A flame-retardant wave-absorbing material based on expanded polystyrene and its preparation method

Abstract

The present invention relates to the technical field of laminated composite materials, and particularly relates to a flame-retardant wave-absorbing material based on expanded polystyrene and a preparation method thereof. The preparation method includes: compounding a graphene azide / ferroferric oxide composite material with propargylated novolac resin through click chemical reaction to obtain a wave-absorbing agent, and compounding the wave-absorbing agent with phenolic resin, flame-retardant functionalized phenolic resin, and ammonium polyphosphate to form a flame-retardant coated resin. After mixing with pre-expanded polystyrene beads, secondary foaming is carried out to obtain an expanded polystyrene-based composite material. Using this as an intermediate layer, it is compounded and hot-pressed with the upper layer and the lower layer to obtain a flame-retardant wave-absorbing material based on expanded polystyrene. This composite material has excellent flame-retardant performance and wave-absorbing performance.

Description

Technical Field

[0001] The present invention relates to the technical field of laminated composite materials, and particularly relates to a flame-retardant wave-absorbing material based on expanded polystyrene and a preparation method thereof. Background Art

[0002] Wave-absorbing materials, namely radar absorbing materials, refer to a class of materials that can absorb and attenuate incident electromagnetic waves, convert electromagnetic energy into other forms of energy and consume it, or make electromagnetic waves disappear through interference. Electromagnetic shielding technology can relatively simply and effectively prevent electromagnetic wave leakage and avoid electromagnetic wave radiation. However, most shielding measures only reflect electromagnetic waves and do not fundamentally attenuate electromagnetic waves, easily causing secondary pollution of electromagnetic radiation. Wave-absorbing materials can absorb and consume the energy of incident electromagnetic waves inside the materials, effectively reducing the energy of reflected electromagnetic waves.

[0003] Wave-absorbing materials can be classified into coating-type wave-absorbing materials and structural wave-absorbing materials according to the forming process; as a structural wave-absorbing material, the foam sandwich structure wave-absorbing composite material combines a wave-absorbing material and a foam sandwich material organically with an advanced composite material as the carrier, which is a new type of wave-absorbing material. The prior art such as Chinese Patent Application CN114670526A discloses a wave-absorbing honeycomb core material and a wave-absorbing honeycomb core sandwich structure, including a honeycomb matrix, a resin bonding part and a wave-absorbing material. The wave-absorbing material metalized hollow glass microspheres are fixed on the honeycomb matrix through resin bonding, improving the electromagnetic wave absorption rate of the material. However, the flame retardancy of the resin bonding part needs to be improved. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a flame-retardant wave-absorbing material based on expanded polystyrene and a preparation method thereof, and the prepared composite material has excellent flame retardancy and wave absorption performance.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present invention is as follows:

[0006] A preparation method of a flame-retardant wave-absorbing material based on expanded polystyrene, comprising the following steps:

[0007] Step (1), mixing graphene, ferric chloride hexahydrate, sodium acetate and a solvent, ultrasonically dispersing, reacting, after the reaction is completed, cooling, centrifuging, filtering, washing and drying to obtain a graphene / iron oxide composite material;

[0008] Mixing 3-(azidopropyl)triethoxysilane, graphene / iron oxide composite material and toluene, reacting, after the reaction is completed, filtering, washing and drying to obtain an azide graphene / iron oxide composite material;

[0009] Mix the graphene azide / iron oxide composite with N,N-dimethylformamide, disperse it by ultrasound, add propargylated novolac resin, and then add pentamethyldiethylenetriamine and copper iodide in a nitrogen atmosphere, react, and after the reaction is completed, centrifuge, filter, and dry to obtain the microwave absorber;

[0010] Step (2): Mix and stir phenolic resin, flame-retardant functionalized phenolic resin, ammonium polyphosphate, and the microwave absorber to obtain the flame-retardant coated resin;

[0011] Among them, the flame-retardant functionalized phenolic resin is prepared by the following steps:

[0012] Mix phenol, sodium hydroxide, the first portion of paraformaldehyde, and water, add hexakis(p-aminophenoxy)cyclotriphosphazene, react, and after the reaction is completed, add the second portion of paraformaldehyde and continue to react. After the reaction is completed, add the third portion of paraformaldehyde and react again. After the reaction is completed, cool to room temperature to obtain the modified phenolic resin;

[0013] Dissolve the modified phenolic resin in N,N-dimethylacetamide, add 4-nitrophthalonitrile and the catalyst potassium carbonate, react, and after the reaction is completed, cool and purify to obtain the flame-retardant functionalized phenolic resin;

[0014] Step (3): Pre-expand the expandable polystyrene beads, and after the pre-expansion is completed, cure to obtain the pre-expanded polystyrene beads;

[0015] Mix and stir the pre-expanded polystyrene beads with the flame-retardant coated resin, dry, place them in a mold after drying, and perform secondary foaming. After the secondary foaming is completed, cool and dry to obtain the foamed polystyrene-based composite material;

[0016] Step (4): Use the foamed polystyrene-based composite material as the middle layer, the glass fiber prepreg as the upper layer, and the carbon fiber material as the lower layer, stack and laminate them in the order of upper layer, middle layer, and lower layer, and perform hot pressing to obtain the flame-retardant microwave-absorbing material based on foamed polystyrene.

[0017] Preferably, in step (1): the mass ratio of graphene, ferric chloride hexahydrate, sodium acetate, and the solvent is 0.03:2 - 2.1:37.5 - 38:835; when preparing the graphene / iron oxide composite material, the reaction conditions are: react at 200 °C for 8 - 10 h.

[0018] Furthermore, the solvent is prepared by mixing ethylene glycol and diethylene glycol monoethyl ether in a mass ratio of 415 - 420:415 - 420.

[0019] Preferably, in the step (1): the mass ratio of 3-(azidopropyl)triethoxysilane, graphene / iron oxide composite, and toluene is 0.18 - 0.2:0.1:100 - 130; when preparing the azide graphene / iron oxide composite, the reaction conditions are: reacting for 24 - 30 h at a temperature of 70 - 80 °C in a light-shielded environment.

[0020] Preferably, in the step (1): the mass ratio of azide graphene / iron oxide composite, N,N-dimethylformamide, propargylated novolac resin, pentamethyldiethylenetriamine, and cuprous iodide is 1:100 - 130:2.8 - 3:0.03:0.28; when preparing the microwave absorbing agent, the reaction conditions are: reacting for 24 - 26 h at a temperature of 25 - 30 °C.

[0021] Preferably, in the step (1), the propargylated novolac resin is prepared through the following steps:

[0022] Mix novolac resin, sodium hydroxide, 3-bromopropyne, water, and methyl ethyl ketone evenly, add a catalyst, react, and after the reaction is completed, purify to obtain the propargylated novolac resin.

[0023] Preferably, when preparing the propargylated novolac resin in the step (1): the mass ratio of novolac resin, sodium hydroxide, 3-bromopropyne, water, methyl ethyl ketone, and the catalyst is 10:3 - 3.2:9 - 9.2:50 - 60:50 - 60:0.1 - 0.14; the reaction conditions are: stirring and reacting at a temperature of 70 - 80 °C for 8 - 10 h.

[0024] Further, the purification operation includes: after the reaction is completed, a crude reaction product is obtained, washed with water 3 - 4 times the mass of the crude reaction product, the organic phase is taken, the solvent is removed by rotary evaporation, and dried at a temperature of 100 - 120 °C for 10 - 14 h.

[0025] Further, the catalyst is triethylbenzylammonium chloride.

[0026] Preferably, in the step (2): the mass ratio of phenolic resin, flame-retardant functionalized phenolic resin, ammonium polyphosphate, and microwave absorbing agent is 50 - 60:40 - 50:5 - 6:20 - 25.

[0027] Preferably, when preparing the flame-retardant functionalized phenolic resin in step (2): the mass ratio of phenol, sodium hydroxide, water, paraformaldehyde, and hexakis(4-aminophenoxy)cyclotriphosphazene is 92-94:0.4-0.5:6:40-46:8-10; the paraformaldehyde includes a first portion of paraformaldehyde, a second portion of paraformaldehyde, and a third portion of paraformaldehyde, and the mass ratio of the first portion of paraformaldehyde, the second portion of paraformaldehyde, and the third portion of paraformaldehyde is 1:1:1; when preparing the modified phenolic resin, the reaction conditions are: reacting at a temperature of 80-90 °C for 1-2 h, continuing to react at a temperature of 80-90 °C for 0.5-1 h, and reacting again at a temperature of 80-90 °C for 1-1.5 h.

[0028] Preferably, when preparing the flame-retardant functionalized phenolic resin in step (2): the mass ratio of the modified phenolic resin, 4-nitrophthalonitrile, and the catalyst potassium carbonate is 60:12-14:15-16; when preparing the flame-retardant functionalized phenolic resin, the reaction conditions are: reacting at a temperature of 75-80 °C for 16-18 h.

[0029] Preferably, the purification operation includes: filtering, taking the filtrate, adding a 0.01 mol / L aqueous hydrochloric acid solution to neutralize to neutrality to obtain a crude reaction product, adding methyl ethyl ketone for extraction in an amount 8-10 times the mass of the crude reaction product, taking the organic phase, rotary evaporating to remove the solvent, and drying at a temperature of 50-60 °C for 8-10 h.

[0030] Preferably, in step (3): the pre-foaming conditions are: pre-foaming in steam with a vapor pressure of 0.4-0.5 MPa at a temperature of 100 °C for 50-55 s; the curing conditions are: curing at room temperature for 12-20 h; the mass ratio of the pre-foamed polystyrene beads to the flame-retardant coating resin is 25:15-18; the secondary foaming conditions are: secondary foaming in steam with a vapor pressure of 0.3-0.4 MPa at a temperature of 120-130 °C for 3-3.5 min; the thickness of the foamed polystyrene-based composite material is 40-50 mm.

[0031] Preferably, in step (4): the hot pressing conditions are: hot pressing at a pressure of 0.15-0.2 MPa and a temperature of 135-145 °C for 2-2.5 h.

[0032] Preferably, a flame-retardant wave-absorbing material based on foamed polystyrene prepared by the preparation method of the flame-retardant wave-absorbing material based on foamed polystyrene as described above.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] In the present invention, the magnetic loss type microwave absorbing material magnetite is compounded with the resistance loss type microwave absorbing material graphene by a solvothermal method to prepare a graphene / magnetite composite material with excellent microwave absorbing performance. Then, it is surface-modified with 3-(azidopropyl)triethoxysilane to obtain an azide-functionalized graphene / magnetite composite material with azide groups on the surface. The azide-functionalized graphene / magnetite composite material undergoes an azide-alkyne click chemical reaction with propargylated novolac resin under the action of a catalyst, so that the novolac resin structure is cured on the surface of the graphene / magnetite composite material to obtain a microwave absorber;

[0035] Among them, the propargylated novolac resin is prepared by reacting novolac resin with 3-bromopropyne, and a nitrogen-containing triazole ring structure will be formed after reacting with the azide-functionalized graphene / magnetite composite material. The introduction of the propargylated novolac resin not only improves the dispersion of the microwave absorber in the flame-retardant coating resin matrix, but also further improves the thermal stability and flame-retardant performance of the matrix.

[0036] In the present invention, hexakis(p-aminophenoxy)cyclotriphosphazene containing a cyclotriphosphazene flame-retardant structure is introduced into the phenolic resin. Through the dehydration condensation reaction between amino groups and aldehyde groups and hydroxymethyl groups, while introducing nitrogen and phosphorus elements into the phenolic resin, the crosslinking density of the phenolic resin is increased. The prepared modified phenolic resin further undergoes an etherification reaction with 4-nitrophthalonitrile to introduce a phthalonitrile structure with good flame-retardant and heat-resistant properties into the modified phenolic resin. The prepared flame-retardant functionalized phenolic resin has excellent flame-retardant performance. After mixing it with phenolic resin, ammonium polyphosphate, and the microwave absorber, a flame-retardant coating resin is prepared;

[0037] In the present invention, by using the resin coating method, expandable polystyrene beads are pre-expanded and then mixed and stirred with the flame-retardant coating resin, so that the flame-retardant coating resin is uniformly coated on the surface of the pre-expanded polystyrene beads as a binder. After molding and secondary foaming, a foamed polystyrene-based composite material is obtained. Using it as the microwave absorbing layer, a glass fiber prepreg with good flame-retardant performance and good wave-transmitting performance and a carbon fiber material with high reflection performance are respectively hot-pressed and bonded on the upper and lower sides to prepare a flame-retardant microwave absorbing material with a three-layer composite structure, which has excellent flame-retardant performance and microwave absorbing performance as a structural microwave absorbing material. Description of the Drawings

[0038] Figure 1 is the process flow chart for preparing the flame-retardant microwave absorbing material based on foamed polystyrene in the present invention;

[0039] Figure 2 is the structural schematic diagram of the flame-retardant microwave absorbing material based on foamed polystyrene prepared in the present invention;

[0040] Figure 3 is the bar chart of the limiting oxygen index in the flame-retardant performance test of Samples 1-7 in the present invention;

[0041] In the figure:

[0042] 1. Upper layer; 2. Middle layer; 3. Lower layer. Specific implementation mode

[0043] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

[0044] Embodiment 1

[0045] This embodiment discloses a preparation method of a flame-retardant wave-absorbing material based on expanded polystyrene, including the following steps:

[0046] Step (1): Mix graphene, ferric chloride hexahydrate, sodium acetate, ethylene glycol, and diethylene glycol in a mass ratio of 0.03:2.1:37.5:415:420, ultrasonically disperse for 15 min, react at 200 °C for 8 h. After the reaction, cool to room temperature, centrifuge, filter, take the filter cake, add water 5 times the mass of the filter cake for washing, and dry at 40 °C for 8 h to obtain a graphene / iron oxide composite material;

[0047] Mix 3-(azidopropyl)triethoxysilane, graphene / iron oxide composite material, and toluene in a mass ratio of 0.19:0.1:120, react in a light-shielded environment at 75 °C for 26 h. After the reaction, filter, take the filter cake, add ethanol 6 times the mass of the filter cake for washing, and dry at 55 °C for 10 h to obtain an azide-functionalized graphene / iron oxide composite material;

[0048] Mix the azide-functionalized graphene / iron oxide composite material with N,N-dimethylformamide, ultrasonically disperse for 5 min, add propargylated novolac resin, and then add ligand pentamethyldiethylenetriamine and catalyst copper iodide in a nitrogen atmosphere. The mass ratio of the azide-functionalized graphene / iron oxide composite material, N,N-dimethylformamide, propargylated novolac resin, pentamethyldiethylenetriamine, and catalyst copper iodide is 1:100:2.8:0.03:0.28, react at 25 °C for 26 h. After the reaction, centrifuge, filter, take the filter cake, and dry in a light-shielded environment at 50 °C for 24 h to obtain a wave-absorbing agent;

[0049] Among them, the propargylated novolac resin is prepared by the following steps:

[0050] Mix the linear phenolic resin, sodium hydroxide, 3-bromopropyne, water, and methyl ethyl ketone evenly, add the catalyst triethylbenzylammonium chloride. The mass ratio of the linear phenolic resin, sodium hydroxide, 3-bromopropyne, water, methyl ethyl ketone, and catalyst is 10:3:9:50:60:0.1. Stir and react at 70 °C for 10 h. After the reaction ends, obtain the crude reaction product, add water for washing in an amount three times the mass of the crude reaction product, take the organic phase, rotary evaporate to remove the solvent, and dry at 100 °C for 14 h to obtain the propargylated linear phenolic resin;

[0051] Step (2): Mix phenolic resin, flame-retardant functionalized phenolic resin, ammonium polyphosphate, and microwave absorbing agent in a mass ratio of 60:40:5:20, and stir at a speed of 400 r / min for 6 min to obtain the flame-retardant coated resin;

[0052] Among them, the flame-retardant functionalized phenolic resin is prepared by the following steps:

[0053] Divide paraformaldehyde into three portions, and the mass ratio of the first portion of paraformaldehyde, the second portion of paraformaldehyde, and the third portion of paraformaldehyde is 1:1:1; Mix phenol, sodium hydroxide, the first portion of paraformaldehyde, and water, add hexakis(4-aminophenoxy)cyclotriphosphazene, and react at 85 °C for 2 h. After the reaction ends, add the second portion of paraformaldehyde and continue to react at 85 °C for 1 h. After the reaction ends, add the third portion of paraformaldehyde and react again at 85 °C for 1 h. After the reaction ends, cool to room temperature to obtain the modified phenolic resin; The mass ratio of phenol, sodium hydroxide, water, paraformaldehyde, and hexakis(4-aminophenoxy)cyclotriphosphazene is 93:0.45:6:44:9;

[0054] Dissolve the modified phenolic resin and the solvent N,N-dimethylacetamide in a mass ratio of 1:4, add 4-nitrophthalonitrile and the catalyst potassium carbonate. The mass ratio of the modified phenolic resin, 4-nitrophthalonitrile, and the catalyst potassium carbonate is 60:12:15. React at 75 °C for 18 h. After the reaction ends, cool to room temperature, filter, take the filtrate, add 0.01 mol / L hydrochloric acid aqueous solution to neutralize to neutrality to obtain the crude reaction product, add methyl ethyl ketone for extraction in an amount eight times the mass of the crude reaction product, take the organic phase, rotary evaporate to remove the solvent, and dry at 50 °C for 10 h to obtain the flame-retardant functionalized phenolic resin;

[0055] Step (3): Place the expandable polystyrene beads in steam, pre-expand in steam with a vapor pressure of 0.4 MPa at 100 °C for 50 s. After the pre-expansion ends, cure at room temperature for 12 h to obtain the pre-expanded polystyrene beads;

[0056] The pre-expanded polystyrene beads and the flame-retardant coating resin are mixed and stirred for 10 min at a mass ratio of 25:15, so that the flame-retardant coating resin uniformly coats the surface of the pre-expanded polystyrene beads. Then, they are dried at 50 °C for 15 min. After drying, they are placed in a mold and secondarily foamed in steam with a vapor pressure of 0.3 MPa at 120 °C for 3.5 min. After the secondary foaming is completed, they are cooled to room temperature and dried at 50 °C for 30 h to obtain a foamed polystyrene-based composite material with a thickness of 40 mm;

[0057] Step (4): Using the foamed polystyrene-based composite material as the intermediate layer, the glass fiber prepreg as the upper layer, and the carbon fiber material as the lower layer, they are laminated and compounded in the order of the upper layer, the intermediate layer, and the lower layer, and hot-pressed at a pressure of 0.15 MPa and a temperature of 135 °C for 2.5 h to obtain a flame-retardant wave-absorbing material based on foamed polystyrene.

[0058] Example 2

[0059] This example discloses a preparation method of a flame-retardant wave-absorbing material based on foamed polystyrene, including the following steps:

[0060] Step (1): Mix the graphene azide / iron tetroxide composite material with N,N-dimethylformamide, ultrasonically disperse for 5 min, add propargylated linear phenolic resin, and then add ligand pentamethyldiethylenetriamine and catalyst copper iodide in a nitrogen atmosphere. The mass ratio of the graphene azide / iron tetroxide composite material, N,N-dimethylformamide, propargylated linear phenolic resin, pentamethyldiethylenetriamine, and catalyst copper iodide is 0.3:110:2.85:0.03:0.28. React at 25 °C for 26 h. After the reaction is completed, centrifuge and filter, take the filter cake, and dry it in a light-shielded environment at 55 °C for 20 h to obtain a wave-absorbing agent;

[0061] Among them, the preparation of the graphene azide / iron tetroxide composite material is the same as that in Example 1; the propargylated linear phenolic resin is prepared through the following steps:

[0062] Mix the linear phenolic resin, sodium hydroxide, 3-bromopropyne, water, and butanone evenly, add catalyst triethylbenzylammonium chloride. The mass ratio of the linear phenolic resin, sodium hydroxide, 3-bromopropyne, water, butanone, and catalyst is 10:3.05:9.05:53:57:0.11. Stir and react at 70 °C for 10 h. After the reaction is completed, obtain the crude reaction product, add water for washing in an amount 3 times the mass of the crude reaction product, take the organic phase, rotary evaporate to remove the solvent, and dry at 110 °C for 12 h to obtain the propargylated linear phenolic resin;

[0063] Step (2): Mix phenolic resin, flame-retardant functionalized phenolic resin, ammonium polyphosphate, and wave-absorbing agent at a mass ratio of 53:47:5.3:22, and stir at a speed of 400 r / min for 8 min to obtain flame-retardant coated resin;

[0064] Among them, the flame-retardant functionalized phenolic resin is prepared by the following steps:

[0065] The preparation of the modified phenolic resin is the same as in Example 1; dissolve the modified phenolic resin and the solvent N,N-dimethylacetamide at a mass ratio of 1:4, add 4-nitrophthalonitrile and the catalyst potassium carbonate, and the mass ratio of the modified phenolic resin, 4-nitrophthalonitrile, and the catalyst potassium carbonate is 60:12.5:15.3. React at 75 °C for 18 h. After the reaction, cool to room temperature, filter, take the filtrate, add 0.01 mol / L hydrochloric acid aqueous solution to neutralize to neutrality to obtain the crude reaction product. Add butanone extraction 8 times the mass of the crude reaction product, take the organic phase, rotary evaporate to remove the solvent, and dry at 55 °C for 8 h to obtain the flame-retardant functionalized phenolic resin;

[0066] Step (3): Place the expandable polystyrene beads in steam, pre-expand at 100 °C in steam with a vapor pressure of 0.45 MPa for 50 s. After the pre-expansion, cure at room temperature for 16 h to obtain pre-expanded polystyrene beads;

[0067] Mix the pre-expanded polystyrene beads and the flame-retardant coated resin at a mass ratio of 25:16 and stir for 10 min to uniformly coat the flame-retardant coated resin on the surface of the pre-expanded polystyrene beads. Dry at 55 °C for 10 min. After drying, place it in a mold and second-expand at 120 °C in steam with a vapor pressure of 0.3 MPa for 3.5 min. After the second expansion, cool to room temperature and dry at 55 °C for 26 h to obtain a foamed polystyrene-based composite material with a thickness of 43 mm;

[0068] Step (4): Use the foamed polystyrene-based composite material as the middle layer, the glass fiber prepreg as the upper layer, and the carbon fiber material as the lower layer, and laminate and composite in the order of the upper layer, the middle layer, and the lower layer. Hot press at a pressure of 0.18 MPa and a temperature of 135 °C for 2.5 h to obtain a flame-retardant wave-absorbing material based on foamed polystyrene.

[0069] Example 3

[0070] This example discloses a preparation method of a flame-retardant wave-absorbing material based on foamed polystyrene, including the following steps:

[0071] Step (1): Mix the graphene azide / iron oxide composite with N,N-dimethylformamide, ultrasonically disperse for 5 min, add propargylated novolac resin, and then add ligand pentamethyldiethylenetriamine and catalyst copper iodide in a nitrogen atmosphere. The mass ratio of the graphene azide / iron oxide composite, N,N-dimethylformamide, propargylated novolac resin, pentamethyldiethylenetriamine, and catalyst copper iodide is 1:115:2.9:0.03:0.28. React at 28 °C for 25 h. After the reaction, centrifuge, filter, take the filter cake, and dry it in a light-shielded environment at 55 °C for 20 h to obtain the wave-absorbing agent;

[0072] Among them, the preparation of the graphene azide / iron oxide composite is the same as that in Example 1; the propargylated novolac resin is prepared by the following steps:

[0073] Mix the novolac resin, sodium hydroxide, 3-bromopropyne, water, and butanone evenly, add the catalyst triethylbenzylammonium chloride. The mass ratio of the novolac resin, sodium hydroxide, 3-bromopropyne, water, butanone, and catalyst is 10:3.1:9.1:55:55:0.12. Stir and react at 75 °C for 9 h. After the reaction, obtain the crude reaction product, add water three times the mass of the crude reaction product for washing, take the organic phase, rotary evaporate to remove the solvent, and dry at 110 °C for 12 h to obtain the propargylated novolac resin;

[0074] Step (2): Mix the phenolic resin, flame-retardant functionalized phenolic resin, ammonium polyphosphate, and wave-absorbing agent in a mass ratio of 55:45:5.5:23, and stir at a speed of 400 r / min for 8 min to obtain the flame-retardant coated resin;

[0075] Among them, the flame-retardant functionalized phenolic resin is prepared by the following steps:

[0076] The preparation of the modified phenolic resin is the same as that in Example 1; dissolve the modified phenolic resin and solvent N,N-dimethylacetamide in a mass ratio of 1:4.5, add 4-nitrophthalonitrile and catalyst potassium carbonate. The mass ratio of the modified phenolic resin, 4-nitrophthalonitrile, and catalyst potassium carbonate is 60:13:15.5. React at 78 °C for 17 h. After the reaction, cool to room temperature, filter, take the filtrate, add 0.01 mol / L hydrochloric acid aqueous solution to neutralize to neutrality to obtain the crude reaction product, add butanone eight times the mass of the crude reaction product for extraction, take the organic phase, rotary evaporate to remove the solvent, and dry at 55 °C for 8 h to obtain the flame-retardant functionalized phenolic resin;

[0077] Step (3): Place the expandable polystyrene beads in steam, and pre-expand them in steam with a vapor pressure of 0.45 MPa at a temperature of 100 °C for 53 s. After the pre-expansion is completed, cure them at room temperature for 16 h to obtain pre-expanded polystyrene beads;

[0078] Mix the pre-expanded polystyrene beads and the flame-retardant coating resin in a mass ratio of 25:16.5 and stir for 13 min to uniformly coat the flame-retardant coating resin on the surface of the pre-expanded polystyrene beads. Dry them at a temperature of 55 °C for 10 min. After drying, place them in a mold and secondarily expand them in steam with a vapor pressure of 0.35 MPa at a temperature of 125 °C for 3.3 min. After the secondary expansion is completed, cool them to room temperature and dry them at a temperature of 55 °C for 26 h to obtain a foamed polystyrene-based composite material with a thickness of 45 mm;

[0079] Step (4): Use the foamed polystyrene-based composite material as the middle layer, the glass fiber prepreg as the upper layer, and the carbon fiber material as the lower layer, and laminate and composite them in the order of the upper layer, the middle layer, and the lower layer. Hot press them at a pressure of 0.18 MPa and a temperature of 140 °C for 2.3 h to obtain a flame-retardant wave-absorbing material based on foamed polystyrene.

[0080] Example 4

[0081] This example discloses a preparation method of a flame-retardant wave-absorbing material based on foamed polystyrene, including the following steps:

[0082] Step (1): Mix the graphene azide / iron tetroxide composite material with N,N-dimethylformamide, ultrasonically disperse it for 5 min, add propargylated linear phenolic resin, and then add ligand pentamethyldiethylenetriamine and catalyst copper iodide in a nitrogen atmosphere. The mass ratio of the graphene azide / iron tetroxide composite material, N,N-dimethylformamide, propargylated linear phenolic resin, pentamethyldiethylenetriamine, and catalyst copper iodide is 1:120:2.95:0.03:0.28. React at a temperature of 30 °C for 24 h. After the reaction is completed, centrifuge and filter, take the filter cake, and dry it in a light-shielded environment at a temperature of 55 °C for 20 h to obtain a wave-absorbing agent;

[0083] Among them, the preparation of the graphene azide / iron tetroxide composite material is the same as that in Example 1; the propargylated linear phenolic resin is prepared by the following steps:

[0084] Mix the linear phenolic resin, sodium hydroxide, 3-bromopropyne, water, and methyl ethyl ketone evenly, add the catalyst triethylbenzylammonium chloride. The mass ratio of the linear phenolic resin, sodium hydroxide, 3-bromopropyne, water, methyl ethyl ketone, and catalyst is 10:3.15:9.15:57:53:0.13. Stir and react at 80 °C for 8 h. After the reaction is completed, obtain the crude reaction product, add water for washing in an amount 3 times the mass of the crude reaction product, take the organic phase, rotary evaporate to remove the solvent, and dry at 110 °C for 12 h to obtain the propargylated linear phenolic resin;

[0085] Step (2): Mix phenolic resin, flame-retardant functionalized phenolic resin, ammonium polyphosphate, and wave-absorbing agent in a mass ratio of 58:42:5.8:24, and stir at a rotation speed of 400 r / min for 8 min to obtain the flame-retardant coated resin;

[0086] Among them, the flame-retardant functionalized phenolic resin is prepared by the following steps:

[0087] The preparation of the modified phenolic resin is the same as that in Example 1; dissolve the modified phenolic resin and the solvent N,N-dimethylacetamide in a mass ratio of 1:5, add 4-nitrophthalonitrile and the catalyst potassium carbonate. The mass ratio of the modified phenolic resin, 4-nitrophthalonitrile, and catalyst potassium carbonate is 60:13.5:15.8. React at 80 °C for 16 h. After the reaction is completed, cool to room temperature, filter, take the filtrate, add 0.01 mol / L hydrochloric acid aqueous solution to neutralize to neutrality to obtain the crude reaction product, add methyl ethyl ketone for extraction in an amount 8 times the mass of the crude reaction product, take the organic phase, rotary evaporate to remove the solvent, and dry at 55 °C for 8 h to obtain the flame-retardant functionalized phenolic resin;

[0088] Step (3): Place the expandable polystyrene beads in steam, pre-expand at 100 °C in steam with a vapor pressure of 0.5 MPa for 55 s. After the pre-expansion is completed, cure at room temperature for 18 h to obtain the pre-expanded polystyrene beads;

[0089] Mix the pre-expanded polystyrene beads and the flame-retardant coated resin in a mass ratio of 25:17 and stir for 15 min to uniformly coat the flame-retardant coated resin on the surface of the pre-expanded polystyrene beads. Dry at 55 °C for 10 min. After drying, place them in a mold and second-expand at 130 °C in steam with a vapor pressure of 0.4 MPa for 3 min. After the second-expansion is completed, cool to room temperature and dry at 55 °C for 26 h to obtain a foamed polystyrene-based composite material with a thickness of 48 mm;

[0090] Step (4): Take the expanded polystyrene-based composite material as the middle layer, the glass fiber prepreg as the upper layer, and the carbon fiber material as the lower layer. Stack and laminate them in the order of upper layer, middle layer, and lower layer, and hot press at a pressure of 0.2 MPa and a temperature of 145 °C for 2 h to obtain a flame-retardant wave-absorbing material based on expanded polystyrene.

[0091] Example 5

[0092] This example discloses a preparation method of a flame-retardant wave-absorbing material based on expanded polystyrene, including the following steps:

[0093] Step (1): Mix the graphene azide / iron oxide composite with N,N-dimethylformamide, ultrasonically disperse for 8 min, add propargylated novolac resin, and then add ligand pentamethyldiethylenetriamine and catalyst copper iodide in a nitrogen atmosphere. The mass ratio of the graphene azide / iron oxide composite, N,N-dimethylformamide, propargylated novolac resin, pentamethyldiethylenetriamine, and catalyst copper iodide is 1:130:3:0.03:0.28. React at a temperature of 30 °C for 24 h. After the reaction, centrifuge, filter, take the filter cake, and dry it in a light-shielded environment at a temperature of 60 °C for 18 h to obtain a wave-absorbing agent;

[0094] Among them, the preparation of the graphene azide / iron oxide composite is the same as that in Example 1; the propargylated novolac resin is prepared through the following steps:

[0095] Mix the novolac resin, sodium hydroxide, 3-bromopropyne, water, and butanone evenly, add catalyst triethylbenzylammonium chloride. The mass ratio of the novolac resin, sodium hydroxide, 3-bromopropyne, water, butanone, and catalyst is 10:3.2:9.2:60:50:0.14. Stir and react at a temperature of 80 °C for 8 h. After the reaction, obtain the crude reaction product, add water for washing with a mass 4 times that of the crude reaction product, take the organic phase, rotary evaporate to remove the solvent, and dry at a temperature of 120 °C for 10 h to obtain the propargylated novolac resin;

[0096] Step (2): Mix the phenolic resin, flame-retardant functionalized phenolic resin, ammonium polyphosphate, and wave-absorbing agent in a mass ratio of 50:50:6:25, and stir at a speed of 400 r / min for 10 min to obtain a flame-retardant coated resin;

[0097] Among them, the flame-retardant functionalized phenolic resin is prepared through the following steps:

[0098] The preparation of the modified phenolic resin is the same as that in Example 1; the modified phenolic resin and the solvent N,N-dimethylacetamide are mixed and dissolved at a mass ratio of 1:5, 4-nitrophthalonitrile and the catalyst potassium carbonate are added, and the mass ratio of the modified phenolic resin, 4-nitrophthalonitrile, and the catalyst potassium carbonate is 60:14:16. The reaction is carried out at 80 °C for 16 h. After the reaction is completed, it is cooled to room temperature, filtered, the filtrate is taken, neutralized to neutral with a 0.01 mol / L hydrochloric acid aqueous solution to obtain the crude reaction product, extracted with butanone 10 times the mass of the crude reaction product, the organic phase is taken, the solvent is removed by rotary evaporation, and dried at 60 °C for 8 h to obtain the flame-retardant functionalized phenolic resin;

[0099] Step (3): Place the expandable polystyrene beads in steam, pre-expand them in steam with a vapor pressure of 0.5 MPa at 100 °C for 55 s. After the pre-expansion is completed, cure them at room temperature for 20 h to obtain the pre-expanded polystyrene beads;

[0100] Mix the pre-expanded polystyrene beads and the flame-retardant coating resin at a mass ratio of 25:18 and stir for 15 min to uniformly coat the flame-retardant coating resin on the surface of the pre-expanded polystyrene beads. Dry at 60 °C for 10 min. After drying, place them in a mold and carry out secondary foaming at 130 °C for 3 min in steam with a vapor pressure of 0.4 MPa. After the secondary foaming is completed, cool to room temperature and dry at 60 °C for 24 h to obtain a foamed polystyrene-based composite material with a thickness of 50 mm;

[0101] Step (4): Use the foamed polystyrene-based composite material as the intermediate layer, the glass fiber prepreg as the upper layer, and the carbon fiber material as the lower layer, and stack and composite them in the order of the upper layer, the intermediate layer, and the lower layer. Hot press at a pressure of 0.2 MPa and a temperature of 145 °C for 2 h to obtain a flame-retardant wave-absorbing material based on foamed polystyrene.

[0102] Comparative Example 1

[0103] This comparative example discloses a preparation method of a material based on foamed polystyrene, including the following steps:

[0104] Step (1): Mix phenolic resin, flame-retardant functionalized phenolic resin, ammonium polyphosphate, and graphene at a mass ratio of 60:40:5:5 and stir at a rotation speed of 400 r / min for 6 min to obtain a flame-retardant coating resin;

[0105] Among them, the flame-retardant functionalized phenolic resin is prepared by the following steps:

[0106] The preparation of the modified phenolic resin is the same as that in Example 1; the modified phenolic resin and the solvent N,N-dimethylacetamide are mixed and dissolved at a mass ratio of 1:4, 4-nitrophthalonitrile and the catalyst potassium carbonate are added, and the mass ratio of the modified phenolic resin, 4-nitrophthalonitrile, and the catalyst potassium carbonate is 60:12:15. The reaction is carried out at 75 °C for 18 h. After the reaction is completed, it is cooled to room temperature, filtered, the filtrate is taken, neutralized to neutral with a 0.01 mol / L hydrochloric acid aqueous solution to obtain a crude reaction product, extracted with 8 times the mass of the crude reaction product of methyl ethyl ketone, the organic phase is taken, the solvent is removed by rotary evaporation, and dried at 50 °C for 10 h to obtain a flame-retardant functionalized phenolic resin;

[0107] Step (3): Place the expandable polystyrene beads in steam, pre-expand them in steam with a vapor pressure of 0.4 MPa at 100 °C for 50 s. After the pre-expansion is completed, cure them at room temperature for 12 h to obtain pre-expanded polystyrene beads;

[0108] Mix the pre-expanded polystyrene beads and the flame-retardant coating resin at a mass ratio of 25:15 and stir for 10 min to uniformly coat the flame-retardant coating resin on the surface of the pre-expanded polystyrene beads. Dry them at 50 °C for 15 min. After drying, place them in a mold and perform secondary foaming at a vapor pressure of 0.3 MPa and 120 °C for 3.5 min. After the secondary foaming is completed, cool to room temperature and dry at 50 °C for 30 h to obtain a foamed polystyrene-based composite material with a thickness of 40 mm;

[0109] Step (4): Use the foamed polystyrene-based composite material as the middle layer, the glass fiber prepreg as the upper layer, and the carbon fiber material as the lower layer, stack and laminate them in the order of the upper layer, the middle layer, and the lower layer, and hot press them at a pressure of 0.15 MPa and 135 °C for 2.5 h to obtain a material based on foamed polystyrene.

[0110] Comparative Example 2

[0111] This comparative example discloses a preparation method of a material based on foamed polystyrene, including the following steps:

[0112] Step (1): Mix the graphene azide / iron oxide composite with N,N-dimethylformamide, ultrasonically disperse it for 5 min, add propargylated linear phenolic resin, and then add the ligand pentamethyldiethylethylenediamine and the catalyst copper iodide in a nitrogen atmosphere. The mass ratio of the graphene azide / iron oxide composite, N,N-dimethylformamide, propargylated linear phenolic resin, pentamethyldiethylethylenediamine, and the catalyst copper iodide is 1:100:2.8:0.03:0.28. React at 25 °C for 26 h. After the reaction is completed, centrifuge and filter, take the filter cake, and dry it in a light-shielded environment at 50 °C for 24 h to obtain a wave-absorbing agent;

[0113] Among them, the preparation of the graphene azide / iron tetroxide composite material is the same as that in Example 1; the propargylated linear phenolic resin is prepared by the following steps:

[0114] Mix the linear phenolic resin, sodium hydroxide, 3-bromopropyne, water, and butanone evenly, add the catalyst triethylbenzylammonium chloride. The mass ratio of the linear phenolic resin, sodium hydroxide, 3-bromopropyne, water, butanone, and the catalyst is 10:3:9:50:60:0.1. Stir and react at 70 °C for 10 h. After the reaction, obtain the crude reaction product, add water three times the mass of the crude reaction product for washing, take the organic phase, rotary evaporate to remove the solvent, and dry at 100 °C for 14 h to obtain the propargylated linear phenolic resin;

[0115] Step (2): Mix the phenolic resin, ammonium polyphosphate, and microwave absorber in a mass ratio of 100:40:5:20, and stir at a speed of 400 r / min for 6 min to obtain the flame-retardant coated resin;

[0116] Step (3): Place the expandable polystyrene beads in steam, pre-expand at 100 °C in steam with a vapor pressure of 0.4 MPa for 50 s. After the pre-expansion, cure at room temperature for 12 h to obtain the pre-expanded polystyrene beads;

[0117] Mix the pre-expanded polystyrene beads and the flame-retardant coated resin in a mass ratio of 25:15 and stir for 10 min to uniformly coat the flame-retardant coated resin on the surface of the pre-expanded polystyrene beads. Dry at 50 °C for 15 min. After drying, place them in a mold and perform secondary foaming at 120 °C in steam with a vapor pressure of 0.3 MPa for 3.5 min. After the secondary foaming, cool to room temperature and dry at 50 °C for 30 h to obtain a foamed polystyrene-based composite material with a thickness of 40 mm;

[0118] Step (4): Use the foamed polystyrene-based composite material as the middle layer, the glass fiber prepreg as the upper layer, and the carbon fiber material as the lower layer. Stack and laminate them in the order of the upper layer, middle layer, and lower layer, and hot press at a pressure of 0.15 MPa and a temperature of 135 °C for 2.5 h to obtain the material based on foamed polystyrene.

[0119] In the above examples and comparative examples:

[0120] The carbon fiber material is self-made and is prepared by the following steps: Take five layers of carbon fiber cloth and stack them for lamination. Brush and roll the epoxy resin on the carbon fiber cloth. The mass ratio of the carbon fiber cloth to the epoxy resin is 3:2. Hot press at 100 °C for 50 min, raise the temperature to 140 °C, and continue hot pressing for 2 h under a pressure of 15 MPa. After cutting, obtain the carbon fiber material;

[0121] Among them, the epoxy resin is prepared by mixing epoxy resin E51, curing agent hexahydrophthalic anhydride (HHPA), and accelerator 2,4,6-tris(dimethylaminomethyl)phenol in a mass ratio of 100:80:0.2; the carbon fiber cloth is T700 carbon fiber cloth, the specification is plain cloth, from Weihai Guangwei Composite Materials Co., Ltd., item number TZ700S.

[0122] The glass fiber prepreg comes from Changzhou Xingao Insulation Materials Co., Ltd., item number WL-300A, with a plain weave, a gram weight of 308g / m2, and a resin content of 30-40%; graphene comes from McLean Biochemical Technology Co., Ltd., with a thickness of 1-10 layers and an average radial size of 5-10μm, item number G762016; 3-(azidopropyl)triethoxysilane comes from

[0123] MacLean Biochemical Technology Co., Ltd., CAS No.: 83315-69-9; linear phenolic resin comes from Green Union Chemical Technology Co., Ltd., with an average molecular weight of 420; phenolic resin comes from Shandong Jining Huakai Resin Co., Ltd., with the item number PF-3213; ammonium polyphosphate comes from West Asia Chemical Co., Ltd., with the item number B20370; hexa(p-aminophenoxy)cyclotriphosphazene comes from Jiangsu Aikon Biomedicine Research and Development Co., Ltd., CAS No.: 13441-26-4; 4-nitrophthalonitrile comes from Aladdin Biochemical Technology Co., Ltd., CAS No.: 31643-49-9; expandable polystyrene beads come from Shenghao Plastic Raw Materials Co., Ltd., brand 301H, particle size 0.3-0.5mm.

[0124] Test example

[0125] (1) Impact resistance and flame retardancy test

[0126] The expanded polystyrene-based composite materials prepared in Examples 1-5 and Comparative Examples 1-2 were respectively recorded as Samples 1-7. The impact resistance and flame retardancy of Samples 1-7 were tested. The specific test results are shown in Table 1:

[0127] Table 1

[0128]

[0129] The testing of the indicators in Table 1 is based on the following standards: the limiting oxygen index is measured with reference to GB / T2406.1-2008 "Determination of Combustion Behavior of Plastics by Oxygen Index Method"; the impact strength is measured with reference to GB / T1043-93 "Determination of Impact Properties of Plastic Simply Supported Beams".

[0130] According to the test results in Table 1, it can be seen that among the materials based on expanded polystyrene prepared by the present invention, the expanded polystyrene-based composite materials have excellent flame retardancy and good impact resistance.

[0131] In Comparative Example 2, the flame-retardant functionalized phenolic resin was not added, lacking the cyclotriphosphazene flame-retardant structure and the phthalonitrile structure with good flame retardancy and heat resistance to improve the flame retardancy of the material. Therefore, the flame retardancy of Comparative Example 2 is lower than that of the examples.

[0132] (2)Wave Absorbing Performance Test

[0133] The wave absorbing performance of the expanded polystyrene-based materials prepared in Examples 1-5 and Comparative Examples 1-2 was tested. The specific test results are shown in Table 2:

[0134] Table 2

[0135]

[0136] The detection basis for the indicators in Table 1 is as follows: The wave absorbing performance is represented by the reflectivity, and it is measured with reference to GJB 2038A-2011 "Test Method for Reflectivity of Radar Absorbing Materials". The test frequency band is 8-18 GHz.

[0137] According to the test results in Table 2, it can be seen that the expanded polystyrene-based materials prepared by the present invention have excellent wave absorbing performance.

[0138] After the magnetic loss type wave absorbing material magnetite is compounded with the resistance loss type wave absorbing material graphene, it helps to improve the impedance matching and allows more electromagnetic waves to enter the wave absorbing material. In Comparative Example 1, only graphene was used as the wave absorbing material, lacking the synergistic effect of the magnetic material magnetite and graphene to improve the wave absorbing performance of the material. Therefore, the wave absorbing performance of Comparative Example 1 is not as good as that of the examples.

[0139] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a flame-retardant wave-absorbing material based on expanded polystyrene, characterized in that, It includes the following steps: Step (1): Mix 3-(azidopropyl)triethoxysilane, graphene / iron oxide composite, and toluene, react. After the reaction is completed, filter, wash, and dry to obtain azide-functionalized graphene / iron oxide composite; Mix linear phenolic resin, sodium hydroxide, 3-bromopropyne, water, and methyl ethyl ketone evenly, add a catalyst, react. After the reaction is completed, purify to obtain propargylated linear phenolic resin; Mix the azide-functionalized graphene / iron oxide composite with N,N-dimethylformamide, ultrasonically disperse, add the propargylated linear phenolic resin, add pentamethyldiethylenetriamine and copper iodide in a nitrogen atmosphere, react at a temperature of 25 - 30 °C for 24 - 26 h. After the reaction is completed, centrifuge, filter, and dry to obtain the wave-absorbing agent; wherein, the mass ratio of the azide-functionalized graphene / iron oxide composite, N,N-dimethylformamide, propargylated linear phenolic resin, pentamethyldiethylenetriamine, and copper iodide is 1:100 - 130:2.8 - 3:0.03:0.28; Step (2): Pre-expand expandable polystyrene beads, and after the pre-expansion is completed, age to obtain pre-expanded polystyrene beads; Mix and stir the pre-expanded polystyrene beads with the flame-retardant coating resin, dry, place in a mold after drying, and perform secondary foaming. After the secondary foaming is completed, cool and dry to obtain a foamed polystyrene-based composite material; Among them, the flame-retardant coating resin is prepared by the following steps: Mix phenolic resin, flame-retardant functionalized phenolic resin, ammonium polyphosphate, and the wave-absorbing agent and stir to obtain the flame-retardant coating resin; Step (3): Use the foamed polystyrene-based composite material as the intermediate layer, composite with the upper layer and the lower layer, and hot-press to obtain a flame-retardant wave-absorbing material based on foamed polystyrene.

2. The preparation method of a flame-retardant wave-absorbing material based on expanded polystyrene according to claim 1, wherein, In the said step (1): When preparing the azide-functionalized graphene / iron oxide composite: The mass ratio of 3-(azidopropyl)triethoxysilane, graphene / iron oxide composite, and toluene is 0.18 - 0.2:0.1:100 - 130; the reaction conditions are: react in a light-shielded environment at a temperature of 70 - 80 °C for 24 - 30 h; The graphene / iron oxide composite is prepared by the following steps: Mix graphene, ferric chloride hexahydrate, sodium acetate, and a solvent, ultrasonically disperse, react. After the reaction is completed, cool, centrifuge, filter, wash, and dry to obtain the graphene / iron oxide composite; Among them, the mass ratio of graphene, ferric chloride hexahydrate, sodium acetate, and the solvent is 0.03:2 - 2.1:37.5 - 38:835; the reaction conditions are: react at a temperature of 200 °C for 8 - 10 h.

3. The preparation method of a flame-retardant wave-absorbing material based on expanded polystyrene according to claim 1, characterized in that, In the said step (1): When preparing the propargylated linear phenolic resin: The mass ratio of linear phenolic resin, sodium hydroxide, 3-bromopropyne, water, methyl ethyl ketone, and the catalyst is 10:3 - 3.2:9 - 9.2:50 - 60:50 - 60:0.1 - 0.14; the reaction conditions are: stir and react at a temperature of 70 - 80 °C for 8 - 10 h.

4. The preparation method of a flame-retardant wave-absorbing material based on expanded polystyrene according to claim 1, characterized in that, In the step (2): The conditions for primary foaming are: primary foaming for 50 - 55 s in steam with a steam pressure of 0.4 - 0.5 MPa at a temperature of 100 °C; the conditions for curing are: curing for 12 - 20 h at room temperature; the mass ratio of the pre - foamed polystyrene beads to the flame - retardant coating resin is 25:15 - 18; the conditions for secondary foaming are: secondary foaming for 3 - 3.5 min in steam with a steam pressure of 0.3 - 0.4 MPa at a temperature of 120 - 130 °C; the thickness of the foamed polystyrene - based composite material is 40 - 50 mm.

5. The preparation method of a flame-retardant wave-absorbing material based on expanded polystyrene according to claim 1, characterized in that, In the preparation of the flame - retardant coating resin in the step (2): The mass ratio of phenolic resin, flame - retardant functionalized phenolic resin, ammonium polyphosphate, and wave - absorbing agent is 50 - 60:40 - 50:5 - 6:20 - 25.

6. The preparation method of a flame-retardant wave-absorbing material based on expanded polystyrene according to claim 5, characterized in that, In the preparation of the flame - retardant functionalized phenolic resin in the step (2), the flame - retardant functionalized phenolic resin is prepared through the following steps: S11. Mix phenol, sodium hydroxide, the first portion of paraformaldehyde, and water, add hexakis(4 - aminophenoxy)cyclotriphosphazene, react, after the reaction ends, add the second portion of paraformaldehyde, continue the reaction, after the reaction ends, add the third portion of paraformaldehyde, and react again. After the reaction ends, cool to room temperature to obtain a modified phenolic resin; S12. Dissolve the modified phenolic resin and N,N - dimethylacetamide, add 4 - nitrophthalonitrile and the catalyst potassium carbonate, react, after the reaction ends, cool and purify to obtain the flame - retardant functionalized phenolic resin.

7. The preparation method of a flame-retardant wave-absorbing material based on expanded polystyrene according to claim 6, wherein When preparing the flame - retardant functionalized phenolic resin: In S11: The mass ratio of phenol, sodium hydroxide, water, paraformaldehyde, and hexakis(4 - aminophenoxy)cyclotriphosphazene is 92 - 94:0.4 - 0.5:6:40 - 46:8 - 10; paraformaldehyde includes the first portion of paraformaldehyde, the second portion of paraformaldehyde, and the third portion of paraformaldehyde, and the mass ratio of the first portion of paraformaldehyde, the second portion of paraformaldehyde, and the third portion of paraformaldehyde is 1:1:1; the reaction conditions are: react at a temperature of 80 - 90 °C for 1 - 2 h, continue to react at a temperature of 80 - 90 °C for 0.5 - 1 h, and react again at a temperature of 80 - 90 °C for 1 - 1.5 h; In S12: The mass ratio of the modified phenolic resin, 4 - nitrophthalonitrile, and the catalyst potassium carbonate is 60:12 - 14:15 - 16; the reaction conditions are: react at a temperature of 75 - 80 °C for 16 - 18 h.

8. The preparation method of a flame-retardant wave-absorbing material based on expanded polystyrene according to claim 1, characterized in that, In the step (3): The upper layer is a glass fiber prepreg, the lower layer is a carbon fiber material, and the hot - pressing conditions are: hot - press at a pressure of 0.15 - 0.2 MPa and a temperature of 135 - 145 °C for 2 - 2.5 h.

9. A flame - retardant and wave - absorbing material based on foamed polystyrene prepared by using the preparation method of a flame - retardant and wave - absorbing material based on foamed polystyrene according to any one of claims 1 - 8.

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