Melting Enthalpy Research Articles

Graphitization modified three-dimensional fully interconnected high porous TiO2 ceramics: A promising carrier material for thermal storage and thermal conductivity enhancement

In this work, porous TiO2 ceramics (PTC) and the graphitization modification of PTC (GPTC) with three-dimensional fully interconnected and uniform pore structure as a carrier for PCM was prepared by the Pickering emulsion method. Compared with PTC, the thermal conductivity and porosity of GPTCs were further improved and the specific surface area of GPTCs was increased by 5.7 times. The results of DSC curves showed that the melting and solidification enthalpy of PEG-GPTC20 were 143.8 J/g and 139.0 J/g, respectively, which only decrease by 0.68 % and 0.35 % after 100 phase change cycles. The experimental thermal conductivity of PEG-GPTC20 composites improved by 3.2 times. The results of non-isothermal crystallization kinetics revealed that the nucleation activation energy: PEG>PEG-PTC > PEG-GPTC, which indicated that GPTCs porous carrier encapsulation was beneficial to the nucleation process of PEG. The PEG-GPTCs composite phase change material designed in this paper has significant advantages in maintaining high thermal conductivity and heat storage performance at the same time while comparing other composites. Therefore, GPTCs are a promising carrier material for thermal storage and thermal conductivity enhancement.

Biocomposites Based on Electrospun Fibers of Poly(3-hydroxybutyrate) and Nanoplatelets of Graphene Oxide: Thermal Characteristics and Segmental Dynamics at Hydrothermal and Ozonation Impact.

In order to create new biodegradable nanocomposites for biomedicine, packaging, and environmentally effective adsorbents, ultra-thin composite fibers consisting of poly(3-hydroxybutyrate) (PHB) and graphene oxide (GO) were obtained by electrospinning. Comprehensive studies of ultrathin fibers combining thermal characteristics, dynamic electron paramagnetic resonance (ESR) probe measurements, and scanning electron microscopy (SEM) were carried out. It is shown that at the addition of 0.05, 0.1, 0.3, and 1% OG, the morphology and geometry of the fibers and their thermal and dynamic characteristics depend on the composite content. The features of the crystalline and amorphous structure of the PHB fibers were investigated by the ESR and DSC methods. For all compositions of PHB/GO, a nonlinear dependence of the correlation time of molecular mobility TEMPO probe (τ) and enthalpy of biopolyether melting (ΔH) is observed. The influence of external factors on the structural-dynamic properties of the composite fiber, such as hydrothermal exposure of samples in aqueous medium at 70 °C and ozonolysis, leads to extreme dependencies of τ and ΔH, which reflect two processes affecting the structure in opposite ways. The plasticizing effect of water leads to thermal destruction of the orientation of the pass-through chains in the amorphous regions of PHB and a subsequent decrease in the crystalline phase, and the aggregation of GO nanoplates into associates, reducing the number of GO-macromolecule contacts, thus increasing segmental mobility, as confirmed by decreasing τ values. The obtained PHB/GO fibrillar composites should find application in the future for the creation of new therapeutic and packaging systems with improved biocompatibility and high-barrier properties.

Effects of explosion puffing on the native structural organization and oil adsorption properties of starch

The effects of explosion puffing (EP) on the native structural organization (i.e., thermal properties, crystalline structure, short-range order, granule morphology and powder properties) and oil adsorption properties of puffed starch (PS) were investigated. The results showed that EP treatment could decrease the melting enthalpy of starch double helices and increase the V-type crystallinity. The highest V-type crystallinity (24.7 %) was obtained when the puffing pressure was 0.4 MPa and the starch:ethanol:water ratio was 1:2:1 (w/w). By controlling the puffing conditions, EP treatment can alter the morphology, and increase the particle size, flowability and specific surface area of PS. The high amorphous proportion and porous sheet structure of PS resulted in the highest oil adsorption capacity when the starch:ethanol:water ratio was 1:1:1 (w/w). Pearson correlation analysis showed that oil adsorption capacity was significantly and positively correlated with the 1022/995 cm−1 value and V-type crystallinity, but negatively correlated with bulk density and angle of repose. Furthermore, oil retention capacity was strongly dependent on V-type crystallinity. These findings demonstrated that EP is an innovative technology with the potential to enhance the V-type crystallinity and adsorption performance of starch.

Smart composite nanofibers based on PLA/PEG with the addition of clove oil as thermal regulators

Smart nanofibers based on PLA and PEG with the addition of clove oil (Eugenia caryophyllus) (EO) were obtained using the electrospinning technique. The nanofibers were characterized by SEM, FT-IR, TGA and DSC. For the PLA/PEG/EO composite (mass ratio 2/1/0.25), the temperature of the maximum decomposition rate was approximately 370°C. This composite exhibited good latent heat energy storage (melting enthalpy 77.5 J/g at 34.7°C). Smart nanofibers can be used as thermal regulators in medicine, electronics, and food and textile industries.

A robust, compatible, and effective core-shell structured phase change materials for controlling the temperature rise caused by cement hydration

Temperature cracks caused by the internal and external temperature gradient pose a threat to the durability of concrete structures. Phase change materials (PCM) offer a feasible solution by absorbing the released heat of cement hydration, yet of which the applications are limited by potential leakage and weak combination with cement matrix. Herein, this study employed silica as a protective shell to inhibit core PCM (n-octadecane, n-OD) from leaking, and enhance the compatibility with Portland cement. The surveyed core-to-shell mass ratios of PCM were chosen as 1:1, 1.5:1, and 2:1. The encapsulation of n-OD was successfully demonstrated by characterization results of Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The microcapsules labeled M3 possessed the highest melting enthalpy of 183.4 J/g due to the highest core-to-shell ratio of 2:1 and exhibited good physico-chemical stability that pertained integrity after the mechanical mixing into cement paste. The effect of complexing M3 into cement paste was further investigated. The increasing dosage of M3 evidently remediated temperature rise that with highest dosage of 30.0 vol%, the maximum central temperature of cement paste decreased by 16.9 °C compared to the reference group. Moreover, it was unravelled that M3 components promote cement hydration and pore filling, thus with such high dosage of 30.0 vol%, the cement sample strength mildly decreased by 22.0%, which is dramatically lower compared with previous studies, i.e., at least ∼58.4% decrease in strength with similar dosage. Hence, the as-prepared M3 microcapsules can serve as promising functional additives for controlling the internal temperature rise of cement-based materials to mitigate the formation of temperature cracks.

An innovative graphene-based phase change composite constructed by syneresis with high thermal conductivity for efficient solar-thermal conversion and storage

Graphene-based phase change composites hold significant potential for solar energy utilization, but their poor thermal conductivity hinders their practical applications. In this work, an air-dried graphene skeleton (AGS) with excellent thermal conductivity enhancement efficiency was constructed by the ice templating method and syneresis, and the air-dried graphene phase change composite (AGP) was subsequently obtained through vacuum-impregnating n-Docosane (C22) into AGS. The syneresis effectively reduced the phonon scattering between graphene sheets within AGS and increased the density of AGS to 0.1701 g/cm³. Therefore, with a graphene skeleton loading of 23.82 wt.%, AGP exhibited excellent thermal conductivity of 9.867 W/(m K), outstanding electrical conductivity of 68.08 S/cm, and remarkable shape stability. Additionally, AGP demonstrated a melting enthalpy of 188.5 J/g and an outstanding solar-thermal conversion efficiency of 93.98%, showing enormous potential for the utilization of solar energy.

Performance analysis of hybrid expanded graphite-NiFe2O4 nanoparticles-enhanced eutectic PCM for thermal energy storage

This current experimental study aims to resolve the demerits of pure PCM by introducing the hybrid nanomaterial-induced composite PCM (HNIPCM) with practical feasibility on solar water heater performance using an indigenously developed setup. To settle out these performance characteristics, expanded graphite (EG) and nickel ferrite nanoparticles (NiFe2O4) with different weight concentrations (ɸ = 1–5 %) were used for the first time as a thermophysical property-enhancing filler material inside a eutectic organic-organic PCM (polyethylene glycol 6000/paraffin wax) by two-step method. A detailed study on the physical and chemical stability, surface morphology, and thermal feasibility of the HNIPCM was conducted to provide the optimized characteristics for the target applications. The energy storage capacity, melting and crystallization temperature, thermal stability, thermal reliability, thermal behaviour, and thermal conductivity were also examined by DSC, TGA, thermal cycling, and charging-discharging, respectively. The HNIPCM with 3 wt% filler concentration revealed comparatively well-balanced thermophysical properties among the prepared samples. The results also showed that the melting point, crystallization point, melting enthalpy, and crystallization enthalpy were changed to 54.55 °C, 48.83 °C, 128.52 J/g, and 129.02 J/g, respectively, for HNIPCM with 3 wt% of filler material in comparison with eutectic PCM of 59.14 °C, 41.23 °C, 154.37 J/g, and 155.21 J/g. An increase in thermal conductivity up to 253.72 %, enhancement in the charging and discharging rate, and good stability up to 500 working cycles with a 12.19 °C decrease in the supercooling were also observed with no physical and chemical alteration. The real-time performance of the prepared HNIPCM was also investigated using a novel indigenously developed solar water heater at different inclination angles (40°, 45°, and 50°), flow rates (1.2 LPM, 2.2 LPM, and 5.2 LPM), and charging periods (90mins, 120mins, and 180mins). Comparatively higher performance at a 45° inclination angle, 2.2LPM water low rate with 68.99 % efficiency (day) and 50.45 % (night) was observed. The enhanced thermophysical properties of the HNIPCM made it suitable for a viable candidate for solar thermal energy, air conditioners, TES, and electronic cooling units.

Thermal performance and corrosion resistance analysis of inorganic eutectic phase change material with one dimensional carbon nanomaterial

The inherent thermal characteristics, supercooling phenomenon, and corrosion issues associated with salt hydrate phase change materials (PCMs) limit their practical applications. In this research work, we report a newly formulated eutectic salt hydrate PCM using a) sodium sulphate decahydrate (SSD) & b) sodium phosphate dibasic dodecahydrate (SPDD); with a focus on customizing its properties to enhance its suitability for low temperature thermal regulation (achieving a melting point of 27.8 °C and a high heat storage capacity of 215 J/g). Additionally, we have successfully reduced the degree of supercooling and introduced corrosion resistant properties to this PCM. To enhance both the thermal energy transfer rate and optical absorbance of the eutectic PCM, we have incorporated one-dimensional (1D) multiwall carbon nanotube (MWCNT) at various weight fractions, extending up to 0.9 %, utilizing a two-step method. The dispersion and chemical stability of SSD/SPDD + MWCNT nanocomposite are verified through the morphological visual and spectral peaks obtained in Fourier transfer infrared spectroscopy. Additionally, studies evaluating the optical and thermal property reveal a substantial 500 % increase in absorbance, a notable 77.9 % reduction in transmissibility, a thermal conductivity increase from 0.464 W/m⋅K to 0.742 W/m⋅K (reflecting a 59.9 % increment), and the retention of a consistent melting enthalpy of 218.6 J/g. This stability is attributed to the intermolecular interaction with MWCNT. Similary, the degree of supercooling (ΔTs) for the SSD/SPDD EPCM containing MWCNT decreased to 2.2 °C from 16.5 °C, marking an 86 % reduction compared to the pure eutectic salt solution. Furthermore, this composite demonstrated enhanced thermal and chemical stability throughout 200 thermal cycles. Auxiliary ANSYS simulation, with transient boundary condition, are provided to analyze the heat transfer interactions between the thermic fluid and the newly developed PCM when integrated into a thermal regulation system. Subsequently, a corrosion analysis of the developed eutectic PCM and the nanocomposite eutectic PCM exhibits a corrosion rate of 0.018 mpy, well below the permissible level (<5mpy). The insights gained from the development of this nanocomposite PCM offer valuable guidance for the design and creation of tailored eutectic PCM for low-temperature thermal regulation systems, resulting in significant energy savings.

Upcycling of PET plastics into diethyl terephthalate for applications as phase change materials in energy harvesting

Polyethylene terephthalate (PET) is an indispensable material in our everyday lives and upcycling of its waste has become a major area of research. Herein, the upcycling of PET waste into phase change materials (PCM) for thermal energy storage applications is presented. Hydrolysed and esterified PET waste affords diethyl terephthalate (DET), which when blended with UV-curing acrylic matrix, trimethylolpropane ethoxy triacrylate (TMPEOTA), forms a composite PCM. Chemical characterisation such as IR and NMR were conducted to confirm the presence of functional groups in the composites. The thermal properties of the composites, such as melting point and thermal degradation were obtained and DET exhibited a relatively high melting enthalpy of 94.1 J/g at about 39.9 °C. The form stability and thermal performance was studied for composites made of different DET loading weight percentages from 50 to 90 %. A loading rate of 80 % (D80) was found to provide best latent heat capacity while maintaining its form stability and minimizing leakage. Finally, to assess the performance of D80 as a thermal storage material, a thermal response test was performed and D80 was able to prevent significant rise in temperature for about 60s during its phase transition as opposed to TMPEOTA control.

Microencapsulation study of bioderived phase change material beeswax with ethyl cellulose shell for thermal energy storage applications

ABSTRACT The commercial shape-stabilized phase change material (PCM) products are obtained from synthetic raw materials. These materials are produced from carbon-intensive petroleum-refining processes. The carbon footprint can be minimized by using biobased products. Beeswax is a naturally available PCM with high phase transition enthalpy comparable to synthetic PCMs. In the previous literature studies, beeswax was shape-stabilized with synthetic materials. In the present study, beeswax was shape-stabilized with biopolymer ethyl cellulose by emulsion solvent evaporation method. The study aims to determine optimum microencapsulation process parameter levels for synthesizing microcapsules with high thermal energy storage (TES) capacity. The optimized process parameters for formulating microcapsules were 60:40 core/shell ratio, 2% PVA concentration, ethyl acetate solvent, and 40°C evaporation temperature. The microcapsules prepared with optimized process parameters were characterized using differential scanning calorimeter (DSC), T-history analysis, Fourier transform infrared (FTIR) spectroscope, and scanning electron microscope (SEM). FTIR and SEM analysis confirmed ethyl cellulose shell formation over the beeswax core. The optimized MPCM formulation possesses 115.8 J/g melting enthalpy with peak phase transition temperature of 58.2°C and thermal conductivity of 0.219 W/mK. The porous structure of the shell reduced melting enthalpy of optimized MPCM formulation to 84.6 J/g after 50 thermal cycles. The synthesized microcapsules comprise sustainable materials and have high TES capacity. The fabricated microcapsules can be used as TES additive in composite and coating formulations in food packaging.

Preparation, characterization, and life cycle assessment of banana rachis-recycled high-density polyethylene composites

Agro-industrial wastes are sustainable resources that have advantages as a reinforcement for polymeric matrices. This study examined the use of banana rachis fiber (BRF) in reinforcing the recycled high-density polyethylene (rHDPE) matrix. For this purpose, polymer composites with 5–20 wt% of BRF were prepared by the extrusion process using a twin-screw extruder and followed a hot press method. The structure of rHDPE/BRF composites and their characteristic peaks of degradation were successfully identified by the Fourier-transformed infrared spectroscopy and thermogravimetric analysis techniques, respectively, revealing a good dispersion of BRF in rHDPE. Differential scanning calorimetry results of the composites demonstrated that melt enthalpy decreases as the amount of BRF increases. XRD diffractograms revealed a crystallinity reduction of rHDPE due to the increase of fiber within the polymer matrix, which is reflected in the characteristic peaks' intensity decrease of HDPE. Variation in thermal and chemical properties with the addition of BRF in rHDPE was successfully evaluated in this study. Life cycle assessment for 1 kg composite production has also been evaluated. The banana rachis-rHDPE composite materials reduce the overall environmental impacts when the filler concentration increases.

Insight into curdlan alleviating quality deterioration of frozen dough during storage: Fermentation properties, water state and gluten structure.

Curdlan was effective in alleviating quality deterioration of frozen dough during storage. This research explored the mechanisms from perspectives of fermentation properties, water state and gluten structure of frozen dough during storage, and the performance of corresponding steamed bread. Results showed that curdlan addition improved the gas-releasing capability and gas-holding capability of frozen dough, meanwhile enhanced the specific volume and textural properties of corresponding steamed bread. The melting enthalpy and NMR results demonstrated that curdlan restricted the conversation of bound water into freezable water, and inhibited the moisture migration in frozen dough. Frozen dough with 0.5% curdlan had significantly lower gluten macropolymers (GMP) depolymerization degree and free sulfhydryl (SH) content than the control, indicating that curdlan alleviated the depolymerization of GMP. Microstructure results proved that the deterioration of the structure was retarded by curdlan. This study contributes to understanding the theories for curdlan alleviating the deterioration of frozen dough during storage.

Design of a stearic acid/boron nitride/expanded graphite multifiller synergistic composite phase change material for thermal energy storage

• Stearic acid was encapsulated by various fillers. • A shape-stabilized composite phase change material was prepared. • Thermal and cycling stability of the prepared composite are excellent. • Thermal conductivity of the prepared composite is 6.349 W•m −1 •K −1 . In order to solve the problems of low thermal conductivity and easy liquid leakage of a stearic acid (SA), the composite phase change material(PCM) was prepared by adding boron nitride (BN) and expanded graphite (EG) to melted SA, and its thermal conductivity, crystal structure, chemical stability, thermal stability, cycle stability, leakage characteristics, heat storage/release characteristics, and temperature response characteristics were characterized. The results showed that the addition of BN and EG significantly improved the thermal conductivity of the material, and they efficiently adsorbed melted SA. The maximum load of SA was 76 wt. % and there was almost no liquid leakage. Moreover, the melting enthalpy and temperature were 154.20 J • g − 1 and 67.85°C, respectively. Compared with pure SA, the SA/BN/EG composite showed a lower melting temperature and a higher freezing temperature. In addition, when the mass fraction of BN and EG was 12 wt. %, the thermal conductivity of the composite was 6.349 W • m −1 • K −1 , which was 18.619 times that of SA. More importantly, the composite showed good stability for 50 cycles of heating and cooling, and the SA / BN / EG-12 hardly decomposes below 200°C, which implies that the working performance of the composite PCM is relatively stable within the temperature range of 100°C. Therefore, the composite can exhibit excellent thermal stability in the field of building heating.

Preparation and properties of vermiculite modified by triphenylbutylphosphonium bromide and PBAT composite film

AbstractIn this study, quaternary phosphonium salt (P4) was prepared, vermiculite (VMT) was modified by P4, and P4@VMT/poly (butylene adipate‐co‐terephthalate) (PBAT) composite film was prepared by the solution method. The structure of the synthesized P4 was determined by nuclear magnetic resonance and infrared. The structure and performance of P4 modified vermiculite were explored and analyzed by particle size, XRD, infrared and micro‐morphology. The structure, thermal properties, crystallization properties, rheological properties, cross‐section morphology, tensile properties and antibacterial properties of pure PBAT film and P4@VMT/PBAT composite film were tested and compared. The results show that the crystallization temperature and melting temperature of P4@VMT/PBAT composite film are higher than those of pure PBAT film. With the increase in P4@VMT content, the thermal stability of the composite film becomes worse, and the crystallization enthalpy, melting enthalpy and crystallinity also decrease, while the storage modulus, loss modulus and complex viscosity of P4@VMT/PBAT composite film increase significantly. In addition, compared with pure PBAT film, the tensile strength of P4@VMT/PBAT‐20% composites decreased by 12.0% and the elongation at break decreased by 95.7%.Highlights Successful synthesis of phosphonium quaternary P4 and modification of vermiculite. The properties of P4@VMT/PBAT composite films with different contents were studied.

Designing Poly(3,4-ethylenedioxythiophene) Polystyrene Sulfonate/Graphene Oxide/Graphene Nanosheet/Polyethylene Glycol Phase-Change Composites with Superior Thermal Management for Photo-thermoelectric Generators.

Recently, growing interest in self-powered devices has led to the invention of new energy conversion devices. Photo-thermoelectric generators (PTEGs) have rapidly developed for their ability to harvest both light and thermal energy, but these devices are overly dependent on the continuity of energy input and cannot sustain output in an emergency situation. In the current study, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/graphene oxide (GO)/graphene nanosheets (GNPs)/polyethylene glycol (PEG) phase-change composites (PCCs) were prepared with freeze-drying and vacuum-filling processes to acquire materials suitable for imparting energy storage characteristics to PTEGs. The melting and crystallization enthalpies of the PCCs fabricated based on the PEDOT:PSS/GO/GNP aerogels can reach 211.5 and 207.6 J g-1, respectively, which increase by nearly 5% compared with pure PEG, and the growth rate of thermal conductivity of the composites is as high as 262.7% (1.12 W m-1 K-1). Meanwhile, the excellent photothermal properties and high-temperature shape stability that pure PEG does not possess can also be imparted to PCCs by the aerogels. The PTEG assembled with PCCs and thermoelectric components can achieve a continuous output of over 1500 s after 300 s of light irradiation. After integrating the output of the device during the lamp on/off period, it is found that the total output of the device during the light-off period (8.4 V and 9.6 mW) can far exceed its total output during the light-on period (2.7 V and 4.4 mW). This work provides guidance for modulating the performance of PCCs and giving PTEGs the ability to operate under emergency or extremely harsh conditions and the prepared PTEGs are highly promising for practical use.

Effectiveness of the different eutectic phase-change materials in cooling asphalt pavement

Choosing a phase-change material (PCM) adapted to the specific phase-change temperature (Tm) required for each temperature condition is of utmost importance in cooling pavements. Eutectic phase-change materials (EPCMs) realize the customization of the desired Tm and reduce the difficulty of matching PCMs. This work aims to investigate the effectiveness of a group of binary/ternary EPCMs with Tm ranging from 30 to 60 ℃ and melting enthalpies of around 200 J/g as thermal regulation components for different asphalt. To achieve this goal, the thermal and rheological properties of phase-change asphalt binders (PCAB) were evaluated by differential scanning calorimeter, thermogravimetric, Fourier transform infrared, and multiple stress creep and recovery tests. The results showed that PCAB with latent heat improved the specific heat capacity, which brought a maximum temperature lag of 134.5 min and a maximum temperature difference of 11 ℃. Similarly, the PCAB remained chemical stability, and its thermal stability complied with the construction temperature specifications. However, the recrystallization of EPCMs was impeded by the molten asphalt binder matrix, resulting in a significant reduction in both the Tm and enthalpy. Therefore, these reductions should be taken into consideration when choosing an EPCM. Additionally, as liquid EPCM softens the binder, the absence of elasticity in solid EPCMs renders the binder stiff, thus reducing its resistance to deformation. These impacts were particularly noticeable in Styrene-Butadiene-Styrene modified asphalt due to the polymer network being dissolved by liquefication-EPCMs. To sum up, EPCMs with a higher Tm (40–60 ℃) may decrease their negative impact on deformation resistance, such as palmitic acid-myristic acid-methyl stearate mixtures.

The electrothermal color-changing fabric based on high-sensitivity thermochromic microcapsules

High sensitivity including low color hydrolysis and a narrow temperature range of color-changing is important to thermochromic microcapsules. However, it is a challenge for conventional ternary thermochromic systems to realize the fast change of colors. A new class of high-sensitivity microcapsules and electrothermal color-changing fabrics were designed and synthesized by introducing CNTs into thermochromic systems via microencapsulation and coating technology. The high sensitivity was attributed to the enhanced filler CNTs and binary core phase change materials (1-Tetradecanol/1-Octadecanol). Moreover, the dosage amount of CNTs, core-to-shell ratios, and particle size on the temperature sensitivity of microcapsules were investigated. From the results, the optimized microcapsules with regular spherical shape exhibited a narrow color-change temperature range of 30–35 ℃ and low color hydrolysis of 11 ℃. As the core wall ratio increased from 1:1–3:1, the color change temperature range of microcapsules became narrower and the color hydrolysis was lower. According to the phase change behaviors, thermochromic microcapsules with a melting enthalpy of 70.64 J/g performed a good thermal regulation capacity. Furthermore, the reversible thermochromic performance of obtained microcapsules remained stable through 500 thermal cycles, demonstrating excellent thermal cycling stability. Combining the obtained microcapsules and electrothermal fabrics, highly sensitive electro-thermochromic (ETC) fabrics by voltage were prepared. Under the supplied voltage of 6 V, the ETC fabrics exhibited outstanding cyclic electrothermal color-changing performance. This unique design concept for high-sensitivity ETC fabrics has great potential applications in personal thermal management, the cooling of electronic devices, visible displays, and so on.

Possibilities of Influencing the Crystallization Process of Bisphenol A- and Bisphenol F-Based Epoxy Resins Used for Hydrophobic Coatings on Concrete.

Crystallization of bisphenol A (DGEBA)- and bisphenol F (DGEBF)-based epoxy resins is a natural property of these oligomers. However, manufacturers of coatings and other systems based on these epoxy resins are making efforts to slow down the crystallization process as much as possible, thereby extending the shelf life and improving the competitiveness of their products. This paper focuses on the kinetics of the crystallization process of epoxy resins and the effect of the presence of a certain degree of crystallinity on selected parameters of epoxy-based materials. Furthermore, an analysis of the impact of a certain degree of crystallinity of the epoxy base on the resulting coating parameters was carried out. The highest value of crystallinity (17%) was achieved in the sample containing the highest proportion of DGEBF in the crystallization phase "c", and the enthalpy of melting (Ht) of the crystalline DGEBF sample was 6.3 J/g. Mechanical parameters as well as chemical and thermal resistance of hydrophobic epoxy systems were investigated. The best abrasion resistance (1.5 cm3/50 cm2) was achieved with the blend containing only amorphous DGEBA. The adhesion of the epoxy samples on concrete was greater than 6.5 MPa. The chemical resistance tests performed showed that, in general, the chemical resistance of epoxy systems decreases with increasing crystallinity content. The tighter arrangement of molecules in the crystalline regions of the epoxy matrix results in an increase in density, strength and hardness. This study presents a comprehensive examination of the crystallization of DGEBA and DGEBF, which is, as yet virtually unavailable. It also contributes to knowledge by outlining the possibility of speeding up or slowing down the crystallization process of epoxy resins, including the principle of selecting nucleating agents.

Thermochromic microencapsulated phase change materials for cold energy storage application in vaccine refrigerator

The development of pharmaceutical cold chain logistics calls for thermochromic microencapsulated phase change materials (TC-MPCMs) to fit the demand of temperature indication and low temperature (2–8 °C) cold storage. In this study, TC-MPCMs for low temperature were constructed by encapsulating crystal violet lactone (CVL), bisphenol A (BPA) and n-tetradecane & n-dodecanol (aliphatic compound) binary system into melamine-formaldehyde (MF) resin. The effects of emulsifier type, n-dodecanol content, and core/shell ratio on the performance of TC-MPCMs were investigated. Results indicate that TC-MPCMs with SMA: gelatin ratio of 2:1 exhibit the best morphology and uniform dispersion, with particle size distribution between 4.5 μm and 19.5 μm. TC-MPCMs with 25 wt% 12OH and core/shell of 1.85 demonstrate excellent property in terms of the encapsulation efficiency, melting enthalpy and color difference, which are 67.80 %, 169.90 J/g and 23.39, respectively. Synthesized TC-MPCMs present outstanding thermal durability during 100 thermal cycles and have an appreciable thermal stability at temperature not exceeding 96 °C. The vaccine refrigerator was designed which can maintain a low temperature (2–8 °C) for 12.8 min.

Modelling the thermodynamic properties of the mixture of water and polyethylene glycol (PEG) with the SAFT-[formula omitted] Mie group-contribution approach

The SAFT-γ Mie group-contribution (GC) equation of state (EoS) is employed to describe the thermodynamic properties of aqueous mixtures of polyethylene glycol (PEG), a polyether of great industrial and scientific interest. This prototypical system is chosen due to the intrinsic complexity of hydrogen-bonding polymers, and represents a critical test of the theory. Water is modelled as a single Mie segment with four association sites and PEG as a linear heteronuclear chain of three types of segments: the associating hydroxymethyl end group (CH2OH); the associating oxygen (cO); and the modified methylene group (CH2OE), which incorporates the effects that the proximity of an electronegative atom has on the electronic environment of the methylene group. The SAFT-γ Mie model parameters characterizing the newly-defined group interactions are estimated to reproduce the liquid–liquid equilibrium (LLE) closed-loop miscibility gaps observed in the orthobaric phase diagram of PEG + water mixtures. The resulting model allows one to predict miscibility gaps in a temperature range between 350 K and 600 K, capturing both the UCST and the LCST within a 2% error with a close description of the overall phase behaviour. The predictive capability of the model is assessed by comparing the calculations with the experimental density of pure PEG, the enthalpy of mixing, and vapour–liquid equilibrium properties of PEG + water mixtures, with a good overall agreement. By coupling the present SAFT model with a recent thermodynamic model describing solubility in semi-crystalline polymers, the solubility of water in PEG below its melting point is semi-quantitatively captured both in the low- and high-humidity regimes. In particular, deliquescence – the melting of semi-crystalline PEG at high relative humidity – is predicted by simply accounting for the melting enthalpy of PEG crystals.