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Phase‐change materials (PCMs) have been widely investigated as candidates for thermal energy storage and solar thermal energy conversion. However, low thermal conductivity and poor shape stability during phase transition processes are detrimental to their practical applications. In this study, we designed composite PCMs based on carbon foam (CF) via the vacuum impregnation method to overcome these problems. CF with 3D interconnected microporous structures and good compressive strength was fabricated from phenolic resin (PF) using a combined process of carbonization and sacrificial template techniques. The developer material is considered a promising support material for PCMs. The as‐prepared polyethylene glycol/CF composite (PCC) exhibited a high energy‐storage density with a melting enthalpy of 135.7 J/g, and the thermal conductivity was enhanced by 109.8% compared to that of pure polyethylene glycol. In addition, the PCC showed excellent thermal stability and leakage‐proof performance after 100 heating/cooling cycles and good compressive strength. Because of the simple preparation process and low cost, PCC is a promising material for various thermal energy storage applications, especially in building energy storage systems. [ABSTRACT FROM AUTHOR]

Bone char (BC) is a promising porous material that can be used for preparing a form-stable composite phase change material (PCM). In this paper, form-stable polyethylene glycol (PEG 6000)/BC composite PCMs were prepared by impregnation method. The PEG was used as the phase change material, and two different particle sizes of BC (0.8-1 mm: BC-1; 0.25-0.8 mm: BC-2) were acted as the supporting materials. The phase composition and chemical structure of the composite PCMs (PEG/BC-1 and PEG/BC-2) were characterized using X-ray diffraction and Fourier transformation infrared. The results indicated that the PEG can be well impregnated into BC pores with good compatibility. Thermal properties and thermal stability of the composite PCMs were determined by differential scanning calorimeter (DSC) and thermogravimetry analysis (TGA). DSC results showed that the maximum impregnation percentage for PEG into BC-1 and BC-2 was 38.77 and 43.91%, respectively, without melted PCM seepage from the composites. The TGA analysis revealed that the composite PCMs had good thermal stability above their working temperature range. The thermal cycle test of 100 melting-freezing cycles showed that the composite PCMs have good thermal reliability and chemical stability. The form-stable composite PCMs can be used as thermal energy storage material for waste heat storage and solar heating system. [ABSTRACT FROM AUTHOR]

Radial mesoporous silica (RMS) sphere was tailor-made for further applications in producing shape-stabilized composite phase change materials (ss-CPCMs) through a facile self-assembly process using CTAB as the main template and TEOS as SiO2 precursor. Novel ss-CPCMs composed of polyethylene glycol (PEG) and RMS were prepared through vacuum impregnating method. Various techniques were employed to characterize the structural and thermal properties of the ss-CPCMs. The DSC results indicated that the PEG/RMS ss-CPCM was a promising candidate for building thermal energy storage applications due to its large latent heat, suitable phase change temperature, good thermal reliability, as well as the excellent chemical compatibility and thermal stability. Importantly, the possible formation mechanisms of both RMS sphere and PEG/RMS composite have also been proposed. The results also indicated that the properties of the PEG/RMS ss-CPCMs are influenced by the adsorption limitation of the PEG molecule from RMS sphere with mesoporous structure and the effect of RMS, as the impurities, on the perfect crystallization of PEG. [ABSTRACT FROM AUTHOR]

Currently, phase change materials (PCMs) composite fibers are typically prepared by electrospinning. However, electrospinning exhibits safety concerns and a low production rate, which limit its practical applications as a cost-effective fiber fabrication approach. Therefore, a novel, and simple centrifugal spinning technology is employed to extrude fibers from composite solutions using a high-speed rotary and perforated spinneret. The composite fibers based on polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) were prepared by centrifugal spinning. The SEM of PVP/PEG composite fibers indicated that the fibrous morphology is well preserved. The DSC and TGA indicated that PVP/PEG composite fibers exhibit good thermal properties. [ABSTRACT FROM AUTHOR]

Shape-stable and high-thermal conductivity composite phase change materials (c-PCMs) composed of polyethylene glycol (PEG) and biological porous carbon (BPC) are investigated. BPC based on potatoes and white radishes are obtained by the carbonization method. The thermal conductivity of the BPC increases with the rising of the carbonization temperature due to the higher graphitization degree. Especially, BPC calcined at 1300 °C for 2 h resulted in the optimum PEG supporting matrix candidate, showing an attractive honeycomb-like microstructure. Calcination above 1300 °C results in the destruction of the shape. BPC/PEG c-PCMs are synthesized via a vacuum impregnation approach. PEG equally distributed in the matrix material with a mass fraction of 85.36% approximately and it could keep its morphological stability after heating at 80 °C for 40 h. Moreover, the highest thermal conductivity is 4.5 W/m K, which is about 10 times higher than the pristine PEG. Furthermore, no chemical interaction is found between the PEG and BPC. The melting and solidifying temperature, and enthalpy not vary upon a 200 thermal cycles test. This confirms the excellent chemical and structure stability for c-PCMs, which are within the most promising materials in the area of building heat preservation by being clean, energy-saving and recycled materials. [ABSTRACT FROM AUTHOR]

In this study, polyethylene glycol/expanded perlite composite with carbon layer phase-change materials were prepared. EP was impregnated with a sucrose solution, followed by carbonation in situ by the carbon-bed method, for obtaining EPC composite, thus providing an important method for enhancing the thermal conductivity of composite PCMs. Scanning electron microscopy images showed that the EPC composite with a highly porous structure composed of rough micro-pores could act as a good supporting material for absorbing molten PEG. The results obtained from differential scanning calorimeter analysis indicated that the values for the latent heat and temperature of PEPC composite during melting were 134.93 J/g and 55.19 °C, respectively, while, these values were 129.27 J/g and 46.71 °C during freezing, respectively. The thermal conductivity of PEPC composite was 0.479 W/(mK), which was 2.975 times that of PEP composite. The results obtained from Fourier transform infrared spectroscopy and thermo-gravimetric analysis showed that PEPC composite exhibited good chemical stability and thermal stability, respectively. Furthermore, thermal cycling tests indicated that PEPC composite exhibited good thermal reliability after 200 melting/freezing cycles. In conclusion, PEPC composite with excellent thermal properties, ideal thermal conductivity, good thermal reliability and chemical stability could act as the promising building filler materials for the sustainable development of energy-efficient buildings. [ABSTRACT FROM AUTHOR]

In this study, novel polyethylene glycol @ Si 3 N 4 nanowires as phase-change materials (PCMs) were developed by using ultrasonic cell disruptor. The results obtained herein indicate that these nanowires can be a potential carrier for preparing PCMs. The results show that PEG is composited in a fluffy nano-network structure of Si 3 N 4 nanowires, which could not be easily leaked from this structure for the solid–liquid phase transition. X-ray diffraction and Fourier transform infrared spectroscopy were employed for investigating the structures of PCMs; the results show that a chemical reaction does not occur between PEG and Si 3 N 4 nanowires. Differential scanning calorimetry analysis results indicated that PCMs exhibit appropriate phase-change temperature and excellent high-phase change enthalpy. From the TGA results, PCMs exhibit perfect thermal stability. The PCMs could perfectly maintain their phase transition after 100 melting–freezing cycles. The thermal conductivity of PCMs-1 was 0.362 W/(mK), which was enhanced by 88.54% in comparison with that to pure PEG. The heat storage or release rate of PCMs is significantly more rapid than that of pure PEG for practical applications. [ABSTRACT FROM AUTHOR]

• Hybrid aerogel was prepared by hydrothermal reaction with 3D porous structure. • The PEG mass fraction in c-PCMs was 97.6 wt%. • The H M and H S value of c-PCMs remained 93.44% and 92.84% after 1000 times cycles. • CGA could meet the demand for packing PCM and improving the heat transfer rate. Phase change materials (PCMs) have attracted more and more attention in the field of latent heat storage. In order to solve the leakage behavior and improve heat transfer performance of polyethylene glycol (PEG), a method of self-assembled hybrid aerogel filled with carbon nanotubes (CNTs) combined with reduced graphene oxide (rGO) nanosheets is proposed herein. The as-prepared CNTs-graphene hybrid aerogel (CGA) with three-dimensional porous structure can be used as a highly adsorptive and stable carrier for PCM. After the vacuum impregnation process, a high-performance PEG/CGA composite PCMs (c-PCMs) is obtained, which exhibits an outstanding PEG loading ratio of 97.6 %. Moreover, after 1000 repeated heating/cooling cycles, the H M and H S value of PEG/CGA c-PCMs remained 93.44 % and 92.84 %. Meanwhile the PEG/CGA c-PCMs remains intact and the loading ratio could still maintain as high as 96.4 %, which proved that PEG/CGA c-PCMs presented reliable thermal cycling stability. The PEG/CGA c-PCMs only takes 603 s to raise from 30 ℃ to 70 ℃, which is much faster than that of pure PEG (813 s) and PEG/GA composite (727 s). And The thermal conductivity of PEG/CGA(0.586 W/(m∙K)) was 186 % times than that of pure PEG(0.314 W/(m∙K)).The introduction of CNTs can not only enhance the adsorption capacity of c-PCMs and alleviate the leakage of PEG, but also improve the heat transfer performance of c-PCMs. These results specify that PEG/CGA c-PCMs can be used as remarkable and stable energy storage materials for environmental thermal management systems. [ABSTRACT FROM AUTHOR]

In this study, novel polyethylene glycol (PEG)/White Carbon Black (WCB) form-stable composite phase changes materials (FS-CPCMs) were prepared by super- ultrasound-assisted, which obviously decreases the reaction time. Test results showed that PEG does not easily leak from the fluffy network structure of WCB during solid-liquid phase transition. Results obtained from XRD and FTIR demonstrated that no new chemical bond is formed between PEG4000 and WCB. Results obtained from DSC and TGA analyses showed that FS-CPCMs exhibit excellent thermal stability and good form-stable performance. The phase change enthalpy of FS-CPCMs reached up to 101.1J/g, and the melting and solidifying times of FS-CPCMs were 34.43% and 30.51% less than that of pure PEG, respectively. The thermal conductivity data showed that WCB acted as the support material is very effective for enhancing the thermal conductivity of the FS-CPCMs. The FS-CPCMs thus prepared were safe, environmentally friendly, and cost-effective; hence, they can be used as potential building materials for the applications of thermal energy storage. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) have attracted growing attention in clean energy storage fields. To improve the thermal conductivity of porous mineral-based composite PCMs (c-PCMs), pretreatment via in-situ carbonization is proposed to fill the pore structure with thermally conductive carbon. After vacuum impregnation, high-performance c-PCMs are obtained, comprising carbon-modified expanded perlite (EPC) and polyethylene glycol (PEG). The modified micro-pores optimize the heat transfer characteristic behaviors in c-PCMs and improve the adsorption stability of PEG. Thus, the load capacity of PEG reaches approximately 73.90 wt% in EPC/PEG c-PCMs, providing excellent chemical and structural stability among perlite matrix, carbon modifier and PEG PCMs. The thermal conductivity of the EPC/PEG c-PCMs is 0.521 W/(m·K), which is almost 1.3 times that of the pristine PEG. These performances indicate that the EPC/PEG c-PCMs could be used as an environmentally friendly material for external wall heat-insulation application. • The micro-pores and carbon skeleton were developed in expanded perlite modified by sucrose after a carbonation process. • Low-cost, high thermal conductivity, shape-stable c-PCMs were composed of modified expanded perlite and polyethylene glycol. • The mass fraction of PEG in PEG/EPC c-PCMs was 73.90% approximately. • The as-prepared c-PCMs exhibited excellent thermal energy storage performance. [ABSTRACT FROM AUTHOR]

Currently, electrospinning technology is the most used spinning technology. However, electrospinning exhibits low production rate and safety hazards, which has led to the development of the novel centrifugal spinning technology to extrude phase change fibres from composite solutions. The flexible composite phase change fibres based on Polyethylene glycol (PEG) and Polyvinylpyrrolidone (PVP) were prepared by centrifugal spinning. Moreover, carbon nanotubes acted as thermally conductive fillers to enhance the thermal conductivity of flexible composite phase change fibres. The microstructures of the fibres were observed with a scanning electron microscope (SEM). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to determine the thermal properties of the fibres. The results showed that the concentrations of PEG and PVP had different influences on the diameter and smoothness of fibres, and the energy storage effect increased with the increasing PEG content. In summary, flexible composite phase change fibres based on PEG and PVP have very good application prospects for thermal insulation. Morphology and microstructure of centrifugal spinning composite fibres: (a) CNTs 1 wt %, (b) CNTs 3 wt %, (c) CNTs 5 wt % and (d) CNTs wrapped in composite fibres. Image 1 • The composite fibres with energy storage effect was prepared by centrifugal spinning. • PEG is encapsulated in PVP fibres with no leakage. • The thermal conductivity of the composite fibres with CNTs is 1.71 times higher than that of without CNTs. • The preparation process of the composite fibres was cost-effective, environment friendly, chemically stability, and harmless. [ABSTRACT FROM AUTHOR]

Recently, electrospinning has been widely applied to prepare phase-change material fibres. However, the practical applications of electrospinning are limited by its low productivity and potential safety hazards. Herein, a simple centrifugal spinning without the drawbacks of electrospinning was applied to fabricate polyethylene glycol-based PCM fibres with nano-SiC as a highly conductive filler, polyacrylonitrile as the supporting material, and N,N-dimethylformamide as the solvent to dissolve the polymers. Results demonstrate that the PCM fibres were formed by physical combination rather than chemical reaction. The shapes of the PCM fibres remained stable during the phase-change process. Based on differential scanning calorimetry, PAN/PEG/SiC PCM fibres containing 4.0 wt% nano-SiC melted at 51.31 °C with a phase-change latent heat of 69.91 J/g. The thermal conductivity of PAN/PEG/SiC PCM fibres was improved by 79% compared to that of PAN/PEG PCM fibres. The good thermophysical properties of the prepared PAN/PEG/SiC PCM fibres show promise for long-term utilization. Image 1 • The PAN/PEG/SiC PCM fibres were prepared by centrifugal spinning. • The polyacrylonitrile (PAN) was satisfactory PEG supporting matrix. • The relationship of highly conductive filler (nano-SiC) and thermal conductivity was deep investigated. [ABSTRACT FROM AUTHOR]