Modified phenolic resin and preparation method thereof

Abstract

The invention relates to modified phenolic resin and a preparation method thereof. The modified phenolic resin comprises the following components in parts by mass: 168-196 parts of a flame-retardant phenolic resin matrix, 12-20 parts of a halloysite nanotube composite material and 20-24 parts of a curing agent, the flame-retardant phenolic resin matrix comprises the following raw materials: phenol, a formaldehyde solution, diphenyl phosphoric acid and oxalic acid. The phenolic resin has the effect of improving the flame retardant property of the phenolic resin.

Description

Technical Field

[0001] The present application relates to the field of phenolic resins, and particularly to a modified phenolic resin and a preparation method thereof. Background Art

[0002] Phenolic resin has good acid resistance, mechanical properties, and heat resistance, and is one of the three major synthetic resins. It has been widely used in the fields of national defense, military industry, construction, transportation, etc.

[0003] However, preliminary experimental studies have shown that when phenolic resin is used as various cabin materials such as building materials and ship materials, its flame retardant performance is still insufficient. Therefore, it is necessary to further improve the flame retardant performance of phenolic resin to meet the requirements of industrial production. Summary of the Invention

[0004] In order to improve the flame retardant performance of phenolic resin, the present application provides a modified phenolic resin and a preparation method thereof.

[0005] The modified phenolic resin and its preparation method provided by the present application adopt the following technical solutions: In the first aspect, the modified phenolic resin provided by the present application adopts the following technical solutions: A modified phenolic resin, comprising the following components in parts by mass: 168 - 196 parts of flame-retardant phenolic resin matrix, 12 - 20 parts of halloysite nanotube composite material, and 20 - 24 parts of curing agent; The raw materials of the flame-retardant phenolic resin matrix include phenol, formaldehyde solution, diphenylphosphoric acid, and oxalic acid.

[0006] By adopting the above technical solutions, diphenylphosphoric acid has good flame retardant performance. The increase in phosphorus content can capture free radicals during the combustion stage to interrupt combustion and produce coke residues as a protective layer for the polymer matrix, thereby improving the flame retardant performance of the resin. At the same time, adding halloysite nanotube composite material to the system can absorb combustion products and insulate heat to reduce flame spread, further improving the flame retardant performance of phenolic resin.

[0007] Preferably, the flame-retardant phenolic resin matrix is prepared by the following method: Mix formaldehyde with water to obtain a formaldehyde solution. After mixing the formaldehyde solution, phenol, oxalic acid, and water, react under oil bath conditions, add diphenylphosphoric acid, continue the reaction, then add water, wash, and let stand. After the water and the resin system are layered, separate the upper water layer to obtain the phenolic resin matrix.

[0008] By adopting the above technical solution, diphenyl phosphoric acid can reduce the content of small molecules in phenolic resin and react with phenolic hydroxyl groups in phenolic resin to form P-O-C bonds, thereby reducing the oxidation sensitivity of phenolic resin at high temperatures. At the same time, it can increase the content of benzene rings in the resin, and a carbonized layer will cover the surface of the resin during combustion to prevent the system from continuing to burn, so as to improve the flame retardant performance of phenolic resin. Preferably, the mass ratio of phenol, formaldehyde and diphenyl phosphoric acid is 2.5:1:(0.17 - 0.19).

[0009] By adopting the above technical solution, preferably, the mass ratio of phenol, formaldehyde and diphenyl phosphoric acid is within the above range, which can effectively improve the stability of the flame retardant phenolic resin matrix.

[0010] Preferably, the halloysite nanotube composite is prepared by the following method: Disperse the modified halloysite nanotubes in acetonitrile, add hexafluorobisphenol A and triethylamine, and ultrasonically disperse to obtain a dispersion; mix hexachlorocyclotriphosphazene with acetonitrile to obtain a hexachlorocyclotriphosphazene solution, add the hexachlorocyclotriphosphazene solution to the dispersion for reaction, centrifuge to obtain the product after the reaction, wash and dry to obtain the halloysite nanotube composite.

[0011] By adopting the above technical solution, using the modified halloysite nanotubes as the matrix, by compounding and aggregating hexafluorobisphenol A and hexachlorocyclotriphosphazene at the silicon-aluminum hydroxyl groups at both ends of the modified halloysite nanotubes, a halloysite nanotube composite is obtained, so that a large amount of P and N elements are attached to the halloysite nanotubes, so that a large number of aromatic ring structures in the phenolic resin can remain in the condensation phase to form carbon slag, producing a good physical barrier effect. This barrier can effectively prevent the penetration of external heat and oxygen, so that the internal matrix is protected and further pyrolysis is reduced, thereby improving the stability and flame retardant performance of phenolic resin.

[0012] Preferably, the mass ratio of hexachlorocyclotriphosphazene, hexafluorobisphenol A and modified halloysite nanotubes is 1:15:(1.7 - 1.9).

[0013] By adopting the above technical solution, preferably, the mass ratio of hexafluorobisphenol A, hexachlorocyclotriphosphazene and modified halloysite nanotubes is within the above range, and a more stable halloysite nanotube composite can be obtained.

[0014] Preferably, the modified halloysite nanotubes include halloysite nanotubes and polyethyleneimine.

[0015] By adopting the above technical solution, the halloysite nanotubes are modified by polyethyleneimine, which can increase the organic functional groups on the surface of halloysite. On the one hand, it can make the halloysite nanotubes more evenly dispersed in the phenolic resin system. On the other hand, it plays a promoting role in the preparation of halloysite nanotube composites.

[0016] Preferably, the modified halloysite nanotubes are prepared by the following method: The halloysite nanotubes are immersed in a sodium hydroxide solution to obtain hydroxylated halloysite nanotubes. The hydroxylated halloysite nanotubes are dispersed in a solvent, epichlorohydrin is added, and after stirring, polyethyleneimine is added. After stirring, centrifugal washing is carried out, followed by freeze-drying and grinding to obtain modified halloysite nanotubes.

[0017] By adopting the above technical solution, after treating the halloysite nanotubes with a sodium hydroxide solution, the surface of the halloysite nanotubes has hydroxyl groups, and polyethyleneimine is grafted onto the surface of the halloysite nanotubes. The modified halloysite nanotubes contain abundant amino groups, which can produce strong molecular interactions with the phenolic groups in the phenolic resin, thus forming a stable interface, and further improving the mechanical properties and stability of the phenolic resin.

[0018] Preferably, the mass ratio between the halloysite nanotubes and polyethyleneimine is (2.4 - 2.6):1.

[0019] By adopting the above technical solution, preferably, the mass ratio between the halloysite nanotubes and polyethyleneimine is within the above range, which can further promote the stability of the modified halloysite nanotubes.

[0020] Preferably, the curing agent is hexamethylenetetramine.

[0021] In the second aspect, the present application provides a method for preparing a modified phenolic resin, adopting the following technical solution: A method for preparing a modified phenolic resin, comprising the following steps: The halloysite nanotube composite is added to the flame-retardant phenolic resin matrix, stirred, a curing agent is added, hot pressing is carried out, and then curing is carried out by heating to obtain a modified phenolic resin product.

[0022] In summary, the present application includes at least one of the following beneficial technical effects: 1. A flame-retardant phenolic resin matrix is prepared from phenol, formaldehyde, and diphenylphosphoric acid, thereby improving the flame retardancy of the phenolic resin. Among them, the phosphorus element in diphenylphosphoric acid can capture free radicals during the combustion stage of the system to interrupt combustion and produce coke residues as a protective layer for the polymer matrix, thereby improving the flame retardancy of the phenolic resin. At the same time, a halloysite nanotube composite material is added to the phenolic resin system, which can absorb combustion products and play a heat insulation effect to further reduce flame spread, thereby improving the flame retardancy of the phenolic resin; 2. Modified halloysite nanotubes are prepared from polyethyleneimine and halloysite nanotubes, so that polyethyleneimine is grafted on the surface of the halloysite nanotubes, which can produce strong molecular interactions with the phenolic groups in the phenolic resin, thereby forming a stable interface, improving the stability of the halloysite nanotubes in the phenolic resin, and at the same time improving the mechanical properties of the phenolic resin; 3. The modified halloysite nanotubes are combined with hexafluorobisphenol A and hexachlorocyclotriphosphazene to obtain a halloysite nanotube composite material with good flame retardancy. The prepared halloysite nanotube composite material contains a large amount of P and N elements, so that a large number of aromatic ring structures in the phenolic resin can remain in the condensed phase to form char residues, producing a physical barrier effect, effectively reducing the penetration of external heat and oxygen, thereby protecting the internal structure and improving the overall stability and flame retardancy of the phenolic resin. Specific embodiments

[0023] The following further elaborates on this application in combination with examples: Raw material description: All raw materials in the examples can be obtained commercially; among them, the solvent is N,N-dimethylformamide solution (CAS No.: 68-12-2), and the curing agent is hexamethylenetetramine (CAS No.: 100-97-0).

[0024] Example 1 Preparation of phenolic resin matrix: 81.74 g of formaldehyde (CAS No.: 50-00-0) is mixed with deionized water to prepare a formaldehyde solution with a mass fraction of 37%. After mixing the prepared formaldehyde solution, 204.36 g of phenol, 3 g of oxalic acid, and 200 g of distilled water, the reaction is carried out for 3 h under an oil bath condition of 90 °C. Then, 13.9 g of diphenylphosphoric acid (CAS No.: 1707-03-5) is added, and the reaction continues for 2 h. Then, 90 ml of distilled water is added, and after washing for 1 h, it is left to stand for 2 h. After the water and the resin system are layered, the upper water layer is separated to obtain the phenolic resin matrix.

[0025] Preparation of modified halloysite nanotubes: 10.59 g of halloysite nanotubes were immersed in 0.3 mol / L sodium hydroxide solution. After stirring for 30 min, hydroxylated halloysite nanotubes were obtained. The hydroxylated halloysite nanotubes were infiltrated into 200 ml of solvent and stirred for 15 min to fully disperse the hydroxylated halloysite nanotubes. Then 80 ml of epichlorohydrin was added, and the mixture was stirred at a speed of 300 r / min for 1 h. Finally, 4.41 g of polyethyleneimine (CAS No.: 9002-98-6) was added and stirring was continued for 20 min. Then the mixture was centrifuged and washed, and freeze-dried at -20 °C. After grinding, modified halloysite nanotubes were obtained.

[0026] Preparation of halloysite nanotube composites: 5.76 g of modified halloysite nanotubes were dispersed in 200 ml of acetonitrile. 50.85 g of hexafluorobisphenol A (CAS No.: 1478-61-1) and 100 ml of triethylamine were added, and the mixture was ultrasonically dispersed at 25 °C for 30 min to obtain a dispersion. 3.39 g of hexachlorocyclotriphosphazene (CAS No.: 940-71-6) was mixed with 50 ml of acetonitrile and stirred at a speed of 500 r / min for 10 min to obtain a hexachlorocyclotriphosphazene solution. The hexachlorocyclotriphosphazene solution was added to the dispersion, and the temperature was raised to 50 °C and reacted for 5 h. After the reaction, the product was centrifuged, washed alternately with deionized water and absolute ethanol 3 times, and finally dried in a vacuum drying oven to obtain halloysite nanotube composites.

[0027] Preparation of modified phenolic resin: 12 g of halloysite nanotube composites were added to 168 g of flame-retardant phenolic resin matrix and stirred at a speed of 200 r / min for 4 h. Then 20 g of curing agent was added, and hot pressing was carried out on a flat vulcanizer at 150 °C. Subsequently, it was transferred to a vacuum drying oven and cured at 100 °C for 2 h, at 130 °C for 2 h, and at 150 °C for 1 h to obtain modified phenolic resin products.

[0028] Example 2 Preparation of phenolic resin matrix: 81.3 g of formaldehyde was mixed with deionized water to prepare a formaldehyde solution with a mass fraction of 37%. The prepared formaldehyde solution, 203.25 g of phenol, 3 g of oxalic acid and 200 g of distilled water were mixed, and then reacted in an oil bath at 90 °C for 3 h. 15.45 g of diphenylphosphoric acid was added and the reaction was continued for 2 h. Then 90 ml of distilled water was added, and after washing for 1 h, it was left standing for 2 h. After the water and the resin system were separated, the upper layer of water was separated to obtain a phenolic resin matrix.

[0029] Preparation of modified halloysite nanotubes: 10.83 g of halloysite nanotubes were immersed in 0.3 mol / L sodium hydroxide solution. After stirring for 30 min, hydroxylated halloysite nanotubes were obtained. The hydroxylated halloysite nanotubes were infiltrated into 200 ml of solvent and stirred for 15 min to fully disperse the hydroxylated halloysite nanotubes. Then 80 ml of epichlorohydrin was added, and the mixture was stirred at a speed of 300 r / min for 1 h. Finally, 4.17 g of polyethyleneimine was added and stirring was continued for 20 min. Then the mixture was centrifuged and washed, freeze-dried in an environment of -20 °C, and ground to obtain modified halloysite nanotubes.

[0030] Preparation of halloysite nanotube composites: 6.37 g of modified halloysite nanotubes were dispersed in 200 ml of acetonitrile. 50.28 g of hexafluorobisphenol A and 100 ml of triethylamine were added, and the mixture was ultrasonically dispersed at 25 °C for 30 min to obtain a dispersion. 3.35 g of hexachlorocyclotriphosphazene was mixed with 50 ml of acetonitrile and stirred at a speed of 500 r / min for 10 min to obtain a hexachlorocyclotriphosphazene solution. The hexachlorocyclotriphosphazene solution was added to the dispersion, and the temperature was raised to 50 °C and reacted for 5 h. After the reaction, the product was centrifuged, washed alternately with deionized water and absolute ethanol 3 times, and finally dried in a vacuum drying oven to obtain halloysite nanotube composites.

[0031] Preparation of modified phenolic resin: 20 g of halloysite nanotube composites were added to 196 g of flame-retardant phenolic resin matrix and stirred at a speed of 200 r / min for 4 h. Then 24 g of curing agent was added, and hot pressing was carried out on a flat vulcanizer at 150 °C. Subsequently, it was transferred to a vacuum drying oven and cured at 100 °C for 2 h, at 130 °C for 2 h, and at 150 °C for 1 h to obtain modified phenolic resin products.

[0032] Example 3 Preparation of phenolic resin matrix: 81.52 g of formaldehyde was mixed with deionized water to prepare a formaldehyde solution with a mass fraction of 37%. The prepared formaldehyde solution, 203.8 g of phenol, 3 g of oxalic acid and 200 g of distilled water were mixed, and then reacted in an oil bath at 90 °C for 3 h. 14.68 g of diphenylphosphoric acid was added and the reaction was continued for 2 h. Then 90 ml of distilled water was added, and after washing for 1 h, it was left to stand for 2 h. After the water and the resin system were layered, the upper layer of water was separated to obtain a phenolic resin matrix.

[0033] Preparation of modified halloysite nanotubes: 10.71 g of halloysite nanotubes were immersed in 0.3 mol / L sodium hydroxide solution. After stirring for 30 min, hydroxylated halloysite nanotubes were obtained. The hydroxylated halloysite nanotubes were infiltrated into 200 ml of solvent and stirred for 15 min to fully disperse the hydroxylated halloysite nanotubes. Then 80 ml of epichlorohydrin was added, and the mixture was stirred at a speed of 300 r / min for 1 h. Finally, 4.29 g of polyethyleneimine was added and stirring was continued for 20 min. Then the mixture was centrifuged and washed, freeze-dried at -20 °C, and ground to obtain modified halloysite nanotubes.

[0034] Preparation of halloysite nanotube composites: 6.07 g of modified halloysite nanotubes were dispersed in 200 ml of acetonitrile. 50.56 g of hexafluorobisphenol A and 100 ml of triethylamine were added, and the mixture was ultrasonically dispersed at 25 °C for 30 min to obtain a dispersion. 3.37 g of hexachlorocyclotriphosphazene was mixed with 50 ml of acetonitrile and stirred at a speed of 500 r / min for 10 min to obtain a hexachlorocyclotriphosphazene solution. The hexachlorocyclotriphosphazene solution was added to the dispersion, and the temperature was raised to 50 °C and reacted for 5 h. After the reaction, the product was centrifuged, washed alternately with deionized water and absolute ethanol 3 times, and finally dried in a vacuum drying oven to obtain halloysite nanotube composites.

[0035] Preparation of modified phenolic resin: 16 g of halloysite nanotube composites were added to 182 g of flame-retardant phenolic resin matrix and stirred at a speed of 200 r / min for 4 h. Then 22 g of curing agent was added, and hot pressing was carried out on a flat vulcanizing machine at 150 °C. Subsequently, it was transferred to a vacuum drying oven and cured at 100 °C for 2 h, at 130 °C for 2 h, and at 150 °C for 1 h to obtain modified phenolic resin products.

[0036] Example 4 Example 4 was based on Example 3. The difference between Example 4 and Example 3 was that in the preparation of the phenolic resin matrix in Example 4, 206.04 g of phenol, 82.42 g of formaldehyde, and 11.54 g of diphenylphosphoric acid were used.

[0037] Example 5 Example 5 was based on Example 3. The difference between Example 5 and Example 3 was that in the preparation of the phenolic resin matrix in Example 5, 201.61 g of phenol, 80.65 g of formaldehyde, and 17.74 g of diphenylphosphoric acid were used.

[0038] Example 6 Example 6 Based on Example 3, the difference between Example 6 and Example 3 is that when preparing the modified halloysite nanotubes in Example 6, 10.16 g of halloysite nanotubes and 4.84 g of polyethyleneimine were used.

[0039] Example 7 Example 7 Based on Example 3, the difference between Example 7 and Example 3 is that when preparing the modified halloysite nanotubes in Example 7, 11.05 g of halloysite nanotubes and 3.95 g of polyethyleneimine were used.

[0040] Example 8 Example 8 Based on Example 3, the difference between Example 8 and Example 3 is that the modified halloysite nanotubes were prepared by the following method: 10 g of halloysite nanotubes and 100 mL of toluene were added to a three-necked flask, stirred in a constant temperature water bath at 60 °C, acetic acid was added until the pH value reached 4, and stirred for 0.5 h. 60 g of toluene and 8 g of methyltrimethoxysilane (CAS No.: 1185-55-3) were mixed evenly and added dropwise to the above three-necked flask within 0.5 h, and then reacted for 2 h. After the reaction, the solution was filtered, and the filtered product was washed 3 times with ethanol and placed in a vacuum drying oven at 80 °C for 12 h to obtain the modified halloysite nanotubes.

[0041] Example 9 Example 9 Based on Example 3, the difference between Example 9 and Example 3 is that when preparing the halloysite nanotube composite material in Example 9, the modified halloysite nanotubes were replaced with unmodified ordinary halloysite nanotubes.

[0042] Example 10 Example 10 Based on Example 3, the difference between Example 10 and Example 3 is that when preparing the halloysite nanotube composite material in Example 10, 3.43 g of hexachlorocyclotriphosphazene, 51.43 g of hexafluorobisphenol A, and 5.14 g of modified halloysite nanotubes were used.

[0043] Example 11 Example 11 Based on Example 3, the difference between Example 11 and Example 3 is that when preparing the halloysite nanotube composite material in Example 11, 3.51 g of hexachlorocyclotriphosphazene, 49.12 g of hexafluorobisphenol A, and 7.37 g of modified halloysite nanotubes were used.

[0044] Comparative Example 1 Comparative Example 1 Based on Example 3, in Comparative Example 1, the halloysite nanotube composite material was replaced with an equal amount of modified halloysite nanotubes.

[0045] Comparative Example 2 Comparative Example 2 was based on Example 3. In Comparative Example 2, diphenylphosphoric acid was not added during the preparation of the phenolic resin matrix.

[0046] Performance detection test Samples of Examples 1-11 and Comparative Examples 1-2 were taken and the following performance tests were carried out: (1) Using "GB / T 2408 Plastics - Determination of burning behavior - Horizontal and vertical methods" as the detection standard, the burning performance of the samples was tested. Each sample was tested 3 times, and the average value was taken, and the test results were filled in Table 1.

[0047] (2) Using "GB / T 2406.2-2009" as the detection standard, the limiting oxygen index of the samples was tested. Each sample was tested 3 times, and the average value was taken, and the test results were filled in Table 1.

[0048] (3) Using "GB / T7124—2008" as the detection standard, the tensile shear strength of the samples was tested. Each sample was tested 3 times, and the average value was taken, and the test results were filled in Table 1.

[0049] (4) Using "GB / T3803—2002" as the detection standard, the impact strength of the samples was tested. Each sample was tested 3 times, and the average value was taken, and the test results were filled in Table 1.

[0050] Table 1 Test performance results of samples of Examples 1-11 and Comparative Examples 1-2 Data analysis It can be seen from Table 1 that the vertical burning grades of Examples 1-3 are all V-0 grade, and the limiting oxygen indexes are all x or above, indicating that the modified phenolic resin prepared in this application has good flame retardant performance; the mechanical properties of Examples 1-3 are all x or above, indicating that the modified phenolic resin prepared in this application has good mechanical properties.

[0051] In Examples 4 and 5 during the preparation of the phenolic resin matrix, the mass ratios between phenol, formaldehyde and diphenylphosphoric acid are not within the scope defined in this application. When the content of diphenylphosphoric acid is too low, the content of benzene rings inside the resin system decreases, and it is difficult to form a sufficient amount of char layer to protect the resin surface during combustion. At the same time, the P content decreases, and the improvement effect on the flame retardant performance of the phenolic resin decreases; when the content of diphenylphosphoric acid is too high, it affects the polycondensation reaction of the resin, generates too many volatiles during high-temperature curing, causes bubbles to form in the system, affects the limiting oxygen index of the resin, and the stability also decreases.

[0052] In Examples 6 and 7, when preparing the modified halloysite nanotubes, the mass ratio between the halloysite nanotubes and polyethyleneimine is not within the range defined in the present application. When the content of polyethyleneimine is too low, the coating performance on the surface of the halloysite nanotubes decreases, making it difficult to further improve the bonding performance between the halloysite nanotubes and the resin interface, thus resulting in a decrease in stability; when the content of polyethyleneimine is too high, it is difficult to further improve the halloysite nanotubes, which may be because the steric hindrance of polyethyleneimine affects the further modification of the halloysite nanotubes.

[0053] In Example 8, methyltrimethoxysilane was used to modify the halloysite nanotubes. After the modification of the halloysite nanotubes with methyltrimethoxysilane, the halloysite nanotubes have a certain dispersibility. However, there is no amino group in methyltrimethoxysilane, so it is impossible to generate strong molecular interactions with the phenolic groups in the phenolic resin, and it is difficult to form a stable interface. Therefore, it is difficult to improve the mechanical properties and stability of the phenolic resin, and methyltrimethoxysilane has no flame retardancy, so the comprehensive performance of Example 8 has decreased.

[0054] In Example 9, when preparing the halloysite nanotube composite material, the halloysite nanotubes were not modified. The dispersibility of the unmodified halloysite nanotubes decreased, and agglomeration occurred in the system, affecting the overall stability of the system. At the same time, it was also difficult to improve the interfacial bonding ability with the phenolic resin, and the flame retardancy of the halloysite nanotubes decreased, so the comprehensive performance of the prepared product was affected.

[0055] In Examples 10 and 11, when preparing the halloysite nanotube composite material, the mass ratio between hexachlorocyclotriphosphazene, hexafluorobisphenol A and the modified halloysite nanotubes is not within the range defined in the present application. When the content of the modified halloysite nanotubes is too low, it is difficult to aggregate more hexachlorocyclotriphosphazene and hexafluorobisphenol A at both ends of the halloysite nanotubes, and the P and N contents of the system decrease, making it difficult to achieve a better flame retardant effect. At the same time, the content of the halloysite nanotubes decreases, and the improvement of the mechanical properties of the phenolic resin system also decreases; when the content of the halloysite nanotubes is too high, the contents of hexachlorocyclotriphosphazene and hexafluorobisphenol A decrease, and it is difficult for the P and N in the system to increase further, affecting the flame retardancy of the halloysite nanotubes.

[0056] In Comparative Example 1, only the modified halloysite nanotubes were added, and the P and N contents in the system decreased significantly, affecting the overall flame retardancy of the halloysite nanotubes.

[0057] In Comparative Example 2, diphenylphosphoric acid was not added when preparing the phenolic resin matrix, the phosphorus content decreased, making it difficult to improve the overall flame retardancy of the resin system, and the thermal stability decreased. At the same time, because it was difficult to increase the content of the benzene ring structure of the phenolic resin, the overall mechanical properties of the resin decreased.

[0058] This specific embodiment is only an interpretation of the present application and does not limit the present application. Through the above description, relevant staff can make various changes and modifications completely within the scope without departing from the technical idea of this application. The technical scope of this application is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A modified phenolic resin, characterized in that: The composition includes the following components by mass: 168-196 parts of flame retardant phenolic resin matrix, 12-20 parts of halloysite nanotube composite material, and 20-24 parts of curing agent; The flame retardant phenolic resin matrix raw materials include phenol, formaldehyde solution, diphenyl phosphoric acid and oxalic acid.

2. A modified phenolic resin according to claim 1, characterized in that: The flame retardant phenolic resin matrix is ​​prepared by the following method: Mix formaldehyde with water to obtain a formaldehyde solution, mix the formaldehyde solution, phenol, oxalic acid and water, react under oil bath conditions, add diphenylphosphoric acid, continue the reaction, add water, wash with water and let stand, wait for the water and resin system to separate, separate the upper water body, and obtain a phenolic resin matrix.

3. A modified phenolic resin according to claim 2, characterized in that: The mass ratio of the phenol, formaldehyde and diphenylphosphoric acid is 2.5:1:(0.17-0.19).

4. A modified phenolic resin according to claim 1, characterized in that: The halloysite nanotube composite material is prepared by the following method: The modified halloysite nanotubes are dispersed in acetonitrile, hexafluorobisphenol A and triethylamine are added, and ultrasonic dispersion is performed to obtain a dispersion; hexachlorocyclotriphosphazene is mixed with acetonitrile to obtain a hexachlorocyclotriphosphazene solution, the hexachlorocyclotriphosphazene solution is added to the dispersion to react, and after the reaction is completed, the product is centrifuged to obtain the product, which is washed and dried to obtain a halloysite nanotube composite material.

5. A modified phenolic resin according to claim 4, characterized in that: The mass ratio of the hexachlorocyclotriphosphazene, hexafluorobisphenol A and the modified halloysite nanotube is 1:15:(1.7-1.9).

6. A modified phenolic resin according to claim 4, characterized in that: The modified halloysite nanotubes include halloysite nanotubes and polyethyleneimine.

7. A modified phenolic resin according to claim 6, characterized in that: The modified halloysite nanotubes are prepared by the following method: The halloysite nanotubes are immersed in a sodium hydroxide solution to obtain hydroxylated halloysite nanotubes, the hydroxylated halloysite nanotubes are dispersed in a solvent, epichlorohydrin is added, polyethyleneimine is added after stirring, the mixture is centrifuged and washed after stirring, freeze-dried, and ground to obtain modified halloysite nanotubes.

8. A modified phenolic resin according to claim 6, characterized in that: The mass ratio between the halloysite nanotubes and polyethyleneimine is (2.4-2.6):

1.

9. A modified phenolic resin according to claim 1, characterized in that: The curing agent is hexamethylenetetramine.

10. A method for preparing the modified phenolic resin according to claim 1, characterized in that: The steps include: The halloysite nanotube composite material is added to a flame-retardant phenolic resin matrix, a curing agent is added after stirring, hot pressing is performed, and then the temperature is increased for curing to obtain a modified phenolic resin product.

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