Preparation and characterization of a novel form-stable phase change material for thermal energy storage

Journal of Thermal Analysis and Calorimetry - A series of novel polymeric form-stable phase change materials (FSPCMs) composed of poly(trimethylolpropane trimethacrylate-stearyl methacrylate) (PTS)...     

Inter-spherulitic/inner-spherulitic localization of PBSU during crystallization of PVDF in PVDF/PBSU blend

In this work, the miscibility effect on the localization of poly(butylene succinate) (PBSU) during the crystallization of PVDF in their blend has been investigated. After annealed at 200 °C and 240 °C, homogeneous and phase-separated structures can be obtained respectively, which was followed by isothermal crystallization at 141 °C. In the case of 200°C, PBSU tends to enrich in inner-spherulitic regions because of the excellent miscibility of the blend and the higher growth rate of PVDF crystals. When the specimen was annealed at 240 °C, phase separation produces PVDF and PBSU domains. Upon cooling to 141 °C, one part of PBSU is miscible with , while the other part of it remains as phase-separated domains due to the high viscosity and slow relaxation of them. The former accounts for the distribution of PBSU in inner-spherulitic regions. In the latter, however, phase-separated structures depress the diffusion of PVDF during its crystallization, leading to the lower magnitude of growth rate of spherulites. Both of them contribute to the localization of PBSU in inter-spherulitic regions. The distribution of PBSU among PVDF spherulites has been validated by long periods, pore size, and mechanical performance of the porous PVDF membranes.     

Surface characteristics and hemocompatibility of PAN/PVDF blend membranes

Polyacrylonitrile (PAN) was blended with polyvinylidine fluoride (PVDF) at various ratios and made into membranes. The hemocompatibility of the resulting membranes was evaluated based on human plasma proteins adsorption, platelet adhesion, thrombus formation, and blood coagulation time. The PAN/PVDF blends exhibited partial miscibility according to the inward shifting of their two glass transition temperatures. The microstructures of blend membranes examined using atomic force microscopy (AFM) indicated that the roughness increased with the PVDF content, and the phase separation was too severe to form a membrane when the PVDF content was more than 30%. The water contact angle of PAN/PVDF blend membranes increased with the PVDF content. By blending with 20 wt% apolar PVDF the adsorption of blood proteins could be reduced, and hence the platelet adhesion and thrombus formation was also reduced. However, when the PVDF content was 30 wt%, severe thrombogenicity was observed due probably to the more porous structure of blend membrane. These results demonstrated that the hemocompatibility would be improved for PAN/PVDF blend membranes with appropriate hydrophilicity and roughness. Copyright © 2005 John Wiley & Sons, Ltd.     

HBPE-g-PVDF/PVDF blend nanofiltration membrane: preparation and characterization

Hyperbranched polyester-grafted poly(vinylidene fluoride) (HBPE-g-PVDF) was synthesized and used as additive in preparation of PVDF blend membranes. HBPE-g-PVDF copolymer was characterized with FTIR and TGA techniques. The prepared membranes were also characterized with SEM, AFM and contact angle measurement. The performance of prepared membranes as nanofiltration membrane was studied by pure water flux (PWF), salt rejection, dynamic and static fouling tests. The results showed that hydrophilicity of prepared membranes greatly increased after blending, and their pore size and pore size distribution and so PWF of blend membranes increased.     

Preparation of PVDF/PEO-PPO-PEO blend microporous membranes for lithium ion batteries via thermally induced phase separation process

Microporous poly(vinylidene fluoride)/polyethylene oxide-co-polypropylene oxide-co-polyethylene oxide (PVDF/PEO-PPO-PEO, or PVDF/F127) blend membranes were prepared via thermally induced phase separation (TIPS) process using sulfolane as the diluent. Then they were soaked in a liquid electrolyte to form polymer electrolytes. The effects of F127 weight fraction on the morphology, crystallinity and porosity of the blend membranes were studied. It was found that both electrolyte uptake of blend membranes and ionic conductivity of corresponding polymer electrolytes increased with the increase of F127 weight fraction. The maximum ionic conductivity was found to reach 2.94 ± 0.02 × 10⁻³ S/cm at 20 °C. Electrochemical stability window was stable up to 4.7 V (vs. Li⁺/Li). The testing results indicated that the PVDF/F127 blend membranes prepared via TIPS process can be used as the polymer microporous matrices of polymer electrolytes for lithium ion batteries.     

PEBA/PVDF blend pervaporation membranes: preparation and performance

In the present research, novel polyether block amide (PEBA)/polyvinyldene fluoride (PVDF) blend pervaporation (PV) membranes were prepared for the removal of isopropyl alcohol (IPA) from the aqueous solution. The membranes obtained at PEBA/PVDF ratios of 100/0, 95/5, and 90/10 were characterized using scanning electron microscopy, thermogravimetric analysis, water contact angle measurement, and tensile test. Moreover, the PV performance of the membranes was assessed via separation of IPA from the aqueous solution. The blended membranes exhibited higher hydrophobicity and separation factor as well as lower permeability in comparison with the pure PEBA membrane. The blended membrane that was prepared at PEBA/PVDF ratio of 95/5 was found as the optimum membrane providing PV separation index of 3171 that appeared to be the maximum value. Copyright © 2016 John Wiley & Sons, Ltd.     

Infrared spectroscopic studies on crystalline phase transition of PVDF and PVDF/hyperbranched polyester blend ultrathin films

In this study, as cast (AC, at 30 °C) and annealed (AN, at 130 °C, 3 h) samples of polyvinylidene fluoride (PVDF) and PVDF/hyperbranched polyester (HBP) (90/10) blend ultrathin films were subjected to heating-cooling (30 → 210 → 30 °C) cycle, and studied for their changes in crystalline phase transition behavior using in-situ Fourier transform infrared-transmission spectroscopy (FTIR-TS) and grazing incident reflection absorption spectroscopy (FTIR-GIRAS) techniques. Factor analysis was employed to extract the pure crystalline and amorphous spectra as well as the percentage content of ferroelectric crystallinity for both the samples. Irrespective of the thermal treatment (AC or AN) and spectral measurement (FTIR-TS or GIRAS) techniques, neat PVDF sample exhibited irreversible phase transitions during heating-cooling cycle associated with the transformation from ordered β-crystalline (1276 cm⁻¹) into disordered amorphous (1234 cm⁻¹) form. Interestingly, annealed PVDF/HBP blend sample measured using FTIR-GIRAS exhibited reversible crystalline phase transition behavior similar to a ‘dipole memory effect’ even after heating to 210 °C (>T_m) and then cooled to 30 °C. Compared to neat PVDF, higher ferroelectric crystallinity and reversible phase transition in PVDF/HBP blend may be attributed to (i) the existence of H-bonding between HBP (CO and OH groups) and PVDF (CH₂ and CF₂) and/or (ii) HBP acting as a nanoparticle in PVDF matrix.     

Synthesis and thermal energy storage properties of a calcium-based room temperature phase change material for energy storage

Journal of Thermal Analysis and Calorimetry - In order to obtain a low-cost, high latent heat and thermostable phase change material with a phase change temperature between 18 and...     

Mechanical properties of PA6/PA12 blend specimens prepared by selective laser sintering

The use of polymeric blends can increase the range of structures and properties of selective laser sintering (SLS) parts. This study investigates the processing of a binary polar system using polyamide 6 (PA6) and polyamide 12 (PA12) by SLS. The mixture composition and processing conditions, and their influence on the dynamic mechanical properties of the specimens manufactured were evaluated. The maximum tan δ values suggest that PA6 and PA12 have similar visco-dissipative behavior. The PA6/PA12 blends behavior varied according to the relaxation phenomena of the pure components, proportionally to the blend composition. The creep test showed that blends with a higher amount of PA6 had greater plastic deformation and less elastic recovery. In the fatigue test the 20/80 and 50/50 blends presented good fatigue resistance under the test conditions.     

Na-montmorillonite clay as thermal energy storage material

Sodium montmorillonite (Na-M) was investigated as an energy storage material. The study was conducted through the adsorption isotherms, infrared (IR) spectroscopic and differential thermal analysis (DTA). The clay systems were subjected to different preheating temperature, 125, 160, and 200°C, before subjecting the clay to the adsorption process carried out. The adsorptive capacities of Na-M ranged between 0.12 and 0.48 g H₂O/g of dry clay, depending on the preheating conditions of the clay. The stored energy of Na-M 781 cal/g when the clay preheated to 200°C, at which the clay has lost all the water molecules that could be evaporated, and become, therefore, able to adsorb the maximum amount of water vapor allowed. Na-M, when appropriately set, could be considered as an energy storage material.     

Efficient electrode material for electrochemical energy storage from organic waste

Journal of Solid State Electrochemistry - Heteroatom functionalities in activated carbons have a positive effect on their electrochemical properties. High surface area, reasonable heteroatom...     

Morphology of a PA / PTFE blend studied by Raman imaging

Raman spectroscopy has been employed for morphological studies on a polymer blend of polyamide-6,6, polytetrafluoroethylene and silicone oil used as a commercial friction bearing. New information about dimensions and distribution of polytetrafluoroethylene clusters in this composite material was revealed by Raman imaging. It was found that the applied processing conditions result in the formation of clusters, which are between 8 μm and 20 μm in diameter and distributed randomly over the whole material. The Raman results were confirmed by SEM images and SEM / EDX elemental mappings. The Raman imaging method has proved to be a good analytical tool for polymer analyses due to the speed of spectra acquisition and the easy sample preparation.     

The microstructural characterization of PA6/PA12 blend specimens fabricated by selective laser sintering

This study investigates the processing of blends of polyamide 6 (PA6) and polyamide 12 (PA12) by selective laser sintering (SLS) using a CO₂ laser. Powder properties of undiluted polymers, mixture composition, and processing parameters, as well as their influence on the microstructure of the specimens manufactured, were evaluated. Polyamides showed higher absorption of laser energy during the sintering of blend specimens, with subsequent thermal energy transfer to the melting of the polymeric phases. The structure of parts obtained by SLS is dependent on the process parameters and the characteristics of the powder material to be processed. The microstructures of PA6/PA12 blend specimens were heterogeneous, with co-continuous and disperse phases depending on the quantity of PA12. The porosity and crystallinity also changed as a function of the component proportions. The use of polymeric blends can increase the range of structures and properties of SLS parts.     

Capric acid/intercalated diatomite as form-stable composite phase change material for thermal energy storage

Journal of Thermal Analysis and Calorimetry - Leakage issue and low thermal conductivity largely restrict feasibility of fatty acid in real application of thermal energy storage (TES). In this...     

Activated carbon derived from marine Posidonia Oceanica for electric energy storage

In this paper, the synthesis and characterization of activated carbon from marine Posidonia Oceanica were studied. The activated carbon was prepared by a simple process namely pyrolysis under inert atmosphere. The activated carbon can be used as electrodes for supercapacitor devices. X-ray diffraction result revealed a polycrystalline graphitic structure. While scanning electron microscope investigation showed a layered structure with micropores. The EDS analysis showed that the activated carbon contains the carbon element in high atomic percentage. Electrochemical impedance spectroscopy revealed a capacitive behavior (electrostatic phenomena). The specific capacity per unit area of the electrochemical double layer of activated carbon electrode in sulfuric acid electrolyte was 3.16 F cm⁻². Cyclic voltammetry and galvanostatic chronopotentiometry demonstrated that the electrode has excellent electrochemical reversibility. It has been found that the surface capacitance was strongly related to the specific surface area and pore size.     

Fabrication of Hydrophilic and Sponge-like PVDF/Brush-like Copolymer Blend Membranes Using Triethylphosphate as Solvent简

Porous PVDF blend membranes with good hydrophilicity and a symmetric structure were prepared by the phase inversion method using amphiphilic brush-like copolymers, P（MMA-r-PEGMA）, as hydrophilic additive and triethylphosphate （TEP） as solvent. P（MMA-r-PEGMA） was synthesized by radical polymerization in TEP. Then the obtained amphiphilic copolymer solution was mixed with PVDF and TEP to prepare the dope solution. The effects of P（MMA-r-PEGMA） content and coagulation composition on membrane morphologies were investigated using scanning electron microscopy （SEM）. The results demonstrated that, even blended with amphiphilic copolymers, a symmetric structure can be formed. Hollow fiber membranes with a mainly symmetric structure were also fabricated. The dry hollow fiber membranes showed good hydrophilicity, high flux and good rejection performance because of their hydrophilic surface and pores wall.     

PVDF/PU blend membrane separator for lithium-ion batteries via non-solvent-induced phase separation (NIPS)

Membrane separator based on the polyvinylidene fluoride (PVDF) is prepared via the non-solvent-induced phase separation (NIPS) method with water and ethanol as non-solvent and a mixture of dimethylformamide (DMF) and acetone as solvent. The effect of various acetone/DMF ratios and non-solvent material on the physical and electrochemical properties of the separator is studied by FE-SEM, tensile strength, electrochemical AC-impedance spectroscopy (EIS), thermal stability, and linear sweep voltammetry (LSV). The charge-discharge studies are carried out by fabricating a lithium foil/polymer electrolyte membrane/LiFePO4 cell. The results show that with the change of solvent and non-solvent, the structure and morphology of the separator change and its physical and electrochemical properties. The results indicate that the membrane sample with non-solvent ethanol, acetone/DMF: 80/20 (wt/wt), and PVDF/PU: 95/5 (wt/wt) shows high porosity (66.3%) and high ionic conductivity (1.34 mS/cm) as well as excellent thermal stability.

     

Preparation and mechanical properties of thermal energy storage microcapsules

A series of heat energy storage microcapsules was prepared using melamine-formaldehyde resin as the shell material and the mechanical properties of the shell were investigated. A phase change material whose melting point was 24 °C was used as core and the quantity of heat involved in phase transition was 225.5 J/g. Average diameter of the microcapsules varied from 5 to 10 μm, and the globular surface was smooth and compact. The mechanical properties of the shell were evaluated by observing the surface morphological structure change after application of pressure by means of scanning electron microscopy. When the mass ratio of the core and shell material is 3:1, a yield point of about 1.1×10⁵ Pa was found and when the compression was increased beyond this point the microcapsules showed plastic behavior. This has been attributed to the cross-link density and to the high degree of reaction of the shell material. Different yield points subsequently reflected differences in the mechanical behavior. It was also found that the mechanical intensity of double-shell microcapsules was better than that of single shelled ones.     

Preparation and transport properties of PPy/PVDF composite membrane

In this work, composite cation‐exchange membrane was prepared by chemical polymerization of pyrrole on the surface of the poly(vinylidene fluoride) (PVDF) membrane using ferric ions. The changes in the surface morphologies of non‐modified and polymer‐modified PVDF membrane were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. The ion‐exchange capacity, water uptake, and fixed group concentration of the composite membrane were investigated. The polypyrrole/PVDF composite membrane was used for the removal of copper (II), chromium (III), iron (III), and aluminum (III) ions from aqueous solution with Donnan dialysis experiments. The flux values (J) and recovery factors (RF) of Cu(II), Cr(III), Fe(III), and Al(III) were obtained. Because of the smaller ion charge and hydration volume, the transport of the Cu(II) ion is higher than that of the other metals. Copyright © 2011 John Wiley & Sons, Ltd.     

Hyperbranched polyurethane as novel solid-solid phase change material for thermal energy storage

A series of novel hyperbranched polyurethane copolymer (HB-PUPCM) using hyperbranched polyester as chain extender was prepared via a two-step process. The phase transition behaviors and morphology of the HB-PUPCM films were investigated using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMA), thermo-gravimetric analysis (TGA), wide-angle X-ray diffraction (WAXD), polarizing optical microscopy (POM) and tapping-mode atomic force microscopy (AFM). HB-PUPCM was proven to a good polymeric solid-solid phase change heat storage material.