A full-bio-based epoxy resin composite material based on cashew phenol modified boron nitride and a preparation method thereof

Abstract

The application discloses a full-biological epoxy resin composite based on cashew phenol modified boron nitride and a preparation method thereof. The phosphorus-containing cashew phenol-based flame-retardant epoxy monomer grafted boron nitride flame-retardant heat conductor and the phosphorus-containing cashew phenol-based flame-retardant curing agent grafted boron nitride flame-retardant heat conductor are prepared based on the technology combining molecular design, graft modification and heat-conducting flame-retardant, cashew phenol-based flame-retardant epoxy monomer is grafted and modified to hydroxylated boron nitride, and the boron nitride is introduced into an epoxy resin to obtain a biological epoxy resin composite with flame retardation and heat conduction, so that the shortcomings of flammability and low thermal conductivity of the epoxy resin are improved, and the application range of the epoxy resin is wider.

Description

Technical Field

[0001] This invention relates to a fully bio-based epoxy resin composite material based on cashew phenol modified boron nitride and its preparation method, belonging to the field of chemical materials technology. Background Technology

[0002] With the global deployment of 5G networks and the rapid development of technologies such as the Internet of Things and artificial intelligence, the demand for high-frequency, high-speed, and high-reliability printed circuit boards (PCBs) has increased dramatically. As the core carrier of electronic devices, the performance of PCBs directly determines signal transmission efficiency, device stability, and energy management capabilities. Therefore, epoxy resin has become one of the key materials in PCB manufacturing due to its low cost, ease of processing, excellent electrical insulation, and chemical stability. However, the characteristics of 5G technology place higher demands on epoxy resins. High power density and miniaturized design exacerbate the challenges of PCB thermal management, necessitating epoxy resin composites that combine high thermal conductivity with flame retardant safety.

[0003] In renewable biomass, cashew nut shell oil is a natural product extracted from cashew nut shell oil. Its chemical structure combines a benzene ring, phenolic hydroxyl groups, and a straight-chain C15 with unsaturated double bonds. The benzene ring imparts rigidity, while the long alkyl chain provides toughness, giving cashew nut shell oil a "combination of rigidity and flexibility," making it a research hotspot in the field of bio-based materials in recent years. Simultaneously, the unsaturated double bonds and phenolic hydroxyl groups in the cashew nut shell oil structure also endow it with good reactivity, enabling the synthesis of high-performance flame retardants through chemical modification. Currently, the application of cashew nut shell oil in epoxy resins mainly involves using it as a modifier or additive to modify epoxy resins before adding it to the epoxy resin. However, the overall proportion of cashew nut shell oil in epoxy resins is relatively small, failing to fully utilize its potential.

[0004] Meanwhile, boron nitride (BN) has become a promising candidate filler due to its good mechanical properties, excellent thermal conductivity, low density, and resistance to chemical corrosion. However, the strong van der Waals forces between BN lamellars easily lead to agglomeration, and its high surface chemical inertness limits its application range. Currently, research on boron nitride as a filler for epoxy resin modification has made some progress. However, current research mainly focuses on adding boron nitride directly to epoxy resin systems after simple modification. For example, in patent CN116515244A, a phosphorus-nitrogen composite modified epoxy resin and its prepared copper-clad laminate, boron nitride is modified with lignin and then directly added to the epoxy resin as a flame retardant additive; in patent CN119708811A, a boron nitride-containing resin composition and its application, boron nitride and a sintering aid are mixed, sintered, and crushed to obtain the modified boron nitride, thereby increasing the filling ratio of boron nitride in the resin.

[0005] Currently, there are no reports on how to prepare a fully bio-based epoxy resin composite material with added bio-based modified boron nitride. How to use cashew phenol to prepare a resin with good flame retardancy and thermal conductivity is crucial for the application of epoxy resin in PCBs. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention introduces a phosphorus-containing cashew nut shell phenol-based flame-retardant epoxy monomer and a phosphorus-containing cashew nut shell phenol-based flame-retardant curing agent. Utilizing their unique chemical structure and reactivity, the dispersion and compatibility issues of boron nitride in epoxy resin are resolved, while simultaneously simplifying the process and reducing costs. Furthermore, the composite material prepared by this invention not only possesses excellent flame-retardant and thermal conductivity properties but also achieves the goals of environmental protection and sustainable development.

[0007] This invention is achieved through the following technical solution:

[0008] The first objective of this invention is to provide a method for preparing a fully bio-based epoxy resin composite material based on cashew phenol-modified boron nitride, comprising the following steps:

[0009] S1. Dissolve cashew nut phenol, acid-binding agent and P-Cl compound in an organic solvent and react at 40-80 °C. After filtering the reaction solution, partially purify the filtrate by washing with water and drying to obtain a phosphorus-containing cashew nut phenol derivative.

[0010] S2. Dissolve the phosphorus-containing cashew phenol derivative and the epoxidizing agent in an organic solvent, react under ice bath conditions, filter the reaction solution, purify part of the filtrate by washing with water, and dry to obtain the phosphorus-containing cashew phenol-based flame-retardant epoxy monomer.

[0011] S3. Add the phosphorus-containing cashew phenol derivative and unsaturated dicarboxylic anhydride sequentially to the reactor and stir continuously until homogeneous. Reflux and condense at 160–200 °C under nitrogen or inert gas protection. After the reaction, dissolve the crude product in an organic solvent, wash and purify, collect the organic phase to remove the solvent, and obtain the phosphorus-containing cashew phenol-based curing agent.

[0012] S4. Take boron nitride powder and add it to a solvent for ultrasonic dispersion. Then add 3-6 mol / L NaOH solution and react at 40-80 °C. After the reaction, dry to obtain hydroxylated boron nitride.

[0013] S5. The phosphorus-containing cashew phenolic flame-retardant epoxy monomer prepared in S2, the hydroxylated boron nitride prepared in S4, the catalyst and the organic solvent are mixed evenly in a reactor and reacted at 80-150 °C. The solid obtained from the reaction is washed with water and dried to obtain an epoxy monomer grafted boron nitride flame-retardant thermal conductive agent.

[0014] S6. Add the phosphorus-containing cashew phenol-based flame retardant curing agent prepared in S3 and the hydroxylated boron nitride prepared in S4 to an organic solvent, and react them at 40-80 °C under vigorous stirring. Wash the solid obtained from the reaction with water and dry it to obtain the curing agent grafted with boron nitride flame retardant and thermally conductive agent.

[0015] S7. Dissolve the epoxy monomer grafted with boron nitride flame-retardant and thermally conductive agent prepared in S5 or the curing agent grafted with boron nitride flame-retardant and thermally conductive agent prepared in S6 in an organic solvent, disperse evenly, and then add it to a certain amount of the phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomer prepared in S2. Subsequently, add the corresponding amount of the phosphorus-containing cashew nut phenol-based flame-retardant curing agent prepared in S3, stir and mix evenly, and then cure at 90-130 ℃ for 1-3 h, at 140-160 ℃ for 1-3 h, and at 170-200 ℃ for 1-3 h to obtain a fully bio-based epoxy resin composite material. Among them, the epoxy monomer grafted with boron nitride flame-retardant and thermally conductive agent or the curing agent grafted with boron nitride flame-retardant and thermally conductive agent accounts for 20-35% of the total mass of the composite material; the molar ratio of the cashew nut phenol-based epoxy monomer to the phosphorus-containing cashew nut phenol-based flame-retardant curing agent is (1-2):1.

[0016] In one embodiment of the present invention, the organic solvent is one or a mixture of several of chloroform, dichloromethane, toluene, xylene, and tetrahydrofuran.

[0017] In one embodiment of the present invention, the amount of organic solvent used is 30-80% of the total mass of the reaction system.

[0018] In one embodiment of the present invention, the P-Cl compound in S1 is one or a mixture of several of the following: diphenyl chlorinated phosphate, diphenylphosphine chloride, phenyl phosphate dichloride, phenyl phosphorus dichloride, phosphorus oxychloride, phosphorus trichloride, and hexachlorocyclotriphosphazene.

[0019] In one embodiment of the present invention, the molar ratio of cashew phenol, acid-binding agent and P-Cl compound in S1 is (1-6):(1-6):1.

[0020] In one embodiment of the present invention, the acid-binding agent in S1 is one or a mixture of several of the following: triethylamine, pyridine, sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

[0021] In one embodiment of the present invention, the epoxidizing agent in S2 is one or a mixture of several of m-chloroperbenzoic acid (m-CPBA), hydrogen peroxide, and peracetic acid.

[0022] In one embodiment of the present invention, the molar ratio of the phosphorus-containing cashew phenol derivative to the epoxidizing agent in S2 is 1:(1-6).

[0023] In one embodiment of the present invention, the molar ratio of the phosphorus-containing cashew phenol derivative to the unsaturated dicarboxylic acid anhydride in S3 is 1:(1-3).

[0024] In one embodiment of the present invention, the unsaturated dicarboxylic anhydride in S3 is one or a mixture of several of maleic anhydride, itaconic anhydride, and citraconic anhydride.

[0025] In one embodiment of the present invention, the mass ratio of boron nitride to sodium hydroxide solution in S4 is 1:(1-5).

[0026] In one embodiment of the present invention, the solvent in step S4 is one or a mixture of several of water, ethanol, and acetone.

[0027] In one embodiment of the present invention, the mass ratio of phosphorus-containing cashew phenolic epoxy monomer to hydroxylated boron nitride in S5 is (1-15):1.

[0028] In one embodiment of the present invention, the catalyst in S5 is one or a mixture of several of triethylamine, sodium hydroxide, boron trifluoride, and boron trifluoride diethyl ether.

[0029] In one embodiment of the present invention, the mass ratio of phosphorus-containing cashew phenol-based flame retardant curing agent to hydroxylated boron nitride in S6 is (1-15):1.

[0030] A second objective of this invention is to provide a fully bio-based epoxy resin composite material based on cashew phenol-modified boron nitride prepared by the method described above.

[0031] A third objective of this invention is to provide the application of the aforementioned cashew phenol-modified boron nitride-based fully bio-based epoxy resin composite material in circuit board manufacturing.

[0032] The beneficial effects of this invention are:

[0033] This invention utilizes phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomers or phosphorus-containing cashew nut phenol-based flame-retardant curing agents to graft boron nitride to prepare flame-retardant and thermally conductive agents. These flame-retardant and thermally conductive agents are then synergistically combined with phosphorus-containing cashew nut phenol-based flame-retardant curing agents and phosphorus-containing cashew nut phenol-based flame-retardant epoxy resin monomers to prepare a fully bio-based epoxy resin composite material. Since all three components use cashew nut phenol, a renewable resource, as a common raw material, high compatibility among the components can be achieved through molecular structure design and reasonable proportioning, effectively solving the problems of boron nitride's tendency to agglomerate and its poor compatibility with epoxy resin. The fully bio-based epoxy resin composite material prepared by the method of this invention exhibits excellent flame-retardant and thermally conductive effects, achieving a balance between these two properties. Detailed Implementation

[0034] The present invention will be further illustrated below with specific examples. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0035] Raw material source:

[0036] Cashew phenol was supplied by Cardläne (Zhuhai, China): a pale yellow liquid composed of 41% triene, 36% diene, 20% monoene, and 3% saturated compounds. Epoxy resin (DGEBA, E-44) was supplied by Hefei Jiangfeng Chemical Co., Ltd. Phenylephrine dichloride (98%), hexachlorocyclotriphosphazene (98%), diphenyl chlorophosphate (97%), 3-chloroperoxybenzoic acid (85%), and boron nitride (10 μm) were all purchased from Aladdin Chemical Co., Ltd. (Shanghai, China). Phosphorus oxychloride, chloroform, dichloromethane, anhydrous sodium sulfate, triethylamine, and 4,4'-diaminodiphenylmethane (DDM) were all purchased from Sinopharm Chemical Reagent Co., Ltd.

[0037] Test method:

[0038] Limiting Oxygen Index (LOI): The sample (size: 100 mm × 6.5 mm × 3.2 mm) was tested on an HC-2 type oxygen index analyzer (Jiangning, China) in accordance with GB / T 2406.2-2009 standard.

[0039] Cone calorimeter test: According to ISO 5660-1 standard, the sample (100 mm × 100 mm × 4 mm) was placed in aluminum foil, and the thermal radiation flux was 50 kW / m². 2 .

[0040] Thermal conductivity testing: Thermal diffusivity (α) and specific heat (Cp) were measured using a laser flash analyzer (LFA 467 Nanoflash, NETZSCH, Germany). The density (ρ) of the specimen was estimated by measuring its volume and mass. The TC value of the sample was obtained using the typical equation: TC = α × Cp × ρ.

[0041] The technical solution of the present invention will be described in detail below with reference to specific embodiments. In the following embodiments, unless otherwise specified, the reagents, materials and equipment used can be purchased commercially, prepared by conventional methods, or commonly used in the industry.

[0042] Example 1: Preparation of a fully bio-based epoxy resin composite material with epoxy monomer grafted boron nitride flame retardant and thermally conductive agent as the modifier.

[0043] (1) In a three-necked flask, 0.2 mol of cashew nut shell powder, 0.2 mol of triethylamine and 0.1 mol of phenyl phosphorus dichloride were dissolved in 250 mL of chloroform and reacted at 70 °C for 5 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filtrate was partially purified, washed with water, and dried to obtain a phosphorus-containing cashew nut shell powder derivative.

[0044] (2) In a three-necked flask, 0.05 mol of a phosphorus-containing cashew nut phenol derivative and 0.3 mol of 3-chloroperoxybenzoic acid were dissolved in 200 mL of dichloromethane and reacted in an ice bath for 5 h. After filtration, the filtrate was partially purified, washed with water, and dried to obtain a phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomer.

[0045] (3) 0.1 mol of phosphorus-containing cashew nut phenol derivative and 0.2 mol of maleic anhydride were added sequentially to a three-necked round-bottom flask and stirred continuously until homogeneous. The mixture was then refluxed at 195 °C for 6 h under a nitrogen atmosphere. Finally, the mixture was cooled to room temperature, and the crude product was dissolved in an organic solvent, washed and purified. The organic phase was collected, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation to obtain the phosphorus-containing cashew nut phenol-based curing agent.

[0046] (4) Take 5 g of boron nitride powder and add it to 50 mL of ethanol for ultrasonic dispersion for 10 min. Then add 100 mL of 5 mol / L NaOH solution and reflux in an oil bath at 100 °C for 20 h. After cooling, filter and dry to obtain hydroxylated boron nitride.

[0047] (5) Mix 0.1 mol of phosphorus-containing cashew phenolic flame-retardant epoxy monomer, 0.2 mol of hydroxylated boron nitride, 0.1 mol of boron trifluoride ether and 100 mL of dichloromethane in a reactor. The reaction temperature is 90 °C and the reaction time is 6 h. The resulting solid is washed with water and dried to obtain epoxy monomer grafted boron nitride flame-retardant thermal conductive agent.

[0048] (6) The phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomers grafted with boron nitride flame-retardant thermal conductive agent, accounting for 20%, 25%, 30%, and 35% of the total mass of the composite material, were dissolved in dichloromethane and ultrasonically dispersed evenly. Then, a certain amount of phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomers were added, followed by the corresponding amount of phosphorus-containing cashew nut phenol-based flame-retardant curing agent. The molar ratio of phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomers to phosphorus-containing cashew nut phenol-based curing agent was 2:1. After stirring and mixing evenly, the mixture was cured at 90–130 °C for 1–3 h, at 140–160 °C for 1–3 h, and at 170–200 °C for 1–3 h to obtain a multifunctional bio-based epoxy resin composite material with flame retardancy, thermal conductivity, and toughening properties, which were respectively named composite material-1, composite material-2, composite material-3, and composite material-4.

[0049] The obtained fully bio-based epoxy resin composite material was subjected to performance testing, and the test results are as follows:

[0050] Table 1

[0051]

[0052] The results show:

[0053] As the amount of phosphorus-containing cashew nut shell phenol-based flame-retardant epoxy monomer grafted with boron nitride flame-retardant thermal conductive agent increases, the limiting oxygen index of the composite material also rises. Simultaneously, the peak heat release rate (PHRR) and total heat release rate (THR) of the composite material gradually decrease. The decrease in PHRR and THR further indicates an improvement in the flame-retardant performance of the composite material. However, when the amount of phosphorus-containing cashew nut shell phenol-based flame-retardant epoxy monomer grafted with boron nitride flame-retardant thermal conductive agent reaches 30%, further addition of this agent causes the limiting oxygen index of the composite material to decrease, and the PHRR to increase. Continuing to increase the amount of this agent does not significantly improve the flame-retardant performance.

[0054] With the continuous increase in the addition of phosphorus-containing cashew nut shell phenol-based flame-retardant epoxy monomer grafted with boron nitride flame-retardant thermal conductive agent, the thermal conductivity of the composite material increases significantly. However, when the addition amount of phosphorus-containing cashew nut shell phenol-based flame-retardant epoxy monomer grafted with boron nitride flame-retardant thermal conductive agent reaches 30%, further addition of this agent causes the thermal conductivity of the composite material to decrease. This is because the addition of nanoparticles alters the phonon scattering and coupling within the material. At low nanoparticle content, the interaction between the nanoparticles and the matrix enhances phonon scattering, reducing the mean free path of phonons and thus increasing thermal conductivity. However, when the nanoparticle content exceeds a certain value, phonon scattering becomes more complex. Excessive nanoparticles cause phonons to encounter more scattering centers during transmission, further reducing the mean free path of phonons and thus inhibiting the increase in thermal conductivity.

[0055] Therefore, it can be considered that when the amount of phosphorus-containing cashew phenol-based flame-retardant epoxy monomer grafted with boron nitride flame-retardant thermal conductive agent reaches 30%, the composite material has good overall performance.

[0056] Example 2: Preparation of a fully bio-based epoxy resin composite material with boron nitride flame retardant and thermally conductive agent grafted as the modifier and curing agent.

[0057] (1) In a three-necked flask, 0.2 mol of cashew nut shell powder, 0.2 mol of triethylamine and 0.1 mol of phenylphosphine dichloride were dissolved in 250 mL of chloroform and reacted at 70 °C for 5 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filtrate was partially purified, washed with water, and dried to obtain a phosphorus-containing cashew nut shell powder derivative.

[0058] (2) In a three-necked flask, 0.05 mol of a phosphorus-containing cashew nut phenol derivative and 0.3 mol of 3-chloroperoxybenzoic acid were dissolved in 200 mL of dichloromethane and reacted in an ice bath for 5 h. After filtration, the filtrate was partially purified, washed with water, and dried to obtain a phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomer.

[0059] (3) 0.1 mol of phosphorus-containing cashew nut phenol derivative and 0.2 mol of maleic anhydride were added sequentially to a three-necked round-bottom flask and stirred continuously until homogeneous. The mixture was then refluxed at 195 °C for 6 h under a nitrogen atmosphere. Finally, the mixture was cooled to room temperature, and the crude product was dissolved in an organic solvent, washed and purified. The organic phase was collected, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation to obtain the phosphorus-containing cashew nut phenol-based curing agent.

[0060] (4) Take 5 g of boron nitride powder and add it to 50 mL of ethanol and sonicate for 10 min. Then add 100 mL of 5 mol / L NaOH solution and reflux in an oil bath at 100 ℃ for 20 h. After cooling, filter and dry to obtain hydroxylated boron nitride.

[0061] (5) 0.2 mol of hydroxylated boron nitride and 0.1 mol of phosphorus-containing cashew phenol-based flame retardant curing agent were loaded into 100 mL of tetrahydrofuran and refluxed at 60 °C for 6 h under vigorous stirring. The resulting solid was washed with water and dried to obtain phosphorus-containing cashew phenol-based flame retardant curing agent grafted with boron nitride flame retardant thermal conductive agent.

[0062] (6) The phosphorus-containing cashew nut phenol-based flame retardant curing agent grafted with boron nitride flame retardant and thermally conductive agent, accounting for 20%, 25%, 30%, and 35% of the total mass of the composite material, was dissolved in dichloromethane and ultrasonically dispersed evenly. Then, it was added to a certain amount of phosphorus-containing cashew nut phenol-based flame retardant epoxy monomer, followed by the corresponding amount of phosphorus-containing cashew nut phenol-based flame retardant curing agent. The molar ratio of phosphorus-containing cashew nut phenol-based flame retardant epoxy monomer to phosphorus-containing cashew nut phenol-based flame retardant curing agent was 4:1. After stirring and mixing evenly, it was cured at 90-130 ℃ for 1-3 h, at 140-160 ℃ for 1-3 h, and at 170-200 ℃ for 1-3 h to obtain a multifunctional all-bio-based epoxy resin composite material with flame retardancy, thermal conductivity, and toughening properties, which were respectively named composite material-5, composite material-6, composite material-7, and composite material-8.

[0063] Example 3: Effect of temperature during grafting hydroxylated boron nitride with different phosphorus-containing cashew nut phenol-based flame retardant curing agents on the preparation of fully bio-based epoxy resin composites with boron nitride grafted as the curing agent and modifier as the curing agent.

[0064] The specific implementation method is the same as that of the preparation method of composite material-7 in Example 2, in which the curing agent is grafted with hydroxylated boron nitride flame retardant thermal conductive agent accounting for 30% of the total mass of the composite material. The difference is that the temperature of grafting hydroxylated boron nitride with phosphorus cashew phenolic flame retardant curing agent in step (5) is adjusted from 60 ℃ to 40 ℃ and 80 ℃, while other conditions remain unchanged. The fully bio-based epoxy resin composite material with curing agent grafted with boron nitride flame retardant thermal conductive agent as the modifier is prepared and is referred to as composite material-9 and composite material-10, respectively.

[0065] The performance of the fully bio-based epoxy resin composite materials obtained in Examples 2 and 3 was tested, and the test results are as follows:

[0066] Table 2

[0067]

[0068] The results show:

[0069] As the amount of phosphorus-containing cashew nut shell phenol-based flame retardant curing agent grafted with boron nitride flame retardant thermal conductive agent continuously increases, the limiting oxygen index (LOI) of the composite material also continuously rises. Simultaneously, the peak heat release rate (PHRR) and total heat release (THR) of the composite material gradually decrease. The decrease in PHRR and THR indicates an improvement in the flame retardant performance of the composite material, a conclusion consistent with the upward trend of the LIO. Meanwhile, with the continuous increase in the amount of phosphorus-containing cashew nut shell phenol-based flame retardant curing agent grafted with boron nitride flame retardant thermal conductive agent, the thermal conductivity of the composite material increases significantly. However, when the amount of phosphorus-containing cashew nut shell phenol-based flame retardant curing agent grafted with boron nitride flame retardant thermal conductive agent reaches 30%, further addition of this agent causes the thermal conductivity of the composite material to begin to decrease.

[0070] The flame retardant and thermal conductivity of the composite material grafted with phosphorus-containing cashew nut phenol-based flame retardant curing agent is better than that of the composite material grafted with phosphorus-containing cashew nut phenol-based flame retardant epoxy monomer. This is because the grafting rate of one phosphorus-containing cashew nut phenol-based flame retardant curing agent grafted with hydroxylated boron nitride is greater than that of one phosphorus-containing cashew nut phenol-based flame retardant epoxy monomer grafted with hydroxylated boron nitride.

[0071] When the temperature for grafting hydroxylated boron nitride onto the phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomer is 40 ℃, the grafting of phosphorus-containing cashew nut phenol-based flame-retardant curing agent with boron nitride is relatively small. The poor compatibility of hydroxylated boron nitride in the epoxy system leads to a decrease in thermal conductivity. When the temperature for grafting hydroxylated boron nitride onto the phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomer is 80 ℃, the reaction produces more byproducts, resulting in a reduced yield of the phosphorus-containing cashew nut phenol-based flame-retardant curing agent grafted with boron nitride, thus further decreasing the thermal conductivity.

[0072] In summary, based on the balance between flame retardant and thermal conductivity, the composite material-7 in Example 2 exhibits the best overall performance.

[0073] Furthermore, based on composite material-7 in Example 2, which has the best overall performance, it is compared with other comparative examples.

[0074] Comparative Example 1: Curing Agent Modification of Non-hydroxyl Boron Nitride

[0075] Specifically, the composite material-7, in Example 2, is the same as that in Example 2, where the curing agent grafted with hydroxylated boron nitride flame retardant and thermally conductive agent accounts for 30% of the total mass of the composite material. The difference is that the curing agent directly modifies boron nitride (boron nitride does not need to be hydroxylated) instead of the curing agent modifying hydroxylated boron nitride, omitting step (4), and keeping other conditions unchanged, to prepare the epoxy resin composite material.

[0076] Comparative Example 2: Direct addition of boron nitride

[0077] Specifically, the composite material-7, which is the same as the curing agent grafted with hydroxylated boron nitride flame retardant and thermally conductive agent in Example 2, accounts for 30% of the total mass of the composite material. The difference is that boron nitride is used instead of the phosphorus-containing cashew phenol-based flame retardant curing agent grafted with boron nitride flame retardant and thermally conductive agent. Steps (4) and (5) are omitted. Other conditions remain unchanged to prepare the epoxy resin composite material.

[0078] Comparative Example 3: Using Alumina

[0079] Specifically, the composite material-7, which is the same as the one in Example 2, in which the curing agent is grafted with hydroxylated boron nitride flame retardant and thermally conductive agent accounting for 30% of the total mass of the composite material, is prepared by using alumina instead of phosphorus-containing cashew phenol-based flame retardant curing agent grafted with boron nitride flame retardant and thermally conductive agent, omitting steps (4) and (5), and keeping other conditions unchanged.

[0080] Comparative Example 4: Eugenol-based curing agent modified boron nitride

[0081] Specifically, the composite material-7, in Example 2, is prepared by grafting hydroxylated boron nitride flame retardant and thermally conductive agent into a curing agent that accounts for 30% of the total mass of the composite material. The difference is that eugenol is used instead of cashew phenol, while other conditions remain unchanged.

[0082] Comparative Example 5: Standalone Commercial

[0083] Specifically, the composite material-7, which is the same as the one in Example 2, in which the curing agent is grafted with hydroxylated boron nitride flame retardant and thermally conductive agent accounting for 30% of the total mass of the composite material, is prepared by using DGEBA instead of the phosphorus-containing cashew phenolic epoxy monomer, omitting step (2), and keeping other conditions unchanged.

[0084] Comparative Example 6: Commercial Hardener

[0085] Specifically, the composite material-7, in Example 2, is prepared with the curing agent grafted with hydroxylated boron nitride flame retardant and thermally conductive agent accounting for 30% of the total mass of the composite material. The difference is that DDM is used instead of the phosphorus-containing cashew phenol-based curing agent, while other conditions remain unchanged.

[0086] Comparative Example 7: Both monomers and curing agents are commercially available.

[0087] Specifically, the composite material-7, which is the same as the one in Example 2, is made by grafting hydroxylated boron nitride flame retardant and thermally conductive agent into the curing agent, which accounts for 30% of the total mass of the composite material. The difference is that DGEBA is used instead of the phosphorus-containing cashew phenol-based epoxy monomer, and DDM is used instead of the phosphorus-containing cashew phenol-based curing agent. Step (2) is omitted, and other conditions remain unchanged to prepare the epoxy resin composite material.

[0088] The epoxy resin composite materials obtained in Comparative Examples 1 to 8 were subjected to performance tests, and the test results are as follows:

[0089] Table 3

[0090]

[0091] The results show:

[0092] In Comparative Example 1, unhydroxylated boron nitride was grafted onto a phosphorus-containing cashew nut phenol-based flame retardant curing agent, which reduced the grafting rate between the two agents and resulted in a decrease in the thermal conductivity of the composite material.

[0093] In Comparative Example 2, hydroxylated boron nitride without graft modification was used, which resulted in poorer dispersibility and compatibility of boron nitride grafted with a phosphorus-containing cashew phenol-based flame retardant curing agent in the epoxy matrix, leading to a decrease in the thermal conductivity of the composite material.

[0094] In Comparative Example 3, alumina was used instead of boron nitride grafted with phosphorus-containing cashew nut phenol-based flame retardant curing agent. Since alumina is mostly spherical, its flame retardant and thermal conductivity are poor. In contrast, boron nitride has a layered structure, and after grafting modification with phosphorus-containing cashew nut phenol-based flame retardant curing agent, its dispersibility and compatibility in the epoxy system are better, resulting in better flame retardant and thermal conductivity.

[0095] In Comparative Example 4, eugenol was used instead of cashew nut shell phenol. Since eugenol has only one double bond, it can only form one epoxy group. The crosslinking density of the eugenol derivative epoxy monomer and the eugenol derivative curing agent after curing is lower than that of the cashew nut shell phenol derivative epoxy monomer and the cashew nut shell phenol derivative curing agent after curing, which reduces the flame retardant effect and thermal conductivity.

[0096] In Comparative Example 5, DGEBA was used instead of the phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomer. The flame-retardant effect was poor, but the thermal conductivity was not much different from that of the phosphorus-containing cashew nut phenol-based flame-retardant composite material.

[0097] In Comparative Example 6, DDM was used instead of the phosphorus-containing cashew nut phenol-based flame retardant curing agent. The flame retardant effect was poor, but the thermal conductivity was not much different from that of the phosphorus-containing cashew nut phenol-based flame retardant composite material.

[0098] In Comparative Example 7, DGEBA and DDM were used to replace the phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomer and the phosphorus-containing cashew nut phenol-based flame-retardant curing agent. The flame-retardant effect was poor, but the thermal conductivity was not much different from that of the phosphorus-containing cashew nut phenol-based flame-retardant composite material.

[0099] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a fully bio-based epoxy resin composite material based on cashew phenol modified boron nitride, comprising the following steps: S1. Dissolve cashew nut phenol, acid-binding agent and phenyl phosphorus dichloride in an organic solvent and react at 40~80 ℃. After filtering the reaction solution, the filtrate is partially purified, washed with water, and dried to obtain a phosphorus-containing cashew nut phenol derivative. S2. Dissolve the phosphorus-containing cashew phenol derivative and the epoxidizing agent in an organic solvent, react in an ice bath, filter the reaction solution, purify part of the filtrate by washing with water, and dry to obtain the phosphorus-containing cashew phenol-based flame-retardant epoxy monomer. S3. Add the phosphorus-containing cashew phenol derivative and unsaturated dicarboxylic anhydride to the reactor in sequence and stir continuously until homogeneous. Reflux and condense at 160~200 ℃ under nitrogen or inert gas protection. After the reaction, dissolve the crude product in an organic solvent, wash and purify, collect the organic phase to remove the solvent, and obtain the phosphorus-containing cashew phenol-based curing agent. S4. Take boron nitride powder and add it to a solvent for ultrasonic dispersion, then add 3~6 mol / L NaOH solution, react at 40~80 ℃, and dry after reaction to obtain hydroxylated boron nitride; S5. The phosphorus-containing cashew phenolic flame-retardant epoxy monomer prepared in S2, the hydroxylated boron nitride prepared in S4, the catalyst and the organic solvent are mixed evenly in a reactor and reacted at 80~150 ℃. The solid obtained from the reaction is washed with water and dried to obtain an epoxy monomer grafted boron nitride flame-retardant thermal conductive agent. S6. Add the phosphorus-containing cashew phenol-based flame retardant curing agent prepared in S3 and the hydroxylated boron nitride prepared in S4 to an organic solvent, and react them at 40~80 °C under vigorous stirring. Wash the solid obtained from the reaction with water and dry it to obtain the curing agent grafted with boron nitride flame retardant and thermally conductive agent. S7. Dissolve the epoxy monomer grafted with boron nitride flame-retardant and thermally conductive agent prepared in S5 or the curing agent grafted with boron nitride flame-retardant and thermally conductive agent prepared in S6 in an organic solvent, disperse evenly, and then add it to a certain amount of the phosphorus-containing cashew nut phenol-based flame-retardant epoxy monomer prepared in S2. Subsequently, add the corresponding amount of the phosphorus-containing cashew nut phenol-based flame-retardant curing agent prepared in S3. After stirring and mixing evenly and evaporating the solvent, cure at 90-130 °C for 1-3 h, at 140-160 °C for 1-3 h, and at 170-200 °C for 1-3 h to obtain a fully bio-based epoxy resin composite material. The epoxy monomer grafted with boron nitride flame retardant and thermally conductive agent or curing agent accounts for 20-35% of the total mass of the composite material; the molar ratio of cashew nut phenol-based epoxy monomer to phosphorus-containing cashew nut phenol-based flame retardant curing agent is (1-2):

1.

2. The preparation method according to claim 1, characterized in that, The acid-binding agent in S1 is one or a mixture of several of the following: triethylamine, pyridine, sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

3. The preparation method according to claim 1, characterized in that, The molar ratio of cashew phenol, acid-binding agent and phenyl dichloride in S1 is (1~6):(1~6):

1.

4. The preparation method according to claim 1, characterized in that, In S2, the oxidizing agent is one or a mixture of several of the following: m-chloroperbenzoic acid, hydrogen peroxide, and peracetic acid.

5. The preparation method according to claim 1, characterized in that, The unsaturated dicarboxylic anhydride in S3 is one or a mixture of maleic anhydride, itaconic anhydride, and citraconic anhydride.

6. The preparation method according to claim 1, characterized in that, The mass ratio of phosphorus-containing cashew phenolic epoxy monomer to hydroxylated boron nitride in S5 is (1~15):1; the mass ratio of phosphorus-containing cashew phenolic flame retardant curing agent to hydroxylated boron nitride in S6 is (1~15):

1.

7. The preparation method according to claim 1, characterized in that, The catalyst mentioned in S5 is one or a mixture of several of the following: triethylamine, sodium hydroxide, boron trifluoride, and boron trifluoride diethyl ether.

8. A fully bio-based epoxy resin composite material based on cashew phenol modified boron nitride prepared by the method of any one of claims 1 to 7.

9. The application of the fully bio-based epoxy resin composite material based on cashew phenol modified boron nitride as described in claim 8 in the preparation of circuit boards.

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