Paraffin Core Research Articles

Impact of Encapsulated Phase Change Material Additives for Improved Thermal Performance of Silicone Gel Insulation

Abstract Passive cooling through phase change materials (PCM) creates beneficial complimentary cooling techniques aimed at providing thermal gradient mitigation during device operation without additional power requirements. These have been well studied but are difficult to implement due to complications concerning effective enclosure of the liquid phase. Encapsulated PCM particles can be embedded in other materials to form composites with form stable solid–liquid phase transitions. This study characterizes a new composite of silicone gel and encapsulated phase change materials (ePCMs) for use as an encapsulant. The ePCMs contain a paraffin core and titania shell resulting in a self-contained solid–liquid phase transition producing an average of 132.9 J/g of latent heat capacity. The gel composites gain latent heat capacity as a linear function of ePCM concentration by weight. The 30% ePCM sample contains 41.0 J/g of latent heat capacity, approximately 30% of ePCM control samples. The specific heat capacity of the silicone gel without ePCMs is 1.539 J/g-° C and 2.825 J/g-° C for the ePCM particles. As the ePCM concentration increases, the specific heat capacity is increased toward the highest value of the pure ePCMs across all temperature ranges. The coefficient of thermal expansion of the composites is increased with ePCM concentration up to a maximum of 96% in the 20% ePCM concentration. The elastic modulus remains relatively constant across ePCM concentrations and temperatures. In the needle–needle breakdown voltage testing the 20% sample has a 6 kV/mm reduction in dielectric strength and higher than 20% ePCM samples show increased variability in strength due to the dispersed particles. Overall, the results from these material characterizations demonstrate the promise of dielectric composites containing ePCM particles to add passive cooling capability into electronics devices without complex structures.

Development of hybrid MgO/GO modified microencapsulated phase change material for thermal energy management: An experimental approach

The microencapsulation technique addresses the concerns of phase change material (PCM) leakage, transportation challenges, and limited efficacy in thermal energy management applications. Nevertheless, the organic shell material has lower thermal conductivity, and significant leakage issues. To improve the ability of heat transfer as well as leakage prevention, a novel form of microencapsulated phase change material (MEPCM) with paraffin core, and melamine formaldehyde (MF) shell modified by hybrid magnesium oxide (MgO), and graphene oxide (GO) thermal conductivity enhancer (TCE) interface is fabricated through the process of in-situ polymerization. The results revealed a well-developed TCE interface layer in between the core, and the shell of the modified spherical microcapsules. The modified MEPCMs exhibited a maximum encapsulation rate of 88.0 %, and 177.84 J/g latent heat of melting. The thermal stability of the MEPCMs is increased by 50 °C to 70 °C, and the thermal conductivity is remarkably elevated to 0.44 W/mK. The leakage rate is significantly reduced by 98.58%. The excellent thermal energy storage/release performance of the modified MEPCMs is attributed to the TCE interface, which serves as an efficient medium for thermal conduction. The modified MEPCMs endure exceptional physical, and thermo-chemical properties, that are relevant for thermal energy management applications.

Preparation and performance of novel magnetic phase-change-microcapsule-supported Bi2WO6 catalyst

The design and synthesis of novel photocatalyst with self-temperature control function is an important topic in the field of advanced environmental functional materials. In this work, submicron-sized magnetic phase change microcapsules composed of paraffin core and Fe3O4-loaded silica shell are prepared, on which the Bi2WO6 crystals is grown in situ through hydrothermal reaction to obtain novel magnetic phase-change-microcapsule-supported Bi2WO6 catalyst (MP@FS/BWO). The MP@FS/BWO has a paraffin encapsulation ratio of 57.1%, and the phase change enthalpy of 105.1 J/g in a temperature range of 50–60 °C, which endows the MP@FS/BWO with a certain self-temperature regulation ability. MP@FS/BWO shows excellent catalytic performance in the decomposition of rhodamine B under the simulated sunlight irradiation. After the light source is turned off, it still has good catalytic ability by maintaining high temperature due to its temperature control function based on the phase transition process. The MP@FS/BWO can be easily recycled by magnetic separation and shows good structural stability and reusability. This work provides a new idea for the development of long-effect and energy-saving outdoor photocatalysts.

Preparation and Characterization of n-Octadecane@SiO2/GO and n-Octadecane@SiO2/Ag Nanoencapsulated Phase Change Material for Immersion Cooling of Li-Ion Battery

Nanoencapsulated phase change materials (NePCMs) are promising thermal energy storage (TES) and heat transfer materials that show great potential in battery thermal management systems (BTMSs). In this work, nanocapsules with a paraffin core and silica shell were prepared using an optimized sol-gel method. The samples were characterized by different methods regarding chemical composition, thermal properties, etc. Then, the nanocapsules were used as the coolant by mixing with insulation oil in the immersion cooling of a simulative battery. The sample doped with Ag on the shell with a core-to-shell ratio of 1:1 showed the best performance. Compared to the sample without doping material, the thermal conductivity increased by 49%, while the supercooling degree was reduced by 35.6%. The average temperature of the simulative battery cooled by nanocapsule slurries decreased by up to 3.95 °C compared to the test performed with pure insulation oil as the coolant. These novel nanocapsules show great potential in the immersion cooling of a battery.

Preparation and performance of magnetic phase change microcapsules with organic-inorganic double shell

Magnetic microcapsulated phase change materials can achieve rapid magnetic localization temperature regulation and magnetic separation recycling. However, the efficient encapsulation of both inorganic magnetic material and organic phase change material is a challenge due to their poor compatibility. In this work, an aqueous dispersion containing methylol melamine and sodium alginate loaded with magnetic Fe 3 O 4 nanoparticles (SA-Fe 3 O 4 ) was prepared and mixed with a paraffin emulsion. After methylol melamine was initiated to in-situ polymerize at the interface of the paraffin emulsion droplets, primary magnetic phase change microcapsules (P-MPCM) composed of a paraffin core and SA-Fe 3 O 4 /melamine formaldehyde resin composite shell were formed. Then, SiO 2 sol particles were adsorbed on the surface of P-MPCM to form the final MPCM with a polymer-SiO 2 double-shell (PS-MPCM). The magnetic polymer-SiO 2 double-shell endows the PS-MPCM with rapid magnetic responsiveness (can be quickly collected under magnetic fields), high phase change enthalpy (184.4 J·g-1) and excellent structural stability. The phase change enthalpy and saturation magnetization of PS-MPCM have changed little after 200 thermal cycles. At the same time, the excellent photothermal conversion efficiency (93.9%) of PS-MPCM benefits for solar energy conversion utilization in actual application. This work provides a new way to obtain MPCM with high thermal conductivity (0.64 W·m-1·K-1), rapid magnetic response and excellent reusability, which can be potentially applied for directional temperature regulation. Magnetic polymer-SiO 2 double-shell phase change microcapsule (PS-MPCM) was prepared. PS-MPCM exhibits high encapsulation ratio of paraffin and Fe 3 O 4 nanoparticles (NPs). Sodium alginate was introduced to achieve efficient and stable loading of Fe 3 O 4 NPs. PS-MPCM exhibits excellent thermal conductivity, magnetic response and reusability. PS-MPCM can be potentially applied for magnetic localization temperature regulation.

ZnO‐Reinforced Thermal Regulating Microcapsules with Double‐Layer Shell via Atomic Layer Deposition

AbstractConventional plain organic or inorganic shell for microcapsules has their own drawbacks, the organic shell has defects in thermal conductivity and stability; while the compactness and coverage of inorganic shell are not satisfactory. Herein, a novel approach to synthesis of organic–inorganic composite double‐layer shell phase change microcapsule (DLSPCM) is proposed, which is achieved by forming inorganic outer shell on the surface of organic shell via atomic layer deposition (ALD). Taking the pristine microcapsule with paraffin core and melamine formaldehyde (MF) shell as an example, MF‐ZnO composite double‐layer shell (DLS) is formed in this paper. The melting enthalpy of DLSPCM obtained by 100 ALD cycles is 159.7 J g−1, which is only 12.1 J g−1 lower than that of paraffin @ MF microcapsules (control sample), while the thermal conductivity of DLSPCM surges by 77.8%, and the thermal energy storage ability and thermal regulation performance are basically maintained. After 900 thermal cycles, the heat storage capacity of DLSPCM obtained by 100 ALD cycles decreased by only 3%. Besides, the photocatalytic performance and antibacterial activity of ZnO‐reinforced DLSPCM are further confirmed. The successful design of DLSPCM via ALD is prospective for the encapsulation, modification, and reinforcement of phase change microcapsules.

Effects of microencapsulated phase change material characteristics on the thermal performance and mechanical behaviour of silty clay

Microencapsulated phase change material (mPCM) possess an excellent heat storage capacity, which could mitigate temperature fluctuation of soil during freezing/thawing in seasonally frozen regions. Two types of mPCM were investigated using scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infra-red spectroscopy and thermal analysis. Experiments including freezing/thawing tests and unconfined compression tests were conducted to evaluate the behaviour of soil treated with different concentrations of mPCM with butyl stearate and paraffin core material (B-PCM and P-PCM, respectively) during freezing/thawing. The mPCM released and absorbed latent heat, decreasing the temperature variation rate of soil. The unconfined compression strength of silty clay with both types of mPCM displayed diverse trends after freeze-thaw cycles. In contrast to flaky agglomeration in B-PCM-treated soil, the characteristic cementated agglomeration existing in soil aggregates exclusively treated by P-PCM was visually captured using SEM, which formed by the interaction of leaked paraffin in P-PCM and soil due to compaction effort. Furthermore, B-PCM alleviated the strength deterioration of silty clay after freezing/thawing, and the core-to-shell ratio strongly affected the soil strength.

Enhancement of the Thermal Performance of the Paraffin-Based Microcapsules Intended for Textile Applications.

Phase changing materials (PCMs) microcapsules MPCM32D, consisting of a polymeric melamine-formaldehyde (MF) resin shell surrounding a paraffin core (melting point: 30–32 °C), have been modified by introducing thermally conductive additives on their outer shell surface. As additives, multiwall carbon nanotubes (MWCNTs) and poly (3,4-ethylenedioxyoxythiophene) poly (styrene sulphonate) (PEDOT: PSS) were used in different parts by weight (1 wt.%, 5 wt.%, and 10 wt.%). The main aim of this modification—to enhance the thermal performance of the microencapsulated PCMs intended for textile applications. The morphologic analysis of the newly formed coating of MWCNTs or PEDOT: PSS microcapsules shell was observed by SEM. The heat storage and release capacity were evaluated by changing microcapsules MPCM32D shell modification. In order to evaluate the influence of the modified MF outer shell on the thermal properties of paraffin PCM, a thermal conductivity coefficient (λ) of these unmodified and shell-modified microcapsules was also measured by the comparative method. Based on the identified optimal parameters of the thermal performance of the tested PCM microcapsules, a 3D warp-knitted spacer fabric from PET was treated with a composition containing 5 wt.% MWCNTs or 5 wt.% PEDOT: PSS shell-modified microcapsules MPCM32D and acrylic resin binder. To assess the dynamic thermal behaviour of the treated fabric samples, an IR heating source and IR camera were used. The fabric with 5 wt.% MWCNTs or 5 wt.% PEDOT: PSS in shell-modified paraffin microcapsules MPCM32D revealed much faster heating and significantly slower cooling compared to the fabric treated with the unmodified ones. The thermal conductivity of the investigated fabric samples with modified microcapsules MPCM32D has been improved in comparison to the fabric samples with unmodified ones. That confirms the positive influence of using thermally conductive enhancing additives for the heat transfer rate within the textile sample containing these modified paraffin PCM microcapsules.

Core shell paraffin/silica nanocomposite: A promising phase change material for thermal energy storage

A facile method has been developed to fabricate nano-encapsulated paraffin wax within silica shell (SNsPCM) by in-situ hydrolysis and polycondensation of silica precursor. SNsPCM composite was studied using field-effect scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), X-ray Diffractometry (XRD), Raman and Fourier transformation infrared spectroscopy (FT-IR), respectively. The results revealed the formation of spherical paraffin nano-structure encapsulated within the shell of SiO2 with diameters ranging from 100 to 200 nm. Thermal stability, determined by differential scanning calorimeter (DSC), and thermogravimetric analyser (TGA), confirm the fabrication of a solid-solid and solid-liquid phase changing nanomaterial (PCnM). Simulations performed for thermal change within the paraffin core bounded by silica shell, for cycles of heating and cooling show excellent pressure durability of silica shell. PCnM behaviour studied using DSC measurement shows reversible fusion and solidification for repeated heating and cooling cycles. The SNsPCM composite with a paraffin encapsulation ratio of 79.89 wt% melted at 54.72 °C with a latent heat of 149.29 J/g and solidified at 52.09 °C with a latent heat of 100.16 J/g. The TGA results show improved thermal stability with an increased encapsulation ratio of PCnM by silica shell. SNsPCM can a potential material for thermal energy storage.

Preparation and Performance of Microencapsulated Phase Change Material with Paraffin Core and SiO2 Shell for High Latent Heat and Low Heat Loss by Sol–Gel Method

Microencapsulated phase change materials (MicroPCM) were prepared via sol–gel method using paraffin as heat storage core and silica as inorganic shell. The morphology feature, chemical structure, thermal properties and thermal stability of MicroPCM were characterized by the field emission scanning electron microscope (FE-SEM), Fourier transform infrared spectroscopy (FTIR), the differential scanning calorimeter (DSC), simultaneous thermal analyzer (STA) and the thermal conductivity meter. The results indicated that MicroPCM were spherical in shape with the shell thickness in the range from 236[Formula: see text]nm to 303[Formula: see text]nm. The stirring speed and TEOS dosage were key factor on the latent heat and supercool effect of MicroPCM. The maximum latent heat of MicroPCM was 240.2[Formula: see text][Formula: see text] with the heat loss of only 0.2[Formula: see text][Formula: see text] in phase transformation when it was prepared at the stirring speed of 400[Formula: see text]r/min and TEOS dosage of 20[Formula: see text]ml. MicroPCM was a promising material for thermal energy storage (TES).

Synthesis and characterization of phase change materials microcapsules with paraffin core/cross-linked hybrid polymer shell for thermal energy storage

Phase change materials microcapsules (PCMM) with cross-linked hybrid polymer shell were developed by in-situ polymerization and paraffin melting at 47 °C was used as PCM. The cross-linked hybrid polymer shell of microcapsules was prepared by copolymerizing methyl methacrylate (MMA), acrylic acid (AA), n‑butyl acrylate (BA), and trimethylpropane triacrylatec (TMPTA) which were employed as crosslinking agents. Microcapsules with core–shell structure were studied by polarizing optical microscope (POM), and their morphologies were obtained by scanning electronic microscope (SEM). Fourier transform infrared (FR-IR) was used to characterize the PCMM with paraffin core. The results of differential scanning calorimetry (DSC) showed that the measured enthalpy of PCMM was significantly higher than the theoretical value, and the increment percentage was as high as 58.7% and 63.9% during the heating/cooling process, respectively. In addition, PCMM's good thermal stability and long-term property were obtained by thermogravimetric analysis (TGA) and thermal cycle test results.

Hydrogen peroxide sol–gel coating of microencapsulated phase change materials by metal oxides

Hydrogen peroxide assisted sol–gel coating of core-shell microcapsules of phase change materials (PCMs) is reported. A doubly coated paraffin core with an inner poly(melamine-formaldehyde) shell and an outer coating of peroxostannate, peroxoantimonate, their mixture or the respective metal oxides are reported. Triple coating of the paraffin core with a poly(melamine-formaldehyde) inner shell, tin oxide middle layer and graphene oxide outer coating is also achieved by hydrogen peroxide sol–gel processing. The latent heats of the microencapsulated PCMs ranged between 122 and 192 J g−1. The sol–gel process involves stabilization of the peroxostannate or peroxoantimonate sol in basic aqueous hydrogen peroxide and subsequent destabilization and deposition of the sol by addition of an antisolvent. Transformation to the metal oxide coating is conducted by chemical reduction with sodium sulfite or by mild heat treatment without leakage of the paraffin core.

Paraffin core-polymer shell micro-encapsulated phase change materials and expanded graphite particles as an enhanced energy storage medium in heat exchangers

The Micro-Encapsulated Phase Change Materials (MEPCMs) with the melting point temperature of 28 °C was used as an energy storage medium to control the thermal behaviour of a heat exchanger. The NEPCM particles were mixed with Expanded Graphite (EG) microparticles to improve the heat transfer rate in the heat exchanger. The MEPCM particles are made of paraffin cores with a particle average size of 45 μm. The paraffin core of the particles can undergo a solid/liquid phase change and store a tremendous amount of thermal energy due to the latent heat of phase change. The heat exchanger is a copper pipe radiator with aluminium fins confined in either a bed of MEPCMs or a composite mixture of MEPCMs + Expanded Graphite (EG) microparticles. The thermophysical properties of MEPCMs and MEPCM + EG were measured. The outcomes show 132% enhancement in thermal conductivity and a 28% decrease in the sensible specific heat of the MEPCM + EG composite with the weight ratio of 70% MEPCM and 30% EG compared to pure MEPCM. The charging and discharging behaviour of heat exchanger for various flow rates and two cases of MEPCM and MEPCM + EG were studied experimentally. The results reveal that using EG notably enhances the heat transfer and capability of the heat exchanger during the charging and discharging process. Using MEPCM + EG reduces the temperature drop at the heat exchanger outlet about 15 °C compared to the case of pure MEPCM.

Enhanced Thermal Buffering of Phase Change Materials by the Intramicrocapsule Sub per Mille CNT Dopant.

Microencapsulation of a carbon nanotube (CNT)-loaded paraffin phase change material, PCM in a poly(melamine-formaldehyde) shell, and the respective CNT-PCM gypsum composites is explored. Although a very low level (0.001-0.1 wt %) of intramicrocapsule loading of CNT dopant does not change the thermal conductivity of the solid, it increases the measured effusivity and thermal buffering performance during phase transition. The observed effusivity of 0.05 wt % CNT-doped PCM reaches 4000 W s-0.5 m-2 K-1, which is higher than the reported effusivity of alumina and alumina bricks and an order of magnitude larger than the solid, CNT-free PCM powder. The CNT dopant (0.015 wt %) in a 30 wt % PCM-plaster composite improved the effusivity by 60% compared to the CNT-free composite, whereas the addition of the same amount of CNTs to the bulk of the plaster does not improve either the effusivity or the thermal buffering performance of the composite. The thermal enhancement is ascribed to a CNT network formation within the paraffin core.

Temperature-humidity dual regulation of a single-core-double-shell microcapsule fabricated by electrostatic-assembly and chemical precipitation.

Humidity and temperature control materials have attracted increasing attention due to their energy saving and intelligent regulation of human comfort in the field of interior building and clothing. Phase change microcapsules have been widely used, however, most of which focus on temperature regulation without humidity control. In this work, we report a novel temperature–humidity dual regulation microcapsule with single-core–double-shell structure. FT-IR and XRD measurements confirmed that the shell materials were successfully fabricated on the paraffin core via electrostatic-assembly and the subsequent chemical precipitation method. SEM, TEM and optical microscope photos showed that the microcapsules were spherical morphology with layer-by-layer shells at a diameter around 2–5 μm. The SiO2 shell was aggregated from nano-sized particles and formed a loose and porous micro-structure, supported by the result of N2 adsorption–desorption isotherms. In addition, the synergistic effect of hydrophilic and porous loose (chitosan/GO/chitosan)–SiO2 double shells endowed the microcapsules with humidity regulation. The constructed microcapsules showed temperature regulation behavior due to its phase change performance of paraffin and good thermal durability after 10 thermal cycles. They also showed stable humidity regulation performance after repeated adsorption/desorption. The simulation experiments of temperature and humidity regulation indicated that the microcapsule could keep the temperature and humidity in a stable range. The as-prepared microcapsules have outstanding temperature and humidity regulation properties, showing an application prospects in energy-saving fields.

Bifunctional Paraffin@CaCO3:Ce3+ Phase Change Microcapsules for Thermal Energy Storage and Photoluminescence

Novel phase change microcapsules (micro-PCMs) composed of a paraffin core and aCe3+-doped calcium carbonate (CaCO3:Ce3+) shell was designed by self-assembly precipitation. The morphology, compositi...

Phase change microcapsules with lead tungstate shell for gamma radiation shielding and thermal energy storage

Novel microencapsulated phase change materials (MEPCMs) composed of the lead tungstate (PbWO4) shell and paraffin core were designed for shielding of gamma radiation as well as thermal energy storage. Such MEPCMs were prepared via self-assembly methods and in-situ precipitation. The PbWO4 shell with excellent photon attenuation can give the resulting MEPCMs an acceptable gamma radiation shielding capability. The chemical composition and structure of microcapsules samples were studied by X-ray diffractometer (XRD) and Fourier-transform infrared spectroscopy (FTIR). The effects of different core/shell mass ratios on the surface morphology and microstructure of the MEPCMs were determined by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), and transmission electronic microscopy (TEM). It was confirmed that the microcapsules exhibit a distinct core-shell structure and a perfect spherical shape. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to present thermal stability and thermal-storage capability of MEPCMs. A high-purity germanium gamma spectrometer to measure the attenuation coefficient of the microcapsules for gamma rays showed that the MECPMs has good γ-rays-shielding property. The multifunction microcapsules in this study have great potential applications for building energy conservation as well as wearable personal protection in nuclear energy engineering.

Synthesis and performance evaluation of paraffin microcapsules with calcium carbonate shell modulated by different anionic surfactants for thermal energy storage

A series of phase change materials (PCMs) microcapsules based on industrial paraffin core and calcium carbonate (CaCO3) shell were successfully synthesized for thermal energy storage. The SEM results revealed that the composites are mainly of spherical morphology. The FT-IR and XRD confirmed that the composites were mainly composed of the vaterite CaCO3, paraffin, and a small amount of calcite CaCO3. Compared with the composites prepared with sodium dodecyl sulfonate (SDS) as anionic surfactant, DSC and TG results of composites prepared with sodium dodecyl benzene sulfonate (SDBS) demonstrated that the encapsulation efficiency increased but the thermal stability decreased. Besides, with the different concentrations of CaCl2, the influence of anionic surfactants on the performance of microcapsules had been discussed. The results exhibited higher encapsulation efficiency of microcapsules with SDBS than that with SDS, even up to ten times. When the mass of CaCl2 is about 0.05 mol, encapsulation efficiency with SDBS can reach up to 20.80%. Accordingly, the super-cooling of PCM was significantly suppressed. From all results, it is worth developing the PCMs microcapsules with CaCO3 shell modulated by different anionic surfactants for thermal energy storage and SDBS is more suitable for preparing PCM@CaCO3 microcapsules.

Thermal-regulation of nonwoven fabrics by microcapsules of n-eicosane coated with a polysiloxane elastomer

Abstract Synthesis of microcapsules composed of a paraffin core coated with polysiloxane, which were developed in one of our laboratories, was adapted for preparation of the microcapsules for thermoregulation of textiles. n-Eicosane with melting temperature 37 °C was used as a phase change material (PCM). Shells of the microcapsules were made of a polysiloxane elastomer. The microcapsules were fabricated in an aqueous emulsion, which was prepared by mechanical co-emulsification of the paraffin with a reactive polysiloxane. The process yielded microcapsules consisting of n-eicosane coated with polysiloxane, which later was cross-linked in the emulsion. Chemical structure of the microcapsules was characterized by FT-IR, 29Si MAS NMR and EDX methods. SEM and TEM techniques were used for studies of microcapsule diameters, diameter distributions and thickness of the polysiloxane shells. Core-shell structure of the microcapsules and complete coating of the paraffin with polysiloxane were confirmed. Phase change enthalpy of the microcapsules was 146 J/g. Encapsulation coefficient (Xen) and energy storage coefficient (Xes) were close, which indicated that the absorbed and released heat was due to the melting and crystallization of n–eicosane, respectively. The PCM microcapsules were incorporated into the needled fabrics using a padding method. SEM, FT-IR and EDX determined their presence and location in the fabrics. It was found that content of the PCM microcapsules in the dry mass of the nonwovens was 37 wt percent. The high value of the coefficient energy storage capability (Ces) for the microcapsules alone, for the microcapsules with binder and for the modified nonwoven were close to 99% and indicated a tight encapsulation of the paraffin by polysiloxane shells. This ensured heat absorption and release during in many cycles. Indeed, the DSC results (over 100 cycles of phase changes) confirm high thermal stability of the microcapsules also in the modified nonwoven. The heat effect corresponding to the phase change was equal 34 J per gram of the modified textile.

Microencapsulated Paraffin Phase-Change Material with Calcium Carbonate Shell for Thermal Energy Storage and Solar-Thermal Conversion.

A series of microencapsulated phase-change materials (MEPCMs) based on paraffin core and calcium carbonate (CaCO3) shell were synthesized, and the effect of emulsifier type and pH value on morphology, structure, and properties of paraffin@CaCO3 MEPCMs were investigated. The results showed that CaCO3 shell was formed in vaterite and calcite crystalline phase when emulsifier was sodium dodecyl benzene sulfonate and styrene-maleic anhydride (SMA), respectively. When sodium dodecyl sulfate was used as an emulsifier, both vaterite and calcite CaCO3 were formed. The forming mechanism of emulsifier type on CaCO3 crystalline phase was studied. Furthermore, phase-change enthalpy and leakage rate of MEPCMs were related with the type of emulsifier and the pH value of the emulsion. With optimum condition of SMA as emulsifier and pH value of 7, paraffin@CaCO3 MEPCMs had an encapsulation ratio at 56.6% and leakage rate at 2.88%, illustrating its considerable heat storage capability and leakage-prevention property. The 50 heating-cooling cycles test indicated that the MEPCMs owned excellent thermal reliability. The thermal conductivity of MEPCMs was significantly improved due to the existence of CaCO3 shell. In addition to excellent thermal storage ability, the paraffin@CaCO3 MEPCMs also owned good mechanical property and light-to-heat energy conversion efficiency. The characteristics of MEPCMs indicated its potential application in solar energy resource.