Functional cement additive based on heat storage phase change microcapsules as well as preparation method and application of functional cement additive

Abstract

The invention discloses a functional cement additive based on heat storage phase change microcapsules and a preparation method thereof, the microstructure of P (SM-MMA-DVB) is of a spherical structure, the size is 200 nm, the P (SM-MMA-DVB) has a core-shell structure, the core structure is octadecane and nanocellulose NCC, the shell structure is a styrene SM, methyl methacrylate MMA and divinylbenzene DVB copolymer, and the particle size of the P (SM-MMA-DVB) is 100 nm. The emulsifier is polyvinylpyrrolidone (PVP) and nano cellulose (NCC), and the initiator is azodiisobutyronitrile (AIBN); the coating efficiency is 80 to 85 percent; and the heat conductivity coefficient of the P (SM-MMA-DVB) ranges from 0.2416 W / (m.K) to 1.2451 W / (m.K). The invention relates to a phase-change cement material based on a core-shell structure P (SM-MMA-DVB) copolymer heat-storage phase-change microcapsule. The phase-change cement material is prepared by compounding the P (SM-MMA-DVB) copolymer heat-storage phase-change microcapsule and a cement matrix, the water contact angle is 89.42 degrees to 106.72 degrees; the hydrophilic property is converted into the hydrophobic property; the microcapsule material accounts for 10-30 wt.% of the total mass of the phase change cement; the heat conductivity coefficient is 0.2416 W / (m.K) to 1.2451 W / (m.K); the cement has phase change energy storage performance, the marked temperature difference between the cement and conventional cement is 5.4-5.8 DEG C, and the average temperature difference between the cement and conventional cement is 5.1-5.8 DEG C.

Description

Technical Field

[0001] This invention relates to the field of thermal energy storage cement-based composite materials, specifically to a functional cement additive based on thermal energy storage phase change microcapsules, its preparation method, and its application. Background Technology

[0002] To improve the heat capacity and thermal inertia of cement-based materials, phase change materials (PCMs) can be microencapsulated and incorporated into the cement matrix to obtain phase change cement materials. For example, based on the previous research results of the inventors of this invention, existing literature 1 (Xiang Cuili, Zhu Houqi, Zou Yongjin, Xing Xiaoxiao, Wei Nini, Sun Lixian, Wang Heng, Yin Dan. A microencapsulated phase change cement material and its preparation method and application: 202511377271.3 [P]. 2025-09-25.) uses melamine-urea-formaldehyde resin (MUF) as the shell material and octadecane as the core material, combined with a Tween 80 / sodium dodecyl sulfate composite emulsion system, to prepare MUF / TS-SDS microencapsulated phase change cement materials, achieving a coating efficiency of 67.5% and a thermal conductivity increase of 39.4% compared to the reference cement. However, since this technical solution uses MUF resin as the shell, it is prone to hydrolysis in alkaline environments, which leads to the degradation of the shell structure and ultimately results in poor long-term heat storage stability and insufficient cycle durability.

[0003] For example, in another previous research result of the inventors of this invention, existing literature 2 (Xiang Cuili, Zhu Houqi, Zou Yongjin, Xing Xiaoxiao, He Yuting, Sun Lixian, Wang Heng, Yin Dan. A core-shell structured P(MMA-MBA) copolymer thermal storage phase change microcapsule and its preparation method and application: 202511834242.5 [P]. 2025-12-08.), in order to enhance the crosslinking density and mechanical strength of the shell, N,N-methylenebisacrylamide (MBA) was introduced as a crosslinking agent and copolymerized with methyl methacrylate (MMA) to prepare P(MMA-MBA) microcapsules, achieving an encapsulation efficiency of 70-75%, and giving the cement composite material obvious hydrophobic properties, while also having good interfacial stability. However, although this technical solution uses MBA as a crosslinking agent and can form a three-dimensional network structure, later studies have shown that the mechanical strength of the obtained microcapsules is low and cannot meet the application requirements under long-term stress conditions, thus resulting in cracking and core material leakage problems.

[0004] To address the hydrolysis and mechanical strength issues present in the inventors' prior art, the emulsification system can be adjusted to improve the adaptability of the microcapsules to cement application conditions, specifically high-alkali and high-salt environments. For example, existing literature 3 (Jiaojiao Zhang, Tianbo Zhao, Yuqiao Chai, Lili Wang. "Preparation and Characterization of High Content Paraffin Wax Microcapsules and Micro / Nanocapsules with Poly Methyl Methacrylate Shell by Suspension-Like Polymerization" [J]. Chinese Journal of Chemistry, 2017, 35: 897–904.) uses suspension polymerization with methyl methacrylate (MMA) as the shell material and paraffin wax as the core material to prepare methyl methacrylate / paraffin wax microcapsules. This technique allows the microcapsules with the core material to exhibit 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.

[0005] To improve the dispersion stability of microcapsules in cementitious matrices, nano-reinforcement and composite emulsification strategies can be employed. For example, existing literature 4 (Zijian Song, Rong Chen, Zihao Huang, Yuhan Gong, Hong Zhao. "Preparation and Characterization of Perfluoropolyether-Silane@EthylCellulose Polymeric Microcapsules" [J]. Polymers, 2024, 16(2), 169.) uses a solvent evaporation method to prepare polymer microcapsules for concrete hydrophobicity using perfluoropolyether silane (PFPE-silane) as the core material and ethyl cellulose (EC) as the wall material. This study investigated the effects of stirring rate and core-shell ratio on the particle size and morphology of the microcapsules and confirmed that microcapsules with an average particle size of approximately 165.71 μm and a concentrated distribution can be obtained by optimizing the process. However, the shell constructed by this technical solution is a single ethyl cellulose material, whose mechanical strength and density mainly rely on the physical entanglement of the polymer itself, lacking the support of a chemical cross-linking network. Furthermore, only gelatin is used as an emulsifier during the emulsification process, and its stabilization mechanism is mainly based on steric hindrance, which has limited ability to suppress van der Waals attraction between microcapsule particles in the highly alkaline and ionically strong environment of cement. The consequences are specifically manifested in the presence of numerous micropores on the surface of the prepared microcapsules, insufficient shell density, and challenges to long-term stability in the complex environment of cement slurry. The core material is prone to premature release through micropores or decomposition due to hydration heat, thus affecting its long-term performance in cement-based composite materials.

[0006] Analysis of existing technologies reveals that current solutions for microencapsulation technology aimed at cement-based thermal storage and functional enhancement still face two key challenges:

[0007] 1. The shell of microcapsules is mostly physically coated or a single polymer system with low chemical cross-linking and insufficient mechanical properties. Under the heat of cement hydration, alkaline environment and external force, it is easy to break or degrade, resulting in core material leakage and functional failure.

[0008] 2. The emulsion stabilization system in the microcapsule preparation process is not very adaptable to the environment. In particular, in the high-alkali and high-salt ion environment unique to cement paste, the stabilization mechanism of conventional emulsifiers is easily weakened, resulting in uneven dispersion of microcapsules, easy agglomeration, and difficulty in forming a uniform and stable dispersion system in composite materials. Summary of the Invention

[0009] The purpose of this invention is to provide a functional cement additive based on heat storage phase change microcapsules, its preparation method, and its application, solving the problems of poor compatibility between phase change materials and cement matrices, easy leakage, and poor thermal conductivity. The specific basic principles involved are as follows:

[0010] Octadecane is used as the core material to provide phase change properties;

[0011] Styrene (SM), methyl methacrylate (MMA), and divinylbenzene (DVB) were used as shell materials, among which...

[0012] SM forms a rigid backbone of polymer main chain through free radical polymerization, providing structural support for microcapsules and promoting stable deposition of shell at the oil-water interface;

[0013] MMA also acts as a comonomer, working synergistically with SM to construct a uniform and dense polymer backbone by adjusting the hydrophilicity-hydrophobicity balance of the copolymer chains.

[0014] DVB is used as a crosslinking agent because its divinyl functional groups can copolymerize and crosslink with the polymer chains of SM and MMA to form a three-dimensional network structure, thereby effectively enhancing the density and mechanical strength of the shell.

[0015] This structure can significantly improve dimensional stability during thermal cycling and durability under long-term service conditions;

[0016] Azobisisobutyronitrile (AIBN) was used as an initiator. Free radicals were generated by the decomposition of AIBN under heating conditions, which initiated the activation and chain growth reactions of SM, MMA and DVB monomers.

[0017] Polyvinylpyrrolidone (PVP) and nanocellulose (NCC) are used as composite emulsifiers. Through the steric hindrance effect of PVP and the interfacial stabilization effect of NCC nanofibers, collision and aggregation of oil droplets during emulsification and polymerization are effectively prevented, forming a stable water-in-oil O / W emulsion system.

[0018] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0019] A core-shell structured P(SM-MMA-DVB) copolymer thermal storage phase change microcapsule is disclosed. The P(SM-MMA-DVB) exhibits a spherical structure with a size of 200 nm and a core-shell structure. The core structure is composed of octadecane and nanocellulose (NCC), while the shell structure is a copolymer of styrene (SM), methyl methacrylate (MMA), and divinylbenzene (DVB). The emulsifiers are polyvinylpyrrolidone (PVP) and nanocellulose (NCC), and the initiator is azobisisobutyronitrile (AIBN).

[0020] The octadecane is used to provide phase change properties;

[0021] The SM provides structural rigidity, stabilizes the oil phase core, and promotes the aggregation of the shell at the oil-water interface.

[0022] The MMA also acts as a copolymer, regulating the hydrophilicity-hydrophobicity balance of the copolymer and synergistically forming a uniform polymer backbone with SM.

[0023] The DVB enhances the density and mechanical strength of the shell by forming a three-dimensional network structure during the polymerization process.

[0024] The NCC, as a nano-reinforcing agent and auxiliary stabilizer, plays a role in improving emulsion stability and enhancing the mechanical properties of the shell.

[0025] The AIBN acts as an initiator, decomposing under heating conditions to generate free radicals, which initiate the free radical copolymerization reaction of SM, MMA and DVB.

[0026] The PVP and NCC together serve as a composite emulsifier / stabilizer, which, through steric hindrance and electrostatic effects, prevents the coalescence of oil phase droplets and forms a stable oil / water (O / W) emulsion system.

[0027] The coating efficiency of P(SM-MMA-DVB) is 80-85%; moreover, it has integrity and stability.

[0028] There were two significant weight loss events. The first event had an initial decomposition temperature T0 of 136.72-156.82℃, an ending temperature T1 of 151.49-228.01℃, and a maximum degradation temperature T2 of 255.78-280.78℃. The second event had an initial decomposition temperature T0 of 343.83-365.32℃, an ending temperature T1 of 410.06-418.75℃, and a maximum degradation temperature T2 of 466.82-483.75℃.

[0029] During the crystallization process of P(SM-MMA-DVB), there is an exothermic peak at 22.56-23.82℃ with an enthalpy of 195.16-233.92 J / g; during the melting process, there is an endothermic peak at 28.32-29.64℃ with an enthalpy of 196.34-234.81 J / g.

[0030] The thermal conductivity of P(SM-MMA-DVB) is 0.2416-1.2451 W / (m·K).

[0031] A method for preparing core-shell structured P(SM-MMA-DVB) copolymer thermal storage phase change microcapsules includes the following steps: First, an oil phase and an aqueous phase are prepared using a one-step method. Specifically, the oil phase is prepared by stirring and dissolving octadecane, styrene (SM), methyl methacrylate (MMA), divinylbenzene (DVB), and carbon nanoparticles (CNP). After dissolution, azobisisobutyronitrile (AIBN) is added and stirred to obtain an 18-SMD solution as the oil phase. The aqueous phase is prepared by stirring and dissolving polyvinylpyrrolidone (PVP), nanocellulose (NCC), and deionized water to obtain a PN aqueous solution as the aqueous phase. Then, the 18-SMD solution is added dropwise to the PN aqueous solution and stirred to emulsify, obtaining an emulsion solution. Finally, the emulsion solution is subjected to a polymerization reaction. After the reaction is complete, the mixture is centrifuged, washed, and vacuum dried to obtain core-shell structured P(SM-MMA-DVB) copolymer thermal storage phase change microcapsules, abbreviated as P(SM-MMA-DVB).

[0032] The conditions for centrifugal washing are: centrifugation speed of 7800-8200 rpm and centrifugation time of 14-16 min; the conditions for vacuum drying are: drying temperature of 33-37℃ and drying time of 23-25 ​​h.

[0033] The mass ratio of octadecane, SM, MMA, DVB, CNP, AIBN, PVP, NCC and deionized water is 10 : 5 : 5 : 2 : (0.1-0.2) : (0.2-0.4) : (1-2) : (15-30) : (185-200).

[0034] The preparation conditions for the oil phase solution are as follows: stirring speed of 450-550 rpm, stirring temperature of 38-42℃, and stirring time of 28-32 min.

[0035] The preparation conditions for the aqueous solution are: stirring speed of 450-550 rpm and stirring time of 18-22 min;

[0036] The conditions for stirring and emulsifying are: stirring speed of 950-1050 rpm, emulsification reaction temperature of 43-47℃, and emulsification reaction time of 38-42 min.

[0037] The conditions for the stirred polymerization are: stirring speed of 750-850 rpm, polymerization temperature of 83-87℃, and polymerization time of 3.8-4.2 h.

[0038] A phase change cement material based on core-shell structured P(SM-MMA-DVB) copolymer thermal storage phase change microcapsules is obtained by compositing P(SM-MMA-DVB) copolymer thermal storage phase change microcapsules with a cement matrix. The specific preparation method is as follows: First, P(SM-MMA-DVB) is soaked in deionized water for 20-28 hours. Simultaneously, cement and deionized water are mixed to obtain cement paste. Then, P(SM-MMA-DVB) is incorporated into the cement paste to obtain the microcapsule phase change cement material. Its water contact angle is 89.42°-106.72°, and it changes from hydrophilic to hydrophobic.

[0039] In the phase change cement material, the microcapsule material accounts for 10-30 wt.% of the total mass.

[0040] There were two distinct weight loss events. In the first weight loss, the initial decomposition temperature T0 was 135.47-156.82℃, the ending temperature T1 was 197.56-213.41℃, and the maximum degradation temperature T2 was 259.36-280.78℃. In the second weight loss, the initial decomposition temperature T0 was 357.52-365.32℃, the ending temperature T1 was 409.32-418.75℃, and the maximum degradation temperature T2 was 471.28-483.75℃.

[0041] During crystallization, an exothermic peak exists at 23.24-23.82℃, with an enthalpy of 13.57-36.95 J / g; during melting, an endothermic peak exists at 27.96-28.32℃, with an enthalpy of 14.75-37.6 J / g.

[0042] The thermal conductivity is 0.2416-1.2451 W / (m·K), which is 291.8-415.4% higher than that of pure microcapsule materials;

[0043] It has phase change energy storage capabilities, and the temperature difference between it and conventional cement is 5.4-5.8℃, with an average temperature difference of 5.1-5.8℃.

[0044] The beneficial technical effects of this invention have been tested and are as follows:

[0045] XRD test results show that P(SM-MMA-DVB) has characteristic peaks of octadecane, which have no effect on the phase transition properties of octadecane.

[0046] SEM test results show that P(SM-MMA-DVB) has a regular spherical structure; after being incorporated into the cement matrix, it is uniformly distributed in the cement hydration products, has good interfacial bonding with cement, and there is no microcapsule breakage phenomenon.

[0047] TG test results showed that P(SM-MMA-DVB) experienced two significant weight loss events. The first event had an initial decomposition temperature T0 of 136.72-156.82℃, an ending temperature T1 of 151.49-228.01℃, and a maximum degradation temperature T2 of 255.78-280.78℃. The second event had an initial decomposition temperature T0 of 343.83-365.32℃, an ending temperature T1 of 410.06-418.75℃, and a maximum degradation temperature T2 of 466.82-483.75℃.

[0048] When P(SM-MMA-DVB) is incorporated into the cement matrix, it also exhibits two distinct weight loss events. The first weight loss begins at temperatures T0 of 135.47-156.82℃, ends at temperatures T1 of 197.56-213.41℃, and reaches a maximum degradation temperature T2 of 259.36-280.78℃. The second weight loss begins at temperatures T0 of 357.52-365.32℃, ends at temperatures T1 of 409.32-418.75℃, and reaches a maximum degradation temperature T2 of 471.28-483.75℃.

[0049] TG test results show that adding P(SM-MMA-DVB) can significantly improve the thermal stability of cement composites.

[0050] DSC test results show that, within the test temperature range of -10 to 50℃, P(SM-MMA-DVB) exhibits an exothermic peak at 22.56-23.82℃ with an enthalpy of 195.16-233.92 J / g during crystallization and an endothermic peak at 28.32-29.64℃ with an enthalpy of 196.34-234.81 J / g during melting.

[0051] When P(SM-MMA-DVB) is incorporated into the cement matrix, within the test temperature range of -10 to 50℃, an exothermic peak is observed at 23.24-23.82℃ during the crystallization process, with an enthalpy value of 13.57-36.95 J / g; and an endothermic peak is observed at 27.96-28.32℃ during the melting process, with an enthalpy value of 14.75-37.6 J / g.

[0052] DSC test results show that the addition of P(SM-MMA-DVB) has no substantial effect on melting temperature and crystallization temperature.

[0053] Furthermore, the coating efficiency calculation results show that the coating efficiency of P(SM-MMA-DVB) is 80-85%.

[0054] The thermal conductivity test results show that the thermal conductivity of P(SM-MMA-DVB) is 0.2416 W / (m·K); after P(SM-MMA-DVB) is incorporated into the cement matrix, the thermal conductivity of the cement composite material is 0.9465–1.2451 W / (m·K), which is 291.8-415.4% higher than that of pure microcapsule material and 16.3-34.6% higher than that of conventional cement.

[0055] The water contact angle test results show that after P(SM-MMA-DVB) is incorporated into the cement matrix, the water contact angle of the cement composite material reaches 89.42°-106.72°, changing from hydrophilic to hydrophobic; adding P(SM-MMA-DVB) can change conventional cement from hydrophilic to hydrophobic.

[0056] Infrared thermal imaging test results show that after P(SM-MMA-DVB) is incorporated into the cement matrix, within a test time of less than 20 minutes, the temperature difference between P(SM-MMA-DVB) and conventional cement is 5.4-5.8℃, with an average temperature difference of 5.1-5.8℃.

[0057] Therefore, the present invention has the following advantages over the prior art:

[0058] 1. By copolymerizing styrene (SM), methyl methacrylate (MMA), and divinylbenzene (DVB) and reinforcing with nanocellulose (NCC), a composite shell with rigidity, a dense three-dimensional network, and nano-reinforcing effect was constructed. This significantly improved the mechanical strength and density of the shell, enabling it to effectively resist stress and alkaline environment erosion in the cement matrix. Simultaneously, a composite emulsion stabilization system of polyvinylpyrrolidone (PVP) and NCC was employed. Through the synergistic effect of steric hindrance and electrostatic stabilization, the uniformity and stability of the emulsion and the high dispersibility of the microcapsules in the cement paste were ensured.

[0059] 2. Using octadecane as the phase change core material, its phase change temperature matches the room temperature regulation range of buildings, giving cement-based materials excellent heat storage and temperature buffering functions. TG and DSC tests show that the microcapsules have high encapsulation efficiency and excellent thermal stability. The cement composite material exhibits significant enthalpy during the phase change process, and its thermal decomposition temperature is significantly higher than that of conventional cement, demonstrating potential for long-term recycling.

[0060] 3. The microcapsule shell has hydrophobic properties. When incorporated into cement, it significantly increases the contact angle of the composite material, reaching a maximum of 106.72°, achieving a transformation from hydrophilic to hydrophobic. Simultaneously, the thermal conductivity of the composite material is significantly improved, reaching a maximum of 1.2451 W / (m·K), which facilitates heat transfer and triggers phase change processes within the material, synergistically achieving heat storage and temperature regulation, hydrophobicity, and thermal management functions.

[0061] 4. The preparation method described herein has clearly defined process parameters and mild reaction conditions, making it suitable for large-scale production. The raw materials used, such as SM, MMA, DVB, NCC, and PVP, are all commercially available and commonly used chemicals, with controllable costs and wide availability. Furthermore, the entire synthesis and compounding process is environmentally friendly and facilitates technology transfer and engineering applications in the building materials field. Attached Figure Description

[0062] Figure 1 XRD pattern of P(SM-MMA-DVB) obtained in Example 1, which is octadecane;

[0063] Figure 2 The image shows the SEM image of P(SM-MMA-DVB) obtained in Example 1;

[0064] Figure 3 The TEM image of P(MMA-MBA) obtained in Example 1;

[0065] Figure 4 The TG plots are for Example 1, Example 2, and Comparative Example 4;

[0066] Figure 5 The DSC diagram of P(SM-MMA-DVB) obtained in Example 1;

[0067] Figure 6 This is a macroscopic diagram of P(SM-MMA-DVB) obtained in Example 1;

[0068] Figure 7 The image shows the SEM image of P(SM-MMA-DVB)-30 obtained in Example 1.

[0069] Figure 8 DSC crystallization and melting diagrams for Examples 1, 2, and 4;

[0070] Figure 9 The contact angle diagrams are for Example 1, Example 2, and Comparative Example 4;

[0071] Figure 10 These are red thermal images of Examples 1, 2, and 4;

[0072] Figure 11 SEM image of P(SM-DVB) prepared for Comparative Example 1;

[0073] Figure 12 SEM image of P(MMA-DVB) prepared for Comparative Example 2;

[0074] Figure 13 SEM image of P(SM-MMA) prepared for Comparative Example 3;

[0075] Figure 14The image shows the SEM image of P(SM-MMA-DVB)-10 obtained in Example 2.

[0076] Figure 15 The image shows the P(SM-MMA-DVB)-20 SEM plot obtained in Comparative Example 4. Detailed Implementation

[0077] 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.

[0078] Example 1

[0079] A method for preparing a functional cement additive based on heat storage phase change microcapsules includes the following steps: a one-step method...

[0080] First, the oil phase and aqueous phase raw materials were prepared. Specifically, the oil phase was prepared by dissolving octadecane, styrene (SM), methyl methacrylate (MMA), divinylbenzene (DVB), and carbon nanoparticles (CNP) under stirring conditions of 40℃, 500 rpm, and 30 min. After dissolution, azobisisobutyronitrile (AIBN) was added and dissolved to obtain an 18-SMD solution as the oil phase. The aqueous phase was prepared by dissolving polyvinylpyrrolidone (PVP), nanocellulose (NCC), and deionized water under stirring conditions of room temperature, 500 rpm, and 20 min to obtain a PN aqueous solution as the aqueous phase.

[0081] Then, under the conditions of stirring emulsification temperature of 45℃, stirring emulsification speed of 1000 rpm, and stirring emulsification time of 40 min, 18-SMD solution was added dropwise to PN aqueous solution for stirring emulsification to obtain emulsion solution;

[0082] Finally, the emulsion solution was subjected to a stirring polymerization reaction at a stirring polymerization temperature of 85℃, a stirring polymerization speed of 800rpm, and a stirring polymerization time of 4h. After the reaction was completed, the solution was centrifuged, washed, and vacuum dried to obtain core-shell structured P(SM-MMA-DVB) copolymer heat storage phase change microcapsules, which are functional cement additives based on heat storage phase change microcapsules, abbreviated as P(SM-MMA-DVB).

[0083] The mass ratio of octadecane, SM, MMA, DVB, CNP, AIBN, PVP, NCC, and deionized water is 10 : 5 : 5 : 2 : 0.1 : 0.2 : 1 : 15 : 185;

[0084] The conditions for centrifugal washing are: centrifugation speed of 8000 rpm and centrifugation time of 15 min;

[0085] The vacuum drying conditions are: drying temperature of 35°C and drying time of 24 hours.

[0086] To confirm the composition of P(SM-MMA-DVB), XRD tests were performed. The test results are as follows. Figure 1 As shown, P(SM-MMA-DVB) exhibits characteristic peaks of octadecane. The test results indicate that P(SM-MMA-DVB) has no effect on the phase transition properties of octadecane.

[0087] To verify the microstructure of P(SM-MMA-DVB), SEM testing was performed. The test results are as follows: Figure 2 As shown, P(SM-MMA-DVB) is spherical with a size of 200 nm.

[0088] To further verify the microstructure of P(SM-MMA-DVB), TEM testing was performed. The test results are as follows: Figure 3 As shown, P(SM-MMA-DVB) has a core-shell structure, with the core being octadecane and the shell being a copolymer of SM, MMA, DVB and NCC, i.e., P(SM-MMA-DVB).

[0089] Based on the combined results of SEM and TEM tests, P(SM-MMA-DVB) is a spherical microcapsule with a core-shell structure.

[0090] To demonstrate the thermal stability of P(SM-MMA-DVB), a TG test was performed. The test results are as follows: Figure 4 As shown in Table 1, P(SM-MMA-DVB) exhibits two significant weight loss events. The first decomposition begins at a temperature of 136.72℃, ends at 228.01℃, and reaches a maximum degradation temperature of 255.78℃. The second decomposition begins at a temperature of 343.83℃, ends at 410.06℃, and reaches a maximum degradation temperature of 466.82℃.

[0091] Table 1 Summary of TG Test Results

[0092]

[0093] To demonstrate the phase transition performance of P(SM-MMA-DVB), DSC testing was performed, and the test results are as follows: Figure 5 As shown in Table 2, P(SM-MMA-DVB) exhibits an exothermic peak at 22.92℃ with an enthalpy of 195.16 J / g during crystallization within the test temperature range of -10 to 50℃; and an endothermic peak at 28.74℃ with an enthalpy of 196.34 J / g during melting.

[0094] Table 2 Melting and Crystallization Temperatures

[0095]

[0096] Furthermore, to prove the encapsulation efficiency of P(SM-MMA-DVB), according to the formula E= (△H m，P(SM-MMA-DVB) +△H f , P(SM-MMA-DVB) ) / (△H m , 正十八烷 +△H f，正十八烷 The calculation was performed by multiplying the result by 100%. The result was a coating efficiency of 83.6%.

[0097] To demonstrate the thermal conductivity of P(SM-MMA-DVB), thermal conductivity tests were conducted. The test results are shown in Table 3. The thermal conductivity of P(SM-MMA-DVB) is 0.2416 W / (m·K).

[0098] To demonstrate the stability, or encapsulation effect, of P(SM-MMA-DVB), a leak-proof test was conducted. The specific method for the leak-proof test was as follows: Since octadecane has a melting point of 29.64℃, if the microcapsules used as the shell structure have defects or incomplete encapsulation, octadecane, as the core material, will leak out. Therefore, the test was conducted at a temperature of 30℃ for 30 minutes. The sample was placed on a clean surface for macroscopic morphology observation, thus performing the leak-proof test. The test results are as follows: Figure 6 As shown, no oil stains or liquid droplets were observed on the surface of P(SM-MMA-DVB). The test results indicate that P(SM-MMA-DVB) possesses integrity and stability.

[0099] To demonstrate the application of P(SM-MMA-DVB) in the field of cement materials, a phase change cement material was prepared by combining P(SM-MMA-DVB) with conventional cement.

[0100] A method for preparing a phase change cement material based on a functional cement additive with heat storage phase change microcapsules includes the following steps: First, P(SM-MMA-DVB) is soaked in deionized water for 24 hours, with P(SM-MMA-DVB) accounting for 30 wt.% of the total mass. Simultaneously, cement and deionized water are mixed to obtain cement paste. Then, P(SM-MMA-DVB) is incorporated into the cement paste to obtain the microcapsule phase change cement material. Specifically, in Example 1, since the amount of P(SM-MMA-DVB) added is 30 wt.%, it is simply referred to as P(SM-MMA-DVB)-30.

[0101] To verify the microstructure of P(SM-MMA-DVB)-30, SEM testing was performed. The test results are as follows: Figure 7As shown, P(SM-MMA-DVB) is spherical and uniformly distributed in the cement. Test results indicate that P(SM-MMA-DVB) exhibits no microcapsule breakage and demonstrates good interfacial bonding with the cement.

[0102] To demonstrate the thermal stability of P(SM-MMA-DVB)-30, a TG test was conducted. Simultaneously, for comparison, a TG test was performed on conventional cement without added P(SM-MMA-DVB). The test results are as follows: Figure 4 As shown in Table 1,

[0103] Conventional cement exhibits two distinct weight loss phases. The first weight loss occurs at the following temperatures: the initial decomposition temperature T0 is 109.63℃, the final decomposition temperature T1 is 151.49℃, and the maximum degradation temperature T2 is 190.16℃. The second weight loss occurs at the following temperatures: the initial decomposition temperature T0 is 353.92℃, the final decomposition temperature T1 is 408.64℃, and the maximum degradation temperature T2 is 468.42℃.

[0104] P(SM-MMA-DVB)-30 also exhibited two significant weight loss events. The first weight loss temperature, i.e., the initial decomposition temperature T0, was 156.82℃, the final temperature T1 was 213.41℃, and the maximum degradation temperature T2 was 280.78℃. The second weight loss temperature, i.e., the initial decomposition temperature T0 was 365.32℃, the final temperature T1 was 418.75℃, and the maximum degradation temperature T2 was 483.75℃.

[0105] TG test results show that adding P(SM-MMA-DVB) can significantly reduce the thermal decomposition weight loss phenomenon of cement, namely P(SM-MMA-DVB)-30, thus significantly improving thermal stability.

[0106] To demonstrate the phase transition performance of P(SM-MMA-DVB)-30, DSC testing was conducted. The test results are as follows: Figure 8 As shown in Table 2, P(SM-MMA-DVB)-30 exhibits an exothermic peak at 23.82℃ with an enthalpy of 36.95 J / g during crystallization within the test temperature range of -10 to 50℃; and an endothermic peak at 28.32℃ with an enthalpy of 37.6 J / g during melting.

[0107] A comparison of the DSC test results of P(SM-MMA-DVB) and P(SM-MMA-DVB)-30 shows that the addition of P(SM-MMA-DVB) has no substantial effect on the melting temperature and crystallization temperature.

[0108] To demonstrate the thermal conductivity of P(SM-MMA-DVB)-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.

[0109] The thermal conductivity of conventional cement is 0.8141 W / (m·K).

[0110] The thermal conductivity of P(SM-MMA-DVB)-30 is 1.2451 W / (m·K).

[0111] Test results show that adding P(SM-MMA-DVB) can significantly improve thermal conductivity, with an improvement of 34.62%.

[0112] Table 3 Thermal conductivity table

[0113]

[0114] To demonstrate the effect of P(SM-MMA-DVB) 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 4 and... Figure 9 As shown,

[0115] Conventional cement has a water contact angle of 42.87°, meaning it is hydrophilic.

[0116] P(SM-MMA-DVB)-30 has a water contact angle of 106.72°, meaning it is hydrophobic.

[0117] Test results show that adding P(SM-MMA-DVB) can change conventional cement from hydrophilic to hydrophobic. This is because the surface of the P(SM-MMA-DVB) shell is rich in hydrophobic groups and has low surface energy. When microcapsules are incorporated into cement, their hydrophobic surfaces form a coating layer in the cement particles and pores, effectively reducing the surface energy of the cement composite material and potentially increasing surface roughness, thus achieving the transformation from hydrophilic to hydrophobic.

[0118] Table 4. Contact angle values ​​and derived quantitative indicators corresponding to different P(SM-MMA-DVB) microcapsule dosages

[0119]

[0120] To demonstrate the effect of P(SM-MMA-DVB) 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 5 and... Figure 10As shown, within a test time of less than 20 minutes, the labeled temperature difference between P(SM-MMA-DVB)-30 and conventional cement was 5.6℃, with an average temperature difference of 5.8℃. This is because, during the heating process, P(SM-MMA-DVB) plays a phase change energy storage role, that is, it absorbs and stores energy, thereby suppressing the temperature rise of the cement matrix.

[0121] Table 5. Comparison of cement composites with different P(SM-MMA-DVB) microcapsule contents with conventional cement labeling and average temperature.

[0122]

[0123] To demonstrate the effect of copolymers, i.e. MMA, on microcapsules, Comparative Example 1 is provided, a phase change microcapsule based on P(SM-DVB) polymer without the addition of MMA.

[0124] Comparative Example 1

[0125] A method for preparing P(SM-DVB) polymer phase change microcapsules without adding MMA is described below. Unless otherwise specified, the steps are the same as in Example 1, except that MMA is not added, only SM and DVB are added, and the resulting polymer phase change microcapsules are named P(SM-DVB).

[0126] To verify the microstructure of P(SM-DVB), SEM testing was performed. The test results are as follows: Figure 11 As shown, P(SM-DVB) exhibits a flocculent structure, i.e., it is not spherical. Test results indicate that polymers formed solely from SM and DVB without the addition of MMA cannot form a dense outer shell with a three-dimensional network structure. This is because MMA can regulate the hydrophilic-hydrophobic balance of the copolymer, promoting its ordered assembly at the oil-water interface. When polymerized solely from SM and DVB, the strong hydrophobicity of SM and the high crosslinking density of DVB result in an excessively rapid polymerization rate, leading to uneven phase separation and making it difficult to form a continuous, dense crosslinked shell on the surface of the emulsion droplets.

[0127] To demonstrate the effect of SM on microcapsules, Comparative Example 2 is provided, a phase change microcapsule without the addition of SM.

[0128] Comparative Example 2

[0129] A method for preparing phase change microcapsules without adding SM is described below. Unless otherwise specified, the steps are the same as in Example 1, except that SM is not added, only MMA and DVB are added, and the resulting polymer phase change microcapsules are named P(MMA-DVB).

[0130] To verify the microstructure of P(MMA-DVB), SEM testing was performed. The test results are as follows: Figure 12As shown, P(MMA-DVB) exhibits a flocculent structure, i.e., it is not spherical. Test results indicate that polymers formed solely from MMA and DVB without the addition of SM also fail to form a dense shell with a three-dimensional network structure. This is because SM provides sufficient hydrophobicity and rigidity to stabilize the oil phase and promote the aggregation of the shell at the oil-water interface. When polymerized solely from MMA and DVB, the strong hydrophilicity of MMA causes the copolymer to tend to disperse in the aqueous phase, making it difficult to effectively enrich and crosslink on the oil droplet surface.

[0131] To demonstrate the effect of DVB on microcapsules, Comparative Example 2 is provided, a phase change microcapsule without the addition of SM.

[0132] Comparative Example 3

[0133] A method for preparing phase change microcapsules without adding DVB is described below. Unless otherwise specified, the steps are the same as in Example 1, except that DVB is not added, only SM and MMA are added, and the resulting polymer phase change microcapsules are named P(SM-MMA).

[0134] To verify the microstructure of P(SM-MMA), SEM testing was performed. The test results are as follows: Figure 13 As shown, P(SM-MMA) exhibits a flocculent structure, meaning it is not spherical. Test results indicate that polymers formed solely from SM and MMA without the addition of SM also fail to form a dense shell with a three-dimensional network structure. This is because DVB can form a three-dimensional network structure during polymerization, endowing the shell with sufficient mechanical strength and density. When SM and MMA are copolymerized alone, linear or branched polymer chains are formed, lacking chemical crosslinking points, resulting in a loose shell structure with low strength, making it prone to cracking and deformation during stirring, centrifugation, or drying.

[0135] Comparative Examples 1, 2, and 3 show that SM, MMA, and DVB need to be introduced simultaneously to achieve synergistic effects in order to realize microcapsules with regular spherical morphology, complete core-shell structure, dense shell, and excellent mechanical strength. Among them, the role of SM is to provide structural rigidity and promote interface assembly, the role of MMA is to regulate the hydrophilicity-hydrophobicity balance to build a uniform framework, and the role of DVB is to enhance the shell strength and density by forming a three-dimensional network through cross-linking.

[0136] To demonstrate the effect of P(SM-MMA-DVB) addition on microcapsule phase change cement materials, Comparative Example 4 and Example 2 are provided, with P(SM-MMA-DVB) addition amounts of 10 wt.% and 20 wt.%, respectively, on microcapsule phase change cement materials.

[0137] Comparative Example 4

[0138] A microcapsule phase change cement material with an addition of 10 wt.% P(SM-MMA-DVB) is described. The steps are the same as in Example 1, except that the addition of P(SM-MMA-DVB) in the preparation of the phase change cement material is 10 wt.%. Therefore, the microcapsule phase change cement material obtained in Example 2 is simply referred to as P(SM-MMA-DVB)-10.

[0139] To verify the microstructure of P(SM-MMA-DVB)-10, SEM testing was performed. The test results are as follows: Figure 14 As shown, the basic microstructure of P(SM-MMA-DVB)-10 is not substantially different from that of P(SM-MMA-DVB)-30, that is, it is spherical and uniformly distributed in cement.

[0140] To demonstrate the thermal stability of P(SM-MMA-DVB)-10, a TG test was performed. The test results are as follows: Figure 4 As shown in Table 1, P(SM-MMA-DVB)-10 also exhibits two significant weight loss events. The first weight loss temperature, i.e., the initial decomposition temperature T0, is 135.47℃, the final temperature T1 is 197.56℃, and the maximum degradation temperature T2 is 259.36℃. The second weight loss temperature, i.e., the initial decomposition temperature T0 is 357.52℃, the final temperature T1 is 409.32℃, and the maximum degradation temperature T2 is 471.28℃.

[0141] To demonstrate the thermal conductivity of P(SM-MMA-DVB)-10, thermal conductivity tests were conducted. The test results are shown in Table 3. The thermal conductivity of P(SM-MMA-DVB)-10 is 0.9465 W / (m·K).

[0142] To demonstrate the hydrophobic properties of P(SM-MMA-DVB)-10, water contact angle tests were conducted. The test results are shown in Table 4 and... Figure 9 As shown, the water contact angle of P(SM-MMA-DVB)-10 is 66.59°, meaning it remains hydrophilic.

[0143] To demonstrate the temperature control performance of P(SM-MMA-DVB)-10, red thermal imaging tests were conducted. The test results are shown in Table 5 and... Figure 10 As shown, within a test time of less than 20 minutes, the temperature difference between P(SM-MMA-DVB)-10 and conventional cement was 5.8℃, with an average temperature difference of 5.1℃.

[0144] Example 2

[0145] A microcapsule phase change cement material with an addition of 20 wt.% P(SM-MMA-DVB) is described. The steps are the same as in Example 1, except that the addition of P(SM-MMA-DVB) in the preparation of the phase change cement material is 20 wt.%. Therefore, the microcapsule phase change cement material obtained in Example 3 is simply referred to as P(SM-MMA-DVB)-20.

[0146] To verify the microstructure of P(SM-MMA-DVB)-20, SEM testing was performed. The test results are as follows: Figure 15 As shown, the basic microstructure of P(SM-MMA-DVB)-20 is not substantially different from that of P(SM-MMA-DVB)-10, that is, it is spherical and uniformly distributed in cement.

[0147] To demonstrate the thermal stability of P(SM-MMA-DVB)-20, a TG test was conducted. The test results are as follows: Figure 4 As shown in Table 1, P(SM-MMA-DVB)-20 also exhibits two significant weight loss events. The first weight loss temperature, i.e., the initial decomposition temperature T0, is 141.25℃, the final temperature T1 is 200.47℃, and the maximum degradation temperature T2 is 278.35℃. The second weight loss temperature, i.e., the initial decomposition temperature T0, is 360.25℃, the final temperature T1 is 410.87℃, and the maximum degradation temperature T2 is 474.14℃.

[0148] To demonstrate the thermal conductivity of P(SM-MMA-DVB)-20, thermal conductivity tests were conducted. The test results are shown in Table 2. The thermal conductivity of P(SM-MMA-DVB)-20 is 1.1508 W / (m·K).

[0149] To demonstrate the hydrophobic properties of P(SM-MMA-DVB)-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(SM-MMA-DVB)-20 is 89.42°, indicating that it is hydrophobic.

[0150] To demonstrate the temperature control performance of P(SM-MMA-DVB)-20, red thermal imaging tests were conducted. The test results are shown in Table 5 and... Figure 10 As shown, within a test time of less than 20 minutes, the temperature difference between P(SM-MMA-DVB)-20 and conventional cement was 5.4℃, with an average temperature difference of 5.6℃.

Claims

1. A functional cement additive based on heat storage phase change microcapsules, characterized in that: The microstructure of P(SM-MMA-DVB) is spherical with a size of 200 nm and a core-shell structure. The core structure consists of octadecane and nanocellulose (NCC), while the shell structure is a copolymer of styrene (SM), methyl methacrylate (MMA), and divinylbenzene (DVB). The emulsifiers are polyvinylpyrrolidone (PVP) and nanocellulose (NCC), and the initiator is azobisisobutyronitrile (AIBN). The octadecane is used to provide phase change properties; The SM provides structural rigidity, stabilizes the oil phase core, and promotes the aggregation of the shell layer at the oil-water interface. The MMA also acts as a copolymer, regulating the hydrophilicity-hydrophobicity balance of the copolymer and synergistically forming a uniform polymer backbone with SM. The DVB enhances the density and mechanical strength of the shell by forming a three-dimensional network structure during the polymerization process. The NCC, as a nano-reinforcing agent and auxiliary stabilizer, plays a role in improving emulsion stability and enhancing the mechanical properties of the shell. The AIBN acts as an initiator, decomposing under heating conditions to generate free radicals, which initiate the free radical copolymerization reaction of SM, MMA and DVB. The PVP and NCC together act as a composite emulsifier / stabilizer, which, through steric hindrance and electrostatic effects, prevents the coalescence of oil phase droplets and forms a stable oil / water (O / W) emulsion system.

2. The functional cement additive according to claim 1, characterized in that: The coating efficiency of P(SM-MMA-DVB) is 80-85%; moreover, it has integrity and stability.

3. The functional cement additive according to claim 1, characterized in that: There were two significant weight loss events. The first event had an initial decomposition temperature T0 of 136.72-156.82℃, an ending temperature T1 of 151.49-228.01℃, and a maximum degradation temperature T2 of 255.78-280.78℃. The second event had an initial decomposition temperature T0 of 343.83-365.32℃, an ending temperature T1 of 410.06-418.75℃, and a maximum degradation temperature T2 of 466.82-483.75℃. During the crystallization process of P(SM-MMA-DVB), there is an exothermic peak at 22.56-23.82℃ with an enthalpy of 195.16-233.92 J / g; during the melting process, there is an endothermic peak at 28.32-29.64℃ with an enthalpy of 196.34-234.81 J / g. The thermal conductivity of P(SM-MMA-DVB) is 0.2416-1.2451 W / (m·K).

4. A method for preparing a functional cement additive based on heat storage phase change microcapsules, characterized in that... Includes the following steps: The process involves a one-step method. First, oil and aqueous phase raw materials are prepared. Specifically, the oil phase is prepared by dissolving octadecane, styrene (SM), methyl methacrylate (MMA), divinylbenzene (DVB), and carbon nanoparticles (CNP) by stirring. After dissolution, azobisisobutyronitrile (AIBN) is added and dissolved to obtain an 18-SMD solution as the oil phase. The aqueous phase is prepared by dissolving polyvinylpyrrolidone (PVP), nanocellulose (NCC), and deionized water by stirring to obtain a PN aqueous solution as the aqueous phase. Then, the 18-SMD solution is added dropwise to the PN aqueous solution and stirred to emulsify, resulting in an emulsion solution. Finally, the emulsion solution is subjected to a polymerization reaction. After the reaction is complete, the mixture is centrifuged, washed, and vacuum dried to obtain core-shell structured P(SM-MMA-DVB) copolymer thermal storage phase change microcapsules, which are functional cement additives based on thermal storage phase change microcapsules, abbreviated as P(SM-MMA-DVB). The conditions for centrifugal washing are: centrifugation speed of 7800-8200 rpm and centrifugation time of 14-16 min; the conditions for vacuum drying are: drying temperature of 33-37℃ and drying time of 23-25 ​​h.

5. The preparation method according to claim 4, characterized in that: The mass ratio of octadecane, SM, MMA, DVB, CNP, AIBN, PVP, NCC and deionized water is 10 : 5 : 5 : 2 : (0.1-0.2) : (0.2-0.4) : (1-2) : (15-30) : (185-200). The preparation conditions for the oil phase solution are as follows: stirring speed of 450-550 rpm, stirring temperature of 38-42℃, and stirring time of 28-32 min. The preparation conditions for the aqueous solution are as follows: stirring speed of 450-550 rpm and stirring time of 18-22 min.

6. The preparation method according to claim 4, characterized in that: The conditions for stirring and emulsifying are: stirring speed of 950-1050 rpm, emulsification reaction temperature of 43-47℃, and emulsification reaction time of 38-42 min. The conditions for the stirred polymerization are: stirring speed of 750-850 rpm, polymerization temperature of 83-87℃, and polymerization time of 3.8-4.2 h.

7. A phase change cement material based on a functional cement additive with heat storage phase change microcapsules, characterized in that: The microcapsule-based phase change cement material is prepared by combining P(SM-MMA-DVB) copolymer thermal storage phase change microcapsules with a cement matrix. The specific preparation method is as follows: First, P(SM-MMA-DVB) is soaked in deionized water for 20-28 hours. Simultaneously, cement and deionized water are mixed to obtain cement paste. Then, P(SM-MMA-DVB) is incorporated into the cement paste to obtain the microcapsule phase change cement material. The water contact angle is 89.42°-106.72°, and the material changes from hydrophilic to hydrophobic. In the phase change cement material, the microcapsule material accounts for 10-30 wt.% of the total mass.

8. The phase change cement material according to claim 7, characterized in that: There were two distinct weight loss events. In the first weight loss, the initial decomposition temperature T0 was 135.47-156.82℃, the ending temperature T1 was 197.56-213.41℃, and the maximum degradation temperature T2 was 259.36-280.78℃. In the second weight loss, the initial decomposition temperature T0 was 357.52-365.32℃, the ending temperature T1 was 409.32-418.75℃, and the maximum degradation temperature T2 was 471.28-483.75℃. During crystallization, an exothermic peak exists at 23.24-23.82℃, with an enthalpy of 13.57-36.95 J / g; during melting, an endothermic peak exists at 27.96-28.32℃, with an enthalpy of 14.75-37.6 J / g. The thermal conductivity is 0.2416-1.2451 W / (m·K), which is 291.8-415.4% higher than that of pure microcapsule materials.

9. The phase change cement material according to claim 7, characterized in that: It has phase change energy storage performance, and the temperature difference between it and conventional cement is 5.4-5.8℃, with an average temperature difference of 5.1-5.8℃.

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