Production method of melamine foamed plastic with ultralow formaldehyde residue

Abstract

The invention provides a production method of melamine foam plastic with ultralow formaldehyde residue, which comprises the following steps: mixing melamine and paraformaldehyde in a molar ratio of 1: (1.5-1.9) with water, carrying out hydroxymethylation reaction, adding an amino-terminated hyperbranched polymer, and carrying out pre-polycondensation reaction, thereby obtaining the melamine foam plastic with ultralow formaldehyde residue. A hyperbranched modified melamine-formaldehyde resin prepolymerization solution is obtained; mixing the hyperbranched modified melamine-formaldehyde resin prepolymer with an emulsifier, a foaming agent, a curing agent, a graphite phase carbon nitride / reduced graphene oxide composite photocatalyst and potassium persulfate serving as a cocatalyst, and performing microwave foaming to obtain a primary foam product; and carrying out post-curing treatment, putting the treated melamine foam into a closed circulating treatment bin provided with a photocatalytic reactor, introducing steam, and carrying out decomposition and purification treatment and drying, so as to obtain the melamine foam plastic with ultralow formaldehyde residue. The invention solves the problems of high residual quantity of formaldehyde in the melamine foam plastic and complex and low-efficiency subsequent treatment process.

Description

Technical Field

[0001] This invention relates to a method for producing melamine foam, specifically a method for producing melamine foam with ultra-low formaldehyde residue, belonging to the field of polymer foam material technology. Background Technology

[0002] Melamine foam is a lightweight polymer material with a three-dimensional network open-cell structure, made from melamine-formaldehyde resin as a matrix through foaming and curing. Due to its inherent high flame retardancy, excellent sound absorption and heat insulation properties, resistance to high and low temperatures, and chemical stability, it is widely used in aerospace, rail transportation, architectural acoustics, industrial insulation, and daily cleaning products.

[0003] The production and application of traditional melamine foam have always faced the problem of formaldehyde residue and release. Formaldehyde, as one of the main raw materials, does not undergo a completely irreversible reaction during resin synthesis. Therefore, the final foam product contains two main sources of formaldehyde: firstly, free formaldehyde remaining from incomplete reactions during synthesis; and secondly, chemically unstable groups formed in the foam structure, such as terminal hydroxymethyl and methylene ether bonds. These groups slowly hydrolyze under humid and hot conditions, continuously releasing new formaldehyde, posing a potential threat to human health and the environment.

[0004] To address this issue, numerous technological explorations have been undertaken. For example, reducing the initial formaldehyde dosage by lowering the molar ratio of formaldehyde to melamine in the raw materials often comes at the cost of sacrificing the crosslinking degree of the resin and the mechanical strength of the final product. Other technologies employ methods such as adding small-molecule formaldehyde scavengers like urea to the resin, or soaking and washing the finished foam and post-treating it with chemical reagents. While these methods have shown some effectiveness, they generally suffer from low efficiency, long processing cycles, potential secondary pollution, increased energy consumption, and higher wastewater treatment costs. Furthermore, some studies have proposed introducing photocatalysts during the resin condensation stage for catalytic degradation under ultraviolet light. However, ultraviolet light has limited penetration depth into high-viscosity and opaque resin foaming slurries, resulting in uneven catalytic efficiency and incomplete degradation, making it difficult to achieve deep removal of formaldehyde from the system. Summary of the Invention

[0005] Based on the above background, the purpose of this invention is to provide a production method for melamine foam with ultra-low formaldehyde residue, thereby solving the problems of high formaldehyde residue in melamine foam and complex and inefficient subsequent processing in the prior art.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] A method for producing ultra-low formaldehyde residue melamine foam, the method comprising the following steps:

[0008] Melamine and paraformaldehyde in a molar ratio of 1:(1.5-1.9) were mixed with water and subjected to hydroxymethylation at a pH of 8.5-9.0. A terminal amino hyperbranched polymer was added to the resulting hydroxymethyl melamine solution, with the amount of terminal amino hyperbranched polymer being 5-15% of the mass of melamine. The pH of the solution was adjusted to 5.5-6.5, and a pre-condensation reaction was carried out until the solution reached the preset viscosity. The reaction was then stopped to obtain a hyperbranched modified melamine-formaldehyde resin prepolymer solution.

[0009] The hyperbranched modified melamine-formaldehyde resin prepolymer liquid is mixed with emulsifier, foaming agent, curing agent, graphitic carbon nitride / reduced graphene oxide composite photocatalyst and potassium persulfate as a co-catalyst to form a foaming slurry. The slurry is then microwave-foamed under visible light irradiation to obtain the initial foam product.

[0010] After the initial foam product undergoes post-curing treatment, it is placed in a closed circulation processing chamber equipped with a photocatalytic reactor. Steam at a temperature of 110-130℃ is introduced into the chamber for decomposition and purification treatment. After the treatment, it is dried to obtain ultra-low formaldehyde residue melamine foam plastic.

[0011] At the resin synthesis source, a low aldehyde-amine ratio and the introduction of terminal amino hyperbranched polymers with a large number of active amine groups are used. This not only efficiently captures free formaldehyde, but also reduces the number of unstable structures by forming more stable chemical bonds through reaction with hydroxymethyl groups. Its unique hyperbranched structure also plays a toughening role. During the foaming process, a visible light responsive photocatalyst is introduced. Taking advantage of the excellent penetrability of visible light, the formaldehyde newly generated during foaming and curing is deeply degraded. The steam catalytic cycle purification method can actively induce and remove residual and potential formaldehyde in the finished product, avoiding the inefficiency and secondary pollution of traditional post-treatment methods.

[0012] Preferably, the terminal amino hyperbranched polymer is a terminal amino hyperbranched polyether, and the preparation method of the terminal amino hyperbranched polyether includes the following steps:

[0013] Starting with trimethylolpropane as the core, under anhydrous and oxygen-free conditions and with potassium hydroxide as the catalyst, anionic ring-opening polymerization was carried out with propylene oxide at 110-120℃. After the reaction was completed, the mixture was neutralized with acid to obtain a terminal hydroxyl hyperbranched polyether with a molecular weight of 4000-6000 g / mol.

[0014] The terminal hydroxyl hyperbranched polyether was placed in a high-pressure reactor, a nickel-copper composite catalyst was added, and ammonia and hydrogen were introduced until the pressure reached 14-15 MPa. The temperature was raised to 200-210°C and the reaction was carried out for 8-10 hours. After the reaction was completed, the mixture was cooled, filtered, and deammoniated to obtain an amino-terminated hyperbranched polyether with an amine value of not less than 15 mg KOH / g.

[0015] Amino-terminated hyperbranched polyethers have a flexible polyether core and a large number of highly active terminal primary amine groups. Compared with linear polymers, their three-dimensional dendritic topology can provide more formaldehyde reaction sites and more effective steric hindrance toughening effect.

[0016] Preferably, in the anionic ring-opening polymerization, the propylene oxide is added dropwise after the reaction system reaches the reaction temperature, and the dropwise addition time is 3-4 hours. The molar ratio of potassium hydroxide to trimethylolpropane is 0.5-0.8:1.

[0017] By slowly adding monomers to effectively control the intense exothermic polymerization reaction and controlling the amount of catalyst, it is beneficial to obtain polymers with a narrower molecular weight distribution. This results in a more regular structure and more uniform performance of the final terminal amino product, thus making the toughening effect and formaldehyde capture ability of melamine resin more stable when it is modified.

[0018] Preferably, the preparation method of the graphitic carbon nitride / reduced graphene oxide composite photocatalyst includes:

[0019] Urea was placed in a covered crucible and heated to 550-600°C in a muffle furnace at a rate of 5-8°C / min. It was then calcined at a constant temperature for 4-5 hours, cooled naturally, and ground to obtain graphitic carbon nitride powder.

[0020] Graphene oxide was ultrasonically dispersed in water to form a graphene oxide dispersion of 0.5-0.7 mg / mL.

[0021] The graphitic carbon nitride powder was added to the graphene oxide dispersion at a mass ratio of 9-10:1, and ultrasonic dispersion was continued for 30-40 minutes. Hydrazine hydrate was added, with the amount of hydrazine hydrate being 2-3 times the mass of graphene oxide. The reaction was stirred in a water bath at 85-95°C. After the reaction was completed, the mixture was filtered and washed alternately with deionized water and ethanol until neutral. Finally, it was dried in a vacuum oven at 55-60°C for 12-14 hours to obtain the graphitic carbon nitride / reduced graphene oxide composite photocatalyst.

[0022] Preferably, when preparing the graphitic carbon nitride powder, after natural cooling and grinding, it is stirred in a nitric acid solution with a concentration of 2-4 mol / L at 60-80°C for 2-3 hours, filtered, washed until neutral, and dried.

[0023] The acid treatment step can etch and strip the bulk graphitic carbon nitride, increasing its specific surface area and exposing more catalytic active sites, giving the graphitic carbon nitride a porous nanosheet structure, thereby improving the light absorption capacity and photogenerated carrier separation efficiency of the photocatalyst.

[0024] Preferably, the emulsifier is sodium dodecylbenzenesulfonate, the foaming agent is n-pentane, and the curing agent is formic acid.

[0025] Sodium dodecylbenzenesulfonate can form a stable oil-in-water emulsion system; n-pentane, as a physical foaming agent, has a moderate boiling point and can provide good foaming effect under microwave heating; formic acid, as an acidic curing agent, has high catalytic efficiency and can ensure that the foam can be quickly cured and formed after foaming.

[0026] Preferably, the temperature of the pre-condensation reaction is controlled at 70-75°C, and the preset viscosity is 220-280 mPa·s.

[0027] Preferably, the post-curing treatment is performed at a temperature of 180-220°C for 1.2-1.5 hours.

[0028] Preferably, the method for preparing the photocatalyst filled in the photocatalytic reactor includes the following steps:

[0029] The graphitic carbon nitride / reduced graphene oxide composite photocatalyst is loaded onto a honeycomb ceramic carrier with a pore density of 300-400 pores / square inch and a wall thickness of 0.15-0.35 mm at a loading rate of 8-10 g / L through impregnation, pulling, drying, and calcination.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] This invention discloses a method for producing ultra-low formaldehyde residue melamine foam, which controls formaldehyde throughout the entire process. Through source capture modification, visible light catalysis during the process, and terminal purification, the formaldehyde release of the resulting melamine foam is reduced to an ultra-low level of 0.05 mg / L. The terminal amino hyperbranched polymer introduced in this invention not only acts as a formaldehyde scavenger to reduce unstable structures at the source, but its unique three-dimensional flexible structure also acts as a toughening agent embedded in the resin network, improving the flexibility and mechanical properties of the foam and overcoming the performance degradation of melamine foam caused by traditional low formaldehyde-amine ratio methods. This invention uses a visible light-responsive graphitic carbon nitride / reduced graphene oxide composite photocatalyst to overcome the problem of poor ultraviolet light penetration, enabling deep in-situ degradation of newly generated formaldehyde inside the high-viscosity foaming slurry during the curing process. The steam catalytic circulation purification method of this invention induces the release and gas-phase catalytic decomposition of residual formaldehyde in the initial foam product, with high treatment efficiency and a cleaner and more environmentally friendly process route. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0033] Figure 1 These are formaldehyde emission variation curves from performance tests of Examples 1-2 and Comparative Examples 1-4 of the present invention. Detailed Implementation

[0034] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0035] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art. Unless otherwise specified, the components or equipment in the following embodiments are general standard parts or components known to those skilled in the art, and their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0036] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In this detailed description, numerous specific details are set forth to facilitate explanation and provide a thorough understanding of the embodiments of the present invention. However, one or more embodiments may be practiced by those skilled in the art without these specific details.

[0037] This invention discloses a method for producing ultra-low formaldehyde residue melamine foam, the method comprising the following steps:

[0038] Melamine and paraformaldehyde in a molar ratio of 1:(1.5-1.9) were mixed with water and subjected to hydroxymethylation at a pH of 8.5-9.0. A terminal amino hyperbranched polymer was added to the resulting hydroxymethyl melamine solution, with the amount of terminal amino hyperbranched polymer being 5-15% of the mass of melamine. The pH of the solution was adjusted to 5.5-6.5, and a pre-condensation reaction was carried out until the solution reached the preset viscosity. The reaction was then stopped to obtain a hyperbranched modified melamine-formaldehyde resin prepolymer solution.

[0039] Hyperbranched modified melamine-formaldehyde resin prepolymer was mixed with emulsifier, foaming agent, curing agent, graphitic carbon nitride / reduced graphene oxide composite photocatalyst and potassium persulfate as a co-catalyst to form a foaming slurry. The slurry was then microwave-foamed under visible light irradiation to obtain the initial foam product.

[0040] After the initial foam product undergoes post-curing treatment, it is placed in a closed circulation processing chamber equipped with a photocatalytic reactor. Steam at a temperature of 110-130℃ is introduced into the chamber for decomposition and purification treatment. After the treatment, it is dried to obtain ultra-low formaldehyde residue melamine foam plastic.

[0041] The design principle of the production method for ultra-low formaldehyde residual melamine foam is explained below.

[0042] In the resin synthesis stage, a low aldehyde-amine ratio (below stoichiometry) is first used to reduce the absolute amount of formaldehyde at the source. More importantly, a terminal amino hyperbranched polymer with a three-dimensional dendritic topology and numerous terminal primary amine groups is introduced. These highly reactive amine groups can capture free formaldehyde molecules in the system and undergo nucleophilic substitution reactions with the hydroxymethyl groups on hydroxymethyl melamine, forming chemically stable methylene amine bonds (-NH-CH2-NH-), replacing the methylene ether bonds (-NH-CH2-O-CH2-NH-) that readily hydrolyze and release formaldehyde under humid and hot conditions. Simultaneously, the flexible core of this polymer is introduced into the rigid triazine ring crosslinked network, providing a toughening effect.

[0043] During foaming and curing, a small amount of formaldehyde molecules still dissociate due to the shift in chemical equilibrium. The graphitic carbon nitride / reduced graphene oxide (g-C3N4 / rGO) composite photocatalyst introduced in this invention, under visible light irradiation, excites electrons in the valence band to the conduction band, forming photogenerated electron-hole pairs. Since the Fermi level of rGO is lower than the conduction band of g-C3N4, the photogenerated electrons rapidly transfer to the rGO surface, effectively suppressing electron-hole recombination. The separated holes possess strong oxidizing properties, directly oxidizing formaldehyde adsorbed on the catalyst surface, while electrons can react with oxygen to generate superoxide radicals, and holes can react with water to generate hydroxyl radicals. These reactive oxygen species can oxidize and decompose formaldehyde into carbon dioxide and water. The excellent penetrability of visible light ensures that this degradation process occurs uniformly throughout the entire foaming slurry system.

[0044] For the small amount of free formaldehyde and unreacted terminal hydroxymethyl groups remaining in the initial foam product, this invention uses high-temperature, high-humidity steam as a hydrolysis promoter to accelerate the hydrolysis of unstable chemical bonds, inducing the release of potential formaldehyde in the solid phase into free formaldehyde in the gas phase. The humid, hot gas carrying formaldehyde is extracted by a circulating fan and sent to a photocatalytic reactor. In this reactor, a photocatalyst supported on honeycomb ceramics completely decomposes the gaseous formaldehyde under visible light irradiation. The purified gas is then returned to the treatment chamber to continue inducing and carrying new formaldehyde molecules. This cycle is repeated until the residual formaldehyde in the initial foam product is removed below the detection limit. Compared with the traditional soaking method, this process is orders of magnitude more efficient and generates virtually no waste liquid.

[0045] The method of the present invention will be further described in detail below with reference to several embodiments and comparative examples.

[0046] Example 1

[0047] Preparation of amino-terminated hyperbranched polyethers

[0048] Starting with trimethylolpropane (TMP), anionic ring-opening polymerization of propylene oxide was carried out under anhydrous and oxygen-free conditions with potassium hydroxide as a catalyst at 115°C. The molar ratio of potassium hydroxide to TMP was 0.7:1. To effectively control the exothermic reaction, propylene oxide was added dropwise after the reaction system reached the specified temperature, with the addition time controlled at 3.5 hours. After polymerization, the mixture was neutralized with acid to obtain a hydroxyl-terminated hyperbranched polyether intermediate with a number-average molecular weight (Mn) of approximately 5100 g / mol. Subsequently, this intermediate was subjected to amination reaction in an autoclave using a nickel-copper composite catalyst. The reaction was carried out at 210°C and 15 MPa for 8 hours under an ammonia and hydrogen atmosphere. After the reaction, post-treatment yielded the target product, an amino-terminated hyperbranched polyether, with an amine value of 18.5 mg KOH / g.

[0049] Preparation of graphitic carbon nitride / reduced graphene oxide composite photocatalyst

[0050] Urea was placed in a covered crucible and heated to 550°C in a muffle furnace at a rate of 5°C / min, and calcined at this temperature for 4 hours to obtain bulk graphitic carbon nitride (g-C3N4). To increase its specific surface area and active sites, the obtained g-C3N4 powder was stirred in a 2 mol / L nitric acid solution at 60°C for 3 hours, filtered, washed until neutral, and dried to obtain acid-treated optimized porous nanosheet g-C3N4.

[0051] Then, acid-treated g-C3N4 powder was mixed with a 0.5 mg / mL aqueous dispersion of graphene oxide at a mass ratio of 10:1. The mixture was homogenized under ultrasonication, and then hydrazine hydrate (twice the mass of graphene oxide) was added, followed by chemical reduction at 95°C. After washing and drying, the final graphitic carbon nitride / reduced graphene oxide composite photocatalyst was obtained.

[0052] Production of ultra-low formaldehyde residual melamine foam

[0053] In a reactor, melamine and paraformaldehyde were mixed at a molar ratio of 1:1.9, water was added, and a hydroxymethylation reaction was carried out at pH 8.8 and 70°C. After a period of reaction, 15% (by weight) of terminal amino-terminated hyperbranched polyether of melamine was added, and the pH of the system was adjusted to 6.0. Prepolymerization was then carried out at 75°C. When the solution viscosity reached 280 mPa·s, the solution was cooled and discharged to obtain a hyperbranched modified melamine-formaldehyde resin prepolymer solution.

[0054] Take 100 parts by weight of the above prepolymer liquid and mix it with 10 parts sodium dodecylbenzenesulfonate (emulsifier), 20 parts n-pentane (foaming agent), 1.5 parts graphitic carbon nitride / reduced graphene oxide composite photocatalyst, 1.0 part potassium persulfate, and 12 parts formic acid (curing agent). Prepare a uniform foaming slurry in a high-speed emulsifier. Place the foaming slurry in a mold, expose it to visible light, and then place it in a microwave oven to foam and mold, obtaining the initial foam product.

[0055] The initial foam sample was post-cured at 200°C for 1.5 hours. Subsequently, it was transferred to a circulating purification chamber for purification under a 120°C steam atmosphere. The gas within the chamber circulated through a photocatalytic reactor, which contained a catalyst prepared by loading a graphitic carbon nitride / reduced graphene oxide composite photocatalyst at a loading of 10 g / L onto a honeycomb ceramic carrier with a pore density of 300-400 pores / square inch and a wall thickness of 0.15-0.35 mm. After purification, the sample was dried with hot air to constant weight to obtain the final product.

[0056] Example 2

[0057] The preparation steps are the same as in Example 1, except that:

[0058] In the production process of ultra-low formaldehyde residue melamine foam, the molar ratio of melamine to paraformaldehyde is adjusted to 1:1.5. The amount of terminal amino hyperbranched polymer added is 5% of the mass of melamine. The final viscosity of the prepolymerization reaction is controlled at 220 mPa·s.

[0059] Comparative Example 1

[0060] The preparation steps are the same as in Example 1, except that:

[0061] Instead of preparing terminal amino hyperbranched polyethers, an equal mass of deionized water was added during the production of ultra-low formaldehyde residue melamine foam. All other steps and parameters were the same as in Example 1.

[0062] Comparative Example 2

[0063] The preparation steps are the same as in Example 1, except that:

[0064] In the production process of ultra-low formaldehyde residue melamine foam, the graphitic carbon nitride / reduced graphene oxide composite photocatalyst was not prepared, and neither was the graphitic carbon nitride / reduced graphene oxide composite photocatalyst nor potassium persulfate was added. All other steps and parameters were the same as in Example 1.

[0065] Comparative Example 3

[0066] The preparation steps are the same as in Example 1, except that:

[0067] In the production process of ultra-low formaldehyde residue melamine foam, the initial foam product, after post-curing treatment, is not transferred to the circulating purification chamber but is directly dried. All other steps and parameters are the same as in Example 1.

[0068] Comparative Example 4

[0069] Using conventional preparation methods, the molar ratio of melamine to formaldehyde was 1:2.5, and 5% urea was added as a scavenging agent for resin synthesis. No photocatalyst was added during foaming. After foaming, the foam was soaked and washed three times in 80°C hot water for 2 hours each time, and then dried.

[0070] The foam samples prepared in the above embodiments and comparative examples were subjected to performance tests. The test methods are as follows, and the test results are shown in Table 1. The formaldehyde release variation curves are shown in the figure. Figure 1 As shown.

[0071] Formaldehyde emission: According to GB / T 18580-2017 "Indoor decoration and renovation materials - formaldehyde emission limits in artificial boards and their products", the samples were placed in an environment of (23±2)℃ and (45±5)%RH for 14 consecutive days.

[0072] Compression permanent deformation: Tested after holding at 70℃ and 50% compression for 22 hours in accordance with GB / T 6669-2008.

[0073] Table 1 Performance test results of the examples and comparative examples

[0074]

[0075] from Figure 1 As can be seen, the formaldehyde release curves of Examples 1 and 2 remained below the instrument detection limit of 0.05 mg / L throughout the entire 14-day test period. Meanwhile, as shown in Table 1, Example 1 exhibited a compression set as low as 6.5%, demonstrating excellent resilience.

[0076] Comparative Example 1, without the addition of the terminal amino hyperbranched polymer, exhibited a formaldehyde release curve significantly higher than that of Example 1, with a formaldehyde release of up to 1.1 mg / L on day 14. More importantly, its compression set value deteriorated sharply to 15.8%. This confirms that the introduced terminal amino hyperbranched polymer not only chemically immobilizes free formaldehyde but also optimizes the foam's skeletal structure as a toughening agent.

[0077] Comparative Example 2, which did not add a photocatalyst during foaming, exhibited a significantly higher formaldehyde release curve than Example 1, with a release of 0.8 mg / L on day 14. Its physical properties (compression set of 6.9%) were similar to those of Example 1, because it also used a terminal amino-terminated hyperbranched polymer. This confirms that the shift in chemical equilibrium during the high-temperature foaming and curing process still releases new formaldehyde. Without photocatalytic degradation during the process, newly generated formaldehyde remains in the cured resin matrix.

[0078] Comparative Example 3, which did not undergo steam catalytic circulation purification, showed a formaldehyde release of 1.5 mg / L on day 14, but its physical properties remained good. This confirms that unstable terminal hydroxymethyl groups and other potential formaldehyde exist in foam plastics. Treating only free formaldehyde and some unstable structures will not prevent the continued release of these potential formaldehydes, leading to long-term excessive formaldehyde emissions.

[0079] The formaldehyde release curve of Comparative Example 4 was the highest throughout, reaching 2.3 mg / L on day 14. Simultaneously, its compression set also reached 12.5%, far inferior to the embodiments of this invention. This indicates that conventional techniques, such as adding urea, have a much lower formaldehyde capture efficiency than the three-dimensional hyperbranched polymer of this invention, while the depth and efficiency of hot water soaking and washing are far inferior to the induced release and catalytic decomposition effect of this invention.

[0080] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for producing ultra-low formaldehyde residue melamine foam, characterized in that: The method includes the following steps: Melamine and paraformaldehyde in a molar ratio of 1:(1.5-1.9) were mixed with water and subjected to hydroxymethylation at a pH of 8.5-9.

0. A terminal amino hyperbranched polymer was added to the resulting hydroxymethyl melamine solution, with the amount of terminal amino hyperbranched polymer being 5-15% of the mass of melamine. The pH of the solution was adjusted to 5.5-6.5, and a pre-condensation reaction was carried out until the solution reached the preset viscosity. The reaction was then stopped to obtain a hyperbranched modified melamine-formaldehyde resin prepolymer solution. The hyperbranched modified melamine-formaldehyde resin prepolymer liquid is mixed with emulsifier, foaming agent, curing agent, graphitic carbon nitride / reduced graphene oxide composite photocatalyst and potassium persulfate as a co-catalyst to form a foaming slurry. The slurry is then microwave-foamed under visible light irradiation to obtain the initial foam product. After the initial foam product undergoes post-curing treatment, it is placed in a closed circulation processing chamber equipped with a photocatalytic reactor. Steam at a temperature of 110-130℃ is introduced into the chamber for decomposition and purification treatment. After the treatment, it is dried to obtain ultra-low formaldehyde residue melamine foam plastic.

2. The production method of ultra-low formaldehyde residue melamine foam according to claim 1, characterized in that: The terminal amino hyperbranched polymer is a terminal amino hyperbranched polyether, and the preparation method of the terminal amino hyperbranched polyether includes the following steps: Starting with trimethylolpropane as the core, under anhydrous and oxygen-free conditions and with potassium hydroxide as the catalyst, anionic ring-opening polymerization was carried out with propylene oxide at 110-120℃. After the reaction was completed, the mixture was neutralized with acid to obtain a terminal hydroxyl hyperbranched polyether with a molecular weight of 4000-6000 g / mol. The terminal hydroxyl hyperbranched polyether was placed in a high-pressure reactor, a nickel-copper composite catalyst was added, and ammonia and hydrogen were introduced until the pressure reached 14-15 MPa. The temperature was raised to 200-210°C and the reaction was carried out for 8-10 hours. After the reaction was completed, the mixture was cooled, filtered, and deammoniated to obtain an amino-terminated hyperbranched polyether with an amine value of not less than 15 mg KOH / g.

3. The production method of ultra-low formaldehyde residue melamine foam according to claim 2, characterized in that: In the anionic ring-opening polymerization, the propylene oxide is added dropwise after the reaction system reaches the reaction temperature, and the dropwise addition time is 3-4 hours. The molar ratio of potassium hydroxide to trimethylolpropane is 0.5-0.8:

1.

4. The production method of ultra-low formaldehyde residue melamine foam according to claim 1, characterized in that: The preparation method of the graphitic carbon nitride / reduced graphene oxide composite photocatalyst includes: Urea was placed in a covered crucible and heated to 550-600°C in a muffle furnace at a rate of 5-8°C / min. It was then calcined at a constant temperature for 4-5 hours, cooled naturally, and ground to obtain graphitic carbon nitride powder. Graphene oxide was ultrasonically dispersed in water to form a graphene oxide dispersion of 0.5-0.7 mg / mL. The graphitic carbon nitride powder was added to the graphene oxide dispersion at a mass ratio of 9-10:1, and ultrasonic dispersion was continued for 30-40 minutes. Hydrazine hydrate was added, with the amount of hydrazine hydrate being 2-3 times the mass of graphene oxide. The reaction was stirred in a water bath at 85-95°C. After the reaction was completed, the mixture was filtered and washed alternately with deionized water and ethanol until neutral. Finally, it was dried in a vacuum oven at 55-60°C for 12-14 hours to obtain the graphitic carbon nitride / reduced graphene oxide composite photocatalyst.

5. The production method of ultra-low formaldehyde residue melamine foam according to claim 4, characterized in that: In preparing the graphitic carbon nitride powder, after natural cooling and grinding, it is stirred in a 2-4 mol / L nitric acid solution at 60-80°C for 2-3 hours, filtered, washed until neutral, and dried.

6. The production method of ultra-low formaldehyde residue melamine foam according to claim 1, characterized in that: The emulsifier is sodium dodecylbenzenesulfonate, the foaming agent is n-pentane, and the curing agent is formic acid.

7. The production method of ultra-low formaldehyde residue melamine foam according to claim 1, characterized in that: The temperature of the prepolymerization reaction is controlled at 70-75°C, and the preset viscosity is 220-280 mPa·s.

8. The production method of ultra-low formaldehyde residue melamine foam according to claim 1, characterized in that: The post-curing treatment is carried out at a temperature of 180-220°C for 1.2-1.5 hours.

9. The production method of ultra-low formaldehyde residue melamine foam according to claim 1, characterized in that: The method for preparing the photocatalyst filled in the photocatalytic reactor includes the following steps: The graphitic carbon nitride / reduced graphene oxide composite photocatalyst is loaded onto a honeycomb ceramic carrier with a pore density of 300-400 pores / square inch and a wall thickness of 0.15-0.35 mm at a loading rate of 8-10 g / L through impregnation, pulling, drying, and calcination.

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