Preparation and application of bio-based intumescent intrinsic flame retardant

Abstract

The invention discloses preparation and application of a bio-based intumescent intrinsic flame retardant, a flame retardant CCL is synthesized through substitution reaction between arginine and cyanuric chloride to serve as a gas source, phytic acid (PA) is selected as an acid source, starch (S) is selected as a gas source, and a three-source-in-one intumescent intrinsic flame retardant CCA-PA-S is constructed in a hydrogen bond self-assembly mode. The flame retardant participates in epoxy group ring opening of EP, and collaborative optimization of flame retardant property and mechanical property is realized.

Description

Technical Field

[0001] The invention belongs to the technical fields of flame retardancy and polymer materials, and relates to a preparation method of a bio-based intumescent intrinsic flame retardant and application of the flame retardant in epoxy resin materials. Background Art

[0002] Epoxy resin (EP) is a thermosetting polymer with an aromatic, aliphatic, or alicyclic compound as its backbone and two or more epoxy groups in its molecular chain. Due to its high bond strength, low cure shrinkage, and excellent electrical insulation, it is widely used in high-end fields such as aerospace, electronic packaging, and composite materials. However, the high content of organic components in the EP molecular chain (such as aromatic ring structures) leads to a high fire load. Combustion is accompanied by intense heat release, large amounts of toxic smoke (benzene, aldehydes), and molten droplets, which seriously restricts its application in demanding flame retardant and safety-critical applications such as rail transit and construction projects. Therefore, the development of EP-based composite materials that combine high flame retardancy with excellent mechanical properties has become a rigid industry demand.

[0003] Flame retardancy mechanisms can be categorized as either vapor-phase or condensed-phase, but achieving optimal results with a single mechanism is difficult. While intumescent flame retardants combine acid, carbon, and gas sources, achieving vapor-phase flame retardancy by releasing inert gas while simultaneously catalyzing condensed-phase carbonization, traditional intumescent flame retardants suffer from core flaws: poor dispersion of the three components within the matrix and low synergistic effects. This not only compromises flame retardancy but also significantly degrades the material's mechanical properties (e.g., a ≥20% decrease in tensile strength).

[0004] In recent years, environmentally friendly bio-based materials have demonstrated unique flame retardancy advantages. This invention utilizes a groundbreaking bio-based raw material: arginine, rich in amino groups, and cyanuric chloride synthesis gas (CCA), a component of cyanuric chloride synthesis gas. Through intermolecular hydrogen bonding, these components are combined with phytic acid (PA, an acid source) and starch (S, a carbon source) to create an integrated flame retardant. The amino groups participate in the epoxy ring-opening cure to optimize mechanical properties, while the triazine structure of cyanuric chloride synergistically enhances thermal stability, fundamentally resolving the incompatibility between flame retardancy and mechanical properties in traditional technologies. Summary of the Invention

[0005] In view of the fact that the existing EP is highly flammable and easily produces a large amount of molten droplets and toxic fumes (such as benzene series and aldehydes) when burned, there is a risk of causing secondary fires, endangering personnel safety and polluting the environment. In addition, the addition of conventional flame retardants easily leads to the deterioration of the mechanical properties of the material (such as decreased tensile strength and impact toughness), making it difficult to balance environmental protection and comprehensive performance requirements. The present invention discloses the preparation and application of a bio-based intumescent intrinsic flame retardant.

[0006] The specific technical solutions are as follows: 1. Flame retardant design 1. Raw material selection: Gas source component: Arginine and cyanuric chloride are reacted by substitution to synthesize arginine-cyanuric chloride condensate (CCA), which contains a triazine structure (thermal stability > 400°C) and a reactive amino group; Acid source component: phytic acid (PA), containing highly active phosphate groups (catalytic carbonization efficiency > 80%); Carbon source components: starch (S), bio-based polyhydroxy carbon source.

[0007] 2. Structural innovation: CCA, PA, and S self-assemble to form an integrated complex through intermolecular hydrogen bonds (CCA-PA-S curve at 3500 cm -1 The strong absorption peak at 1100-1150cm is due to the stretching vibration of hydrogen bonds. -1 The COP=O characteristic peak appears at the bottom of the tube), achieving nano-scale dispersion of the three components.

[0008] 2. Preparation Method (1) Synthesis of CCA: Arginine and cyanuric chloride were dissolved in ice deionized water at a molar ratio of 2.0-3.0:1, and an emulsifier was added at a concentration of 3-8% by mass of cyanuric chloride. The system temperature was controlled to be ≤5°C. Specifically, the emulsifier was Tween-60, and the amount was 4-6% by mass of cyanuric chloride. Add cyanuric chloride in portions over 1-2 hours, and simultaneously add 8-12% NaOH solution dropwise, maintaining the pH value of the system at 6.0-7.0, and react for 1.5-2.5 hours; Add water to make the solid content of the system reach 15-25%, and freeze-dry to obtain flame retardant CCA; (2) Synthesis of CCA-PA: Dissolve phytic acid in deionized water, stir at room temperature for 0.5-1.5 h, add CCA obtained in step (1) and continue stirring for 0.5-1.5 h; the mass ratio of phytic acid to CCA is (1.5-1.7):1; The mixture was heated to 55-65°C under a nitrogen atmosphere for 2-4 hours, cooled to room temperature, and then the pH was adjusted to 6.5-7.5. The mixture was freeze-dried to obtain the flame retardant CCA-PA. (3) Synthesis of CCA-PA-S: The flame retardant CCA-PA and starch were dissolved in deionized water at a mass ratio of 1:2 to 2:1, reacted at 75-85 °C for 4-6 h under a nitrogen atmosphere, and freeze-dried to obtain the flame retardant CCA-PA-S.

[0009] Preferably, the mass ratio of CCA-PA to starch is 1:(1~2).

[0010] 3. Application Method Disperse the flame retardant in anhydrous ethanol at an addition rate of 8-18 wt%. Add fluidized epoxy resin and stir in a water bath at 65-75°C. Remove the solvent under vacuum and inject into the mold. Pre-cure at 75-85°C for 0.5-1 hour and finally cure at 120-140°C for 6-8 hours.

[0011] Compared to existing technologies, the synthetic flame retardant CCA-PA-S in this invention is derived from environmentally friendly raw materials. The abundant amino groups in the flame retardant participate in the ring-opening process of epoxy groups and, upon combustion, decompose into non-combustible gases such as N2 and NH3, exerting gas-phase flame retardancy. The presence of acidic substances catalyzes carbonization of the matrix, forming a protective layer that isolates the matrix from heat and oxygen exchange in the surrounding environment. While maintaining excellent mechanical properties, the flame retardancy is significantly enhanced, overcoming the negative impact of traditional physically blended flame retardants on the mechanical properties of the resin matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is the infrared spectra of CC and A as well as CCA, CCA-PA, and CCA-PA-S prepared in the examples of the present invention.

[0013] Figure 2 1 is the XRD pattern of CCA, CCA-PA, and CCA-PA-S prepared in the examples of the present invention.

[0014] Figure 3 These are the thermogravimetric spectra of pure EP and EP / 10% CCA, EP / 10% CCA-PA, EP / 10% CCA-PA-S and EP / 15% CCA-PA-S prepared in Examples 1, 2, 7 and 8 of the present invention.

[0015] Figure 4 It is a vertical combustion test chart of pure EP and EP / 10%CCA, EP / 10%CCA-PA, EP / 10%CCA-PA-S and EP / 15%CCA-PA-S prepared in Examples 1, 2, 7 and 8 of the present invention.

[0016] Figure 5 These are digital photos and microscopic morphology images of the carbon layers of pure EP and EP / 10%CCA, EP / 10%CCA-PA, EP / 10%CCA-PA-S and EP / 15%CCA-PA-S prepared in Examples 1, 2, 7 and 8 of the present invention.

[0017] Figure 6 These are the test graphs of the bending properties (a) and tensile properties (b) of pure EP and EP / 10%CCA, EP / 10%CCA-PA, EP / 10%CCA-PA-S and EP / 15%CCA-PA-S prepared in Examples 1, 2, 7 and 8 of the present invention. DETAILED DESCRIPTION

[0018] The present invention will be further explained below with reference to specific embodiments.

[0019] Example 1 Weigh the measured amount of arginine and deionized water into a four-necked flask, add the measured amount of emulsifier Tween-60 (5% by weight of the cyanuric chloride), maintain the temperature at 0-5°C, and stir evenly. Maintaining the temperature, add the measured amount of cyanuric chloride powder to the flask in three portions over 1.5 hours. Simultaneously, add the measured amount of NaOH solution (10% by weight) dropwise over 4 hours to stabilize the pH at around 6.5. After the addition of the materials, continue the reaction at 0-5°C for 2 hours. Add water to bring the solids content to 20%, resulting in a light milky yellow liquid. Freeze-dry the mixture to obtain the flame retardant CCA.

[0020] EP was placed in an oven and heated at 80°C to obtain fluidized EP; 4 g of CCA was dispersed in 15 mL of anhydrous ethanol, placed in a water bath at 70°C and stirred, and then 30 ml of fluidized EP was added and stirred thoroughly to form a uniform solution. The anhydrous ethanol in the uniform solution was removed with a vacuum filter until no obvious bubbles appeared. The obtained mixture was poured into a preheated mold, transferred to an oven, cured at 80°C for 30 min, heated to 130°C and kept warm for 8 h to obtain an intrinsic flame retardant material 10 wt% CCA.

[0021] Example 2 CCA was prepared as in Example 1.

[0022] 6.3 mL of phytic acid was dispersed in 100 mL of deionized water and stirred at room temperature for 1 hour to form a homogeneous solution. 5 g of the flame retardant CCA was then added and stirred for another hour. The mixture was then heated to 60°C under a nitrogen atmosphere for 3 hours. After cooling to room temperature, the pH of the solution was adjusted to 7 and freeze-dried to obtain the flame retardant CCA-PA.

[0023] EP was placed in an oven and heated at 80°C to obtain fluidized EP; 4 g of CCA was dispersed in 15 mL of anhydrous ethanol, placed in a water bath at 70°C and stirred, and then 30 ml of fluidized EP was added and stirred thoroughly to form a uniform solution. The anhydrous ethanol in the uniform solution was removed with a vacuum filter until no obvious bubbles appeared. The obtained mixture was poured into a preheated mold and transferred to an oven. It was cured at 80°C for 30 min, heated to 130°C and kept warm for 8 h to obtain an intrinsic flame retardant material 10 wt% CCA-PA.

[0024] Example 3 CCA-PA was prepared according to Example 2.

[0025] The flame retardant CCA-PA and S were dissolved in 50 mL of deionized water in a mass ratio of (1:1), reacted at 80°C for 5 h under a N2 atmosphere, and the flame retardant CCA-PA-S was obtained by freeze drying.

[0026] EP was placed in an oven and heated at 80°C to obtain fluidized EP; 4 g of CCA-PA-S was dispersed in 15 mL of anhydrous ethanol, placed in a water bath at 70°C and stirred, and then 30 ml of fluidized EP was added and stirred thoroughly to form a uniform solution. The anhydrous ethanol in the uniform solution was removed with a vacuum filter until no obvious bubbles appeared. The obtained mixture was poured into a preheated mold and transferred to an oven. It was cured at 80°C for 30 min, heated to 130°C and kept warm for 8 h to obtain the intrinsic flame retardant material EP / 10wt%CCA-PA-S.

[0027] Example 4 CCA-PA-S was prepared according to Example 3.

[0028] EP was placed in an oven and heated at 80°C to obtain fluidized EP; 6 g of CCA-PA-S was dispersed in 15 mL of anhydrous ethanol, placed in a water bath at 70°C and stirred, and then 30 ml of fluidized EP was added and stirred thoroughly to form a uniform solution. The anhydrous ethanol in the uniform solution was removed with a vacuum filter until no obvious bubbles appeared. The obtained mixture was poured into a preheated mold and transferred to an oven. It was cured at 80°C for 30 min, heated to 130°C and kept warm for 8 h to obtain the intrinsic flame retardant material EP / 15wt%CCA-PA-S.

[0029] Example 5 CCA-PA was prepared according to Example 2.

[0030] The flame retardant CCA-PA and S were dissolved in 50 mL of deionized water in a mass ratio of 1:2, reacted at 80°C for 5 h under a N2 atmosphere, and the flame retardant CCA-PA-S was obtained by freeze drying.

[0031] EP was placed in an oven and heated at 80°C to obtain fluidized EP; 4 g of CCA-PA-S was dispersed in 15 mL of anhydrous ethanol, placed in a water bath at 70°C and stirred, and then 30 ml of fluidized EP was added and stirred thoroughly to form a uniform solution. The anhydrous ethanol in the uniform solution was removed with a vacuum filter until no obvious bubbles appeared. The obtained mixture was poured into a preheated mold and transferred to an oven. It was cured at 80°C for 30 min, heated to 130°C and kept warm for 8 h to obtain the intrinsic flame retardant material EP / 10wt%CCA-PA-S.

[0032] Example 6 CCA-PA-S was prepared according to Example 5.

[0033] EP was placed in an oven and heated at 80°C to obtain fluidized EP; 6 g of CCA-PA-S was dispersed in 15 mL of anhydrous ethanol, placed in a water bath at 70°C and stirred, and then 30 ml of fluidized EP was added and stirred thoroughly to form a uniform solution. The anhydrous ethanol in the uniform solution was removed with a vacuum filter until no obvious bubbles appeared. The obtained mixture was poured into a preheated mold and transferred to an oven. It was cured at 80°C for 30 min, heated to 130°C and kept warm for 8 h to obtain the intrinsic flame retardant material EP / 15wt%CCA-PA-S.

[0034] Example 7 CCA-PA was prepared according to Example 2.

[0035] The flame retardant CCA-PA and S were dissolved in 50 mL of deionized water in a mass ratio of (2:1), reacted at 80°C for 5 h under a N2 atmosphere, and the flame retardant CCA-PA-S was obtained by freeze drying.

[0036] EP was placed in an oven and heated at 80°C to obtain fluidized EP; 4 g of CCA-PA-S was dispersed in 15 mL of anhydrous ethanol, placed in a water bath at 70°C and stirred, and then 30 ml of fluidized EP was added and stirred thoroughly to form a uniform solution. The anhydrous ethanol in the uniform solution was removed with a vacuum filter until no obvious bubbles appeared. The obtained mixture was poured into a preheated mold and transferred to an oven. It was cured at 80°C for 30 min, heated to 130°C and kept warm for 8 h to obtain the intrinsic flame retardant material EP / 10wt%CCA-PA-S.

[0037] Example 8 CCA-PA-S was prepared according to Example 7.

[0038] EP was placed in an oven and heated at 80°C to obtain fluidized EP; 6 g of CCA-PA-S was dispersed in 15 mL of anhydrous ethanol, placed in a water bath at 70°C and stirred, and then 30 ml of fluidized EP was added and stirred thoroughly to form a uniform solution. The anhydrous ethanol in the uniform solution was removed with a vacuum filter until no obvious bubbles appeared. The obtained mixture was poured into a preheated mold and transferred to an oven. It was cured at 80°C for 30 min, heated to 130°C and kept warm for 8 h to obtain the intrinsic flame retardant material EP / 15wt%CCA-PA-S.

[0039] The structural characterization and performance evaluation of the products prepared in the above examples are as follows: Figure 1The infrared spectra of CC, A, CCA, CCA-PA, and CCA-PA-S are shown. Comparing the three curves of CC, A, and CCA, we find that 808 cm -1 The C-Cl stretching vibration peak at 1654 cm -1 The -C=N absorption peak at 3132cm-1 broadens, indicating the successful synthesis of CCA. -1 The new peak at 3500 cm is the characteristic peak formed by the reaction between guanidine and hydroxyl groups. -1 The strong absorption peak at 1100-1150cm is due to the stretching vibration of hydrogen bonds. -1 The COP=O characteristic peak that appears at indicates the successful synthesis of CCA-PA-S.

[0040] Figure 2 The XRD spectra of CCA, CCA-PA, and CCA-PA-S are shown. The sharp diffraction peaks in the CCA curve indicate a highly ordered crystal structure. In contrast, the introduction of PA and S (CCA-PA and CCA-PA-S) significantly decreases the diffraction peak intensity, indicating a decrease in crystalline order and an increase in disorder.

[0041] Figure 3 Thermogravimetric spectra of pure EP and EP / 10% CCA, EP / 10% CCA-PA, EP / 10% CCA-PA-S, and EP / 15% CCA-PA-S prepared in examples of the present invention are shown. Pure EP exhibits a char yield of only 13.19% at 800°C, indicating a low char-forming capacity. In contrast, the EP / CCA-PA-S exhibits a higher char yield, which helps form an effective physical barrier, blocking heat transfer and suppressing the release of combustible gases.

[0042] Figure 4 Digital images show the UL-94 testing process for pure EP and EP / 10% CCA, EP / 10% CCA-PA, EP / 10% CCA-PA-S, and EP / 15% CCA-PA-S prepared according to examples of the present invention. Pure EP combustion is accompanied by noticeable droplets and significant heat release. In stark contrast, the EP / 10% CCA-PA-S composite material self-extinguishes within 8 seconds, demonstrating highly effective flame retardancy.

[0043] Figure 5These are digital photos and microscopic morphology images of the carbon layers of pure EP and EP / 10%CCA, EP / 10%CCA-PA, EP / 10%CCA-PA-S and EP / 15%CCA-PA-S prepared in accordance with the embodiments of the present invention. The carbon residue of EP is in a state of almost complete combustion, with only a small amount of coke remaining. By observing the microstructure of the carbon residue through a scanning electron microscope (SEM), it can be seen that there are obvious cracks and holes on its surface. This broken and incomplete carbon layer structure cannot provide effective thermal protection and barrier for the EP material, resulting in the flammability of the EP material. The EP / 10%CCA-PA-S composite material forms a continuous and tight carbon layer, which can isolate the contact between oxygen and flammable volatiles, inhibit the transfer of combustion heat, and exert a condensed phase flame retardant effect. At the same time, Raman spectroscopy shows that compared with EP, the I of EP / 10%CCA-PA-S is D / I G Lower values ​​indicate a higher degree of graphitization and a more stable structure. Figure 6 Figures (a) and (b) show the flexural properties of pure EP and EP / 10% CCA, EP / 10% CCA-PA, EP / 10% CCA-PA-S, and EP / 15% CCA-PA-S prepared in accordance with the present invention. The test results show that compared to pure EP, the tensile strength, flexural strength, and flexural modulus of EP / 10% CCA-PA-S increased by 51.4%, 39.1%, and 44.3%, respectively. This enhancement is primarily attributed to the -OH and NH groups in CCA-PA-S reacting with EP groups to form a crosslinking network. As the flame retardant CCA-PA-S content increases to 15% (EP / 15% CCA-PA-S), the flexural and tensile strengths of the EP composite decrease. This is likely due to incomplete reaction of the -OH and NH groups in CCA-PA-S with epoxy groups at high addition levels.

[0044] Table 1 Effects of different ratios of CCA-PA-S flame retardant on key parameters of cone calorimetry (CCT) test of EP composites Wherein, PHRR is the peak heat release rate, THR is the total heat release, PSPR is the peak smoke generation rate, TSP is the total smoke release, PCOP is the peak carbon monoxide production rate, and PCO2P is the peak carbon dioxide generation rate; The cone calorimetry (CCT) test data in Table 1 show that when the mass ratio of CCA-PA to S is 2:1 (i.e., EP / 10%CCA-PA-S (2:1)), the composite material exhibits the best flame retardant properties.

Claims

1. A method for preparing a bio-based intumescent intrinsic flame retardant, characterized in that: The following steps are involved: (1) Synthesis of CCA: Dissolve arginine and cyanuric chloride in ice deionized water at a molar ratio of 2.0-3.0:1, add 3-8% of cyanuric chloride by weight of emulsifier, and control the system temperature to ≤5°C; Add cyanuric chloride in portions over 1-2 hours, and simultaneously add 8-12% NaOH solution dropwise, maintaining the pH value of the system at 6.0-7.0, and react for 1.5-2.5 hours; Add water to make the solid content of the system reach 15-25%, and freeze-dry to obtain flame retardant CCA; (2) Synthesis of CCA-PA: Dissolve phytic acid in deionized water, stir at room temperature for 0.5-1.5 h, add CCA obtained in step (1) and continue stirring for 0.5-1.5 h; The mixture was heated to 55-65°C under a nitrogen atmosphere for 2-4 hours, cooled to room temperature, and then the pH was adjusted to 6.5-7.

5. The mixture was freeze-dried to obtain the flame retardant CCA-PA. (3) Synthesis of CCA-PA-S: The flame retardant CCA-PA and starch were dissolved in deionized water at a mass ratio of 1:2 to 2:1, reacted at 75-85 °C for 4-6 h under a nitrogen atmosphere, and freeze-dried to obtain the flame retardant CCA-PA-S.

2. The preparation method according to claim 1, wherein: The emulsifier in step (1) is Tween-60, and the amount used is 4-6% of the mass of cyanuric chloride.

3. The preparation method according to claim 1, wherein: The mass ratio of phytic acid to CCA in step (2) is (1.5-1.7):

1.

4. The preparation method according to claim 1, wherein: The mass ratio of CCA-PA to starch in step (3) is 2:

1.

5. A bio-based intumescent intrinsic flame retardant prepared by the method according to any one of claims 1 to 4, characterized in that: The flame retardant is CCA-PA-S, wherein CCA, PA and S are connected by intermolecular hydrogen bonds, and its infrared spectrum is 3500cm -1 The characteristic absorption peak of hydrogen bond appears at 1100-1150cm -1 There is a COP=O characteristic peak at .

6. Use of the bio-based intumescent intrinsic flame retardant according to claim 5 in epoxy resin, characterized in that: include: Disperse the flame retardant in anhydrous ethanol at an addition rate of 8-18 wt%; Add fluidized epoxy resin and stir to mix in a water bath at 65-75°C; After vacuum removal of the solvent, inject it into the mold, pre-cure at 75~85℃ for 0.5~1h, and finally cure at 120~140℃ for 6~8h.

7. The use according to claim 6, characterized in that: The flame retardant is added in an amount of 10-15 wt% of the total weight of the mixture.

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