Crystallization Enthalpy Research Articles

Green and facile production of phase change composites supporting by carbonized rattan for thermal management

Thermal energy management and storage are pivotal to promote economic expansion and industrial production, and the advancement of eco-friendly and convenient phase change material (PCM) production is imperative to confront the pressing issues surrounding energy sustainability. The exploration of rattan with naturally hierarchical pore structure encompassing slits, pits, vessels and sieve tubes, as a support material for the encapsulation of PCM has been investigated. Rattan stems (RS) with abundant macropores are eminently suited for the absorption of PCM. Moreover, carbonized rattan (CR), derived through the pyrolysis of RS, possesses a high proportion of micropores and mesopores, effectively preventing PCM leakage. The CR/paraffin phase change composite material (CPPM) attained a melting enthalpy of 113.50J/g, a crystallization enthalpy of 112.50J/g, and an encapsulation efficiency of 60.88%. The leakage test revealed that CPPM maintained its structural integrity and demonstrated leak-proof performance. Photothermal conversion and energy storage experiments indicated that CPPM efficiently mitigated temperature fluctuations and exhibited substantial energy storage potential. Therefore, this research establishes CR as an optimal PCM multi-functional support, rendering it apt for practical applications in thermal energy management systems.

Naphthalene-Containing Epoxy Resin: Phase Structure, Rheology, and Thermophysical Properties

Naphthalene is a fungicide that can also be a phase-change agent owing to its high crystallization enthalpy at about 80 °C. The relatively rapid evaporation of naphthalene as a fungicide and its shape instability after melting are problems solved in this work by its placement into a cured epoxy matrix. The work’s research materials included diglycidyl ether of bisphenol A as an epoxy resin, 4,4′-diaminodiphenyl sulfone as its hardener, and naphthalene as a phase-change agent or a fungicide. Their miscibility was investigated by laser interferometry, the rheological properties of their blends before and during the curing by rotational rheometry, the thermophysical features of the curing process and the resulting phase-change materials by differential scanning calorimetry, and the blends’ morphologies by transmission optical and scanning electron microscopies. Naphthalene and epoxy resin were miscible when heated above 80 °C. This fact allowed obtaining highly concentrated mixtures containing up to 60% naphthalene by high-temperature homogeneous curing with 4,4′-diaminodiphenyl sulfone. The initial solubility of naphthalene was only 19% in uncured epoxy resin but increased strongly upon heating, reducing the viscosity of the reaction mixture, delaying its gelation, and slowing cross-linking. At 20–40% mass fraction of naphthalene, it almost entirely retained its dissolved state after cross-linking as a metastable solution, causing plasticization of the cured epoxy polymer and lowering its glass transition temperature. At 60% naphthalene, about half dissolved within the cured polymer, while the other half formed coarse particles capable of crystallization and thermal energy storage. In summary, the resulting phase-change material stored 42.6 J/g of thermal energy within 62–90 °C and had a glass transition temperature of 46.4 °C at a maximum naphthalene mass fraction of 60% within the epoxy matrix.

Fabrication, characterization, and fat substitution application in chocolate spreads of methyl cellulose and xanthan gum foam-templated oleogels

Food-grade oleogels were prepared by lyophilizing the foam-template of methyl cellulose (MC) and xanthan gum (XG). The cryogels prepared using MC exhibited low density, high porosity and firmness, as well as high oil absorption capacity (OAC) and oil binding capacity (OBC). Furthermore, the addition of XG improved properties of cryogels. As the concentrations of MC and XG were incremented, notable enhancements in the cryogels' density and firmness were observed, accompanied by a corresponding decrease in porosity. Upon attaining MC concentration of 1.2 % and XG concentration of 0.3 %, the OBC of the cryogels surpassed 90 %. SEM images revealed that the cryogels possessed a dense and highly uniform porous network structure. Furthermore, oleogels formulated using the higher viscosity variant of MC (designated as MC3) exhibited greater firmness and apparent viscosity, resulting in the formation of a robust network structure that demonstrated excellent thermal stability. The incorporation of oleogels into chocolate spreads significantly enhanced textural and rheological characteristics, while simultaneously decreasing their enthalpy of crystallization. Notably, the partial substitution of these oleogels in the spreads yielded a crystalline morphology that was indistinguishable from those prepared solely with saturated fats, indicating a successful integration and preservation of desirable structural attributes.

Preparation and melt-spun applications of PA6-based Poly(Amide-Ether) copolymers phase change fibers with passive temperature management

Phase change fiber, as an intelligent fiber material used in passive thermal management, can balance the temperature of the microenvironment near human skin. However, the traditional blending method makes phase change material prone to leakage during the processing and applications. Herein, this work introduces the phase change material PTMEG into the polyamide 6 (PA6) chain through melt polymerization to prepare a series of PA6-based poly(amide-ether) copolymers. Copolymers exhibit an obvious microphase separation structure, with the PA6 segments and the PTMEG segments can form independent crystalline and amorphous regions. PTMEG in copolymers through polymerization method exhibits better thermal stability compared with the blended way, which effectively solves the leakage problem of phase change materials. The copolymers can be directly melt-spun (1500 m/min) to prepare PA6-based phase change fibers. The fiber can maintain excellent mechanical properties (breaking strength of 2.12 cN/dtex). Meanwhile, the crystallization enthalpy and melting enthalpy of the PTMEG in the fiber are 10.59 J/g and 12.44 J/g, respectively. The thermal management time of the fiber in the hot environment is 349 s, and the maximum temperature difference is lower 5.6 ℃ from the PA6 fiber. In addition, the exothermic duration in a cold environment is 536 s, and the maximum temperature difference is higher 1.1 °C from the PA6 fiber. Meanwhile, the thermal enthalpy of the fiber remained stable (fluctuation within 2 %) after 20th thermal cycles, and the loss rate is less than 2 % after washing at 25 ℃, 50 ℃ and 90 ℃. The fiber exhibits good thermal stability, water washability and cyclic stability. Preparation of high enthalpy polymers directly by copolymerization will provide new ideas for phase change fibers for apparel.

Crystallization modeling of two semi-crystalline polyamides during material extrusion additive manufacturing

In this work, a heat transfer model is developed for thermally-driven material extrusion additive manufacturing of semicrystalline polymers that considers the heat generated during crystallization by coupling crystallization kinetics with heat transfer. The materials used in this work are Technomelt PA 6910, a semicrystalline hot melt adhesive with sub-ambient glass transition temperature (Tg) and slow crystallization, and PA 6/66, a traditional semicrystalline polyamide with a higher Tg and fast crystallization. The coupled model shows that the released heat during crystallization depends on material selection, with Technomelt PA 6910 and PA 6/66’s temperatures increased by less than 1 °C and up to 6.3 °C, respectively, due to enthalpy of crystallization. Increasing the layer time decreases the layer temperature as well as the initial crystallinity. However, its effect on final crystallinity in Technomelt PA 6910 is negligible due to continued crystallization of the material after printing. Experimental validation shows good agreement for Technomelt PA 6910, but consistently underpredicts PA 6/66 crystallinity. Increasing modeled environmental temperature leads to better agreement with experimental results for PA 6/66, suggesting that higher temperatures may have been experienced. Shear-induced crystallization may also be contributing to crystallinity in this material. The results from this model highlight the importance of and interrelationships between material and processing parameter selection and can aid in achieving quality prints from semicrystalline thermoplastics.

Thermal analysis, flexural mechanical properties and FTIR analysis of an HDPE matrix composite reinforced with alumina and silicon carbide

This research developed an HDPE composite reinforced with Al2O3 and 1% SiC in the proportions of pure HDPE, 40 %, 50 % and 60 % of ceramic load. The mechanical flexural test showed results of sMAX 19.09 ± 2.89 MPa and E 1806 ± 400 MPa for the A60 group and concluded that with ceramic loadings above 60 % contribute to crystallization in the regions around the particles. TGA analysis showed initial degradation at 409 °C and final degradation between 499 and 504 °C, with a residue in pure HDPE of 0.46%. The DSC curves showed an endothermic peak at 132 °C and crystallization around 119 °C, and the crystallinity of the HDPE was 95.29 %, and the analyses showed a decrease in the enthalpy of fusion and crystallization with increasing ceramic loading due to the decrease in the polymer fraction in the composite. DMA analysis showed that temperatures above the Tg of the crystalline phases were the mechanism that contributed most to the storage modulus. FTIR analysis showed several interactions in different bands between the 3 compounds in the composite.

1-Tetradecanol phase change material microcapsules coating on cotton fabric for enhanced thermoregulation

Rising climate change and extreme weather conditions underpin thermoregulation limitations of conventional textiles. This study investigates enhancing the thermal properties of cotton fabric by incorporating synthesized 1-tetradecanol (TD) phase change material (PCM) microcapsules. Characterization of the TD microcapsules was performed using dynamic light scattering (DLS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The microcapsules (average size of 0.49 μm) displayed a melting enthalpy (∆Hm) of 105 J·g−1 and a crystallization enthalpy (∆Hc) of 51 J·g−1. The microcapsules were mixed with the acrylic binder in three different ratios (75:25, 50:50, and 25:75). Hydrothermal, knife-over-roll, and pad-dry-cure methods were employed for coating microcapsules to cotton fabric. Microcapsule coating on cotton fabric using hydrothermal coating with a 75:25 microcapsule binder ratio achieved the highest add-on (55 %) and good durability after 25 home washes. The thermal insulation R-value of the coated fabric was enhanced (0.0029 m2 K·W−1) at 40 °C. The real-time test showed a temperature difference of 2.8 °C and thermal imaging displayed lower emissivity for TD-coated fabric. The TD microcapsule coating offers a promising method for developing climate-responsive textiles, enhancing thermal comfort, and reducing energy consumption in heating and cooling systems.

Water retention and heat storage characteristics of phase change hydrogel in cooling pavement

Phase change hydrogel (PCH) combines the heat storage characteristics of phase change material with the water retention capacity of hydrogel, showing great potential in cooling pavement applications. This study aims to investigate the water retention and heat storage properties of PCH in cooling pavement, providing new insights for mitigating the urban heat island effect. Based on the principle of osmotic pressure, polyethylene glycol (PEG) solution was actively absorbed by superabsorbent polymers (SAP) to form stable PCH. By infusing the asphalt mixture skeleton with PCH-containing phase change grouting material (PCGM), a temperature-regulating phase change grouting pavement (PCGP) can be obtained. Morphological characterization showed that PCH was uniformly distributed in PCGM and effectively locked PEG during high temperature and water absorption/release processes without leakage. PCH imparted excellent water retention properties to PCGM, with a saturation water absorption rate of 44.1 %, which is 6.2 times higher than the control group, and a water retention rate of 34.31 % after heating at 60 °C for 12 hours. Furthermore, PCGM exhibited considerable heat storage performance, with a melting enthalpy of 15.74 J/g and a crystallization enthalpy of 12.07 J/g. Based on these, PCGP demonstrated outstanding temperature-regulating ability, reducing surface temperatures by 9.3 °C and 11.6 °C under dry and saturated conditions, respectively, compared to control pavement. In conclusion, this study provides a theoretical basis for the development of novel cooling pavement materials and shows great potential for its wide application in urban infrastructure construction.

Toward 3D printability prediction for thermoplastic polymer nanocomposites: Insights from extrusion printing of PLA-based systems

The development of new thermoplastic-based nanocomposites for, as well as using, 3D printing requires extensive experimental testing. One typically goes through many failed, or otherwise sub-optimal, iterations before finding acceptable solutions (e.g. compositions, 3D printing parameters). It is desirable to reduce the number of such iterations as well as exclude failed experiments that often require laborious disassembly and cleaning of the 3D printer. This issue could be addressed if we were able to understand, and ultimately predict ahead of experiments if a given material can be 3D printed successfully. Herein, we report on our investigations into forecasting the printing and resultant properties of polymer nanocomposites while encompassing both material properties and printing parameters, enabling the model to generalize across various thermoplastics and additives. To do so, nanocomposites of two different commercially available bio-based PLAs with varying concentrations of nanoclay (NC) and graphene nanoplatelets (GNP) were prepared using a twin-screw extruder. The thermal and rheological properties of the nanocomposites were analyzed. These materials were printed at varying temperature and flow using a pellet printer. The quality of the printing was evaluated by measuring weight fluctuation, internal diameter of cylindrical specimen, and surface uniformity. The interactions between material properties and printing parameters are complex but captured effectively by a machine learning model, specifically we demonstrate such a predictive model to forecast printability and, printing quality utilizing a Random Forest algorithm. Printability was predicted by developing a classification model with constraints based on the weight fluctuation (ΔW) of the printed sample w.r.t. the optimal print; defining “not printable” for −1.0≤ΔW<−0.8 and “printable” for ΔW≥−0.8. The classification model for predicting printability, performed well with an accuracy of 92.8% and identified flow index and complex viscosity, contributing 52% to the model’s importance. Another model to predict ΔW of the only on successful prints also showed strong performance, emphasizing the importance of viscoelastic properties, thermal stability, and printing temperature. For diameter change (ΔDi), the Random Forest model identified flow consistency index, complex viscosity, and thermal stability as influential parameters, with crystallization enthalpy gaining increased importance, reflecting its role in crystallization and shrinkage. In contrast, the surface roughness average (RA) model had lower performance, yet revealed remarkable insights regarding the feature importance with crystallization enthalpy and complex viscosity being most significant.

Enhancing the dyeability of polyurethane fibers by introducing protonated tertiary amine groups

Traditional polyurethane fibers (CPUF) are widely used in the preparation of blend clothing in order to improve the elasticity and comfort of fabrics. However, there has been a problem of low acid dye adsorption for CPUF, resulting in light hue of dyed CPUF. In this work, a poly (HMDI-BHOPA) was prepared with dicyclohexylmethane 4,4′-diisocyanate (HMDI) and 1,4-(2-hydroxyethyl) piperazine (BHOPA), and then added into the CPUF spinning solution for the preparation of modified polyurethane fibers (BPUFs) through dry-spinning technology. Tertiary amine groups were introduced after the addition of poly (HMDI-BHOPA), which could be protonated at acidic conditions to form binding sites for acid dyes, further enhancing the adsorption capacity of the fibers. Nuclear magnetic resonance spectroscopy (1H and 13C NMR) was used to confirm the structure of poly (HMDI-BHOPA). The results of differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA) demonstrated that the addition of poly (HMDI-BHOPA) had little effect on the glass transition temperature and thermal stability of BPUFs. The addition of poly (HMDI-BHOPA) affected the ordered arrangement of hard segments and reduced crystallization enthalpy of hard and soft segments in polyurethane. Hence, the elastic recovery of BPUFs showed little change, and the elongation at break and break strength decreased compared to CPUF. Zeta potential testing results showed that BPUFs was protonated under acidic conditions. Dyeing results proved the enhancement of dyeability of BPUFs. The dyeing kinetics and thermodynamics of acid dyes on BPUFs were studied to investigate the dyeing mechanism. From the dyeing kinetics results, both CPUF and BPUFs fitted Elovich model. From dyeing thermodynamics results, Langmuir model showed a better applicability for BPUFs at a low pH and temperature condition, while Freundlich model fitted better for CPUF.

Silk Fabrics Modified with Photothermal Phase Change Microcapsules for Personal Thermal Management.

With the development of technology, personal heat management has become a focus of attention. Phase change fabrics, as intelligent materials, are expected to be widely used in multiple fields, bringing comfortable, intelligent and convenient living experience. In this study, miniature phase change microcapsules (MPCM) with n-octadecane as core and poly(methyl methacrylate) as shell were successfully prepared. Using the in-situ reduction property of polydopamine, gold nanoparticles were deposited on the surface of the microcapsules, which retained the heat storage function and imparted photothermal and antibacterial properties. The MPCM with photothermal conversion function was modified on the surface of silk fabric using aqueous polyurethane after verified by comprehensive material characterisation techniques. Under the near infrared light of 808 nm wavelength and 0.134 W/cm² irradiation intensity, the MPCM@PDA@Au modified silk fabrics showed excellent photothermal conversion performance, which could be increased from 25°C to 60°C in 50s. After the light source was cut off, the fabrics showed good heat release ability, with melting enthalpy and crystallisation enthalpy reaching 41.58 J/g and 43.3 J/g, respectively, which were not changed after repeated cycles. After the light source is cut off, the fabric has good heat release ability, and the enthalpy of melting and crystallisation reaches 41.58 J/g and 43.3 J/g, respectively, and the photothermal efficiency remains unchanged after many cycles of use, which proves that it has excellent durability and stability. The antimicrobial test shows that the fabric has significant antibacterial effect on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). MPCM@PDA@Au silk fabrics bring new possibilities for the future of personal thermal management and antimicrobial protection in the field of medical health, outdoor sports and other areas of broad application prospects, heralding the birth of a series of innovative applications and solutions.

Unraveling the Role and Impact of Alumina on the Nucleation and Reversibility of β‐LiAl in Aluminum Anode Based Lithium‐Ion Batteries

AbstractAluminum, due to its high abundance, very attractive theoretical capacity, low cost, low (de−) lithiation potential, light weight, and effective suppression of dendrite growth, is considered as a promising anode candidate for lithium‐ion batteries (LIBs). However, its practical application is hindered due to multiple detrimental challenges, including the formation of an amorphous surface oxide layer, pulverization, and insufficient lithium diffusion kinetics in the α‐phase. These outstanding intrinsic challenges need to be addressed to facilitate the commercial production of Al‐based batteries. The native passivation layer, Al2O3, plays a critical role in the nucleation and reversibility of lithiating aluminum and is thoroughly investigated in this study using high precision electrochemical micro calorimetry. The enthalpy of crystallization of β‐LiAl is found to be 40.5 kJ mol−1, which is in a strong agreement with the value obtained by calculation using Nernst equation (40.04 kJ mol−1). Surface treatment of the active material by the addition of 25 nm of alumina increases the nucleation energy barrier by 83 % over the native oxide layer. After the initial nucleation, the added alumina does not negatively impact the reversibility at 0.1 C rate, suggesting the removal of alumina is not necessary for improving the cyclability of aluminum anode based lithium‐ion batteries. Moreover, the coulombic efficiencies are also found to be slightly higher in the alumina treated samples compared to the untreated ones.

Transition mechanism and thermokinetic analysis of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics for nuclear waste forms based on in-situ synthesis

In this study, the novelly designed Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics were utilized as nuclear waste form to simultaneously immobilize simulated fission products Sr and actinide nuclides. The phase transition mechanism, thermokinetics and densification behavior of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics based on in-situ synthesis were systemically analyzed by XRD, in-situ XPS, TG-DSC, SEM and density measurements. The results demonstrate that the formation of Ce0.5Sm0.5PO4 solid solution phase preceded that of Sr0.5Zr2(PO4)3 phase, of which there is a valence change of Ce from Ce4+ to Ce3+ before 1023 K. Additionally, as for the exothermic crystallization enthalpy, change of exothermic crystallization enthalpy and activation energy, the values of Sr0.5Zr2(PO4)3 and Ce0.5Sm0.5PO4 phases in composite ceramics are 286.17 – 515.61 mJ, 19.11 – 35.38 J/g, 702.45 kJ/mol and 145.21 – 232.44 mJ, 9.26 – 15.44 J/g, 450.04 kJ/mol, respectively. It is then indicated that the formation of Ce0.5Sm0.5PO4 phase is definitely more favorable than that of Sr0.5Zr2(PO4)3 phase. Simultaneously, the relative densities of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics are more than 95 % when the sintering temperature exceeds 1273 K.

Flexible phase change film based on lignin-derived porous carbon/Eicosane for wearable thermal management and microwave absorption

A flexible phase-change film with thermal management and microwave absorption capabilities was developed for use in wearable devices. The film was created using a solution casting method based on a porous carbon-loaded eicosane (LP33/EI) material. LP33 served as the porous encapsulation medium, while Eicosane (EI) acted as the phase change component. The flexible substrate was a blend of polyvinyl alcohol (PVA) and bacterial cellulose nanocellulose (BC). The ultrathin film had a thickness of 0.262 mm, and LP33/EI-4 exhibited exceptional mechanical strength of 188 MPa. Testing revealed that the phase transition process had melting and crystallization enthalpies of 134.71 J/g and 126.11 J/g, respectively. The encapsulation structure effectively prevented any leakage during the phase transition process. Under simulated solar irradiation of 200 mW/cm2, LP33/EI-4 achieved a photothermal conversion efficiency (η) of 89.46 %. Additionally, the porous LP33 structure and high dielectric loss contributed to remarkable microwave absorption capabilities of −42 dB in the X-band and − 52 dB in the Ku-band. Overall, LP33/EI films demonstrated exceptional performance in thermal management, energy storage, and microwave absorption, making them an ideal choice for a variety of applications in wearable devices.

Delivery and utilization of photo‐energy for temperature control using a light‐driven microfluidic control device at −40 °C

AbstractLow‐temperature energy harvest, delivery, and utilization pose significant challenges for thermal management in extreme environments owing to heat loss during transport and difficulty in temperature control. Herein, we propose a light‐driven photo‐energy delivery device with a series of photo‐responsive alkoxy‐grafted azobenzene‐based phase‐change materials (a‐g‐Azo PCMs). These a‐g‐Azo PCMs store and release crystallization and isomerization enthalpies, reaching a high energy density of 380.76 J/g even at a low temperature of −63.92 °C. On this basis, we fabricate a novel three‐branch light‐driven microfluidic control device for distributed energy recycling that achieves light absorption, energy storage, controlled movement, and selective release cyclically over a wide range of temperatures. The a‐g‐Azo PCMs move remote‐controllably in the microfluidic device at an average velocity of 0.11–0.53 cm/s owing to the asymmetric thermal expansion effect controlled by the temperature difference. During movement, the optically triggered heat release of a‐g‐Azo PCMs achieves a temperature difference of 6.6 °C even at a low temperature of −40 °C. These results provide a new technology for energy harvest, delivery, and utilization in low‐temperature environments via a remote manipulator.

Preparation and properties of triphenyl octylphosphonium bromide‐modified vermiculite and its PBAT composite films

AbstractAs living standards improve, there is a growing demand for fresher, healthier and more sustainable food options, with a concomitant challenge to develop new biodegradable packaging. This investigation centres around the synthesis of quaternary phosphonium salt (triphenyl octylphosphonium bromide P8) and use it to modify vermiculite (VMT). The structure of P8 was determined using both NMR and FTIR. The structural investigation and performance analysis of P8‐modified vermiculite (P8@VMT) were carried out by particle size, XRD, FTIR and microstructure. In addition, P8@VMT/PBAT composite films were prepared by solution method using PBAT as matrix material and P8@VMT as filler. The properties of P8@VMT/PBAT composite films were compared to those of pure PBAT films using TGA, DSC, SEM, and antibacterial tests. Results showed that the melting and crystallization temperatures of P8@VMT/PBAT composite films were higher than those of pure PBAT films. However, increasing the content of P8@VMT led to a decrease in thermal stability as well as melting enthalpy, crystallization enthalpy, and crystallinity. On the other hand, loss modulus, storage modulus, and complex viscosity significantly increased with the addition of P8@VMT. Compared to pure PBAT film, P8@VMT/PBAT‐20% composites exhibited a 19.6% reduction in tensile strength and a 94.7% decrease in elongation at break due to the presence of quaternary phosphonium salt (P8) used as a modifier for VMT during melt blending method preparation.Highlights Quaternary phosphonium salt P8 was successfully synthesized. PBAT/P8@VMT composite films with different P8@VMT were prepared. P8@VMT improves compatibility between VMT and PBAT. PBAT/P8@VMT composite films have antimicrobial effects. The PBAT/P8@VMT composite films are biodegradable.

Semi-analytical and experimental heat input study of additively manufactured Zr-based bulk metallic glass: Insights into nano- and global-scale relaxation and crystallization

Laser powder bed fusion (LPBF) of Zr-based bulk metallic glasses (BMGs) has recently attracted attention due to its capacity for microstructure control, the potential for custom-tailored properties, and its versatile applicability across various industries. It is crucial to strike a balance between relative density, relaxation, and crystallinity tailored to a specific application when 3D printing amorphous components. However, prior findings have not revealed an exclusive study concerning low fractions of crystallinity (<5 vol%) and atomic-scale effects during the LPBF process, e.g. the relaxation degree of the amorphous structure. This study employs a systematic experimental approach, complemented by semi-analytical modeling, to comprehensively recognize the nano- and macro-scale amorphous structure and the associated mechanical behavior. Differential scanning calorimetry (DSC) along with flexural stress-strain measurements disclose that the highest relaxation and crystallization enthalpies, which are obtained for samples printed with lower heat input, are not in correlation with the desired mechanical properties. On the contrary, samples printed with a heat input of ΔH=44 reveal the maximum density range (up to 99.97 %) and showcase laboratory-XRD amorphous structure. This results in the highest flexural strength (up to 2080 MPa) and elastic deformation range (up to 2.6 %), along with the lowest Young’s modulus span (60–70 GPa). In this case, the crystallinity (0.02–0.2 vol%) associated with the desired mechanical properties is calculated from the modeling results. The outcomes indicate increased heating/ cooling rates corresponding to the amplified heat input, with cooling rates reaching up to 5×104 °C/s and heating rates up to 6×105 °C/s. However, underlying layers are subjected to reduced heating and cooling rates. This observation not only validates the intricate thermal dynamics in LPBF but also elucidates the crystalline formation in heat-affected zones (HAZs) with associated lower heating and cooling rates.

Characterization of the microstructure, interfacial properties and crystallization behaviours of milk fat globule and membrane isolated from acidified bovine milk and sweet whey

Milk fat globule and membrane (MFGs/MFGM) ingredients are the main source of the phospholipid supplementation in the dairy industry. Their physicochemical properties and functionalities play important roles in their application. This study investigated the effect of acidification (pH 6.30 and pH 5.30) on the microstructure, interfacial and thermal properties of MFGs/MFGM sourced from bovine milk (control pH 6.70). Meanwhile, sweet whey was prepared to mimic the raw material used in the industrial production of MFGs/MFGM (MFGM-C). The study revealed a broad particle size distribution of MFGs/MFGM at pH 5.30, while smaller particles were found in MFGM-C. This was confirmed by confocal scanning microscopy (CLSM) images, which showed that few intact MFGs existed in the MFGM-C. Fourier Transform Infrared Spectroscopy (FTIR) indicated more peaks belonging to protein-lipids associations presented at pH 6.30. Additionally, the interfacial tension of MFGs/MFGM at pH 6.30 was significantly lower than at pH 6.70 and 5.30. X-ray Diffraction Spectra (XRD) showed that the fat in MFGM-C exhibited no detectable crystalline structures, and fewer α and β′ crystals appeared at pH 6.30. All MFGs/MFGM from bovine milk or whey exhibited both exothermic and endothermal events. The smallest heat enthalpy of crystallization (ΔHC) and melting (ΔHM) was observed in MFGM-C, followed by those at pH 6.30. Compared to MFGs/MFGM at pH 6.70, pH 6.30 induced more profound effects on the interfacial and thermal properties of MFGs/MFGM than pH 5.30. Acidification and the use of different raw materials lead to differentiation in the physicochemical and techno-functionalities of MFGs/MFGM.

Preparation of n-Tetradecane Phase Change Microencapsulated Polyurethane Coating and Experiment on Anti-Icing Performance for Wind Turbine Blades

Icing is a common physical phenomenon, and the icing of wind turbine blades can significantly affect the performance of wind turbines. Therefore, researching methods to prevent icing is of great significance, and the coating method of anti-icing is an effective way to delay icing, with advantages such as low energy consumption and easy implementation. In this study, using the coating method as the background, tetradecane phase change microcapsules were prepared, with a melting enthalpy of 90.8 J/g and a crystallization enthalpy of 96.3 J/g, exhibiting good coverage and energy storage efficiency. After mixing tetradecane phase change microcapsules (PCMS) with polyurethane coating (PUR) and coating them on wind turbine blades, after a 5 min icing wind tunnel test, the coating could significantly delay the icing on the blade surface, with the highest anti-icing rate reaching 60.41%. This indicates that the coating has a good anti-icing effect and provides basic research data for exploring new anti-icing methods.

Study on the preparation and properties of TiO2@n-octadecane phase change microcapsules for regulating building temperature

Aiming at regulating building temperature in summer, the preparation and optimization of TiO2@n-octadecane microcapsules were studied in this paper, which is significant to energy conservation. N-octadecane and TiO2 act as the core material and shell material, respectively. The SEM, FT-IR, DSC, TGA, and infrared thermal imaging were used to analyze the TiO2@n-octadecane microcapsules. Aiming at the enthalpy of phase transition and encapsulation rate of microcapsules, the reaction vessel, emulsifier, stirring rate, amount of acetic acid, and droplet-adding rate for preparing microcapsules were optimized. Furthermore, the microcapsules with the best properties were mixed into concrete to analyze their temperature regulation performance, mechanical strength, fire resistance, thermogravimetry, and cyclic stability. The effect of microcapsule proportions on the temperature regulation ability of concrete at different temperatures was also studied. The key findings are as follows: Firstly, the TiO2@n-octadecane microcapsules exhibit a stable core–shell structure and a size of about 1 μm. The highest melting enthalpy, crystallization enthalpy, and encapsulation rate of TiO2@n-octadecane microcapsules are 120 J/g, 116 J/g, and 54.1 %, respectively. The microcapsules only consist of TiO2 and n-octadecane without any chemical reactions. Secondly, the concrete incorporating the TiO2@n-octadecane microcapsules shows a faster phase change reaction, inhibiting temperature rise or fall effectively, and preventing leakage. Thirdly, compared with ordinary concrete, 5 mm concrete with 20 % TiO2@n-octadecane microcapsules can extend its temperature below 28.5 °C for 15.7, 14.0, and 7.6 min at 30 °C, 35 °C, and 40 °C, respectively. Finally, the compressive strength of concrete with 0 %∼20 % MPCMs satisfies the requirements for concrete applications. It also has excellent fire resistance and thermal stability. Moreover, incorporating MPCMs into concrete can significantly reduce the pyrolysis of MPCMs.