Core-shell structure P (MMA-MBA) copolymer heat storage phase change microcapsule as well as preparation method and application thereof

Abstract

The invention discloses a core-shell structure P (MMA-MBA) copolymer heat-storage phase-change microcapsule, the microstructure is of a spherical structure, the core-shell structure is adopted, the core structure is hexadecane, the shell structure is a methyl methacrylate (MMA) and N, N-methylene bisacrylamide (MBA) copolymer, the emulsifier is lauryl sodium sulfate (SDS), the initiator is potassium persulfate, and the pH value of the core-shell structure P (MMA-MBA) copolymer heat-storage phase-change microcapsule is 7-8. And the coating efficiency is 70-75%. The preparation method comprises the following steps: 1, preparing an oil phase and a water phase; and 2, polymerization reaction of the microcapsule. A phase change cement material based on a core-shell structure P (MMA-MBA) copolymer heat storage phase change microcapsule is prepared by compounding the P (MMA-MBA) copolymer heat storage phase change microcapsule and a cement matrix, and has hydrophobicity; obvious weightlessness exists in two times.

Description

Technical Field

[0001] This invention relates to the field of cement-based composite materials for thermal energy storage, specifically to a core-shell structured P(MMA-MBA) copolymer thermal storage phase change microcapsule, its preparation method, and its application. Background Technology

[0002] Conventional cement suffers from low inherent heat capacity and poor thermal inertia. The heat storage performance of cement-based materials can be improved by combining them with phase change materials (PCMs). A common method involves microencapsulating the PCM and then directly incorporating it into the cement matrix. For example, existing literature 1 ("Preparation and Characterization of HighContent Paraffin Wax Microcapsules and Micro / Nanocapsules with Poly MethylMethacrylate Shell by Suspension-Like Polymerization") uses suspension polymerization with methyl methacrylate (MMA) as the shell and paraffin wax as the core material to prepare MMA / paraffin wax microcapsules. This technique results in microcapsules with a core material exhibiting good thermal stability. However, this technical solution has a problem: the shell is composed of a single polymer. Although pentaerythritol tetraacrylate (PETRA) is introduced as a crosslinking agent to improve the mechanical strength of the shell, the resulting shell still suffers from low density and low mechanical strength. Specifically, when such microcapsules are incorporated into the cement matrix, under the alkaline environment generated by cement hydration and long-term stress conditions, the ester groups in the single polymer PMMA are prone to hydrolysis under strong alkaline conditions, leading to the breakage of the polymer main chain or the shedding of side chains, thus affecting the long-term heat storage stability and durability of the composite material. The direct cause of the above problems stems from the basic technical principle of this solution: the outer shell is formed by MMA polymerization, supplemented by PETRA crosslinking reinforcement, but the chemical structure and crosslinking network of the shell material are singular.

[0003] To improve the stability of microcapsules in a cement environment, synthetic resin wall materials can be used for reinforcement. For example, existing literature 2 (Preparation and application of microcapsule containing sodium potassium tartrate for self-healing of cement) uses in-situ polymerization to prepare microcapsules for cement self-healing using urea-formaldehyde resin as the shell material and sodium potassium tartrate as the core material. This existing literature shows that the stirring rate can significantly affect the particle size of the microcapsules, i.e., regulate the microstructure of the microcapsules, and thus affect their performance. However, the emulsification system used in this technical solution is a compound system of nonionic surfactants Span85 and OP-10 and anionic surfactant dodecylbenzenesulfonic acid. However, in the highly alkaline and highly ionic environment unique to cement paste, the stabilizing effect of nonionic surfactants is easily weakened by environmental influences, and the electrostatic repulsion provided by anionic surfactants is also shielded by the large number of cations in the system, resulting in the inability to form a sufficiently strong and durable steric hindrance or electrostatic stabilization mechanism. The specific consequences are that even if the stirring rate is optimized, the van der Waals forces between particles cannot be overcome during the synthesis and post-processing of microcapsules, resulting in obvious agglomeration. Consequently, the microcapsules cannot form a continuous, uniform and stable dispersion system in the cement paste.

[0004] Analysis of existing technologies reveals that the technical approach of microencapsulating phase change materials and incorporating them into a cement matrix to improve their thermal storage performance has two main problems:

[0005] 1. The microcapsule shell has a single polymer structure, which results in insufficient density and mechanical strength. It is prone to damage in the alkaline environment of cement and under stress, thus losing its protective effect on the core material, i.e. leakage occurs. In addition, the interfacial bonding between the microcapsule shell and the cement matrix is ​​weak.

[0006] 2. The agglomeration of microcapsules during preparation and compounding, i.e. poor dispersibility, makes it impossible to form a uniform and stable dispersion system in cement paste. Summary of the Invention

[0007] The purpose of this invention is to provide a core-shell structured P(MMA-MBA) copolymer thermal storage phase change microcapsule, its preparation method, and its application, solving the problems of poor compatibility, easy leakage, and poor thermal conductivity of phase change materials with cement matrices. The specific underlying principles are as follows:

[0008] Hexadecane is used as the core material to provide phase change properties;

[0009] Methyl methacrylate (MMA) and N,N-methylenebisacrylamide (MBA) were used as shell materials, wherein,

[0010] MMA forms a polymer backbone through free radical polymerization, providing structural support for microcapsules;

[0011] MBA acts as both a crosslinking agent and a copolymer. Due to the bifunctional group of MBA, the acrylamide structure undergoes a copolymerization reaction with the methyl methacrylate chain to form a three-dimensional crosslinked network structure, thereby effectively enhancing the compactness and mechanical strength of the shell.

[0012] This structure can significantly improve stability in the alkaline environment generated by cement hydration and under long-term stress conditions;

[0013] Potassium persulfate was used as an initiator. The sulfate radicals generated by the decomposition of potassium persulfate under heating conditions initiated the activation and chain propagation reaction of methyl methacrylate and N,N-methylenebisacrylamide monomers.

[0014] Sodium dodecyl sulfate (SDS) is used as an emulsifier. SDS ionizes to release negatively charged sulfate ions, which are adsorbed at the oil / water interface. Through electrostatic repulsion, it effectively prevents the collision and aggregation of oil droplets during emulsification and polymerization, forming a stable water-in-oil (O / W) emulsion system.

[0015] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0016] A core-shell structured P(MMA-MBA) copolymer thermal storage phase change microcapsule exhibits a spherical microstructure and a core-shell structure. The core is hexadecane, and the shell is a copolymer of methyl methacrylate (MMA) and N,N-methylenebisacrylamide (MBA). Sodium dodecyl sulfate (SDS) is used as the emulsifier, and potassium persulfate is used as the initiator.

[0017] The hexadecane is used to provide phase change properties;

[0018] The MMA forms a polymer backbone through free radical polymerization, which serves as a structural support.

[0019] The MBA acts as both a crosslinking agent and a copolymer. By utilizing the bifunctional groups of MBA, the acrylamide structure undergoes a copolymerization reaction with the methyl methacrylate chain to form a three-dimensional crosslinked network structure, which enhances the compactness and mechanical strength of the shell.

[0020] The potassium persulfate, acting as an initiator, decomposes under heating conditions to generate sulfate free radicals, which play a role in initiating the activation and chain growth reaction of methyl methacrylate and N,N-methylenebisacrylamide monomers.

[0021] The SDS, as an emulsifier, ionizes to release negatively charged sulfate ions, which are adsorbed at the oil / water interface. Through electrostatic repulsion, it prevents the oil droplets from colliding and coalescing during the emulsification and polymerization process, thus forming a stable water-in-oil O / W emulsion system.

[0022] The initial decomposition temperature T0 of P(MMA-MBA) is 136.04-137.04℃, the final decomposition temperature T1 is 236.13-237.13℃, and the maximum degradation temperature T2 is 421.66-422.66℃.

[0023] During the crystallization process of P(MMA-MBA), there is an exothermic peak at 10.73-11.73℃ with an enthalpy of 194.14-195.14 J / g; during the melting process, there is an endothermic peak at 17.41-18.41℃ with an enthalpy of 195.87-196.87 J / g.

[0024] The coating efficiency of P(MMA-MBA) is 70-75%.

[0025] A method for preparing heat storage phase change microcapsules based on core-shell structured P(MMA-MBA) copolymer includes the following steps:

[0026] Step 1, Preparation of oil and aqueous phases: Under certain conditions, hexadecane, methyl methacrylate (MMA), and N,N-methylenebisacrylamide (MBA) are stirred and dissolved to obtain a 16-MM solution as the oil phase. At the same time, under certain conditions, sodium dodecyl sulfate (SDS) is stirred and dissolved with deionized water. After dissolution, glacial acetic acid is added to adjust the pH value to obtain an SDS aqueous solution as the aqueous phase.

[0027] In step 1, the mass ratio of hexadecane, MMA, MBA, SDS, potassium persulfate and deionized water is 20:40:1:(2-4):(1-2):(400-500);

[0028] In step 1, the conditions for preparing the oil phase solution are: stirring speed of 400-600 rpm, stirring and dissolution temperature of 35-45℃, and stirring time of 25-35 min.

[0029] In step 1, the conditions for preparing the aqueous solution are: stirring speed of 250-350 rpm and stirring time of 25-35 min; and adjusting the pH value using glacial acetic acid.

[0030] Step 2, the polymerization reaction of microcapsules: Under certain conditions, the 16-MM solution obtained in Step 1 is added dropwise to the SDS aqueous solution obtained in Step 1 and stirred and emulsified to obtain an emulsion solution. Then, under certain conditions, potassium persulfate is added to the emulsion solution and stirred and mixed to obtain a reaction solution. Finally, under certain conditions, the reaction solution is stirred and polymerized. After the reaction is completed, the obtained product is centrifuged and vacuum dried to obtain core-shell structured P(MMA-MBA) copolymer heat storage phase change microcapsules, abbreviated as P(MMA-MBA).

[0031] In step 2, the conditions for stirring and emulsification are: stirring speed of 700-900 rpm, reaction temperature of 35-45℃, and reaction time of 15-25 min.

[0032] In step 2, the stirring and mixing conditions are: stirring speed of 400-500 rpm, reaction temperature of 35-45℃, and reaction time of 5-10 min.

[0033] In step 2, the conditions for stirring polymerization are: stirring speed of 150-250 rpm, stirring temperature of 65-75℃, and stirring time of 3-5 h.

[0034] In step 2, the centrifugation conditions are: centrifugation speed of 7500-8500 rpm and centrifugation time of 10-20 min; the vacuum drying conditions are: drying temperature of 30-40℃ and drying time of 20-28 h.

[0035] A phase change cement material based on core-shell structured P(MMA-MBA) copolymer thermal storage phase change microcapsules is obtained by combining P(MMA-MBA) copolymer thermal storage phase change microcapsules with a cement matrix. The specific preparation method is as follows: First, P(MMA-MBA) is soaked in deionized water for 20-28 hours. Simultaneously, cement and deionized water are mixed to obtain cement paste. Then, P(MMA-MBA) is incorporated into the cement paste to obtain the microcapsule phase change cement material. The contact angle is 64.21-75.86°, exhibiting hydrophobicity. In the phase change cement material, the microcapsule material accounts for 10-30 wt.% of the total mass.

[0036] There were two distinct weight loss events. The first weight loss occurred at temperatures of 95-100℃. The second weight loss occurred at temperatures of 391.24-392.24℃ (initial decomposition temperature T0), 402.26-403.26℃ (final decomposition temperature T1), and 412.14-413.14℃ (maximum degradation temperature T2). The weight loss ranged from 61.8-62.8% to 58.3-59.3%, with a weight loss range of 3.5-4.5 wt.%.

[0037] Within the test temperature range of -10 to 50℃, an exothermic peak exists at 10.53-10.58℃ during crystallization, with an enthalpy of 19.94-33.41 J / g; an endothermic peak exists at 15.23-15.35℃ during melting, with an enthalpy of 20.47-34.78 J / g; the thermal conductivity is 0.4218-0.5147 W / (m·K), which is 43.9-54.0% lower than that of conventional cement; within a test time of less than 25 minutes, the temperature difference between the cement and the standard temperature of conventional cement is 5.8-7.9℃, with an average temperature difference of 5.1-7.6℃.

[0038] The beneficial technical effects of this invention have been tested and are as follows:

[0039] XRD test results show that P(MMA-MBA) has a characteristic peak of hexadecane, which has no effect on the phase transition properties of hexadecane.

[0040] SEM test results show that P(MMA-MBA) has a regular spherical structure; after being incorporated into the cement matrix, it is uniformly distributed in the cement hydration products, with good interfacial bonding between cement particles, and there is no microcapsule breakage phenomenon.

[0041] TG test results show that the initial decomposition temperature T0 of P(MMA-MBA) is 136.04℃, the final decomposition temperature T1 is 236.13℃, and the maximum degradation temperature T2 is 421.66℃. After P(MMA-MBA) is incorporated into the cement matrix, there are two significant weight losses. The first weight loss occurs at 100℃, due to the evaporation of free water; the second weight loss occurs at 350-420℃, due to the decomposition of the cement hydration product Ca(OH)2. Adding P(MMA-MBA) can significantly reduce the thermal decomposition weight loss phenomenon of cement, specifically P(MMA-MBA)-30, thus significantly improving its thermal stability.

[0042] DSC test results show that, within the test temperature range of -10 to 50℃, P(MMA-MBA) exhibits an exothermic peak at 10.73℃ with an enthalpy of 194.14 J / g during crystallization and an endothermic peak at 17.41℃ with an enthalpy of 195.87 J / g during melting. After P(MMA-MBA) is incorporated into the cement matrix, within the test temperature range of -10 to 50℃, P(MMA-MBA)-30 exhibits an exothermic peak at 10.53-10.58℃ with an enthalpy of 19.94-33.41 J / g during crystallization and an endothermic peak at 15.23-15.35℃ with an enthalpy of 20.47-34.78 J / g during melting. A comparison of the DSC test results of P(MMA-MBA) and P(MMA-MBA)-30 shows that the addition of P(MMA-MBA) has no substantial effect on the melting temperature and crystallization temperature.

[0043] Furthermore, the coating efficiency calculation results show that the coating efficiency of P(MMA-MBA) is 70-75%.

[0044] The thermal conductivity test results show that the thermal conductivity of P(MMA-MBA) is 0.2700-0.2900 W / (m·K); after P(MMA-MBA) is incorporated into the cement matrix, the thermal conductivity of the cement composite material is reduced to 0.4218–0.5147 W / (m·K), which is 43.9-54.0% lower than that of conventional cement.

[0045] The water contact angle test results show that after P(MMA-MBA) is incorporated into the cement matrix, the water contact angle of the P(MMA-MBA) cement composite material reaches 64.21-75.86°, which means it is hydrophobic; adding P(MMA-MBA) can change conventional cement from hydrophilic to hydrophobic.

[0046] Infrared thermal imaging test results show that after P(MMA-MBA) is incorporated into the cement matrix, within a test time of 25 minutes, the nominal temperature difference between P(MMA-MBA) and conventional cement is 5.8-7.9℃, with an average temperature difference of 5.1-7.6℃.

[0047] Therefore, the present invention has the following advantages over the prior art:

[0048] 1. By introducing MBA as a crosslinking comonomer to form a three-dimensional crosslinked network shell with MMA, the density and mechanical strength of the shell are significantly improved, enhancing its resistance to hydrolysis and damage in the highly alkaline environment of cement. Simultaneously, SDS is used as an emulsifier, ensuring the uniformity and stability of the emulsion through an electrostatic stabilization mechanism, effectively preventing the agglomeration of microcapsules during preparation and compounding, and achieving uniform dispersion in the cement paste.

[0049] 2. Using hexadecane as the phase change core material, its phase change temperature range closely matches the building's comfortable temperature range, endowing the cement-based material with excellent heat storage and temperature regulation functions. TG and DSC tests show that the microcapsules and their cement composite materials maintain good enthalpy during the phase change process, and their thermal decomposition temperature is significantly higher than that of conventional cement, indicating that they possess excellent thermal stability and long-term recycling potential.

[0050] 3. The microcapsule shell has hydrophobic properties. When incorporated into cement, it can increase the contact angle of the composite material to 64.21-75.86°, achieving a transformation from hydrophilic to hydrophobic. Simultaneously, the thermal conductivity of the composite material decreases to 0.4218-0.5147 W / (m·K), a reduction of 43.9-54.0% compared to conventional cement. It also possesses both heat insulation and seepage prevention functions, forming a multifunctional cement-based composite material system with synergistic heat storage, temperature regulation, hydrophobicity, and heat insulation properties.

[0051] 4. The preparation method described herein has clearly defined process parameters, mild reaction conditions, and requires no complex equipment, making it suitable for large-scale production. The raw materials used, such as MMA, MBA, hexadecane, and SDS, are all commercially available and commonly used chemicals, which are low in cost and widely available. Furthermore, the entire synthesis and compounding process is environmentally friendly, making it easy to achieve technology transfer and engineering applications in the field of building materials. Attached Figure Description

[0052] Figure 1 XRD pattern of P(MMA-MBA) obtained in Example 1, which is hexadecane;

[0053] Figure 2 The image shown is a SEM image of P(MMA-MBA) obtained in Example 1.

[0054] Figure 3 The TEM image of P(MMA-MBA) obtained in Example 1;

[0055] Figure 4 The TG diagrams are for Examples 1, 2, and 3.

[0056] Figure 5 The DSC diagram of P(MMA-MBA) obtained in Example 1;

[0057] Figure 6 This is a macroscopic diagram of P(MMA-MBA) obtained in Example 1;

[0058] Figure 7 The image shows the SEM image of P(MMA-MBA)-30 obtained in Example 1.

[0059] Figure 8 The following are DSC crystallization and melting diagrams for Examples 1, 2, and 3;

[0060] Figure 9 The contact angle diagrams are for Examples 1, 2, and 3.

[0061] Figure 10 These are red thermal imaging images of Examples 1, 2, and 3;

[0062] Figure 11 SEM image of P(MMA) prepared for Comparative Example 1;

[0063] Figure 12 SEM image of P(MMA-MBA)-SDS prepared for Comparative Example 2;

[0064] Figure 13 The image shows the SEM image of P(MMA-MBA)-10 obtained in Example 2.

[0065] Figure 14The image shown is a P(MMA-MBA)-20 SEM image obtained in Example 3. Detailed Implementation

[0066] The present invention will be further described in detail through embodiments and with reference to the accompanying drawings, but this is not intended to limit the scope of the invention.

[0067] Example 1

[0068] A method for preparing core-shell structured P(MMA-MBA) copolymer thermal storage phase change microcapsules includes the following steps:

[0069] Step 1, Preparation of oil and aqueous phases: First, under the conditions of stirring temperature of 40℃, stirring speed of 500 rpm, and stirring time of 30 min, hexadecane, methyl methacrylate (MMA), and N,N-methylenebisacrylamide (MBA) were stirred and dissolved to obtain a 16-MM solution as the oil phase. At the same time, under the conditions of stirring temperature of room temperature, stirring speed of 300 rpm, and stirring time of 30 min, sodium dodecyl sulfate (SDS) and deionized water were stirred and dissolved. After dissolution, glacial acetic acid was added to adjust the pH value to 3-4 to obtain an SDS aqueous solution as the aqueous phase.

[0070] Step 2, the polymerization reaction of microcapsules: First, under the conditions of stirring emulsification temperature of 40℃, stirring emulsification speed of 800 rpm, and stirring emulsification time of 20 min, the 16-MM solution obtained in Step 1 was added dropwise to the SDS aqueous solution obtained in Step 1 for stirring and emulsification to obtain an emulsion solution; then, under the conditions of stirring mixing speed of 500 rpm and stirring mixing time of 5 min, potassium persulfate was added to the emulsion solution for stirring and mixing to obtain a reaction solution; finally, under the conditions of stirring polymerization temperature of 70℃, stirring polymerization speed of 200 rpm, and stirring polymerization time of 4 h, the reaction solution was stirred and polymerized. After the reaction was completed, the obtained product was centrifuged and vacuum dried to obtain core-shell structured P(MMA-MBA) copolymer heat storage phase change microcapsules, abbreviated as P(MMA-MBA);

[0071] The mass ratio of hexadecane, MMA, MBA, SDS, potassium persulfate, and deionized water is 20:40:1:2:1:400;

[0072] In step 2, the centrifugation conditions are: centrifugation speed of 8000 rpm and centrifugation time of 15 min; the vacuum drying conditions are: drying temperature of 35℃ and drying time of 24 h.

[0073] To confirm the composition of P(MMA-MBA), XRD tests were performed. The test results are as follows: Figure 1As shown, P(MMA-MBA) exhibits characteristic peaks of hexadecane. The test results indicate that P(MMA-MBA) has no effect on the phase transition properties of hexadecane.

[0074] To verify the microstructure of P(MMA-MBA), SEM testing was performed. The test results are as follows: Figure 2 As shown, P(MMA-MBA) is spherical;

[0075] To further verify the microstructure of P(MMA-MBA), TEM testing was performed. The test results are as follows: Figure 3 As shown, P(MMA-MBA) has a core-shell structure; the core structure is hexadecane, and the shell structure is a copolymer of methyl methacrylate (MMA) and N,N-methylenebisacrylamide (MBA), namely P(MMA-MBA).

[0076] Based on the combined results of SEM and TEM tests, P(MMA-MBA) is a spherical microcapsule with a core-shell structure.

[0077] To demonstrate the thermal stability of P(MMA-MBA), a TG test was performed. The test results are as follows: Figure 4 As shown, the initial decomposition temperature T0 of P(MMA-MBA) is 136.04℃, the final decomposition temperature T1 is 236.13℃, and the maximum degradation temperature T2 is 421.66℃.

[0078] To demonstrate the phase transition performance of P(MMA-MBA), DSC testing was performed, and the test results are as follows: Figure 5 As shown in Figure 1 and Table 1, within the test temperature range of -10 to 50℃, P(MMA-MBA) exhibits an exothermic peak at 10.73℃ with an enthalpy of 194.14 J / g during crystallization and an endothermic peak at 17.41℃ with an enthalpy of 195.87 J / g during melting.

[0079] Table 1 Melting and Crystallization Temperatures

[0080]

[0081] Furthermore, to prove the encapsulation efficiency of P(MMA-MBA), according to the formula E=(△H m，P(MMA-MBA) +△H f , P(MMA-MBA) ) / (△H m，正十六烷 +△H f，正十六烷 The calculation was performed by multiplying the result by 100%, and the coating efficiency was found to be 72.75%.

[0082] To demonstrate the thermal conductivity of P(MMA-MBA), thermal conductivity tests were conducted. The test results are shown in Table 2, where the thermal conductivity of P(MMA-MBA) is 0.2832 W / (m·K).

[0083] To demonstrate the stability, or encapsulation effect, of P(MMA-MBA), a leak-proof test was conducted. The specific method for the leak-proof test was as follows: since hexadecane is liquid at room temperature, if the microcapsules (shell structure) have defects or incomplete encapsulation, the hexadecane core material will leak out. Therefore, at room temperature, the sample was placed on a clean surface for macroscopic morphology observation over a period of 30 minutes to perform the leak-proof test. The test results are as follows: Figure 6 As shown, no oil stains or liquid droplets appeared on the surface of P(MMA-MBA). The test results indicate that P(MMA-MBA) possesses integrity and stability.

[0084] To demonstrate the application of P(MMA-MBA) in the field of cement materials, a phase change cement material was prepared by combining P(MMA-MBA) with conventional cement.

[0085] A method for preparing a phase change cement material based on core-shell structured P(MMA-MBA) copolymer thermal storage phase change microcapsules includes the following steps: First, with P(MMA-MBA) accounting for 30 wt.% of the total mass, the P(MMA-MBA) is soaked in deionized water for 24 hours. Simultaneously, cement and deionized water are mixed to obtain cement paste. Then, P(MMA-MBA) is incorporated into the cement paste to obtain the microcapsule phase change cement material. In specific embodiment 1, because the amount of P(MMA-MBA) added is 30 wt.%, it is simply referred to as P(MMA-MBA)-30.

[0086] To verify the microstructure of P(MMA-MBA)-30, SEM testing was performed. The test results are as follows: Figure 7 As shown, spherical P(MMA-MBA) is uniformly distributed in the cement. Test results indicate that P(MMA-MBA) has a good interfacial bond with the cement, and there is no microcapsule breakage.

[0087] To demonstrate the thermal stability of P(MMA-MBA)-30, a TG test was conducted. Simultaneously, for comparison, a TG test was performed on conventional cement without added P(MMA-MBA). The test results are as follows: Figure 4 As shown,

[0088] Conventional cement exhibits two significant weight losses. The first loss occurs at 100℃, due to the evaporation of free water. The second loss occurs at the following temperatures: the initial decomposition temperature T0 is 349.10℃, the final decomposition temperature T1 is 406.06℃, and the maximum degradation temperature T2 is 436.81℃. The weight loss decreases from 63.1% to 56.7%, a range of 6.4 wt.%. This is attributed to the decomposition of the cement hydration product Ca(OH)₂.

[0089] P(MMA-MBA)-30 also exhibited two significant weight loss events. The first weight loss occurred at 100℃; the second weight loss occurred at the following temperatures: the initial decomposition temperature T0 was 391.24℃, the final decomposition temperature T1 was 402.26℃, and the maximum degradation temperature T2 was 412.14℃. The weight loss decreased from 61.8% to 58.3%, a reduction of 3.5 wt.%, which is only 54.7% of that of conventional cement.

[0090] TG test results show that adding P(MMA-MBA) can significantly reduce the thermal decomposition weight loss phenomenon of cement, namely P(MMA-MBA)-30, thus significantly improving thermal stability.

[0091] To demonstrate the phase transition performance of P(MMA-MBA)-30, DSC testing was conducted. The test results are as follows: Figure 8 As shown in Table 2, within the test temperature range of -10 to 50℃, P(MMA-MBA)-30 exhibits an exothermic peak at 10.58℃ with an enthalpy of 33.41 J / g during crystallization and an endothermic peak at 15.35℃ with an enthalpy of 34.78 J / g during melting.

[0092] A comparison of the DSC test results of P(MMA-MBA) and P(MMA-MBA)-30 shows that the addition of P(MMA-MBA) has no substantial effect on the melting temperature and crystallization temperature.

[0093] To demonstrate the thermal conductivity of P(MMA-MBA)-30, thermal conductivity tests were conducted. Simultaneously, for comparison, the thermal conductivity of conventional cement was also tested. The test results are shown in Table 3.

[0094] The thermal conductivity of conventional cement is 0.9175 W / (m·K);

[0095] The thermal conductivity of P(MMA-MBA)-30 is 0.4218 W / (m·K);

[0096] Test results show that adding P(MMA-MBA) can significantly reduce thermal conductivity, with a reduction of 45.97%.

[0097] Table 2 Thermal Conductivity Table

[0098]

[0099] To demonstrate the effect of P(MMA-MBA) on hydrophobicity, water contact angle tests were conducted. Simultaneously, for comparison, water contact angle tests were performed on conventional cement. The test results are shown in Table 3 and... Figure 9 As shown,

[0100] Conventional cement has a water contact angle of 45.26°, meaning it is hydrophilic.

[0101] P(MMA-MBA)-30 has a water contact angle of 75.86°, indicating that it is hydrophobic.

[0102] Test results show that adding P(MMA-MBA) can change conventional cement from hydrophilic to hydrophobic. This is because the shell structure of the microcapsules is hydrophobic polymethyl methacrylate (PMMA). When mixed with conventional cement, it forms a dense and complete hydrophobic layer on the surface of the cement, effectively masking the original hydrophilic groups of the conventional cement, thus significantly improving its hydrophobicity.

[0103] Table 3. Contact angle values ​​and derived quantitative indicators corresponding to different P(MMA-MBA) microcapsule dosages.

[0104]

[0105] To demonstrate the effect of P(MMA-MBA) on temperature control performance, red thermal imaging tests were conducted. Simultaneously, for comparison, red thermal imaging tests were performed on conventional cement. The test results are shown in Table 4 and... Figure 10 As shown, within a test time of 25 minutes, the labeled temperature difference between P(MMA-MBA)-30 and conventional cement was 7.9℃, with an average temperature difference of 7.6℃. This is because, during the heating process, P(MMA-MBA) undergoes a phase change, meaning it absorbs and stores heat, thus inhibiting the temperature rise of the cement matrix.

[0106] Table 4 Comparison of cement composites with different P(MMA-MBA) microcapsule contents with conventional cement labeling and average temperature.

[0107]

[0108] To demonstrate the effect of copolymers, i.e., MBA, on microcapsules, Comparative Example 1 is provided, a phase change microcapsule based on a single polymer, P(MMA), without the addition of MBA.

[0109] Comparative Example 1

[0110] A method for preparing P(MMA) single polymer phase change microcapsules without the addition of MBA, unless otherwise specified, is the same as that in Example 1, except that in step 1, N,N-methylenebisacrylamide (MBA) is not added, only methyl methacrylate (MMA) is added, and the resulting P(MMA) single polymer phase change microcapsules are named P(MMA).

[0111] To verify the microstructure of P(MMA), SEM testing was performed. The test results are as follows: Figure 11 As shown, P(MMA) exhibits a flocculent structure, i.e., it is not spherical. The test results indicate that without the addition of MBA, the single polymer formed by polymerization using only MMA as a monomer cannot form a dense shell with a three-dimensional network structure. The reason is that the single polymer lacks cross-linking points, resulting in a linear molecular chain structure. Therefore, it cannot stably encapsulate and shrink into regular spherical microcapsules at the oil-water interface, which manifests as the formation of flocculent or amorphous aggregates.

[0112] To demonstrate the effect of SDS on microcapsules, Comparative Example 2 is provided, a phase change microcapsule without the addition of SDS.

[0113] Comparative Example 2

[0114] A method for preparing phase change microcapsules without adding SDS is described below. Unless otherwise specified, the steps are the same as in Example 1, except that in step 2, SDS is not added, and the resulting phase change microcapsules are named P(MMA-MBA)-SDS.

[0115] To verify the microstructure of P(MMA-MBA)-SDS, SEM testing was performed. The test results are as follows: Figure 12 As shown, P(MMA-MBA)-SDS forms spherical aggregates, indicating severe aggregation. Test results show that without SDS as an emulsifier, stable microcapsules cannot be formed. This is because the absence of SDS leads to excessively large droplet sizes and interfacial instability when the oil phase is dispersed in the aqueous phase. Furthermore, during the polymerization reaction, the electrostatic repulsion and steric hindrance cannot stabilize the microcapsule particles, ultimately resulting in the formation of spherical aggregates in the product.

[0116] To demonstrate the effect of P(MMA-MBA) content on microcapsule phase change cement materials, Examples 2 and 3 are provided, with P(MMA-MBA) contents of 10 wt.% and 20 wt.%, respectively, for microcapsule phase change cement materials.

[0117] Example 2

[0118] A microcapsule phase change cement material with a P(MMA-MBA) content of 10 wt.% is prepared. The steps are the same as in Example 1, except that the P(MMA-MBA) content is 10 wt.% in the preparation of the phase change cement material. Therefore, the microcapsule phase change cement material obtained in Example 2 is simply referred to as P(MMA-MBA)-10.

[0119] To verify the microstructure of P(MMA-MBA)-10, SEM testing was performed. The test results are as follows: Figure 13 As shown, the basic microstructure of P(MMA-MBA)-10 is not substantially different from that of P(MMA-MBA)-30, that is, spherical P(MMA-MBA) is uniformly distributed in cement.

[0120] To demonstrate the thermal stability of P(MMA-MBA)-10, a TG test was performed. The test results are as follows: Figure 4 As shown, there were also two significant weight loss events. The first weight loss temperature was 100℃; the second weight loss temperature, i.e. the initial decomposition temperature T0, was 335.15℃, the final temperature T1 was 399.54℃, and the maximum degradation temperature T2 was 412.35℃. The weight loss was from 59.2% to 55.3%, with a weight loss range of 3.9 wt.%.

[0121] To demonstrate the thermal conductivity of P(MMA-MBA)-10, thermal conductivity tests were conducted. The test results are shown in Table 2. The thermal conductivity of P(MMA-MBA)-10 is 0.5147 W / (m·K).

[0122] To demonstrate the hydrophobic properties of P(MMA-MBA)-10, water contact angle tests were conducted. The test results are shown in Table 3 and... Figure 9 As shown, the water contact angle of P(MMA-MBA)-10 is 64.21°, indicating that it is hydrophobic.

[0123] To demonstrate the temperature control performance of P(MMA-MBA)-10, red thermal imaging tests were conducted. The test results are shown in Table 4 and... Figure 10 As shown, within a test time of less than 25 minutes, the temperature difference between P(MMA-MBA)-10 and conventional cement was 5.8℃, with an average temperature difference of 5.1℃.

[0124] Example 3

[0125] A microcapsule phase change cement material with a P(MMA-MBA) content of 20 wt.% is described. The steps are the same as in Example 1, except that the P(MMA-MBA) content is 20 wt.% in the preparation of the phase change cement material. Therefore, the microcapsule phase change cement material obtained in Example 3 is simply referred to as P(MMA-MBA)-20.

[0126] To verify the microstructure of P(MMA-MBA)-20, SEM testing was performed. The test results are as follows: Figure 14 As shown, the basic microstructure of P(MMA-MBA)-20 is not substantially different from that of P(MMA-MBA)-10, that is, spherical P(MMA-MBA) is uniformly distributed in cement.

[0127] To demonstrate the thermal stability of P(MMA-MBA)-20, a TG test was conducted. The test results are as follows: Figure 4 As shown, there were also two significant weight loss events. The first weight loss temperature was 100℃; the second weight loss temperature, i.e. the initial decomposition temperature T0, was 336.97℃, the final temperature T1 was 400.25℃, and the maximum degradation temperature T2 was 413.78℃. The weight loss was from 57.6% to 53.8%, with a weight loss range of 3.8 wt.%.

[0128] To demonstrate the thermal conductivity of P(MMA-MBA)-20, thermal conductivity tests were conducted. The test results are shown in Table 2. The thermal conductivity of P(MMA-MBA)-20 is 0.4712 W / (m·K).

[0129] To demonstrate the hydrophobic properties of P(MMA-MBA)-20, water contact angle tests were conducted. The test results are shown in Table 3 and... Figure 9 As shown, the water contact angle of P(MMA-MBA)-20 is 69.78°, indicating that it is hydrophobic.

[0130] To demonstrate the temperature control performance of P(MMA-MBA)-20, red thermal imaging tests were conducted. The test results are shown in Table 4 and... Figure 10 As shown, within a test time of less than 25 minutes, the marked temperature difference between P(MMA-MBA)-10 and conventional cement was 6.7℃, and the average temperature difference was 6.9℃.

Claims

1. A core-shell structured P(MMA-MBA) copolymer heat storage phase change microcapsule, characterized in that: The micro-morphology is a spherical structure, and has a core-shell structure, wherein the core structure is hexadecane, the shell structure is a methyl methacrylate MMA and N,N-methylene bisacrylamide MBA copolymer, the emulsifier is sodium dodecyl sulfate SDS, and the initiator is potassium persulfate, wherein The hexadecane provides phase change performance; The MMA forms a polymer main chain skeleton through radical polymerization, and plays a structural support role; The MBA acts as a crosslinking agent and a copolymer at the same time, and a three-dimensional crosslinked network structure is formed through copolymerization of the acrylamide structure and the methyl methacrylate chain by using the dual functional groups of the MBA, thereby enhancing the compactness and mechanical strength of the shell layer; The potassium persulfate acts as an initiator and decomposes to generate sulfate radicals under heating conditions, thereby playing a role in initiating the activation and chain growth reaction of the methyl methacrylate and N,N-methylene bisacrylamide monomers; The SDS acts as an emulsifier, and a negatively charged sulfate ion is ionized from the SDS and adsorbed on the oil / water interface, thereby playing a role in preventing the collision and coalescence of oil phase droplets in the emulsification and polymerization process through electrostatic repulsion, and forming a stable oil-in-water O / W emulsion system.

2. The phase change microcapsule according to claim 1, characterized by: The P(MMA-MBA) has an initial decomposition temperature T0 of 136.04-137.04℃, an end temperature T1 of 236.13-237.13℃, and a maximum degradation temperature T2 of 421.66-422.66℃; In the crystallization process of the P(MMA-MBA), there is an exothermic peak at 10.73-11.73℃, and the enthalpy value is 194.14-195.14 J / g; in the melting process, there is an endothermic peak at 17.41-18.41℃, and the enthalpy value is 195.87-196.87 J / g.

3. The phase change microcapsule according to claim 1, wherein: The coating efficiency of the P(MMA-MBA) is 70-75%.

4. A method for preparing core-shell structure P(MMA-MBA) copolymer heat storage phase change microcapsules, characterized in that The method comprises the following steps: Step 1, preparation of the oil phase and the water phase, under certain conditions, hexadecane, methyl methacrylate MMA and N,N-methylene bisacrylamide MBA are stirred and dissolved to obtain a 16-MM solution as the oil phase, and at the same time, under certain conditions, sodium dodecyl sulfate SDS and deionized water are stirred and dissolved, and after dissolution, glacial acetic acid is added to adjust the pH value to obtain an SDS aqueous solution as the water phase; Step 2, polymerization reaction of the microcapsule, under certain conditions, the 16-MM solution obtained in step 1 is added dropwise into the SDS aqueous solution obtained in step 1 for stirring and emulsification to obtain an emulsified solution, then, under certain conditions, potassium persulfate is added into the emulsified solution for stirring and mixing to obtain a reaction liquid, finally, under certain conditions, the reaction liquid is subjected to stirring and polymerization reaction, after the reaction is completed, the obtained product is subjected to centrifugation and vacuum drying to obtain a core-shell structure P(MMA-MBA) copolymer heat storage phase change microcapsule, which is abbreviated as P(MMA-MBA).

5. The method of claim 4, wherein: In step 1, the mass ratio of the hexadecane, the MMA, the MBA, the SDS, the potassium persulfate and the deionized water is 20:40:1:(2-4):(1-2):(400-500). In the step 1, the conditions for preparing the oil phase solution are that the stirring speed is 400-600 rpm, the stirring dissolution temperature is 35-45 DEG C, and the stirring time is 25-35 min. In the step 1, the conditions for preparing the water phase solution are that the stirring speed is 250-350 rpm, the stirring time is 25-35 min, and the pH value is adjusted by using glacial acetic acid.

6. The method of claim 4, wherein: In the step 2, the conditions for stirring emulsification are that the stirring speed is 700-900 rpm, the reaction temperature is 35-45 DEG C, and the reaction time is 15-25 min. In the step 2, the conditions for stirring mixing are that the stirring speed is 400-500 rpm, the reaction temperature is 35-45 DEG C, and the reaction time is 5-10 min. In the step 2, the conditions for stirring polymerization are that the stirring polymerization speed is 150-250 rpm, the stirring polymerization temperature is 65-75 DEG C, and the stirring polymerization time is 3-5 h. In the step 2, the conditions for centrifugation are that the centrifugation speed is 7500-8500 rpm, and the centrifugation time is 10-20 min; the conditions for vacuum drying are that the drying temperature is 30-40 DEG C, and the drying time is 20-28 h.

7. A phase change cement material based on core-shell structure P(MMA-MBA) copolymer microcapsules for heat storage, characterized in that: The phase change microcapsule heat storage material is obtained by compounding P(MMA-MBA) copolymer with a cement matrix, and the specific preparation method is as follows: first, P(MMA-MBA) is soaked in deionized water for 20-28 h, and at the same time, cement and deionized water are mixed to obtain cement paste, then P(MMA-MBA) is added into the cement paste to obtain a microcapsule phase change cement material; the contact angle is 64.21-75.86 DEG, and the material has hydrophobicity.

8. The method of claim 7, wherein: In the phase change cement material, the microcapsule material accounts for 10-30 wt.% of the total mass, i.e., the content is 10-30 wt.%.

9. The microencapsulated phase change cementitious material of claim 7, wherein: There are two obvious weight losses, the first weight loss temperature is 95-100 DEG C; the second weight loss temperature, i.e., the initial decomposition temperature T0 is 391.24-392.24 DEG C, the end temperature T1 is 402.26-403.26 DEG C, the maximum degradation temperature T2 is 412.14-413.14 DEG C, and the weight loss is from 61.8-62.8% to 58.3-59.3%, with a weight loss amplitude of 3.5-4.5 wt.%.

10. The microencapsulated phase change cementitious material of claim 7, wherein: In the test temperature range of-10-50 DEG C, there is an exothermic peak in the crystallization process at 10.53-10.58 DEG C, and the enthalpy value is 19.94-33.41 J / g; there is an endothermic peak in the melting process at 15.23-15.35 DEG C, and the enthalpy value is 20.47-34.78 J / g; The thermal conductivity is 0.4218-0.5147 W / (m·K), which is reduced by 43.9-54.0% compared with conventional cement; within a test time of 25 min, the labeled temperature difference with conventional cement is 5.8-7.9 DEG C, and the average temperature difference is 5.1-7.6 DEG C.

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