A method for preparing high-efficiency magnesium-based flame retardant by etching technology

Abstract

This invention relates to a method for preparing a high-efficiency magnesium-based flame retardant using etching technology, comprising the following steps: S1, dissolving potassium ferricyanide in deionized water, simultaneously adding salt solution and alkali solution while controlling the pH value; the resulting suspension A is aged, filtered, washed, and freeze-dried to obtain ferricyanide-intercalated magnesium-based LDH; S2, dispersing the ferricyanide-intercalated magnesium-based LDH in deionized water, adding nickel salt solution under continuous stirring, aging, filtering, washing, and freeze-drying to obtain Prussian blue analog-intercalated and surface-functionalized magnesium-based LDH-PBAs; S3, dispersing the magnesium-based LDH-PBAs in deionized water, adding diethylenetriaminepentamethylidene phosphoric acid solution under continuous stirring while controlling the pH value; the resulting suspension B is etched, filtered, washed, and freeze-dried to obtain the high-efficiency magnesium-based flame retardant. This invention is simple, low-cost, and can achieve the UL-94 V-0 rating for flame-retardant composite materials with low addition amounts.

Description

Technical Field

[0001] This invention relates to the field of flame retardant materials, and more particularly to a method for preparing a high-efficiency magnesium-based flame retardant using etching technology. Background Technology

[0002] Epoxy resins, as an important class of thermosetting polymers, possess excellent mechanical and adhesive properties and chemical resistance, holding an irreplaceable position in advanced composite materials, electronic packaging, aerospace, and other fields. However, like other polymers, the hydrocarbon backbone structure of epoxy resins makes them inherently highly flammable, releasing large amounts of heat and toxic fumes during combustion, posing a serious threat to life and property. To improve the flame retardant properties of epoxy resins, the main approach currently is to add flame retardants. Among these, additive flame retardants have become the mainstream solution due to their simple processing and wide applicability, compared to intrinsically flame-retardant polymers which are complex to synthesize and expensive. However, traditional halogenated flame retardants are increasingly limited due to environmental and health risks. Therefore, developing novel flame retardants that are both environmentally friendly and highly efficient has become a core issue that urgently needs to be addressed in this field.

[0003] Magnesium-based solid hydrogen hydroxides (LDHs), as a typical two-dimensional nanomaterial, can absorb a large amount of heat and release structural water upon thermal decomposition, thus possessing the dual functions of gas-phase dilution, cooling, and solid-phase physical barrier construction. Therefore, they are considered promising candidates for halogen-free flame retardants. my country is rich in salt lake resources, containing abundant magnesium resources, providing a unique raw material foundation for the development of magnesium-based LDH flame retardants. However, the intrinsic physical barrier effect of magnesium-based LDHs is difficult to form a continuous and dense protective layer at low filler concentrations, and their ability to catalyze polymer crosslinking to char is limited, resulting in insufficient flame retardant efficiency when used alone as a flame retardant, often requiring higher addition levels to achieve ideal results. In recent years, researchers have attempted to functionalize magnesium-based LDHs through intercalation modification or surface functionalization to improve their flame retardant efficiency. However, while the aforementioned modification strategies can provide some improvement through elemental synergy or interface optimization, they have failed to effectively solve the problem of low catalytic char formation efficiency of magnesium-based LDH. Even at low addition levels (below 5 wt%), epoxy composites still struggle to pass the UL-94 vertical burning V-0 rating test. Therefore, significantly improving the catalytic char formation efficiency of magnesium-based LDH through material structure innovation, and thus achieving high-efficiency flame retardancy at low addition levels, is one of the important ways to promote its application. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a simple and low-cost method for preparing high-efficiency magnesium-based flame retardants using etching technology.

[0005] To address the above problems, the present invention provides a method for preparing a high-efficiency magnesium-based flame retardant using etching technology, comprising the following steps: S1. Dissolve potassium ferricyanide in CO2-free water to obtain a potassium ferricyanide solution with a concentration of 39.5 g / L. Then, add the salt solution and alkali solution dropwise to the potassium ferricyanide solution simultaneously, and control the pH of the mixed solution at 10±0.5. After the addition is completed, continue stirring for 20 to 40 min, and use nitrogen protection throughout the process. Then, age the resulting suspension A at 65 to 85 °C for 12 to 36 h, and after filtration, washing and freeze drying, obtain ferricyanide intercalated magnesium-based LDH. S2 disperses the ferricyanide-intercalated magnesium-based LDH in deionized water to obtain a solution with a concentration of 32 g / L; then, a nickel salt solution is added under continuous stirring, and stirring is continued for 20-40 min after the addition is complete; then, it is aged at room temperature for 6-18 h, and after filtration, washing and freeze-drying, Prussian blue analogue (PBAs) intercalated and surface-functionalized magnesium-based LDH-PBAs are obtained. S3 disperses the magnesium-based LDH-PBAs in deionized water to obtain a magnesium-based LDH-PBAs solution with a concentration of 30 g / L; then, diethylenetriaminepentamethylenephosphoric acid (DTPMP) solution is added under continuous stirring, and the pH of the mixture is controlled at 6±0.5; then, the resulting suspension B is etched at 55-75 °C for 12-24 h, and after filtration, washing and freeze-drying, a high-efficiency magnesium-based flame retardant is obtained.

[0006] In step S1, the salt solution refers to a mixed aqueous solution of magnesium salt and aluminum salt; the magnesium salt is magnesium chloride or magnesium nitrate; the aluminum salt is aluminum chloride or aluminum nitrate, and the molar concentration of the aluminum salt is 0.10-0.15 mol / L, the molar concentration ratio of magnesium salt to aluminum salt is 2:1; the molar ratio of potassium ferricyanide to aluminum salt is 1:1.

[0007] In step S1, the alkaline solution refers to a sodium hydroxide solution or potassium hydroxide solution with a concentration of 0.6–0.8 mol / L.

[0008] In step S2, the concentration of the nickel salt solution is 20-32 g / L. The nickel salt in the solution is nickel nitrate or nickel chloride, and the mass ratio of the nickel salt to the ferricyanide intercalated magnesium-based LDH is 1:1-2.

[0009] In step S3, the concentration of the diethylenetriamine pentamethylmethylene phosphoric acid (DTPMP) solution is 50–75 g / L, and the mass ratio of DTPMP to magnesium-based LDH-PBAs in the solution is 1:2–3.

[0010] Compared with the prior art, the present invention has the following advantages: 1. This invention utilizes Prussian blue analogues (PBAs) intercalation modification combined with surface functionalization treatment of magnesium-based dihydrogen hydrides (LDHs) to simultaneously introduce transition metal ions into the interlayer and surface of the magnesium-based LDH, thereby effectively promoting the catalytic crosslinking and char formation reaction of the polymer matrix during combustion. This strategy fully utilizes the abundant transition metal catalytic active centers in PBAs, significantly enhancing the catalytic char formation ability of the magnesium-based LDH. This allows the composite material to rapidly construct a protective char layer with good thermal stability and structural integrity in the early stages of pyrolysis and combustion, laying the foundation for subsequent flame retardant effects.

[0011] 2. This invention utilizes diethylenetriaminepentamylate (DTPMP) to etch the intercalated and surface-functionalized magnesium-based LDH-PBAs composite flame retardant. As a multidentate ligand, DTPMP can selectively remove some unstable metal-ligand coordination bonds in the PBA structure, effectively increasing the exposure of catalytic active sites while maintaining the integrity of its framework structure. The etched flame retardant provides more catalytic active centers during combustion, further accelerating the crosslinking and charring reaction of the polymer matrix, thus enabling the epoxy composite material to achieve a UL-94 vertical burning V-0 rating even with a relatively low addition amount.

[0012] 3. The method of the present invention is simple, low-cost, and easy to implement. Attached Figure Description

[0013] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0014] Figure 1 The images show SEM images of PBA intercalated and surface-functionalized magnesium-based LDH-PBAs (a) and DTPMP-etched high-efficiency magnesium-based flame retardant (b) obtained in Example 1 of this invention.

[0015] Figure 2 The images show UL-94 vertical burning test results for pure EP, PBA intercalated and surface-functionalized magnesium-based LDH-PBAs epoxy composite material (EP / LDH-PBAs) obtained in Example 1 of this invention, and DTPMP-etched high-efficiency magnesium-based flame retardant epoxy composite material (EP / LDH-PBAs@D). Detailed Implementation

[0016] Design principle of this invention: Based on the structural characteristics of magnesium-based layered double hydroxide (LDH) materials, [Fe(CN)6] was simultaneously introduced into the interlayer and surface of magnesium-based LDH via a co-precipitation method. 3-By coordinating anions and using them as precursors to grow Prussian blue analogues (PBAs) in situ, intercalation modification and surface functionalization of magnesium-based LDH are achieved using PBAs. This design fully utilizes the abundant transition metal catalytic active centers in PBAs, enabling the synergistic introduction of rich transition metal catalytic active components into the interlayer and surface of magnesium-based LDH. This effectively promotes the catalytic crosslinking and char formation of the matrix during polymer combustion, providing a structural basis for enhancing the catalytic char formation capability of magnesium-based LDH.

[0017] Building upon this foundation, diethylenetriaminepentamylate (DTPMP) was added as an etchant to controllably etch the magnesium-based LDH-PBAs composite flame retardant. DTPMP molecules possess strong coordination capabilities, selectively removing some unstable metal-ligand bonding units from the PBA framework structure. This effectively increases the exposure of catalytic active sites while maintaining the integrity of the basic PBA framework structure, further enhancing its catalytic char formation efficiency. This design principle balances the introduction of catalytically active components with the full exposure of active sites, aiming to address the technical challenge of insufficient flame retardant performance at low addition levels of magnesium-based LDH flame retardants from the perspective of improving catalytic char formation efficiency.

[0018] A method for preparing a high-efficiency magnesium-based flame retardant using etching technology includes the following steps: S1. Dissolve potassium ferricyanide in CO2-free water to obtain a potassium ferricyanide solution with a concentration of 39.5 g / L. Then, add the salt solution and alkali solution dropwise to the potassium ferricyanide solution simultaneously, and control the pH value of the mixed solution at 10±0.5. After the addition is completed, continue stirring for 20 to 40 min, and use nitrogen protection throughout the process. Then, age the resulting suspension A at 65 to 85 °C for 12 to 36 h, and after filtration, washing and freeze drying, obtain ferricyanide intercalated magnesium-based LDH.

[0019] Wherein: salt solution refers to a mixed aqueous solution of magnesium salt and aluminum salt; magnesium salt is magnesium chloride or magnesium nitrate; aluminum salt is aluminum chloride or aluminum nitrate, and the molar concentration of aluminum salt is 0.10-0.15 mol / L, the molar concentration ratio of magnesium salt to aluminum salt is 2:1; the molar ratio of potassium ferricyanide to aluminum salt is 1:1.

[0020] Alkaline solution refers to sodium hydroxide or potassium hydroxide solution with a concentration of 0.6–0.8 mol / L.

[0021] S2 disperses ferricyanide-intercalated magnesium-based LDH in deionized water to obtain a solution with a concentration of 32 g / L. Subsequently, a nickel salt solution with a concentration of 20–32 g / L is added under continuous stirring. The nickel salt in this solution is either nickel nitrate or nickel chloride, and the mass ratio (g / g) of the nickel salt to the ferricyanide-intercalated magnesium-based LDH is 1:1–2. After the addition is complete, stirring is continued for 20–40 min. Then, the mixture is aged at room temperature for 6–18 h, followed by filtration, washing, and freeze-drying to obtain Prussian blue analogue (PBAs) intercalated and surface-functionalized magnesium-based LDH-PBAs.

[0022] S3 disperses magnesium-based LDH-PBAs in deionized water to obtain a magnesium-based LDH-PBAs solution with a concentration of 30 g / L. Subsequently, a diethylenetriaminepentamethylenephosphoric acid (DTPMP) solution with a concentration of 50–75 g / L is added under continuous stirring, and the pH of the mixture is controlled at 6 ± 0.5. The mass ratio (g / g) of DTPMP to magnesium-based LDH-PBAs in the DTPMP solution is 1:2–3. Then, the resulting suspension B is etched at 55–75 °C for 12–24 h, and after filtration, washing, and freeze-drying, a high-efficiency magnesium-based flame retardant is obtained.

[0023] Example 1 A method for preparing a high-efficiency magnesium-based flame retardant using etching technology includes the following steps: S1. Dissolve 3.95 g of potassium ferricyanide (0.012 mol) in 100 mL of de-CO2 water to obtain a potassium ferricyanide solution, which is then transferred to a three-necked flask. Subsequently, 100 mL of a mixed salt solution of magnesium chloride (0.24 mol / L) and aluminum chloride (0.12 mol / L) and sodium hydroxide solution (0.7 mol / L) are simultaneously added dropwise to the potassium ferricyanide solution, and the pH of the mixed solution is controlled at 10 ± 0.5. After the addition is complete, stirring is continued for 30 min, and nitrogen protection is used throughout the process. Then, the resulting suspension A is transferred to an oven and aged at 75 ℃ for 24 h. After filtration, washing, and freeze-drying, magnesium ferricyanide intercalated LDH is obtained.

[0024] S2 dispersed 3.20 g of ferricyanide-intercalated magnesium-based LDH in 100 mL of deionized water to obtain a solution with a concentration of 32 g / L; then, 100 mL of nickel nitrate solution (25 g / L) was added dropwise while stirring continuously, and stirring was continued for 30 min after the addition was completed; then, it was aged at room temperature for 12 h, and after filtration, washing and freeze-drying, Prussian blue analogue (PBAs) intercalated and surface-functionalized magnesium-based LDH-PBAs were obtained.

[0025] S3 dispersed 3.00 g of magnesium-based LDH-PBAs in 100 mL of deionized water, and then added 20 mL of a 75 g / L diethylenetriamine pentamethylidene phosphoric acid (DTPMP) solution while stirring continuously, and controlled the pH of the mixture at 6±0.5; then, the resulting suspension B was transferred to an oven and etched PBAs at 65 ℃ for 18 h, and after filtration, washing and freeze drying, a high-efficiency magnesium-based flame retardant was obtained.

[0026] like Figure 1 As shown, SEM images of the PBA intercalated and surface-functionalized magnesium-based LDH-PBAs prepared in Example 1 are shown. Figure 1 (a) It can be seen that its surface is covered with uniformly dispersed PBA particles. The abundant transition metal catalytic active centers in PBA provide a structural basis for improving the catalytic carbonization ability of magnesium-based LDH. The high-efficiency magnesium-based flame retardant etched by DTPMP ( Figure 1 (b) Small particles can still be seen adhering to the surface of magnesium-based LDH, but the particle size is significantly smaller than before etching. This indicates that DTPMP etching of PBAs retains the original framework structure, but increases the exposure of catalytic active sites, which is expected to significantly improve the catalytic carbonization ability of magnesium-based LDH, generate a dense carbon layer, and improve the flame retardant properties of epoxy composites.

[0027] [Flame retardant performance test] Epoxy composites were prepared by adding the same amount (3 wt%) of PBA intercalated and surface-functionalized magnesium-based LDH-PBAs and DTPMP-etched high-efficiency magnesium-based flame retardant (LDH-PBAs@D) obtained in Example 1 of this invention to epoxy resin (EP). The flame retardant properties (UL-94 vertical burning) of the composites were tested and compared with pure EP. The results are as follows: Figure 2 As shown.

[0028] Figure 2 The figures show the UL-94 vertical burning test results for pure EP, EP / LDH-PBAs, and EP / LDH-PBAs@D. As can be seen from the figures, pure EP continues to burn after ignition, is not self-extinguishing, and has no rating (NR). When 3 wt% LDH-PBAs were added, the EP / LDH-PBAs composite material achieved a UL-94 V-1 rating. This indicates that the introduction of transition metal ions (Fe2+, Fe3+, Fe ... 3+ / Ni 2+During combustion, it can play a certain role in catalytic char formation, promoting the cross-linking of the polymer matrix to form a protective char layer, thereby effectively improving the flame retardant properties of EP. However, even with a low addition of 3 wt%, EP / LDH-PBAs still cannot pass the more stringent UL-94 V-0 rating test. In contrast, the composite material with the same amount (3 wt%) of LDH-PBAs@D successfully passed the UL-94 V-0 rating test. This significant improvement is attributed to the etching treatment of DTPMP: on the one hand, DTPMP selectively removes some unstable metal-ligand coordination bonds in the PBA structure, exposing more transition metal catalytic active centers while maintaining the integrity of the framework structure, greatly improving the efficiency of catalytic cross-linking and char formation, and prompting the composite material to quickly build a dense char layer in the early stage of combustion; on the other hand, DTPMP molecules are rich in nitrogen and phosphorus elements. During combustion, nitrogen can release non-flammable gases to play a gas-phase dilution role, while phosphorus can promote polymer dehydration and char formation and participate in the formation of phosphorus-containing cross-linked structures, forming a multi-faceted synergistic effect with transition metal catalytic char formation, further strengthening the construction of the solid-phase barrier. The above results indicate that the DTPMP etching strategy successfully achieved high-efficiency flame retardancy of magnesium-based LDH flame retardants at low addition levels through a dual mechanism of "exposing active sites to enhance catalytic char formation" and "nitrogen / phosphorus synergistic construction of an efficient barrier".

[0029] Example 2 A method for preparing a high-efficiency magnesium-based flame retardant using etching technology includes the following steps: S1. Dissolve 4.94 g of potassium ferricyanide (0.015 mol) in 125 mL of de-CO2 water to obtain a potassium ferricyanide solution, which is then transferred to a three-necked flask. Subsequently, 100 mL of a mixed salt solution of magnesium nitrate (0.30 mol / L) and aluminum nitrate (0.15 mol / L) and a potassium hydroxide solution (0.8 mol / L) are simultaneously added dropwise to the potassium ferricyanide solution, and the pH of the mixed solution is controlled at 10 ± 0.5. After the addition is complete, stirring is continued for 40 min, and nitrogen protection is used throughout the process. Then, the resulting suspension A is transferred to an oven and aged at 85 ℃ for 36 h. After filtration, washing, and freeze-drying, magnesium ferricyanide intercalated LDH is obtained.

[0030] S2 dispersed 3.20 g of ferricyanide-intercalated magnesium-based LDH in 100 mL of deionized water, and then added 80 mL of 20 g / L nickel chloride solution with continuous stirring. After the addition was complete, stirring was continued for 20 min. Then, it was aged at room temperature for 6 h, and after filtration, washing and freeze drying, Prussian blue analogue (PBAs) intercalation and surface-functionalized magnesium-based LDH-PBAs were obtained.

[0031] S3 dispersed 3.00 g of magnesium-based LDH-PBAs in 100 mL of deionized water, and then added 20 mL of a 50 g / L diethylenetriamine pentamethylidene phosphoric acid (DTPMP) solution while stirring continuously. The pH of the mixture was controlled at 6 ± 0.5. The resulting suspension B was then transferred to an oven and etched into PBAs at 55 °C for 12 h. After filtration, washing, and freeze-drying, a high-efficiency magnesium-based flame retardant was obtained.

[0032] Example 3 A method for preparing a high-efficiency magnesium-based flame retardant using etching technology includes the following steps: S1. Dissolve 3.29 g of potassium ferricyanide (0.010 mol) in 83.4 mL of CO2-free water to obtain a potassium ferricyanide solution, which is then transferred to a three-necked flask. Subsequently, 100 mL of a mixed salt solution of magnesium chloride (0.20 mol / L) and aluminum chloride (0.10 mol / L) and a sodium hydroxide solution (0.6 mol / L) are simultaneously added dropwise to the three-necked flask, with the pH of the mixed solution controlled at 10 ± 0.5. After the addition is complete, stirring is continued for 20 min, with nitrogen protection throughout the process. Then, the resulting suspension A is transferred to an oven and aged at 65 °C for 12 h. After filtration, washing, and freeze-drying, magnesium ferricyanide-intercalated LDH is obtained.

[0033] S2 dispersed 3.20 g of ferricyanide-intercalated magnesium-based LDH in 100 mL of deionized water, and then added 100 mL of nickel nitrate solution with a concentration of 32 g / L while stirring continuously. After the addition was complete, stirring was continued for 40 min. Then, the mixture was aged at room temperature for 18 h, and after filtration, washing and freeze-drying, Prussian blue analogue (PBAs) intercalated and surface-functionalized magnesium-based LDH-PBAs were obtained.

[0034] S3 dispersed 3.00 g of magnesium-based LDH-PBAs in 100 mL of deionized water, and then added 20 mL of a 60 g / L diethylenetriamine pentamethylidene phosphoric acid (DTPMP) solution while stirring continuously, and controlled the pH of the mixture at 6 ± 0.5; then, the resulting suspension B was transferred to an oven and etched PBAs at 75 ℃ for 24 h, and after filtration, washing and freeze drying, a high-efficiency magnesium-based flame retardant was obtained.

Claims

1. A method for preparing a high-efficiency magnesium-based flame retardant using etching technology, comprising the following steps: S1. Dissolve potassium ferricyanide in CO2-free water to obtain a potassium ferricyanide solution with a concentration of 39.5 g / L. Then, add the salt solution and alkali solution dropwise to the potassium ferricyanide solution simultaneously, and control the pH of the mixed solution at 10±0.

5. After the addition is completed, continue stirring for 20 to 40 min, and use nitrogen protection throughout the process. Then, age the resulting suspension A at 65 to 85 °C for 12 to 36 h, and after filtration, washing and freeze drying, obtain ferricyanide intercalated magnesium-based LDH. S2 disperses the ferricyanide-intercalated magnesium-based LDH in deionized water to obtain a solution with a concentration of 32 g / L; then, a nickel salt solution is added under continuous stirring, and stirring is continued for 20-40 min after the addition is complete; then, it is aged at room temperature for 6-18 h, and after filtration, washing and freeze-drying, Prussian blue analog intercalated and surface-functionalized magnesium-based LDH-PBAs are obtained. S3 disperses the magnesium-based LDH-PBAs in deionized water to obtain a magnesium-based LDH-PBAs solution with a concentration of 30 g / L; then, diethylenetriamine pentamethylidene phosphoric acid solution is added under continuous stirring, and the pH of the mixture is controlled at 6±0.5; then, the resulting suspension B is etched at 55-75 °C for 12-24 h, and after filtration, washing and freeze-drying, a high-efficiency magnesium-based flame retardant is obtained.

2. The method for preparing a high-efficiency magnesium-based flame retardant using etching technology as described in claim 1, characterized in that: In step S1, the salt solution refers to a mixed aqueous solution of magnesium salt and aluminum salt; the magnesium salt is magnesium chloride or magnesium nitrate; the aluminum salt is aluminum chloride or aluminum nitrate, and the molar concentration of the aluminum salt is 0.10-0.15 mol / L, the molar concentration ratio of magnesium salt to aluminum salt is 2:1; the molar ratio of potassium ferricyanide to aluminum salt is 1:

1.

3. The method for preparing a high-efficiency magnesium-based flame retardant using etching technology as described in claim 1, characterized in that: In step S1, the alkaline solution refers to a sodium hydroxide solution or potassium hydroxide solution with a concentration of 0.6–0.8 mol / L.

4. The method for preparing a high-efficiency magnesium-based flame retardant using etching technology as described in claim 1, characterized in that: In step S2, the concentration of the nickel salt solution is 20–32 g / L. The nickel salt in the solution is nickel nitrate or nickel chloride, and the mass ratio of the nickel salt to the ferricyanide intercalated magnesium-based LDH is 1:1–2.

5. The method for preparing a high-efficiency magnesium-based flame retardant using etching technology as described in claim 1, characterized in that: In step S3, the concentration of the diethylenetriamine pentamethylphosphoric acid solution is 50–75 g / L, and the mass ratio of diethylenetriamine pentamethylphosphoric acid to magnesium-based LDH-PBAs in the solution is 1:2–3.

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