A temperature-regulating fiber made of PEG-based smart copolymer

A poly(ethylene glycol) (PEG)-based thermoplastic shape memory polyurethane was synthesized via bulk polymerization. The corresponding fiber, as a temperature-regulating fiber, was fabricated via melt spinning. The prepared 100-dtex fiber had a tenacity of 0.7 cN/dtex and breaking elongation of about 488%. The fiber's phase change behaviors, crystalline morphology, dynamic mechanical properties, and temperature-resistant performance were investigated using polarizing optical microscopy, differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetry. The PEG soft segment phase transfer between crystalline and amorphous states resulted in heat storage and release. The hydrogen-bonded hard segment phase, serving as ‘physical cross-links,’ restricted the free movement of soft segments, hence at temperatures above the PEG phase melting transition, the fiber still possessed certain mechanical strength. The differential scanning calorimetry results indicated that the fiber had large latent heat-storage capacity of about 100 J/g with a crystallizing temperature of 20.9 °C and a melting temperature of 44.7 °C. The dynamic mechanical analysis results showed that the fiber has a plateau elastic modulus in the region above the PEG phase melting transition and below 160 °C. The thermogravimetry results suggested that the fiber had a much broader applicable temperature range compared to pure PEG. The thermo-mechanical cyclic tensile testing results showed that the fiber had good shape memory effect with the shape fixity ratio more than 85.8% and the recovery ratio above 95.4%.     

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.     

Polyurethane/graphite nano-platelet composites for thermal energy storage

In this work new polyurethane-based phase change materials containing segments of poly(ethylene glycol) with average molar mass of 8000 g/mol with and without chain extender and modified with graphite nano-platelets have been fabricated and characterized. Structure, morphology and phase behaviour of these solid-solid phase change materials were investigated, as well as the thermal stability and conductivity. The heat of phase transition was in the range of 118.0–164.5 J/g for polyurethane without chain extender and 128.0–148.5 J/g for polyurethane with chain extender. The highest heat of phase transition and crystallinity were found for system modified with 0.3% of graphite nano-platelets in polyurethane without chain extender. Modulated differential scanning calorimetry results showed some changes in the phase transition behaviour and the crystallinity of the polyurethane matrix due to graphite nano-platelets confinement effect. Enhancements in the thermal stability in polyurethane modified with graphite nano-platelets, attributed to the barrier effect, were found based on thermogravimetric analysis data. The thermal conductivity increased with an increase of graphite nano-platelets content for both polyurethane systems, with and without chain extender, which is important for modern thermal energy storage applications.     

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.     

Development of thermo-regulating polypropylene fibre containing microencapsulated phase change materials

Phase change materials are used for thermal management solution in textiles because of the automatic acclimatising properties of textiles. Most of the phase change materials used in textiles is usually found in the range of 28–32 °C of their melting point. This paper reports a type of smart monofilament fibre development incorporated with microencapsulated phase change material through melt spinning process. Up to 12% microcapsules are successfully incorporated into the polypropylene monofilament showing 9.2 J/g of latent heat. Some of the mechanical properties of the developed fibre are also studied together with the surface morphology of monofilament. A statistical model is developed for latent heat, tenacity and modulus of monofilament fibre and is validated by experimental values. The fibre properties predicted by the developed models are agreed very well to the experiments results.     

The structural ordering of thin silicon films at the amorphous to nano-crystalline phase transition by GISAXS and Raman spectroscopy

Thin silicon films were deposited by the plasma-enhanced chemical vapour deposition method using microwave (MW) and standard radio frequency (RF) gas discharge in silane gas diluted by hydrogen in the range that produces a mixture of amorphous and crystalline phases. The samples were analysed by Raman spectroscopy and grazing incidence small-angle X-ray scattering (GISAXS), while the threshold for the transition between the amorphous and crystalline phase was checked by the change in electrical conductivity. The crystalline fraction, estimated by Raman spectroscopy, varied between 0% and 70% while the individual crystal sizes were between 3 and 9 nm. However, the size distribution was broad suggesting also the existence of smaller and larger crystals.The “particles” observed by GISAXS, most probably voids, were in the range between 2 and 12 nm. The voids in samples deposited by MW plasma were larger when closer to the surface. Their shape indicated the formation of a columnar structure perpendicular to the surface, more pronounced at higher temperature. The samples deposited by RF plasma and low power had spherically symmetric “particles” with uniform size across the depth of the samples. An increase of the RF power resulted in the formation of a columnar structure parallel to the surface. The observed differences are discussed in relation to the difference in growing kinetics of the used deposition methods.     

Synthesis and thermal energy storage characteristics of polystyrene-graft-palmitic acid copolymers as solid-solid phase change materials

A series of polystyrene graft palmitic acid (PA) copolymers as novel polymeric solid-solid phase change materials (PCMs) were synthesized. In solid-solid PCMs, polystyrene is the skeleton and PA is a functional side chain that stores and releases heat during its phase transition process. The heat storage of copolymers is due to phase transition between crystalline and amorphous states of the soft segment PA in copolymer and the hard segment polystyrene restricted the free movement of molecular chains of the soft segments even above the phase transition temperature. The copolymers always remain in the solid state during the phase transition processing and therefore they are described as form-stable PCM. Fourier transform infrared spectroscopy (FT-IR) and polarization optical microscopy (POM) analyses were performed to investigate the chemical structures and crystalline morphology. Thermal energy storage properties, thermal reliability and thermal stability of the PCMs were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) methods. Thermal conductivities of the PCMs were also measured using thermal property analyzer. The analysis results indicated that the PA chains were successfully grafted onto the polystyrene backbone and the copolymers showed typical solid-solid phase transition properties. Moreover, thermal cycling test showed that the copolymers have good thermal reliability and chemical stability although they were subjected to 5000 heating/cooling cycling. The synthesized polystyrene-graft-PA copolymers as novel solid-solid PCMs have considerable potential for such as underfloor heating, thermo-regulated fibers and heating and cooling of agricultural greenhouses. Especially, the polystyrene-graft-PA copolymer including 75% PA is the most attractive PCM due to its highest latent heat storage capacity in the synthesized copolymer PCMs.     

Electrospun phase change fibers based on polyethylene glycol/cellulose acetate blends

Ultrafine phase change fibers based on polyethylene glycol (PEG)/cellulose acetate (CA) blends in which PEG acts as a model phase change material (PCM) and CA acts as a supporting material, were successfully prepared via electrospinning. The effect of PEG content on the morphology, crystalline properties, phase change behaviors and tensile properties of the composite fibers was studied systematically by field-emission scanning electron microscopy (FE-SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and a tensile tester, respectively. The SEM observation indicates that maximum PEG content in the fibers could reach up to 70 wt%, and the morphology and average diameter of the composite fibers vary with PEG content. Thermal analysis results show that the latent heats of the phase change fibers increase with the increasing of PEG content in the fibers, and the PEG/CA fibers with high enthalpies have a good capability to regulate their interior temperature as the ambient temperature alters. Therefore, the developed phase change fibers have enormous applicable potentials in thermal energy storage and temperature regulation.     

An assessment of mixed type PCM-gypsum and shape-stabilized PCM plates in a building for passive solar heating

Thermal performance of two phase change material (PCM) composites, mixed type PCM-gypsum and shape-stabilized PCM plates, has been numerically evaluated in a passive solar building in Beijing with an enthalpy model. Effects of the melting temperature and phase transition zone of the PCM are analyzed and a comparison between the two types of PCM composites is performed. The results show that: (1) for the present conditions, the optimal melting temperature is about 21 °C; (2) PCM composites with a narrow phase transition zone provide better thermal performance; (3) both mixed type PCM-gypsum and shape-stabilized PCM plates effectively shave the indoor temperature swing by 46% and 56%, respectively; (4) the shape-stabilized phase change material (SSPCM) plates respond more rapidly than the mixed type PCM-gypsum and prove to be thermally more effective in terms of utilizing the latent heat.     

Thermal and mechanical characterization of injection moulded high density polyethylene/paraffin wax blends as phase change materials

Thermal and mechanical properties of blends based on high density polyethylene and paraffin wax were investigated. The blends were prepared from 5 to 50 vol. % of paraffin wax employing a twin-screw extruder. Thermal behaviour of samples was determined by differential scanning calorimetry, thermogravimetric and dynamic mechanical analyses. A displacement of melting temperature of polyethylene was detected as a consequence of the plasticization effect of wax. These results revealed that melting temperatures and latent heats of samples are suitable for their application as phase change materials. Blends were processed by injection moulding which is an advantageous method to obtain pieces of this kind of materials. The evolution of loss tangent versus temperature of injected samples showed the lack of miscibility between the components of the blend. Tensile tests were carried out to characterize the mechanical strength of blends. Elongation at break decreased as paraffin wax content increased, and Young's modulus decreased with wax content but in the case of blends with a 30 vol. % of wax and more, brittle rupture occurred and no yield point was observed.     

Study of close contact melting of ice from a sliding heated flat plate

A study is conducted to examine the effect of the relative motion between a PCM block and a heated flat plate in the process of close contact melting of a high Prandtl number phase change material. An analytical model is proposed and experimental results are reported. Results indicate that the relative velocity between the PCM block and the plate starts to play an important role in the close contact melting process when Re > 10⁴. Three distinct melting regimes are identified: for Re < 3 × 10⁵, close contact melting is the dominant mode of heat transfer in the melt layer. The relative motion may reduce the melting time by up to 66% compare to the melting time observed from a heated surface at rest. For Re > 5 × 10⁵, the thickness of the liquid melt layer is so small (δ¹ < 8 × 10⁻⁴) that the melting process is hindered and abrasion is observed. Finally, for 3 × 10⁵ < Re < 5 × 10⁵, a transition regime bridges the contact melting regime to the abrasion regime.     

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.     

Semicrystalline proton-conductive membranes with sulfonated amorphous phases

Proton-conductive membranes, exhibiting high chemical and thermomechanical resistance, have been obtained by s-PS films with the β crystalline phase and a sulfonated amorphous phase. These membranes can be obtained by a solid-state procedure on δ form films, which allows an easy and uniform sulfonation of the phenyl rings of the amorphous phase and preserves the crystalline phase, followed by suitable thermal treatments leading to the δ → β crystal-to-crystal transition. The high degree of sulfonation of the amorphous phase makes this phase highly hydrophilic and proton conductive while the presence of the high melting and thermodynamically stable β phase assures high chemical and thermomechanical stability.     

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 three-dimensional numerical model for a convection-diffusion phase change process during laser melting of ceramic materials

Using a fixed-grid source-based method, a three-dimensional numerical model for a convection-diffusion phase change process during laser melting of ceramic materials has been studied. The model was applied to a realistic binary phase diagram containing a eutectic composition, including both an isothermal phase change occurring at a distinct temperature and a phase change taking place over a temperature range (the “mushy” region phase change). The effects of latent heat of fusion and fluid flow in the melt pool on the temperature, velocity fields and shape of the melt pool were analysed and compared. Results indicated that the effects of latent heat of fusion were more significant than those of fluid flow for two simulation cases, considered in the model. The best prediction accuracy for the profiles of the melt/solid interfaces was achieved from the developed model by considering both the latent heat of fusion and fluid flow in the melt pool.     

Stearic acid/polymethylmethacrylate composite as form-stable phase change materials for latent heat thermal energy storage

The aim of this research is to prepare of a novel form-stable composite phase change material (PCM) for the latent heat thermal energy storage (LHTES) in buildings, passive solar space heating or functional fluid by entrapping of SA into PMMA cell through ultraviolet curing dispersion polymerization. The composite PCM was characterized using scanning electron microscope (SEM) and Fourier transformation infrared (FT-IR) analysis technique. The results show that the form-stable microencapsulated PCM with core/shell structure was formed and the maximum encapsulated proportion of SA in the composite was 51.8 wt.% without melted PCM seepage from the composite. In the shape stabilized microencapsulated PCM, the polymer acts as supporting material to form the microcapsule cell preventing the leakage of PCM from the composite and the SA acts as a PCM encapsulated in the cell of PMMA resin. The oxygen atom of carbonyl group of skeleton is interacted with the hydrogen atom of hydroxyl group of SA. Thermal properties, thermal reliability and heat storage/release performance of the composite PCM were determined by differential scanning calorimetry (DSC), FT-IR and thermal cycling test analysis. The melting and freezing temperatures and the latent heats of the composite PCM were measured as 60.4 °C, 50.6 °C and 92.1 J/g, 95.9 J/g, respectively. The results of DSC, FT-IR and thermal cycling test are all show that the thermal reliability of the composite PCM has an imperceptible change. This conclusion indicates that the composite has a good thermal and chemical stability.     

Ternary polymer electrolyte with enhanced ionic conductivity and thermo-mechanical properties for lithium-ion batteries

Cellulose is the main building block of plant's cell wall that provides structural stability. This idea inspired us to use modified cellulose (Networked cellulose) to provide thermal and mechanical stability to a polymer electrolyte system. The system composed of polyethylene glycol (PEG) (or tetraethylene glycol dimethyl ether (TEGDME)), polyethylene oxide (PEO), networked cellulose (NC) and LiClO₄ as a salt. The PEG (or TEGDME) was used as a high mobility phase for lithium ions, PEO acted as a binder and NC provided structural support for the quasi-solid polymer electrolytes. A high conductivity of the order of 10⁻⁴ S cm⁻¹ was obtained at room temperature. Dynamic mechanical analysis of PEG (or TEGDME):PEO:NC (70:20:10 wt%) showed an improvement of storage modulus as compared to the pristine PEO in the 60–120 °C temperature range. Differential scanning calorimetry (DSC)/Thermal gravimetry analysis (TGA) revealed that the developed ternary polymer electrolyte is thermally stable in the lithium-ion battery operational temperature range.     

Preparation and properties of caprylic‐nonanoic acid mixture/expanded graphite composite as phase change material for thermal energy storage

To satisfy the application demands for latent heat storage in the temperature range from 5°C to 15°C, an original composite phase change material (PCM), CA‐NA/EG (caprylic‐nonanoic acid/expanded graphite), was prepared and characterized. For CA‐NA/EG, the mass ratio of CA and NA was 8:2, and the mass percentage of the CA‐NA in CA‐NA/EG composite PCM was determined as 90% by leakage test. The melting and freezing points of the CA‐NA/EG were 6.84°C and 9.34°C, and corresponding latent heats were 108.75 kJ/kg and 107.67 kJ/kg. In addition, its thermal conductivity, thermal stability and reliability were investigated by thermal conductivity apparatus (TCA), thermal gravimetric analyzer (TGA), and accelerated thermal cycle test for 100 melt/freeze cycles, respectively. The results showed that the CA‐NA/EG had a good thermal stability and an excellent thermal reliability. Moreover, the thermal conductivity of CA‐NA/EG had an improvement of 25% than that of the CA‐NA. On the other hand, the accelerated thermal cycle test also indicated that the CA‐NA/EG had no supercooling during all melt/freeze cycles. Therefore, the prepared composite PCM, CA‐NA/EG, can be applied for low‐temperature thermal energy storage owing to its proper melting temperature, acceptable latent heat and thermal conductivity, excellent thermal stability and reliability.     

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).     

Thermal conductivity and latent heat thermal energy storage characteristics of paraffin/expanded graphite composite as phase change material

This study aimed determination of proper amount of paraffin (n-docosane) absorbed into expanded graphite (EG) to obtain form-stable composite as phase change material (PCM), examination of the influence of EG addition on the thermal conductivity using transient hot-wire method and investigation of latent heat thermal energy storage (LHTES) characteristics of paraffin such as melting time, melting temperature and latent heat capacity using differential scanning calorimetry (DSC) technique. The paraffin/EG composites with the mass fraction of 2%, 4%, 7%, and 10% EG were prepared by absorbing liquid paraffin into the EG. The composite PCM with mass fraction of 10% EG was considered as form-stable allowing no leakage of melted paraffin during the solid–liquid phase change due to capillary and surface tension forces of EG. Thermal conductivity of the pure paraffin and the composite PCMs including 2, 4, 7 and 10 wt% EG were measured as 0.22, 0.40, 0.52, 0.68 and 0.82 W/m K, respectively. Melting time test showed that the increasing thermal conductivity of paraffin noticeably decreased its melting time. Furthermore, DSC analysis indicated that changes in the melting temperatures of the composite PCMs were not considerable, and their latent heat capacities were approximately equivalent to the values calculated based on the mass ratios of the paraffin in the composites. It was concluded that the composite PCM with the mass fraction of 10% EG was the most promising one for LHTES applications due to its form-stable property, direct usability without a need of extra storage container, high thermal conductivity, good melting temperature and satisfying latent heat storage capacity.