Form-stable Phase Change Materials Research Articles

Physical-Entanglements-Supported Polymeric Form Stable Phase Change Materials with Ultrahigh Melting Enthalpy.

With the rapid development of new energy and the upgrading of electronic devices, structurally stable phase change materials (PCMs) have attracted widespread attentions from both academia and industries. Traditional cross-linking, composites, or microencapsulation methods for preparation of form stable PCMs usually sacrifice part of the phase change enthalpy and recyclability. Based on the basic polymer viscoelasticity and crystallization theories, here, a kind of novel recyclable polymeric PCM is developed by simple solution mixing ultrahigh molecular weight of polyethylene oxide (UHMWPEO) with its chemical identical oligomer polyethylene glycol (PEG). Rheological and leakage-proof experiments confirm that, even containing 90% of phase change fraction PEG oligomers, long-term of structure stability of PCMs can be achieved when the molecular weight of UHMWPEO is higher than 7000kg mol-1 due to their ultralong terminal relaxation time and large number of entanglements per chain. Furthermore, because of the reduced overall entanglement concentration, phase change enthalpy of PCMs can be greatly promoted, even reaching to ≈185 J g-1, which is larger than any PEG-based form stable PCMs in literatures. This work provides a new strategy and mechanism for designing physical-entanglements-supported form stable PCMs with ultrahigh phase change enthalpies.

Epoxy resin/ aluminium hydroxide/expanded graphite synergistic effects on advancing flame retardancy, mechanical structure and thermal management of octadecanoic acid and octadecanol-based eutectic phase change materials

In the present research, a novel approach wherein a flame-retardant composite phase change material (PCMs) is devised by incorporating eutectic PCMs, epoxy resin (ER), aluminium hydroxide (ATH), and expanded graphite (EG). This innovative formulation capitalizes on the synergistic interaction between ER and ATH, alongside the porous structure of EG, resulting in a triple-layer encapsulation of the eutectic PCMs. The outcome of this formulation is marked by remarkable thermal stability, even under extreme conditions such as exposure to temperatures as high as 800 °C. Notably, one of the representative samples, denoted as S5, showcases impressive attributes with a thermal conductivity of 1.335 W∙m-1K−1 and a substantial phase change latent heat of 150.4 J∙g−1. It was observed an increase in latent heat up to 181.3 J∙g−1 after 100 heating–cooling cycles of composite PCMs. This indicates the good thermal reliability of the form-stable composite PCMs synthesized. Moreover, the composite PCMs exhibit outstanding mechanical properties, especially S5 which showed a 14.69 % and 400.12 % increase in compression strength and compression modulus compared with pure eutectic PCM (S0), respectively. Besides, the ternary composition of ER, ATH, and EG enhances the flame retardancy of the composite PCMs, yielding a substantial reduction of 67.33 % in peak heat release rate and 50.38 % in total heat release. This collaborative effect also establishes a robust defense mechanism against the rapid propagation of flames, as exemplified by the attainment of a V-0 rating in the UL-94 test. As a result, the flame-retardant ER/ATH/EG ternary-based form-stable composite PCM presents itself as a promising candidate for ensuring both safety and efficiency in thermal management applications.

Preparation and characterization of eicosane-paraffin/expanded graphite/polyurethane as form-stable composite phase change materials with wide phase change temperature range

Phase change materials (PCMs) with wide phase change temperature range, high latent heat, good thermal conductivity, and shape stability are essential for applications such as solar energy conservation and thermal management of electronic devices. Form-stable composite PCMs (FSCPCMs) with a broad phase change temperature range of 18–65 °C were successfully developed by using a mixture of eicosane and paraffin mixture along with cross-linking polyurethane as PCM, expanded graphite as thermally conductive filler and supporting material. The prepared FSCPCMs demonstrated excellent thermal stability and thermal conductivity with a latent heat up to 142.5 J/g. In conclusion, the synthesized FSCPCMs exhibit promising potential for practical applications in thermal energy storage.

Novel PVA-based foams for cold chain logistics with high efficiency

The rapid advancement of fresh e-commerce has driven the growth of the cold chain logistics, which spurs a significant demand for the upgrading of the phase change material (PCM) ensuring the transported items maintain at the required low temperature. This paper reported a novel form-stable phase change material poly (vinyl alcohol) (PVA) -based foams (FPCMPFs) with high efficiency fabricated by combining thermal foaming of PVA and in-situ polymerization of polyacrylic acid (PAA). The constructed double network structure improved the water storage to as high as 85.81 wt%, and enhanced the mechanical strength to maintain the shape stability even under 60 % compressive strain, which endowed FPCMPFs with good cold storage performance with high latent heat of 309.6 J/g, and prevented the water leakage in use. 65 g FPCMPFs located in a 7.0 × 7.0 × 10.5 cm box extended the storage time of the precooled grapes at -1-0 °C keeping at 5 °C from 28.7 min to 229.1 min, demonstrating the significant prospects for application in the cold chain logistics.

Form-stable Na2CO3-NaCl/mullite phase change composite with SiC enhanced thermal conductivity for high temperature thermal storage

High-temperature energy storage technologies are gaining prominence to meet the needs of concentrating solar power plants and industrial waste heat recovery. In this study a series of form-stable phase change materials are prepared by a simple and efficient cold compression sintering method. In this method, Na2CO3-NaCl will be mixed with mullite ceramic powder; simultaneously, SiC nanoparticles are introduced to improve the thermal conductivity of the material. The leakage, microstructure, chemical compatibility and thermal physical properties of the prepared composites are systematically analyzed using Fourier-transform infrared spectroscopy, X-ray powder diffraction, Scanning electron microscope, Differential Scanning Calorimetry and Thermogravimetric. The results of the study show that good chemical compatibility of the components in the composites, and the latent heat of melting of the encapsulated composites as well as the sample with added SiC are 266.97 J/g and 217.63 J/g, respectively, while the latent heat of crystallization is 197.37 J/g and 151.13 J/g, respectively. Compared to the thermal conductivity of PCMs (0.41 W/(m·K)), the thermal conductivity of the sample with 20 % SiC added is 1.83 W/(m·K), an increase of 8.7 times. Thermal cycling and reliability tests show that even after 300 cycles, good chemical compatibility is maintained between the components in composites, and the phase change properties and quality remain stable. In addition, the thermal storage cost of FSPCM-M40-S20 is 1.90 $/MJ. Therefore, we believe that the prepared Na2CO3-NaCl/mullite/SiC FSPCM has promising applications in high-temperature thermal energy storage, especially in solar power generation and industrial waste heat recovery.

Biodegradable polylactic acid/polyethylene glycol blends as form-stable phase change materials for thermal energy storage and management

Polyethylene glycol (PEG) is a commonly used phase change material for thermal energy storage. It can store amounts of heat in the process of phase transition, whereas the solid-to-liquid transition requires it to be form-stabilized before application. In this study, a phase change composite with form-stability and processibility is prepared by simply blending PLA with PEG at 180 °C, reaching a maximum PEG loading of 90 wt%. The preparation is easy, cheap, environmental-benign, and scalable. Besides, the obtained PLA/PEG (PLEG) composites are feasible for regulating the thermal behaviors of batteries operated at high rates, providing a low-cost and simple approach to improving the cyclability of fast-charging batteries.

High thermal conductivity and high energy density compatible latent heat thermal energy storage enabled by porous Al2O3@Graphite ceramics composites

Phase change material (PCM) is an ideal heat storage material with huge latent heat and nearly constant phase change temperature, but there are serious problems in application such as leakage and low thermal conductivity. Porous ceramic is widely used in PCM packaging because of its advantages of controllable porosity and high thermal conductivity. Porous Al2O3 ceramics were prepared by foaming injection coagulation method. In order to improve the thermal conductivity of porous ceramic matrix, Porous Al2O3@Graphite Ceramics (PAGC) were prepared by sucrose decomposition. Form-Stable Phase Change Materials (FSPCMs) were prepared by adsorption of Lauric Acid/Myristic Acid (LA/MA) in PAGC by vacuum impregnation method. SEM showed that the prepared PAGC had a three-dimensional interpenetrating structure and high porosity. TEM and XPS showed that alumina skeleton were uniformly coated with graphite. After PAGC impregnated by LA/MA, the maximum PCM storage reached 62.11 wt %. The maximum latent heat of FSPCMs reaches 83.33 J/g. Thermogravimetric analysis, thermal cycling test and Fourier transform infrared spectroscopy show that the prepared FSPCMs has good thermal stability, thermal reliability, chemical stability and compressive strength. More importantly, the thermal conductivity of the prepared FSPCMs is greatly improved, reaching up to 3.73 W/mK. It is 20.72 times the original PCM, mainly due to the synergistic effect of the Al2O3 skeleton and the graphite coating to build a continuous highway for heat transfer. This study provides a practical means to greatly improve the thermal conductivity of FSPCMs, which will promote the practical application of FSPCMs.

Photo-curable bio-based comb/bottle brush epoxy resin/beeswax/copper foam phase change materials with high enthalpy value, high conductivity, and multifunctional properties

At present, the demand for green energy has reached a new height in history, and thermal energy storage technology has been widely used to reduce energy consumption. It is still a challenge to develop bio-based polymeric form-stable phase change materials (FSPCMs) with high enthalpy value and thermal conductivity (TC), short curing time, and multifunctional properties. This work not only exploited a series of adjustable and photo-curable comb/bottle brush bio-based epoxy resin/beeswax (bw) FSPCMs with the above superiorities, but also revealed the effects of cross-linking density on the energy storage capacity and encapsulation rate of the FSPCMs. As a result, the optimal system can encapsulate the maximum amount of bw (60 wt%) and obtain the highest enthalpy value (142.1 J/g) with only 0.5% enthalpy loss. Through further introducing the optimal curing system into the copper (Cu) foam, the electromagnetic interference shielding property, TC, tensile strength, and photo-thermal conversion efficiency of the final composite (modified by Cu of 95% porosity) can reach 110 dB, 2.387 W m−1K−1, 2.81 MPa, and 80%, respectively, and the enthalpy value (84.2 J/g) is still satisfactory. This study can provide theoretical guidance for the structural design of reliable fast photo-curable bio-based polymeric FSPCMs with excellent phase change performances and multifunctional properties.

Development of novel form-stable PCM-biochar composites and detailed characterization of their morphological, chemical and thermal properties

Storing heat with phase change materials has the potential for several modern-day applications such as building thermal regulation, isothermal solar drying, electronic cooling, etc. However, to suitably incorporate latent heat energy storage systems, the challenges of leakage and low thermal conductivity of these materials need to be addressed. In this direction, biochar derived from abundantly available biomass feedstocks has been explored to develop form-stable, environmentally compatible energy storage materials. Biochar has been derived from wheat straw and softwood and has been analysed for their surface structure and utilised in the preparation of form-stable phase change material. The biochar derived from softwood was found to have a superior porous structure with a surface area of 441 m2/g compared to wheat straw. Biochar and phase change material Rubitherm 28 (RT28) were blended at various wt% and tested for leakage. The composite with 50 wt% of softwood biochar and RT28 had the lowest leakage rate. The developed green phase change-bio composite with minimum leakage has been thoroughly evaluated for its chemical and thermal properties. The latent heat of fusion has been found to be 228.6 J/g, 132.3 J/g and 51.6 J/g, for the RT28, softwood biochar composite, and wheat straw biochar composite respectively. Thermal conductivity was also higher for the composites than that of RT28. The thermal cycling reliability is suitable for thermal storage applications as there is a minimal alteration in the thermal properties observed after 200 cycles. The melting enthalpy of the new and aged composites after 200 cycles has been found to be 136.6 J/g and 132.42 J/g, respectively. The composite with minimal leakage and high thermal conductivity can potentially revolutionise the area of low temperature latent heat storage. The properties of the form-stable phase change-bio composite synthesised in this work make it suitable for application in the field of thermal management of photovoltaic modules, electronic devices, and buildings.

Selection of PEG-Matrix Combinations to Achieve High Performance Form-Stable Phase Change Materials for Building Applications

The construction sector’s pursuit of sustainability, driven by growing concerns about climate change and resource depletion, requires innovative solutions to reduce the energy consumption necessary to ensure thermal comfort in buildings. The introduction of phase change materials (PCMs) in construction elements represents an effective solution to these problems. PCMs are, in fact, able to regulate internal temperature by storing and releasing thermal energy during their phase transitions. In particular, polyethylene glycol (PEG)-based organic PCMs offer high heat storage capacity, compatibility with building materials, and minimal environmental impact. They are often used in building applications incorporated in an inert matrix, using the “form-stable method”. This article critically examines various matrices proposed in the existing literature to realize PEG-based PCMs, with the aim of analyzing their influence on the final characteristics of any PCM. In addition, an attempt to correlate the quantity of PEG with the heat stored and released by the PCM is presented, using a linear regression model applied to groups of matrices of the same chemical nature. The results of these analyses would, in fact, provide useful indications for an optimal choice of the PEG/matrix system capable of responding to specific application needs, particularly in the building sector.

Preparation and characterization of polyurethane/lauric acid-stearic acid as form-stable phase change materials with a wide phase transition temperature range

The current study employed a solvent-free method to prepare a series of crosslinked polyurethane/lauric acid-stearic acid composite form-stable phase change materials (FSPCMs). FTIR, SEM, and XRD results collectively indicate that lauric acid (LA) and stearic acid (SA) have been successfully adsorbed into the polyurethane (PU) mesh-like structure, maintaining their respective crystalline characteristics and exhibiting good compatibility. DSC and TGA data show the wide phase transition temperature range of FSPCMs from 39.6 °C to 70.0 °C, with decomposition commencing at 190.4 °C and the latent heat of FSPCM reaching 181.9 J/g. In conclusion, the broad phase transition temperature range and high latent heat of FSPCMs make them particularly suitable for thermal energy storage.

Green conversion of delignified sorghum straw and polyethylene glycol into form-stable phase change materials with promising solar energy capture, transition, and storage capabilities

Phase change materials (PCMs) have attracted considerable attention as a thermal energy management technology for thermal storage. However, achieving high energy-storing abilities, low leakage rates, and solar absorption abilities simultaneously in PCMs remains greatly challenging. This research proposed a green strategy for preparing sorghum straw-based PCMs. By facile delignification and solvothermal process, delignified sorghum straw (DSS) and carbon quantum dots (CQDs) derived from removal lignin are prepared. The obtained PEG@CQDs/DSS possessed considerable reusable stabilities, excellent photo-thermal conversion properties, and thermal energy management capacities due to the delicate micropores and intrinsic noncovalent interactions among components. Especially, the PEG@CQDs-7.5/DSS exhibited superior solar-thermal conversion capabilities (with conducive photo-thermal conversion efficiency ~90.84%), and kept stable after 100 cycles of heating and cooling, in which the melting enthalpy value is ~168.1 J/g (enthalpy efficiency of ~91.11%). In conclusion, the synthesized PCMs showed potential for application in energy-saving and building thermal management.

Preparation and temperature regulation properties of TiO2/CNTs-based form-stable phase change materials

Multiscale TiO2/carbon nanotubes (CNTs) nanofibrous mats were prepared by depositing TiO2 nanofibers on the drawing CNTs membrane as the supporting materials of quinary fatty acid eutectics for thermal storage or release. The morphology, phase change property and the temperature regulation performance were characterized by Scanning electron microscopy (SEM), Differential scanning calorimetry (DSC) and the device made in lab. The results indicated that channel-like structured TiO2 fibers distributed randomly on every layer of the drawing aligned CNTs fiber membrane, forming three-dimensional (3D) reticulate structure, which is beneficial to the adsorption of phase change materials (PCMs). DSC results showed the phase change enthalpy of as-prepared form-stable phase change materials (FSPCMs) was about 100 J·g−1, and there is no significant decrease after 100 cycles. The temperature regulation test showed that composite fabrics composed of FSPCMs had the obvious buffering effect on the temperature change compared with pure cotton fabrics. The results demonstrated TiO2/CNT nanofibrous mats are promising supporting materials of FSPCMs in the field of intelligent temperature regulation fabrics.

Carbonated balsa-based shape-stable phase change materials with photothermal conversion and application in greenhouse

Greenhouse enables to promote plant yield through creating optimal environment. Efficient solar energy conversion and storage is a promising strategy to address energy shortage issue of greenhouse in winter. This paper prepares form-stable composite phase change materials (PCMs) to store solar energy efficiently. Lightweight and porous balsa wood subjected to high-temperature carbonization is designed to simultaneously solve the liquid leakage, enhance the thermal conductivity, and improve the photothermal conversion and thermal energy storage of PCM. OP44E and SEBS are utilized as PCM and thickener, followed by vacuum impregnation into the carbonized balsa wood (CW). Results indicate that carbon content of CW increases with the augment of carbonization temperature. Shaping effects of CW and SEBS endow composite PCMs to have highest adsorption rate of 92.7 wt% with enthalpy over 190 J/g. Composite PCMs reveal reliable thermal properties and thermal stability below 100 °C. Composite PCMs have photothermal conversion larger than 88 % under a xenon lamp radiation. Temperature of PCMs on the shallow layer is higher owing to its photothermal conversion capacity. Greenhouse test indicates that CW/OP44E/SEBS greenhouse gains higher PCM temperature of 71.5 °C at 70 min, compared to 40.3 °C in empty and OP44E/SEBS cases. CW/OP44E/SEBS greenhouse maintaining indoor temperature over 20 °C lasts 15.3 min longer than empty and OP44E/SEBS greenhouses. In addition, form-stable composite PCMs featured with excellent thermal stability and photothermal conversion are capable of maintaining stable indoor temperature of greenhouse, indicating potential in the field of agricultural building temperature regulation.

Polypyrrole-modified flax fiber sponge impregnated with fatty acids as bio-based form-stable phase change materials for enhanced thermal energy storage and conversion

In this study, we integrated organic phase change materials, decanoic acid (DA) and palmitic acid (PA), into bio-based samples made from sodium alginate (SA) and flax fiber (FF). We also synthesized conductive polypyrrole (PPy) coating through in situ polymerization to create two thermal energy storage and conversion systems with distinct phase change temperatures (32 °C and 63 °C). The PPy coating exhibited uniform polymerization, resulting in electrical conductivity (1.52 ± 0.07 S/m) and thermal conductivity (0.453 ± 0.02 W/mK). The conductive sponge, similar to the plain sponge, had a porous microstructure (85 % porosity) that allowed successful impregnation of 60 % and 74 % of DA and PA, resulting in outstanding energy storage and conversion properties. Specifically, the conductive sponges with DA and PA achieved phase change enthalpies of 100.98 J/g and 154.52 J/g, respectively. DA/PPy@Sponge demonstrated exceptional durability after thermal cycling tests. Furthermore, the conductive sample efficiently converted electrical energy into thermal energy along the conductive path, making it suitable for storing generated heat as both sensible and latent heat, as well as capturing and storing solar energy. Overall, the developed conductive phase change materials offer shape stabilization, high thermal energy storage capacity, and efficient electric/photo-to-thermal conversion properties. These attributes make them promising candidates for diverse applications in energy harvesting, storage, and management in electronics, buildings, transportation, and other relevant fields.

Experimental and analytical studies on latent heat of hydrated salt/modified EG-based form-stable composite PCMs for energy storage application

Expanded graphite (EG) is often used to encase phase change materials (PCMs) and improve their thermal performance. However, EG's effectiveness when used with disodium hydrogen phosphate dodecahydrate (DHPD) as a hydrated salt is diminished, due to its hydrophobic property. This study proposes modifying the hydrophobic surface of EG with highly hydrophilic nanoparticles, such as SiO2 and TiO2, to address this shortcoming and boost its hydrophilicity. Herein, the nanoparticles were synthesized by the sol-gel technique and mixed with EG to construct a modified EG (MEG). The microstructure, morphology, and adsorption ability of MEG were analyzed. Additionally, the thermal properties, as well as the thermal stability of form-stable composite PCMs, were investigated. The results revealed that by varying the mass ratio of SiO2@TiO2 in MEG, the supercooling degree of the form-stable composite PCMs decreased by 77.36%–78.49%. With 9% SiO2@TiO2 in MEG, the water contact angle of MEG was optimal, and the form-stable composite PCMs prepared (DSMEG3) exhibited a phase change temperature and latent heat of 32.88 °C and 142.13 J/g, respectively. This experimental latent heat was slightly lower than the calculated latent heat by 0.12 J/g. Meanwhile, the supercooling degree decreased to 3.01 °C, and the thermal conductivity increased to 1.23 W/(m ∙ K), which was 1.73 times than that of DHPD. Moreover, DSMEG3 also showed good shape stability, preventing leakage. Therefore, the form-stable composite PCMs, as prepared, are a great potential candidate for the energy storage applications.

Carbon-negative heat-stored limestone calcined clay cement mortar containing form-stable phase change materials

Heat-stored cement-based materials (HSCMs) with form-stable phase change materials (PCMs) have exhibited tremendous opportunities for energy conservation and emission reduction in buildings. In this study, a novel HSCM system was designed by incorporating form-stable PCMs into limestone calcined clay cement (LC3) mortar, in which a highly compatible form-stable PCM was constructed by the three-step method including the synthesis of red mud-based geopolymer hollow microsphere (RMHM), the impregnation of n-Octadecane (ODE) into RMHM and the surface precipitation of CaCO3. The microstructures, phase transition properties, chemical compatibility and thermal stability of the two resulting form-stable PCMs (namely ODE/RMHM and ODE/RMHM@CaCO3) were evaluated. A comparative analysis was conducted to reveal the influence mechanism of ODE/RMHM and ODE/RMHM@CaCO3 on the microstructural evolution, hydration reaction, mechanical and thermal properties of LC3 mortar. Moreover, the numerical model method confirmed the significant role of the prepared LC3-based in temperature control and energy conservation in building. In addition, the obtained LC3-based HSCM could achieve a short dynamic payback period and sequestered huge of carbon emissions for service life. In overall, this work opened up a novel path of economically feasible carbon-negative building materials with form-stable PCM.

Energy harvesting and electricity production through dissolved carbon dioxide by connecting two form-stable phase change materials

Herein, we report a new solar energy harvesting approach by connecting two form-stable phase change materials in a moist environment with dissolved carbon dioxide (CO2).

Recent advances in phase change materials for thermal energy storage.

Efficient storage of thermal energy can be greatly enhanced by the use of phase change materials (PCMs). The selection or development of a useful PCM requires careful consideration of many physical and chemical properties. In this review of our recent studies of PCMs, we show that linking the molecular structures of organic molecules to their physical properties can be used to focus attention on the most useful PCMs, including eutectic mixtures. Two of the major limitations concerning broader use of phase change materials are low thermal conductivity, especially for organic phase change materials, and suitable containment. We have addressed both issues in our recent investigations of novel form-stable composite PCMs with a freeze-cast matrix. The use of thorough experimental investigations, including cycling of materials hundreds or thousands of times through the melt-freeze processes, promotes our goals of advancing the use of PCMs for increased energy efficiency and sustainability.

Thermal energy storage materials designed from recycled Tetra Pak waste and paraffin waxes with enhanced photothermal conversion efficiencies

The phase change material (PCM)-integrated solar water heaters have great potential to save energy by utilizing renewable resources and to extend working hours even after sunsets. The PCM composites fabricated with recycled waste products lead to the circular economy which would contribute significantly to the sustainable development goals. In this work, Tetra Pak waste (TP) was used to prepare a form-stable PCM composite by mixing with paraffin wax (PW) and expanded graphite (EG) to integrate with solar water heaters. Two different PWs with melting points of 44 (RT44) and 64 (RT64) were used in the lower and higher temperature ranges of domestic water heating applications, respectively. The prepared composites exhibited enhanced thermal conductivity (1.1–1.15 W/m.°C), heat storage capacity (98.5–105.6 J/g), and photothermal conversion efficiency (85% and 55% for composites with RT44 and RT64, respectively). The numerical analysis conducted on a validated model helped to estimate the optimum composite thickness for specific solar exposure time. The fabricated PCM composite promoted the recycling of TP waste into useful products and was efficient in maintaining a higher nocturnal water temperature in the solar water heater.