Cemil Alkan

Encapsulated Fatty Acids in an Acrylic Resin as Shape-stabilized Phase Change Materials for Latent Heat Thermal Energy Storage

Abstract This article aims to prepare novel shape-stabilized phase change materials (PCMs) by encapsulating fatty acids (stearic acid [SA], palmitic acid [PA], and myristic acid [MA]) as a PCM in an acrylic resin (Eudragit E) as supporting material and to determine latent heat thermal energy storage (LHTES) properties. The maximum percentage of all fatty acids in the shape-stabilized PCMs was found to be 70 wt% in which no fatty acid seepage was observed as the blends were heated over the melting points of the fatty acids. The optic microscope (OM) investigation demonstrated that fatty acid domains were coated by Eudragit E. Fourier transform infrared (FT-IR) results revealed that the interactions between Eudragit E and fatty acids were only adequate for adhesion of Eudragit E on fatty acid domains. Single phase was observed for the blends by OM, and interactions between the components were investigated by FT-IR spectroscopy. The melting and freezing temperatures and latent heats of the shape-stabilized PCMs were measured by the differential scanning calorimetry (DSC) method. Based on the results, it was concluded that Eudragit E/MA, Eudragit E/PA, and Eudragit E/SA blends (30/70 wt%) have good utility potential for LHTES purposes in terms of their satisfying thermal properties and advantages of easy preparation in desired dimensions, direct usefulness function in LHTES systems, and cost effectiveness.

Steady-state thermal comfort properties of fabrics incorporated with microencapsulated phase change materials

This study focused on assessing the thermal comfort properties of the fabrics incorporating microencapsulated phase change materials (microPCMs) under steady-state condition. Air permeability and water vapor permeability of the fabrics were also investigated. Poly(methyl methacrylate)/n-hexadecane microcapsules were applied to the cotton and cotton/polyester fabrics using pad-cure methods. Thermal comfort properties of the fabrics were measured using Alambeta. The results indicated that the thickness of the fabrics incorporated with microcapsules increased depending on the amount of microcapsules added on the fabric. Thermal conductivity of the fabrics treated with polyurethane (PU) resin decreased while addition of microPCMs had almost no effect on the thermal conductivity. However, thermal resistance of the fabric increased as the fabric thickness increased or the thermal conductivity decreased. Air permeability and water vapor permeability of the fabrics treated with microPCMs were found to be lower than those of pristine fabrics while water vapor permeability of the fabrics treated with PU was found higher than pristine fabrics.

Synthesis of poly(methyl methacrylate-co-acrylic acid)/n-eicosane microcapsules for thermal comfort in textiles

Homogeneous distribution by adsorption is one of the key issues for application of microencapsulated materials to textiles. This study focused on production and characterization of poly(methyl methacrylate-co-acrylic acid)/n-eicosane microencapsulated phase change materials (MEPCMs) as textile thermal comfort additives with a functional outer surface. For this reason, methyl methacrylate was copolymerized with acrylic acid at three different ratios. The chemical structure, thermal energy storage properties, and thermal stability of microcapsules were investigated by FT-IR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis techniques, respectively. Microcapsules were found to have a thermal energy storage capacity of 50.9–90.9 J/g in the 31.74–36.30℃ temperature interval and they release between −88.4 and −40.2 J/g in the 33.88–35.59℃ temperature interval. Using a scanning electron microscope and a particle size instrument, the spherical morphology and particle size distribution of were determined for the microcapsules produced. The average particle sizes were 22.53 µm, 21.87 µm, and 11.73 µm for microcapsules with increasing amount of acrylic acid content. The microcapsules were thermally stable up to at least 120℃.

Preparation and textile application of poly(methyl methacrylate-co-methacrylic acid)/n-octadecane and n-eicosane microcapsules

In this study, a series of microencapsulated phase change materials with poly(methyl methacrylate-co-methacrylic acid) P(MMA-co-MAA) shell and n-octadecane or n-eicosane core were synthesized by emulsion polymerization method. The aim was to produce microencapsulated n-alkanes having functional groups on their outer surface, so that functional groups would help increasing physical interactions between microcapsules and fiber surface. Therefore, methyl methacrylate (MMA), ethylene glycoldimethacrylate (EGDM), and methacrylic acid (MAA) were copolymerized in oil phase of n-alkane. FT-IR results proved the successful synthesis of P(MMA-co-MAA) shell of microencapsulated n-alkanes. The DSC results indicated that the microencapsulated n-alkanes have considerable latent heat storage capacity in a range of 58–145 J/g. The average melting and freezing temperatures of the microencapsulated n-alkanes were measured as 27 and 26 °C for n-octadecane and 36 and 35 °C for n-eicosane, respectively. The microcapsules were of spherical and compact shape with particle sizes between 15 and 32 μm. The microcapsules on the cotton fabric applied by pad-dry-cure method were found highly durable and they showed sufficient stability upon several washings and rub fastness. Thermo-regulating properties of the fabrics were declared as a result of thermal history measurements.

Thermal energy storage characteristics of micro-nanoencapsulated heneicosane and octacosane with poly(methylmethacrylate) shell

Abstract In this study, PMMA/heneicosane (C21) and PMMA/octacosane (C28) micro-nano capsules were fabricated via emulsion polymerisation method. The chemical structures of the fabricated capsules were verified with the FT-IR spectroscopy analysis. The results of POM, SEM and PSD analysis indicated that most of the capsules were consisted of micro/nano-sized spheres with compact surface. The DSC measurements showed that the capsules had melting temperature in the range of about 39–60 °C and latent heat energy storage capacity in the range of about 138–152 J/g. The results of TGA showed that sublimit temperature values regarding the first degradation steps of both capsules were quite over the phase change or working temperatures of encapsulated paraffins. The thermal cycling test exhibited that the capsules had good thermal reliability and chemical stability. Additionally, the prepared capsules had reasonably high thermal conductivity.

Polyethyl Methacrylate (PEMA)/Fatty Acids Blends as Novel Phase Change Materials for Thermal Energy Storage

This study deals with the preparation and characterization of polyethyl methacrylate/fatty acid blends as a novel form-stable phase change material for latent heat thermal energy storage applications. In the blends, fatty acids act as a phase change material when polyethyl methacrylate is operated as a supporting material. The fatty acids could be retained by 50 wt% into polyethyl methacrylate without melted phase change material seepage from the blends. Therefore, these blends are called form stable composite phase change materials and they have utility advantage without encapsulation in passive latent heat thermal energy storage applications. The prepared fatty acid/polyethyl methacrylate blends (50/50 w/w%) as form-stable phase change material was characterized using optic microscopy and Fourier transform infrared spectroscopy methods and the results showed that the polyethyl methacrylate was physically and chemically compatible with the fatty acids. Thermal properties and thermal stabilities of the form-stable phase change materials were measured using differential scanning calorimetry. Differential scanning calorimetry results indicated that the melting temperatures and latent heats of the prepared phase change materials are in the range of 30.67–61.09°C and 86.93–107.75 J/g, respectively. The thermal cycling test, including 5,000 cycling processes, was conducted to determine the thermal reliability of the synthesized form-stable phase change materials, and it is found that phase change materials were thermally and chemically stable after thermal cycling. On the basis of all the results, it was concluded that form stable polyethyl methacrylate/fatty acids composite phase change materials had important potential for practical latent heat thermal energy storage applications, such as under floor space heating of buildings and passive solar space heating of buildings by using wallboard, plasterboard, or floors impregnated with a form stable phase change material.

Poly(ethylene-co-1-tetradecylacrylate) and poly(ethylene-co-1-octadecylacrylate) copolymers as novel solid–solid phase change materials for thermal energy storage

Poly(ethylene-co-1-tetradecylacrylate) (EcoTDA) and poly(ethylene-co-1-octadecylacrylate) (EcoODA) copolymers were synthesized using poly(ethylene-co-acrylic acid) (EcoA) copolymers with 5 and 20% acrylic acid contents, respectively, and fatty alcohols (1-tetradecanol and 1-octadecanol) as novel polymeric solid–solid phase change materials. Chemical structure, thermal property, and crystalline morphology of the copolymers were characterized by using Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), and polarized optical microscopy, respectively. Poly(ethylene-co-1-tetradecylacrylate) and poly(ethylene-co-1-octadecylacrylate) copolymers have two reversible phase transitions in DSC thermograms, that is, they have two morphologically different phases to transform from solid to amorphous connected each other. The change in surface morphology is only by color tone after the low-temperature phase transition as it was discrete to single color amorphous after the high-temperature phase transition according to microscopy. This property makes them resistant to flow above the first transition where thermal energy is stored for utility. Microindentation test proved that the hardness and reduced modulus values are considerably low after the solid–solid phase transition, but it is still measurable as a solid material.

Microencapsulation of Three-Component Thermochromic System for Reversible Color Change and Thermal Energy Storage

In this study, poly(methyl methacrylate)/thermochromic system (PMMA/TS) and poly(methyl methacrylate-comethacrylic acid)/thermochromic system (P(MMA-co-MA)/TS) microcapsules were prepared by using emulsion polymerization method. The thermochromic system was consisting of crystal violet lactone (CVL) as a leuco dye, bisphenol-A (BPA) as a color developer, and 1-tetradecanol (TD) as a solvent. Microcapsules with different ratio of core/shell were synthesized to examine the effect of core/shell ratio on the properties of microcapsules. Phase transition temperatures and enthalpies, morphology, and particle size distributions of the microcapsules were analyzed using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and particle size analyzer instruments, respectively. FT-IR spectroscopy was used to prove the presence of the thermochromic system in the microcapsules. UV-Vis absorption bands of the thermochromic system (TS) and microencapsulated thermochromic system (MTS) at both below and above the melting temperature of the solvent were obtained by using a UV-Vis spectrophotometer. The visible color change depending on temperature was monitored for each microcapsule individually by using a digital camera. Spherical morphology and unimodal particle size distribution of the microcapsules were determined by means of SEM photographs and particle size distribution curve analysis. The mean particle sizes of the produced microcapsules varied in a range of 16.0-35.2 μm. The digital camera photographs and the UV-Vis absorbance curves proved that color changed between dark blue and light blue depending upon the temperature change. Meanwhile, the produced microcapsules were proven for an excellent heat storage capacity for thermal energy storage owing to phase changing of the tetradecanol solvent used in the thermochromic system. The melting enthalpy of the microcapsules ranged from 145.5 J/g to 193.4 J/g.

Synthesis and characterization of 1,4-diazophenylenebridged Cu-phthalocyanine polymer

Abstract A novel type of phthalocyanine polymer, 1,4-diazophenylene-bridged Cuphthalocyanine, was prepared from the diazonium salt of diaminobenzene and Cu(II) 1,8,15,22-tetraaminophthalocyanine. The polymer is partially soluble in tetrahydrofuran, dichloromethane, and dimethylformamide. Characterization of the polymer was performed by IR and UV-visible spectroscopy, X-ray diffraction, ash analysis, viscometry, differential scanning calorimetry and thermogravimetric analysis. The molecular weight of the soluble part of the polymer was determined by ebullioscopy. Electrical conductivity of the polymer and its doped samples were determined by the 4-probe technique. It was found that the electrical conductivity increased up to 10-4 S/cm after doping. The redox behaviour of the polymer was investigated utilizing cyclic voltammetry.