Hyperbranched flame retardant as well as preparation method and application thereof

Abstract

The invention discloses a hyperbranched flame retardant as well as a preparation method and application thereof. The flame retardant is prepared by the following steps: dehydrating and pre-polymerizing a boron-containing component (such as tetrahydroxy diborane) and dihydric alcohol (such as 1, 3-propylene glycol), and condensing with trihydroxymethyl phosphine oxide. 4 parts of the flame retardant is added into epoxy resin, phosphorus-containing free radicals can be released in a gas phase for quenching and smoke suppression, a compact boron-containing expanded carbon layer is formed in a condensed phase, and synergistic flame retardance is achieved. The hyperbranched structure can be embedded into an epoxy network, synchronous reinforcement and toughening are achieved, the impact strength is improved by 123.5%, and the tensile strength is improved by 47.7%. The flame retardant has efficient flame retardance (the limit oxygen index is 33.9%, UL-94V-0 level), high transparency and excellent mechanical properties, and is suitable for epoxy resin composite materials in the fields of electronic packaging, aerospace and the like.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant epoxy resin composite materials. More specifically, it relates to a hyperbranched flame retardant, its preparation method, and its application. Background Technology

[0002] Epoxy resins, due to their three-dimensional network structure formed during thermosetting, possess excellent mechanical properties, high transparency, low shrinkage, and strong adhesion, making them important polymer materials. However, epoxy resins have a limiting oxygen index of only 23%–26%, making them highly flammable and releasing large amounts of toxic black smoke, severely limiting their application in the flame retardant field. While traditional halogenated flame retardants are highly efficient, their combustion byproducts have bioaccumulative toxicity and have been gradually banned by international regulations. Phosphorus-based halogen-free flame retardants, such as ammonium polyphosphate and aluminum hypophosphite, are environmentally friendly, but they suffer from inherent defects such as poor compatibility, the need for high addition amounts (≥15 parts) to achieve flame retardancy, complete loss of transparency after introduction, and severe degradation of mechanical properties. Current multi-element synergistic systems can partially improve flame retardant efficiency, but cannot reverse the industry-wide problems of mechanical property collapse and transparency loss.

[0003] Therefore, developing a novel flame retardant that combines high flame retardancy, transparency retention, and simultaneous enhancement of mechanical properties at low addition levels has become a key path to overcome the bottleneck of high-end epoxy resin applications. Summary of the Invention

[0004] This invention provides a hyperbranched flame retardant, its preparation method, and its application to solve the problems of flammability of epoxy resin and poor compatibility, loss of transparency, and deterioration of mechanical properties caused by the addition of commercial flame retardants. The flame retardant significantly improves the flame retardancy of epoxy resin when added at an amount of 2-10 parts, and achieves a UL-94V-0 rating with a limiting oxygen index of up to 33.9% within an addition range of 4-8 parts, while maintaining the high transparency and mechanical properties of the matrix. In a preferred embodiment, only 4 parts are needed to achieve a dual flame retardant mechanism in both the gas phase and condensed phase: phosphorus free radicals in the gas phase efficiently quench the combustion chain reaction and inhibit smoke generation; boron elements in the condensed phase promote the formation of a dense, expanded glassy carbon layer, effectively blocking heat and oxygen exchange. Of particular note is that the hyperbranched molecular chain can be embedded in the three-dimensional cross-linked network of epoxy resin, achieving stress dispersion and toughening effects through branching nodes. This not only enhances the flame retardant properties but also significantly improves the mechanical properties of epoxy resin, effectively overcoming the technical defects of traditional phosphorus-based flame retardants, which require high addition amounts, leading to a decline in mechanical properties and loss of transparency.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] On one hand, the present invention provides a hyperbranched flame retardant, wherein the flame retardant is obtained by the condensation reaction of the intermediate obtained by the dehydration reaction of the boron-containing component and the diol with tris(hydroxymethyl)phosphine oxide.

[0007] Furthermore, the molar ratio of the boron-containing component to the diol is 1:4.5.

[0008] Furthermore, the molar ratio of the boron-containing component to tris(hydroxymethyl)phosphine oxide is 1:1.5 to 1:3.0.

[0009] Furthermore, the boron-containing component is selected from one of tetrahydroxydiborane, boric acid, aminophenylboronic acid, ammonium pentaborate, or triethanolamine borate.

[0010] Furthermore, the diol is selected from one of 1,2-ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol.

[0011] Furthermore, the trimethylolphosphine oxide was purchased from Hubei Xingfa Chemical Group Co., Ltd. The tetrahydroxydiborane (98% purity) and 1,3-propanediol (98% purity) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0012] In another aspect, the present invention provides a method for preparing the hyperbranched flame retardant as described above, comprising the following steps:

[0013] The boron-containing component is reacted with a diol to undergo a dehydration reaction, yielding an intermediate product.

[0014] The intermediate product was condensed with trimethylolphosphine oxide to obtain the hyperbranched flame retardant.

[0015] Furthermore, the dehydration reaction is carried out at a temperature of 130–150°C for 3–5 hours.

[0016] Furthermore, the condensation reaction is carried out at a temperature of 70–160°C for 8–12 hours.

[0017] Furthermore, the preparation method includes the following steps:

[0018] S1. At room temperature, the boron-containing component and the diol are mixed at a molar ratio of 1:4.5, heated to 150°C, and separated for four hours until no more water appears in the separator to obtain the intermediate product.

[0019] S2. The intermediate product and tris(hydroxymethyl)phosphine oxide were mixed at 70°C and reacted for 4 hours. The temperature was then increased to 150°C and maintained for 4 hours. After the reaction was completed and cooled to room temperature, the mixture was placed in a vacuum oven and dried overnight at -0.1 MPa and 80°C to obtain a colorless and transparent product.

[0020] In another aspect, the present invention provides the application of the above-mentioned hyperbranched flame retardant in the preparation of flame-retardant epoxy resin composite materials. The application includes: compounding the hyperbranched flame retardant at a low addition amount of 2-10 parts with 100 parts of epoxy resin and 15-25 parts of curing agent to prepare a composite material possessing high flame retardancy, high transparency, and excellent mechanical properties.

[0021] In another aspect, the present invention provides a flame-retardant epoxy resin composite material, comprising epoxy resin, curing agent and hyperbranched flame retardant as described above.

[0022] Furthermore, the raw materials of the composite material contain the following components:

[0023] 100 parts epoxy resin, 15-25 parts curing agent, and 2-10 parts of the hyperbranched flame retardant.

[0024] Furthermore, the epoxy resin is either bisphenol A type epoxy resin or bisphenol F type epoxy resin.

[0025] Further, the curing agent is either 4,4'-diaminodiphenyl sulfone or 4,4'-diaminodiphenylmethane.

[0026] Further, the matrix bisphenol A type epoxy resin (DGEBA: E-44), curing agent 4,4'-diaminodiphenylmethane (DDM), and the flame retardant are mixed in proportion, stirred evenly, and then subjected to vacuum degassing. Subsequently, the mixture is transferred to a mold for thermosetting to obtain the composite material.

[0027] Furthermore, the vacuum degree of the vacuum degassing is not higher than -0.1MPa, the degassing temperature is 100℃, and it is first cured at 100℃ for two hours, and then cured at 120℃ for two hours.

[0028] The beneficial effects of this invention are as follows:

[0029] This invention provides a hyperbranched flame retardant system based on the synergistic effect of boron and phosphorus, which exhibits significant environmental protection characteristics. By introducing boron to construct a special molecular structure, it can catalyze the formation of a high-strength expanded char layer during epoxy resin combustion, effectively improving flame retardant performance. This flame retardant exhibits excellent compatibility with the epoxy resin matrix, does not affect the degassing behavior during curing, and the resulting composite material remains colorless and transparent, fully preserving the original optical properties of the matrix. In terms of mechanical properties, the special molecular configuration of the flame retardant can form a good interpenetrating structure with the three-dimensional network of epoxy resin, resulting in a significant improvement in key mechanical indicators such as tensile strength, impact toughness, and elongation at break compared to unmodified epoxy resin. Attached Figure Description

[0030] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0031] Figure 1 This is a schematic diagram of the synthesis process of the flame retardant HBDT used in Examples 1, 2, and 3.

[0032] Figure 2 The diagram shows tensile, impact, and stress-strain parameters of Example 2 and Comparative Example 1 (pure epoxy resin).

[0033] Figure 3 The curves for heat release rate (HRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) of Example 2 and Comparative Example 1 in the cone calorimetry test are shown.

[0034] Figure 4 Digital photographs of the transparency of the epoxy resin composites in Examples 1, 2, and 3.

[0035] Figure 5 The TGA test curves are for Example 4 and Comparative Example 1. Detailed Implementation

[0036] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0037] The trimethylolphosphine oxide was purchased from Hubei Xingfa Chemical Group Co., Ltd. The tetrahydroxydiborane (98% purity) and 1,3-propanediol (98% purity) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Unless otherwise specified, other reagents are commercially available. In the following examples, the parts of each component are based on 100 parts by weight of epoxy resin.

[0038] Example 1

[0039] This embodiment provides a flame-retardant epoxy resin composite material and its preparation method. The composite material comprises the following components by weight:

[0040] Bisphenol A type epoxy resin (DGEBA, E-44): 100 parts;

[0041] Curing agent 4,4'-diaminodiphenylmethane (DDM): 21.8 parts;

[0042] Flame retardant HBDT: 8 parts.

[0043] Its preparation method includes the following steps:

[0044] S1. At room temperature, the boron-containing component is mixed with a diol at a molar ratio of 1:4.5, heated to 150°C, and separated for four hours until no more water appears in the separator, thus obtaining the intermediate product.

[0045] S2. The intermediate product, tris(hydroxymethyl)phosphine oxide (and boron-containing components in a molar ratio of 1:1.5) were mixed at 70°C and reacted for 4 hours. The temperature was then increased to 150°C and maintained for 4 hours. After the reaction was completed and cooled to room temperature, the mixture was placed in a vacuum oven and dried overnight at -0.1 MPa and 80°C to finally obtain the colorless and transparent product HBDT.

[0046] S3. Place 100 parts of epoxy resin in a beaker and preheat it at 500 rpm under a hot plate at 90°C to increase its fluidity. Then, dissolve 8 parts of flame retardant HBDT in 10 mL of methanol and mix it with the epoxy resin. After the methanol has completely evaporated, add 21.8 parts of DDM and stir briefly to dissolve the DDM. Then, immediately transfer it to a vacuum oven at 100°C for vacuum degassing. Degas for 20 minutes at a pressure of -0.1 MPa. Then, pour it into the corresponding test mold and cure it at 100°C for two hours, and then at 120°C for two hours to obtain the flame-retardant epoxy composite material.

[0047] The flame-retardant epoxy resin prepared in this embodiment and Comparative Example 1 (pure epoxy resin) were subjected to performance tests. The limiting oxygen index (LOI) of Example 1 was measured to be 33.9%, and it successfully passed the UL-94 standard test. It self-extinguished rapidly after being removed from the flame, and no molten droplets ignited the degreased cotton, achieving a V-0 rating. In contrast, the oxygen index of Comparative Example 1 was only 26%, and it did not receive a rating in the UL-94 test. Molten droplets ignited the degreased cotton.

[0048] Example 2

[0049] This embodiment provides a flame-retardant epoxy resin composite material and its preparation method. The composite material comprises the following components by weight:

[0050] Bisphenol A type epoxy resin (DGEBA, E-44): 100 parts;

[0051] Curing agent 4,4'-diaminodiphenylmethane (DDM): 21.8 parts;

[0052] Flame retardant HBDT: 6 parts.

[0053] Its preparation method includes the following steps:

[0054] S1. At room temperature, the boron-containing component is mixed with a diol at a molar ratio of 1:4.5, heated to 150°C, and separated for four hours until no more water appears in the separator, thus obtaining the intermediate product.

[0055] S2. The intermediate product, tris(hydroxymethyl)phosphine oxide (and boron-containing components in a molar ratio of 1:1.5) were mixed at 70°C and reacted for 4 hours. The temperature was then increased to 150°C and maintained for 4 hours. After the reaction was completed and cooled to room temperature, the mixture was placed in a vacuum oven and dried overnight at -0.1 MPa and 80°C to finally obtain the colorless and transparent product HBDT.

[0056] S3. Place 100 parts of epoxy resin in a beaker and preheat it at 500 rpm under a hot plate at 90°C to increase its fluidity. Then, dissolve 6 parts of flame retardant HBDT in 10 mL of methanol and mix it with the epoxy resin. After the methanol has completely evaporated, add 21.8 parts of DDM and stir briefly to dissolve the DDM. Then, immediately transfer it to a vacuum oven at 100°C for vacuum degassing. Degas for 20 minutes at a pressure of -0.1 MPa. Then, pour it into the corresponding test mold and cure it at 100°C for two hours, and then at 120°C for two hours to obtain the flame-retardant epoxy composite material.

[0057] The flame-retardant epoxy resin prepared in this embodiment and Comparative Example 1 (pure epoxy resin) were subjected to performance tests. Figure 2 The tensile and impact strengths (a) and stress-strain curves (b) of Example 2 and Comparative Example 1 are shown. Compared to the pure sample, the tensile and impact strengths of Example 2 increased by 40.0% and 88.6%, respectively, while the elongation at break also increased from the original 5.5 to 7.2, an increase of 30.9%. This demonstrates that the addition of the flame retardant HBDT can significantly improve the mechanical properties of epoxy resin.

[0058] also, Figure 3 The results of cone calorimetry tests for Example 2 and Comparative Example 1 are shown, including curves for heat release rate (HRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP). The sample from Example 2 exhibited excellent flame retardant properties; its peak HRR, THR, and TSP values ​​were reduced by 49.2%, 36.3%, and 40.5%, respectively, compared to pure epoxy resin, and the peak SPR also decreased from 0.29 m... 2 / s decreased to 0.22m 2 / s. The significant reduction in the peak values ​​of heat release and smoke release parameters indicates that the flame retardancy of the material was effectively improved after the addition of HBDT.

[0059] Example 3

[0060] This embodiment provides a flame-retardant epoxy resin composite material and its preparation method. The composite material comprises the following components by weight:

[0061] Bisphenol A type epoxy resin (DGEBA, E-44): 100 parts;

[0062] Curing agent 4,4'-diaminodiphenylmethane (DDM): 21.8 parts;

[0063] Flame retardant HBDT: 4 parts.

[0064] Its preparation method includes the following steps:

[0065] S1. At room temperature, the boron-containing component is mixed with a diol at a molar ratio of 1:4.5, heated to 150°C, and separated for four hours until no more water appears in the separator, thus obtaining the intermediate product.

[0066] S2. The intermediate product, tris(hydroxymethyl)phosphine oxide (and boron-containing components in a molar ratio of 1:1.5) were mixed at 70°C and reacted for 4 hours. The temperature was then increased to 150°C and maintained for 4 hours. After the reaction was completed and cooled to room temperature, the mixture was placed in a vacuum oven and dried overnight at -0.1 MPa and 80°C to finally obtain the colorless and transparent product HBDT.

[0067] S3. Place 100 parts of epoxy resin in a beaker and preheat it at 500 rpm under a hot table at 90°C to increase its fluidity. Then, dissolve 4 parts of flame retardant HBDT in 10 mL of methanol and mix it with the epoxy resin. After the methanol has completely evaporated, add 21.8 parts of DDM and stir briefly to dissolve the DDM. Then, immediately transfer it to a vacuum oven at 100°C for vacuum degassing. Degas for 20 minutes at a pressure of -0.1 MPa. Then, pour it into the corresponding test mold and cure it at 100°C for two hours, and then at 120°C for two hours to obtain the flame-retardant epoxy composite material.

[0068] Figure 4 The materials prepared in Examples 1, 2, and 3 all exhibit excellent optical transparency. All materials are clear and transparent, without turbidity, whitening, or precipitation. This result demonstrates that the hyperbranched flame retardant HBDT has good compatibility and refractive index matching with the epoxy resin matrix, and can efficiently impart flame retardancy. This characteristic makes the composite material particularly suitable for applications with stringent transparency requirements, such as transparent encapsulation of high-end electronic devices, optical lenses, transparent display covers, and as an alternative to fire-resistant glass.

[0069] Example 4

[0070] This embodiment provides a flame-retardant epoxy resin composite material and its preparation method. The composite material comprises the following components by weight:

[0071] Bisphenol A type epoxy resin (DGEBA, E-44): 100 parts;

[0072] Curing agent 4,4'-diaminodiphenylmethane (DDM): 21.8 parts;

[0073] Flame retardant HBDT-HP: 8 parts.

[0074] Its preparation method includes the following steps:

[0075] S1. At room temperature, the boron-containing component is mixed with a diol at a molar ratio of 1:4.5, heated to 150°C, and separated for four hours until no more water appears in the separator, thus obtaining the intermediate product.

[0076] S2. The intermediate product, tris(hydroxymethyl)phosphine oxide (and boron-containing components in a molar ratio of 1:3.0) were mixed at 70°C and reacted for 4 hours. The temperature was then increased to 150°C and maintained for 4 hours. After the reaction was completed and cooled to room temperature, the mixture was placed in a vacuum oven and dried overnight at -0.1 MPa and 80°C to finally obtain the colorless and transparent product HBDT-HP.

[0077] S3. Place 100 parts of epoxy resin in a beaker and preheat it at 500 rpm under a hot plate at 90°C to increase its fluidity. Then, dissolve 8 parts of flame retardant HBDT-HP in 10 mL of methanol and mix it with the epoxy resin. After the methanol has completely evaporated, add 21.8 parts of DDM and stir briefly to dissolve the DDM. Then, immediately transfer it to a vacuum oven at 100°C for vacuum degassing. Degas for 20 minutes at a pressure of -0.1 MPa. Then, pour it into the corresponding test mold and cure it at 100°C for two hours, and then at 120°C for two hours to obtain the flame-retardant epoxy composite material.

[0078] The composite material obtained in this embodiment was tested. Its limiting oxygen index (LOI) was 33.9%, and it passed the UL-94V-0 rating. Most importantly, Figure 5 Thermogravimetric analysis (TGA) of the material was shown. Under a nitrogen atmosphere, Example 4 achieved a char residue of 22.0% at 800°C, significantly higher than Comparative Example 1 (14.8%) without HBDT-HP. The high char residue demonstrates that the flame retardant possesses excellent char-forming ability and effectively insulates against heat and oxygen.

[0079] Comparative Example 1

[0080] This comparative example provides a pure epoxy resin composite material and its preparation method. The composite material comprises the following components by weight:

[0081] Bisphenol A type epoxy resin (DGEBA, E-44): 100 parts;

[0082] Curing agent 4,4'-diaminodiphenylmethane (DDM): 21.8 parts;

[0083] 100 parts of epoxy resin were placed in a beaker and preheated at 500 rpm under a hot table at 90°C to increase its fluidity. Then, 21.8 parts of DDM were added and stirred briefly to dissolve the DDM. The mixture was then immediately transferred to a vacuum oven at 100°C for vacuum degassing at a pressure of -0.1 MPa for 20 minutes. The mixture was then poured into the corresponding test mold and cured at 100°C for two hours, followed by curing at 120°C for two hours to obtain pure epoxy material.

[0084] Comparative Example 2

[0085] This comparative example provides a flame-retardant epoxy resin composite material and its preparation method. The composite material comprises the following components in parts by weight:

[0086] Bisphenol A type epoxy resin (DGEBA, E-44): 100 parts;

[0087] Curing agent 4,4'-diaminodiphenylmethane (DDM): 21.8 parts;

[0088] Flame retardant HBDT: 1 part.

[0089] Its preparation method includes the following steps:

[0090] S1. At room temperature, the boron-containing component is mixed with a diol at a molar ratio of 1:4.5, heated to 150°C, and separated for four hours until no more water appears in the separator, thus obtaining the intermediate product.

[0091] S2. The intermediate product, tris(hydroxymethyl)phosphine oxide (and boron-containing components in a molar ratio of 1:1.5) were mixed at 70°C and reacted for 4 hours. The temperature was then increased to 150°C and maintained for 4 hours. After the reaction was completed and cooled to room temperature, the mixture was placed in a vacuum oven and dried overnight at -0.1 MPa and 80°C to finally obtain the colorless and transparent product HBDT.

[0092] S3. Place 100 parts of epoxy resin in a beaker and preheat it at 500 rpm under a hot plate at 90°C to increase its fluidity. Then, dissolve 1 part of flame retardant HBDT in 10 mL of methanol and mix it with the epoxy resin. After the methanol has completely evaporated, add 21.8 parts of DDM and stir briefly to dissolve the DDM. Then, immediately transfer it to a vacuum oven at 100°C for vacuum degassing. Degas for 20 minutes at a pressure of -0.1 MPa. Then, pour it into the corresponding test mold and cure it at 100°C for two hours, and then at 120°C for two hours to obtain the flame-retardant epoxy composite material.

[0093] Comparative Example 3

[0094] This comparative example provides a flame-retardant epoxy resin composite material and its preparation method. The composite material comprises the following components in parts by weight:

[0095] Bisphenol A type epoxy resin (DGEBA, E-44): 100 parts;

[0096] Curing agent 4,4'-diaminodiphenylmethane (DDM): 21.8 parts;

[0097] Flame retardant intermediate: 4 parts; Flame retardant trimethylolphosphine oxide: 4 parts;

[0098] Its preparation method includes the following steps:

[0099] S1. At room temperature, the boron-containing component is mixed with a diol at a molar ratio of 1:4.5, heated to 150°C, and separated for four hours until no more water appears in the separator, thus obtaining the intermediate product.

[0100] S2. Place 100 parts of epoxy resin in a beaker and preheat it at 500 rpm under a hot plate at 90°C to increase its fluidity. Then, dissolve 4 parts of flame retardant synthesis intermediate and 4 parts of trimethylolphosphine oxide in 10 mL of methanol and mix with the epoxy resin. After the methanol has completely evaporated, add 21.8 parts of DDM and stir briefly to dissolve the DDM. Then, immediately transfer the mixture to a vacuum oven at 100°C for vacuum degassing at a pressure of -0.1 MPa for 20 minutes. Then, pour the mixture into the corresponding test mold and cure it at 100°C for two hours, followed by curing at 120°C for two hours to obtain the epoxy composite material.

[0101] Comparative Example 4

[0102] This comparative example provides a flame-retardant epoxy resin composite material and its preparation method. The composite material comprises the following components in parts by weight:

[0103] Bisphenol A type epoxy resin (DGEBA, E-44): 100 parts;

[0104] Curing agent 4,4'-diaminodiphenylmethane (DDM): 21.8 parts;

[0105] Flame retardant ammonium polyphosphate: 8 parts;

[0106] 100 parts of epoxy resin were placed in a beaker and preheated at 500 rpm under a hot plate at 90°C to increase its fluidity. Then, 8 parts of ammonium polyphosphate were uniformly dispersed in 10 mL of methanol and mixed with the epoxy resin. After the methanol was completely evaporated, 21.8 parts of DDM were added and stirred briefly to dissolve the DDM. The mixture was then immediately transferred to a vacuum oven at 100°C for vacuum degassing at a pressure of -0.1 MPa for 20 minutes. The mixture was then poured into the corresponding test mold and cured at 100°C for two hours, followed by curing at 120°C for two hours to obtain the epoxy composite material.

[0107] Comparative Example 5

[0108] This comparative example provides a flame-retardant epoxy resin composite material and its preparation method. The composite material comprises the following components in parts by weight:

[0109] Bisphenol A type epoxy resin (DGEBA, E-44): 100 parts;

[0110] Curing agent 4,4'-diaminodiphenylmethane (DDM): 21.8 parts;

[0111] Flame retardant aluminum hypophosphite: 8 parts;

[0112] 100 parts of epoxy resin were placed in a beaker and preheated at 500 rpm under a hot plate at 90°C to increase its fluidity. Then, 8 parts of aluminum hypophosphite were uniformly dispersed in 10 mL of methanol and mixed with the epoxy resin. After the methanol was completely evaporated, 21.8 parts of DDM were added and stirred briefly to dissolve the DDM. The mixture was then immediately transferred to a 100°C vacuum oven for vacuum degassing at a pressure of -0.1 MPa for 20 minutes. The mixture was then poured into the corresponding test mold and cured at 100°C for two hours, followed by curing at 120°C for two hours to obtain the epoxy composite material.

[0113] The conventional mechanical properties and combustion performance of epoxy resin composites were tested according to the following standards, and the results are shown in Table 1.

[0114] Impact strength of cantilever beam: Tested according to GB / T1043.1-2018 standard, the impact energy is 2J;

[0115] Tensile strength: Tested according to GB / T1040.1-2018 standard, at a test speed of 5 mm / min;

[0116] Flammability: Tested according to LOI standard in accordance with GB / T 2406-2015 and UL-94 standard in accordance with GB / T2408-2008.

[0117] Figure 1 This is a schematic diagram of the synthesis process of the flame retardant HBDT used in Examples 1, 2, and 3.

[0118] Figure 2 The diagram shows tensile, impact, and stress-strain parameters of Example 2 and Comparative Example 1 (pure epoxy resin).

[0119] Figure 3 The curves for heat release rate (HRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) of Example 2 and Comparative Example 1 in the cone calorimetry test are shown.

[0120] Figure 4 Digital photographs of the transparency of the epoxy resin composite materials in Examples 1, 2, and 3.

[0121] Figure 5 The TGA test curves are for Example 4 and Comparative Example 1.

[0122] Table 1

[0123] Conclusion: Table 1 shows that Examples 1-3 all achieved a V-0 rating in the vertical burning test. With increasing HBDT content, the LOI value also increased, reaching a maximum of 33.9%. Total heat release and total smoke release gradually decreased, demonstrating excellent flame retardant and smoke suppression effects. Example 4 used a higher phosphorus content HBDT-HP flame retardant variant, designed to improve charring efficiency. Tests showed that this scheme achieved a char residue rate of 22.0%, and its flame retardant performance (UL-94V-0, LOI 32.5%) was comparable to Examples 1-3. In contrast, the flame retardant effects of Comparative Examples 1, 3, 4, and 5 were less than satisfactory. The introduction of pure epoxy, a blend of flame retardant intermediates and trimethylolphosphine oxide, ammonium polyphosphate, and aluminum hypophosphite, at the current addition levels, failed to pass the vertical burning rating test, and the improvement in LOI value was very limited. Comparative Example 2 exhibited relatively poor flame retardant performance, reaching only a V-2 rating with a limiting oxygen index of 29.5%. This is related to the low amount of HBDT flame retardant added (only 1 part), which falls outside the range described in this invention, thus failing to achieve superior flame retardant performance. Regarding mechanical properties, Examples 1-4, due to their hyperbranched structure and embedding effect with the three-dimensional network in the matrix, showed significant enhancement effects on mechanical properties. In contrast, commercially available flame retardants ammonium polyphosphate and aluminum hypophosphite were completely incompatible with the epoxy resin matrix, causing significant stress concentration after curing, thereby damaging the mechanical properties.

[0124] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A hyperbranched flame retardant, characterized in that: The intermediate obtained by the dehydration reaction of a boron-containing component with a diol is then condensed with tris(hydroxymethyl)phosphine oxide. The structure contains multiple P–O and B–O bonds, and has multiple terminal hydroxyl groups and phosphophosphine ether branches. Its hyperbranched skeleton has the following characteristics: Boron is embedded in the molecular backbone in the form of B–O–C; Phosphorus is distributed on the periphery of the molecule in the form of P–CH2–O–C branched chains; It contains multiple trimethylolphosphine structural units, which is beneficial for char formation; It exhibits a dendritic hyperbranched structure with high functionality and high thermal stability. It has the structure shown in the following general formula:

2. The method for preparing the hyperbranched flame retardant as described in claim 1, characterized in that, Includes the following steps: The boron-containing component is reacted with a diol to undergo a dehydration reaction, yielding an intermediate product. The intermediate product was condensed with trimethylolphosphine oxide to obtain the hyperbranched flame retardant; The boron-containing component is one of tetrahydroxydiborane, boric acid, aminophenylboronic acid, ammonium pentaborate, or triethanolamine borate, and the diol is one of 1,2-ethylene glycol, 1,3-propanediol, 1,4-butanediol, or 1,5-pentanediol.

3. The method for preparing the hyperbranched flame retardant as described in claim 2, characterized in that, The molar ratio of the boron-containing component to the diol is 1:4.5; The molar ratio of the boron-containing component to tris(hydroxymethyl)phosphine oxide is 1:1.5 to 1:3.

0.

4. The method for preparing the hyperbranched flame retardant as described in claim 2, characterized in that, The dehydration reaction is carried out at a temperature of 130–150°C for 3–5 hours. The condensation reaction is carried out at a temperature of 70–160°C for 8–12 hours.

5. A flame-retardant epoxy resin composite material, characterized in that: Composed of epoxy resin, curing agent, and hyperbranched flame retardant as described in claim 1, the flame-retardant epoxy composite material comprises the following components by weight: 100 parts epoxy resin; 15-25 parts of curing agent; 2 to 10 parts of the hyperbranched flame retardant.

6. The composite material as described in claim 5, characterized in that, The epoxy resin is either bisphenol A type epoxy resin or bisphenol F type epoxy resin.

7. The composite material as described in claim 5, characterized in that, The curing agent is either 4,4'-diaminodiphenyl sulfone or 4,4'-diaminodiphenylmethane.

8. A method for preparing a flame-retardant epoxy resin composite material as described in claim 5 or 6, characterized in that, Includes the following steps: Heat the epoxy resin to 60-100℃ and stir until homogeneous; Add the hyperbranched flame retardant to it and continue stirring for 10-30 minutes to disperse it evenly. Add the curing agent, mix well, and then degas. The mixture is poured into a mold and cured at 100°C for two hours, then at 120°C for two hours. After cooling, it is demolded to obtain the flame-retardant composite material.

9. The application of the flame-retardant epoxy resin composite material as described in claim 8 in the preparation of products in the fields of construction, automobiles, electronics, transparent encapsulation of electronic devices, and aerospace.

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