Preparation method of flame retardant based on phytic acid modified hydroxyapatite and flame retardant wood

Abstract

The application provides a preparation method of a flame retardant based on phytic acid modified hydroxyapatite and a flame-retardant wood, and the preparation method comprises the following steps: mixing hydroxyapatite and a modifier, wherein the modifier is a phytic acid solution, and performing modification treatment to obtain modified hydroxyapatite; and mixing the modified hydroxyapatite, hexakisamino cyclotriphosphazene and water to obtain the flame retardant based on the phytic acid modified hydroxyapatite. The flame retardant based on the phytic acid modified hydroxyapatite prepared by the application can be stably loaded in wood and help to form a carbonization protective layer during heating or combustion, so as to improve the flame retardant performance of the wood, and is suitable for the flame retardant treatment of wood materials for buildings, furniture and decoration.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant treatment technology for wood materials, specifically relating to a flame retardant based on phytic acid-modified hydroxyapatite and a method for preparing flame retardant wood. Background Technology

[0002] Wood is lightweight, easy to process, renewable, and has good decorative properties, making it widely used in construction, furniture, interior decoration, and packaging. However, wood is mainly composed of organic components such as cellulose, hemicellulose, and lignin, which are prone to pyrolysis and combustion when exposed to fire or high temperatures, releasing flammable volatiles and causing flame spread. Therefore, improving the flame-retardant properties of wood is an important technical issue for the safe application of wood materials.

[0003] Existing methods for flame retardant treatment of wood mainly include impregnation, coating, chemical grafting, and composite modification. Among these, impregnation allows flame retardant components to penetrate the porous structure of wood, and is characterized by its relatively simple process and wide applicability. However, conventional inorganic salts or small-molecule flame retardants have limited fixation stability in wood and are prone to migration or loss in humid or wet environments, affecting flame retardant durability. On the other hand, some halogenated flame retardant systems or organic synthetic flame retardant systems often suffer from insufficient environmental friendliness, smoke toxicity, or poor compatibility with the wood interface.

[0004] Hydroxyapatite possesses good thermal and chemical stability, making it suitable as an inorganic flame retardant or insulating component in flame-retardant systems. However, when used alone, hydroxyapatite's ability to enhance the flame retardancy of wood is quite limited. Therefore, it is necessary to provide a flame retardant that combines inorganic barrier properties, good fixation stability, and excellent flame-retardant effect to improve the flame-retardant properties and stability of flame-retardant treatments in wood. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a flame retardant based on phytic acid modified hydroxyapatite and a method for preparing flame retardant wood.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0007] A method for preparing a flame retardant based on phytic acid-modified hydroxyapatite includes the following steps: (1) Hydroxyapatite and a modifier are mixed and modified to obtain modified hydroxyapatite; the modifier is phytic acid solution; (2) The modified hydroxyapatite, hexaaminocyclotriphosphazene obtained in step (1) and water are mixed to obtain a flame retardant based on phytic acid modified hydroxyapatite.

[0008] In a further improvement of the above preparation method, in step (1), the mass ratio of hydroxyapatite to modifier is 1:3 to 30. In step (2), the mass-to-volume ratio of the modified hydroxyapatite, hexaaminocyclotriphosphazene, and water is 2.5g~20g∶0.5g~10g∶50mL~100mL.

[0009] The above preparation method is further improved in step (1), wherein the phytic acid solution contains 1% to 3% phytic acid by mass and the pH value of the phytic acid solution is 7 to 8; the preparation method of the phytic acid solution is as follows: dissolve the phytic acid aqueous solution in water, adjust the pH value of the system to 7 to 8, and obtain the phytic acid solution; the mass ratio of the phytic acid aqueous solution to water is 1 to 3: 97 to 99, the mass percentage of the phytic acid aqueous solution is 70%, and the pH value of the system is adjusted by using an alkaline solution.

[0010] The above preparation method is further improved in step (1) by including a metal salt in the modifier, wherein the metal salt is one or more of copper sulfate, zinc chloride, ferric chloride and magnesium chloride; the preparation method of the modifier is as follows: phytic acid aqueous solution and metal salt are dissolved in water, and the pH value of the system is adjusted to 7-8 to obtain phytic acid solution; the mass ratio of phytic acid aqueous solution, metal salt and water is 1-3:0.4-3:97-99, the mass percentage of phytic acid aqueous solution is 70%, and the pH value of the system is adjusted by alkaline solution.

[0011] The above preparation method is further improved in step (1), wherein the modification treatment is: ultrasonic treatment for 30 min to 40 min, followed by stirring at 20℃ to 30℃ for 2 h to 3 h, followed by separation, washing and drying; the drying temperature is 40℃ to 60℃. In step (2), the mixing is carried out under ultrasonic conditions for a duration of 30 min to 40 min.

[0012] The above preparation method is further improved in step (1) by mixing calcium source, phosphate, urea and water and carrying out a hydrothermal reaction to obtain hydroxyapatite; the mass-volume ratio of calcium source, phosphate, urea and water is 4g~15g∶3g~5g∶8g~10g∶100mL, the calcium source is one or more of calcium nitrate tetrahydrate, calcium phytate and calcium chloride hexahydrate, the phosphate is ammonium dihydrogen phosphate, and the hydrothermal reaction is carried out at a temperature of 100℃~120℃ for 3h~4h.

[0013] The above preparation method is further improved in step (2), where the preparation method of the hexaaminocyclotriphosphazene includes the following steps: S1. Dissolve hexachlorocyclotriphosphazene in an organic solvent to obtain a hexachlorocyclotriphosphazene solution; S2. Under a nitrogen atmosphere, the ammonia source, acid-binding agent and organic solvent are mixed and cooled to 0℃~5℃ to obtain a mixed solution; S3. The hexachlorocyclotriphosphazene solution obtained in step S1 is added dropwise to the mixture obtained in step S2 to carry out the reaction. After centrifugation, rotary evaporation under reduced pressure and vacuum drying, hexaaminocyclotriphosphazene is obtained. The mass ratio of hexachlorocyclotriphosphazene, ammonia source, and acid-binding agent is 3.5–4.5:16.5–17.5:12.2–13.2, wherein the ammonia source is ammonia water and the acid-binding agent is triethylamine; in steps S1 and S2, the organic solvent is 1,4-dioxane; the reaction temperature is 20°C–25°C, the reaction time is 48 h–52 h, and the reaction is carried out under a nitrogen atmosphere.

[0014] As a general technical concept, the present invention provides a flame retardant based on phytic acid modified hydroxyapatite prepared by the above-mentioned method for preparing flame retardants based on phytic acid modified hydroxyapatite.

[0015] As a general technical concept, the present invention provides an application of the above-mentioned flame retardant based on phytic acid modified hydroxyapatite in the preparation of flame retardant wood.

[0016] The above-mentioned application, further improved, includes the following steps in the preparation method of flame-retardant wood: immersing wood in a flame retardant based on phytic acid-modified hydroxyapatite, performing vacuum impregnation, and then cleaning and drying to obtain flame-retardant wood; the vacuum impregnation temperature is 20℃~30℃, the vacuum degree of the vacuum impregnation is -0.09 MPa, the vacuum impregnation time is 4h~8h, the drying temperature is 50℃~60℃, and the drying time is 8h~12h.

[0017] Compared with the prior art, the advantages of the present invention are as follows: (1) In view of the problems of insufficient stability of the bonding between the flame retardant and the wood interface, easy migration of flame retardant components and limited flame retardant effect in the existing wood flame retardant treatment system, the present invention creatively provides a method for preparing a flame retardant based on phytic acid modified hydroxyapatite. Modified hydroxyapatite is used as the flame retardant component. The phosphorus-containing groups in phytic acid can promote dehydration and char formation during the heating process of wood. Hydroxyapatite, as an inorganic calcium and phosphorus component, can provide a thermally stable skeleton and barrier effect. The combination of the two helps to form a more continuous charred protective layer. Then, hexaaminocyclotriphosphazene and modified hydroxyapatite are used to jointly construct the flame retardant. The nitrogen-containing, phosphorus-containing structure and active amino groups in hexaaminocyclotriphosphazene help to enhance the interaction between modified hydroxyapatite and wood cell wall components, and improve the fixation stability of the flame retardant in wood. At the same time, water is used as the main dispersion medium. Phytic acid has good aqueous phase dispersion and pH adjustable characteristics, which is suitable for hydroxyapatite surface modification and subsequent wood vacuum impregnation treatment. The preparation method of this invention has advantages such as relatively mild process conditions and green environmental protection; the flame retardant based on phytic acid modified hydroxyapatite obtained therefrom can be stably loaded into wood and helps to form a carbonized protective layer during heating or combustion, thereby improving the flame retardant performance of wood, and is suitable for flame retardant treatment of wood materials for building, furniture and decoration.

[0018] In this invention, phytic acid is used to modify hydroxyapatite. Phytic acid simultaneously performs multiple functions, including modifying the surface of hydroxyapatite, improving the interfacial compatibility with wood, and promoting char formation under heat. These functions cannot be replaced by conventional organophosphorus flame retardants. Specifically, a) from a molecular structure perspective, phytic acid molecules contain multiple phosphate groups, which can coordinate or interact with calcium ions on the surface of hydroxyapatite under neutral or weakly alkaline conditions. This allows phytic acid to be stably loaded onto the surface of hydroxyapatite, constructing inorganic flame-retardant particles modified with phosphorus-containing organic acids. When used to prepare flame-retardant wood, it can form an interfacial coordination between "phytic acid-hydroxyapatite-wood cell wall"; b) from a theoretical phosphorus content perspective, phytic acid has a theoretical phosphorus content of approximately 28.2 wt%, which provides more phosphorus-containing active sites. This facilitates the dehydration and charring of components such as cellulose and hemicellulose during the heating process of wood, thereby improving the flame-retardant effect.

[0019] In this invention, a flame retardant is constructed by combining hexaaminocyclotriphosphazene and modified hydroxyapatite. Hexaaminocyclotriphosphazene is used as a crosslinking / fixing component with phosphorus-containing, nitrogen-containing structures and multiple amino active sites. Its functions include improving the aqueous phase suitability of the flame retardant, enhancing the interaction between the flame retardant and the wood cell wall, and improving the fixation stability of the flame retardant in wood. Specifically, a) from the perspective of molecular structure (see formula (1)), hexaaminocyclotriphosphazene contains six amino groups. These amino groups can form hydrogen bonds, ionic interactions, or other interfacial interactions with the hydroxyl groups of cellulose and hemicellulose in wood and the phosphate groups on the surface of phytic acid-modified hydroxyapatite, thereby helping to improve the fixation stability of the flame retardant in the pores and cell walls of wood; b) from the perspective of theoretical elemental content, the theoretical phosphorus content of hexaaminocyclotriphosphazene is about 40.2 wt%, and the theoretical nitrogen content is about 54.5 wt%. Hexaaminocyclotriphosphazene can provide a higher proportion of phosphorus and nitrogen flame retardant elements, which helps to form a phosphorus- and nitrogen-containing carbonized structure during heating; c) from the perspective of process adaptability, hexaaminocyclotriphosphazene has good water phase applicability and can form a uniformly composed flame retardant together with modified hydroxyapatite.

[0020] (1).

[0021] (2) In the preparation method of the present invention, the modifier also contains metal salts, which can form coordination / complex structures with phytic acid, thereby improving the stability of the char layer structure and the inorganic barrier effect, providing a synergistic effect for improving the thermal stability of wood flame retardant treatment and inhibiting flame spread, and ultimately improving the flame retardant durability of wood. Specifically, the metal ions (copper, zinc, iron, magnesium, etc.) in the metal salts can form coordination structures with phytic acid, which helps to construct a metal-phytic acid-hydroxyapatite composite network. During subsequent heating or combustion, the metal ions can promote the stabilization of the residual char structure, improve the density and antioxidant capacity of the char layer, and help inhibit the transfer of heat, oxygen and combustible volatiles. Attached Figure Description

[0022] Figure 1 The images show the surface morphology of hydroxyapatite (HAP) and modified hydroxyapatite (PA@HAP) in Example 1 and modified hydroxyapatite in Example 2 of this invention. Figure 1 In the examples, (a) is the hydroxyapatite in Example 1, (b) is the modified hydroxyapatite in Example 1, and (c) is the modified hydroxyapatite in Example 2.

[0023] Figure 2 XPS images of hydroxyapatite (HAP) and modified hydroxyapatite (PA@HAP) in Example 1 of this invention. Figure 2In the figure, (a) is the XPS full spectrum of HAP and PA@HAP, (b) is the high-resolution Ca 2p spectrum of HAP, (c) is the high-resolution Ca 2p spectrum of PA@HAP, (d) is the high-resolution P 2p spectrum of HAP, (e) is the high-resolution P 2p spectrum of PA@HAP, and (f) is the high-resolution C 1s spectrum of PA@HAP.

[0024] Figure 3 This is a diagram showing the limiting oxygen index of epoxy resin (EP) and flame retardants (EP / HAP, EP / PA@HAP, EP / Cu-PA@HAP) in this invention.

[0025] Figure 4 This is a thermal release diagram of epoxy resin (EP) and flame retardant (EP / HAP, EP / PA@HAP, EP / Cu-PA@HAP) in this invention. Figure 4 In the figure, (a) represents the heat release rate and (b) represents the total heat release.

[0026] Figure 5 This is a diagram showing the toxic emissions of epoxies from epoxy resin (EP) and flame-retardant wood (EP / HAP, EP / PA@HAP, EP / Cu-PA@HAP) in this invention. Figure 5 In the figure, (a) represents the total amount of smoke generated, (b) represents the smoke generation rate, (c) represents the CO generation rate, and (d) represents the CO2 generation rate. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. All materials and instruments used in the following embodiments are commercially available.

[0028] Example 1: A method for preparing a flame retardant based on phytic acid-modified hydroxyapatite according to the present invention includes the following steps: (1) Preparation of hydroxyapatite At room temperature, 11.81 g of calcium nitrate tetrahydrate and 3.45 g of ammonium dihydrogen phosphate were dissolved in 100 mL of deionized water. The mixture was continuously magnetically stirred at 500 r / min for 30 min. During stirring, 9 g of urea was gradually added as a co-precipitant to obtain a mixed solution. The mixed solution was transferred to a stainless steel hydrothermal reactor and heated to 120 °C at a heating rate of 10 °C / min, and held at that temperature for 3 h. After the reaction was completed, the mixture was naturally cooled to room temperature. The reaction product was centrifuged for 10 min at a speed of 7000 r / min to 8000 r / min to separate the product. The product was then washed with deionized water and sonicated for 5 min. The centrifugation and sonication cycles were repeated three times to remove unreacted substances. The washed product was dried at 60 °C for 12 h and ground into powder to obtain hydroxyapatite, denoted as HAP.

[0029] (2) Preparation of modified hydroxyapatite 2.86 g of phytic acid aqueous solution with a mass percentage of 70% was dissolved in 97.14 g of deionized water, and then 2 mol / L sodium hydroxide solution was added dropwise to adjust the pH of the system to 7.3 to obtain phytic acid solution; 10 g of hydroxyapatite obtained in step (1) was added to 100 g of the above phytic acid solution, and ultrasonic treatment was performed for 30 min, followed by continuous magnetic stirring at 25℃ (room temperature) for 2 h for modification treatment; the treated product was centrifuged for 10 min to separate the product at a centrifugation speed of 8000 r / min, and then washed with deionized water and ultrasonicated for 5 min. The centrifugation and ultrasonication were repeated three times to remove unreacted substances. The washed product was placed in a 60℃ oven to dry to obtain modified hydroxyapatite, denoted as PA@HAP.

[0030] (3) Preparation of hexaaminocyclotriphosphazene (3.1) Place 3.47 g of hexachlorocyclotriphosphazene in a beaker containing 100 mL of 1,4-dioxane and stir magnetically at 600 r / min at room temperature until completely dissolved to obtain a hexachlorocyclotriphosphazene solution.

[0031] (3.2) Under a nitrogen atmosphere, add 100 mL of 1,4-dioxane to a three-necked flask, cool it to 0°C in an ice bath, add 16.8 g of ammonia and 12.14 g of triethylamine in sequence, and stir magnetically at 900 r / min to mix evenly to obtain a mixture.

[0032] (3.3) The hexachlorocyclotriphosphazene solution obtained in step (3.1) was slowly added dropwise to the mixture obtained in step (3.2) through a constant pressure dropping funnel, and the dropping rate was controlled at 1 mL / min. After the addition was completed, the ice bath was removed, and the reaction was continuously stirred at 25 °C for 48 h under nitrogen protection. After the reaction was completed, the reaction product was centrifuged at 8000 r / min for 10 min, and the supernatant was collected. Then, the solvent and unreacted low-boiling-point substances were removed by vacuum rotary evaporation at 70 °C and a vacuum degree of -0.09 MPa. The vacuum rotary evaporation residue was placed in a vacuum drying oven and vacuum dried at 40 °C and -0.1 MPa for 48 h to obtain hexaaminocyclotriphosphazene.

[0033] (4) Preparation of flame retardants Add 2.5 g of the modified hydroxyapatite obtained in step (2) and 0.5 g of the hexaaminocyclotriphosphazene obtained in step (3.3) to 50 mL of deionized water and sonicate for 30 min to obtain a flame retardant based on phytic acid modified hydroxyapatite.

[0034] Example 2: A method for preparing a flame retardant based on phytic acid-modified hydroxyapatite according to the present invention includes the following steps: (1) Preparation of hydroxyapatite At room temperature, 11.81 g of calcium nitrate tetrahydrate and 3.45 g of ammonium dihydrogen phosphate were dissolved in 100 mL of deionized water. The mixture was magnetically stirred continuously at 500 r / min for 30 min. During the stirring process, 9 g of urea was gradually added as a co-precipitant to obtain a mixed solution. The mixed solution was transferred to a stainless steel hydrothermal reactor and heated to 120 °C at a heating rate of 10 °C / min, and held at that temperature for 3 h. After the reaction was completed, the mixture was naturally cooled to room temperature. The reaction product was centrifuged for 10 min at a speed of 7000 r / min to 8000 r / min to separate the product. The product was then washed with deionized water and sonicated for 5 min. The centrifugation and sonication cycles were repeated three times to remove unreacted substances. The washed product was dried at 60 °C for 12 h and ground into powder to obtain hydroxyapatite.

[0035] (2) Preparation of modified hydroxyapatite 2.86 g of phytic acid aqueous solution with a mass percentage of 70% and 2.16 g of copper sulfate were dissolved in 97.14 g of deionized water, and then 2 mol / L sodium hydroxide solution was added dropwise to adjust the pH of the system to 7.3, thus obtaining a phytic acid solution containing copper ions. 10 g of hydroxyapatite obtained in step (1) was added to 100 g of the above phytic acid solution containing copper ions, and ultrasonic treatment was performed for 30 min. Then, the mixture was continuously magnetically stirred at 25℃ (room temperature) for 2 h for modification treatment. The treated product was centrifuged for 10 min at a centrifugation speed of 8000 r / min, and then washed with deionized water and ultrasonicated for 5 min. The centrifugation and ultrasonication were repeated three times to remove unreacted substances. The washed product was dried in a 60℃ oven to obtain modified hydroxyapatite, denoted as Cu-PA@HAP.

[0036] (3) Preparation of hexaaminocyclotriphosphazene (3.1) Place 3.47 g of hexachlorocyclotriphosphazene in a beaker containing 100 mL of 1,4-dioxane and stir magnetically at 600 r / min at room temperature until completely dissolved to obtain a hexachlorocyclotriphosphazene solution.

[0037] (3.2) Under a nitrogen atmosphere, add 100 mL of 1,4-dioxane to a three-necked flask, cool it to 0°C in an ice bath, add 16.8 g of ammonia and 12.14 g of triethylamine in sequence, and stir magnetically at 900 r / min to mix evenly to obtain a mixture.

[0038] (3.3) The hexachlorocyclotriphosphazene solution obtained in step (3.1) was slowly added dropwise to the mixture obtained in step (3.2) through a constant pressure dropping funnel, and the dropping rate was controlled at 1 mL / min. After the addition was completed, the ice bath was removed, and the reaction was continuously stirred at 25 °C for 48 h under nitrogen protection. After the reaction was completed, the reaction product was centrifuged at 8000 r / min for 10 min, and the supernatant was collected. Then, the solvent and unreacted low-boiling-point substances were removed by vacuum rotary evaporation at 70 °C and a vacuum degree of -0.09 MPa. The vacuum rotary evaporation residue was placed in a vacuum drying oven and vacuum dried at 40 °C and -0.1 MPa for 48 h to obtain hexaaminocyclotriphosphazene.

[0039] (4) Preparation of flame retardants Add 2.5 g of the modified hydroxyapatite obtained in step (2) and 0.5 g of the hexaaminocyclotriphosphazene obtained in step (3.3) to 50 mL of deionized water and sonicate for 30 min to obtain a flame retardant based on phytic acid modified hydroxyapatite.

[0040] Figure 1The images show the surface morphology of hydroxyapatite (HAP) and modified hydroxyapatite (PA@HAP) in Example 1 and modified hydroxyapatite in Example 2 of this invention. Figure 1 In the examples, (a) is the hydroxyapatite in Example 1, (b) is the modified hydroxyapatite in Example 1, and (c) is the modified hydroxyapatite in Example 2. Figure 1 SEM images show that HAP exhibits a typical sheet / nanosheet stacked structure. Figure 1 (a) shows that the lamellar edges are clear and have a high specific surface area. This two-dimensional layered structure is expected to form a "maze effect" during polymer combustion, which is beneficial for blocking the migration of heat and combustible volatiles and promoting continuous char coverage. After phytic acid modification, PA@HAP still maintains obvious lamellar morphology ( Figure 1 (b) and (c) showed no significant morphological collapse or granulation, indicating that the surface modification process did not destroy the two-dimensional framework structure of HAP, which provided a morphological basis for its subsequent formation of a physical shielding carbon layer in the condensed phase.

[0041] Figure 2 XPS images of hydroxyapatite (HAP) and modified hydroxyapatite (PA@HAP) in Example 1 of this invention. Figure 2 In the image, (a) is the XPS full spectrum of HAP and PA@HAP, (b) is the high-resolution Ca 2p spectrum of HAP, (c) is the high-resolution Ca 2p spectrum of PA@HAP, (d) is the high-resolution P 2p spectrum of HAP, (e) is the high-resolution P 2p spectrum of PA@HAP, and (f) is the high-resolution C 1s spectrum of PA@HAP. Figure 2 As can be seen from (a), both HAP and PA@HAP contain Ca, P, O, and C elements. Combined with the atomic percentage statistics in (a), the P and O content of phytic acid-modified PA@HAP is increased, consistent with the expectation of introducing a "phosphorus-rich / oxygen-rich organic layer on the surface." Figure 2 As can be seen from (b), HAP corresponds to Ca 2p at approximately 347 eV and 350.5 eV, respectively. 3 / 2 Ca 2p 1 / 2 , for Ca 2+ Typical characteristics. From Figure 2 As can be seen from (c), PA@HAP still maintains Ca 2p 3 / 2 and Ca 2p 1 / 2 The bimodal morphology, but with a slight shift in peak position, indicates that the phosphate groups of phytic acid react with the Ca on the surface of hydroxyapatite. 2+ Chelation occurs, altering the local electronic environment of Ca, but without disrupting the bulk lattice of HAP. From Figure 2 As can be seen from (d), the P2p of HAP exhibits a single PO4 group. 3- Related components; from Figure 2 As can be seen from (e), the P 2p of PA@HAP can be decomposed into PO4 ions. 3- The additional component, "POC," originates from the phosphate ester bond (POC) in the phytic acid molecule, indicating that phytic acid is chemically introduced and participates in surface structure construction, rather than solely through weak physical adsorption. Figure 2 As can be seen from (f), the C 1s region of PA@HAP exhibits CC / CH (≈284.8 eV), CO (≈286.2 eV), and a high-binding-energy oxygen-containing carbon component, among which the CO component is highly consistent with the phytic acid / inositol ring structure. Overall, the XPS spectra confirm that a stable phosphorus-rich organic-inorganic composite interface is formed on the surface of the modified hydroxyapatite (PA@HAP) of this invention.

[0042] Example 3: The application of a flame retardant based on phytic acid-modified hydroxyapatite in the preparation of flame-retardant wood includes the following steps: Dry wood chips were immersed in a container containing the flame retardant based on phytic acid-modified hydroxyapatite prepared in Example 1. The wood chips had dimensions of 130 mm × 13 mm × 3 mm. Subsequently, the container containing the wood chips was placed in a vacuum drying oven and vacuum impregnated for 4 h at 25°C (room temperature) and a vacuum degree of -0.09 MPa. After impregnation, the wood surface was cleaned with deionized water to remove any residual substances, and then dried at 60°C for 12 h to obtain flame-retardant wood, denoted as Wood / PA@HAP / HCPA.

[0043] Example 4: The application of a flame retardant based on phytic acid-modified hydroxyapatite in the preparation of flame-retardant wood includes the following steps: Dry wood chips were immersed in a container containing the flame retardant based on phytic acid-modified hydroxyapatite prepared in Example 5. The wood chips had dimensions of 130 mm × 13 mm × 3 mm. Subsequently, the container containing the wood chips was placed in a vacuum drying oven and vacuum-impregnated for 4 h at 25°C (room temperature) and a vacuum degree of -0.09 MPa. After impregnation, the wood surface was cleaned with deionized water to remove any residual substances, and then dried at 60°C for 12 h to obtain flame-retardant wood, denoted as Wood / Cu-PA@HAP / HCPA.

[0044] Comparative Example 1: The application of a hydroxyapatite flame retardant in the preparation of flame-retardant wood includes the following steps: (1) Take 5 g of hydroxyapatite obtained in step (1) of Example 1 and 5 g of hexaaminocyclotriphosphazene obtained in step (3.3) of Example 1. Add the above hydroxyapatite and hexaaminocyclotriphosphazene to 50 mL of deionized water and sonicate for 30 min to obtain hydroxyapatite flame retardant.

[0045] (2) The dried wood chips were soaked in a container containing the hydroxyapatite flame retardant prepared in step (1). The size of the wood chips was 130 mm × 13 mm × 3 mm. Then, the container containing the wood chips was placed in a vacuum drying oven and vacuum impregnated for 4 h at 25°C (room temperature) and a vacuum degree of -0.09 MPa. After impregnation, the residual substances on the surface of the wood were washed with deionized water and dried at 60°C for 12 h to obtain flame-retardant wood, denoted as Wood / HAP / HCPA.

[0046] Combustion tests were conducted on untreated wood, the flame-retardant wood prepared in Examples 3 and 4, and Comparative Example 1, according to the UL-94 vertical burning test method. The test results are shown in Table 1. In Table 1, the untreated wood is the same as the dried wood chips used in Example 3, with dimensions of 130 mm × 13 mm × 3 mm, indicating that it has not undergone flame-retardant treatment.

[0047] Table 1. Results of vertical burning tests on flame-retardant wood

[0048] Table 1 shows that the untreated wood failed to self-extinguish within the test time after the first ignition. The flame-retardant wood prepared in Comparative Example 1, treated with hydroxyapatite and hexaaminocyclotriphosphazene, was self-extinguishing. Compared to Comparative Example 1, the flame-retardant wood prepared in Example 3 showed shorter flaming times after both the first and second ignitions, indicating that phytic acid-modified hydroxyapatite helps improve the flame-retardant performance of wood. The flame-retardant wood prepared in Example 4, using copper ions in synergy with phytic acid-modified hydroxyapatite, also self-extinguished after two ignitions, demonstrating that metal ions in synergy with phytic acid-modified hydroxyapatite can be used in wood flame-retardant treatment systems.

[0049] To compare and verify the effects of hydroxyapatite (HAP) and modified hydroxyapatite (PA@HAP, Cu-PA@HAP), HAP, PA@HAP, Cu-PA@HAP and 100g of epoxy resin (EP) were mixed respectively. The amount of HAP, PA@HAP and Cu-PA@HAP was 20g. The mixture was cured in an oven at 60℃ for 5h and then cured at 100℃ for 2h to obtain different flame retardants, which were denoted as EP / HAP, EP / PA@HAP and EP / Cu-PA@HAP respectively.

[0050] Figure 3 This is a limiting oxygen index diagram for the epoxy resin (EP) and flame retardants (EP / HAP, EP / PA@HAP, EP / Cu-PA@HAP) used in this invention. Figure 3 As can be seen, the LOI of epoxy resin (EP) is 20.68%, exhibiting typical flammable characteristics. Compared to EP, the LOIs of EP / HAP, EP / PA@HAP, and EP / Cu-PA@HAP increased to 21.19%, 23.55%, and 24.90%, respectively, with corresponding increases of 0.51, 2.87, and 4.22 percentage points. This indicates that hexagonal boron nitride nanosheets and their surface chemical regulation can significantly increase the minimum oxygen concentration required for the epoxy system to maintain combustion, thereby increasing the difficulty of combustion.

[0051] Cone calorimetry can quantitatively assess the heat release and smoke toxicity release characteristics of materials under near-real fire irradiation conditions.

[0052] Figure 4 This is a thermal release diagram of epoxy resin (EP) and flame retardant (EP / HAP, EP / PA@HAP, EP / Cu-PA@HAP) in this invention. Figure 4 In the table, (a) represents the heat release rate, and (b) represents the total heat release. Figure 4 It can be seen that, compared with epoxy resin (EP), the heat release intensity of EP / HAP, EP / PA@HAP, and EP / Cu-PA@HAP is significantly reduced. The peak heat release rate (pHRR) of EP is as high as 1198.64 kW·m. -2 It exhibited violent combustion characteristics; the pHRR of EP / HAP, EP / PA@HAP, and EP / Cu-PA@HAP decreased to 860.16 kW·m. -2 867.57kW·m -2 750.63kW·m -2 Compared to EP, the pHRR reduction of EP / HAP, EP / PA@HAP, and EP / Cu-PA@HAP was 28.2%, 27.6%, and 37.4%, respectively. Among them, EP / Cu-PA@HAP showed the most significant inhibition of pHRR, indicating that it can more effectively reduce the peak heat release during combustion, thereby reducing the risk of early-stage heat feedback in a fire. Total heat release (THR) also showed a decreasing trend, with EP having a THR of 146.3 MJ·m⁻¹. -2 Meanwhile, EP / HAP, EP / PA@HAP, and EP / Cu-PA@HAP decreased to 125.6 MJ·m -2 124.7 MJ·m -2 126.3 MJ·m -2The corresponding reductions were 14.1%, 14.8%, and 13.7%, indicating that the introduction of flame retardants can effectively reduce the cumulative heat release during the material combustion process.

[0053] Figure 5 This is a diagram showing the toxic emissions of epoxies from epoxy resin (EP) and flame-retardant wood (EP / HAP, EP / PA@HAP, EP / Cu-PA@HAP) in this invention. Figure 5 In the diagram, (a) represents the total smoke generation, (b) represents the smoke generation rate, (c) represents the CO generation rate, and (d) represents the CO2 generation rate. The combustion of wood typically produces large amounts of smoke particles and toxic gases, posing a serious threat to life. Therefore, the ability to suppress smoke and toxic gases is also an important indicator for assessing the fire safety of wood. Figure 5 It can be seen that the total smoke production (TSP) and peak smoke production rate (pSPR) of EP are 22.49 m. 2 With 0.21m 2 ·s -1 The TSP and pSPR of EP / HAP decreased to 17.77m. 2 With 0.18m 2 ·s -1 The TSP and pSPR of EP / PA@HAP decreased to 16.11m. 2 With 0.17m 2 ·s -1 Compared to EP, EP / PA@HAP showed the best smoke suppression effect with a 28.4% decrease in TSP and a 19.0% decrease in pSPR. The TSP and pSPR of EP / Cu-PA@HAP were 19.39 m... 2 With 0.18m 2 ·s -1 While still superior to pure EP, its TSP is higher than that of EP / PA@HAP, indicating that Cu synergy is more prominent in suppressing the heat release peak. Furthermore, the CO release peak (COP) reflects the degree of incomplete combustion. The COP of EP is 0.005 g·s⁻¹. -1 EP / HAP, EP / PA@HAP, and EP / Cu-PA@HAP were reduced to 0.004 g·s⁻¹. -1 0.0028 g·s -1 0.0024 g·s -1 Among them, EP / Cu-PA@HAP showed the largest decrease (52%), indicating that it has a more significant inhibitory effect on the release of toxic incomplete combustion products. The CO2 release peak (CO2P) varied in different systems, with EP / HAP showing a value of 0.032 g·s⁻¹. -1 The minimum EP / PA@HAP ratio is 0.020 g·s. -1The EP / Cu-PA@HAP ratio is 0.029 g·s⁻¹. -1 The results show that different flame retardant systems have different effects on the degree of combustion oxidation and the path of gaseous products.

[0054] In summary, the cone calorimetry results show that EP / HAP, EP / PA@HAP, and EP / Cu-PA@HAP can all effectively reduce the heat release and smoke / toxic gas release of EP. EP / Cu-PA@HAP performs best in suppressing heat release intensity and reducing toxic gas release, while EP / PA@HAP has a greater advantage in smoke suppression performance. These results are consistent with the trend of UL-94, which indirectly demonstrates that the phytic acid surface chemical regulation and metal ion synergistic phytic acid modification of hydroxyapatite flame retardants in this invention can significantly optimize the overall fire safety of wood.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing a flame retardant based on phytic acid-modified hydroxyapatite, characterized in that, Includes the following steps: (1) Hydroxyapatite and a modifier are mixed and modified to obtain modified hydroxyapatite; the modifier is phytic acid solution; (2) The modified hydroxyapatite, hexaaminocyclotriphosphazene obtained in step (1) and water are mixed to obtain a flame retardant based on phytic acid modified hydroxyapatite.

2. The method for preparing the flame retardant based on phytic acid-modified hydroxyapatite according to claim 1, characterized in that, In step (1), the mass ratio of hydroxyapatite to modifier is 1:3 to 30; In step (2), the mass-to-volume ratio of the modified hydroxyapatite, hexaaminocyclotriphosphazene, and water is 2.5g~20g∶0.5g~10g∶50mL~100mL.

3. The method for preparing the flame retardant based on phytic acid-modified hydroxyapatite according to claim 2, characterized in that, In step (1), the phytic acid solution contains 1% to 3% phytic acid by mass, and the pH value of the phytic acid solution is 7 to 8. The phytic acid solution is prepared by dissolving an aqueous phytic acid solution in water and adjusting the pH value of the system to 7 to 8 to obtain the phytic acid solution. The mass ratio of the aqueous phytic acid solution to water is 1 to 3: 97 to 99, the aqueous phytic acid solution contains 70% phytic acid by mass, and the pH value of the system is adjusted by using an alkaline solution.

4. The method for preparing the flame retardant based on phytic acid-modified hydroxyapatite according to claim 2, characterized in that, In step (1), the modifier further includes a metal salt, which is one or more of copper sulfate, zinc chloride, ferric chloride and magnesium chloride; the modifier is prepared by dissolving phytic acid aqueous solution and metal salt in water, adjusting the pH of the system to 7-8, and obtaining phytic acid solution; the mass ratio of phytic acid aqueous solution, metal salt and water is 1-3:0.4-3:97-99, the mass percentage of phytic acid aqueous solution is 70%, and the pH of the system is adjusted by alkaline solution.

5. The method for preparing the flame retardant based on phytic acid-modified hydroxyapatite according to any one of claims 1 to 4, characterized in that, In step (1), the modification treatment is as follows: ultrasonic treatment for 30 min to 40 min, followed by stirring at 20℃ to 30℃ for 2 h to 3 h, followed by separation, washing, and drying; the drying temperature is 40℃ to 60℃. In step (2), the mixing is carried out under ultrasonic conditions for a duration of 30 min to 40 min.

6. The method for preparing the flame retardant based on phytic acid-modified hydroxyapatite according to any one of claims 1 to 4, characterized in that, In step (1), the preparation method of the hydroxyapatite is as follows: calcium source, phosphate, urea and water are mixed and subjected to hydrothermal reaction to obtain hydroxyapatite; the mass-volume ratio of the calcium source, phosphate, urea and water is 4g~15g∶3g~5g∶8g~10g∶100mL, the calcium source is one or more of calcium nitrate tetrahydrate, calcium phytate and calcium chloride hexahydrate, the phosphate is ammonium dihydrogen phosphate, and the hydrothermal reaction is carried out at a temperature of 100℃~120℃ for 3h~4h.

7. The method for preparing the flame retardant based on phytic acid-modified hydroxyapatite according to any one of claims 1 to 4, characterized in that, In step (2), the preparation method of the hexaaminocyclotriphosphazene includes the following steps: S1. Dissolve hexachlorocyclotriphosphazene in an organic solvent to obtain a hexachlorocyclotriphosphazene solution; S2. Under a nitrogen atmosphere, the ammonia source, acid-binding agent and organic solvent are mixed and cooled to 0℃~5℃ to obtain a mixed solution; S3. The hexachlorocyclotriphosphazene solution obtained in step S1 is added dropwise to the mixture obtained in step S2 to carry out the reaction. After centrifugation, rotary evaporation under reduced pressure and vacuum drying, hexaaminocyclotriphosphazene is obtained. The mass ratio of hexachlorocyclotriphosphazene, ammonia source, and acid-binding agent is 3.5–4.5:16.5–17.5:12.2–13.2, wherein the ammonia source is ammonia water and the acid-binding agent is triethylamine; in steps S1 and S2, the organic solvent is 1,4-dioxane; the reaction temperature is 20°C–25°C, the reaction time is 48 h–52 h, and the reaction is carried out under a nitrogen atmosphere.

8. A flame retardant based on phytic acid modified hydroxyapatite prepared by the preparation method of the flame retardant based on phytic acid modified hydroxyapatite as described in any one of claims 1 to 7.

9. The application of the flame retardant based on phytic acid-modified hydroxyapatite as described in claim 8 in the preparation of flame-retardant wood.

10. The application according to claim 9, characterized in that, The method for preparing the flame-retardant wood includes the following steps: immersing the wood in a flame retardant based on phytic acid-modified hydroxyapatite, performing vacuum impregnation, and then cleaning and drying to obtain the flame-retardant wood; the vacuum impregnation temperature is 20℃~30℃, the vacuum degree of the vacuum impregnation is -0.09 MPa, the vacuum impregnation time is 4h~8h, the drying temperature is 50℃~60℃, and the drying time is 8h~12h.

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