CN114316920A - A kind of high thermal conductivity phase change microcapsule and its preparation method and application - Google Patents
A kind of high thermal conductivity phase change microcapsule and its preparation method and application Download PDFInfo
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Abstract
The invention discloses a high-thermal-conductivity phase-change microcapsule and a preparation method and application thereof, wherein the high-thermal-conductivity phase-change microcapsule comprises a shell layer and a phase-change core material, the shell layer is composed of polymethyl methacrylate and oleophylic modified graphene, and the oleophylic modified graphene accounts for 2-8 wt% of the weight of the shell layer. According to the invention, aluminum chloride is used as a catalyst, graphene and C12-C18 carboxylic acid react in an alcohol-water solution at 70-80 ℃, so that C12-C18 oleophylic groups are grafted to the surface of the graphene, and thus the oleophylic modified graphene is obtained. The oleophylic modified graphene is added in the methyl methacrylate crosslinking process, so that a phase change microcapsule shell layer with high thermal conductivity can be prepared, the shell layer is compact, and the risk of leakage of a phase change core material can be reduced.
Description
Technical Field
The invention relates to the technical field of microcapsule preparation, in particular to a high-thermal-conductivity phase-change microcapsule for inhibiting concrete temperature cracks and a preparation method and application thereof.
Background
The hydration heat release of concrete easily causes uneven internal and external heating, so that a large number of temperature cracks are generated, the phenomenon is more obvious in the pouring process of large-volume concrete of a bridge, and the health and the safety of the bridge structure are seriously influenced. At present, the conventional solutions are: the water-cement ratio of the concrete is improved, the alkali-activated slag cementing material and the embedded water pipe are added, and the like, but the problems of long concrete setting time, low early strength, high economic cost and the like exist in the above solution. Therefore, how to effectively suppress the generation of temperature cracks at low cost and in a short period of time is one of the current research directions in which the bridge field focuses attention.
The phase-change material is a heat absorption and storage material which can maintain the ambient temperature to be stable through self-gain and loss of water or phase state change; the microencapsulation technology can wrap the phase-change material in a solid and compact shell layer, thereby further solving the problem that the phase-change material is leaked in the heat storage process and ensuring that the phase-change material has more engineering practicability. Because the conventional phase-change microcapsule usually uses a high molecular polymer with poor heat conductivity as a shell material, the phase-change microcapsule has poor sensitivity to environmental temperature change when realizing a temperature control function. In addition, the high molecular polymer shell material is easy to age in an environment with frequent temperature change, and the risk of leakage of the core material is increased.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a high-thermal-conductivity phase-change microcapsule for inhibiting concrete temperature cracks, which is sensitive to environmental temperature change and low in core material leakage risk, and a preparation method and application thereof.
The technical scheme provided by the invention is as follows:
in a first aspect, the invention provides a high-thermal-conductivity phase-change microcapsule for inhibiting concrete temperature cracks, which comprises a shell layer and a phase-change core material, wherein the shell layer is composed of polymethyl methacrylate and oleophylic modified graphene, and the oleophylic modified graphene accounts for 2 wt% -8 wt% of the shell layer.
Preferably, in the technical scheme, the oleophylic modified graphene is graphene with a surface grafted with C12-C18 oleophylic groups.
Preferably, the lipophilic modified graphene is prepared by the following steps: under the catalysis of aluminum chloride, reacting graphene with C12-C18 carboxylic acid in an alcohol-water solution at 70-80 ℃ to generate oleophylic modified graphene; preferably, the C12-C18 carboxylic acid is palmitic acid.
Preferably, the weight ratio of the graphene to the C12-C18 carboxylic acid is 1: 0.08-0.1.
Preferably, the phase change core material comprises n-tetradecane and n-hexadecane in a weight ratio of 1:1 to 1: 3.
In a second aspect, the present invention provides a method for preparing the above-mentioned phase-change microcapsule with high thermal conductivity for inhibiting concrete temperature crack, comprising the following steps:
dissolving polyvinyl alcohol powder in deionized water to obtain a surfactant solution;
adding the core material into a surfactant solution under the condition of stirring in a water bath at 45-55 ℃ to obtain a first emulsion;
dissolving benzoyl peroxide powder in methyl methacrylate to obtain a shell material solution;
adding the shell material solution and the lipophilic modified graphene into the first emulsion under the conditions of water bath at 55-65 ℃ and stirring at 50-100 r/min to obtain a second emulsion;
raising the temperature of the second emulsion to 75-80 ℃, and increasing the stirring speed to 150-250 r/min to obtain microcapsule suspension;
and filtering the microcapsule suspension, washing and drying the filter residue to obtain the high-heat-conductivity phase-change microcapsule for inhibiting the temperature crack of the concrete.
Preferably, the phase-change core material consists of n-tetradecane and n-hexadecane in a weight ratio of 1: 1-1: 3, and the n-tetradecane and the n-hexadecane are mixed until standing without layering before being added into the surfactant solution.
Preferably, the concentration of the polyvinyl alcohol in the surfactant solution is 0.1-0.2 g/L.
In the above aspect, the amount of the polyvinyl alcohol powder in the first emulsion is preferably 10% to 30% of the total weight of the n-tetradecane and the n-hexadecane.
In a third aspect, the invention provides an application of a high-thermal-conductivity phase-change microcapsule for inhibiting concrete temperature cracks as a concrete temperature crack inhibitor.
The principle of the invention is as follows:
according to the invention, an ethanol aqueous solution is used as a solvent, aluminum chloride is used as a catalyst to catalyze palmitic acid to perform an esterification reaction with hydroxyl on the surface of graphene, so that the palmitic acid is grafted to the surface of the graphene, and the oleophylic modified graphene is obtained. The oleophylic modified graphene improves the compatibility of graphene and methyl methacrylate, so that the shell material is more compact, the risk of leakage of the phase change core material is reduced, and the pollution of polluting alkane to the environment is avoided; meanwhile, due to the fact that the graphene has high heat-conducting performance, the sensitivity of the shell material to the change of the environmental temperature is improved, and the temperature stability is enhanced.
The invention uses the mixture of n-tetradecane and n-hexadecane as the phase-change core material, when the ambient temperature rises to the phase-change point of the phase-change core material, the phase-change core material is changed, and absorbs the heat of the surrounding environment, so as to reduce the rising rate of the temperature of the concrete member. Through calculation of a Schdelle formula (1), the phase change core material of the phase change microcapsule consists of alkanes with different phase change points, so that the microcapsule has a wider phase change interval:
in the formula xA-the molar fraction of the mixture of the main component a;
ΔHA-latent heat of phase transition, J/mol, of pure compound a;
Tf-melting temperature, K, of pure compound a;
t-phase transition temperature, K, of the mixture containing Compound A;
r-gas Normal mature, 8.315J/mol.
The invention has the following advantages and beneficial effects:
according to the invention, n-tetradecane and n-hexadecane are used as phase change core materials of the phase change microcapsule, and polymethyl methacrylate and lipophilic modified graphene are used as shell materials, so that the phase change microcapsule has the advantages of low raw material cost and simple process, and has the advantages of compact shell layer material, small risk of leakage of the phase change core materials, high shell layer thermal conductivity and sensitivity to environmental temperature change.
Drawings
FIG. 1 is a schematic structural diagram of a high thermal conductivity phase change microcapsule for inhibiting concrete temperature cracks according to the present invention; wherein, 1 is a shell layer, and 2 is a phase-change core material.
Fig. 2 is a heat conductivity coefficient change diagram of a high heat conductivity phase change microcapsule with different amounts of oleophylic modified graphene added to a shell layer.
Fig. 3 shows the retention rate of the self-mass of the high-thermal-conductivity phase-change microcapsule added with different amounts of oleophylic modified graphene in the shell layer after 100 times of temperature cycle experiments at 0-80 ℃.
Fig. 4 is a scanning electron microscope image of the phase change microcapsule with high thermal conductivity prepared in example 1.
Fig. 5 is a scanning electron microscope image of the phase change microcapsule with high thermal conductivity prepared in example 2.
Fig. 6 is a scanning electron microscope image of the phase change microcapsule with high thermal conductivity prepared in example 3.
Fig. 7 is a DSC diagram of the phase change microcapsule with high thermal conductivity prepared in example 1.
FIG. 8 is a graph showing compressive strength of concrete cured for 7 days with different amounts of phase change microcapsules (example 1).
Fig. 9 is a point line graph of the highest central temperature during hydration of concrete with different amounts of highly heat conductive phase change microcapsules (example 1).
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be further described with reference to the accompanying drawings.
Referring to fig. 1, the high thermal conductivity phase change microcapsule for inhibiting concrete temperature cracks provided by the embodiment of the present invention is spherical particles in appearance, the microcapsule is composed of a phase change core material with a temperature control function and a shell layer wrapping the phase change core material, the phase change core material is composed of n-tetradecane and n-hexadecane in a weight ratio of 1: 1-1: 3, and the shell layer is composed of polymethyl methacrylate and oleophylic modified graphene, wherein the oleophylic modified graphene accounts for 2 wt% -8 wt% of the shell layer. The phase change microcapsule with high thermal conductivity has a core-shell structure, and the phase change core material in the microcapsule is protected by the shell layer and is not in direct contact with the surrounding environment, so that the heat storage density of the phase change core material is guaranteed; the shell layer made of polymethyl methacrylate and lipophilic modified graphene has high mechanical strength, so that the damage of additional materials (such as phase change materials and aggregates) to the time mechanical property of concrete is reduced, and the damage of a phase change core material to the basic property of a concrete test piece in the phase change process is reduced.
The method for preparing the high-thermal-conductivity phase-change microcapsule for inhibiting the temperature crack of the concrete, which is provided by the following embodiment, comprises the following steps of:
mixing n-tetradecane and n-hexadecane in a weight ratio of 1: 1-1: 3 until standing is carried out without layering to obtain core material liquid;
dissolving polyvinyl alcohol powder in deionized water to obtain a surfactant solution;
controlling the water bath temperature to be 50 ℃, and adding core material liquid into a surfactant solution according to the use amount of polyvinyl alcohol which is 10-30% of the total weight of phase change core materials (n-tetradecane and n-hexadecane) under the condition that the stirring speed is 150-300 r/min to obtain a first emulsion;
dissolving benzoyl peroxide powder in methyl methacrylate to obtain a shell material solution; wherein the weight ratio of the benzoyl peroxide to the methyl methacrylate is 1: 30-1: 50;
adding a shell material solution and the lipophilic modified graphene into the first emulsion under the conditions of water bath at 55-65 ℃ and stirring at 50-100 r/min, and pre-polymerizing methyl methacrylate to obtain a second emulsion; the rotating speed of the step is controlled to be 50 r/min-100 r/min because the pre-polymerization reaction is carried out in the early stage, only a small amount of reaction exists among methyl methacrylate, and the rotating speed is too high, so that the methyl methacrylate is easily separated from the core material;
raising the temperature of the second emulsion to 75-80 ℃, and increasing the stirring speed to 150-250 r/min to start the polymerization reaction of methyl methacrylate to obtain a microcapsule suspension; the rotating speed is increased to 150 r/min-250 r/min because part of methyl methacrylate monomers are polymerized into long-chain structures after methyl methacrylate prepolymerization is finished, the influence of increasing the rotating speed on the structures among the core walls is small, and the increase of the rotating speed is favorable for the balling property and the dispersibility of the microcapsules;
and filtering the microcapsule suspension, and washing and drying the filter residue in sequence to obtain the high-heat-conductivity phase-change microcapsule for inhibiting the temperature crack of the concrete.
The reason for using the two-step polymerization is to make the shell coating more complete.
The method for preparing the high-thermal-conductivity phase-change microcapsule for inhibiting the concrete temperature crack, provided by the invention, has the advantages of low cost and simple process, and is suitable for large-scale production.
The high thermal conductivity phase change microcapsule for inhibiting concrete temperature cracks and the preparation method thereof provided by the present invention are described in detail below with reference to the examples.
Example 1
(1) Dissolving 0.44g of palmitic acid and 0.8g of aluminum chloride hexahydrate in 200mL of ethanol water solution (the ethanol concentration is 200g/L), adding 5g of graphene, heating in a water bath while stirring (75 ℃, 300r/min) to obtain oleophylic modified graphene suspension, filtering the oleophylic modified graphene suspension, and drying filter residues to obtain oleophylic modified graphene powder.
(2) Mixing n-tetradecane and n-hexadecane in a weight ratio of 1:1 until the mixture is completely mutually soluble, standing and not layering to obtain the core material liquid.
0.4g of benzoyl peroxide powder was dissolved in 20g of methyl methacrylate (in a liquid state), and the resulting solution was stirred to completely dissolve the benzoyl peroxide powder, thereby preparing a shell solution.
1g of polyvinyl alcohol powder is dissolved in 100mL of deionized water (water bath temperature is 90 ℃) to obtain a surfactant solution, the surfactant solution is poured into a three-neck flask, and the three-neck flask is placed in a 50 ℃ water bath environment for heat preservation.
(3) Adding 10g of core material liquid into the surfactant solution, heating in a water bath while stirring (the water bath temperature is 50 ℃, and the stirring speed is 150r/min), and obtaining a first emulsion; respectively adding the shell material solution and the oleophylic modified graphene powder into the first emulsion according to the mixing amount of the oleophylic modified graphite in the shell layer of 0 wt%, 2 wt%, 4 wt%, 6 wt% and 8 wt%, heating and stirring while heating in a water bath (the water bath temperature is 60 ℃, the stirring speed is 100r/min, and the reaction time is 10min), and obtaining a second emulsion.
(4) And increasing the water bath temperature of the second emulsion to 75 ℃, increasing the stirring speed by 150r/min, and reacting for 2 hours to obtain a microcapsule suspension.
(5) And filtering the microcapsule suspension, washing filter residues with deionized water, and drying in a constant-temperature air-blast drying oven at 40 ℃ for 1 day to obtain the high-thermal-conductivity phase-change microcapsule.
Example 2
(1) Dissolving 0.44g of palmitic acid and 0.8g of aluminum chloride hexahydrate in 200mL of ethanol water solution (the ethanol concentration is 200g/L), adding 5g of graphene, heating in a water bath while stirring (75 ℃, 300r/min) to obtain an oleophylic modified graphene suspension, filtering the oleophylic modified graphene suspension, and drying filter residues to obtain oleophylic modified graphene powder.
(2) Mixing n-tetradecane and n-hexadecane in a weight ratio of 1:3 until the mixture is completely mutually soluble, standing and not layering to obtain the core material liquid.
0.2g of benzoyl peroxide powder was dissolved in 20g of methyl methacrylate (in a liquid state), and the resulting solution was stirred to completely dissolve the benzoyl peroxide powder, thereby preparing a shell solution.
1g of polyvinyl alcohol powder is weighed and dissolved in 100mL of deionized water (water bath temperature is 90 ℃) to obtain a surfactant solution, the surfactant solution is poured into a three-neck flask, and the three-neck flask is placed in a 50 ℃ water bath environment for heat preservation.
(3) Adding 10g of core material liquid into a surfactant solution, heating in a water bath while stirring (the water bath temperature is 50 ℃, and the stirring speed is 150r/min), and obtaining a first emulsion; adding the shell material solution and 0.5g of oleophylic modified graphene powder into the first emulsion, heating while stirring in a water bath (the water bath temperature is 60 ℃, the stirring speed is 100r/min, and the reaction time is 10min), and obtaining a second emulsion.
(4) And increasing the water bath temperature of the second emulsion to 75 ℃, increasing the stirring speed by 150r/min, and reacting for 2 hours to obtain a microcapsule suspension.
(5) And filtering the microcapsule suspension, washing filter residues with deionized water, and drying in a constant-temperature air-blast drying oven at 40 ℃ for 1 day to obtain the high-thermal-conductivity phase-change microcapsule.
Example 3
(1) Dissolving 0.44g of palmitic acid and 0.8g of aluminum chloride hexahydrate in 200mL of ethanol water solution (the ethanol concentration is 200g/L), adding 5g of graphene, heating in a water bath while stirring (75 ℃, 300r/min) to obtain oleophylic modified graphene suspension, filtering the oleophylic modified graphene suspension, and drying filter residues to obtain oleophylic modified graphene powder.
(2) Mixing n-tetradecane and n-hexadecane in a weight ratio of 1:1 until the mixture is completely mutually soluble, standing and not layering to obtain the core material liquid.
0.4g of benzoyl peroxide powder was dissolved in 20g of methyl methacrylate (in a liquid state), and the resulting solution was stirred to completely dissolve the benzoyl peroxide powder, thereby preparing a shell solution.
1g of polyvinyl alcohol powder is dissolved in 100mL of deionized water (water bath temperature is 90 ℃) to obtain a surfactant solution, the surfactant solution is poured into a three-neck flask, and the three-neck flask is placed in a 50 ℃ water bath environment for heat preservation.
(3) Adding 30g of core material liquid into the surfactant solution, heating in a water bath while stirring (the water bath temperature is 50 ℃, and the stirring speed is 150r/min), and obtaining a first emulsion; adding the shell material solution and 0.5g of oleophylic modified graphene powder into the first emulsion, heating while stirring in a water bath (the water bath temperature is 60 ℃, the stirring speed is 100r/min, and the reaction time is 10min), and obtaining a second emulsion.
(4) And increasing the water bath temperature of the second emulsion to 75 ℃, increasing the stirring speed by 250r/min, and reacting for 2 hours to obtain a microcapsule suspension.
(5) And filtering the microcapsule suspension, washing filter residues with deionized water, and drying in a constant-temperature air-blast drying oven at 40 ℃ for 1 day to obtain the high-thermal-conductivity phase-change microcapsule.
Table 1 compatibility with and change in heat conductivity of the shell before and after graphene modification
| Unmodified graphene | Oleophilic modified graphene | |
| Presence of modified graphene | Less, and deposited in the lower half | Is more and uniformly distributed |
| Test block thermal conductivity (W/mK) | 0.231 | 0.364 |
Table 1 shows the compatibility of graphene and polymethyl methacrylate before and after oleophilic modification. Wherein, 0.5g of graphene before and after oleophylic modification is respectively 20g of methyl methacrylate and is uniformly mixed, a polymethyl methacrylate solid test block is prepared in a cubic body mould with the sectional area of 1cm multiplied by 1cm, and the upper half part of the test block is cut off for observation and heat conductivity coefficient test. The experimental result shows that compared with unmodified graphene, the compatibility of the oleophylic modified graphene and polymethyl methacrylate (shell material) is obviously improved, and more graphene enters the shell material. Due to the increase of the content of the graphene in the shell material, the heat conductivity coefficient of the shell material is increased more obviously. Therefore, the lipophilic modified graphene is more beneficial to the increase of the heat conductivity coefficient of the shell material, so that the sensitivity of the microcapsule to temperature change is improved.
Fig. 2 is a graph of the change of the thermal conductivity coefficient of the high thermal conductivity phase change microcapsule prepared by adding different amounts of the oleophilic modified graphene into the shell layer in example 1. The experiment result shows that the lipophilic modified graphene has high heat conductivity coefficient, and the heat conductivity of the high-heat-conductivity phase-change microcapsule prepared in the embodiment 1 is enhanced along with the increase of the doping amount of the lipophilic modified graphene.
Fig. 3 shows the retention rate of the self-mass of the phase change microcapsule with high thermal conductivity, which is prepared by adding different amounts of oleophylic modified graphene into the shell layer in example 1, after 100 times of temperature cycle experiments at 0-80 ℃. The experimental result shows that with the increase of the doping amount of the oleophylic modified graphene, the mass loss of the high-thermal-conductivity phase-change microcapsule for inhibiting temperature cracks prepared in the embodiment 1 after temperature circulation is reduced. Although the sealing rate of the shell material polymethyl methacrylate is reduced due to self aging after a temperature cycle experiment, the compatibility of the oleophylic modified graphene and the polymethyl methacrylate is increased, the filling effect is realized in the shell, and the leakage of the phase change core material is inhibited. Therefore, the addition of the oleophylic modified graphene is beneficial to improving the thermal stability and the coating efficiency of the high-thermal-conductivity phase-change microcapsule.
FIG. 4 is a scanning electron microscope image of the phase change microcapsule with high thermal conductivity prepared in example 1, wherein the particle size of the phase change microcapsule with high thermal conductivity is 800-2500 μm; FIG. 5 is a scanning electron microscope image of the phase change microcapsule with high thermal conductivity prepared in example 2, wherein the particle size of the phase change microcapsule with high thermal conductivity is 800-2500 μm; FIG. 6 is a scanning electron microscope image of the phase change microcapsule with high thermal conductivity prepared in example 3, wherein the particle size of the phase change microcapsule with high thermal conductivity is 800-2500 μm. It can be seen from fig. 4-6 that the phase change microcapsules with high thermal conductivity prepared in examples 1-3 all have good balling property. Fig. 7 is a Differential Scanning Calorimetry (DSC) chart of the phase-change microcapsule with high thermal conductivity prepared in example 1, and it can be seen from fig. 7 that the phase-change temperature of the phase-change microcapsule with high thermal conductivity is 9.45 ℃, and the temperature control range is wide.
The phase change microcapsules with high thermal conductivity prepared in example 1 were mixed into concrete with a standard mix ratio in the mixing amounts of 0 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt% and 10 wt%, to prepare concrete test pieces. FIG. 8 is a graph of compressive strength of a concrete sample after being cured for 7 days, and the result shows that the compressive strength of the concrete sample can be increased by properly adding the phase change microcapsule with high thermal conductivity prepared in example 1. Fig. 9 is a point line graph of the maximum value of the central temperature in the concrete hydration process, and the result shows that the high thermal conductivity phase change microcapsule can obviously reduce the temperature rise in the concrete hydration process, and the result in fig. 8 shows that the high thermal conductivity phase change microcapsule has an inhibiting effect on the temperature crack of the concrete sample.
In conclusion, the phase change microcapsule with high thermal conductivity prepared by the invention is introduced into concrete, the temperature rise rate of the concrete in the hydration process can be effectively reduced and the generation of cracks in the concrete can be inhibited by utilizing the phase change heat absorption characteristic of the phase change microcapsule, and the phase change microcapsule with high thermal conductivity can be used as a concrete temperature crack inhibitor.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
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