned vigorously and released a large amount of heat in the combustion experiment, exhibiting the highest peak heat release rate (PHRR) (1751.51 kW / m²) and total heat release (THR) (151.10 MJ / m²) among all tested samples. In contrast, the addition of LDH and LDH-CNTs to EP reduced the PHRR and THR values of EP@LDH and EP@LDH-CNTs, which is attributed to the heat absorbed by LDH pyrolysis and the generated metal oxides acting as a physical barrier to inhibit combustion and heat release. The simultaneous introduction of LDH, CNTs, and MMT into EP further reduces the PHRR and THR values of EP@LDH-CNTs+MMT compared to EP@LDH and EP@LDH-CNTs, highlighting the synergistic effect of LDH-CNTs and MMT in enhancing flame retardant properties and suppressing heat release from the EP matrix. The PHRR and THR of EP@LDH-CNTs+MMT are reduced by 30.42% and 5.35% respectively compared to pure EP. Notably, the designed LDH-CNTs-MMT ternary in-situ composite material exhibits superior flame retardant performance in the EP matrix compared to LDH-CNTs+MMT. Compared to EP, LDH-CNTs-MMT reduces the PHRR and THR of EP@LDH-CNTs-MMT by 46.89% and 35.12% respectively, indicating that the constructed core-shell structure effectively suppresses combustion development and slows heat release. This can be attributed to the endothermic pyrolysis of LDH, the cooling and dilution effect of water vapor generated from LDH decomposition, and the formation of a high-quality residual carbon layer.
[0029] The above embodiments and comparative examples are merely illustrative of the concept and implementation of the present invention and are not intended to limit it. Under the concept of the present invention, technical solutions without substantial changes are still within the scope of protection.
Claims
1. A method for preparing a novel composite flame-retardant material, characterized in that, Includes the following steps: (a) Functionalized carbon nanotubes were dispersed in a solvent and ultrasonically dispersed to obtain a uniform dispersion of functionalized carbon nanotubes. (b) Add the precursor metal salt of the bimetallic hydroxide, montmorillonite particles and alkaline solute to the uniform dispersion of functionalized carbon nanotubes, and stir to obtain an alkaline mixture. (c) Under reflux conditions of 80~140℃, the alkaline mixture obtained is subjected to hot water hydrolysis reaction. After the reaction is completed, it is separated, washed until pH=7, and dried to obtain a new type of composite flame retardant material.
2. The preparation method of the novel composite flame-retardant material as described in claim 1, characterized in that, In step (a), the functionalized carbon nanotube is one of single-walled or multi-walled carbon nanotubes functionalized with hydroxyl, carboxyl, or epoxy groups.
3. The method for preparing a novel composite flame-retardant material as described in claim 1, characterized in that, In step (b), the precursor for the synthesis of the bimetallic hydroxide is a chloride, sulfate, or nitrate of a divalent metal such as magnesium, zinc, copper, or cobalt, or a chloride, sulfate, or nitrate of a trivalent metal such as aluminum, iron, or chromium, with a molar ratio of divalent to trivalent metal ranging from 3:2 to 3:1; the alkaline solute is at least one of urea, melamine, thiourea, or sodium hydroxide.
4. The preparation method of a novel composite flame-retardant material as described in claim 1, characterized in that, In step (c), the hot hydrolysis reaction time is 4 to 8 hours.
5. The method for preparing a novel composite flame-retardant material as described in claim 1, characterized in that, In step (a), the ultrasonic dispersion time is 30-60 minutes and the power is 100-200W; in step (b), the stirring speed is 500-800 rpm; in step (c), centrifugation is used and the mixture is washed with water and ethanol until pH=7.
6. A novel composite flame-retardant material, characterized in that... It is prepared by the preparation method of the novel composite flame retardant material according to any one of claims 1 to 5.