Synthesis and thermal properties of poly(styrene-co-ally alcohol)-graft-stearic acid copolymers as novel solid–solid PCMs for thermal energy storage

A series of poly(styrene-co-allyalcohol)-graft-stearic acid copolymers were synthesized as novel polymeric solid–solid phase change materials (SSPCMs). The graft copolymerization reactions between poly(styrene-co-allyalcohol) and stearoyl chloride were verified by Fourier transform infrared (FT-IR) and Proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy techniques. The crystal morphology of the SSPCMs was investigated using polarized optical microscopy (POM) technique. Thermal energy storage properties of the synthesized SSPCMs were measured using differential scanning calorimetry (DSC) analysis. The POM results showed that the crystalline phase of the copolymers transformed to amorphous phase above their phase transition temperatures. Thermal energy storage properties of the synthesized SSPCMs were investigated by differential scanning calorimetry (DSC) and found that they had typical solid–solid phase transition temperatures in the range of 27–30 °C and high latent heat enthalpy between 34 and 74 J/g. Especially, the copolymer with the mole ratio of 1/1 (poly(styrene-co-allyalcohol)/stearoyl chloride) is the most attractive one due to the highest latent heat storage capacity among them. The results of DSC and FT-IR analysis indicated that the synthesized SSPCMs had good thermal reliability and chemical stability after 5000 thermal cycles. Thermogravimetric (TG) analysis results suggested that the synthesized SSPCMs had high thermal resistance. In addition, thermal conductivity measurements signified that the synthesized PCMs had higher thermal conductivity compared to that of poly(styrene-co-allyalcohol). The synthesized copolymers as novel SSPCMs have considerable potential for thermal energy storage applications such as solar space heating and cooling in buildings and greenhouses.     

β-Cyclodextrin grafted on alkali lignin as a dispersant for coal water slurry

A modified alkali lignin (AL) was synthesized by introducing β-cyclodextrin (β-CD) into AL with epichlorohydrin (EPI) copolymerization, which resulted in incorporating β-CD with AL by ether linkage. As a dispersant, β-CD copolymerized AL (β-CD-AL) was added into coal water slurry and its efficiency was evaluated. The effects of β-CD content on the performance of β-CD-AL were investigated via analyzing dispersity, zeta potential, and adsorption capacity. The results illustrated that β-CD-AL behaved better dispersion owing to the high slurry concentration at fixed apparent viscosity, which was mainly attributed to the synergistic effects of electrostatic repulsive force and steric hindrance. Steric hindrance originated from the side chain of β-CD gives better stability and less adsorption amount.     

Preparation and characterization of polyethylene glycol/active carbon composites as shape-stabilized phase change materials

Shape-stabilized phase change materials (PCMs) composed of polyethylene glycol (PEG) and mesoporous active carbon (AC) were prepared by a blending and impregnating method. Various techniques were carried out to characterize the structural and thermal properties of the composites. Lower phase change temperatures and enthalpies were observed as the weight percentage and molecular weight of PEG was decreased. The crystallinity of PEG in the PCMs decreased with the increase in the AC content. The activation energy of the PEG phase change decreased with higher PEG weight percentages. We conclude that the phase change properties of the PEG/AC PCMs are influenced by the adsorption confinement of the PEG segments from the porous structure of AC and also the interference of AC by acting as an impurity with perfect PEG crystallization.     

Preparation and characterization of cross-linking PEG/MDI/PE copolymer as solid–solid phase change heat storage material

Phase change materials (PCMs) are a series of functional materials with storing and releasing energy properties. PCMs can impact small environment around them through storing and releasing energy during phase change process. Phase change latent heat of PCMs has two main characters: one is high enthalpy and capacity of per unit volume and the other is that the temperature over phase change process keeps constant or changes slightly. PCMs have been widely used in lots of fields such as solar energy storing, smart housing, thermo-regulated fibers and agricultural greenhouse.In this article, a novel solid–solid phase change heat storage material was synthesized via the two-step condensation reaction of high molecule weight polyethylene glycol (PEG10000) with pentaerythritol (PE) and 4,4′-diphenylmethane diisocyanate (MDI). To characterize the resulting product in comparison with pristine PEG10000, Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), polarization optical microscopy (POM) and wide-angle X-ray diffraction (WAXD) measurements were employed to investigate their ingredients, thermal properties and crystalline behaviors. The results indicated that the cross-linking PCM showed typical solid–solid phase transition property, and its phase change enthalpy and crystallinity reached 152.97 kJ/kg and 81.76%, respectively.     

Synthesis of solid–solid phase change material for thermal energy storage by crosslinking of polyethylene glycol with poly (glycidyl methacrylate)

Polyethylene glycol (PEG10000)/poly (glycidyl methacrylate) (PGMA) crosslinked copolymer as a novel solid–solid phase change material (SSPCM) was successfully synthesized through the ring-opening crosslinking reaction of end-carboxyl groups in carboxyl polyethylene glycol (CPEG) and epoxy groups in PGMA. Fourier transform infrared spectroscopy (FT-IR), polarizing optical microscopy (POM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and thermogravimetry (TG) were employed to study the chemical structure, crystalline properties, phase transition behaviors and the thermal stability of the copolymer, respectively. The results from WAXD patterns and POM images show that the crystalline form of the copolymer is similar with that of pure PEG, and the PEG soft segment phase transition between crystalline and amorphous states results in heat storage and release of the copolymer. Due to the crosslinking network restricted the free movement of the soft segments, at temperature above the PEG phase melting transition, the copolymer was still solid. The DSC results indicate that the copolymer imparts balanced and reversible phase change behaviors at the temperature range of 25–60 °C, and it has high latent heat storage capacity of more than 70 J/g. The TG results suggest that the copolymer had a much broader applicable temperature range compared with pure PEG.     

Preparation and performance of form-stable polyethylene glycol/silicon dioxide composites as solid–liquid phase change materials

This work mainly involved the preparation and characterization of form-stable polyethylene glycol (PEG)/silicon dioxide (SiO₂) composite as a novel solid–liquid phase change material (PCM). In this study, the polyethylene glycol/silicon dioxide composites as form-stable, solid–liquid phase change material (PCM) was prepared. In this new material, the polyethylene glycol acts as the latent heat storage material and silicon dioxide serves as the supporting material, which provides structural strength and prevents the leakage of the melted polyethylene glycol. Results indicated that the composite remained solid when the weight percentage of silicon dioxide was higher than 15%. Moreover, the polyethylene glycol was observed to disperse into the network of the solid silicon dioxide by investigation of the structure of the composite PCMs using a scanning electronic microscope (SEM). The properties of the porous materials and phase change materials were characterized using Fourier transformation infrared spectroscope (FTIR). The transition process was observed using polarizing optical microscope (POM) and dynamic thermo mechanic analysis (DMA). The melting temperatures and latent heats of the form-stable PEG/SiO₂ composite PCMs were determined using differential scanning calorimeter (DSC).     

Recyclable solid-solid phase-change materials cross-linked by reversible oxime?carbamate bonds for solar energy storage

Polymeric solid-solid phase-change materials (SSPCMs) possessing excellent shape stability and adaptability are able to store renewable thermal energy in an economically feasible and environmentally friendly way. Integration of chemical cross-links colorless and recyclability in a single SSPCM is challenging and interesting at present. Herein, the oxime carbamate bond was firstly introduced in chemically cross-linked polyurethanes to prepare recyclable SSPCMs, in which finely dispersed PEG segments function as phase-change components as well as polymeric skeletons. The excellent thermal energy storage capacity (with the enthalpy reached up to 101 J/g) and remarkable thermal stability of the synthesized SSPCMs had been confirmed. Moreover, the as-prepared SSPCMs can be recycled and reprocessed by simple hot pressing because of the reversibility of oxime carbamate bond. This SSPCM combines good thermal storage capacity and appealing recyclability, exhibiting sustained usability for energy storage.     

Design of three-dimensional interconnected porous hydroxyapatite ceramic-based composite phase change materials for thermal energy storage

In this article, three-dimensional connected porous hydroxyapatite ceramics (PHCs) were prepared by using the Pickering emulsion template, which possessing controlled pore structure simply by adjusting the solid content from 35 to 55 wt%. The polyethylene glycol (PEG) and PHCs were compounded by vacuum impregnation to acquire composite phase change materials (CPCMs) with admirable shape stability. The SEM and EDS images showed that PEG was successfully adsorbed in the pore, and the results of FT-IR, XRD, TGA, and thermal cycles test, demonstrated the CPCMs possessed satisfactory chemical stability, favorable thermal stability, and wonderful thermal reliability. The maximum package ratio obtained was 66 wt%, which was supported by the PHC sample prepared with a solid content of 40 wt%. Moreover, the phase transition temperature and latent heat during melting and solidification were 53.41°C and 117.5 J/g, 36.49°C and 111.1 J/g, respectively. Therefore, the prepared PCM composites had a controlled pore structure, stable chemical properties, high latent heat, and excellent thermal reliability, making it a reliable application of thermal energy storage.     

Preparation of methanation catalysts for high temperature SOEC by β-cyclodextrin-assisted impregnation of nano-CeO2 with transition metal oxides

The aim of this work was to prepare and examine the catalytic activity of nanometric CeO₂ decorated with transition metal oxides – Ni, Co, Cu, Fe and Mn – towards a high-temperature methanation process under SOEC CO₂/H₂O simulated co-electrolysis conditions. Samples were prepared using the wet impregnation method via the conventional process and with the addition of native cyclodextrin. The influence of β-cyclodextrin (βCD) onto the size, dispersion and integration of the obtained metal nanoparticles was investigated. The differences between the catalysts’ reducibility revealed that samples prepared from βCD-containing solutions, in most cases, resulted in the creation of smaller Me_xO_y NPs on the surface of the substrate material compared to those prepared using traditional nitrate solutions. The samples containing Ni and Co were the only ones that observably catalysed methane synthesis. The high dispersion and integration of NPs prepared via the proposed synthesis route resulted in increased catalytic activity and enhanced stability, which was most pronounced for the Co-impregnated sample. The methane production peak for Ni-βCD/CeO₂ at 375 °C was characterised by nearly 99% CO conversion and 80% selectivity towards CH₄ production. Co-βCD/CeO₂ reached 84% CO conversion and almost 60% methane selectivity at 450 °C. The usage of CeO₂ coupled with βCD for the preparation of catalysts for high-temperature methane synthesis for use in SOECs gave promising results for further application.     

Thermal properties and crystallization kinetics of pentaglycerine/graphene nanoplatelets composite phase change material for thermal energy storage

Solid-solid phase change materials (SSPCMs) used in thermal energy storage (TES) system attract much attention in recent days. Here, graphene nanoplatelets (GnPs) were introduced into pentaglycerine (PG) with mass ratios of 1 wt%, 2 wt%, and 4 wt% to obtain PG/GnPs PCMs. The structure and thermal property of PG/GnPs PCMs were characterized by SEM, XPS, FT-IR, POM, DSC, thermal conductivity tester, and heat transfer performance test system. The effect of GnPs on the crystallization kinetic of PG was investigated by isoconversional method. The results indicated that PG and GnPs were uniformly mixed together by physical reaction. GnPs reduced the subcooling and enhanced the thermal conductivity of the PG/GnPs. The heat transfer rate of PG/GnPs was improved during to the high thermal conductivity. Crystallization kinetic results presented that the activation energy increases with the GnP content. In summary, GnPs improved the thermal behaviors of PG.     

The shape-stabilized phase change materials composed of polyethylene glycol and various mesoporous matrices (AC, SBA-15 and MCM-41)

In order to obtain stable phase change composites with a high PEG load and enthalpy, a series of polyethylene glycol (PEG) based phase change composites with different mesoporous materials (active carbon and silica molecular sieves) were prepared by a simple approach. Various characterization techniques were carried out to investigate the properties of the composites. It was observed that both the porous characteristics and surface properties of the mesoporous stabilizers combined affected the crystallinity and phase change behavior of PEG. Among the various composites, PEG/AC PCMs with 80 wt% of PEG had the largest latent heat, a relatively low melting point, the least supercooling and a higher heat storage efficiency. This study will provide insight into the fabrication of stabilized polymer based high performance phase change systems for heat storage application.     

A phase density based enthalpy model for laser assisted phase change process

Diffusion dominated laser assisted phase change process in a pure metal is numerically investigated using the enthalpy based fixed-grid approach. The single equation based on the total enthalpy (sensible and latent heat) is used in the whole domain (solid, liquid and vapor) to describe the transport processes in individual phases. To simulate in line with the experiment for laser drilled cavity in a cylinder, density variation due to change of phase has been taken into account in the proposed axisymmetric model. The proposed model also includes temperature dependent thermal properties. An iterative enthalpy update equation is developed to capture the evolution of the complicated melt as well as vapor front. To resemble a true laser beam, a Gaussian laser pulse is irradiated on the substrate surface. The drilled cavity depth predicted using the proposed model is compared with the available experimental results and a good agreement is found.     

Thermal energy storage properties of polyethylene glycol grafted styrenic copolymer as novel solid-solid phase change materials

Polymeric solid-solid phase change materials (S-SPCMs) are functional materials with phase transition-heat storing/releasing ability. With this respect, a series of polyethylene glycol (PEG) grafted styrenic copolymer were produced as novel S-SPCMs. PEGs with three different molecular weights were used for synthesis of isocyanate-terminated polymers (ITPs). To achieve cross-linking S-SPCMs, the ITPs were grafted with styrene-co-ally alcohol) (PSAA) at three different PSAA:PEG mole ratios. The produced polymers were characterized using Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (¹H NMR), and X-ray diffraction (XRD) technique. The crystalline-amorphous phase transitions of the polymers were examined using polarized optical microscopy (POM). The FT-IR, NMR, and XRD results confirmed the expected chemical structures and crystallization performances of the polymers. Thermal energy storage (TES) properties of the S-SPCMs were determined by differential scanning calorimetry (DSC). The DSC results revealed that the polymers with grafting ratio of PSAA:PEG(1:1) had phase transition enthalpies between about 74 and 142 J/g and phase transition temperatures between about 26°C and 57°C. Thermogravimetric analysis (TGA) measurements demonstrated that the S-SPCMs were resistant to thermal decomposition until about 300°C. Thermal conductivities of the produced S-SPCMs were measured in a range of about 0.18 to 0.19 W/mK. Furthermore, TES properties of the S-SPCMs were slightly changed as their chemical structures were remained after 5000 thermal cycles. By overall evaluation of the findings, it can be foreseen that particularly PSAA-g-PEG(1:1) polymers can be considered as promising S-SPCMs for some TES practices such as air conditioning of buildings, thermoregulation of food packages, automobile components, electronic devices, and solar photovoltaic panels.     

End group modification of polyethylene glycol (PEG): A novel method to mitigate the supercooling of PEG as phase change material

Polyethylene glycol (PEG) is a kind of phase change material with high phase change enthalpy and good compatibility with the environment. However, there is relatively large supercooling for PEG, limiting their practical applications. To reduce their supercooling degree, herein we use three different small molecules (acryloyl chloride, acetyl chloride, and thionyl chloride) to modify PEG and study the effects of different end group modification on their phase change properties. Fourier‐transform infrared (FTIR) and proton nuclear magnetic resonance (¹H‐NMR) spectroscopy are used to confirm the molecular structure of the PEG with different molecular weights and functionalities after chemical modification. Crystal structures of the PEG before and after the modification are verified by X‐ray diffractometry (XRD) method and show no change. Differential scanning calorimetry (DSC) results show that the end group modification is quite effective for mitigating the supercooling of PEG with double ‐OH end groups but not effective for PEG with mono ‐OH end group. The mechanism for the change of supercooling behavior is proposed. The costs of different modification methods are estimated and compared.     

Poly(vinyl alcohol)/sulfated β-cyclodextrin for direct methanol fuel cell applications

We report a composite membrane based on poly(vinyl alcohol) and sulfated β-cyclodextrin in this paper. TGA and SEM tests provide direct evidence of the thermal stability and the uniform structure of the composite membranes. The performances of the composite membranes are investigated in terms of swelling behavior, methanol permeability and proton conductivity as function of sulfated β-cyclodextrin content. We find that the introduction of sulfated β-cyclodextrin can reduce water uptake. The temperature dependence of proton conductivity reveals that the proton conducting activation energy of the composite membranes is similar to that of Nafion 115, in other words, both the vehicle and Grotthus mechanisms are assumed to be responsible for the composite membranes’ proton transfer. Methanol permeability decreases as the methanol feed concentration increases from 2 M to 20 M. Both proton conductivity and methanol permeability increases with increasing sulfated β-cyclodextrin. The selectivity of the composite membranes defined as the ratio of proton conductivity to methanol permeability obtains the maximum of 1.710 × 10⁴ S s cm⁻³ at the composition of 17 wt.% sulfated β-cyclodextrin. The MEAs fabricate with these membranes are tested, no distinct change occurred to the composite membranes after the MEAs operating for 288 h. These data indicates the chemical and electrochemical stability of the membranes and their potential application in direct methanol fuel cells.     

泡沫铜强化石蜡相变蓄热特性的数值分析

通过构建泡沫金属内固液相变传热模型,对方腔蓄热单元中泡沫铜强化石蜡相变蓄热特性进行数值分析。数值模型采用考虑泡沫金属真实结构的等效导热系数通用模型,并兼顾石蜡在融化前后与金属骨架之间的热非平衡效应。通过求解模型得到方腔内石蜡固液界面演化规律与温度分布,进而对蓄热过程进行火用分析。结果表明:当前数值模型能较好地预测泡沫铜内固液相变传热;泡沫铜显著改善了石蜡相变的空间均匀性,减小了蓄热区温度梯度,使蓄热速率和火用效率得到有效提高。     

Enhanced saccharification of SO2 catalyzed steam-exploded corn stover by polyethylene glycol addition

Corn stover is a renewable, low cost and abundant feedstock in China. Its effective utilization is crucial for providing bioenergy, releasing environmental pollution and increasing farmers’ income. This aim of this study was to obtain the efficient saccharification of SO₂ catalyzed steam-exploded corn stover (SSECS) by polyethylene glycol (PEG) addition. According to the results, adding PEG6000 could lower the enzyme loading by 33.3%. With 20% solid loading, the highest glucose concentration of 102 g L⁻¹ and 91.3% saccharification yield were obtained using 30 CBU (g glucan)⁻¹ ??-glucosidase and 10 FPU (g glucan)⁻¹ cellulase in presence of PEG6000. In addition, protein and enzyme activities assays in the supernatants revealed that PEG could facilitate the desorption of enzyme protein from lignocellulose. These indicated that PEG addition not only can enhance enzymatic saccharification at high substrate concentration, but also can improve enzyme recycling by reducing the enzyme activity loss caused by adsorption during the hydrolysis.     

A novel nonmetal intercalated high crystalline g-C3N4 photocatalyst for efficiency enhanced H2 evolution

Introducing nickel foam as assistant, a novel nonmetal intercalated high crystalline graphitic carbon nitride (g-C₃N₄) catalyst was successfully fabricated by β-cyclodextrin (β-CD) pretreated melamine with one step thermal polymerization process. The final results show that 0.3-NCCN presented a remarkably visible-light (λ > 400 nm) photocatalytic H₂ evolution reaching 9297  μmol g^?1 h^?1, and the reaction process follows the zero-order kinetic model. The increase in crystallization of 0.3-NCCN implies a higher-ordered arrangement of tris-s-triazine. The nonmetal interlayer formed by oxygen-contained graphitized carbon can extend the π-conjugated system. Both above significantly benefit the rapid migration and separation of charge-carrier. Moreover, the narrowed band gap provides a stronger thermodynamic driving force for improving the photocatalytic water splitting efficiency. Our work paved a new method to construct high performance photocatalyst for water splitting.     

A poly(ethylene glycol)-based smart phase change material

A shape memory thermoplastic polyurethane (PU) as a phase change material (PCM) was synthesized by employing poly(ethylene glycol) (PEG) as the soft segment via bulk polymerization. Its phase separation structure, crystalline morphology, phase change behaviors, dynamic mechanical properties and melt-processing ability were investigated using polarizing optical microscopy, atomic force microscopy, differential scanning calorimetry, dynamic mechanical analysis, thermogravimetry and melt flow index. A well-formed phase separation structure in the PEG-based polyurethane (PEGPU) was found which accounts for most of the material phase change properties and shape memory effect. The PEG soft segment phase transition between crystalline and amorphous states resulted in heat storage and release of the PEGPU. Due to the hydrogen bonded hard segment phase serving as “physical cross-linking” restricted the free movement of the soft segments, at temperature above the PEG phase melting transition, the PEGPU was still solid. The differential scanning calorimetry results indicated that the PEGPU had high latent heat storage capacity of more than 100 J/g. The dynamic mechanical analysis results showed that it had a plateau elastic modulus about 40 MPa in the region above the PEG phase melting transition while below 150 °C. The thermogravimetry results suggested that the PEGPU had a much broader applicable temperature range compared with pure PEG. The melt flow index results indicated that the material had a good melt-processing ability. The material shape fixity ratio was more than 84% and shape recovery ratio up to 93.7% obtained from thermomechanical cyclic tensile testing.     

Microencapsulation of a eutectic PCM using in situ polymerization technique for thermal energy storage

In the present work, microencapsulated phase change material (M-PCM) has been synthesized with eutectic mixture (75% SA + 25% CA) as core and melamine formaldehyde (MF) as shell using in situ polymerization. Advanced instrumental techniques like field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR), particle size analyzer (PSA), thermogravimetric/differential thermal analysis (TG/DTA), differential scanning calorimetry (DSC), and thermal conductivity analyzer (TCi) were used to characterize the synthesized M-PCM, and impact of effective parameters like pH and agitator speed on the encapsulation process was also elucidated. Results obtained reveal that at the optimized pH (3.2) and agitator speed (1500 rpm) M-PCM possess smooth surface morphology, spherical in shape with particle size of 10.41 μm. Based on FT-IR analysis, it was observed that the synthesized M-PCM was uniformly encapsulated by MF resin with eutectic mixture in the core. The encapsulation process results in the improvement of the thermal stability of eutectic mixture, it increases from 202.5 to 212.3°C, and the encapsulation efficiency of the M-PCM is found to be 85.3%. The melting point and latent heat of fusion of M-PCM were found to be 34.5°C and 103.9 kJ/kg, respectively.