Preparation method of melamine resin foam

Abstract

The invention provides a preparation method of melamine resin foam, and belongs to the technical field of organic polymers. Melamine, paraformaldehyde, an amino acid solution and sodium hydroxide are used as main materials of resin; adding a specific comonomer, and carrying out a prepolymerization reaction; then adding sodium alkyl benzene sulfonate and an amino acid solution; additionally adding nano particles to carry out a repolymerization reaction; then adding a mixed additive composed of sodium alkyl benzene sulfonate, n-pentane, formic acid and the like for microwave foaming; the melamine resin foam is obtained; the mechanical property is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic polymers, and particularly relates to a preparation method of melamine resin foam. Background Art

[0002] Melamine foam (also known as melamine foam) is a thermosetting elastic organic rubber and plastic foam formed by microwave foaming of melamine polyformaldehyde resin, with a fine three-dimensional network structure with high open pores. It has the advantages of good heat insulation, stability, heat and humidity resistance, sound absorption and light weight, and is widely used in building acoustics, professional acoustics, rail vehicles, automobile manufacturing, shipbuilding, aerospace applications, pipeline insulation, high-temperature insulation, low-temperature insulation, power stations, filtration applications, large equipment manufacturing, antistatic, 5G base stations, white goods, supercapacitors, industrial cleaning, household cleaning, furniture manufacturing and other fields.

[0003] However, melamine foam also has the following inherent defects:

[0004] The high brittleness, weak tensile and compressive properties of melamine foam are its core shortcoming. The tear strength of traditional melamine foam is low (only about 0.5 - 1.5 kPa), the elastic modulus is small, and it is easy to break or brittlely rupture during use. For example, in automobile manufacturing, its large volume caused by high open porosity and material fragility limit its application in the trend of lightweight. To improve toughness, some enterprises try to introduce toughening agents such as polyvinyl alcohol (PVA), but it may sacrifice flame retardancy or increase costs.

[0005] Melamine foam is formed by the polycondensation of melamine and formaldehyde, and it is difficult to completely remove free formaldehyde in the finished product; long-term volatilization will cause harm to human health and the environment. It is necessary to reduce formaldehyde release by means of modified resins or adsorbents. Summary of the Invention

[0006] The purpose of the present invention is to propose a preparation method to improve the mechanical properties for the problem of high brittleness of current melamine foam.

[0007] To achieve the above purpose, the present invention provides a preparation method of melamine resin foam, including the following steps:

[0008] S1 Weighing: According to mass parts, it includes the following components:

[0009]

[0010] S2 Pre-polymerization: Add melamine and paraformaldehyde to the reaction kettle, adjust the pH to 10.5 - 11.5 with strong base; stir and mix to carry out hydroxymethylation reaction; then add 2,3-dimethyl-2,3-diphenylbutane, maleic anhydride, dibenzoylmethane, peroxide catalyst and amino acid solution and continue to mix to carry out grafting reaction; obtain prepolymer;

[0011] S3 Re - polymerization: Surfactant, the remaining amino acid solution, and nano - silica are added to the prepolymer. After heating, it is stirred at high speed and then reacted to obtain the re - polymer.

[0012] S4 Foaming: n - pentane, formic acid, and surfactant are added to the re - polymer. After stirring evenly, it is foamed.

[0013] Preferably, it further includes the step:

[0014] S5 Post - treatment: After foaming, it is dried with hot air and then cut into the required shape; the finished product is obtained.

[0015] Preferably, the surfactant in step S1 is an anionic surfactant.

[0016] Preferably, the foaming agent in step S1 is one of the following: n - butane, n - pentane, n - hexane.

[0017] Preferably, the peroxide catalyst in step S2 is dicumyl peroxide (DCP) or benzoyl peroxide (BPO).

[0018] Preferably, in step S2, the reaction temperature of the hydroxymethylation reaction is 70 - 85°C; the stirring rate ≥ 200 rpm; the reaction time is 1 - 2 h.

[0019] Preferably, in step S2, the grafting reaction is divided into two stages:

[0020] The reaction time of the first stage is 20 - 30 min; the reaction temperature is 70 - 85°C;

[0021] The reaction time of the second stage is 10 - 15 min; the reaction temperature is 100 - 120°C.

[0022] Preferably, in step S3, the stirring rate ≥ 2000 rpm; the time is ≥ 10 min.

[0023] Preferably, in step S3, the temperature of the heating reaction is 80 - 90°C; the time is 60 - 75 min.

[0024] Preferably, in step S4, the foaming process is microwave foaming.

[0025] Preferably, the D90 of the nano - silica ≤ 20 nm; the specific surface area ≥ 200 m 2 / g.

[0026] In the present invention, an initiator (2,3-dimethyl-2,3-diphenylbutane) is used to chemically graft two monomers (maleic anhydride, dibenzoylmethane) simultaneously; 2,3-dimethyl-2,3-diphenylbutane is a broad-spectrum free radical initiator, and its advantage lies in a relatively high decomposition temperature (about 150 °C), strong stability of the generated free radicals, which can reduce side reactions (such as crosslinking or degradation), thereby more efficiently initiating the grafting of the two monomers simultaneously.

[0027] Maleic anhydride (MAH) is a highly polar unsaturated anhydride. Through free radical grafting reaction, it is introduced into the polymer main chain to form anhydride groups, significantly improving the breaking tensile stress of the material.

[0028] When dibenzoylmethane (DBM) is grafted alone, it does not greatly improve the mechanical properties; however, in the present invention, its keto group structure participates in the free radical reaction, moderately regulating the crosslinking degree in the grafting reaction; balancing the rigidity and toughness of the material; thereby achieving the effect of improving toughness; and on the premise of the same addition amount, the mechanical improvement degree of the combination of dibenzoylmethane and maleic anhydride is better than that of maleic anhydride alone.

[0029] In the pre-polymerization stage of step S2 of the present invention, a three-stage reaction is adopted to precisely control the reaction process to prevent excessive polymerization at this stage; among them, the grafting reaction is carried out at two different temperatures. In the low-temperature stage, the monomer with lower reactivity (MAH) is grafted; in the high-temperature reaction, the second monomer (DBM) is activated for grafting; during this process, by utilizing the continuous decomposition characteristic of a single initiator (2,3-dimethyl-2,3-diphenylbutane), a relatively high grafting rate can be achieved without additional equipment. Peroxide catalysts are used in the grafting reaction, such as dicumyl peroxide (DCP) or benzoyl peroxide (BPO).

[0030] In the present invention, the amino acid solution added is generally glycine or lysine; it is used to regulate the reaction process, improve the resin crosslinking density and storage stability; the -NH2 of the amino acid undergoes a condensation reaction with the hydroxymethyl group (-CH2OH) of the melamine-formaldehyde resin to form a **-NH-CH2-O-** crosslinking bond, constructing a three-dimensional network; playing a role in improving the mechanical properties.

[0031] Moreover, when using the amino acid solution as a reaction component, its amino group undergoes a condensation reaction with free formaldehyde, reducing the content of free formaldehyde in the resin. At the same time, multi-stage hydroxymethylation reaction and alkaline condition regulation contribute to improving the formaldehyde conversion rate, reducing the formaldehyde release risk of foam products from the source.

[0032] Adding nano-silica in the present invention can significantly improve the mechanical strength of the foam. The present invention is prepared by a microwave foaming process, and the introduction of nano-materials may further optimize the pore structure uniformity and improve the brittleness and tear strength. Defining the performance indicators of nano-silica is to ensure the effect of improving the mechanical properties.

[0033] In the present invention, the nano-silica is mainly physically dispersed, but there are some chemical grafting reactions; although the nano-silica is added in step S3 (re-polymerization stage), at this time the prepolymer has completed the hydroxymethylation reaction (S2), there are still a large number of active groups in the system (such as hydroxymethyl -CH2OH, anhydride groups of maleic anhydride, -NH2 / -COOH of amino acids); the following reactions exist:

[0034] Esterification reaction (with maleic anhydride):

[0035] SiO2-OH + maleic anhydride → ΔSiO2-O-CO-CH=CH-COOH

[0036] Condensation reaction (with hydroxymethyl or amino group):

[0037] SiO2-OH + HO-CH2-resin → SiO2-O-CH2-resin + H2O

[0038] In the present invention, a strong base is used to adjust the pH value, generally sodium hydroxide or potassium hydroxide.

[0039] The surfactant is an anionic surfactant, generally sodium alkylbenzene sulfonate.

[0040] The beneficial technical effects of the present invention are at least as follows:

[0041] Through the raw material modification by chemical grafting reaction, process stage control and microwave foaming technology of the present invention, significant advantages are shown in aspects such as foam uniformity, mechanical properties, and environmental protection; at the same time, through the application of nano-materials and composite cross-linking agents, a significant improvement in mechanical properties, especially in improving brittleness, is achieved. Detailed implementation manners

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative efforts shall fall within the protection scope of the present invention.

[0043] In the description of the present invention, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality of" means two or more, unless otherwise specifically defined.

[0044] In the description of the present invention, the term "for example" is used to mean "serving as an example, illustration, or explanation". Any embodiment described as "for example" in the present invention is not necessarily construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use the present invention. In the following description, details are set forth for purposes of explanation. It should be understood that those of ordinary skill in the art can recognize that the present invention can be implemented without the use of these specific details. In other instances, well-known structures and processes are not elaborated in detail to avoid obscuring the description of the present invention with unnecessary details. Therefore, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

[0045] Unless otherwise specified, the experimental methods used in the specific embodiments are all conventional methods, and the materials, reagents, etc. used, unless otherwise specified, can all be obtained from commercial sources.

[0046] In the present invention, unless otherwise specified, "%" represents mass percentage; the raw materials, reagents, etc. used are all conventional commercially available products.

[0047] The nano-silica used in the present invention has the model number PST-QO2; the particle size D90 = 20 nm; the specific surface area = 200 m 2 / g; the pH is 5 - 7; the apparent density is 0.1 g / cm 3 ; the silica content is ≥99.5%.

[0048] In the present invention, the water used is preferably pure water (RO water).

[0049] In the present invention, the baking method and conditions are not particularly limited.

[0050] Example 1

[0051] A method for preparing melamine resin foam, comprising the following steps:

[0052] S1 Weighing: Calculated by mass parts, it includes the following components:

[0053]

[0054]

[0055] S2 Pre-polymerization: Melamine and paraformaldehyde are added to a closed reactor equipped with a safety valve, and a positive pressure of 0.3 MPa is maintained; the pH is adjusted to 11 with sodium hydroxide; stirring and mixing are carried out to initiate the hydroxymethylation reaction; then 2,3-dimethyl-2,3-diphenylbutane, maleic anhydride, dibenzoylmethane, diisopropylbenzene peroxide and half of the glycine solution are added and mixed continuously, and a small amount of ethanol is added to assist in fusion; the grafting reaction occurs; a prepolymer is obtained.

[0056] The reaction temperature of the hydroxymethylation reaction is 70 °C, the stirring speed is 20 rpm; the reaction time is 1.5 h.

[0057] The first-stage reaction time of the grafting reaction is 20 min; the reaction temperature is 85 °C.

[0058] The second-stage reaction time is 10 min; the reaction temperature is 120 °C.

[0059] S3 Re-polymerization: Half of the sodium alkylbenzenesulfonate, the remaining glycine solution and nano-silica are added to the prepolymer, and after heating, high-speed stirring is carried out, and then the reaction occurs to obtain a re-polymer.

[0060] The stirring rate is 2000 rpm; the time is 10 min.

[0061] The temperature of the heating reaction is 90 °C; the time is 60 min.

[0062] S4 Foaming: n-Pentane, formic acid and the remaining sodium alkylbenzenesulfonate are added to the re-polymer, and after stirring evenly, foaming occurs.

[0063] The microwave power is 500 W, and the foaming time is 2 min.

[0064] S5 Post-treatment: After foaming, hot air drying is carried out, and then it is cut into the required shape; the finished product is obtained.

[0065] Example 2

[0066] A method for preparing melamine resin foam, comprising the following steps:

[0067] S1 Weighing: Calculated by mass parts, it includes the following components:

[0068]

[0069]

[0070] S2 Pre-polymerization: Melamine and paraformaldehyde are added to a closed reactor equipped with a safety valve, and a positive pressure of 0.3 MPa is maintained; the pH is adjusted to 10.5 with sodium hydroxide; stirring and mixing are carried out to occur the hydroxymethylation reaction; then 2,3-dimethyl-2,3-diphenylbutane, maleic anhydride, dibenzoylmethane and half of the glycine solution are added and continue to mix, and a small amount of ethanol is added to assist in fusion; the grafting reaction occurs; the prepolymer is obtained;

[0071] The reaction temperature of the hydroxymethylation reaction is 70 °C, and the stirring speed is 20 rpm; the reaction time is 2 h;

[0072] The first-stage reaction time of the grafting reaction is 20 min; the reaction temperature is 85 °C;

[0073] The second-stage reaction time is 10 min; the reaction temperature is 120 °C.

[0074] S3 Re-polymerization: Half of the sodium alkylbenzenesulfonate, the remaining glycine solution and nano-silica are added to the prepolymer, and after heating, high-speed stirring is carried out, and then the reaction occurs to obtain the re-polymer;

[0075] The stirring rate is 2000 rpm; the time is 10 min.

[0076] The temperature of the heating reaction is 90 °C; the time is 60 min.

[0077] S4 Foaming: n-Pentane, formic acid and the remaining sodium alkylbenzenesulfonate are added to the re-polymer, and after stirring evenly, foaming occurs.

[0078] The microwave power is 500 W, and the foaming time is 2 min.

[0079] S5 Post-treatment: After foaming, hot air drying is carried out, and then it is cut into the required shape; the finished product is obtained.

[0080] Example 3

[0081] A method for preparing melamine resin foam, comprising the following steps:

[0082] S1 Weighing: Calculated by mass parts, it includes the following components:

[0083]

[0084] S2 Pre-polymerization: Melamine and paraformaldehyde are added to a closed reactor equipped with a safety valve, and a positive pressure of 0.3 MPa is maintained; the pH is adjusted to 11.5 with sodium hydroxide; stirring and mixing are carried out to occur the hydroxymethylation reaction; then 2,3-dimethyl-2,3-diphenylbutane, maleic anhydride, dibenzoylmethane and half of the lysine solution are added and continue to mix, and a small amount of ethanol is added to assist in fusion; the grafting reaction occurs; the prepolymer is obtained;

[0085] The reaction temperature of the hydroxymethylation reaction is 85 °C, and the stirring speed is 20 rpm; the reaction time is 1 h;

[0086] The reaction time of the first stage of the grafting reaction is 30 min; the reaction temperature is 70 °C;

[0087] The reaction time of the second stage is 15 min; the reaction temperature is 100 °C.

[0088] S3 Repolymerization: Add half of the sodium alkylbenzenesulfonate, the remaining lysine solution, and nano-silica to the prepolymer, stir at high speed after heating, and then react to obtain the repolymer;

[0089] The stirring rate is 2000 rpm; the time is 10 min.

[0090] The temperature for the heating reaction is 80 °C; the time is 75 min.

[0091] S4 Foaming: Add n-pentane, formic acid, and the remaining sodium alkylbenzenesulfonate to the repolymer, stir evenly and then foam.

[0092] The microwave power is 500 W, and the foaming time is 2 min.

[0093] S5 Post-treatment: After foaming, dry in hot air, and then cut into the required shape; the finished product is obtained.

[0094] Example 4

[0095] A method for preparing melamine resin foam, which is different from Example 1 in that: glycine is not added in both Step S2 and Step S3; the corresponding mass is supplemented with an equal amount of melamine and all added at one time in Step S2.

[0096] Example 5

[0097] A method for preparing melamine resin foam, which is different from Example 1 in that: nano-silica is not added; the corresponding mass is supplemented with an equal amount of melamine and all added at one time in Step S2.

[0098] Example 6

[0099] A method for preparing melamine resin foam, which is different from Example 1 in that: maleic anhydride is not added; the corresponding mass is supplemented with an equal amount of dibenzoylmethane.

[0100] Example 7

[0101] A method for preparing melamine resin foam, which is different from Example 1 in that: dibenzoylmethane is not added; the corresponding mass is supplemented with an equal amount of maleic anhydride.

[0102] Example 8

[0103] A preparation method of melamine resin foam, which is different from that of Example 1 in that dibenzoylmethane and maleic anhydride are not added; the corresponding mass is supplemented with an equal amount of melamine and all are added at one time in step S2.

[0104] Example 9

[0105] A preparation method of melamine resin foam, which is different from that of Example 1 in that dibenzoylmethane and maleic anhydride are not added; the corresponding mass is supplemented with an equal amount of 2-hydroxyethyl acrylate (HEA).

[0106] Example 10

[0107] A preparation method of melamine resin foam, which is different from that of Example 1 in that dibenzoylmethane is not added; the corresponding mass is replaced with an equal amount of styrene (st).

[0108] Example 11

[0109] A preparation method of melamine resin foam, which is different from that of Example 1 in that in the prepolymerization of step S2, the reaction time of the grafting reaction is 30 min; the reaction temperature is 120 °C.

[0110] Example 12

[0111] A preparation method of melamine resin foam, which is different from that of Example 1 in that in the prepolymerization of step S2, the reaction time of the grafting reaction is 30 min; the reaction temperature is 85 °C.

[0112] Example 13

[0113] The preparation method of melamine resin foam includes the following steps:

[0114] S1 Weighing: Calculated by mass parts, it includes the following components:

[0115]

[0116] S2 Prepolymerization: Add melamine and paraformaldehyde to the reaction kettle, adjust the pH to 8 with sodium hydroxide; stir and mix to carry out the hydroxymethylation reaction; obtain the prepolymer;

[0117] The reaction temperature of the hydroxymethylation reaction is 70 °C, the stirring speed is 20 rpm; the reaction time is 1.5 h;

[0118] S3 Repolymerization: Add half of the sodium alkylbenzenesulfonate to the prepolymer, raise the temperature and stir at high speed, and then carry out the reaction under heating to obtain the repolymer;

[0119] The stirring rate is 2000 rpm; the time is 10 min.

[0120] The temperature of the temperature-rising reaction is 90 °C; the time is 60 min.

[0121] S4 Foaming: Add n-pentane, formic acid and the remaining sodium alkylbenzenesulfonate to the polymer, stir evenly and then foam.

[0122] The microwave power is 500 W, and the foaming time is 2 min.

[0123] S5 Post-treatment: After foaming, dry with hot air, and then cut into the required shape; the finished product is obtained.

[0124] Performance Testing

[0125] Perform performance testing on the products obtained in the above examples. The testing items include:

[0126] Elastic modulus: According to the method described in "GB / T 8813-2020 Determination of Compressive Properties of Rigid Cellular Plastics".

[0127] Compressive strength: According to "GB / T 8813-2020 Determination of Compressive Properties of Rigid Cellular Plastics", select the strength at 70% compressive deformation.

[0128] Tensile stress at break: According to the method described in "GB / T 8813-2020 Determination of Compressive Properties of Rigid Cellular Plastics".

[0129] Relative elongation at break: According to the method described in "GB / T 8813-2020 Determination of Compressive Properties of Rigid Cellular Plastics".

[0130] The test results are shown in Table 1.

[0131] Table 1

[0132]

[0133] As shown in Table 1, in the present invention:

[0134] Without adding amino acids (Example 4), since the flexible chain segments of the amino acid solution will destroy the continuity of the rigid network of melamine; the flexible chain segments formed by amino acid grafting can inhibit crack propagation. When not added, the crosslinking density of the molecular chains is higher and the rigidity is enhanced; and the absence of amino acids results in the lack of an energy dissipation structure in the foam, and the cell walls are more prone to brittle fracture under compressive loads; in addition, the plastic deformation ability provided by amino acids disappears, and the material exhibits typical brittle fracture characteristics. Finally, although the elastic modulus has a slight increase, the compressive strength, tensile stress at break and relative elongation at break decrease significantly.

[0135] Without adding nano-silica (Example 5), the interfacial bonding force between the resin matrix and the filler is insufficient, resulting in a decrease in the stress transfer efficiency. The absence of nano-silica prevents the material from hindering crack propagation through rigid particles or absorbing energy through flexible chain segments. When no nano-particles are added, the strength of the cell walls during the foaming process is insufficient, and large-sized holes are likely to occur. Eventually, the elastic modulus, compressive strength, fracture tensile stress, and relative elongation rate all decrease.

[0136] Examples 6, 7, 8, 9, and 10 test the changes in different mechanical property indexes when using different modified monomers or without modification; from the results, it can be seen that only when maleic anhydride and dibenzoylmethane are compounded, the comprehensive performance is the best; replacement or absence may cause an increase in a certain index, but the other indexes will show a significant decrease.

[0137] During the long-term high-temperature reaction of S2 prepolymerization (Example 11), the high temperature accelerates the cross-linking reaction, and the molecular chains are over-crosslinked to form a rigid network. The increase in the initial cross-linking density improves the strength, but over-crosslinking causes the embrittlement of the cell walls and a long-term decrease in strength; the rigid network lacks toughness, and stress concentration leads to brittle fracture. The densification of the cross-linking network completely inhibits the slippage of molecular chains. Although the elastic modulus and compressive strength increase slightly, it will cause a serious decrease in the fracture tensile stress and relative elongation rate.

[0138] During the long-term low-temperature reaction of S2 prepolymerization (Example 12), the insufficient reaction activity results in a low cross-linking degree, and the molecular chains are in a loose linear structure; the incompletely cross-linked resin matrix cannot effectively support the load, and the cells are prone to collapse; the number of hydrogen bonds and covalent bonds between the molecular chains is insufficient, and the interfacial bonding force is weak; the flexible chain segments (amino acids) are not fully grafted, and the residual linear molecular chains provide the ability of plastic deformation. Although the relative elongation rate can be increased significantly; it will cause a serious decrease in the elastic modulus, compressive strength, and fracture tensile stress.

[0139] The above detailed description is a specific description of one of the feasible embodiments of the present invention, and this embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or change without departing from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A method for preparing melamine resin foam, characterized in that, It includes the following steps: S1 Weighing: It includes the following components calculated by mass parts: S2 Pre-polymerization: Add melamine and paraformaldehyde into the reaction kettle, adjust the pH to 10.5 - 11.5 with strong base; stir and mix to carry out the hydroxymethylation reaction; then add 2,3-dimethyl-2,3-diphenylbutane, maleic anhydride, dibenzoylmethane, peroxide catalyst and amino acid solution and continue to mix to carry out the grafting reaction; obtain the prepolymer; S3 Re-polymerization: Add surfactant, the remaining amino acid solution and nano-silica into the prepolymer, raise the temperature and stir at high speed, and then react to obtain the re-polymer; S4 Foaming: Add n-pentane, formic acid and surfactant into the re-polymer, stir evenly and then foam.

2. The method for preparing the melamine resin foam according to claim 1, wherein It also includes the step: S5 Post-treatment: After foaming, dry with hot air, and then cut into the required shape; obtain the finished product.

3. The preparation method of the melamine resin foam according to claim 1, wherein, The surfactant in the step S1 is an anionic surfactant.

4. The preparation method of the melamine resin foam according to claim 1, wherein The foaming agent in the step S1 is one of the following: n-butane, n-pentane, n-hexane.

5. The preparation method of the melamine resin foam according to claim 1, characterized in that, In the step S2, the reaction temperature of the hydroxymethylation reaction is 70 - 85 °C; the stirring rate ≥ 200 rpm; the reaction time is 1 - 2 h.

6. The preparation method of the melamine resin foam according to claim 1, characterized in that, In the step S2, the grafting reaction is divided into two stages: The reaction time of the first stage is 20 - 30 min; the reaction temperature is 70 - 85 °C; The reaction time of the second stage is 10 - 15 min; the reaction temperature is 100 - 120 °C.

7. The preparation method of the melamine resin foam according to claim 1, characterized in that, In the step S3, the stirring rate ≥ 2000 rpm; the time is ≥ 10 min.

8. The production method of the melamine resin foam according to claim 1, characterized in that, In the step S3, the temperature of the temperature-raising reaction is 80 - 90 °C; the time is 60 - 75 min.

9. The preparation method of the melamine resin foam according to claim 1, characterized in that, In the step S4, the foaming process is microwave foaming.

10. The method for preparing the melamine resin foam according to claim 1, characterized in that, The D90 of the nano-silica is ≤ 20 nm; the specific surface area is ≥ 200 m 2 / g.

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