Low formaldehyde residual melamine resin composite material and preparation method thereof

Abstract

The present application relates to melamine resin polymer material technical field, specifically to a kind of low formaldehyde residual melamine resin composite material, including modified melamine resin prepolymer, curing agent, filler;Modified melamine resin prepolymer is obtained by reaction with bismaleimide by furan modified melamine resin prepolymer;Curing agent includes ammonium sulfamate, tri (2-furyl) phosphine or N-maleimide ethylenediamine;Filler includes aminosilica, talcum powder, calcium carbonate or montmorillonite.Furan ring inhibits formaldehyde release by steric hindrance;Furan modified melamine resin forms high-density six-membered ring crosslinking network by Diels-Alder reaction, further locks free formaldehyde;The polar group of curing agent forms bond with resin molecule, cooperates the physical barrier effect of filler, jointly inhibits formaldehyde migration diffusion, furan ring rigid skeleton and six-membered ring crosslinking network limit molecular chain thermal motion, improve the high temperature resistance of composite material.

Description

Technical Field

[0001] This application relates to the field of melamine resin polymer materials technology, specifically to a melamine resin composite material with low formaldehyde residue and its preparation method. Background Technology

[0002] Melamine resin, also known as melamine-formaldehyde resin, is widely used in tableware, coatings, and building materials due to its excellent mechanical properties and heat resistance. However, the dual problems of free formaldehyde release and performance degradation at high temperatures during melamine resin synthesis severely limit its further development. In traditional processes, the molar ratio of formaldehyde to melamine is ≥3:1, resulting in a free formaldehyde content of 0.3%-0.5% in the product. Furthermore, the thermal oxidative degradation of the resin molecular chains under high-temperature environments (such as tableware disinfection and long-term use of building materials) further exacerbates the risk of formaldehyde release. For example, high-formaldehyde melamine adhesives used in furniture manufacturing exhibit a significantly increased formaldehyde volatilization rate at high temperatures compared to room temperature, posing a continuous threat to indoor air quality. Formaldehyde has been classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC) of the World Health Organization, posing a significant threat to human health. Long-term exposure may lead to respiratory diseases, cancer, and other health problems, and also pollutes the environment and disrupts the ecological balance.

[0003] To address this issue, existing technologies have explored various methods. Physical adsorption methods (such as activated carbon) exhibit decreasing adsorption capacity over time; excessive addition of small-molecule scavengers (such as urea) reduces resin cross-linking, leading to decreased viscosity and shortened shelf life; while alternative aldehyde sources (such as dialdehyde starch) can reduce formaldehyde residue, insufficient aldehyde group activity results in reduced cross-linking density, causing the resin to soften during long-term use above 120°C. Existing high-temperature resistant technologies improve heat resistance by adding rigid fillers, but this often results in formaldehyde control failure. For example, Chinese patent CN102702676B discloses a method for manufacturing a composite modified melamine resin for toilet seat liners, using polyvinyl alcohol modification to improve creep resistance. Although this raises the heat distortion temperature to 180°C, the hydroxyl groups of polyvinyl alcohol adsorb formaldehyde, forming a secondary pollution source, causing the product's formaldehyde release to increase to 0.25%.

[0004] Therefore, how to achieve efficient control of free formaldehyde while ensuring the original mechanical properties and heat resistance stability of melamine resin, and how to build a synergistic mechanism that takes into account both environmental protection and high-temperature stability, has become a core issue that urgently needs to be addressed in the field of melamine resin. This is of great significance for promoting the sustainable development of related industries such as green building materials and high-temperature industrial materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a melamine resin composite material with low formaldehyde residue and its preparation method. The method involves preparing a melamine resin prepolymer using melamine and formaldehyde as raw materials, modifying it with furan compounds, and then forming a stable covalent cross-linked structure through a Diels-Alder reaction with bismaleimide. With the synergistic regulation of curing agent and filler interface enhancement, the melamine resin composite material achieves optimized low formaldehyde residue and heat resistance.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] In a first aspect, this application provides a melamine resin composite material with low formaldehyde residue and a method for preparing the same, comprising a modified melamine resin prepolymer, a curing agent, and a filler; the modified melamine resin prepolymer is obtained by reacting a furan-modified melamine resin prepolymer with bismaleimide; the furan-modified melamine resin prepolymer is obtained by reacting furan-formaldehyde and a melamine resin prepolymer; the melamine resin prepolymer is obtained by reacting melamine and formaldehyde; the curing agent comprises at least one selected from ammonium aminosulfonate, tris(2-furanyl)phosphine, and N-maleimide-ethylenediamine (NMEDA); the filler comprises at least one selected from aminated silica, talc, calcium carbonate, and montmorillonite.

[0008] In this application, under alkaline conditions, the amino groups in melamine molecules undergo hydroxymethylation with formaldehyde, forming a melamine resin prepolymer containing hydroxymethyl (-CH2OH) via nucleophilic addition. Furan compounds (furan formaldehyde) undergo nucleophilic addition-dehydration reactions with unreacted amino groups in the melamine resin prepolymer via active groups (aldehyde groups) in their molecules, generating imine bonds, thereby forming a furan-modified melamine resin prepolymer. Based on the concentration-driven principle of reaction kinetics, the collision probability between the aldehyde groups and amino groups in high-concentration furan formaldehyde is higher than that in free formaldehyde, making it easier to occupy reaction sites. Secondly, regarding structural compatibility, the aldehyde groups in furan formaldehyde are directly connected to electron-rich furan rings, and the planar heterocyclic structure has low steric hindrance, resulting in a better spatial matching degree with the remaining amino groups in the melamine molecule than with unsubstituted free formaldehyde.

[0009] The furan ring in the modified prepolymer acts as a diene and undergoes a Diels-Alder cycloaddition reaction with the maleimide group (dienophile) of bismaleimide at 90~110℃ to form a stable six-membered ring crosslinked structure. The six-membered ring crosslinked structure can resist the thermal motion and depolymerization of molecular chains at high temperatures, thereby improving the heat resistance of the resin. At the same time, the high-density crosslinked structure further locks in residual formaldehyde molecules and reduces formaldehyde release.

[0010] Ammonium aminosulfonate, tris(2-furanyl)phosphine, or NMEDA curing agents, chosen as the reaction control center, serve two purposes: firstly, they catalyze the condensation reaction between residual hydroxymethyl groups in the prepolymer, forming a denser three-dimensional network; secondly, their presence may optimize the polarity of the reaction environment, favoring the Diels-Alder reaction. By reducing unreacted active groups and structural defects, the crosslinking degree and heat resistance of the material are improved.

[0011] The filler achieves performance optimization through interface enhancement and structural reinforcement: the surface-modified filler forms chemical bonds with the resin matrix through its surface active groups, constructing a strong and tough interface transition zone. It can not only fill the micropores in the resin network to reduce stress concentration points, but also disperse external loads through its own rigid skeleton, alleviating the brittleness of the resin matrix caused by high-density cross-linking. In addition, the introduction of the filler forms a physical barrier structure, which slows down the heat and small molecule transfer path inside the material.

[0012] Preferably, the melamine resin prepolymer is prepared by reacting melamine and formaldehyde; the mass ratio of melamine to formaldehyde is (1-2):1.

[0013] Preferably, the mass ratio of furanaldehyde to melamine resin prepolymer is (1-3):20; and the mass ratio of furan-modified melamine resin prepolymer to bismaleimide is (5-10):1.

[0014] Preferably, the purity of the curing agent is ≥98%, and the mass ratio of the curing agent to the modified melamine resin prepolymer is 1:(16-20).

[0015] Preferably, the mass ratio of the filler to the modified melamine resin prepolymer is (1:8) to (3:5).

[0016] Secondly, this application provides a method for preparing a melamine resin composite material with low formaldehyde residue, comprising the following steps:

[0017] S1. Preparation of furan-modified melamine resin prepolymer: Melamine and formaldehyde are added to a reaction vessel, pH is adjusted, and the mixture is stirred to carry out the first heating reaction to obtain melamine resin prepolymer. After introducing inert gas, furan-formaldehyde is added to carry out the second heating reaction to obtain furan-modified melamine resin prepolymer.

[0018] S2. Preparation of modified melamine resin prepolymer: The furan-modified melamine resin prepolymer is transferred to a high-speed shear mixer through the bottom outlet. Bismaleimide is added through the feed port, and a third heating reaction is carried out while maintaining the inert gas supply. The first high-speed shear mixing is performed, and cross-linking is carried out through the Diels-Alder reaction to obtain the modified melamine resin prepolymer.

[0019] S3. Preparation of mixture: The modified melamine resin prepolymer is transferred to a high-speed shear mixer through the bottom outlet of the reactor. The filler is added to the modified melamine resin prepolymer in three batches through a graded feeding device. The mixture is then subjected to a second high-speed shear mixing to obtain the mixture.

[0020] S4. Curing and Molding: After adding the curing agent to the mixture and stirring, the mixture is transferred to a hydraulic molding equipment for curing and molding to obtain a melamine resin composite material with low formaldehyde residue.

[0021] Preferably, the pH value in step S1 is 8.0-9.0, the first heating temperature reaction temperature is 60-70℃ and the time is 1-3h; the inert gas includes one of argon or nitrogen, and the inert gas flow rate is 0.5-1L / min; the second heating temperature reaction temperature is 75-85℃ and the time is 1-3h.

[0022] Preferably, the third heating reaction in step S2 is carried out at a temperature of 90~110℃ for 1-2 hours, and the inert gas flow rate is 0.3~0.5L / min; the first high-speed shear mixing speed is 500~600rpm and the time is 2~4 hours.

[0023] Preferably, in step S3, the amount of filler added in three separate steps is 40%, 30%, and 30% of the total filler amount, respectively; the rotation speed of the second high-speed shearing is 1500~2000 rpm and the time is 1-2 hours.

[0024] Preferably, the curing process described in step S4 involves first preheating to 80-100°C, applying 5-6 MPa pressure and holding for 30-50 minutes, then raising the temperature to 160-170°C and applying 7-8 MPa pressure, holding for 2-3 hours, and finally cooling to room temperature.

[0025] Compared with the prior art, the beneficial effects of this application are as follows:

[0026] This application provides a method for preparing melamine resin with low formaldehyde residue. First, by modifying the melamine resin prepolymer with furanaldehyde, the furan ring partially replaces formaldehyde in the reaction and inhibits formaldehyde release through steric hindrance. The furan-modified melamine resin further locks in free formaldehyde through a high-density six-membered ring crosslinking network formed by the Diels-Alder reaction, reducing the escape of small molecules due to structural defects. Simultaneously, the polar groups of the curing agent form secondary bonds with the resin molecules, synergistically inhibiting formaldehyde migration and diffusion, thereby reducing formaldehyde residue. Second, the rigid skeleton of the furan ring and the high-strength covalent network formed by Diels-Alder crosslinking enhance the rigidity and deformation resistance of the resin matrix. The filler forms a strong and tough interfacial transition zone with the resin through surface-active groups, both filling micropores to reduce stress concentration and dispersing external loads through the rigid skeleton, alleviating the brittleness problem caused by high-density crosslinking in traditional melamine resins and improving the toughness of the composite material. Third, the p-π conjugated system of the furan ring ensures a uniform distribution of the electron cloud, forming a stable molecular framework. The six-membered ring generated through the Diels-Alder reaction has a low-stretch σ-bond structure with high bond energy, crosslinking the prepolymer chains into a three-dimensional network and restricting the thermal motion of molecular chains at high temperatures. The curing agent activates residual active groups, promoting a more complete crosslinking reaction, thereby improving the density of the three-dimensional network and strengthening the restriction on the thermal motion of molecular chains. Its polar groups form secondary bonds with the resin, enhancing intermolecular forces, inhibiting chain segment slippage at high temperatures, and further improving the resistance to high-temperature decomposition. The physical barrier effect of the filler slows down the heat and oxygen transfer path, increases the heat distortion temperature and thermal oxidation stability of the composite material, and thus improves the high-temperature resistance of the composite material. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a process for preparing a melamine resin composite material with low formaldehyde residue. Detailed Implementation

[0028] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the application will be further described in detail below with reference to embodiments. However, this should not be construed as limiting the scope of this application to the following examples. All other embodiments obtained by those skilled in the art without creative effort without departing from the above-described methodological spirit of this application are within the scope of protection of this application.

[0029] In this application, the terminology used is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0030] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] The following will describe in detail, with reference to different embodiments, a melamine resin composite material with low formaldehyde residue and its preparation method provided in this application.

[0033] Example 1

[0034] like Figure 1 As shown, this embodiment provides a method for preparing a melamine resin composite material with low formaldehyde residue, including the following steps:

[0035] S1. Preparation of furan-modified melamine resin prepolymer: Melamine and formaldehyde in a mass ratio of 1:1 are added to a reaction vessel, the pH is adjusted to 8.0, and the mixture is stirred. The first heating reaction is carried out for 1 hour at a temperature of 60°C to obtain melamine resin prepolymer. After introducing nitrogen gas at a flow rate of 0.5 L / min, furan-formaldehyde is added, wherein the mass ratio of furan-formaldehyde to melamine resin prepolymer is 1:20. The second heating reaction is carried out for 1 hour at a temperature of 75°C to obtain furan-modified melamine resin prepolymer.

[0036] S2. Preparation of modified melamine resin prepolymer: The furan-modified melamine resin prepolymer is transferred to a high-speed shear mixer through the bottom outlet. Bismaleimide is added through the feed port. The mass ratio of furan-modified melamine resin prepolymer to bismaleimide is 10:1. The third heating reaction is carried out for 1 hour at 90°C, and nitrogen gas is introduced at a flow rate of 0.3 L / min. The speed is adjusted to 500 rpm for the first high-speed shear mixing reaction for 1 hour. Crosslinking is carried out through Diels-Alder reaction for 2 hours to obtain the modified melamine resin prepolymer.

[0037] S3, Mixture: The modified melamine resin prepolymer is transferred to a high-speed shear mixer through the bottom outlet of the reactor. Aminated silica is added to the modified melamine resin prepolymer in three batches through a staged feeding device. The mass ratio of aminated silica to modified melamine resin prepolymer is (1:8). The amount of aminated silica added in the three batches is 40%, 30%, and 30% of the total filler amount, respectively. The second high-speed shear mixing reaction is carried out at a speed of 1500 rpm for 1 hour to obtain the mixture.

[0038] S4. Curing and Molding: Add ammonium aminosulfonate to the mixture, wherein the mass ratio of ammonium aminosulfonate to modified melamine resin prepolymer is 1:16. Stir and transfer to a hydraulic molding equipment for curing and molding. First, preheat to 80°C, apply 5MPa pressure and hold for 30 minutes, then raise the temperature to 160°C and pressurize to 7MPa, hold for 2 hours, and finally cool to room temperature to obtain a melamine resin composite material with low formaldehyde residue.

[0039] Example 2

[0040] like Figure 1 As shown, this embodiment provides a method for preparing a melamine resin composite material with low formaldehyde residue, characterized by comprising the following steps:

[0041] S1. Preparation of furan-modified melamine resin prepolymer: Melamine and formaldehyde in a mass ratio of 3:2 were added to a reaction vessel, the pH was adjusted to 8.5, and the mixture was stirred. The first heating reaction was carried out for 2 hours at a temperature of 65°C to obtain melamine resin prepolymer. After introducing argon gas at a flow rate of 0.8 L / min, furan-formaldehyde was added, wherein the mass ratio of furan-formaldehyde to melamine resin prepolymer was 1:10. The second heating reaction was carried out for 2 hours at a temperature of 80°C to obtain furan-modified melamine resin prepolymer.

[0042] S2. Preparation of modified melamine resin prepolymer: The furan-modified melamine resin prepolymer is transferred to a high-speed shear mixer through the bottom outlet. Bismaleimide is added through the feed port. The mass ratio of furan-modified melamine resin prepolymer to bismaleimide is 7:1. The third heating reaction is carried out for 1.5 hours at 100°C, and argon gas is introduced at a flow rate of 0.4 L / min. The speed is adjusted to 550 rpm for the first high-speed shear mixing reaction for 3 hours. Crosslinking is carried out through Diels-Alder reaction for 3 hours to obtain the modified melamine resin prepolymer.

[0043] S3, Mixture: The modified melamine resin prepolymer is transferred to a high-speed shear mixer through the bottom outlet of the reactor. Calcium carbonate is added to the modified melamine resin prepolymer in three stages through a staged feeding device. The mass ratio of calcium carbonate to modified melamine resin prepolymer is 1:4. The amount of calcium carbonate added in the three stages is 40%, 30%, and 30% of the total calcium carbonate, respectively. The second high-speed shear mixing reaction is carried out at 1800 rpm for 1.5 hours to obtain the mixture.

[0044] S4. Curing and Molding: Tris(2-furanyl)phosphine is added to the mixture, wherein the mass ratio of tris(2-furanyl)phosphine to modified melamine resin prepolymer is 1:18. The mixture is stirred and transferred to a hydraulic molding equipment for curing and molding. First, it is preheated to 90°C, and then pressured at 5.5MPa for 40 minutes. Then, the temperature is raised to 165°C and pressure is increased to 7.5MPa. The temperature and pressure are maintained for 2.5 hours. Finally, it is cooled to room temperature to obtain a melamine resin composite material with low formaldehyde residue.

[0045] Example 3

[0046] like Figure 1 As shown, this embodiment provides a method for preparing a melamine resin composite material with low formaldehyde residue, characterized by comprising the following steps:

[0047] S1. Preparation of furan-modified melamine resin prepolymer: Melamine and formaldehyde in a mass ratio of 2:1 were added to a reaction vessel, the pH was adjusted to 9.0, and the mixture was stirred. The first heating reaction was carried out for 3 hours at a temperature of 70°C to obtain melamine resin prepolymer. After introducing nitrogen gas at a flow rate of 1L / min, furan-formaldehyde was added, wherein the mass ratio of furan-formaldehyde to melamine resin prepolymer was 3:20. The second heating reaction was carried out for 3 hours at a temperature of 85°C to obtain furan-modified melamine resin prepolymer.

[0048] S2. Preparation of modified melamine resin prepolymer: The furan-modified melamine resin prepolymer is transferred to a high-speed shear mixer through the bottom outlet. Bismaleimide is added through the feed port. The mass ratio of furan-modified melamine resin prepolymer to bismaleimide is 5:1. The third heating reaction is carried out at 110℃, and nitrogen gas is introduced at a flow rate of 0.5L / min. The speed is adjusted to 600rpm for the first high-speed shear mixing reaction for 4 hours. Crosslinking is carried out through Diels-Alder reaction for 4 hours to obtain the modified melamine resin prepolymer.

[0049] S3, Mixture: The modified melamine resin prepolymer is transferred to a high-speed shear mixer through the bottom outlet of the reactor. The filler is added to the modified melamine resin prepolymer in three batches through a graded feeding device. The mass ratio of montmorillonite to modified melamine resin prepolymer is 3:5. The filler added in three batches is 40%, 30%, and 30% of the total filler in sequence. The second high-speed shear mixing reaction is carried out at a speed of 2000 rpm for 2 hours to obtain the mixture.

[0050] S4. Curing and Molding: Add NMEDA to the mixture, wherein the mass ratio of NMEDA to modified melamine resin prepolymer is 1:20. Stir and transfer to a hydraulic molding equipment for curing and molding. First, preheat to 100°C, apply 6MPa pressure and hold for 50 minutes, then raise the temperature to 170°C and pressurize to 8MPa, hold for 3 hours, and finally cool to room temperature to obtain a melamine resin composite material with low formaldehyde residue.

[0051] Comparative Example 1

[0052] This comparative example provides a method for preparing a melamine resin composite material with low formaldehyde residue, which differs from Example 3 in that furanaldehyde is not added in step S1.

[0053] Comparative Example 2

[0054] This comparative example provides a method for preparing a melamine resin composite material with low formaldehyde residue, which differs from Example 3 in that bismaleimide is not added in step S2.

[0055] Comparative Example 3

[0056] This comparative example provides a method for preparing a melamine resin composite material with low formaldehyde residue. The difference between this method and Example 3 is that step S4 uses the traditional curing agent hexamethylenetetramine.

[0057] Performance testing:

[0058] 1. Free formaldehyde content test: The acetylacetone method was used. Melamine resin composite samples from Examples 1-3 and Comparative Examples 1-3 were dissolved in water, and acetylacetone reagent was added and heated for color development. The absorbance at 412 nm was measured using a spectrophotometer to quantify free formaldehyde. By quantifying the free formaldehyde in the resin through the colorimetric reaction, the concentration of residual free formaldehyde after melamine resin synthesis was detected, and the effectiveness of a low-formaldehyde-residue melamine resin preparation method in controlling formaldehyde residue was evaluated.

[0059] 2. Mechanical property testing: Mechanical properties were determined through three-point bending and tensile tests. Melamine resin composite material samples of Examples 1-3 and Comparative Examples 1-3 were prepared according to the standard. The three-point bending test measured the bending strength by applying a concentrated load, and the tensile test measured the elongation at break by axial tension. The bending strength and elongation at break of the melamine resin were evaluated.

[0060] 3. Formaldehyde Emission Test: Using the desiccator method, the melamine resin composite material samples from Examples 1-3 and Comparative Examples 1-3 were placed in a desiccator, and the released formaldehyde was absorbed with distilled water. The release amount was quantified by spectrophotometry after acetylacetone color development. The formaldehyde released by the resin was collected and quantified using the absorption liquid. The amount of formaldehyde released by the melamine resin in a simulated real-world environment was used to assess its environmental safety.

[0061] 4. Thermal aging test: The melamine resin composite material samples of Examples 1-3 and Comparative Examples 1-3 were placed at a constant high temperature of 200℃ for 500h, and their mechanical properties (such as tensile strength and impact strength) or mass changes were tested, and the performance retention rate was calculated.

[0062] Table 1 Performance test data of Examples 1-3 and Comparative Examples 1-3

[0063] Group Free formaldehyde content (%) Bending strength (MPa) Elongation at break (%) Formaldehyde release (mg / L) Example 1 0.08 85 2.8 0.3 Example 2 0.06 88 3.0 0.2 Example 3 0.05 90 3.2 0.15 Comparative Example 1 0.18 72 2.0 0.6 Comparative Example 2 0.16 75 2.2 0.8 Comparative Example 3 0.25 68 1.8 1.2

[0064] As shown in Table 1, the examples introduce a rigid furan ring structure into the molecular chain through the nucleophilic addition reaction of furan formaldehyde with melamine resin prepolymer. The conjugated π bond of the furan ring forms a stable system with the triazine ring of melamine resin. Because the formaldehyde already bound to the resin structure undergoes a reverse reaction or decomposition reaction with the active site of -NH2, it is released back as free formaldehyde. The steric hindrance effect suppresses the release of free formaldehyde, reducing the free formaldehyde content to a minimum of 0.05% (Example 3), which is 61.1% lower than the 0.18% in Comparative Example 1 without furan modification.

[0065] Bismaleimide and furan rings form a three-dimensional cross-linked network through a Diels-Alder reversible addition reaction. This network structure can physically encapsulate unreacted formaldehyde molecules, resulting in a formaldehyde release level as low as 0.15 mg / L in this example, a reduction of 81.25% compared to 0.8 mg / L in Comparative Example 2 without bismaleimide. The curing agents used in this example, such as ammonium aminosulfonate and tris(2-furanyl)phosphine, contain multiple active functional groups (e.g., -SO3H, -PH2) in their molecular structure, exhibiting higher reaction efficiency with the resin matrix than traditional hexamethylenetetramine. The reaction leaves very few small molecule byproducts, resulting in an 80% reduction in free formaldehyde content (0.05%) in Example 3 compared to 0.25% in Comparative Example 3 using a traditional curing agent.

[0066] Table 2. Thermal aging test performance data of Examples 1-3 and Comparative Examples 1-3

[0067] sample Tensile strength retention rate (%) Impact strength retention rate (%) Quality retention rate (%) Example 1 76.2 73.5 95.5 Example 2 78.6 75.8 96.1 Example 3 81.3 78.7 96.8 Comparative Example 1 52.5 49.3 89.5 Comparative Example 2 44.1 40.2 86.8 Comparative Example 3 55.3 51.5 90.6

[0068] As shown in Table 2, Examples 1-3 introduced a rigid furan ring structure into the molecular chain through furan modification. Its conjugated π-bond system forms a stable network with the triazine ring of the melamine resin. The p-π conjugation of the furan ring ensures a uniform electron cloud distribution and increases bond energy, making it less prone to breakage or oxidative decomposition at high temperatures, thus providing a heat-resistant foundation for the resin matrix. The structural stability ensured that the mass retention rate of the examples remained above 95.5% after aging at 200℃ for 500 hours. In Comparative Example 1, without furan-formaldehyde modification, the lack of the conjugated stabilizing effect of the furan ring led to easy thermal oxidative degradation of the melamine resin molecular chain at high temperatures, resulting in main chain breakage and the escape of small molecules, with a mass retention rate of only 89.5%.

[0069] Examples 1-3 demonstrate the formation of a six-membered ring crosslinking network through the Diels-Alder reaction of bismaleimide with the furan ring. This structure exhibits high bond energy and low intra-ring tension, effectively restricting the thermal motion of the molecular chains at high temperatures. Therefore, Example 3 exhibits a tensile strength retention rate of 81.3% and an impact strength retention rate of 78.7%. In contrast, Comparative Example 2, which lacks a dense six-membered ring crosslinking network, shows a greater likelihood of disordered movement and slippage of the molecular chains at high temperatures, leading to a sharp decline in mechanical properties. The tensile strength retention rate is only 44.1%, and the impact strength retention rate is only 40.2%.

[0070] The specialized curing agents used in the examples, such as ammonium aminosulfonate and tris(2-furanyl)phosphine, activate residual active groups through proton transfer, promoting a more complete crosslinking reaction and resulting in a denser three-dimensional network structure. Simultaneously, their polar groups form secondary bonds with resin molecules, enhancing intermolecular forces and inhibiting chain slippage and thermal decomposition chain reactions at high temperatures. Comparative Example 3 used the traditional curing agent hexamethylenetetramine, which has low crosslinking efficiency and is prone to decomposition and release of small molecules, leading to numerous defects in the network structure. These defects easily become the starting point for thermal decomposition at high temperatures. Therefore, although the tensile strength retention rate (55.3%) and impact strength retention rate (51.5%) were higher than Comparative Example 2, they were 26 and 27.2 percentage points lower than Example 3, respectively, verifying the necessity of the curing agent and the crosslinking system synergistically enhancing thermal stability.

[0071] In summary, the embodiments, through the synergistic mechanism of furan-modified melamine resin, Diels-Alder crosslinking reinforcement structure, and special curing agent, are superior to the comparative examples in terms of low formaldehyde residue (free and released amounts), mechanical properties (strength and toughness), and high-temperature thermal aging stability, reducing formaldehyde release rate while improving high-temperature resistance.

[0072] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0073] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A melamine resin composite material with low formaldehyde residue, characterized in that, The composite material comprises a modified melamine resin prepolymer, a curing agent, and a filler; the modified melamine resin prepolymer is prepared by reacting a furan-modified melamine resin prepolymer with bismaleimide; the furan-modified melamine resin prepolymer is prepared by reacting furan-formaldehyde with a melamine resin prepolymer; the melamine resin prepolymer is prepared by reacting melamine with formaldehyde; the curing agent comprises at least one selected from ammonium aminosulfonate, tris(2-furanyl)phosphine, and N-maleimide-ethylenediamine; the filler comprises at least one selected from aminated silica, talc, calcium carbonate, and montmorillonite; the preparation method of the melamine resin composite material includes the following steps: S1. Melamine and formaldehyde are added to a reaction vessel, pH is adjusted, and the mixture is stirred to carry out the first heating reaction to obtain melamine resin prepolymer. After introducing an inert gas, furanaldehyde is added to carry out the second heating reaction to obtain furan-modified melamine resin prepolymer. S2. The furan-modified melamine resin prepolymer is transferred to a high-speed shear mixer through the bottom outlet. Bismaleimide is added through the feed port, and a third heating reaction is carried out while maintaining the inert gas supply. The first high-speed shear mixing is performed to obtain the modified melamine resin prepolymer. S3. The modified melamine resin prepolymer is transferred to a high-speed shear mixer through the bottom outlet of the reactor. The filler is added to the modified melamine resin prepolymer in three batches through a graded feeding device. The mixture is then subjected to a second high-speed shear mixing to obtain a mixture. S4. After adding the curing agent to the mixture and stirring, transfer it to a hydraulic molding equipment for curing and molding to obtain a melamine resin composite material with low formaldehyde residue. The mass ratio of melamine to formaldehyde is (1-2):1; the mass ratio of furanaldehyde to melamine resin prepolymer is (1-3):20; the mass ratio of furan-modified melamine resin prepolymer to bismaleimide is (5-10):1; the temperature of the third heating reaction is 90~110℃ and the time is 1-2h; the flow rate of the inert gas is 0.3~0.5L / min.

2. The melamine resin composite material with low formaldehyde residue according to claim 1, characterized in that, The purity of the curing agent is ≥98%, and the mass ratio of the curing agent to the modified melamine resin prepolymer is 1:(16-20).

3. The melamine resin composite material with low formaldehyde residue according to claim 1, characterized in that, The mass ratio of the filler to the modified melamine resin prepolymer is (1:8) to (3:5).

4. The melamine resin composite material with low formaldehyde residue according to claim 1, characterized in that, In step S1, the pH value is 8.0-9.0, the temperature of the first heating reaction is 60-70℃, and the time is 1-3h; the inert gas includes one of argon and nitrogen, and the flow rate of the inert gas is 0.5-1L / min; the temperature of the second heating reaction is 75-85℃, and the time is 1-3h.

5. The melamine resin composite material with low formaldehyde residue according to claim 1, characterized in that, In step S2, the temperature of the third heating reaction is 90~110℃ and the time is 1-2h, and the flow rate of the inert gas is 0.3~0.5L / min; the rotation speed of the first high-speed shear mixing is 500~600rpm and the time is 2~4 hours.

6. The melamine resin composite material with low formaldehyde residue according to claim 1, characterized in that, In step S3, the amount of filler added in three separate steps is 40%, 30%, and 30% of the total filler amount, respectively; the rotation speed of the second high-speed shearing is 1500~2000 rpm, and the time is 1-2 hours.

7. The melamine resin composite material with low formaldehyde residue according to claim 1, characterized in that, The curing and molding method described in step S4 is as follows: first, preheat to 80~100℃, apply 5~6MPa pressure and hold for 30~50 minutes, then raise the temperature to 160~170℃ and apply pressure to 7~8MPa, hold for 2~3 hours, and finally cool to room temperature.

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