CN112920449B - Normal-pressure drying preparation method of low-density high-strength phenolic resin aerogel with extremely low shrinkage rate - Google Patents
Normal-pressure drying preparation method of low-density high-strength phenolic resin aerogel with extremely low shrinkage rate Download PDFInfo
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- 229920001568 phenolic resin Polymers 0.000 title claims abstract description 183
- 239000005011 phenolic resin Substances 0.000 title claims abstract description 183
- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical compound [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 title claims abstract description 181
- 239000004964 aerogel Substances 0.000 title claims abstract description 94
- 238000001035 drying Methods 0.000 title claims abstract description 63
- 238000002360 preparation method Methods 0.000 title claims abstract description 23
- 239000011240 wet gel Substances 0.000 claims abstract description 42
- 229920001187 thermosetting polymer Polymers 0.000 claims abstract description 41
- VKYKSIONXSXAKP-UHFFFAOYSA-N hexamethylenetetramine Chemical compound C1N(C2)CN3CN1CN2C3 VKYKSIONXSXAKP-UHFFFAOYSA-N 0.000 claims abstract description 40
- 229920001169 thermoplastic Polymers 0.000 claims abstract description 28
- 239000004416 thermosoftening plastic Substances 0.000 claims abstract description 28
- 238000000034 method Methods 0.000 claims abstract description 24
- 235000010299 hexamethylene tetramine Nutrition 0.000 claims abstract description 20
- 239000004312 hexamethylene tetramine Substances 0.000 claims abstract description 20
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims description 53
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 25
- 238000010438 heat treatment Methods 0.000 claims description 23
- 239000002243 precursor Substances 0.000 claims description 22
- 229960004011 methenamine Drugs 0.000 claims description 19
- 238000006243 chemical reaction Methods 0.000 claims description 11
- 239000000499 gel Substances 0.000 claims description 11
- 239000011148 porous material Substances 0.000 claims description 9
- 239000004966 Carbon aerogel Substances 0.000 claims description 7
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 claims description 7
- 238000002156 mixing Methods 0.000 claims description 2
- 239000002994 raw material Substances 0.000 abstract description 10
- 238000005336 cracking Methods 0.000 abstract description 8
- 239000012744 reinforcing agent Substances 0.000 abstract description 4
- 239000003431 cross linking reagent Substances 0.000 abstract description 3
- 230000007613 environmental effect Effects 0.000 abstract description 3
- 230000006835 compression Effects 0.000 description 13
- 238000007906 compression Methods 0.000 description 13
- 238000009413 insulation Methods 0.000 description 12
- 230000001965 increasing effect Effects 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- 230000010355 oscillation Effects 0.000 description 5
- 229920005989 resin Polymers 0.000 description 5
- 239000011347 resin Substances 0.000 description 5
- 238000001816 cooling Methods 0.000 description 4
- 239000000835 fiber Substances 0.000 description 4
- 239000010410 layer Substances 0.000 description 4
- 238000002791 soaking Methods 0.000 description 4
- 238000002679 ablation Methods 0.000 description 3
- 239000003990 capacitor Substances 0.000 description 3
- 230000009970 fire resistant effect Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical group [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 231100000053 low toxicity Toxicity 0.000 description 2
- 238000004321 preservation Methods 0.000 description 2
- 239000011241 protective layer Substances 0.000 description 2
- 238000012876 topography Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000012669 compression test Methods 0.000 description 1
- 239000007822 coupling agent Substances 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N phenol group Chemical group C1(=CC=CC=C1)O ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 239000000779 smoke Substances 0.000 description 1
- 239000011343 solid material Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 238000007158 vacuum pyrolysis Methods 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
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- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
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- C08J2205/00—Foams characterised by their properties
- C08J2205/02—Foams characterised by their properties the finished foam itself being a gel or a gel being temporarily formed when processing the foamable composition
- C08J2205/026—Aerogel, i.e. a supercritically dried gel
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- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2361/00—Characterised by the use of condensation polymers of aldehydes or ketones; Derivatives of such polymers
- C08J2361/04—Condensation polymers of aldehydes or ketones with phenols only
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- C08J2461/00—Characterised by the use of condensation polymers of aldehydes or ketones; Derivatives of such polymers
- C08J2461/04—Condensation polymers of aldehydes or ketones with phenols only
- C08J2461/06—Condensation polymers of aldehydes or ketones with phenols only of aldehydes with phenols
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Abstract
The invention belongs to the technical field of aerogel preparation, and particularly relates to a low-density high-strength phenolic resin aerogel normal-pressure drying preparation method with extremely low shrinkage rate. The invention aims at the problems that the phenolic resin aerogel prepared by taking the thermoplastic phenolic resin as the raw material can be obviously shrunk and cracked and the drying time is too long in the normal pressure drying process. Thermosetting phenolic resin in a certain proportion is added into a thermoplastic phenolic resin solution to serve as an aerogel reinforcing agent, and hexamethylenetetramine is used as a cross-linking agent, so that the low-density high-strength phenolic resin aerogel which is almost free of shrinkage can be prepared under the normal pressure drying condition. The invention has the advantages that: the problems of remarkable shrinkage, cracking and overlong time of the phenolic resin wet gel in the normal pressure drying process are solved. The preparation method has the advantages of simple process, environmental protection, safety, low cost and high efficiency. The prepared phenolic resin aerogel can not generate observable deformation and shrinkage, and can realize near-net forming according to application requirements.
Description
Technical Field
The invention belongs to the technical field of aerogel preparation, and particularly relates to a low-density high-strength phenolic resin aerogel normal-pressure drying preparation method with extremely low shrinkage rate.
Background
The aerogel serving as a three-dimensional porous solid material has extremely low density, extremely high porosity and specific surface area, so that the aerogel has excellent performances of heat insulation, sound insulation, adsorption, catalysis and the like, and is widely applied to the aspects of acoustics, optics, mechanics, thermal science and electricity. The phenolic resin is a low-flammability material with excellent temperature resistance, and has the advantages of low smoke rate and low toxicity in a high-temperature environment. The phenolic resin aerogel can be applied to the fields of fire-resistant sound-insulation heat-insulation layers of buildings, ablation heat-insulation layers of airship returning cabins and the like. In addition, as the phenolic resin aerogel has higher carbon residue rate, the cracking derivative can be applied to the fields of super capacitors, high-temperature heat insulation in vacuum or inert atmosphere environment and the like.
The method for preparing the phenolic resin aerogel by directly utilizing the thermoplastic phenolic resin and the hexamethylenetetramine as the raw materials is one of the existing methods, and has the characteristics of low cost, low toxicity, simple process, low requirement on equipment and the like. However, this method has an excessively long preparation period and is liable to collapse of the skeleton and shrinkage of the size during atmospheric drying. The ultrahigh porosity, specific surface area and ultralow density are particularly important properties for aerogel materials, however, the more severe the shrinkage of the prepared phenolic resin aerogel is relative to the amount of the organic solvent, the problems of the aerogel density increase, the pore shrinkage, even the generation of cracks and the like are directly caused. Meanwhile, the size shrinkage can cause the prepared phenolic resin aerogel to have poor designability and can not realize near-net forming. The existing technical means for reducing the normal pressure drying shrinkage rate of the phenolic resin aerogel mainly comprise the following steps: for example, by increasing the concentration of the thermoplastic phenolic resin in the precursor solution, the strength of the aerogel generated is higher when the concentration of the resin is higher, so that the shrinkage rate in the normal pressure drying process can be reduced to a certain extent, but the problem of overlarge aerogel density is also brought; for another example, the normal-pressure drying shrinkage rate of the phenolic resin aerogel can be reduced to a certain extent by greatly increasing the sol-gel reaction time and the reaction temperature, but the preparation time and the cost are also greatly increased; the shrinkage of the phenolic resin aerogel in the normal pressure drying process can be inhibited by introducing a three-dimensional fiber reinforced phase into the phenolic resin aerogel, but cracks and debonding can be generated inside the aerogel due to the binding of fibers in the normal pressure drying process; in addition, the shrinkage rate of the phenolic resin aerogel in the normal pressure drying process can be reduced to a certain extent by introducing other coupling agents. In order to solve the problem that the method still has a certain shrinkage rate or defect in the normal-pressure drying process, the invention adds a certain proportion of thermosetting phenolic resin into the thermoplastic phenolic resin solution to further enhance the skeleton strength of the aerogel so that the aerogel can resist the capillary force generated by evaporation of liquid in wet gel pores in the normal-pressure drying process, and the low-density high-strength phenolic resin aerogel which is almost free of shrinkage is prepared by the normal-pressure drying method. Compared with the method of directly adopting the thermoplastic phenolic resin and the hexamethylenetetramine as the raw materials, the method has higher efficiency, lower cost and can obtain the phenolic resin aerogel with lower density. In addition, all preparation periods of equipment needing to be used in the method do not exceed 12h, so that the labor and material cost caused by long-time operation of the equipment is reduced, the night operation of the equipment can be avoided, and the method is safer and more reliable.
Disclosure of Invention
The invention aims at the problem that the phenolic resin aerogel prepared by taking the thermoplastic phenolic resin and the hexamethylenetetramine as raw materials can shrink and crack obviously in the normal pressure drying process. Adding thermosetting phenolic resin in a certain proportion into a thermoplastic phenolic resin solution to serve as a skeleton reinforcing agent of aerogel, taking hexamethylenetetramine as a cross-linking agent of resin, taking ethylene glycol as a solvent, performing sol-gel reaction to obtain phenolic resin wet gel, replacing the wet gel with absolute ethyl alcohol, and performing normal-pressure drying to obtain the low-density high-strength phenolic resin aerogel with extremely low shrinkage, wherein the shrinkage of the prepared phenolic resin aerogel with different contents of all components in a precursor solution is different, and a sample with the minimum shrinkage is not more than 0.2%.
The technical scheme of the invention is as follows:
a low-density high-strength phenolic resin aerogel normal-pressure drying preparation method with extremely low shrinkage rate specifically comprises the following steps:
(1) mixing thermoplastic phenolic resin, thermosetting phenolic resin, hexamethylenetetramine and glycol in a certain proportion to prepare a precursor solution;
(2) pouring the precursor solution obtained in the step (1) into a closed container, and obtaining phenolic resin wet gel through sol-gel reaction;
(3) replacing glycol in the phenolic resin wet gel in the step (2) with absolute ethyl alcohol to obtain absolute ethyl alcohol phenolic resin wet gel;
(4) and (4) drying the absolute ethyl alcohol phenolic resin wet gel subjected to replacement in the step (3) under normal pressure to obtain the phenolic resin aerogel.
Further, in the precursor solution in the step (1), the concentration of the glycol solution of the thermoplastic phenolic resin is 0.1-0.2 g/ml; the mass ratio of the thermosetting phenolic resin to the thermoplastic phenolic resin is 1: 2-10; the mass ratio of the hexamethylene tetramine to the thermoplastic phenolic resin is 1: 5-10.
Further, the precursor solution preparation process in the step (1) is to mix the thermoplastic phenolic resin, the thermosetting phenolic resin and the ethylene glycol and then dissolve the mixture at the temperature of 150-180 ℃ for 0.5-1h, and then dissolve the hexamethylenetetramine under the temperature of 25 ℃ by ultrasonic oscillation for 2-3h to obtain the precursor solution.
The raw materials of the resin in the step (1) are all cheap industrial resin, and the regulation and control of the mechanical property, density, porosity and specific surface area of the phenolic resin aerogel can be realized by adjusting the proportion of each component in the solution, wherein the thermosetting phenolic resin is used as an aerogel reinforcing agent and can inhibit the shrinkage and cracking of wet gel in the normal pressure drying process, and the higher the content of the thermosetting phenolic resin is, the higher the density and strength of the phenolic resin aerogel is.
Further, the sol-gel reaction temperature in the step (2) is 120-180 ℃, and the time is 3-6 h.
Further, the sol-gel reaction in the step (2) is divided into two sections: firstly, carrying out sol-gel reaction at 120 ℃ for 1-3h, and then further gelling at 150-180 ℃ for 2-3h to obtain the phenolic resin wet gel.
Further, the replacement process in the step (3) is to mix absolute ethyl alcohol and the phenolic resin wet gel according to the volume ratio of 3-5:1, replace ethylene glycol by the absolute ethyl alcohol, wherein the replacement temperature is 150-.
Further, the normal pressure drying process in the step (4) is drying the absolute ethyl alcohol phenolic resin wet gel for 8-12h at 25 ℃, then drying for 2-3h at 40 ℃, and finally heating to 60 ℃ and drying for 9-10h to obtain the phenolic resin aerogel.
The invention has the beneficial effects that:
1) aiming at the problem that phenolic resin aerogel prepared by taking thermoplastic phenolic resin and hexamethylenetetramine as raw materials can shrink obviously in the normal-pressure drying process, the shrinkage problem of phenolic resin wet gel in the drying process is solved by adding a certain proportion of thermosetting phenolic resin as a reinforcing agent of an aerogel framework, and the phenolic resin aerogel with extremely low shrinkage rate is obtained. Wherein, fig. 1 and fig. 2 respectively show the micro-morphologies of the phenolic resin aerogel obtained by adding thermosetting phenolic resin and not adding thermosetting phenolic resin, and the phenolic resin aerogel has obvious pore shrinkage. In addition, the prepared phenolic resin aerogel is almost free of deformation and shrinkage, and near net forming can be realized according to application requirements. And aiming at the three-dimensional fiber reinforced phenolic resin aerogel composite material, the phenolic resin aerogel with extremely low shrinkage rate can not generate torn cracks, overlarge pores and the like in the fiber because of the problem of severe shrinkage.
2) When the concentration of the prepared phenolic resin solution is lower, the prepared wet gel is easier to shrink in the process of drying at normal pressure, the shrinkage degree is higher, and when the concentration is lower than a certain degree, the phenolic resin aerogel loses the pore structure because of too severe shrinkage in the process of drying at normal pressure. Compared with the preparation method which directly adopts the thermoplastic phenolic resin and the hexamethylenetetramine as the raw materials, the method can further reduce the total dosage of the two resins on the basis of the existing technical means, and still can achieve the effect of almost no shrinkage, thereby obtaining the phenolic resin aerogel with higher porosity and lower density. In the preparation method without adding the thermosetting phenolic resin, if the dosage of the phenolic resin is further reduced, the aerogel can be seriously shrunk, even cracked and lose the pore structure.
3) The method has the advantages of simple preparation process, environmental protection, safety, low cost, high efficiency and the like. The prepared sample has excellent compression resistance, and cracks or fractures do not occur even if the sample is compressed by 90% (as shown in figure 3). And has a certain elasticity, no crack or fracture is generated after 100 compression-rebound times under the condition of 50% strain, and the rebound rate of the 99 th time is kept at 50% (as shown in figure 4).
4) In addition, the mechanical property, the density, the porosity, the specific surface area and the like of the phenolic resin aerogel can be changed by adjusting the content of each component, and the phenolic resin aerogel has stronger designability. The adjustment and control of the mechanical properties are shown in fig. 5, which shows a stress-strain curve of the phenolic resin aerogel with different component contents when the compressive strain is 60% (wherein, PA15-9/1-7/2 shows that the concentration of the thermoplastic phenolic resin relative to ethylene glycol is 0.15g/ml, the ratio of the thermoplastic phenolic resin to hexamethylenetetramine is 9:1, and the ratio of the thermoplastic phenolic resin to the thermosetting phenolic resin is 7: 2). It can be seen from the figure that samples with different component contents have different compression resistance and show a certain regularity, and the higher the content of the added thermosetting phenolic resin, the better the compression resistance, and the better the resistance to the capillary shrinkage force in the normal pressure drying process. In addition, due to different raw material dosages, the density, the porosity and the specific surface area of the raw materials are different and have certain regularity.
5) In the invention, as the phenolic resin has higher carbon residue rate, the phenolic resin can be directly converted into the carbon aerogel after being subjected to high-temperature vacuum pyrolysis at 1000 ℃ for 1-2h by 800-.
6) The phenolic resin aerogel in the invention can be used in the fields of building fire-resistant sound-insulation heat-insulation layers, aircraft ablation protective layers and the like. Meanwhile, the cracking derivative can be applied to the fields of super capacitors, high-temperature heat insulation in vacuum or inert atmosphere environments and the like.
Drawings
FIG. 1 shows the microstructure of the aerogel complete skeleton after the thermosetting phenolic resin is added.
Fig. 2 is a microstructure of an aerogel skeleton collapse without added thermosetting phenolic resin.
Figure 3 is a 90% stress-strain curve for aerogel compression after addition of a thermosetting phenolic resin.
Figure 4 is a 50% strain compression-rebound curve for 100 cycles of aerogel after addition of thermosetting phenolic resin.
Figure 5 is a 60% stress-strain curve for 5 aerogel compression after addition of thermosetting phenolic resin.
FIG. 6 is a microstructure of aerogel cracked derivatives after addition of thermosetting phenolic resin.
Fig. 7 is a microstructure of a cleaved derivative of aerogel without added thermosetting phenolic resin.
Detailed Description
The following further describes a specific embodiment of the present invention with reference to the drawings and technical solutions.
Example 1
In this example, two kinds of phenolic resin aerogels with thermosetting phenolic resin added and without thermosetting phenolic resin added were prepared respectively. The specific implementation mode is as follows:
(1) adding 1.5g of powdered thermoplastic phenolic resin and 0.214g of powdered thermosetting phenolic resin into 10ml of ethylene glycol solution to serve as a group 1 (containing thermosetting phenolic resin), adding 1.714g of powdered thermoplastic phenolic resin into 10ml of ethylene glycol solution to serve as a group 2 (containing no thermosetting phenolic resin and having the same total content of phenolic resin in the two groups of solutions), placing the two groups of phenolic resin solutions on a heating platform at 150 ℃ for heating for 30min, cooling, adding 0.214g of hexamethylenetetramine into the two groups of solutions respectively, and dissolving for 3h by ultrasonic oscillation assistance to obtain a precursor solution;
(2) pouring the prepared precursor solution into a closed container, and preserving heat for 1h in a heating box at the temperature of 120 ℃ and preserving heat for 3h at the temperature of 150 ℃ to obtain phenolic resin wet gel;
(3) taking out the crosslinked phenolic resin wet gel, soaking the crosslinked phenolic resin wet gel in 50ml of absolute ethyl alcohol, and placing the soaked phenolic resin wet gel on a heating platform at 180 ℃ for replacement for 6 hours to obtain absolute ethyl alcohol phenolic resin wet gel;
(4) and (3) drying the replaced sample at 25 ℃ for 8h, heating the sample in a drying oven at 40 ℃ for 2h, and finally drying the sample at 60 ℃ for 10h to obtain two phenolic resin aerogels.
Wherein the sample of group 1 containing thermosetting phenolic resin had a porosity of 88.99% and a density of 0.1436g/cm3The shrinkage rate is 3.8 percent, and the micro-morphology is shown in figure 1; sample set 2, which did not contain the thermosetting phenolic resin, had a porosity of 81.09% and a density of 0.2448g/cm3The shrinkage rate is 15.37%, the micro-topography is shown in fig. 2, and the micro-topography of the two groups shows that the pore shrinkage of the sample in the group 2 is very obvious compared with that of the sample in the group 1.
Example 2
In this embodiment, the compression performance of several phenolic resin aerogels with different contents of thermosetting phenolic resin or hexamethylenetetramine added thereto is tested and compared (as shown in fig. 5), the stronger the compression resistance, the stronger the resistance of the phenolic resin aerogel to normal pressure drying shrinkage, and further, the compressive stress-strain curve can further prove that the added thermosetting phenolic resin can resist the shrinkage capillary force generated in the drying process by enhancing the strength of the aerogel skeleton. The specific implementation mode is as follows:
(1) respectively weighing 5 groups of thermoplastic phenolic resins with the mass of 1.5g, respectively adding 0.428g of thermosetting phenolic resin into the first 3 groups, respectively adding 0.214g of thermosetting phenolic resin into the remaining one group (namely, the 4 th group), adding 0.642g of thermosetting phenolic resin into the remaining last group (namely, the 5 th group), respectively adding the five groups of phenolic resins into 10ml of ethylene glycol, heating the mixture on a heating platform at 180 ℃ for 30min, respectively adding 0.167g, 0.214g and 0.3g of hexamethylenetetramine into the first three groups after cooling, respectively adding 0.214g of hexamethylenetetramine into the 4 th group and the 5 th group, and dissolving the mixtures for 3h by ultrasonic oscillation assistance to obtain 5 groups of precursor solutions with different raw material ratios;
(2) pouring the prepared precursor solution into a self-made mold, and preserving heat for 2h in a heating box at 120 ℃ and preserving heat for 3h at 150 ℃ to obtain phenolic resin wet gel;
(3) taking out the crosslinked phenolic resin wet gel, soaking the crosslinked phenolic resin wet gel in 30ml of absolute ethyl alcohol, and placing the soaked phenolic resin wet gel on a heating platform at the temperature of 150 ℃ for replacement for 5 hours to obtain absolute ethyl alcohol phenolic resin wet gel;
(4) drying the replaced sample at 25 ℃ for 8h, then heating in a drying oven at 40 ℃ for 3h, and finally drying at 60 ℃ for 9h to obtain 5 groups of phenolic resin aerogel with extremely low shrinkage, wherein the sample PA15-7/1-7/1 with the largest shrinkage is not more than 4%, and the sample PA15-5/1-7/2 with the smallest shrinkage is not more than 0.2%;
(5) mechanical property tests are carried out on 5 groups of samples, and the result shows that the more thermosetting phenolic resin is added, the stronger the compression resistance of the phenolic resin aerogel is (according to the fact that the added thermosetting phenolic resin respectively corresponds to three curves of red, orange and yellow in a graph 5 from low to high), and the compression resistance of the phenolic resin aerogel shows a trend that the compression resistance is firstly reduced and then increased along with the increase of the consumption of the cross-linking agent hexamethylenetetramine (respectively corresponds to three curves of blue, orange and green in a graph 5), wherein the stronger the compression resistance of the samples is also smaller in the normal pressure drying shrinkage rate;
(6) the PA15-5/1-7/2 sample of fig. 5 was further subjected to compression tests, as shown in fig. 3 and fig. 4, wherein fig. 3 shows a stress-strain curve obtained by compressing the aerogel by 90%, no cracking of the sample was observed, but the sample was plastically deformed greatly, wherein fig. 4 shows a cyclic compression-rebound curve of the aerogel, the strain was 100 times at 50% cycle, no cracking of the sample was observed, and the rebound rate was maintained at 50% after 99 times of compression.
Example 3
In this embodiment, a precursor solution (containing thermosetting phenolic resin) with a low phenolic resin concentration is used to prepare a low-density high-strength phenolic resin aerogel with a very low shrinkage rate (< 2%) under normal pressure drying, and the low-density high-strength phenolic resin aerogel is cracked at 800 ℃ to obtain a carbon aerogel (fig. 6), and the specific implementation manner is as follows:
(1) adding 1.166g of powdered thermoplastic phenolic resin and 0.334g of powdered thermosetting phenolic resin into 10ml of ethylene glycol, placing the mixture on a heating platform at 150 ℃ for heating for 30min, cooling, adding 0.2332g of hexamethylenetetramine, and dissolving for 2h by ultrasonic oscillation to obtain a precursor solution;
(2) pouring the prepared precursor solution into a closed container, and preserving heat for 1h in a heating box at the temperature of 120 ℃ and preserving heat for 3h at the temperature of 150 ℃ to obtain phenolic resin wet gel;
(3) taking out the crosslinked phenolic resin wet gel, soaking the crosslinked phenolic resin wet gel in 50ml of absolute ethyl alcohol, and placing the soaked phenolic resin wet gel on a heating platform at the temperature of 150 ℃ for replacement for 8 hours to obtain absolute ethyl alcohol phenolic resin wet gel;
(4) drying the replaced sample at 25 ℃ for 12h, heating in a drying oven at 40 ℃ for 3h, and drying at 60 ℃ for 9h to obtain the almost non-shrinkage phenolic resin aerogel with the porosity, density and shrinkage of 90.55 percent and 0.1204g/cm respectively3And 1.2%;
(5) the phenolic resin aerogel is subjected to heat preservation for 2 hours at 800 ℃ in a vacuum environment to obtain the carbon aerogel, the micro morphology of which is shown in figure 6, and the carbon aerogel has uniform pore distribution.
Comparative example 1
This comparative example prepared a phenolic aerogel with a normal pressure drying shrinkage of 25.86% using a precursor solution (without thermosetting phenolic resin) having the same concentration of phenolic resin as in example 3 and cracked at 800 ℃ to obtain a carbon aerogel (fig. 7), and the specific embodiment is as follows:
(1) adding 1.5g of powdery thermoplastic phenolic resin into 10ml of ethylene glycol, placing the mixture on a heating platform at 150 ℃ for heating for 30min, cooling, adding 0.2332g of hexamethylenetetramine, and dissolving for 2h by ultrasonic oscillation to obtain a precursor solution;
(2) pouring the prepared precursor solution into a closed container, and preserving heat for 1h in a heating box at the temperature of 120 ℃ and preserving heat for 3h at the temperature of 150 ℃ to obtain phenolic resin wet gel;
(3) taking out the crosslinked phenolic resin wet gel, soaking the crosslinked phenolic resin wet gel in 50ml of absolute ethyl alcohol, and placing the soaked phenolic resin wet gel on a heating platform at the temperature of 150 ℃ for replacement for 8 hours to obtain absolute ethyl alcohol phenolic resin wet gel;
(4) the replaced sample is firstly dried for 12 hours at 25 ℃, then heated for 3 hours in a drying oven at 40 ℃, and finally dried for 9 hours at 60 ℃, the sample shrinks very obviously, and the porosity, density and shrinkage are 71.16 percent and 0.3040g/cm respectively3And 25.86%;
(5) the micro morphology of the obtained carbon aerogel is shown in FIG. 7 after the phenolic resin aerogel is subjected to heat preservation for 2 hours in a vacuum environment at 800 ℃, and the fact that the aerogel is severely shrunk and loses the porous characteristic due to insufficient cracking can be seen.
In the invention, the phenolic resin is rapidly dissolved in the ethylene glycol in a heating mode in the process of preparing the precursor solution, so that the dissolving time is greatly shortened; the replacement process does not need to replace the absolute ethyl alcohol, and the mutual flow between the absolute ethyl alcohol and the glycol is driven by a flat plate heating method by utilizing the principle that the convection phenomenon can occur when the fluid is heated unevenly, so that the replacement time is greatly shortened; in addition, the aerogel has higher compression resistance, so that the drying can be carried out at higher temperature and higher speed, and the drying time is greatly shortened. In conclusion, the invention has the characteristics of simple preparation process, low cost, short preparation period, safety, environmental protection, strong size designability and the like. The prepared product has excellent mechanical property, and can be applied to the fields of fire-resistant sound-insulation heat-insulation layers of buildings, ablation protective layers of airship re-entry cabins and the like. In addition, the cracking derivative can also be applied to the fields of super capacitors, high-temperature heat insulation in vacuum or inert atmosphere environments and the like. The present invention is not limited to the above embodiment, and the ratio of each phase may be increased as necessary without departing from the scope of the present invention.
Claims (10)
1. A low-density high-strength phenolic resin aerogel normal-pressure drying preparation method with extremely low shrinkage rate is characterized by comprising the following steps:
(1) mixing thermoplastic phenolic resin, thermosetting phenolic resin, hexamethylenetetramine and glycol in a certain proportion to prepare a precursor solution;
(2) pouring the precursor solution obtained in the step (1) into a closed container, and obtaining phenolic resin wet gel through sol-gel reaction;
(3) replacing glycol in the phenolic resin wet gel in the step (2) with absolute ethyl alcohol to obtain absolute ethyl alcohol phenolic resin wet gel;
(4) and (4) drying the absolute ethyl alcohol phenolic resin wet gel subjected to replacement in the step (3) under normal pressure to obtain the phenolic resin aerogel.
2. The atmospheric drying method for preparing low-density high-strength phenolic resin aerogel with extremely low shrinkage rate as claimed in claim 1, wherein in the precursor solution of step (1), the concentration of the glycol solution of the thermoplastic phenolic resin is 0.1-0.2 g/ml; the mass ratio of the thermosetting phenolic resin to the thermoplastic phenolic resin is 1: 2-10; the mass ratio of the hexamethylene tetramine to the thermoplastic phenolic resin is 1: 5-10.
3. The normal pressure drying preparation method of the low-density high-strength phenolic resin aerogel with the extremely low shrinkage rate as claimed in claim 1 or 2, characterized in that the precursor solution preparation process in step (1) is to mix the thermoplastic phenolic resin, the thermosetting phenolic resin and the ethylene glycol and then dissolve them at the temperature of 150-.
4. The method for preparing low-density high-strength phenolic resin aerogel with extremely low shrinkage at normal pressure and drying as claimed in claim 1 or 2, wherein the sol-gel reaction temperature in step (2) is 120-180 ℃ and the time is 3-6 h.
5. The method for preparing low-density high-strength phenolic resin aerogel with extremely low shrinkage at normal pressure and drying as claimed in claim 3, wherein the sol-gel reaction temperature in step (2) is 120-180 ℃ for 3-6 h.
6. The method for preparing the low-density high-strength phenolic resin aerogel with extremely low shrinkage at normal pressure and dry according to claim 4, is characterized in that the sol-gel reaction in the step (2) is divided into two stages: firstly, carrying out sol-gel reaction at 120 ℃ for 1-3h, and then further gelling at 150-180 ℃ for 2-3h to obtain the phenolic resin wet gel.
7. The normal pressure drying preparation method of low-density high-strength phenolic resin aerogel with extremely low shrinkage rate as claimed in claim 1, 2, 5 or 6, wherein the replacement process in step (3) is to mix absolute ethyl alcohol and phenolic resin wet gel according to the volume ratio of 3-5:1, replace ethylene glycol with absolute ethyl alcohol at the replacement temperature of 150-.
8. The normal pressure drying preparation method of low-density high-strength phenolic resin aerogel with extremely low shrinkage rate as claimed in claim 3, wherein the replacement process in step (3) is to mix absolute ethyl alcohol and phenolic resin wet gel according to a volume ratio of 3-5:1, replace ethylene glycol with absolute ethyl alcohol, wherein the replacement temperature is 150-.
9. The method for preparing the low-density high-strength phenolic resin aerogel with extremely low shrinkage at normal pressure by drying according to the claims 1, 2, 5, 6 or 8, wherein the normal pressure drying process in the step (4) is drying the absolute ethyl alcohol phenolic resin wet gel at 25 ℃ for 8-12h, then drying at 40 ℃ for 2-3h, and finally heating to 60 ℃ for drying for 9-10h to obtain the phenolic resin aerogel.
10. The normal pressure drying preparation method of low-density high-strength phenolic resin aerogel with extremely low shrinkage rate as claimed in claim 1, 2, 5, 6 or 8, wherein the prepared low-density high-strength phenolic resin aerogel can be converted into carbon aerogel with uniformly distributed pores through 1-2h under the vacuum condition of 800-1000 ℃.
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| CN111040233A (en) * | 2019-11-29 | 2020-04-21 | 华东理工大学 | Foam framework reinforced organic aerogel and preparation method thereof |
| CN111748172A (en) * | 2019-03-29 | 2020-10-09 | 中国科学院化学研究所 | Modified phenolic resin and preparation method and application thereof |
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