CN114933732B - Composite super-thermal-insulation aerogel with active and passive structures and preparation method thereof - Google Patents
Composite super-thermal-insulation aerogel with active and passive structures and preparation method thereof Download PDFInfo
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Abstract
The invention provides a composite super-heat-insulation aerogel with an active and passive structure and a preparation method thereof. The aerogel containing the active heat absorption structure and the passive heat insulation structure has light weight, low heat conductivity and super heat insulation performance in a high-temperature environment, and therefore has great potential in the field of heat preservation and insulation, particularly in the heat insulation application in the high-temperature environment.
Description
Technical Field
The invention belongs to the field of composite material heat insulation, and particularly relates to super heat insulation aerogel with an active absorption and passive heat insulation structure, and a preparation method and application thereof.
Background
In recent years, insulation materials have been rapidly developed and temperature and heat transfer control are of paramount importance in many fields. Particularly for firefighters and spacemen, extremely high temperature environments are often encountered, and efficient heat insulation materials are urgently needed. In addition, in high altitude areas or desert areas, special strong ultraviolet radiation and high temperature environments exist, and heat insulation materials with excellent performance are required.
Common insulation materials can be divided into two categories. One type is a porous structured passive insulation material, including fibers, foams, aerogels, and the like. Among them, the aerogel has been receiving attention because the special structure of low density and high porosity can greatly reduce the heat convection and heat conduction effects, thereby exhibiting excellent heat insulation properties. Some of the recent research efforts have even produced aerogel Thermal Insulation Materials with Thermal conductivities less than air (Thermal conductivity 0.026W/mK) (Ghaffari Mosanzadeh, S.; alshrah, M.; saadtnia, Z.double Dian height Back Polymer adhesives with Enhanced Thermal Insulation. Macromolecular Materials and Engineering,2020,305,1900777; qin, Y.; peng, Q.; zhu, Y.Lightweight, mechanical flexible and mechanical Insulation rGO/Polyvinylide foam with isolated silica nanoparticles 3262-4903). However, it is particularly noted that when the ambient temperature is high, heat can be transmitted directly by heat radiation without passing through air. At this time, even if the thermal conductivity of the aerogel material is lower than that of air (0.03W/mK), even close to vacuum, the aerogel material cannot effectively block heat.
The second type of insulating material is typically a phase change material. Phase change materials are materials that undergo a phase transition over a range of temperatures, thereby consuming thermal energy. By utilizing the characteristic of the phase-change material, heat can be well absorbed, and the temperature can be well isolated. However, since the phase-change material generally absorbs heat through the transition from the solid state to the liquid state, the liquid state causes inconvenience in storage and use. In recent years, there have been few studies on application of a porous material as a packaging container in which a phase change material is stored in the field of heat insulation. However, leakage of the phase-change material is always inevitable.
Disclosure of Invention
The invention aims to solve the defects in the prior art and provides a composite super-heat-insulation aerogel with an active and passive structure and a preparation method thereof.
The invention adopts the following technical scheme:
the utility model provides a compound super thermal-insulated aerogel that possesses passive structure of initiative contains initiative heat absorption structure and passive thermal-insulated structure simultaneously, and initiative heat absorption structure is azobenzene and cyclodextrin inclusion structure, and passive hot protective structure is for having the aerogel open cell structure of multistage size.
The base material of the composite super-heat-insulation aerogel with the active and passive structure is two or more than two hydrophilic polymers, wherein the polymer with a plurality of cyclodextrins is called a host polymer, and the polymer with a plurality of azobenzene groups is called a guest polymer.
The host polymer has more than 10 cyclodextrin groups, the guest polymer has more than 10 azobenzene groups, and the molar ratio of the cyclodextrin groups to the azobenzene groups is 1:1-1:5.
The inclusion of host and guest is generated between the cyclodextrin group and the azobenzene group.
The porous material has a hierarchical pore structure of nanometer and micron, and the porosity is more than 89.5%.
The solid content is 5-25mg/mL.
The thermal conductivity is 0.0397W/mK or less.
At high temperatures (greater than 100 degrees celsius), the thermal insulation capability is superior to that of thermal insulation materials with the same thermal conductivity.
Under the ultraviolet environment, the heat insulation capability is better than that of a heat insulation material with the same heat conductivity.
The invention also provides a preparation method of the composite super heat insulation aerogel with the active and passive structure, which comprises the following steps:
(1) Dissolving the host polymer crosslinked cyclodextrin and the guest polymer azo modified chitosan in water respectively, and then uniformly mixing the host and guest mixtures according to the molar ratio of the cyclodextrin to the azobenzene of 1:1-1. The total solid content in the mixed solution is controlled to be 5-25mg/mL, and the optimized content is 7-15mg/mL. Self-assembling the uniform mixed solution for 4-12 hours at normal temperature to form the clathrate hydrogel.
(2) And (3) pre-freezing the clathrate compound hydrogel in a refrigerator, and freeze-drying the frozen sample in a vacuum freeze dryer to obtain the super-heat-insulation aerogel sample.
The freeze drying temperature is-45 deg.C to-55 deg.C, pressure is 5-15Pa, and freezing time is 12-72 hr.
The invention has the beneficial effects that:
the invention is different from the traditional habitual thinking, and provides a novel heat insulation material design concept that: when a classical aerogel structure is constructed, a thermal response polymer which can generate molecular isomerization and host-guest disentanglement in a high-temperature environment is used as a skeleton matrix material of the aerogel. In particular, azobenzene groups can be thermally isomerized. Azobenzene is one of the most widespread chromophores, which undergoes cis-trans isomerization under UV irradiation or high temperature (Zhi Mirsky, D.; cho, E.; grossman, J.C. solid-State Solar Thermal Fuels for Heat Release applications, 2016,6,1502006.). Additionally, azobenzene may also be included in the internal cavity of the cyclodextrin via host-guest interactions. Upon heating, the azobenzene binding capacity to the cyclodextrin is reduced, resulting in de-inclusion, which results in a loss of thermal energy.
The porous aerogel is obtained by self-assembling a host polymer carrying a plurality of cyclodextrins and a guest polymer carrying a plurality of azophenyl groups to form a host-guest inclusion compound hydrogel, and then further freezing and drying the host polymer and the guest polymer. First, the aerogel had a porosity of 89.5% or more and a very low density (8.09 mg/cm) 3 -15.55mg/cm 3 ) Therefore, the solid heat conduction can be effectively reduced. Meanwhile, the air flow is limited by the pore structure with the size of only nanometer level, and the generation of thermal convection can be greatly reduced. The material is made to show the characteristic of low thermal conductivity (the thermal conductivity is less than 0.04W/mK) of the passive heat insulation material. More importantly: the framework material of the special aerogel is a host-guest polymer containing azobenzene, when the host-guest polymer is exposed to high temperature (or strong ultraviolet irradiation), azo isomerization and unpacking can occur inside the framework substrate, the heat energy conducted through heat radiation is actively dissipated, the defects of a passive heat insulation material are overcome, and the material has more excellent heat insulation performance compared with a porous material with the same heat conductivity. Different from the phase change heat insulation material: isomerization and resolution are physical state changes that occur between solids, and are not solid-liquid phase transitions, and do not produce a liquid phase, and therefore, there are no packaging and leakage problems.
The invention provides application of a composite super-heat-insulation aerogel with an active and passive structure in preparation of a heat-insulation protective material and/or a light heat-resistant material. Experimental results show that the azo modified chitosan/cross-linked cyclodextrin super-insulation composite aerogel prepared by adjusting the molar ratio of the host polymer cross-linked cyclodextrin to the guest polymer azo modified chitosan has low density, low thermal conductivity and higher water absorption and shows a water-activated shape memory behavior, and the heat can be automatically dissipated by utilizing the isomerization of azo groups in the aerogel and/or the de-inclusion action of the azo groups and the cyclodextrin to realize the super-insulation performance, so that the composite aerogel has wide application prospects in a plurality of important fields such as aerospace, national defense, fire control, traffic and the like.
Drawings
FIGS. 1 (a) to 1 (c) are scanning electron micrographs of the azo-modified chitosan/crosslinked cyclodextrin composite aerogel, wherein 1 (a), 1 (b) and 1 (c) are images of example 1 at different magnifications, respectively;
FIG. 2 (a) is an infrared thermal imaging diagram of azo-modified chitosan/cross-linked cyclodextrin composite aerogel (visible light environment) at 185 ℃ in a high-temperature heating table;
fig. 2 (b) is an infrared thermal imaging diagram of azo-modified chitosan/cross-linked cyclodextrin composite aerogel (ultraviolet environment) on a heating table at a high temperature of 185 ℃;
FIG. 2 (c) is an infrared thermal imaging of chitosan aerogel (visible light environment) at 185 ℃ high temperature heating stage;
FIG. 3 is a flow chart of the preparation of the present invention.
Detailed Description
To make the objects, technical solutions and advantages of the present invention clearer and more complete, the technical solutions of the present invention are described below clearly, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the scope of protection of the present invention.
Example 1 preparation of azo-modified chitosan/cross-linked cyclodextrin composite aerogel
As shown in FIG. 3, 1. Preparation of azo-modified aqueous Chitosan Dispersion
30mg of azo-modified chitosan (molecular weight: 60000-80000, azo graft ratio 72.62%) was dispersed in 4mL of a 2% acetic acid solution and stirred at room temperature for 3 hours.
2. Preparation of aqueous dispersions of crosslinked beta-cyclodextrin
34.5mg of crosslinked beta-cyclodextrin (molecular weight: 68000) was dispersed in 2mL of distilled water and stirred at room temperature for 3 hours.
3. Preparation of clathrate hydrogel
Mixing azo modified chitosan aqueous dispersion and cross-linked beta-cyclodextrin aqueous dispersion according to the molar ratio of cyclodextrin to azobenzene of 1:1.1, and mixing uniformly. The total solid content in the mixture was controlled to be 11mg/mL. The homogeneous mixture was then placed in a room temperature self-assembly for 4 hours to form an inclusion hydrogel.
4. Preparation of azo modified chitosan/cross-linked cyclodextrin composite aerogel
And pre-freezing the clathrate compound hydrogel in a refrigerator, and freeze-drying the frozen sample in a vacuum freeze dryer (50 ℃ below zero and 10 Pa) for 48 hours to obtain the azo modified chitosan/cross-linked cyclodextrin composite aerogel (CSAOZO/PCD).
Example 2 preparation of azo-modified sodium alginate/cross-linked cyclodextrin composite aerogel
As shown in FIG. 3, 1. Preparation of azo-modified sodium alginate aqueous dispersion
30mg of azo-modified sodium alginate (molecular weight: 100000-150000, azo graft ratio 49.98%) was dispersed in 4mL of distilled water and stirred at 35 ℃ for 5 hours.
2. Preparation of aqueous dispersions of crosslinked beta-cyclodextrin
60mg of crosslinked beta-cyclodextrin was dispersed in 2mL of distilled water and stirred at room temperature for 4h.
3. Preparation of clathrate hydrogel
Uniformly mixing the azo modified alginic acid aqueous dispersion and the cross-linked beta-cyclodextrin aqueous dispersion according to the molar ratio of the cyclodextrin to the azobenzene of 1:2. The total solid content in the composite liquid is controlled to be 15mg/mL. The homogeneous mixture was then placed in a room temperature self-assembly for 7 hours to form an inclusion hydrogel.
4. Preparation of azo modified alginic acid/cross-linked cyclodextrin composite aerogel
And pre-freezing the clathrate compound hydrogel in a refrigerator, and freeze-drying the frozen sample in a vacuum freeze dryer at (-50 ℃ and 10 Pa) for 72 hours to obtain the azo modified alginic acid/cross-linked cyclodextrin composite aerogel.
Example 3 preparation of azo-modified Chitosan/Cyclodextrin-modified Chitosan composite aerogel
As shown in FIG. 3, 1. Preparation of azo-modified aqueous Chitosan Dispersion
60mg of azo-modified chitosan (molecular weight: 60000-80000, azo graft ratio 72.62%) was dispersed in 3mL of a 2% acetic acid solution and stirred at room temperature for 3 hours.
2. Preparation of cyclodextrin modified chitosan aqueous dispersion
90mg of cyclodextrin-modified chitosan (molecular weight: 60000-80000, cyclodextrin grafting yield 30.56%) was dispersed in 3mL of 3% acetic acid solution and stirred at room temperature for 6h.
3. Preparation of clathrate hydrogel
Uniformly mixing the azo modified chitosan aqueous dispersion and the cyclodextrin modified chitosan aqueous dispersion according to the molar ratio of the cyclodextrin to the azobenzene of 2:3. The total solid content in the mixed solution was controlled to be 25mg/mL. The homogeneous mixture was then placed in a room temperature self-assembly for 12 hours to form an inclusion hydrogel.
4. Preparation of azo modified chitosan/cyclodextrin modified chitosan composite aerogel
And (3) pre-freezing the clathrate hydrogel in a refrigerator, and freeze-drying the frozen sample in a vacuum freeze dryer at (-50 ℃ and 10 Pa) for 60 hours to obtain the azo modified chitosan/cyclodextrin modified chitosan composite aerogel.
Example 4 preparation of azo-modified sodium alginate/cyclodextrin-modified chitosan composite aerogel as shown in fig. 3, 1 preparation of azo-modified sodium alginate aqueous dispersion
168mg of azo-modified sodium alginate (molecular weight: 100000-150000, azo graft ratio 49.98%) was dispersed in 4mL of distilled water and stirred at 35 ℃ for 5 hours.
2. Preparation of cyclodextrin modified chitosan aqueous dispersion
84mg of cyclodextrin-modified chitosan (molecular weight 60000-80000, cyclodextrin grafting ratio 30.56%) was dispersed in 2mL of 1.5% acetic acid solution and stirred at room temperature for 3h.
3. Preparation of clathrate hydrogel
Uniformly mixing the azo modified alginic acid aqueous dispersion and the cyclodextrin modified chitosan aqueous dispersion according to the molar ratio of the cyclodextrin to the azobenzene of 2:1. The total solid content in the mixed solution was controlled to be 42mg/mL. The homogeneous mixture was then placed in a room temperature to self-assemble for 9 hours to form the inclusion hydrogel.
4. Preparation of azo modified alginic acid/cyclodextrin modified chitosan composite aerogel
And pre-freezing the clathrate compound hydrogel in a refrigerator, and freeze-drying the frozen sample in a vacuum freeze dryer at (-50 ℃ and 10 Pa) for 36 hours to obtain the azo modified alginic acid/cyclodextrin modified chitosan composite aerogel.
Example 5 preparation of azo-modified Chitosan/cellulose nanocrystal grafted Cyclodextrin
As shown in FIG. 3, 1. Preparation of azo-modified aqueous Chitosan Dispersion
120mg of azo-modified chitosan (molecular weight: 60000-80000, azo graft ratio 72.62%) was dispersed in 4mL of 4% acetic acid solution and stirred at room temperature for 3 hours.
2. Preparation of cellulose nanocrystalline grafted cyclodextrin water dispersion
80mg of cellulose nanocrystal-grafted cyclodextrin was dispersed in 2mL of distilled water and stirred at room temperature for 6 hours.
3. Preparation of clathrate hydrogel
Uniformly mixing the azo modified chitosan aqueous dispersion and the cellulose nanocrystalline grafted cyclodextrin aqueous dispersion according to the molar ratio of the cyclodextrin to the azobenzene of 3:2. The total solid content in the mixed solution was controlled to 33mg/mL. The homogeneous mixture was then placed in self-assembly at room temperature for 4 hours to form the inclusion hydrogel.
4. Preparation of azo modified chitosan/cellulose nanocrystalline grafted cyclodextrin composite aerogel
And (3) pre-freezing the clathrate hydrogel in a refrigerator, and freeze-drying the frozen sample in a vacuum freeze-drying machine for 55 hours at (-50 ℃ and 10 Pa) to obtain the azo modified chitosan/cellulose nanocrystal grafted cyclodextrin composite aerogel.
Comparative example 1 preparation of Cross-Linked Cyclodextrin aerogel
1. Preparation of aqueous dispersions of crosslinked cyclodextrins
150mg of crosslinked beta-cyclodextrin (molecular weight: 68000) was dispersed in 6mL of distilled water and stirred at room temperature for 5 hours.
2. Preparation of crosslinked cyclodextrin aerogels
Pre-freezing cyclodextrin water dispersion in refrigerator, freeze-drying the frozen sample in vacuum freeze-drying machine (-50 deg.C, 10 Pa) for 72 hr to obtain cross-linked cyclodextrin aerogel.
Comparative example 2 preparation of chitosan aerogel
1. Preparation of aqueous Chitosan Dispersion
185mg of chitosan (molecular weight: 60000-80000) was dispersed in 6mL of a 2% acetic acid solution and stirred at room temperature for 8h.
2. Preparation of chitosan aerogel
Pre-freezing the chitosan aqueous dispersion in a refrigerator, and freeze-drying the frozen sample in a vacuum freeze-drying machine for 72h (50 ℃ C., 10 Pa) to obtain the chitosan aerogel.
Test example 1 micro-morphology of azo-modified chitosan/cross-linked cyclodextrin composite aerogel
1. Test method
The aerogel prepared in example 1 was used, the appearance of the surface of the aerogel was observed by a scanning electron microscope, and the aerogel was subjected to a gold-spraying treatment before observation.
2. Test results
SEM pictures of the composite aerogel are shown in fig. 1 (a) -1 (c). The inside of the aerogel prepared by slow freezing can form a continuous three-dimensional honeycomb network-shaped pore structure.
Test example 2 thermal conductivity of azo-modified chitosan/cross-linked cyclodextrin composite aerogel
1. Test method
The thermal conductivity of the aerogel prepared in example 1 and comparative examples 1 and 2 was measured by a thermal conductivity tester. And completing the test of the heat conductivity coefficient in a transient isotropy and heat capacity mode. The thermal conductivity λ is the product of the thermal diffusion coefficient Cp, the heat capacity α and the density ρ, and the units are W m -1 K -1 、mm 2 s -1 、J g -1 K -1 、g cm -3 . The test results are shown in table 1.
2. Test results
TABLE 1 thermal conductivity of aerogels in the examples of the invention
Test example 3 high temperature heat insulating property of composite aerogel of the present invention
1. Test method
The aerogels prepared in example 1 and comparative example 2 (chitosan aerogel without azobenzene and host-guest inclusion compound in the aerogel system of comparative example 2, the thermal conductivity is 0.0384W/mk as in example 1) were taken, the samples were placed on a high-temperature heating table at 185 ℃, and the upper surfaces of the samples were photographed at intervals of time by a thermal infrared imager to record the temperatures. The test distance was 18mm.
2. Test results
As shown in fig. 2 (a) -2 (c), the CSAZO/CD aerogel surface temperature was maintained at about 40 ℃ after being placed on a 185 ℃ high temperature hot table for 10 minutes, and the CSAZO/CD aerogel surface temperature fluctuated with the increase of the placing time, did not continuously increase, but rather decreased. Comparative example 2 has the same thermal conductivity as example 1, but since comparative example 2 does not contain an azo group and does not have an active heat absorption structure, the temperature of the surface of the aerogel continues to rapidly increase with time. The thermal insulation of the CSAZO/CD aerogel was tested under uv light and the aerogel showed superior and stable thermal insulation than under visible light. As can be seen, even though the CSAOZO/CD composite aerogel is placed on a high-temperature hot table at 185 ℃ for 10 minutes, the surface temperature of the aerogel can be kept at about 30 ℃ which is far lower than the body temperature of a human body. It is obvious that even though the thermal conductivity is the same, the CSAZO/CD aerogel has an active absorption structure and a passive thermal insulation structure, and therefore, the CSAZO/CD aerogel has more excellent high-temperature thermal insulation performance under both visible light environment and ultraviolet light environment.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (7)
1. The composite super-heat-insulation aerogel with the active and passive structure is characterized in that a host polymer carrying a plurality of cyclodextrins and a guest polymer carrying a plurality of azobenzene groups are self-assembled to form a host-guest inclusion compound hydrogel, and then the host-guest inclusion compound hydrogel is further frozen and dried to obtain porous aerogel; wherein the molar ratio of the host polymer cyclodextrin to the azobenzene in the guest polymer is 1:1-1; the composite super-heat-insulation aerogel with the active and passive structures simultaneously comprises an active heat absorption structure and a passive heat insulation structure, wherein the active heat absorption structure is an inclusion structure of a guest polymer with a plurality of azobenzene groups and a host polymer with a plurality of cyclodextrin groups, and the passive heat insulation structure is an aerogel open pore structure with multi-stage sizes; wherein, the open pore structure of the aerogel is a hierarchical pore structure with nanometer and micron levels, and the porosity is more than 89.5 percent.
2. The composite super thermal insulation aerogel with the active and passive structure as claimed in claim 1, wherein the solid content of the composite super thermal insulation aerogel with the active and passive structure is 5-25mg/mL.
3. The composite super thermal insulation aerogel with an active and passive structure as claimed in claim 1, wherein the thermal conductivity of the composite super thermal insulation aerogel with an active and passive structure is below 0.04W/mK.
4. The composite super thermal insulation aerogel with an active and passive structure as claimed in claim 1, wherein the thermal insulation capability of the composite super thermal insulation aerogel with an active and passive structure is better than that of a thermal insulation material with the same thermal conductivity at a temperature higher than 100 ℃.
5. The composite super thermal insulation aerogel with the active and passive structure as claimed in claim 1, wherein the thermal insulation capability of the composite super thermal insulation aerogel with the active and passive structure is better than that of a thermal insulation material with the same thermal conductivity under an ultraviolet environment.
6. The preparation method of the composite super thermal insulation aerogel with the active and passive structure as claimed in any one of claims 1 to 5, comprising:
step 1, respectively dissolving a host polymer crosslinked cyclodextrin and a guest polymer azo modified chitosan in water, uniformly mixing a host-guest mixture according to the molar ratio of the cyclodextrin to the azobenzene of 1:1-1, 1.5, controlling the total solid content in the mixed solution to be 5-25mg/mL, and carrying out self-assembly on the uniform mixed solution at normal temperature for 4-12 hours to form an inclusion compound hydrogel;
and 2, placing the clathrate compound hydrogel into a refrigerator for pre-freezing, and then freezing and drying the frozen sample in a vacuum freeze dryer to obtain the super heat insulation aerogel sample.
7. The preparation method of the composite super thermal insulation aerogel with the active and passive structure as claimed in claim 6, wherein the temperature of freeze drying in step 2 is-45 ℃ to-55 ℃, the pressure is 5Pa to 15Pa, and the freezing time is 12 hours to 72 hours.
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| CN202210375635.4A CN114933732B (en) | 2022-04-11 | 2022-04-11 | Composite super-thermal-insulation aerogel with active and passive structures and preparation method thereof |
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| CN202210375635.4A CN114933732B (en) | 2022-04-11 | 2022-04-11 | Composite super-thermal-insulation aerogel with active and passive structures and preparation method thereof |
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