Bio-based core-shell structure flame retardant and application thereof in bio-based board

Abstract

The invention discloses a bio-based core-shell structure flame retardant and an application thereof in a bio-based plate. According to the invention, a phosphorus-carbon synergistic flame-retardant core-shell structure flame retardant is developed by taking a phosphorus-containing halogen-free flame retardant as a core and carrying out free radical copolymerization reaction on a furfuryl alcohol (FA) derivative containing phosphorus in different oxidation states and bismaleimide (BMI) with a charring function to form a cross-linked flame-retardant macromolecular shell layer. The core-shell flame retardant is proportionally mixed with crushed materials of a biological base material and an adhesive, and the mixture is subjected to hot press molding to obtain the flame-retardant biological base material. The flame retardant provided by the invention not only can endow a biological base material with good flame retardance and mechanical properties, but also can solve the problem of long-term durability of the biological base material.

Description

Technical Field

[0001] This invention belongs to the technical field of artificial boards and flame retardant materials, specifically relating to a bio-based core-shell structure flame retardant and its application in bio-based boards. Background Technology

[0002] With increasing global emphasis on sustainable development, bio-based materials have garnered significant attention as a sustainable material. Made from low-value agricultural waste such as straw and reeds, and produced through bonding technology, they offer advantages in reducing resource waste and environmental pollution. Bio-based materials, due to their renewability, environmental friendliness, and low carbon emissions, are widely used in construction, furniture, and vehicle interiors. Bio-based boards, such as bamboo, straw boards, and wood-plastic composites, are important alternatives to traditional petroleum-based materials, reducing dependence on fossil resources and offering advantages such as good biodegradability and minimal environmental impact over their lifecycle. However, bio-based materials are primarily composed of organic components such as cellulose, hemicellulose, and lignin, which are highly flammable under high temperatures or fire, releasing large amounts of heat and toxic fumes during combustion, severely limiting their application in safety fields. Therefore, to address the fire resistance and flame retardancy issues of bio-based materials, research is urgently needed on low-value, long-lasting fire-retardant technologies to improve their fire resistance rating and flame retardancy time, reduce smoke toxicity, and enhance their safety in industries such as building decoration and furniture manufacturing.

[0003] In recent years, researchers have increasingly recognized the decisive influence of the spatial configuration and polarity distribution of heterocyclic groups in the molecular structure on the interfacial compatibility, reactivity, and thermal conversion behavior of bio-based polymer materials, focusing on structural design and performance regulation. Studies by Fu Yao et al. have shown that, compared to traditional benzene ring structures, furan rings exhibit significant differences in bond angle distribution, charge polarization, and π-electron cloud distribution due to the introduction of oxygen heteroatoms, thus endowing them with higher reactivity and stronger interfacial interaction capabilities. Specifically, the COC bond angle in furan groups is more open than that of the benzene ring carbon skeleton, while the electronegativity difference introduced by the oxygen atoms within the ring gives furan rings a distinct dipole characteristic. This "asymmetric polarity + special bond angle" structure enhances hydrogen bonding and dipole-dipole interactions with polar groups containing hydroxyl and ether bonds, and also significantly increases its tendency to undergo ring-opening, condensation, and carbonization reactions under thermal conditions. Therefore, furanyl groups are considered a class of bio-based functional structural units that possess both high reactivity and excellent char-forming potential. However, in existing flame-retardant bio-based board systems, the advantages of furanyl structures have not been fully utilized. On the one hand, traditional phosphorus-based flame retardants mostly exist in the form of small molecules or inorganic salts, with rigid molecular structures and a single polarity distribution, resulting in limited interfacial compatibility with bio-based fiber materials. On the other hand, flame retardants are prone to migration, precipitation, or moisture absorption failure within the material, making it difficult to maintain stable flame-retardant performance under long-term service conditions. This, to some extent, limits the in-depth application of furanyl structures in the field of flame-retardant modification.

[0004] Existing core-shell flame retardant designs primarily focus on improving the integrity of the coating, with less emphasis on targeted design of the shell structure to address the specific properties of bio-based materials, considering factors such as molecular bond angle regulation and polar synergy. This is particularly true in bio-based panel systems, where components like cellulose, hemicellulose, and lignin possess highly polar and complex multi-scale interfacial structures. If the shell structure cannot achieve effective matching at the molecular scale, it becomes difficult to simultaneously achieve flame retardant efficiency, mechanical properties, and durability.

[0005] Based on the aforementioned issues, it is necessary to start from the molecular structure design source, introducing furanyl structures with special bond angles and polarity distribution characteristics, and further constructing them synergistically with phosphorus-containing functional units. This allows the furanyl structure to capture free radicals in the gas phase during combustion and promote the rapid formation and densification of the char layer in the condensed phase. Simultaneously, by introducing this structure into the flame retardant system in a core-shell form, flame retardant migration can be effectively inhibited, and its dispersibility and interfacial compatibility in bio-based materials can be improved, thereby achieving a synergistic enhancement of flame retardancy, smoke suppression, toxicity reduction, and long-term durability.

[0006] Based on the above theoretical foundation, this invention proposes a core-shell structure flame retardant with a halogen-free flame retardant as the core and a phosphorus-containing furanyl derivative crosslinked to form a shell. It introduces Fu Yao's research ideas on the regulation of furanyl bond angle and polarity into the design of flame retardant materials, providing a new technical path for the long-term flame retardant modification of bio-based boards. Summary of the Invention

[0007] To overcome the problem that halogen-free flame retardants in existing bio-based materials migrate and precipitate during long-term use, leading to a decline in the durability and flame retardant performance of the bio-based materials, this invention provides a bio-based core-shell structured flame retardant and its application in bio-based boards. This flame retardant not only imparts excellent flame retardant and mechanical properties to bio-based materials but also solves the problem of long-term durability.

[0008] This invention relates to a bio-based core-shell structured flame retardant, comprising a core and a shell structure. The core is a halogen-free flame retardant, and the shell structure is a polymer containing phosphorus in different oxidation states, furfuryl alcohol with char-forming functions, and bismaleimide. The mass ratio of the core to the shell structure is 100:5~25.

[0009] The halogen-free flame retardant is selected from one or more of melamine phosphate, melamine polyphosphate, melamine cyanurate, ammonium polyphosphate, piperazine pyrophosphate, aluminum hypophosphite, and aluminum phosphonate, mixed in any proportion.

[0010] The preparation method of the bio-based core-shell structured flame retardant of the present invention includes the following steps:

[0011] A halogen-free flame retardant (FR) was added to a solvent and stirred and dispersed evenly under a nitrogen atmosphere. Then, a phosphorus furfuryl alcohol derivative, bismaleimide, and a free radical initiator were added, and the mixture was heated to 60-80℃ and reacted for 4-12 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and washed. The resulting product was dried in an oven at 60-80℃ to constant weight to obtain solid products (FTD@FR, FDC@FR, FDH@FR, and FDP@FR).

[0012] The free radical initiator is selected from one or more of cyclohexanone peroxide, benzoyl peroxide, tert-butyl hydroperoxide, azobisisobutyronitrile, and azobisisoheptanenitrile. The added mass of the free radical initiator is 0.5%-5% of the mass of the phosphorus-containing furfuryl alcohol derivative monomer.

[0013] The molar ratio of the phosphorus-containing furfuryl alcohol derivative to the bismaleimide is 1:1.

[0014] The solvent is selected from one or more solvents such as tetrahydrofuran, dimethyl sulfoxide, cyclohexane, cyclohexanone, chloroform, toluene, xylene, benzene, dioxane, ethyl acetate, acetone, and butanone.

[0015] The phosphorus-containing furfuryl alcohol derivative is selected from one or more of FTD, FDC, FDH, and FDP, and its structure is shown below:

[0016]

[0017] The phosphorus-containing furfuryl alcohol derivative was prepared by the following method:

[0018] Furfuryl alcohol (FA) and triethylamine (TEA) are added to a solvent and stirred, then heated to 40-60 °C. After uniform dispersion, diphenylphosphine chloride, diphenylphosphine chloride, phenylphosphine dichloride, or diphenyl chlorinated phosphate are added dropwise to the system, and the reaction is carried out for 4-8 h. After the reaction is completed, the mixture is cooled to room temperature, washed with hydrochloric acid, saturated brine, and sodium bicarbonate solution, and dehydrated with anhydrous magnesium sulfate. The solvent is then recovered by rotary evaporation after filtration to obtain the product FTD, FDC, FDH, or FDP (furfuryl alcohol grafted with diphenylphosphine chloride, furfuryl alcohol grafted with diphenylphosphine chloride, furfuryl alcohol grafted with phenylphosphine dichloride, or furfuryl alcohol grafted with diphenyl chlorinated phosphate).

[0019] The application of the bio-based core-shell structure flame retardant in the preparation of bio-based boards.

[0020] Specifically, the bio-based core-shell structure flame retardant, bio-based fragments, and adhesive are mixed uniformly in a high-speed mixer, and then the mixture is evenly spread in a mold and vulcanized for different times in a flat vulcanizing machine to prepare flame-retardant bio-based boards.

[0021] The components, by mass, include: 85-100 parts of bio-based fragments, 5-10 parts of bio-based core-shell structure flame retardant, and 5 parts of adhesive.

[0022] The bio-based fragments are selected from one or more bio-based materials such as straw, reeds, rice straw, wood, and bamboo, and mixed in any proportion.

[0023] The adhesive is selected from one or more of polyurethane, epoxy resin, lignin, and soybean protein adhesives, mixed in any proportion.

[0024] The vulcanization temperature is 160-180℃, the vulcanization time is 30-60min, and the pressure is 5-10MPa.

[0025] When the bio-based core-shell structure flame retardant of this invention is used in bio-based boards, it has excellent flame retardant and aging resistance functions such as long-term resistance to migration and exudation, thereby meeting the requirements of long-term flame retardancy and durability of flame-retardant bio-based boards.

[0026] Compared with existing technologies, the superior effects of this invention are reflected in:

[0027] 1. This invention introduces phosphorus compounds of different oxidation states, along with furfuryl alcohol and bismaleimide, which have char-forming functions, into the shell layer of a flame retardant. These compounds polymerize within the shell layer to form a flame-retardant polymer shell containing phosphorus of different oxidation states and excellent char-forming functions. The shell layer not only works synergistically with the core flame retardant to provide core-shell flame retardancy, but the core flame retardant also synergizes with the +5 and low-valence phosphorus in the flame-retardant shell layer, and the shell layer itself, combined with bismaleimide and furfuryl alcohol, which have char-forming functions, can also provide synergistic flame retardancy in both the gas phase and condensed phase. By applying core-shell structured flame retardants to bio-based materials, low-valent phosphorus flame retardants capture free radicals during combustion, interrupting the combustion chain reaction and thus exerting a gas-phase flame retardant effect. High-valent phosphorus acts as a condensed-phase flame retardant, and together with furfuryl alcohol, bismaleimide, and bio-based materials such as reed straw, it promotes carbonization, increases the char residue of the bio-based material, and reduces the release of pyrolysis gases and smoke particles, thereby improving the flame retardant, smoke suppression, and detoxification properties and flame retardant rating of the bio-based material; further enhancing the fire-retardant performance of flame-retardant bio-based boards.

[0028] 2. In the bio-based core-shell structured flame retardant of this invention, the microencapsulated shell is a phosphorus-containing and benzene-ring-structured organic macromolecular polymer formed by free radical polymerization of a phosphorus-containing furfuryl alcohol derivative and bismaleimide. By controlling the ratio of furfuryl alcohol to bismaleimide, a cross-linked, dense flame-retardant macromolecular shell can be formed. This not only improves the dispersibility and interfacial compatibility of the halogen-free flame retardant core in the bio-based substrate, thereby improving the mechanical and flame-retardant properties of the bio-based substrate, but also reduces the hydrophilicity and hygroscopicity of the halogen-free flame retardant. As a result, after 4 weeks of damp heat aging at 80°C and 85% humidity, it still exhibits excellent flame-retardant properties, thereby improving the durability of the bio-based substrate and enhancing its long-term durability and safety in industries such as building decoration, furniture manufacturing, etc. Attached Figure Description

[0029] Figure 1 The left and right figures show the phosphorus and proton NMR spectra of FDC. The chemical structure of FTD was characterized by proton NMR. The left figure shows the proton NMR spectrum of FDC, where the chemical shifts at 7.26 pmm, 5.12 pmm, and 8.0 pmm-7.0 pmm correspond to protons on carbons 1 of CDCl3, CH2Cl2, and the benzene and furan rings, respectively. The range of 6.25 pmm-6.10 pmm corresponds to protons on carbons 2 and 3 of the furan ring. The new characteristic peak at 4.95 pmm corresponds to proton 6 of the -CH2- group attached to P in FDC. The proton peak area ratio is 4:7:2:2, which is consistent with the number of protons at different positions. The right figure shows the phosphorus NMR spectra of FDC and diphenylphosphine chloride, where both are singlets with chemical shifts of 42.5 pmm and 31.7 pmm, respectively. All of the above confirms the successful synthesis of FDC.

[0030] Figure 2The left image shows the NMR spectrum of FTD. The chemical structure of FTD can be characterized by NMR spectroscopy. The left image shows the 1H NMR spectrum of FTD, where the solvent peak at 7.26 ppm is CDCl3. Multiple peaks in the range of 7.0 ppm to 8.0 ppm are mainly attributed to the diphenyl structure and protons on the furan ring. The new characteristic peak in the range of 5.0 ppm to 6.0 ppm is attributed to the methylene protons bonded to oxygen atoms. The right image shows the phosphorus NMR spectrum of FTD. Only a single phosphorus peak appears in the spectrum, indicating that the phosphorus atom in the product has a simple chemical environment and the target product structure is well-defined. Combining the 1H and phosphorus NMR analysis results, it can be confirmed that FTD has been successfully synthesized.

[0031] Figure 3 The left image shows the TGA (left figure) and DTG (right figure) curves for APP, FTD@APP, FDH@APP, FDC@APP, and FDP@APP. From... Figure 3 As can be seen, the weight loss of FTD / FDH / FDC / FDP@APP in the medium and high temperature range is "widened / delayed", and the residual carbon is higher than that of APP, indicating that the organic shell promotes char formation and improves high temperature stability.

[0032] Figure 4 The TGA (Figure a) and DTG curves (Figure b) for fire-retardant boards based on straw are shown. From... Figure 4 As can be seen from the data, the weight loss rate of the straw substrate during the main pyrolysis stage decreased after adding different FTD / FDH / FDC / FDP@APP, and the residual char was significantly higher than that of the pure sample, indicating that the composite flame retardant promotes dehydration and char formation and improves thermal stability.

[0033] Figure 5 The TGA (Figure a) and DTG curves (Figure b) for fire-retardant boards based on reeds are shown. From... Figure 5 As can be seen from the data, after adding different FTD / FDH / FDC / FDP@PAPP, the weight loss rate of the straw substrate during the main pyrolysis stage decreased, and the residual char was significantly higher than that of the pure sample, indicating that the composite flame retardant promotes dehydration and char formation and improves thermal stability.

[0034] Figure 6 SEM images for APP (image a), FTD@APP (image b), FDC@APP (image c), FDH@APP (image d), and FDP@APP (image e). From Figure 6 As can be seen, the APP particles have relatively smooth surfaces and well-defined edges, exhibiting the typical crystalline or regular particle morphology of inorganic salts. After coating, the APP surface becomes significantly thicker and rougher. A thin film or microparticle-like substance can be observed encapsulating the APP surface. This indicates that the copolymerization reaction between the furan rings in the shell and BMI forms a cross-linked network on the APP surface, successfully "encapsulating" the inorganic particles. Detailed Implementation

[0035] To further illustrate the technical solution of the present invention, preferred embodiments are described below in conjunction with examples. However, it should be understood that these descriptions are merely for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0036] Detection method:

[0037] Mechanical property testing (METS universal testing machine, China): The static bending strength, modulus of elasticity, and internal bond strength of the bio-based substrate are tested using a universal testing machine, according to the standard GB / T 17657-2022 Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels. The sample size is 210×50×8 mm. 3 The static bending strength and modulus of elasticity were tested. According to the standard GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", the sample size was 50×50×8 mm. 3 The internal bond strength was tested. According to the standard GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", the sample size was 100×100×8 mm. 3 To test the moisture absorption performance.

[0038] The limiting oxygen index (LOI) of different samples was tested using an HC-2 oxygen index meter (Jiangning Analytical Instruments Co., Ltd., China). The sample size was 100 × 6.5 × 8 mm. 3 The testing standard is in accordance with GB / T2406-2008.

[0039] The vertical flammability rating of the fire-resistant panels was evaluated using a vertical flammability tester (CFZ-2, Jiangning Analytical Instruments Co., Ltd., China). The sample size was 130 × 12.7 × 3 mm. 3 According to GB / T 2408-2021 standard.

[0040] The combustion performance of the fire-resistant boards was tested using a cone calorimeter (TTech-GB / T6172, Suzhou Taistech Testing Instruments Technology Co., Ltd.). The external heat flux was 35 kW / m². 2 The sample size is 100×100×8 mm. 3 The testing standard is based on ISO 5660.

[0041] The damp heat aging procedure was set up in accordance with the accelerated aging approach of ETAG 004:2013. After the artificial accelerated aging of the samples was completed, the samples were removed and placed in a standard environment to be conditioned until their mass was constant before subsequent performance tests were conducted.

[0042] Example 1:

[0043] 1. Preparation of FTD

[0044] 9.81 g of FA and 1.01 g of triethylamine (TEA) phosphorus chloride were dispersed in a dichloromethane solution. The dichloromethane solution containing diphenylphosphine chloride was added dropwise to a three-necked flask at 0 °C. After the addition was complete, the reaction mixture was vigorously stirred at room temperature for 5 h. Subsequently, the organic layer was washed four times with a saturated sodium chloride solution and then dried with anhydrous MgSO4. The pale yellow oil of the product FTD was obtained by rotary evaporation.

[0045] 2. Preparation of FDC

[0046] 9.81 g FA and 1.01 g TEA were dispersed in 200 mL of chloroform and then added to a three-necked flask equipped with a mechanical stirrer. 23.7 g diphenylphosphine chloride was then dispersed in the chloroform solution. The chloroform solution containing diphenylphosphine chloride was added dropwise to the three-necked flask at 3°C. After the addition was complete, the reaction mixture was vigorously stirred at room temperature for 4 h. Subsequently, the organic layer was washed four times with saturated sodium chloride solution and then dried over anhydrous MgSO4. The pale yellow oil of the product FDC was obtained by rotary evaporation.

[0047] 3. Preparation of FDH

[0048] 9.81 g FA and 2.02 g TEA were dispersed in 250 mL tetrahydrofuran and then added to a three-necked flask equipped with a mechanical stirrer. 9.75 g phenylphosphine dichloride was then dispersed in the tetrahydrofuran solution. The tetrahydrofuran solution containing diphenylphosphine dichloride was added dropwise to the three-necked flask at 5 °C. After the addition was complete, the reaction mixture was vigorously stirred at room temperature for 6 h. Subsequently, the organic layer was washed four times with saturated sodium chloride solution and dried over anhydrous MgSO4. The pale yellow oil of the product FDC was obtained by rotary evaporation.

[0049] 4. Preparation of FDP

[0050] 9.81 g FA and 1.01 g TEA were dispersed in 200 mL of chloroform and then added to a three-necked flask equipped with a mechanical stirrer. 26.9 g diphenyl chlorophosphate was then dispersed in the chloroform solution. The chloroform solution containing diphenyl chlorophosphate was added dropwise to the three-necked flask at 6 °C. After the addition was complete, the reaction mixture was vigorously stirred at room temperature for 5 h. Subsequently, the organic layer was washed four times with saturated sodium chloride solution and then dried over anhydrous MgSO4. The pale yellow oil of the product FDP was obtained by rotary evaporation.

[0051] Example 2:

[0052] 1. Add 100 g of ammonium polyphosphate (APP) and 100 mL of DMF to a 500 mL three-necked flask. Stir under nitrogen purging until evenly dispersed, then add 6.02 g of FTD, 3.58 g of BMI, and 0.2 g of azobisisobutyronitrile. After dissolution, heat to 80 °C and react for 6 h. After the reaction is complete, cool to room temperature, filter, wash, and dry. The resulting product is dried in an oven at 60 °C to constant weight to obtain the solid product (FTD@APP).

[0053] 2. Add 100 g of ammonium polyphosphate (APP) and 100 mL of DMF to a 500 mL three-necked flask. Stir under nitrogen purging until evenly dispersed, then add 5.96 g of FDC, 3.58 g of BMI, and 0.2 g of azobisisobutyronitrile. After dissolution, heat to 80 °C and react for 6 h. After the reaction is complete, cool to room temperature, filter, wash, and dry. The resulting product is dried in an oven at 60 °C to constant weight to obtain the solid product (FDC@APP).

[0054] 3. Add 100 g of ammonium polyphosphate (APP) and 100 mL of DMF to a 500 mL three-necked flask. Stir under nitrogen purging until evenly dispersed, then add 6.16 g of FDH, 3.58 g of BMI, and 0.2 g of azobisisobutyronitrile. After dissolution, heat to 80 °C and react for 6 h. After the reaction is complete, cool to room temperature, filter, wash, and dry. The resulting product is dried in an oven at 60 °C to constant weight to obtain the solid product (FDH@APP).

[0055] 4. Add 100 g of ammonium polyphosphate (APP) and 100 mL of DMF to a 500 mL three-necked flask. Stir under nitrogen purging until evenly dispersed, then add 6.6 g of FDP, 3.58 g of BMI, and 0.2 g of azobisisobutyronitrile. After dissolution, heat to 80 °C and react for 6 h. After the reaction is complete, cool to room temperature, filter, wash, and dry. The resulting product is dried in an oven at 60 °C to constant weight to obtain the solid product (FDP@APP).

[0056] 5. Mix straw, core-shell structure flame retardant, and MDI adhesive in a high-speed mixer until homogeneous according to the specified mass ratio. Manually and evenly spread the adhesive-coated material into a mold with dimensions of 250×250mm×8mm and pre-press it into shape. To better demonstrate the bonding performance of MDI adhesive on straw boards, the hot-pressing temperature is set to 170℃ based on the curing properties of the MDI adhesive. Furthermore, to ensure sufficient removal of internal moisture and proper curing, the hot-pressing pressure is set to 4.5 to 5.5 MPa, and the hot-pressing time is set to 3 minutes.

[0057] To further verify the performance of the core-shell structured flame retardant with phosphorus-containing benzene ring flame retardant units, we replaced the core-shell structured flame retardant with equal amounts of pure sample, 5% uncoated APP, and 10% uncoated APP in flame-retardant bio-based boards. We designed comparative formulations as shown in Table 1 and conducted limiting oxygen index, vertical burning, cone calorimetry, mechanical property, and 4-week damp heat aging tests at 80℃ and 85% humidity. Table 1 shows the formulation and main performance parameters of the flame-retardant boards. Table 2 shows the mechanical properties and combustion performance (Cone) test results of the straw flame-retardant boards.

[0058]

[0059]

[0060] Based on the formulation design logic and performance test data of the straw-based fire-retardant board in this experiment, the following core conclusions can be drawn through systematic analysis: Core-shell structure modification treatment can significantly improve the flame retardant performance of ammonium polyphosphate (APP). When the amount of core-shell structure flame retardant added to the board is 5%, the UL-94 vertical burning rating of all relevant samples reaches V-0, and the limiting oxygen index (LOI) is not lower than 38.9%. The peak heat release rate (pHRR) and total heat release (THR) are reduced by more than 34% compared with the blank sample (without any flame retardant added). At the same time, the amount of smoke and toxic gas (CO) released is significantly suppressed. The overall flame retardant performance is significantly better than the uncoated APP and flame retardant monomer modified sample. Among the four core-shell structure flame retardants (FTD@APP, FDC@APP, FDH@APP, and FDP@APP) used in this experiment, FDC@APP exhibited the best overall performance. Its corresponding sample 3 demonstrated outstanding performance in combustion performance (pHRR, THR, LOI), mechanical properties (elastic modulus), and damp heat aging stability. FTD@APP showed the second best overall performance. Both can be considered as preferred flame retardants for this type of fire-retardant straw-based board. Furthermore, the compatibility of core-shell structure flame retardants with straw substrates and MDI adhesives is significantly better than that of flame retardant monomers, effectively mitigating the destructive effect of flame retardants on the mechanical properties of the board and achieving a synergistic balance between flame retardancy and practicality. While uncoated APP can improve the flame retardancy of the board to some extent, it leads to a significant decrease in the board's mechanical properties and exhibits poor damp heat aging stability. Therefore, it is not suitable as a standalone high-efficiency flame retardant for this type of fire-retardant bio-based board.

[0061] Example 3:

[0062] 1. Add 100 g piperazine pyrophosphate (PAPP) and 100 mL DMF to a 500 mL three-necked flask. Stir under nitrogen purging until evenly dispersed, then add 6.02 g FTD, 3.58 g BMI, and 0.2 g azobisisobutyronitrile. After dissolution, heat to 80 °C and react for 6 h. After the reaction is complete, cool to room temperature, filter, wash, and dry. The resulting product is dried in an oven at 60 °C to constant weight to obtain the solid product (FTD@PAPP).

[0063] 2. Add 100 g piperazine pyrophosphate (PAPP) and 100 mL DMF to a 500 mL three-necked flask. Stir under nitrogen purging until evenly dispersed, then add 5.96 g FDC, 3.58 g BMI, and 0.2 g azobisisobutyronitrile. After dissolution, heat to 80 °C and react for 6 h. After the reaction is complete, cool to room temperature, filter, wash, and dry. The resulting product is dried in an oven at 60 °C to constant weight to obtain the solid product (FDC@PAPP).

[0064] 3. Add 100 g piperazine pyrophosphate (PAPP) and 100 mL DMF to a 500 mL three-necked flask. Stir under nitrogen purging until evenly dispersed, then add 6.16 g FDH, 3.58 g BMI, and 0.2 g azobisisobutyronitrile. After dissolution, heat to 80 °C and react for 6 h. After the reaction is complete, cool to room temperature, filter, wash, and dry. The resulting product is dried in an oven at 60 °C to constant weight to obtain the solid product (FDH@PAPP).

[0065] 4. Add 100 g piperazine pyrophosphate (PAPP) and 100 mL DMF to a 500 mL three-necked flask. Stir under nitrogen purging until evenly dispersed, then add 6.6 g FDP, 3.58 g BMI, and 0.2 g azobisisobutyronitrile. After dissolution, heat to 80 °C and react for 6 h. After the reaction is complete, cool to room temperature, filter, wash, and dry. The resulting product is dried in an oven at 60 °C to constant weight to obtain the solid product (FDP@PAPP).

[0066] 5. Mix the reeds, microencapsulated flame retardant, and epoxy adhesive in a high-speed mixer until homogeneous according to the specified mass ratio. Manually and evenly spread the glued material into a mold with dimensions of 250×250mm×8mm and pre-press it into shape. To better demonstrate the bonding performance of the epoxy adhesive on the straw board, the hot-pressing temperature is set to 170℃ based on the curing properties of the epoxy adhesive. Furthermore, to ensure sufficient removal of internal moisture and proper curing, the hot-pressing pressure is set to 4.5 to 5.5 MPa, and the hot-pressing time is set to 3 minutes.

[0067] To further verify the performance of the core-shell structured flame retardant with phosphorus-containing benzene ring flame retardant units, we designed the comparative formulations shown in Table 3 and conducted limiting oxygen index, vertical burning, cone calorimetry, and mechanical property tests on them. Table 3 shows the formulation and main performance parameters of the reed-based flame-retardant board. Table 4 shows the test results of the mechanical properties and combustion performance (Cone) of the reed-based flame-retardant board.

[0068]

[0069]

[0070] Based on the formulation design and performance test results of reed-based flame-retardant boards, the following conclusions can be drawn: Core-shell modification of piperazine pyrophosphate (PAPP) can effectively improve its flame-retardant efficiency in reed boards. Under the condition of 10% flame retardant addition, the UL-94 vertical burning rating of all core-shell structure flame retardant samples reached V-0, the limiting oxygen index was higher than 40.1%, the peak heat release rate was reduced by more than 34% compared with the blank sample, and the release of smoke and toxic CO was significantly suppressed. The overall flame-retardant effect was better than that of unmodified PAPP. Among the four core-shell structure flame retardants prepared, FDC@PAPP showed the best overall performance, with its corresponding sample exhibiting the best performance in terms of combustion performance, static bending strength, elastic modulus, and damp heat aging stability; FTD@PAPP was second best. Both can be considered as preferred flame-retardant systems for reed-based flame-retardant boards. Core-shell structure modification significantly improves the interfacial compatibility between flame retardants, reed fibers, and epoxy adhesives, reducing the negative impact of flame retardant components on the mechanical properties of the board, enabling the material to maintain good mechanical properties while achieving high flame retardancy. While uncoated PAPP can improve the flame retardancy rating of the board, it significantly damages mechanical properties and exhibits poor stability in humid and hot environments, making it difficult to meet the application requirements of high-performance flame-retardant reed-based boards on its own.

[0071] Based on the above experimental results, the following conclusions can be drawn:

[0072] (1) The core-shell structure flame retardant with phosphorus-containing benzene ring structure flame retardant unit has improved compatibility and dispersibility in bio-based substrates. Its physical and mechanical properties and flame retardant properties are superior to those of flame-retardant bio-based boards without halogens.

[0073] (2) The core-shell structure flame retardant system with phosphorus-containing benzene ring structure flame retardant unit has the advantages of being environmentally friendly, halogen-free, and having good long-term durability. It is also simple to process and suitable for large-scale application. It can be applied in industries such as building decoration, furniture manufacturing, etc.

[0074] In summary, the core-shell structure flame retardant containing phosphorus-containing benzene ring flame retardant units is a highly efficient, durable, environmentally friendly, low-smoke, halogen-free flame retardant suitable for plant fiber-based composite materials. It is particularly suitable for flame retardant modification and green manufacturing of agricultural residue bio-based materials such as straw and reeds, providing a new technical path and engineering implementation solution for the development of renewable bio-based materials.

Claims

1. A bio-based core-shell structured flame retardant, characterized in that: The bio-based core-shell structured flame retardant consists of a core and a shell structure, wherein the core is a halogen-free flame retardant and the shell structure is a polymer containing furfuryl alcohol derivatives and bismaleimide.

2. The bio-based core-shell structured flame retardant according to claim 1, characterized in that: The mass ratio of the core to the shell structure is 100:5~25.

3. The bio-based core-shell structured flame retardant according to claim 1, characterized in that: The halogen-free flame retardant is selected from one or more of melamine phosphate, melamine polyphosphate, melamine cyanurate, ammonium polyphosphate, piperazine pyrophosphate, aluminum hypophosphite, and aluminum phosphonate, mixed in any proportion.

4. The method for preparing the bio-based core-shell structured flame retardant according to claim 1, 2 or 3, characterized in that... Includes the following steps: The halogen-free flame retardant was added to the solvent and stirred and dispersed evenly under a nitrogen atmosphere. Then, a phosphorus furfuryl alcohol derivative, bismaleimide, and a free radical initiator were added, and the mixture was heated to 60-80℃ and reacted for 4-12 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and washed. The resulting product was dried in an oven at 60-80℃ to constant weight to obtain a solid product.

5. The preparation method according to claim 4, characterized in that: The free radical initiator is selected from one or more of cyclohexanone peroxide, benzoyl peroxide, tert-butyl hydroperoxide, azobisisobutyronitrile, and azobisisoheptanenitrile.

6. The preparation method according to claim 4, characterized in that: The solvent is selected from one or more solvents such as tetrahydrofuran, dimethyl sulfoxide, cyclohexane, cyclohexanone, chloroform, toluene, xylene, benzene, dioxane, ethyl acetate, acetone, and butanone.

7. The preparation method according to claim 4, characterized in that: The phosphorus-containing furfuryl alcohol derivative is selected from one or more of FTD, FDC, FDH, and FDP, and its structure is shown below: 。 8. The application of the bio-based core-shell structure flame retardant as described in claim 1, 2 or 3 in the preparation of bio-based boards.

9. The application according to claim 8, characterized in that: The bio-based core-shell structure flame retardant, bio-based fragments and adhesive are mixed in a high-speed mixer until uniform, and then the mixture is evenly spread in a mold and vulcanized in a flat vulcanizing machine to prepare a flame-retardant bio-based board. The bio-based fragments are selected from one or more bio-based materials such as straw, reeds, rice straw, wood, and bamboo, mixed in any proportion; The adhesive is selected from one or more of polyurethane, epoxy resin, lignin, and soybean protein adhesives, mixed in any proportion.

10. The application according to claim 9, characterized in that: The components, by mass, include: 85-100 parts of bio-based fragments, 5-10 parts of bio-based core-shell structure flame retardant, and 5 parts of adhesive.

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