A phenolic resin composite material with good mechanical properties and a preparation method thereof

Abstract

The application relates to the technical field of phenolic resin-based composite materials, and discloses a phenolic resin composite material with good mechanical properties and a preparation method thereof, which comprises 100 parts of phenolic resin, 10-20 parts of modified polyurethane prepolymer, 5-15 parts of hydroxyl-terminated polysulfone, 20-35 parts of magnesium oxide, 10-20 parts of kaolin, 8-15 parts of KH550 modified graphene, 2-5 parts of calcium stearate and 0.5-2 parts of hexamethylenetetramine in terms of weight percentage, and is obtained after mixing, mold pressing, and curing; the raw material ratio for synthesizing the polysulfone is controlled to prepare the hydroxyl-terminated polysulfone prepolymer; the raw material ratio for synthesizing the polyurethane is controlled, and long-chain imide diol is used as a chain extender to prepare the isocyanate-terminated polyurethane prepolymer; the polysulfone and the polyurethane structure are stably inlaid in the phenolic resin matrix, so that the prepared phenolic resin composite material has good mechanical properties, heat resistance and wear resistance.

Description

Technical Field

[0001] This invention relates to the field of phenolic resin-based composite materials, specifically to a phenolic resin composite material with good mechanical properties and its preparation method. Background Technology

[0002] Phenolic resins are a widely used class of thermosetting resins with excellent flame retardancy, electrical insulation, and good dimensional stability. Due to the readily available raw materials, they have been widely used in key fields such as aerospace, transportation, electronics, and building materials. However, the methylene groups in traditional phenolic resin structures are prone to oxidation, the phenolic hydroxyl groups readily absorb water, and the tight packing of rigid square rings makes the resin matrix brittle. This results in defects such as high brittleness, high shrinkage, and poor processability, making phenolic resins susceptible to fracture under external forces. This significantly limits their application in fields requiring high material toughness and restricts their expansion in high-strength structural components. Therefore, developing a phenolic resin composite material with good mechanical properties is of significant practical importance.

[0003] Currently, the toughening modification of phenolic resins mostly adopts physical blending modification methods, which blend phenolic resins with elastomers such as nitrile rubber, chloroprene rubber, or polyvinyl butyral to improve the toughness of phenolic resins. Although this method improves the toughness of the resin to a certain extent, the strength decreases significantly, and the durability of the product is reduced. Due to the limitations of the molding method, it is difficult to plasticize the phenolic resin and the modified elastomer, making the modification effect even less ideal. Patent No. CN114989560B discloses a high-performance composite material based on modified phenolic resin and its preparation method. A phenolic resin intermediate is prepared by catalytic polycondensation reaction using a porous solid acid catalyst, and quaternary ammonium salt cage-type polysilsesquioxane (POSS) and acrylate are introduced for chemical modification. Although the heat resistance is improved by the POSS nanostructure, the carbon fiber content is only 10-15%, and the enhancement effect on bending strength and impact toughness is limited, which is difficult to meet the high damage tolerance requirements of the aerospace field. Patent No. CN117719180A discloses a high-silica / phenolic resin composite material and its preparation method. Through steps such as pre-compression, molding, pre-curing and curing, the low-cost manufacturing of large-size composite materials is achieved. However, the high-silica fiber and the phenolic resin matrix rely only on physical adsorption and lack chemical bonding, resulting in insufficient interlaminar shear strength. Furthermore, without the introduction of flexible segments or dynamic cross-linking structures, the brittleness of the material is not fundamentally improved.

[0004] Currently, people improve the toughness of phenolic resins by introducing long, flexible molecular chains. However, introducing long, flexible molecular chains can significantly affect its heat resistance. This application, from the perspective of chemical modification, uses -NCO-terminated polyurethane as a modifying monomer and employs chemical copolymerization to introduce "rigid-flexible interlocking" polyurethane elastic units into the network structure of phenolic resin. The elastic structural units in the product structure are chemically bonded to the phenolic resin, thereby improving the toughness of the phenolic resin while maintaining high mechanical strength and heat resistance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a phenolic resin composite material with good mechanical properties and its preparation method. This invention solves the problems of high brittleness and easy breakage of traditional phenolic resins, and has higher mechanical properties, better heat resistance and wider application range.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a phenolic resin composite material with good mechanical properties includes the following steps: 100 parts by weight of phenolic resin, 10-20 parts by weight of modified polyurethane prepolymer and 5-15 parts by weight of hydroxyl-terminated polysulfone are placed on a micro twin-screw extruder and melt-blended at 130-150℃ for 5-10 minutes. Then, 20-35 parts by weight of magnesium oxide, 10-20 parts by weight of kaolin, 8-15 parts by weight of KH550 modified graphene, 2-5 parts by weight of calcium stearate and 0.5-2 parts by weight of hexamethylenetetramine are added and mixed on an open plasticizer. The materials are then pulverized, molded, and cured to obtain a phenolic resin composite material with good mechanical properties.

[0008] The preparation method of hydroxyl-terminated polysulfone is as follows: Under a nitrogen atmosphere, bisphenol A, 4,4-dichlorodiphenyl sulfone, potassium carbonate and N,N-dimethylacetamide are added to a reaction flask, and the mixture is slowly heated to 50-60℃. After complete dissolution, toluene is added, and the mixture is heated to reflux for dehydration for 1-3 hours. The temperature is then raised to 150-170℃ for polycondensation reaction for 5-8 hours. After the reaction is completed, the mixture is cooled to room temperature, washed alternately with distilled water and methanol, and dried to obtain hydroxyl-terminated polysulfone.

[0009] Furthermore, the compression molding temperature is 160-180℃, the pressure is 10-20MPa, and the time is 3-5min.

[0010] Furthermore, the curing conditions are as follows: first, cure at 150-165℃ for 4-6 hours, then cure at 175-190℃ for 1-3 hours.

[0011] Furthermore, the molar ratio of bisphenol A, 4,4-dichlorodiphenyl sulfone, and potassium carbonate is 1.05-1.2:1:2.5-3.5.

[0012] Furthermore, the preparation method of the modified polyurethane prepolymer includes the following steps:

[0013] Step S1: Under a nitrogen atmosphere, add pyromellitic dianhydride and glacial acetic acid to a reaction flask, stir until homogeneous, add 8-amino-1-octanol, stir to react, and after the reaction is complete, cool to room temperature, filter, wash with deionized water, recrystallize from toluene to obtain long-chain pyromellitic imide diol.

[0014] Step S2: Add 20-30 parts by weight of toluene diisocyanate and N,N-dimethylformamide to a four-necked flask. Under nitrogen protection, heat the mixture to 50-65°C with mechanical stirring at 200-300 rpm. Add 100 parts of vacuum-dehydrated polyether polyol to the flask and stir to mix. Heat to 70-80°C, add 0.1-0.3 parts of dibutyltin dilaurate and 2-10 parts of long-chain pyromellitic imide diol. After the addition is complete, keep the mixture at this temperature for 2-6 hours, then cool and discharge the material. Allow it to stand to defoam, and the modified polyurethane prepolymer is obtained.

[0015] Furthermore, in step S1, the molar ratio of pyromellitic dianhydride and 8-amino-1-octanol is 1:2.1-2.3.

[0016] Furthermore, in step S1, the reaction temperature is 100-120℃ and the reaction time is 16-32h.

[0017] Furthermore, in step S2, the polyether polyol is polypropylene glycol with a molecular weight of 2000.

[0018] Furthermore, in step S2, the vacuum dehydration temperature is 100-120℃, the vacuum degree is 0.05-0.1MPa, and the dehydration time is 1-2h.

[0019] By adopting the above technical solution, the beneficial effects of the present invention are as follows:

[0020] This application controls the raw material ratio of polysulfone synthesis, using excess bisphenol A to prepare hydroxyl-terminated polysulfone prepolymer; then controls the raw material ratio of polyurethane synthesis, using excess toluene diisocyanate and employing long-chain imide diol as a chain extender to prepare isocyanate-terminated polyurethane prepolymer. This allows the hydroxyl groups of the polysulfone prepolymer and phenolic resin to react with the isocyanate groups of the polyurethane prepolymer to form a urethane structure, achieving copolymerization. The polysulfone and polyurethane structures are stably "embedded" inside the phenolic resin matrix, giving the composite material good mechanical, heat resistance, and wear resistance properties.

[0021] (1) Excellent mechanical properties: The sulfone group of polysulfone forms a highly conjugated diphenyl sulfone structure with the two adjacent benzene rings, forming a very stable, rigid, and integrated system, which allows the main chain to absorb a large amount of heat energy without breaking the main chain; the chain extension of long-chain pyromellitic imide diol brings high-density hydrogen bonds to the polyurethane material. These high-density hydrogen bonds form physical cross-linking points with a certain strength within and between chain segments, thus giving the material good toughness; in addition, due to the high flexibility of the long chain itself, the molecular chain has a high degree of curling. At the same time, pyromellitic imide is a rigid group with large steric hindrance and strength, which can hinder the movement of chain segments during the process of external force, and can to a certain extent The modified polyurethane prepolymer hinders the relative movement of chain segments during material deformation, thus endowing the material with good flexural strength, resulting in high toughness and good mechanical strength. Simultaneously, the terminal isocyanate groups of the modified polyurethane prepolymer can participate in the cross-linking and curing of the phenolic resin, forming good hydrogen bonds, making the cross-linked network denser and more uniformly dispersed within the phenolic resin network system, thus better exerting its reinforcing effect. Furthermore, the hydroxyl groups of the polysulfone prepolymer react with the isocyanate groups of the polyurethane prepolymer to form a urethane structure, which is uniformly dispersed within the composite matrix, allowing it to interpenetrate within the cross-linked system to form a semi-interpenetrating network structure, further enhancing and toughening the material.

[0022] (2) Good heat resistance: The network structure formed by the cross-linking and curing of the terminal isocyanate groups of the modified polyurethane prepolymer and the phenolic resin has a unique "microphase separation" structure in the macromolecular conformation of the composite material. The hard chain segments of various sizes in the polyurethane chain are suspended and dispersed at the interface of the matrix, which makes it difficult for the material to slide and deform when heated, thus improving the heat resistance. On the other hand, the hydroxyl groups of the polysulfone prepolymer react with the isocyanate groups of the polyurethane prepolymer, thereby stably "embedding" the heat-resistant polysulfone structure inside the phenolic resin matrix. The rigid groups of polysulfone can be highly oriented, and the chemical cross-linking makes the molecular chains tightly packed, increases the intermolecular forces between the main chain macromolecules, and makes it difficult for the molecular chain segments to move, further enhancing the heat resistance of the composite material.

[0023] (3) The wear resistance is significantly improved: As a liquid crystal polymer, modified polyurethane can form aggregated micro-regions in the phenolic resin matrix, which is beneficial to the plastic deformation of the matrix material under load, reduces the detachment of material surface particles, and improves the load-bearing capacity of the composite material, thereby improving the wear resistance. The amino groups on the surface of KH550 modified graphene react with the phenolic hydroxyl groups of phenolic resin to generate new chemical bonds, promote the dispersion in phenolic resin, effectively improve the adhesion between the matrix resin and KH550 modified graphene, and enable KH550 modified graphene to play a micro-nano reinforcement and layered structure self-lubricating role. When subjected to shear force during friction, the surface of the composite material is not easy to wear, thus improving the wear resistance of the composite material. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Unless otherwise stated, the raw materials and reagents used in this application are all commercially available products, or can be prepared by known methods.

[0025] Preparation of KH550 modified graphene: Graphene oxide was reacted with a 2% KH550 solution (the mass ratio of graphene oxide to KH550 was 1:20) at 80℃ for 24h. Then, the solution was washed and filtered three times with deionized water and dried under vacuum at 60℃ to obtain KH550 modified graphene.

[0026] Pyromellitic dianhydride, CAS number 89-32-7.

[0027] 8-Amino-1-octanol, CAS number 19008-71-0.

[0028] Example 1

[0029] (1) Under a nitrogen atmosphere, 40 mmol of pyromellitic dianhydride and 160 mL of glacial acetic acid were added to a reaction flask. After stirring evenly, 88 mmol of 8-amino-1-octanol was added, and the mixture was reacted at 110 °C for 24 h. After cooling to room temperature, the mixture was filtered, washed with deionized water, and recrystallized from toluene to obtain long-chain pyromellitic imide diol. The preparation reaction formula is as follows:

[0030]

[0031] (2) Add 25g of toluene diisocyanate and 40mL of N,N-dimethylformamide to a four-necked flask. Under nitrogen protection, heat the mixture to 60°C with mechanical stirring at 250r / min. Add 100g of polypropylene glycol with a molecular weight of 2000 after vacuum dehydration at 110°C and 0.08MPa for 2h and stir to mix. Heat the mixture to 75°C and add 0.2g of dibutyltin dilaurate and 2g of long-chain pyromellitic imide diol. After the addition is complete, keep the mixture at the temperature for 4h, then cool it down and discharge the material. Let it stand to defoam and obtain the modified polyurethane prepolymer.

[0032] (3) Under a nitrogen atmosphere, 32.4 mmol of bisphenol A, 30 mmol of 4,4-dichlorodiphenyl sulfone, 90 mmol of potassium carbonate and 120 mL of N,N-dimethylacetamide were added to the reaction flask. The mixture was slowly heated to 55 °C. After complete dissolution, toluene was added, and the mixture was heated to reflux for 2 h to remove water. The temperature was then raised to 160 °C for 7 h to carry out the polycondensation reaction. After the reaction was completed, the mixture was cooled to room temperature, washed alternately with distilled water and methanol, and dried to obtain hydroxyl-terminated polysulfone.

[0033] (4) Place 100g of phenolic resin, 10g of modified polyurethane prepolymer and 5g of hydroxyl-terminated polysulfone on a micro twin-screw extruder and melt-blend at 140°C for 8min. Then add 30g of magnesium oxide, 15g of kaolin, 8g of KH550 modified graphene, 4g of calcium stearate and 1g of hexamethylenetetramine and mix them on an open plasticizer. Then crush the material and mold it at 170°C and 15MPa for 4min. Then cure it at 160°C for 5h and then at 180°C for 2h to obtain a phenolic resin composite material with good mechanical properties.

[0034] Example 2

[0035] (1) Under a nitrogen atmosphere, 320 mmol of pyromellitic dianhydride and 960 mL of glacial acetic acid were added to the reaction flask. After stirring evenly, 672 mmol of 8-amino-1-octanol was added. The reaction was carried out at 120 °C for 16 h. After cooling to room temperature, the mixture was filtered, washed with deionized water, and recrystallized from toluene to obtain long-chain pyromellitic imide diol.

[0036] (2) Add 20g of toluene diisocyanate and 35mL of N,N-dimethylformamide to a four-necked flask. Under nitrogen protection, heat the mixture to 65°C with mechanical stirring at 300r / min. Add 100g of polypropylene glycol with a molecular weight of 2000 after vacuum dehydration at 120°C and 0.1MPa for 1h and stir to mix. Heat the mixture to 80°C and add 0.3g of dibutyltin dilaurate and 4g of long-chain pyromellitic imide diol. After the addition is complete, keep the mixture at the temperature for 2h, then cool it down and discharge the material. Let it stand to defoam and obtain the modified polyurethane prepolymer.

[0037] (3) Under a nitrogen atmosphere, 315 mmol of bisphenol A, 300 mmol of 4,4-dichlorodiphenyl sulfone, 750 mmol of potassium carbonate and 600 mL of N,N-dimethylacetamide were added to the reaction flask. The mixture was slowly heated to 60 °C. After complete dissolution, toluene was added and the mixture was heated to reflux for dehydration for 1 h. The temperature was then raised to 170 °C for polycondensation reaction for 5 h. After the reaction was completed, the mixture was cooled to room temperature and washed alternately with distilled water and methanol. After drying, hydroxyl-terminated polysulfone was obtained.

[0038] (4) Place 100g of phenolic resin, 12g of modified polyurethane prepolymer and 8g of hydroxyl-terminated polysulfone on a micro twin-screw extruder and melt-blend at 150°C for 5min. Then add 20g of magnesium oxide, 20g of kaolin, 12g of KH550 modified graphene, 2g of calcium stearate and 0.5g of hexamethylenetetramine and mix them on an open plasticizer. Then crush the material and mold it at 180°C and 20MPa for 3min. Then cure it at 165°C for 4h and then at 175°C for 1h to obtain a phenolic resin composite material with good mechanical properties.

[0039] Example 3

[0040] (1) Under a nitrogen atmosphere, 150 mmol of pyromellitic dianhydride and 750 mL of glacial acetic acid were added to the reaction flask. After stirring evenly, 345 mmol of 8-amino-1-octanol was added. The reaction was carried out at 100 °C for 32 h. After cooling to room temperature, the mixture was filtered, washed with deionized water, and recrystallized from toluene to obtain long-chain pyromellitic imide diol.

[0041] (2) Add 30g of toluene diisocyanate and 50mL of N,N-dimethylformamide to a four-necked flask. Under nitrogen protection, heat the mixture to 50°C with mechanical stirring at 200r / min. Add 100g of polypropylene glycol with a molecular weight of 2000 after vacuum dehydration at 100°C and 0.05MPa for 2h and stir to mix. Heat the mixture to 70°C and add 0.1g of dibutyltin dilaurate and 6g of long-chain pyromellitic imide diol. After the addition is complete, keep the mixture at the temperature for 6h, then cool it down and discharge the material. Let it stand to defoam and obtain the modified polyurethane prepolymer.

[0042] (3) Under a nitrogen atmosphere, 144 mmol of bisphenol A, 120 mmol of 4,4-dichlorodiphenyl sulfone, 420 mmol of potassium carbonate and 600 mL of N,N-dimethylacetamide were added to the reaction flask. The mixture was slowly heated to 50 °C. After complete dissolution, toluene was added and the mixture was heated to reflux for dehydration for 3 h. The temperature was then raised to 150 °C for polycondensation reaction for 8 h. After the reaction was completed, the mixture was cooled to room temperature and washed alternately with distilled water and methanol. After drying, hydroxyl-terminated polysulfone was obtained.

[0043] (4) Place 100g of phenolic resin, 15g of modified polyurethane prepolymer and 10g of hydroxyl-terminated polysulfone on a micro twin-screw extruder and melt-blend at 130°C for 10min. Then add 35g of magnesium oxide, 10g of kaolin, 10g of KH550 modified graphene, 2g of calcium stearate and 2g of hexamethylenetetramine and mix them on an open plasticizer. Then crush the material and mold it at 160°C and 10MPa for 5min. Then cure it at 150°C for 4h and then at 175°C for 1h to obtain a phenolic resin composite material with good mechanical properties.

[0044] Example 4

[0045] (1) Under a nitrogen atmosphere, 100 mmol of pyromellitic dianhydride and 400 mL of glacial acetic acid were added to the reaction flask. After stirring evenly, 225 mmol of 8-amino-1-octanol was added. The reaction was carried out at 115 °C for 18 h. After cooling to room temperature, the mixture was filtered, washed with deionized water, and recrystallized from toluene to obtain long-chain pyromellitic imide diol.

[0046] (2) Add 28g of toluene diisocyanate and 45mL of N,N-dimethylformamide to a four-necked flask. Under nitrogen protection, heat the mixture to 55°C with mechanical stirring at 260r / min. Add 100g of polypropylene glycol with a molecular weight of 2000 after vacuum dehydration at 105°C and 0.06MPa for 2h and stir to mix. Heat the mixture to 70°C and add 0.3g of dibutyltin dilaurate and 8g of long-chain pyromellitic imide diol. After the addition is complete, keep the mixture at the temperature for 3h, then cool it down and discharge the material. Let it stand to defoam and obtain the modified polyurethane prepolymer.

[0047] (3) Under a nitrogen atmosphere, 92 mmol of bisphenol A, 80 mmol of 4,4-dichlorodiphenyl sulfone, 260 mmol of potassium carbonate and 230 mL of N,N-dimethylacetamide were added to the reaction flask. The mixture was slowly heated to 50 °C. After complete dissolution, toluene was added and the mixture was heated to reflux for dehydration for 3 h. The temperature was then raised to 165 °C for polycondensation reaction for 8 h. After the reaction was completed, the mixture was cooled to room temperature and washed alternately with distilled water and methanol. After drying, hydroxyl-terminated polysulfone was obtained.

[0048] (4) Place 100g of phenolic resin, 18g of modified polyurethane prepolymer and 12g of hydroxyl-terminated polysulfone on a micro twin-screw extruder and melt-blend at 145°C for 10min. Then add 30g of magnesium oxide, 15g of kaolin, 13g of KH550 modified graphene, 4g of calcium stearate and 1.5g of hexamethylenetetramine and mix them on an open plasticizer. Then crush the material and mold it at 175°C and 16MPa for 5min. Then cure it at 160°C for 5h and then at 180°C for 2h to obtain a phenolic resin composite material with good mechanical properties.

[0049] Example 5

[0050] (1) Under a nitrogen atmosphere, 500 mmol of pyromellitic dianhydride and 1850 mL of glacial acetic acid were added to the reaction flask. After stirring evenly, 1000 mmol of 8-amino-1-octanol was added. The reaction was carried out at 120 °C for 28 h. After cooling to room temperature, the mixture was filtered, washed with deionized water, and recrystallized from toluene to obtain long-chain pyromellitic imide diol.

[0051] (2) Add 24g of toluene diisocyanate and 45mL of N,N-dimethylformamide to a four-necked flask. Under nitrogen protection, heat the mixture to 60°C with mechanical stirring at 280r / min. Add 100g of polypropylene glycol with a molecular weight of 2000 after vacuum dehydration at 105°C and 0.1MPa for 2h and stir to mix. Heat the mixture to 80°C and add 0.25g of dibutyltin dilaurate and 10g of long-chain pyromellitic imide diol. After the addition is complete, keep the mixture at the temperature for 6h, then cool it down and discharge the material. Let it stand to defoam and obtain the modified polyurethane prepolymer.

[0052] (3) Under a nitrogen atmosphere, 480 mmol of bisphenol A, 450 mmol of 4,4-dichlorodiphenyl sulfone, 1260 mmol of potassium carbonate and 1530 mL of N,N-dimethylacetamide were added to the reaction flask. The mixture was slowly heated to 50 °C. After complete dissolution, toluene was added and the mixture was heated to reflux for dehydration for 2 h. The temperature was then raised to 165 °C for polycondensation reaction for 8 h. After the reaction was completed, the mixture was cooled to room temperature and washed alternately with distilled water and methanol. After drying, hydroxyl-terminated polysulfone was obtained.

[0053] (4) Place 100g of phenolic resin, 20g of modified polyurethane prepolymer and 15g of hydroxyl-terminated polysulfone on a micro twin-screw extruder and melt-blend at 140°C for 10min. Then add 25g of magnesium oxide, 20g of kaolin, 15g of KH550 modified graphene, 3g of calcium stearate and 2g of hexamethylenetetramine and mix them on an open plasticizer. Then crush the material and mold it at 175°C and 18MPa for 5min. Then cure it at 160°C for 6h and then at 180°C for 2h to obtain a phenolic resin composite material with good mechanical properties.

[0054] Comparative Example 1

[0055] (1) Add 25g of toluene diisocyanate and 40mL of N,N-dimethylformamide to a four-necked flask. Under nitrogen protection, heat the mixture to 60°C with mechanical stirring at 250r / min. Add 100g of polypropylene glycol with a molecular weight of 2000 after vacuum dehydration at 110°C and 0.08MPa for 2h and stir to mix. Heat the mixture to 75°C and add 0.2g of dibutyltin dilaurate and 2g of 1,4-butanediol. After the addition is complete, keep the mixture at the temperature for 4h, then cool it down and discharge the material. Let it stand to defoam and obtain polyurethane prepolymer.

[0056] (2) 100g of phenolic resin, 10g of polyurethane prepolymer and 5g of hydroxyl-terminated polysulfone (prepared in Example 1) were placed on a micro twin-screw extruder and melt-blended at 140°C for 8 min. Then, 30g of magnesium oxide, 15g of kaolin, 8g of KH550 modified graphene, 4g of calcium stearate and 1g of hexamethylenetetramine were added and mixed on an open plasticizer. The material was then crushed and molded at 170°C and 15MPa for 4 min. Then, it was cured at 160°C for 5 h and then cured at 180°C for 2 h to obtain a phenolic resin composite material.

[0057] Comparative Example 2

[0058] 100g of phenolic resin and 5g of hydroxyl-terminated polysulfone (prepared in Example 1) were placed on a micro twin-screw extruder and melt-blended at 140°C for 8 minutes. Then, 30g of magnesium oxide, 15g of kaolin, 8g of KH550 modified graphene, 4g of calcium stearate and 1g of hexamethylenetetramine were added and mixed on an open plasticizer. The material was then pulverized and molded at 170°C and 15MPa for 4 minutes. It was then cured at 160°C for 5 hours and then cured at 180°C for 2 hours to obtain a phenolic resin composite material.

[0059] Comparative Example 3

[0060] 100g of phenolic resin was placed on a micro twin-screw extruder and melted at 140℃ for 8 minutes. Then, 30g of magnesium oxide, 15g of kaolin, 4g of calcium stearate and 1g of hexamethylenetetramine were added and mixed on an open plasticizer. The material was then pulverized and molded at 170℃ and 15MPa for 4 minutes. It was then cured at 160℃ for 5 hours and then cured at 180℃ for 2 hours to obtain a phenolic resin composite material.

[0061] Impact performance test: The test was conducted using a pendulum impact testing machine in accordance with GB / T 2567-2008 standard. The sample size was 120mm×10mm×4mm.

[0062] Bending performance test: According to GB 1040-92 standard, the test was conducted using an electronic universal testing machine. Three points were taken on the specimen to test the width and thickness of the specimen, and the average value was taken. The specimen size was 120mm×10mm×4mm, the span was 60mm, and the speed was 2mm / min.

[0063] Table 1 Mechanical property testing

[0064]

[0065] The test results in the table above show that with the increase of modified polyurethane prepolymer and hydroxyl-terminated polysulfone content, the impact toughness and flexural strength of the composite material are improved to varying degrees. Among them, the impact toughness in Example 4 reaches 11.31 kJ / m. 2 The flexural strength is 76.90 MPa. This is because, on the one hand, the chain extension of the long-chain pyromellitic imide diol introduces high-density hydrogen bonds into the polyurethane material. These high-density hydrogen bonds form physical cross-linking points with a certain strength within and between chain segments, thus endowing the material with good toughness. On the other hand, due to the high flexibility of the long chain itself and the high degree of molecular chain coiling, and the fact that pyromellitic imide is a rigid group with significant steric hindrance and strength, it can hinder the movement of chain segments during external force application. This can, to a certain extent, impede the relative movement of chain segments during material deformation, thereby endowing the material with good flexural strength, resulting in a material that possesses both high toughness and good mechanical strength. On the other hand, the terminal isocyanate groups of the modified polyurethane prepolymer can participate in the cross-linking and curing of phenolic resin, forming good hydrogen bonding, making the cross-linking network denser and uniformly dispersed in the network system of phenolic resin, thus better exerting the reinforcing effect. In addition, the hydroxyl groups of the polysulfone prepolymer react with the isocyanate groups of the polyurethane prepolymer to form a urethane structure, which is uniformly dispersed in the interior of the composite matrix, allowing it to penetrate the cross-linking system to form a semi-interpenetrating network structure, further enhancing and toughening the composite.

[0066] Comparative Example 1 does not contain flexible long-chain pyromellitic imide diol, so the flexible structure of the polyurethane is not obvious and the impact toughness is poor. Comparative Example 2 does not contain modified polyurethane and has not formed a cross-linked network structure, so its mechanical properties are not as good as those of the examples. The phenolic resin in Comparative Example 3 is unmodified and has the worst mechanical properties.

[0067] Heat resistance test: After the modified phenolic resin is cured, it is ground into 120-140 mesh powder and thermal analysis is performed using a differential thermal balance. Under flowing air, the test temperature is increased from 25℃ to 700℃ at a heating rate of 10℃ / min.

[0068] Table 2 Heat Resistance Test

[0069]

[0070] As shown in the test results above, the heat resistance of the composite material gradually increases with the increase of modified polyurethane prepolymer and hydroxyl-terminated polysulfone content. The initial thermal decomposition temperature in Example 5 was 328.9℃, which was 43.3℃ higher than that of the unmodified phenolic resin. This is because, on the one hand, the network structure formed by the cross-linking and curing of the terminal isocyanate groups of the modified polyurethane prepolymer and the phenolic resin creates a unique "microphase separation" structure in the macromolecular conformation of the composite material. The microcrystalline regions of hard segments of various sizes in the polyurethane chain are suspended and dispersed at the interface of the matrix, making it difficult for the material to slide and deform when heated, thus improving the heat resistance. On the other hand, the hydroxyl groups of the polysulfone prepolymer react with the isocyanate groups of the polyurethane prepolymer, thereby stably "embedding" the heat-resistant polysulfone structure inside the phenolic resin matrix. The rigid groups of the polysulfone can be highly oriented, and the chemical cross-linking makes the molecular chains tightly packed, increases the intermolecular forces between the main chain macromolecules, and makes it difficult for the molecular chain segments to move, further enhancing the heat resistance of the composite material.

[0071] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a phenolic resin composite material with good mechanical properties, characterized in that, The preparation method includes the following steps: by weight, 100 parts of phenolic resin, 10-20 parts of modified polyurethane prepolymer and 5-15 parts of hydroxyl-terminated polysulfone are placed on a micro twin-screw extruder and melt-blended at 130-150℃ for 5-10 minutes. Then, 20-35 parts of magnesium oxide, 10-20 parts of kaolin, 8-15 parts of KH550 modified graphene, 2-5 parts of calcium stearate and 0.5-2 parts of hexamethylenetetramine are added and mixed on an open plasticizer. Then, the material is crushed, molded and cured to obtain a phenolic resin composite material with good mechanical properties. The preparation method of the hydroxyl-terminated polysulfone is as follows: Under a nitrogen atmosphere, bisphenol A, 4,4-dichlorodiphenyl sulfone, potassium carbonate and N,N-dimethylacetamide are added to a reaction flask, and the mixture is slowly heated to 50-60°C. After complete dissolution, toluene is added, and the mixture is heated to reflux for dehydration for 1-3 hours. The temperature is then raised to 150-170°C for polycondensation reaction for 5-8 hours. After the reaction is completed, the mixture is cooled to room temperature, washed alternately with distilled water and methanol, and dried to obtain hydroxyl-terminated polysulfone. The preparation method of the modified polyurethane prepolymer includes the following steps: Step S1: Under a nitrogen atmosphere, add pyromellitic dianhydride and glacial acetic acid to a reaction flask, stir until homogeneous, add 8-amino-1-octanol, stir to react, after the reaction is complete, cool to room temperature, filter, wash with deionized water, recrystallize from toluene to obtain long-chain pyromellitic imide diol. Step S2: Add 20-30 parts by weight of toluene diisocyanate and N,N-dimethylformamide to a four-necked flask. Under nitrogen protection, heat the mixture to 50-65°C with mechanical stirring at 200-300 rpm. Add 100 parts of vacuum-dehydrated polyether polyol to the flask and stir to mix. Heat to 70-80°C, add 0.1-0.3 parts of dibutyltin dilaurate and 2-10 parts of long-chain pyromellitic imide diol. After the addition is complete, keep the mixture at this temperature for 2-6 hours, then cool and discharge the material. Allow it to stand to defoam, and the modified polyurethane prepolymer is obtained.

2. The method for preparing the phenolic resin composite material with good mechanical properties according to claim 1, characterized in that, The molding temperature is 160-180℃, the pressure is 10-20MPa, and the time is 3-5min.

3. The method for preparing the phenolic resin composite material with good mechanical properties according to claim 1, characterized in that, The curing conditions are as follows: first, cure at 150-165℃ for 4-6 hours, then cure at 175-190℃ for 1-3 hours.

4. The method for preparing the phenolic resin composite material with good mechanical properties according to claim 1, characterized in that, The molar ratio of bisphenol A, 4,4-dichlorodiphenyl sulfone, and potassium carbonate is 1.05-1.2:1:2.5-3.

5.

5. The method for preparing the phenolic resin composite material with good mechanical properties according to claim 1, characterized in that, In step S1, the molar ratio of pyromellitic dianhydride and 8-amino-1-octanol is 1:2.1-2.

3.

6. The method for preparing the phenolic resin composite material with good mechanical properties according to claim 1, characterized in that, In step S1, the reaction temperature is 100-120℃ and the reaction time is 16-32h.

7. The method for preparing the phenolic resin composite material with good mechanical properties according to claim 1, characterized in that, In step S2, the polyether polyol is polypropylene glycol with a molecular weight of 2000.

8. The method for preparing the phenolic resin composite material with good mechanical properties according to claim 1, characterized in that, In step S2, the vacuum dehydration temperature is 100-120℃, the vacuum degree is 0.05-0.1MPa, and the dehydration time is 1-2h.

9. A phenolic resin composite material with good mechanical properties, characterized in that, It is obtained by the preparation method according to any one of claims 1-8.

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