A hydrophobic microporous urea-formaldehyde foam material and preparation method thereof

Abstract

The present invention discloses a hydrophobic microporous urea-formaldehyde foam material and a preparation method thereof, which belong to the field of polymer chemical modification. The preparation of the above-mentioned urea-formaldehyde foam material includes the following raw materials: urea-formaldehyde resin modified by amphiphilic macromolecules, a foaming agent and a curing agent, the amphiphilic macromolecules including a hydrophilic end and a hydrophobic end, the hydrophilic end is used for reaction connection with the urea-formaldehyde resin, and the hydrophobic end is used for reaction connection with the foaming agent. The present invention connects the amphiphilic macromolecule bond to the urea-formaldehyde molecular network, so that it self-assembles in the urea-formaldehyde water-based system to form a micro-nano assembly structure with rich morphology; adjusts the affinity of the foaming agent and the hydrophobic chain segments in the assembly structure, induces the foaming agent to be dispersed in the hydrophobic chain segment aggregates of the assembly, and simultaneously regulates the foaming and curing process, restricts the nucleation and growth of the foam cells and fixes them inside or around the hydrophobic chain segment aggregates of the micro-nano assembly, exerts the strong hydrophobic coating effect of the hydrophobic chain segments on the bubble wall, gives the urea-formaldehyde foam a long-lasting hydrophobic function, and realizes the construction of a microporous structure.

Description

Technical Field

[0001] The present invention relates to the field of polymer chemical modification, and in particular to a hydrophobic microporous urea-formaldehyde foam material and a preparation method thereof. Background Art

[0002] Currently commonly used building insulation foam materials, such as polystyrene (EPS) and polyurethane (PU), have excellent overall performance, but they are not heat-resistant and are highly flammable. The combustion process produces large amounts of smoke and highly toxic gases, posing serious safety risks. Urea-formaldehyde (UF) foam is a thermosetting amino foam material. Its combustion produces large amounts of inert gases such as NH3 and CO2, while also forming a dense carbonized layer on the foam surface, which prevents further flame spread and achieves flame retardancy without the addition of flame retardants. Compared with traditional insulation foam materials such as EPS and PU, UF foam not only has low production costs but also offers advantages such as high-temperature resistance, low smoke density, and the absence of droplets during combustion, making it an ideal alternative to existing building insulation foam materials. However, the large number of polar groups in the UF molecular chain makes it poorly water-resistant and easily absorbs water. This absorption of water results in significant weight gain in products, significantly reducing thermal insulation performance. Therefore, the large-scale application of UF foam-based building exterior insulation products remains a long way to go.

[0003] However, limited research has focused on the hydrophobicity and water resistance of urea-formaldehyde resins and foams. Patent application number 201910048016.2 utilizes surface treatment technology to introduce long-chain alkyl and siloxane compounds onto the surface of urea-formaldehyde foam, creating a hydrophobic and water-repellent coating. This reduces water absorption and improves the foam's hydrophobic properties. Patent application number 201410611186.4 prepares melamine-modified urea-formaldehyde foam. The introduction of melamine significantly increases the number of triazine rings in the system, increasing the activation energy for urea-formaldehyde hydrolysis and significantly improving the foam's water resistance. Other researchers have introduced the silane coupling agent KH550 during the synthesis of urea-formaldehyde resin, significantly reducing the number of hydrophilic groups and improving the material's water resistance. However, the introduction of reactive monomers significantly affects the molecular structure and synthetic reactivity of urea-formaldehyde, which in turn affects the mechanical properties of the product. The surface hydrophobic coating is prone to shedding over time, allowing water molecules to gradually diffuse into the pores and disrupt the pore structure. In addition, based on the unique molecular structure of urea-formaldehyde and its water-based foaming method, the construction of its microporous structure is extremely challenging, and there is currently no relevant literature report. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a hydrophobic microporous urea-formaldehyde foam material with good durability and excellent comprehensive performance. Another purpose of the present invention is to provide a method for preparing the above-mentioned hydrophobic microporous urea-formaldehyde foam material.

[0005] Technical solution: The hydrophobic microporous urea-formaldehyde foam material described in the present invention includes the following raw materials in parts by mass: 100 parts of urea-formaldehyde resin modified with amphiphilic macromolecules, 3-18 parts of foaming agent and 1-15 parts of curing agent, wherein the amphiphilic macromolecule includes a hydrophilic end and a hydrophobic end, the hydrophilic end includes a hydrophilic chain segment or a hydrophilic group, and the hydrophobic end includes a hydrophobic chain segment or a hydrophobic group; the hydrophilic end is used to react and connect with the urea-formaldehyde resin, and the hydrophilic end can participate in the synthesis reaction of urea-formaldehyde, and the hydrophobic end is used to react and connect with the foaming agent, and the hydrophobic end has a strong affinity with the foaming agent.

[0006] Preferably, the hydrophobic microporous urea-formaldehyde foam material comprises the following raw materials in parts by mass: 100 parts of urea-formaldehyde resin modified with amphiphilic macromolecules, 8-10 parts of foaming agent and 4-6 parts of curing agent.

[0007] Furthermore, the raw materials of the amphiphilic macromolecule-modified urea-formaldehyde resin include the following components in parts by mass: 1-15 parts of amphiphilic macromolecule, 100 parts of formaldehyde solution with a mass fraction of 37%, and 26-65 parts of urea.

[0008] Preferably, the raw materials of the amphiphilic macromolecule-modified urea-formaldehyde resin include the following components in parts by mass: 8-12 parts of amphiphilic macromolecules, 100 parts of 37 wt% formaldehyde solution and 40-43 parts of urea.

[0009] Furthermore, the mass ratio of the amphiphilic macromolecule to the foaming agent is 0.6-0.9:1.

[0010] Furthermore, the solubility of the amphiphilic macromolecule in water is greater than 0.1 g / 100 g.

[0011] Furthermore, the hydrophilic end is one or more of a primary amino group, a secondary amino group, an epoxy group, a carbamate group, a hydroxyl group, a ketone group, a phenolic hydroxyl group, an isocyanate group, and an acyl chloride group.

[0012] Furthermore, the hydrophobic end is one or more of a long-chain alkyl segment, an organosilicon segment, a phenyl group, a halogenated alkyl group, an alkyl group containing an aromatic group, an ester, an ether, an amine, or an amide, a polyoxypropylene group, an alkyl group containing a double bond, and a functional fluorine segment.

[0013] Preferably, the amphiphilic macromolecule is cetyl polyethylene glycol / polypropylene glycol-10 / 1 dimethylsiloxane (the hydrophilic chain segment is polyethylene glycol / polypropylene glycol containing active hydroxyl groups, and the hydrophobic chain segment is polydimethylsiloxane), a long-chain alkyl monocarboxyl amphiphilic porphyrin (the hydrophilic chain segment is a porphyrin containing an active carboxyl group, and the hydrophobic chain segment is a long-chain alkyl group), or an amino polyether modified silicone oil (the hydrophilic chain segment is a polyether containing an active amino group, and the hydrophobic chain segment is silicone oil).

[0014] Furthermore, the foaming agent is one or more of n-pentane, cyclopentane, n-hexane, 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane, 2,2-dimethylbutane, cyclohexane, cyclopentane, n-heptane, 2-methylhexane, 3-methylhexane, 2,4-dimethylpentane, 2,3-dimethylpentane, 2,2-dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane, 2,2,3-trimethylbutane, n-heptane, 2-methylhexane, 3-methylhexane, and dimethylvinylchlorosilane.

[0015] Preferably, the foaming agent is cyclopentane, 2-methylhexane or 2-methylpentane.

[0016] Furthermore, the curing agent is formic acid.

[0017] The preparation method of the hydrophobic microporous urea-formaldehyde foam material comprises the following steps:

[0018] (1) Preparation of urea-formaldehyde resin modified by amphiphilic macromolecules: adding amphiphilic macromolecules to a 37% formaldehyde solution by mass to obtain a reaction system, reacting at 30-50°C for 0.5-1.5h, adjusting the pH value of the system to 7.5-8.5 after the reaction, adding the first batch of urea, reacting at 50-75°C for 0.5-1.5h, adjusting the pH value of the system to 4.5-5.2 after the reaction, reacting for 2-4h, adding the second batch of urea, continuing the reaction until the system is atomized, adjusting the pH value of the system to 7.5-8.7, finally adding the third batch of urea, and reacting for 20-50min to obtain urea-formaldehyde resin modified by amphiphilic macromolecules;

[0019] (2) The urea-formaldehyde resin liquid modified with the amphiphilic macromolecule, the foaming agent and the curing agent are fully stirred and mixed, and foaming and curing are carried out in a foaming mold to obtain a hydrophobic microporous urea-formaldehyde foam material.

[0020] Furthermore, in step (1), the amount of the first batch of urea accounts for 50-82% of the total urea quality, and the amount of the second batch of urea accounts for 13-37.5% of the total urea quality; the reagent used for pH adjustment is 5-20wt% NaOH solution or 5-20wt% formic acid solution.

[0021] Furthermore, in step (2), the foaming treatment is carried out under the following conditions: foaming at 40-110° C. for 20-90 min.

[0022] Principle of the invention: The present invention connects amphiphilic macromolecules with different hydrophilic and hydrophobic ends into the urea-formaldehyde molecular network, so that they self-assemble in the urea-formaldehyde water-based resin system to form a micro-nano assembly structure with rich morphology; adjusts the affinity of the foaming agent with the hydrophobic end of the assembly, induces the foaming agent to disperse in the hydrophobic end aggregate, and at the same time regulates the foaming process to restrict the nucleation and growth of the foam cells and fix them inside or around the aggregate to achieve customization of the microporous structure; at the same time, when the foam cells are dispersed in the hydrophobic chain segment aggregate, the foam wall is firmly coated by the hydrophobic chain segment, giving the urea-formaldehyde foam a long-lasting hydrophobic function, and obtaining a hydrophobic microporous UF foam material.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) Different from the traditional microporous construction method, the present invention is based on the controllable self-assembly of amphiphilic macromolecules in the UF water-based resin system, and at the same time regulates the affinity between the foaming agent and the hydrophobic end of the micro-nano assembly and the foaming and curing process, restricts and fixes the nucleation and growth of the foam pores inside or around the micro-nano assembly, and realizes the construction of a microporous structure. The microporous structure is almost a fully closed-cell structure, which can effectively passivate the crack tip under the action of external force, limit the crack expansion, greatly improve the toughness and strength of the foam, and obtain a strong UF foam material; (2) The present invention cleverly utilizes the hydrophilic and hydrophobic properties of amphiphilic macromolecules to construct the chemical bonding effect between its hydrophilic end and the UF molecule, and at the same time exerts the hydrophobic coating effect of the hydrophobic end on the bubble wall, thereby improving the durable hydrophobic function of the foam and reducing the water absorption rate of the foam. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diagram of the cell structure of the hydrophobic microporous urea-formaldehyde foam prepared in Example 1;

[0025] Figure 2 This is a graph showing the water contact angle and water absorption rate of the hydrophobic microporous urea-formaldehyde foam prepared in Example 1. DETAILED DESCRIPTION

[0026] The present invention is further described below with reference to specific embodiments and accompanying drawings.

[0027] Example 1: The hydrophobic microporous urea-formaldehyde foam material provided in this example includes the following raw materials in parts by mass: 100 parts of urea-formaldehyde resin modified by amphiphilic macromolecular cetyl polyethylene glycol / polypropylene glycol-10 / 1 dimethylsiloxane (the hydrophilic chain segment is polyethylene glycol / polypropylene glycol containing active hydroxyl groups, and the hydrophobic chain segment is polydimethylsiloxane), 8 parts of cyclopentane as a foaming agent, and 4 parts of formic acid as a curing agent.

[0028] The preparation method of the hydrophobic microporous urea-formaldehyde foam material comprises the following steps:

[0029] (1) 8 parts of cetyl polyethylene glycol / polypropylene glycol-10 / 1 dimethylsiloxane (the hydrophilic segment is polyethylene glycol / polypropylene glycol containing active hydroxyl groups, and the hydrophobic segment is polydimethylsiloxane) are added to 100 parts of 37% formaldehyde solution and reacted at 30°C for 0.5h; the pH of the system is adjusted to 7.5 with 15% NaOH solution, the first batch of urea (20 parts) is added, and the reaction is carried out at 55°C for 0.5h; then the pH of the system is adjusted to 4.5 with 5% formic acid solution and the reaction is carried out for 2.5h; the second batch of urea (15 parts) is added and the reaction is continued until the system is atomized; then the pH of the system is adjusted to 7.5 with 15% NaOH solution, the third batch of urea (5 parts) is added, and the reaction is carried out for 20min before the material is taken out to obtain a urea-formaldehyde composite water-based resin liquid;

[0030] (2) Add 8 parts of cyclopentane and 4 parts of formic acid to 100 parts of urea-formaldehyde composite water-based resin liquid, stir at high speed for 5 minutes, pour into a foaming mold, and foam at 60°C for 30 minutes to obtain a hydrophobic microporous urea-formaldehyde foam material.

[0031] Example 2: The hydrophobic microporous urea-formaldehyde foam material provided in this example includes the following raw materials in parts by mass: 100 parts of urea-formaldehyde resin modified by monocarboxyl amphiphilic porphyrin with amphiphilic macromolecular long-chain alkyl (the hydrophilic chain segment is porphyrin containing active carboxyl groups, and the hydrophobic chain segment is a long-chain alkyl group), 4 parts of 2-methylhexane as a foaming agent, and 5 parts of formic acid as a curing agent.

[0032] The preparation method of the hydrophobic microporous urea-formaldehyde foam material comprises the following steps:

[0033] (1) 5 parts of monocarboxyl amphiphilic porphyrin with long-chain alkyl groups (the hydrophilic segment is a porphyrin containing an active carboxyl group, and the hydrophobic segment is a long-chain alkyl group) are added to 100 parts of 37% formaldehyde solution and reacted at 50°C for 1 hour; the pH of the system is adjusted to 8.2 with a 5% NaOH solution, the first batch of urea (35 parts) is added, and the reaction is carried out at 75°C for 1.5 hours; then the pH of the system is adjusted to 5.1 with a 10% formic acid solution and the reaction is carried out for 4 hours; the second batch of urea (6 parts) is added and the reaction is continued until the system is atomized; then the pH of the system is adjusted to 8.5 with a 5% NaOH solution, the third batch of urea (2 parts) is added, and the reaction is carried out for 40 minutes before the material is taken out to obtain a urea-formaldehyde composite water-based resin liquid;

[0034] (2) 4 parts of 2-methylhexane and 5 parts of formic acid were added to 100 parts of urea-formaldehyde composite water-based resin liquid, stirred at high speed for 15 minutes, poured into a foaming mold, and foamed at 100°C for 50 minutes to obtain a hydrophobic microporous urea-formaldehyde foam material.

[0035] Example 3: The hydrophobic microporous urea-formaldehyde foam material provided in this example includes the following raw materials in parts by mass: 100 parts of urea-formaldehyde resin modified with amphiphilic macromolecular amino polyether modified silicone oil (the hydrophilic chain segment is a polyether containing an active amino group, and the hydrophobic chain segment is silicone oil), 10 parts of a foaming agent 2-methylpentane, and 6 parts of a curing agent formic acid.

[0036] The preparation method of the hydrophobic microporous urea-formaldehyde foam material comprises the following steps:

[0037] (1) Add 12 parts of amino polyether modified silicone oil (the hydrophilic chain is a polyether containing active amino groups, and the hydrophobic chain is silicone oil) to 100 parts of 37% formaldehyde solution and react at 40°C for 0.8h; adjust the pH of the system to 8.0 with 10% NaOH solution, add the first batch of urea (30 parts), and react at 60°C for 1h; then adjust the pH of the system to 4.9 with 15% formic acid solution and react for 3h; add the second batch of urea (10 parts), and continue to react until the system is atomized; then adjust the pH of the system to 8.5 with 10% NaOH solution, add the third batch of urea (3 parts), react for 30min, and then take out the material to obtain a urea-formaldehyde composite water-based resin liquid;

[0038] (2) Add 10 parts of 2-methylpentane and 6 parts of formic acid to 100 parts of urea-formaldehyde composite water-based resin liquid, stir at high speed for 10 minutes, pour into a foaming mold, and foam at 70°C for 40 minutes to obtain a hydrophobic microporous urea-formaldehyde foam material.

[0039] Comparative Example 1: The preparation method of the urea-formaldehyde foam material provided in this comparative example is as follows:

[0040] (1) 100 parts of 37% formaldehyde solution were added to a three-necked flask, the pH of the system was adjusted to 7.6 with 8% NaOH solution, the first batch of urea (25 parts) was added, and the reaction was carried out at 45°C for 1.5 hours; then the pH of the system was adjusted to 4.8 with 8% formic acid solution, and the reaction was carried out for 3.5 hours; the second batch of urea (15 parts) was added, and the reaction was continued until the system was atomized; then the pH of the system was adjusted to 7.7 with 8% NaOH solution, the third batch of urea (6 parts) was added, and the reaction was carried out for 30 minutes before the material was taken out to obtain a urea-formaldehyde water-based resin liquid;

[0041] (2) 9 parts of pentane and 5 parts of formic acid were added to 100 parts of urea-formaldehyde water-based resin liquid, stirred at high speed for 10 minutes, poured into a foaming mold, and foamed at 65°C for 60 minutes to obtain a urea-formaldehyde foam material.

[0042] Comparative Example 2: The preparation method of the urea-formaldehyde foam material provided in this comparative example is as follows:

[0043] (1) 7 parts of monocarboxyl amphiphilic porphyrin with long-chain alkyl groups (the hydrophilic segment is a porphyrin containing an active carboxyl group, and the hydrophobic segment is a long-chain alkyl group) are added to 100 parts of 37% formaldehyde solution and reacted at 35°C for 1 hour; the pH of the system is adjusted to 8.1 with 15% NaOH solution, the first batch of urea (40 parts) is added, and the reaction is carried out at 75°C for 1.5 hours; then the pH of the system is adjusted to 4.7 with 15% formic acid solution and the reaction is carried out for 4 hours; the second batch of urea (10 parts) is added, and the reaction is continued until the system is atomized; then the pH of the system is adjusted to 8.6 with 15% NaOH solution, the third batch of urea (2 parts) is added, and the reaction is carried out for 20 minutes before the material is taken out to obtain a urea-formaldehyde composite water-based resin liquid;

[0044] (2) 7 parts of sodium bicarbonate and 4 parts of formic acid were added to 100 parts of urea-formaldehyde composite water-based resin liquid, stirred at high speed for 10 minutes, poured into a foaming mold, and foamed at 110°C for 45 minutes to obtain a urea-formaldehyde composite foam material.

[0045] Comparative Example 3: The preparation method of the urea-formaldehyde foam material provided in this comparative example is as follows:

[0046] (1) 30 parts of amino polyether modified silicone oil (the hydrophilic chain is a polyether containing an active amino group, and the hydrophobic chain is silicone oil) are added to 100 parts of 37% formaldehyde solution and reacted at 40°C for 1.5 hours; the pH of the system is adjusted to 8.0 with a 10% NaOH solution, and the first batch of urea (35 parts) is added and reacted at 65°C for 1.5 hours; then the pH of the system is adjusted to 4.7 with a 10% formic acid solution and reacted for 3.5 hours; the second batch of urea (8 parts) is added and the reaction is continued until the system is atomized; then the pH of the system is adjusted to 8.3 with a 10% NaOH solution, and the third batch of urea (3 parts) is added. After reacting for 35 minutes, the material is taken out to obtain a urea-formaldehyde composite water-based resin liquid;

[0047] (2) Add 10 parts of 2-methylpentane and 7 parts of formic acid to 100 parts of urea-formaldehyde composite water-based resin liquid, stir at high speed for 10 minutes, pour into a foaming mold, and foam at 100°C for 45 minutes to obtain a urea-formaldehyde composite foam material.

[0048] Comparative Example 4: The difference from Example 1 is that the amount of foaming agent used is 2 parts (the mass ratio of amphiphilic macromolecule to foaming agent is 2.7:1).

[0049] Comparative Example 5: The difference from Example 1 is that the amount of foaming agent used is 20 parts (the mass ratio of amphiphilic macromolecule to foaming agent is 0.27:1).

[0050] Comparative Example 6: The difference from Example 1 is that the amphiphilic macromolecule is replaced by the hydrophilic material polyvinyl alcohol.

[0051] Comparative Example 7: The difference from Example 1 is that the hydrophobic material polydimethylsiloxane is used instead of the amphiphilic macromolecule.

[0052] The urea-formaldehyde foaming materials prepared in Examples 1 to 3 and Comparative Examples 1 to 7 were subjected to performance tests. The results are shown in Table 1 below.

[0053] As shown in Table 1 below, the pore size of the urea-formaldehyde foaming material prepared in Example 1 is 5-10 μm, and its electron microscope image is as follows: Figure 1 As shown in the figure, the pores are regular in shape and present a nearly circular closed-cell structure; the water contact angle of the foam and the water absorption rate after immersion in water for 7 days are shown in the figure. Figure 2 As shown in the figure, its contact angle is 145.6°, and its hydrophobicity is good. After 7 days of immersion, the water absorption rate increases less. On the 7th day, the water absorption rate is only 10.12%, and the compressive strength is 24.71MPa.

[0054] In Example 2, a urea-formaldehyde resin modified with a porphyrin containing a large number of heterocyclic structures effectively blocks hydrophilic groups, improving the hydrophobicity of the urea-formaldehyde foam. Its water contact angle was 147.1°, and its water absorption after immersion in water for seven days was only 9.08%. The addition of a low-content blowing agent (4 parts 2-methylhexane) reduced the expansion ratio and cell size of the urea-formaldehyde foam, resulting in a narrow cell size distribution of 2-8 μm. The compressive strength increased to 26.98 MPa.

[0055] In Example 3, urea-formaldehyde resin was modified with aminopolyether-modified silicone oil. After foaming, the foam had a water contact angle of 146.1° and a water absorption rate of 11.01% after immersion in water for 7 days. The addition of a larger amount of blowing agent (10 parts of 2-methylpentane) resulted in a higher expansion ratio for the urea-formaldehyde foam, a wide cell size distribution within the range of 3-11 μm, and a compressive strength of 23.09 MPa.

[0056] In Comparative Example 1, the urea-formaldehyde resin was not modified with amphiphilic macromolecules. The measured pore size was larger than that in Example 1, the water contact angle was small, the hydrophobicity was poor, and the compressive strength was only 0.31 MPa. This shows that the addition of amphiphilic macromolecules can reduce the pore size of the urea-formaldehyde foaming material and improve its mechanical properties and hydrophobic properties.

[0057] In Comparative Example 2, sodium bicarbonate is used as a urea-formaldehyde resin foaming agent, which has a weak affinity with the hydrophobic chain segments of the long-chain alkyl monocarboxyl amphiphilic porphyrin. The micro-nano assembly structure formed by the amphiphilic macromolecules in the urea-formaldehyde resin liquid cannot effectively regulate the pore size and the hydrophobic properties of the foam. The pore size of the obtained urea-formaldehyde foam is significantly increased compared with Example 2, distributed in the range of 20-160 μm, the water contact angle is reduced to 129.7°, the water absorption rate after immersion in water for 7 days increases to 19.21%, and the compressive strength is only 0.89 MPa. It can be seen that the good affinity of the foaming agent with the hydrophobic chain segments of the amphiphilic macromolecules helps to obtain a hydrophobic and high-strength urea-formaldehyde foam material.

[0058] In Comparative Example 3, an excessive amount of amphiphilic macromolecular amino polyether modified silicone oil was added, which was unable to fully participate in the synthesis reaction of the urea-formaldehyde resin and was still dispersed in the urea-formaldehyde resin liquid as free molecules. During the foaming and curing process, a large number of free molecules were "expelled", and the system showed macroscopic phase separation. The pore size of the obtained foam was larger than that of Example 1, the water contact angle was reduced, the durable hydrophobicity was poor, and the compressive strength was reduced to 16.09 MPa. It can be seen that the addition of an appropriate amount of amphiphilic macromolecules can improve the compressive strength and hydrophobicity of urea-formaldehyde foam.

[0059] In Comparative Example 4, the amount of foaming agent used is only 2 parts, the foaming ratio of urea-formaldehyde is reduced, the pore size is smaller than that of Example 1, the water contact angle is 146.8°, the water absorption rate after immersion in water for 7 days is 10.58%, and the compressive strength increases to 27.78 MPa. It can be seen that a lower amount of foaming agent can obtain a smaller pore size and higher mechanical strength.

[0060] In Comparative Example 5, the amount of foaming agent used is 20 parts, the foaming ratio of urea-formaldehyde increases sharply, the pore size increases significantly to 150-400 μm compared with Example 1, the water contact angle is 136.3°, the water absorption rate after immersion in water for 7 days increases to 18.11%, and the compressive strength is only 0.34 MPa. It can be seen that excessive foaming agent will mask the regulating effect of the amphiphilic macromolecular assembly on the pore size and the hydrophobic properties of the foam, and it is impossible to obtain microporous hydrophobic urea-formaldehyde foam.

[0061] In Comparative Example 6, the urea-formaldehyde resin was modified with a hydrophilic material, polyvinyl alcohol, and the hydrophilic group content of the system was increased. Compared with Example 1, the water contact angle of the foam was reduced to 116.5°, and the water absorption rate after immersion in water for 7 days increased to 27.08%, showing strong hydrophilicity; at the same time, its pore size was 25-165 μm, and the compressive strength was 0.41 MPa. It can be seen that the introduction of hydrophilic materials into the urea-formaldehyde system cannot achieve the construction of a microporous structure and the improvement of hydrophobic properties.

[0062] In Comparative Example 7, the hydrophobic material polydimethylsiloxane modified urea-formaldehyde resin cannot be dissolved in water, so it cannot participate in the urea-formaldehyde resin synthesis reaction and is dispersed as a free molecule in the urea-formaldehyde water-based system. During the foaming and curing process, polydimethylsiloxane is gradually "expelled" and migrates to the foam surface to form an uneven hydrophobic coating, which reduces the water contact angle of the foam compared with Example 1. The water absorption rate increases to 17.13% after immersion in water for 7 days, the pore size is 20-170μm, and the compressive strength is 0.38MPa. It can be seen that the introduction of hydrophobic materials into the urea-formaldehyde system can improve its hydrophobic properties to a certain extent, but a microporous reinforced structure cannot be obtained.

[0063] Table 1 Properties of urea-formaldehyde foaming materials obtained from Examples 1 to 3 and Comparative Examples 1 to 7

[0064]

Claims

1. A hydrophobic microporous urea-formaldehyde foam material, characterized in that: The raw materials include the following by mass: 100 parts of urea-formaldehyde resin modified by amphiphilic macromolecules, 3-18 parts of blowing agent and 1-15 parts of curing agent, wherein the amphiphilic macromolecule includes a hydrophilic end and a hydrophobic end, the hydrophilic end includes a hydrophilic chain segment or a hydrophilic group, and the hydrophobic end includes a hydrophobic chain segment or a hydrophobic group; the hydrophilic end is used for reaction and connection with the urea-formaldehyde resin, the hydrophilic end participates in the synthesis reaction of urea-formaldehyde, and the hydrophobic end has a strong affinity with the blowing agent; the raw materials of the urea-formaldehyde resin modified by the amphiphilic macromolecules include the following components by mass: amphiphilic macromolecules 1-15 parts by weight, 100 parts by weight of a 37% formaldehyde solution, and 26-65 parts by weight of urea; the foaming agent is one or more of n-pentane, n-hexane, 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane, 2,2-dimethylbutane, cyclohexane, cyclopentane, 2,4-dimethylpentane, 2,3-dimethylpentane, 2,2-dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane, 2,2,3-trimethylbutane, n-heptane, 2-methylhexane, 3-methylhexane, and dimethylvinylchlorosilane.

2. The hydrophobic microporous urea-formaldehyde foam material according to claim 1, characterized in that: The mass ratio of the amphiphilic macromolecule to the foaming agent is 0.6-0.9:1, and the solubility of the amphiphilic macromolecule in water is greater than 0.1g / 100g.

3. The hydrophobic microporous urea-formaldehyde foam material according to claim 1, characterized in that: The hydrophilic end is one or more of a primary amino group, a secondary amino group, an epoxy group, a carbamate group, a hydroxyl group, a ketone group, a phenolic hydroxyl group, an isocyanate group, and an acyl chloride group.

4. The hydrophobic microporous urea-formaldehyde foam material according to claim 1, characterized in that: The hydrophobic end is one or more of a long-chain alkyl segment, an organosilicon segment, a phenyl group, a halogenated alkyl group, an alkyl group containing an aromatic group, an ester, an ether, an amine, or an amide, a polyoxypropylene group, an alkyl group containing a double bond, and a functional fluorine segment.

5. The hydrophobic microporous urea-formaldehyde foam material according to claim 1, characterized in that: The curing agent is formic acid.

6. A method for preparing the hydrophobic microporous urea-formaldehyde foam material according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Preparation of urea-formaldehyde resin modified by amphiphilic macromolecules: adding amphiphilic macromolecules to a 37 wt% formaldehyde solution, reacting at 30-50°C for 0.5-1.5h, adjusting the pH value of the system to 7.5-8.5, adding the first batch of urea, reacting at 50-75°C for 0.5-1.5h, adjusting the pH value of the system to 4.5-5.2, reacting for 2-4h, adding the second batch of urea, continuing the reaction until atomization occurs in the system, adjusting the pH value of the system to 7.5-8.7, finally adding the third batch of urea, and reacting for 20-50min to obtain urea-formaldehyde resin modified by amphiphilic macromolecules; (2) The urea-formaldehyde resin liquid modified with amphiphilic macromolecules, the foaming agent and the curing agent are fully stirred and mixed, and foaming and curing are carried out in a foaming mold to obtain a hydrophobic microporous urea-formaldehyde foam material.

7. The preparation method according to claim 6, characterized in that In step (1), the amount of the first batch of urea accounts for 50-82% of the total urea quality, and the amount of the second batch of urea accounts for 13-37.5% of the total urea quality; the reagent used for pH adjustment is 5-20 wt% NaOH solution or 5-20 wt% formic acid solution.

8. The preparation method according to claim 6, characterized in that In step (2), the foaming treatment conditions are: foaming at 40-110° C. for 20-90 min.

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