Degradable flame-retardant phenolic aerogel as well as preparation method and application thereof

Abstract

The invention discloses degradable flame-retardant phenolic aerogel as well as a preparation method and application thereof, and the preparation method comprises the following steps: mixing a phenolic compound, an aldehyde compound, water, arylboronic acid or a derivative thereof and a catalyst according to a ratio, and carrying out primary hydrothermal reaction at 70-100 DEG C for 0.5-3 hours; after the first hydrothermal reaction is completed, cooling, then adding a flame retardant, and carrying out a second hydrothermal reaction at 120-160 DEG C for 0.5-6 hours to obtain phenolic hydrogel; freezing and drying the phenolic aldehyde hydrogel, and curing to obtain phenolic aldehyde aerogel; the flame retardant is selected from at least one of aluminum hydroxide, magnesium oxychloride, antimony trioxide and zinc borate. The additive flame retardant is added at the later stage of the hydrothermal reaction, so that the damage to the network structure of the phenolic resin is avoided, the heat resistance and the mechanical property of the phenolic aerogel are prevented from being reduced, and the phenolic aerogel is obvious in light weight effect, good in flame retardant property and good in mechanical property.

Description

Technical Field

[0001] The invention belongs to the technical field of electrode material preparation, and specifically relates to a degradable flame-retardant phenolic aerogel and a preparation method and application thereof. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Aerogel is a nano-scale porous network structure composed of colloidal particles or polymers. It has excellent properties such as low thermal conductivity, low density, and low dielectric constant, and has broad application prospects. Aerogel has high porosity and small pore size, which can effectively block air, hinder the combustion process, and reduce the flame propagation speed. Moreover, aerogel has extremely low thermal conductivity, and the infinitely extended heat conduction path can absorb combustion heat, reduce the flame temperature, and make it difficult to maintain the thermal decomposition temperature. It has good flame retardant properties and thermal insulation effects.

[0004] Phenolic aerogel is usually prepared from highly active phenol and aldehyde monomers through a sol-gel process and an aging process to obtain an organic wet gel, which is then subjected to a solvent replacement process and a special drying process. Its preparation cycle is long, the monomer is expensive and toxic, the supercritical drying equipment is expensive, and the operation process is complicated and dangerous, making it difficult to achieve commercial production. In addition, since the solidified phenolic resin neither dissolves nor melts, phenolic aerogel is difficult to degrade and recycle. For the interior and secondary load-bearing structures (such as antenna beams, floors, head covers, etc.) of rail transit vehicles prepared from phenolic aerogel, when its service life ends, or after the interior and other structures of the vehicle are updated, a large amount of solid waste is generated. If the phenolic aerogel is difficult to degrade and recycle, a large amount of solid waste will be accumulated, occupying a large amount of valuable space, and causing pollution to the environment.

[0005] In addition, for the load-bearing structure in rail transit vehicles, high requirements are placed on the mechanical properties of the matrix material, and in order to ensure the safety of the vehicle, high requirements are placed on the flame retardant properties of related materials. However, the flame retardant properties of phenolic aerogel need to be improved, and the mechanical properties of phenolic aerogel are relatively weak, making it difficult to meet increasingly high application requirements. Summary of the invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide a degradable flame-retardant phenolic aerogel and a preparation method and application thereof.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a degradable flame-retardant phenolic aerogel, comprising the following steps:

[0009] After mixing the phenolic compound, the aldehyde compound, water, the arylboronic acid or its derivative and the catalyst in proportion, the first hydrothermal reaction is carried out at 70-100° C. for 0.5-3 h;

[0010] After the first hydrothermal reaction is completed, the temperature is lowered, and then a flame retardant is added thereto, and a second hydrothermal reaction is carried out at 120-160° C. for 0.5-6 h to obtain a phenolic hydrogel;

[0011] The phenolic hydrogel is freeze-dried and solidified to obtain a phenolic aerogel;

[0012] The flame retardant is selected from at least one of aluminum hydroxide, strong magnesium oxide, antimony trioxide and zinc borate.

[0013] In some embodiments, the molar ratio of the phenolic compound, the aldehyde compound, the catalyst and the arylboronic acid or its derivative is 100:50-90:0.5-5:10-40.

[0014] Preferably, the molar ratio of the phenolic compound, water and flame retardant is 100:0 to 50:1-15.

[0015] When using formaldehyde aqueous solution, no additional water is needed. When using powdered paraformaldehyde, water needs to be added.

[0016] In some embodiments, the phenolic compound is one or a mixture of phenol, o-cresol, m-cresol, p-cresol, naphthol, nonylphenol, cardanol, propylphenol, butylphenol, pentylphenol or decylphenol.

[0017] In some embodiments, the aldehyde compound is a mixture of one or more of aqueous formaldehyde solution, paraformaldehyde, acetaldehyde, trioxymethylene or furfural.

[0018] The formaldehyde aqueous solution is commercially available formalin, in which the mass percentage of formaldehyde is about 37%.

[0019] In some embodiments, the catalyst is selected from at least one of potassium carbonate, sodium carbonate, aqueous ammonia, magnesium oxide, barium hydroxide, or triethylamine.

[0020] In some embodiments, the aryl boronic acid or its derivative is selected from at least one of phenylboronic acid, hydroxymethylphenylboronic acid, biphenylboronic acid, diphenylboronic acid, dimethylphenylboronic acid, isopropylphenylboric acid, 1,4-phenyldiboric acid, methylphenylboric acid, ethylphenylboric acid, and butylphenylboric acid.

[0021] In some embodiments, the temperature of the first hydrothermal reaction is 80-100° C. and the time is 1-3 h.

[0022] Preferably, the temperature of the first hydrothermal reaction is 85-90° C. and the time is 1.5-2.5 h.

[0023] In some embodiments, the temperature of the second hydrothermal reaction is 120-160° C. and the time is 2-6 h.

[0024] Preferably, the temperature of the second hydrothermal reaction is 140-160° C. and the time is 2-4 h.

[0025] In some embodiments, the freeze-drying step is: first freezing the phenolic hydrogel at -15 to -25°C for 10 to 20 hours, and then freeze-drying to obtain the phenolic xerogel.

[0026] Preferably, the curing conditions are: curing the obtained phenolic xerogel at 110-130° C. for 1-3 h, and then curing it at 170-190° C. for 2-5 h, to obtain phenolic aerogel.

[0027] Further preferably, the curing conditions are: curing the obtained phenolic xerogel at 115-125° C. for 1.5-2.5 h, and then curing at 170-180° C. for 3-5 h, to obtain phenolic aerogel.

[0028] More preferably, the curing conditions are: curing the obtained phenolic xerogel at 120° C. for 2 h, and then curing it at 175° C. for 4 h, to obtain phenolic aerogel.

[0029] In some embodiments, after the second hydrothermal reaction is completed and the temperature is lowered, a step of soaking and washing the product with deionized water is also included.

[0030] The number of soaking and washing is 2-5 times, preferably 3 times.

[0031] In a second aspect, the present invention provides a degradable flame-retardant phenolic aerogel prepared by the preparation method.

[0032] In a third aspect, the present invention provides the use of the degradable flame-retardant phenolic aerogel in preparing rail transit vehicle interiors or secondary load-bearing structures.

[0033] In some embodiments, the secondary load-bearing structure is an antenna beam, a floor, or a head cover.

[0034] In a fourth aspect, the present invention provides a degradation and recovery method of the degradable flame-retardant phenolic aerogel, comprising the following steps: immersing the phenolic aerogel or the phenolic aerogel-based solid waste in an organic solvent or a mixture of an organic solvent and water at 30-90° C. until degradation is complete.

[0035] In some embodiments, the organic solvent is ethanol or acetone.

[0036] Preferably, in the mixture of the organic solvent and water, the mass ratio of the organic solvent to water is 0.2-20:1.

[0037] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0038] In view of the defect that traditional phenolic aerogel is difficult to degrade, the present invention introduces degradable dynamic boric acid phenol ester structure and BOB structure, and uses the characteristics of hydrolysis or alcoholysis to give phenolic aerogel degradability.

[0039] Adding the additive flame retardant in the later stage of the hydrothermal reaction avoids the destruction of the phenolic resin network structure, thereby avoiding the decrease of the heat resistance and mechanical properties of the phenolic aerogel, and effectively improving the mechanical properties of the phenolic aerogel; the additive flame retardant has no chemical bond with the phenolic aerogel, so it does not affect the degradability of the phenolic aerogel;

[0040] The preparation process is simple to operate, has low energy consumption, low cost, and is easy to control;

[0041] The degradation process is safe, environmentally friendly, green and pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0043] Figure 1 This is the degradation process of the phenolic aerogel in the mixed solution of ethanol and water in the embodiment of the present invention. DETAILED DESCRIPTION

[0044] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0045] The present invention will be further described below in conjunction with the embodiments.

[0046] Example 1

[0047] A method for preparing a degradable flame-retardant phenolic aerogel comprises the following steps:

[0048] Phenol, paraformaldehyde, water, phenylboric acid and potassium carbonate were mixed in proportion and subjected to the first hydrothermal reaction at 90°C for 2h;

[0049] After the first hydrothermal reaction is completed, the temperature is lowered, and then aluminum hydroxide is added thereto, and a second hydrothermal reaction is carried out at 130° C. for 3 hours. After the second hydrothermal reaction is completed, the temperature is naturally lowered, and after solid-liquid separation, the product is soaked and washed three times with deionized water to obtain a phenolic hydrogel;

[0050] The molar ratio of phenol, paraformaldehyde, potassium carbonate, phenylboric acid, water and aluminum hydroxide is 100:60:4:30:30:10;

[0051] The phenolic hydrogel was frozen at -20°C for 15 hours and then freeze-dried using a freeze dryer to obtain a phenolic xerogel. The phenolic xerogel was first cured at 120°C for 2 hours and then cured at 180°C for 4 hours to obtain a phenolic aerogel.

[0052] Example 2

[0053] A method for preparing a degradable flame-retardant phenolic aerogel comprises the following steps:

[0054] After mixing o-cresol, acetaldehyde, water, hydroxymethylphenylboric acid and sodium carbonate in proportion, the first hydrothermal reaction was carried out at 70° C. for 3 h;

[0055] After the first hydrothermal reaction is completed, the temperature is lowered, and then antimony trioxide is added thereto, and a second hydrothermal reaction is carried out at 160° C. for 2 h. After the second hydrothermal reaction is completed, the temperature is naturally lowered, and after solid-liquid separation, the product is soaked and washed three times with deionized water to obtain a phenolic hydrogel;

[0056] The molar ratio of o-cresol, acetaldehyde, sodium carbonate, hydroxymethylphenylboric acid, water and antimony trioxide is 100:50:5:40:50:15;

[0057] The phenolic hydrogel was frozen at -20°C for 10 hours and then freeze-dried using a freeze dryer to obtain a phenolic xerogel. The phenolic xerogel was first cured at 130°C for 2 hours and then cured at 170°C for 3 hours to obtain a phenolic aerogel.

[0058] Example 3

[0059] A method for preparing a degradable flame-retardant phenolic aerogel comprises the following steps:

[0060] After m-cresol, trioxymethylene, water, dimethylphenylboric acid and magnesium oxide were mixed in proportion, the first hydrothermal reaction was carried out at 80°C for 3h;

[0061] After the first hydrothermal reaction is completed, the temperature is lowered, and then zinc borate is added thereto, and a second hydrothermal reaction is carried out at 120° C. for 5 hours. After the second hydrothermal reaction is completed, the temperature is naturally lowered, and after solid-liquid separation, the product is soaked and washed three times with deionized water to obtain a phenolic hydrogel;

[0062] The molar ratio of m-cresol, trioxymethylene, magnesium oxide, dimethylphenylboric acid, water and zinc borate is 100:50:0.5:40:10:1;

[0063] The phenolic hydrogel was frozen at -20°C for 20 hours and then freeze-dried using a freeze dryer to obtain a phenolic xerogel. The phenolic xerogel was first cured at 130°C for 3 hours and then cured at 170°C for 2 hours to obtain a phenolic aerogel.

[0064] The relevant performance parameters of the phenolic aerogels prepared in Examples 1-3 were tested, and the test results are shown in Table 1.

[0065] The test method for the residual carbon rate is as follows: using a thermal gravimetric analyzer, heating the temperature to 800°C at a rate of 10°C / min in a nitrogen atmosphere, with a nitrogen flow rate of 35 mL / min.

[0066] The test method for compressive strength is as follows: refer to GB / T 1448-2005 standard, the specimen is Type I specimen, and the size is 30mm×10mm×10mm.

[0067] The test method for the degradation rate is as follows: take 1g of phenolic aerogel, put it into a 10ml single screw cap glass bottle containing 3.6g of mixed solvent, screw on the cap (do not screw it completely), and degrade at 70℃ for 2h. Filter the degraded solution and dry it at 90℃ to constant weight. Figure 1 shown.

[0068] Table 1

[0069] Example Residual carbon rate (%) Compression strength(MPa) Degradation rate (%) Example 1 65.7 1.08 99.5 Example 2 64.2 1.56 97.2 Example 3 64.9 1.84 95.4

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a degradable flame-retardant phenolic aerogel, characterized in that: The steps include: After mixing the phenolic compound, the aldehyde compound, water, the arylboronic acid or its derivative and the catalyst in proportion, the first hydrothermal reaction is carried out at 70-100° C. for 0.5-3 h; After the first hydrothermal reaction is completed, the temperature is lowered, and then a flame retardant is added thereto, and a second hydrothermal reaction is carried out at 120-160° C. for 0.5-6 h to obtain a phenolic hydrogel; The phenolic hydrogel is freeze-dried and solidified to obtain a phenolic aerogel; The flame retardant is selected from at least one of aluminum hydroxide, strong magnesium oxide, antimony trioxide and zinc borate.

2. The method for preparing the degradable flame-retardant phenolic aerogel according to claim 1, characterized in that: The molar ratio of the phenolic compound, the aldehyde compound, the catalyst and the arylboronic acid or its derivative is 100:50-90:0.5-5:10-40; Preferably, the molar ratio of the phenolic compound, water and flame retardant is 100:0 to 50:1-15.

3. The method for preparing the degradable flame-retardant phenolic aerogel according to claim 1 or 2, characterized in that: The phenolic compound is one or a mixture of phenol, o-cresol, m-cresol, p-cresol, naphthol, nonylphenol, cardanol, propylphenol, butylphenol, pentylphenol or decylphenol; Or, the aldehyde compound is a mixture of one or more of formaldehyde solution, paraformaldehyde, acetaldehyde, trioxymethylene or furfural; Or, the catalyst is selected from at least one of potassium carbonate, sodium carbonate, ammonia water, magnesium oxide, barium hydroxide or triethylamine; Or, the aryl boronic acid or its derivative is at least one selected from phenylboronic acid, hydroxymethylphenylboric acid, biphenylboric acid, diphenylboric acid, dimethylphenylboric acid, isopropylphenylboric acid, 1,4-phenyldiboric acid, methylphenylboric acid, ethylphenylboric acid, and butylphenylboric acid.

4. The method for preparing the degradable flame-retardant phenolic aerogel according to claim 1 or 2, characterized in that: The temperature of the first hydrothermal reaction is 80-100°C and the time is 1-3h; Preferably, the temperature of the first hydrothermal reaction is 85-90° C. and the time is 1.5-2.5 h.

5. The method for preparing the degradable flame-retardant phenolic aerogel according to claim 4, characterized in that: The temperature of the second hydrothermal reaction is 120-160°C and the time is 2-6h; Preferably, the temperature of the second hydrothermal reaction is 140-160° C. and the time is 2-4 h.

6. The method for preparing the degradable flame-retardant phenolic aerogel according to claim 1, characterized in that: The freeze drying comprises: first freezing the phenolic hydrogel at -15 to -25°C for 10 to 20 hours, and then freeze drying to obtain the phenolic xerogel; Preferably, the curing conditions are: curing the obtained phenolic xerogel at 110-130° C. for 1-3 hours, and then curing at 170-190° C. for 2-5 hours to obtain phenolic aerogel; Preferably, the curing conditions are: curing the obtained phenolic xerogel at 115-125° C. for 1.5-2.5 h, and then curing at 170-180° C. for 3-5 h to obtain phenolic aerogel; Preferably, the curing conditions are: curing the obtained phenolic xerogel at 120° C. for 2 h, and then curing it at 175° C. for 4 h, to obtain phenolic aerogel.

7. A degradable flame-retardant phenolic aerogel, characterized in that: Prepared by the preparation method described in any one of claims 1 to 6.

8. Use of the degradable flame-retardant phenolic aerogel according to claim 7 in preparing rail transit vehicle interiors or secondary load-bearing structures; Preferably, the secondary bearing structure is an antenna beam, a floor or a head cover.

9. The method for degrading and recycling the degradable flame-retardant phenolic aerogel according to claim 7, characterized in that: The method comprises the following steps: immersing the phenolic aerogel or the phenolic aerogel-based solid waste in an organic solvent or a mixed solution of an organic solvent and water at 30-90° C. until degradation is complete.

10. The method for recycling the degradable flame-retardant phenolic aerogel according to claim 9, characterized in that: The organic solvent is ethanol or acetone; Preferably, in the mixture of the organic solvent and water, the mass ratio of the organic solvent to water is 0.2-20:1.

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