Phase Change Materials Microcapsules Research Articles

Pore-scale numerical investigation on the thermal storage properties of packed-bed systems with phase change material microcapsules

Phase change material (PCM) microcapsules are gaining increasing attention because it can overcome the shortage of PCM macrocapsules and increase the heat transfer area, while the pore-scale thermal performance of the PCM microcapsule packed-bed systems, as well as the influence of packing methods and microcapsule sizes on thermal storage, is still poorly understood. This paper introduces various spherical PCM microcapsule pack models, including single-layered, diameter-changed two-layered, and three-layered packing models, to investigate the charging process at pore scale. The indices of thermal storage properties such as charging time, temperature distribution, phase change fraction, pressure drop and thermocline degradation are studied with the finite element method. In the single-layered thermal storage system, the results show that the charging process can be improved by reducing the capsule size and using cross-packing methods. When the capsule size is reduced from 2 to 0.5 mm with cross packing, the charging time can be shortened by 72.97%, but remarkable pressure drop is created. The results indicate that the overall thermal storage performance of multi-layered packed-bed systems is better than that of single-layered packed-bed systems. The charging time of the diameter-changed two-layered and three-layered thermal storage systems can be reduced up to 16.21% and 24.32%, respectively, compared to the single-layered in-line pack with a d = 2 mm. The filling sequence plays a key role in multi-layered thermal systems. A packed-bed system with a diameter decreasing along the heat transfer fluid (HTF) flow direction has a better capacity to reduce thermocline degradation than other packed-bed systems.

The preparation and characterization of phase change material microcapsules with multifunctional carbon nanotubes for controlling temperature

The preparation and characterization of phase change material microcapsules with multifunctional carbon nanotubes for controlling temperature

Improved heating floor thermal performance by adding PCM microcapsules enhanced by single and hybrid nanoparticles

AbstractA heating floor is a low‐temperature emitter consisting of pipelines in which a fluid circulates between 35°C and 45°C. To ensure energy efficiency, occupant comfort, and building material durability, proper heat management is crucial in buildings. By using phase change materials (PCMs) in building envelopes, the indoor temperature can be regulated through the storage and release of thermal energy, which reduces energy consumption and enhances occupant comfort. In this study, we evaluated numerically a heating floor that incorporates a PCM enhanced by nanoparticles (NePCM). The aim of the numerical analysis is to assess the impact of the addition of single and hybrid nanoparticles in different proportions to the PCM layer on the thermal performance of the PCM‐based floor. Therefore, two main objectives are defined. The primary is to take advantage of the storage capacity of a PCM layer by integrating it into the ground; second, to evaluate the hot water temperature levels effect on the floor's performance. Additionally, we address the low thermal conductivity of PCM by enhancing PCM microcapsules with single and hybrid nanoparticles and comparing them to pure PCM. The numerical results obtained show that positioning the PCM microcapsules above the heating tubes (upper position) provides an optimum improvement in thermal performance. Moreover, the addition of hybrid nanoparticles within the base PCM, 1% of Cu mixed with 4% of Al2O3, allows an increase of 4°C, which relates to a reduction of 18% in the internal temperature amplitude and a phase shift of 6 h 30 min compared with the conventional heated floor in which there is no PCM.

Phase change material microcapsules with DOPO/Cu modified halloysite nanotubes for thermal controlling of buildings: Thermophysical properties, flame retardant performance and thermal comfort levels

Although the microencapsulated phase change material (MPCM) with organic core-shell structure is an effective means to encapsulate phase change material (PCM), it has the defects of low thermal conductivity and flammability. Herein, the flame retardant halloysite nanotubes (c-HNTs) doped by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and Cu nanoparticles were successfully inserted in the MPCM to form a highway to heat transfer. The related examination and surface morphology showed that the DOPO structure anchored by Cu nanoparticles was grafted on the surface of halloysite nanotubes (HNTs) and the c-HNTs were successfully embedded in MPCM. The thermogravimetric analysis (TGA) proved that c-MPCM has the best thermal stability when compared to other samples, which is caused by the presence of c-HNTs. The differential scanning calorimetry (DSC) test indicated that MPCM delays the heat transfer to the capric acid while the HNTs improve this situation as thermal conduction channels. Then, the MPCM samples were added to the epoxy resin (EP). In the cone calorimetry test, we found that the heat and smoke release rate of EP composite is obviously reduced. Finally, the temperature control ability test of MPCM demonstrated that the EP composite with c-HNTs has the minimum temperature fluctuation. These properties will greatly stimulate the application of c-MPCM in insulation materials.

Microencapsulation of bio-based phase change materials with silica coated inorganic shell for thermal energy storage

This study investigates the use of cenospheres to encapsulate a low-cost, bio-based phase change material (PCM) derived from refined edible vegetable oil. Chemical etching was applied on the cenospheres to create holes through which melted PCM was loaded to produce a PCM microcapsule. Subsequently, a silica-based coating was applied to seal the perforations and prevent leakage of PCM from the microcapsule. Microstructural, chemical compatibility, thermal, and leakage properties of the produced silica coated PCM microcapsule (SCPCM) were assessed. No leakage was found for this new microcapsule, and higher thermal stability and conductivity were noted. Thermal decomposition of the PCM in SCPCM was delayed by about 16 °C attributable to the silica coating. An enhanced compressive strength performance was achieved at 10 vol% of sand replacement with SCPCM. 20–30 vol% replacement of sand with cenosphere microcapsules seems to be the optimal range for reasonable compressive strength. The workability of the mortar incorporated with SCPCM decreased when the replacement level increased to more than 30 vol% due to the hydrophilic nature of the silica deposit. This study has demonstrated the potential of cenospheres as inorganic shell for PCMs and the potential for incorporation of SCPCM into construction materials for thermal energy storage (TES).

A novel hybrid anti-icing surface combining an aqueous self-lubricating coating and phase-change materials

The ability of phase change materials (PCMs) to absorb and release large amounts of latent heat has led to great interest in their use in anti-icing applications. Combining PCMs and other passive icephobic strategies such as self-lubricating coatings could enhance anti-icing performance. Here, an icephobic coating is fabricated by impregnating an elastomeric matrix containing PEG-PDMS copolymers with PCM microcapsules. First, a selected mixture of n-dodecane and n-tetradecane is encapsulated within urea–formaldehyde shells using in-situ polymerization. Various concentrations of microcapsules are then added into the self-lubricated PDMS coating and 2.5 wt% of hydroxyl-terminated PEG-PDMS copolymer. Differential scanning calorimetry confirms that the PCM-embedded coating has colder ice nucleation temperatures than the self-lubricating coatings lacking microcapsules. The release of latent heat by the PCMs likely preserves the liquid-like layer for a more extended time and delays ice nucleation. The presence of PCM microcapsules can positively affect self-lubricating characteristics of the matrix containing the PEG-PDMS copolymer to further reducing ice adhesion. The presence of a liquid-like layer lowers ice adhesion strength and decreases ice accumulation on surfaces. These particular properties are further enhanced by the incorporated PCM microcapsules and their ability to release latent heat. Finally, the durability of the fabricated coatings is confirmed after multiple icing/de-icing cycles. Such PCM-impregnated coatings therefore offer potential uses for diverse icephobic applications.

The thermal behavior and flame retardant performance of phase change material microcapsules with halloysite nanotube

Phase change material (PCM) has the potential to be added in coatings for energy-saving while the drawback of low thermal conductivity, poor thermal stability and flammability restrict its application. In this study, a novel halloysite nanotube (HNT) doped PCM (H-PCM) microcapsule was successfully prepared and applied in epoxy resin (EP) coatings (H-PCM-EP) to achieve temperature control. Many characteristics of the prepared PCM microcapsule were examined such as surface morphology, phase transformation performance and combustion data. The results indicated that the H-PCM microcapsule with a clear core-shell structure were successfully prepared. In comparison with the pristine PCM microcapsule, the H-PCM microcapsule had better thermostability and thermal conductivity. While the melting process of capric acid in H-PCM microcapsule advanced from 31.62 °C to 31.04 °C when compared with PCM microcapsule, which was considered as the bridge-like function of HNT. Moreover, the flammability and temperature control ability of H-PCM-EP were also investigated. The data of the peak heat release rate, total heat release, and total smoke release showed that the addition of HNT in PCM microcapsule can significantly reduce the influence of PCM in EP composites on fire hazards. Notably, the results of the small room model test and infrared thermal imager suggested that the application of H-PCM-EP can regulate inner room temperature and maintain a comfortable temperature range with less fluctuation. These properties will promote the application of the H-PCM microcapsule in temperature control coatings.

Thermal performance of a phase change material (PCM) microcapsules containing Au nanoparticles in a nanochannel: A molecular dynamics approach

This research studied the thermal performance of phase change material (PCM) microcapsules containing gold (Au) nanoparticles (NPs) in a nanochannel (NC) using molecular dynamics (MD) simulations. The MD simulation method is a reliable method for studying at micro and nano scales. In this simulation, the physical equilibrium was studied in the first stage by examining the simulated structure's kinetic and total energies. In the second stage, the thermal performance of simulated structure was surveyed. The thermal performance of structures was studied at different initial temperatures and initial pressure and the number of metal layers in NC shells. The results show that by increasing the initial temperature, the charging and discharging time, the viscosity and phase transition time decrease, and heat flux (HF) and thermal conductivity (TC) increase. Moreover, by changing the initial pressure (from 0 to 5 bar), the simulated samples' charging and discharging time, HF, and TC did not change much. This atomic behavior in the simulated samples shows that the simulated samples could operate without a drop in different initial conditions. The results indicate that by increasing the number of metal layers in the NC shells from 1 to 12, the force on fluid–structure increased, and consequently, the charging and discharging times increase to 2.54 ns and 3.40 ns. On the other hand, increasing the number of metal layers led to decreasing HF and TC of structures to 287.37 W/m2 and 1.18 W/m.K. Therefore, the dimensions of designed structures in atomic microcapsules to perform the heat transfer process were important. Increasing the shell thickness in these structures will reduce the heat transfer in the structures under study.

Encapsulation of polyethylene glycol as a phase change material using alginate microbeads to prevent temperature fluctuation- Case study: Fish packaging

Encapsulated PCM (phase change materials) has been developed to provide a thermal buffering system for food packaging. In this study, polyethylene glycol 400 (PEG) as a PCM was encapsulated in alginate in concentrations of 30, 40 and 50% (W/V) using calcium chloride (CaCl 2 ) in concentrations of 0.5, 1, 1.5%. Crystallization temperature, melting temperature and melting enthalpy of PCM decreased after encapsulation. The optimum encapsulated PEG (50% of PEG and 0.5% CaCl 2 ) had a diameter of 2.21 ± 0.54 μm. FTIR analysis of encapsulated microcapsules indicated characteristic peaks of alginate and pure PEG. TGA analysis showed more thermal stability for encapsulated PCM than pure PCM. After 100 thermal cyclic test microencapsulated beads showed some decrease in melting enthalpy, while other features of encapsulated PCM were almost intact. Encapsulated PCM was used for fish packaging to determine its effectiveness in controlling temperature fluctuation. When the packages were removed from the freezer, fish samples with the package containing encapsulated PCM and control package reached to 0 °C after 6500s and 3000s, 5 °C after 9030s and 4040s, 10 °C after 11520s and 5053s, and 25 °C after 19000s and 8200s, respectively. The data showed that using encapsulated PEG in fish packaging had a positive effect on preserving pH, water holding capacity, total volatile basic nitrogen, and thiobarbituric acid value. The results demonstrated that alginate could effectively encapsulate PEG, and the produced encapsulated PCM can be used for increasing of shelf life of perishable food during temperature fluctuations. • Novel food packaging materials were developed using alginate based PCM microcapsules. • The efficiency to maintain the cold temperature in packaged fish increased. • The shelf-life of product emproved by application of encapsulated PEG in packages.

Phase change materials microcapsules reinforced with graphene oxide for energy storage technology

Phase change materials (PCMs) are considered one of the most promising energy storage methods owing to their beneficial effects on a larger latent heat, smaller volume change, and easier controlling than other materials. PCMs are widely used in solar energy heating, industrial waste heat utilization, energy conservation in the construction industry, and other fields. To avoid leakage, phase separation, and volatile problems of PCMs, the encapsulation technique typically uses organic polymer materials as shell structures of microcapsules. Furthermore, using inorganic materials to enhance the thermal property of phase change microcapsules is a popular approach in recent research. Especially, graphene oxide (GO) with high thermal conductivity was used as a common thermal conducting additive to improve the thermal performance of phase change microcapsules. Due to its amphiphilic property, GO combined with PCM microcapsules can achieve a variety of nanostructures for thermal energy storage. In this paper, four aspects have been summarized: configuration of PCMs, methods of combining GO with phase change microcapsules, position and content of GO, and applications of PCM/GO microcapsules. This work attempts to discuss preparation methods and heat-conducting properties of the PCM/GO microcapsules, which helps to better promote the application-targeted design and greatly improve the thermal properties of PCM microcapsules for various applications.

Preparation and characterization of phase change material microcapsules with modified halloysite nanotube for controlling temperature in the building

Microencapsulated phase change material (mPCM) with effective heat transfer and flame retardant is highly desirable given today’s increasing energy demand. In this article, the halloysite nanotube (D-HNT) was modified by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and then inserted into the mPCM (D-H-mPCM) successfully. The transmission electron microscope, X-ray photoelectron spectroscopy and FT-IR results showed that the DOPO is grafted in both interior and exterior walls of halloysite nanotube (HNT), and the D-HNT is successfully inserted into mPCM. According to thermogravimetric analysis tests, D-H-mPCM was the best thermally stable sample among other mPCM for the existence of HNT and DOPO. The differential scanning calorimetry tests showed that the latent heat of D-H-mPCM was 113.52 J/g, and the D-HNT embedded in the mPCM greatly contributes to the heat transfer of the PMMA shell. To detect the flame retardancy and temperature control performance of mPCM samples, D-H-mPCM was incorporated into epoxy resin (EP-D-H-mPCM). The data of the cone calorimeter test suggested the EP-D-H-mPCM exhibited the lowest peak of heat release rate (pHRR) and total heat release (THR) of 572.65 kW/m2 and 93.95 MJ/m2 respectively. Finally, the small room model test and infrared thermal imager test showed the application of D-H-mPCM in EP can regulate indoor temperature and moderate temperature fluctuation. This work provides a new methodology to improve both thermal conductivity and flame retardancy of mPCM.

Low temperature energy storage by bio-originated calcium alginate-octyl laurate microcapsules

Octyl laurate phase change material (PCM) was microencapsulated by calcium alginate for eco-friendly low temperature energy storage. The PCM microcapsules were prepared by repeated interfacial coacervation followed by crosslinking method. In order to enhance the antibacterial properties of the as prepared capsules, the calcium alginate shell was functionalized by Ag nanoparticles. Calcium alginate-octyl laurate microcapsules possessed high latent heat of fusion values (130.8 and 128.6 J g−1 on melting and cooling, respectively) which did not significantly change when Ag nanoparticles were entrapped in the shell (127.5 and 125.2 J g−1 for melting and freezing enthalpy changes). Based on these values 71.0 and 69.0% maximal PCM content in the microcapsules were determined by the differential scanning calorimetry method. Both of the Ag-loaded and unloaded calcium alginate-octyl laurate PCM capsules maintained the high heat storing capacity after 250 warming and cooling cycles, which proved they did not suffer from leakage after the accelerated thermal test.

Phase change material microcapsules for smart temperature regulation of drilling fluids for gas hydrate reservoirs

In natural gas hydrate drilling operations, hydrate decomposition can lead to serious wellbore instability. In this study, the use of encapsulated phase change materials (PCMs) is proposed to smartly regulate the temperature of drilling fluids to inhibit hydrate decomposition. PCM microcapsules containing tetradecane in the core and a melamine-urea-formaldehyde resin as the shell were prepared by in-situ polymerization. The structure and properties of the PCM microcapsules were characterized, the temperature-regulating performance of the microcapsule and its effect on borehole stability were analyzed, and the compatibility was evaluated. The results showed that the melting point and latent heat of the PCM microcapsules were 6.7 °C and 116 J/g, respectively. The surface of microcapsules was hydrophilic and negatively charged, and the shell had good shear strength and sealability. PCM microcapsules effectively reduced the heating/cooling rate and the highest temperature of aqueous suspensions, thus decreasing the borehole enlargement rate. The temperature-regulating performance was unchanged after 15 heating/cooling cycles. After adding 5–10 wt% microcapsules, the rheological and filtration properties of the water-based drilling fluid remained in a reasonable range, indicating that the PCM microcapsules were compatible with drilling fluids. This study provides a new method for inhibiting hydrate decomposition in gas hydrate drilling.

Regulating asphalt pavement temperature using microencapsulated phase change materials (PCMs)

The use of phase change materials (PCMs) to regulate pavement temperatures has been previously studied, with the most successful studies using porous aggregates to stabilize the PCMs. However, this technique can lead to issues with PCM leakage and low PCM content. A less studied method is the use of PCM microcapsules, which also presents challenges since most microcapsules are not strong nor stable enough to survive the high temperatures and compressive forces experienced during asphalt mixture production and placement. This work presents a study of the properties of a new commercial microcapsule type with robust walls and high thermal stability, that are expected to overcome the aforementioned issues. Results from differential scanning calorimetry and thermogravimetric analysis confirmed the microcapsules exhibited high latent heats (200 J/g) and are thermally stable below 400 °C. Additionally, approximately 90% of the capsules remained unbroken after being milled at 140 °C for 20 min, suggesting they are capable of withstanding the mixing and compaction stages of asphalt pavement construction. When PCM microcapsules were added to HMA, thermal cycling experiments showed that specimens containing 10 and 20 vol% PCM exhibited temperature lags of 5 to 10 °C from the control mixture, as they approached the PCM melting/freezing temperature. These results confirm the ability of microencapsulated PCMs to regulate asphalt pavement temperature. However, results from measurements conducted at 40 °C and 1 Hz showed a 75% reduction of the dynamic modulus in specimens containing PCM microcapsules, which could indicate that the addition of these materials also affect asphalt mixture stiffness.

Influence of the Physical State of Microencapsulated PCM on the Pressure Drop of Slurry in a Circular Channel.

Phase Change Material (PCM) is mainly used in thermal energy storage. The addition of small PCM particles to the working fluid circulating in the heat exchange systems allowed to increase the amount of transported energy thanks to the use of latent heat—the heat of phase change. Encapsulating PCM in microcapsules avoids the disadvantages of PCM emulsions and makes the resulting slurry an attractive heat energy carrier. The paper presents the effect of the aggregate state of PCM enclosed in microcapsules on the flow resistance of the slurry through a rectilinear tubular channel. The tests were carried out with the use of a tube with an internal diameter of 4 mm and a measuring section length of 400 mm. A slurry of 21.5 wt.% PCM microcapsules (MPCM) was used as the working fluid in distilled water. A slurry with temperatures of 18.4 °C (PCM encapsulated in a solid state), 26.1 °C (PCM is in a phase change), and 30.5 °C (PCM in a liquid state) flowed through the measuring section. The mass flow rate of the MPCM slurry reached 70 kg/h (Remax = 2150). It was shown that the higher the Re number, the higher the value of the flow resistance, and the more clearly this value depended on the temperature of the slurry. Detailed analyses indicate that the observed changes were not the result of a change in the viscosity of the slurry, but its density depending on the state of the PCM. Significant changes in the density of the slurry in the range of the phase transition temperature are the result of significant changes in the volume of the microcapsule containing the phase change material in different aggregate states.

CuS Nanoparticle-Based Microcapsules for Solar-Induced Phase-Change Energy Storage

Phase-change microcapsules with photothermal conversion capabilities have been the focus of research in the energy storage field. In this study, a route is developed to prepare photothermal conversion and phase-change energy storage microcapsules by copper sulfide-stabilized Pickering emulsion with dodecanol tetradecyl ester as the phase-change material (PCM) and melamine formaldehyde resin (MF) as a shell. Spherical CuS particles with a diameter of approximately 10 nm are first synthesized by a facile hydrothermal reaction. The obtained CuS nanoparticles are used not only as a stabilizer but also as a photothermal conversion material in the preparation of the microcapsules. Then, the PCM microcapsules are prepared by a one-pot interfacial polymerization route and showed a well-defined core–shell structure with an average size of approximately 7 μm. The synthesized microcapsules have a latent heat of up to 180.3 J/g and an encapsulation efficiency of 81.36%. Meanwhile, the thermal conductivity of the microcapsules increased by 115–254% compared to the core material due to the hybrid shell filled with CuS nanoparticles. The photothermal conversion capacity of the synthesized microcapsules is measured and calculated to be up to 85.6%, achieving light-induced phase change and further inducing the passive thermal cycle. This study provides a potential candidate for the application of light-induced energy storage microcapsules in fabric insulation, solar hot water heating systems, and solar thermal power systems.

Cenosphere-based PCM microcapsules with bio-inspired coating for thermal energy storage in cementitious materials

Phase change materials (PCMs) provide passive storage of thermal energy in buildings to flatten heating and cooling load profiles and minimize peak energy demands. After microencapsulated into a protective shell, they can be directly added to cementitious materials to add thermal energy storage capacity to the material. However, existing studies show that the strength of the produced materials can be drastically reduced by the added PCM microcapsules. To overcome this drawback, this study develops a novel PCM microcapsule using the cenosphere as the protective shell, together with a bio-inspired dopamine coating. As hollow fly ash particles, cenosphere shells are much harder and stronger than commonly used polymer based protective shells. While the strong binding ability of dopamine to diverse surfaces through covalent and non-covalent interactions provides better bonding between the PCM microcapsule and the surrounding cement paste. For these reasons, the strength of the produced cement mortar can be greatly improved by this microcapsule. An experimental study shows that a 35% increase in compressive strength has been achieved by adding 10 wt% of the new PCM microcapsule into the cement mortar. Microstructure examination and hydration products analysis revealed that the dopamine coating facilitates the hydration of the cement and produces a denser and stronger interface between the microcapsule and the cement paste. As a result, a novel PCM microcapsule is developed which not only integrates latent heat storage capacity to the cement mortar but also enhance the compressive strength of the mortar, which cannot be achieved by any other PCM microcapsules.

An intelligent icephobic coating based on encapsulated phase change materials (PCM)

The phase change materials (PCMs) have attracted great interest for applications as smart icephobic coatings because of their capability to restore and release energy. PCMs release a large amount of energy as latent heat upon freezing, which is a stimuli-response behavior for anti-icing applications. Such materials embedded within coatings can be applied to exposed infrastructures to protect them against icing. Here, we encapsulated a mixture of PCMs in a urea–formaldehyde (UF) shell by in situ polymerization and then incorporated the microcapsules into a polydimethylsiloxane (PDMS) coating. Microcapsules 5–15 µm in diameter having a shell thickness of about 200 nm were fabricated. Investigating the chemical composition of the fabricated microcapsules confirmed that PCM material was successfully encapsulated within the UF shell. Moreover, the differential scanning calorimetry (DSC) analysis showed that the PCM preserved its phase-change characteristics when encapsulated and embedded within the matrix. Increasing the abundance of microcapsules within the coating lowered the ice nucleation temperature, verified by DSC, and increased the freezing-delay time because of PCM latent heat release. We utilized a custom-made apparatus, called micro-push-off set-up that allowed us to measure ice adhesion at the exact moment that the water droplet was completely frozen. Therefore, it was observed that the presence of the PCM microcapsules reduced ice adhesion strength, through either possible mechanism of the formation of quasi-liquid layer (QLL) or thermal expansion differences. Furthermore, lower ice adhesion resulted in reduced ice accumulation on the PCM-containing coatings, verified by the static accumulation test (SAT).

Frost Resistance and Meso-deterioration Analysis of Microcapsulated Phase Change Materials Modified Concrete

The damage of concrete by freeze–thaw has always been a key issue affecting the safe operation and service of projects in cold regions. In this paper, concrete modified by microcapsulated phase change materials (mPCMs) was evaluated for its frost resistance; the evolution of its internal pore structure and meso-deterioration during freeze–thaw cycles was investigated by industrial computerized tomography; additionally, NanoSiO2 was incorporated for secondary modification to reduce strength loss as the frost resistance of phase change concrete increased. The results show that the incorporation of mPCMs effectively inhibits heat diffusion and temperature change in concrete, conducive to frost resistance, and the freeze–thaw life of phase change concrete increases drastically compared to ordinary concrete. With increasing mPCMs, increment in porosity within concrete decreases and the overall pore distribution tends to be dominated by relatively large pores. When the content of mPCMs exceeds 10%, the pore structure is relatively stable during freeze–thaw. However, the incorporation of mPCMs also reduces the strength of concrete. Under the guarantee of certain strength, the optimal content of mPCMs is initially chosen for 10%; the optimal content of nanomaterials added for reinforcement is 1.5%, with a strength improvement of 11.68%.

Preparation and characterization of multifunctional phase change material microcapsules with modified carbon nanotubes for improving the thermal comfort level of buildings

Excellent temperature regulation and flame retardancy are the keys to the wide application of phase change material microcapsules (MPCMs) in building fields. In this study, the flame retardant carbon nanotube (d-CNT) modified by 9,10-dihydro-9-oxa-10 phosphaphenanthrene-10-oxide (DOPO) was successfully embedded into the MPCM (d-c-MPCM) by in-situ polymerization. The scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) experimental results showed that DOPO was grafted onto the carbon nanotube (CNT) surface and the d-CNT was successfully added to the microcapsule with a particle size of 150 nm. The d-c-MPCM displayed better thermal stability than other MPCMs due to the presence of CNT and DOPO, which was demonstrated by thermogravimetric analysis (TGA) and micro-combustion calorimeter (MCC) tests. The differential scanning calorimetry (DSC) results of MPCMs showed that the phase transition temperature and latent heat of d-c-MPCM are 31.14 ℃ and 103.21 J/g, respectively. The flame retardancy and temperature control ability of microcapsules were detected by adding d-c-MPCM to the rigid polyurethane foam (RPUF/d-c-MPCM). In the cone calorimeter test, RPUF/d-c-MPCM significantly reduced the heat release and increased the residual mass of foam during combustion. These improvements in thermal stability and flame retardancy resulted from the synergistic effect of CNT and DOPO on the formation of char layer. Finally, the small room model and infrared thermal imager results proved that RPUF/d-c-MPCM made indoor temperature fluctuation more gentle, and the maximum indoor temperature is only 26.6 ℃. These unique properties will significantly facilitate the practical application of the MPCMs in building insulation materials.