Dynamic Thermal Properties Research Articles

The first principle calculation of structural, electronic, magnetic, elastic, thermal and lattice dynamical properties of fully compensated ferrimagnetic spin-gapless heusler alloy Zr2MnGa

The first principle calculation for geometry optimization, elastic, electronic, magnetic, thermal, transport and lattice-dynamical properties of new spin gapless full heusler compound Zr₂MnGa were studied within Density Functional Theory approach (DFT). The material obeys Slater Pauling (SP) rule and exhibit spin gapless semiconducting behavior with fully compensated ferrimagnetism (FCF). To the best of our knowledge, various mechanical, thermal, transport and lattice dynamical properties like elastic constant, bulk modulus and Debye temperature are reported for the first time using density functional theory (DFT). The structure satisfies all stability criteria and is thus found stable at equilibrium value of lattice constant. Zr₂MnGa crystallizes in inverse heusler structure which is stable at ground state and have zero magnetic moment per unit cell, following Slater Pauling (SP) rule. The calculated results indicate that the material exhibits SGS character at its equilibrium lattice constant i.e. there is an indirect energy gap of about 0.31 eV between conduction band and valence band at EF level of minority or majority spin channel, while there is no gap between the majority electrons in valence band and minority electrons in conduction band. Higher value of ZT and Seebeck coefficient (S) increases the efficiency of thermoelectric devices with greater output current and voltage. Obtained results support strong candidature of Zr2MnGa compound as promising material in spintronics devices.

Lightweight composite timber façade wall with improved thermal response

For the construction of modern energy-efficient buildings, lightweight construction is becoming very popular among designers. EU legislation encourages such design, especially if wood, as a sustainable material, is used. However, lightweight building envelope construction, in general, exhibits poor dynamic thermal properties, which are particularly pronounced in prefabricated metal walls and thin wooden or composite building panels, such as door fillers or opaque parts (parapets) of prefabricated walls with the glazing of the skeleton-built buildings. The aim of this research was the development of a composite timber façade wall, which will not exceed the thickness of building elements, such as doors and windows, and will meet the requirements of energy efficiency and have improved dynamic thermal properties. The composite timber building element with a thickness of 68 mm, which includes two layers of advanced technologies: vacuum insulation panel (VIP) and phase change material (PCM), was developed and optimized. The optimization included a parametric study on VIP and PCM panels’ position in the thin, lightweight building wall. The research has shown that dynamic thermal properties comparable to the heavyweight building envelope constructions (time lag of the heat wave up to 12 h) can be achieved; moreover, the thermal transmittance is considerably reduced.

A facile route to fluoroalkylsiloxane polymers having resistance to corrosive acidic conditions: Synthesis and characterization

Polysiloxanes having 3,3,3-trifluoropropyl (TFP) groups attached to the silicon atom are highly attractive by virtue of their unique properties such as extreme solvent resistance and broad service temperatures. Though fluoroalkylsiloxane polymers are known for their resistance to hydrocarbon solvents and oils, reports on room temperature curable fluoroalkylsiloxane polymer based coatings that are resistant to corrosive acidic and oxidative environments are very rare. In this paper, for the first time, we report the synthesis of vinyl terminated fluorosilicone copolymer, poly(methyltrifluoropropyl-co-methylvinyl) siloxane (V-PFMVS) with very high TFP content (77mol%) and 23mol% vinyl content, and its comparison of properties with non-fluorinated counterpart, vinyl terminated poly(dimethyl-co-methylvinyl) siloxane (V-PDMVS). The synthesised copolymers were obtained in high yields of 70–75% with number average molecular weight (Mn) of 65,000 and were cured using cyclic hydridosiloxane via hydrosilylation route. Cured V-PFMVS exhibited increased hydrophobicity compared to cured V-PDMVS (contact angle 113° vs. 91°). The corresponding silica reinforced composites also were processed and evaluated for dynamic mechanical and thermal properties as well as response to various environments including hexane, conc. HNO3 and HF. Swelling studies proved the role of -CH2CH2CF3 groups in imparting excellent resistance to hexane and better resistance to corrosive acidic environments as illustrated by the low weight loss after exposure to conc. HNO3 and HF in the case of V-PFMVS/composite. Lap shear strength (LSS) evaluation on aluminium substrate proved its capability asa promising adhesive. The superior properties of the V-PFMVS/composite are correlated to its chemical composition.

Poly(butylene terephthalate)/Glycerol-based Vitrimers via Solid-State Polymerization

A new type of semicrystalline vitrimer was prepared via the incorporation of glycerol into the amorphous phase of poly(butylene terephthalate) (PBT) by solid-state (co)polymerization (SSP). A near quantitative incorporation of the glycerol was confirmed by NMR spectroscopy. Wide-angle X-ray diffraction, differential scanning calorimetry (DSC), and temperature-modulated DSC showed that the PBT/glycerol-based vitrimers maintain the crystallization characteristics of normal PBT. By a change in the cross-link density of the PBT/glycerol-based vitrimers, a wide range of thermal, rheological and mechanical properties were obtained; e.g., the rubbery plateau modulus at 270 °C could be tuned from 0.07 to 3 MPa. The characteristic vitrimer behavior was demonstrated by stress relaxation and oscillatory frequency sweep experiments. In addition, these semicrystalline vitrimers can be recycled multiple times by compression molding without a substantial loss in dynamic mechanical and thermal properties.

Preparation and Properties of Castor Oil-Based Dual Cross-Linked Polymer Networks with Polyurethane and Polyoxazolidinone Structures

Dual cross-linked polymer networks (DCPNs) are novel copolymers containing two different cross-linking polymers with superior comprehensive properties. The aim of this study was to explore the feasibility of preparation of novel castor oil-based DCPNs material. First, two novel biobased reactive monomers of epoxidized castor oil (ECO) and ricinoleic acid epoxy (RAE), containing both hydroxy and epoxy groups, were synthesized from castor oil (CO). Their chemical structures were characterized by Fourier transforminfrared spectroscopy (FTIR) and 1H-nuclear magnetic resonance (1H NMR) analysis. Both hydroxy and epoxy groups can react with the isocyanate groups of toluene-2,4-diisocyanate (TDI), and then two renewable resource-based DCPNs of RAE/TDI and ECO/TDI, containing both polyurethane (PU) and polyoxazolidinone (POXDN) molecular structures, were designed and prepared. The tensile properties, gel content (GC), hardness, fractured surface morphologies, thermostabilities, and dynamic mechanical and thermal properties of these renewable resource-based copolymers were all investigated. Results show that the tensile properties, GC, hardness, and glass transition temperature (Tg) of the fabricated DCPNs were superior to those of the pure CO/TDI copolymerized system. The fabricated DCPNs, particularly RAE/TDI, were found to have good tensile strength of 12.47 MPa and the highest elongation at break of 154.99%, and its thermostability was also increased greatly compared with that of the pure CO/TDI copolymerized system.

Effect of chlorinated polyethylene on dynamic mechanical and thermal properties of SAN/EPDM blends in dependence of mixing conditions

The effect of chlorinated polyethylene (CPE) on the compatibilization and thermal properties of styrene-acrylonitrile copolymers (SAN)/Ethylele-Propylene-Diene-polyMethylene rubber (EPDM) blends (80/20) was investigated. Two different mixing procedures were employed, that is, single- and two-step blending. In the single-step process, EPDM was melt blended with CPE and SAN simultaneously, which led to a droplet morphology. In the two-step process, first, a masterbatch of EPDM and CPE in SAN was prepared, and then mixed with further amounts of SAN and CPE in order to reach the same fixed blend ratio of 80/20 for SAN/EPDM. The morphology changed from EPDM droplets for the one-step mixing to co-continuous for the two-step blending process. This morphological change was reflected in a change of the complex modulus. The characteristics of thermogravimetric analysis (TGA) curves (T1%, T5%, T30%, and T50%) were examined, as indicators for improved thermal stability of the blends. The intermolecular interaction characterized by the Kwei equation showed higher values for the blends prepared by the two-step mixing procedure. The dynamic mechanical analysis supported the occurrence of chain scission in the SAN phase at the beginning of aging and cross-linking of SAN at higher temperatures and longer times as a result of cyclization of CN groups in SAN.

Investigation on the effect of the thermal dynamic, evaporation, and alternative material properties in a laser melt pool with a developed 2D model based on the VOSET method

ABSTRACTThe melt pool is the general process of the laser additive manufacturing process. An in-depth understanding of the evolution of the melt pool will facilitate obtaining an optimum mechanical performance. In this paper, a novel 2D transient model is presented, which considers most physical phenomena taking place in the laser melt process and incorporates a coupled multiphase capture method. This model is validated by comparing it to Han’s research. Then an investigation on the transient thermal dynamic in the melt pool including quenching time is carried out, and the effects of evaporation and alternative material properties on the evolution of the melt pool are discussed. The results show that the deformation of the free surface and the temperature in the workpiece both increase with energy input. After quenching, the temperature in the workpiece decreases sharply and the melt pool also shrinks. The evaporation effect is vigorous in the center of the melt pool and negligible in the periphery. The material properties have significant influence on the evolution process because the convection and diffusion in the melt pool are directly dominated by them.

Dynamic mechanical, thermal and wear analysis of Ni-P coated glass fiber/Al₂O₃ nanowire reinforced vinyl ester composite

Hybrid polymer composites nowadays are increasingly used in many engineering products which are subjected to wear, dynamic mechanical and thermal applications. So in the present study, we have investigated the evaluation of dynamic mechanical, thermal and wear properties of vinyl ester hybrid composite strengthened with Ni-P coated E-glass fiber and Al₂O₃ nanowires as reinforcement at different concentrations. Nickel-Phosphorus is plated over the glass fiber substrate by means of the electroless plating method. The best optimum bath composition was determined after many trials and used for the proper plating process. From the outcome of the result, it is clear that the storage modulus has a trend to increase with increase in the concentration of Ni-P coated glass fiber (GF) and further increases when Al₂O₃ nanowires are used as the reinforcement. The glass transition temperature is also shifted to the higher temperature in the process. From the thermogravimetric analysis, it is clear that the thermal stability of the composite steps up with the addition of Al₂O₃ nanowires as fillers and Ni-P/GF as reinforcement. The wear properties are analyzed and the morphology of the coated and worn-out surfaces are studied by means of scanning electron micrographs and optical microscope images.

Analysis of Changes in Thermomechanical Properties and Structure of Polyamide Modified with Fly Ash from Biomass Combustion

Study of performance of polyamide with fly ash addition with different contents of filler was carried out. In this article studies were performed: dynamical mechanical properties, thermal properties and structure research. The profiles of changes in the value of storage modulus E′ and tangent of mechanical loss angle tgδ depend on the temperature and frequency of vibrations. The crystallinity degree was examined using DSC methodology whereas the structure was analysed by means of the optical microscope. The increase in the value of storage modulus versus temperature and vibration frequency for the samples with addition of filler and the increase in the crystallinity degree and polymer matrix with reduced addition of fly ash were observed. A reduction in size of the structural components was also found, particularly for the composites with filler content.Graphical

Proton mobility and thermal conductivities of fuel cell polymer membranes: Molecular dynamics simulation

Fuel cell polymer membranes such as the Dow, Nafion and Aciplex membranes as the core of the proton exchange membrane fuel cell (PEMFC) play an important role in maintaining high intrinsic proton conductivity. For investigating the dynamic properties and thermal properties of fuel cell polymer membranes, the proton mobility and thermal conductivities of the Dow, Nafion and Aciplex membranes were calculated by using molecular dynamics (MD) simulations. Compared with the Dow and the Nafion membranes, the Aciplex membrane presented a better mobility of water molecules and hydronium ions at 350K and it showed a better thermal property due to its side chain is long enough to form a “highway” of heat conduction. The results indicated that both the structure of side chain and temperature have effect on the dynamic properties and thermal properties of fuel cell polymer membranes.

A Modified Constitutive Model and Dynamic Recrystallization Behavior of High‐N Mn18Cr18 Alloy

High‐N Mn18Cr18 alloy is mainly used as drill collar (DC) and retaining rings due to its non‐magnetism and outstanding corrosion resistance. This work focuses on studying the dynamic recrystallization (DRX) behavior and thermal mechanical properties of high‐N Mn18Cr18 alloy through isothermal single‐pass compression tests on Gleeble‐3500 simulator at the temperatures from 900–1200 °C and strain rates from 0.001–1 s−1. Flow stress curves combined with metallographic analysis indicate that DRX tends to occur at high deformation temperatures and low strain rates. The deformation activation energy of high‐N Mn18Cr18 alloy is 331.775 kJ mol−1. Besides, fifth order polynomial fitting for determining critical strain and nonlinear curve fitting for extrapolating work hardening stress are presented. Based on kinetics equations of DRX and the dislocation density model, constitutive model is been set up to predict the flow stress behavior. Comparisons between the experimental and the predicted flow stress values indicate good forecast precision of the established model.

Synergistic Conductivity and Electromagnetic Interference Shielding Effectiveness of Epoxy/Carbon Fiber and Epoxy/Carbon Black Composites via Mixing with Bamboo Charcoal

This study was aimed at preparing electromagnetic interference (EMI) shielding materials based on carbon black (CB), carbon fiber (CF), bamboo charcoal (BC), and epoxy resin. The effects of adding bamboo charcoal on the mechanical properties and electrical resistivity of epoxy composites were studied. Scanning electron microscopic (SEM) analysis, electrical resistivity, and electromagnetic interference (EMI) shielding effectiveness were also investigated. The composites were prepared at 120 °C by the curing-molding method through blending the fillers in epoxy resin. The results revealed that the BC/CB and BC/CF composites had perfect conductive network structure and resulted in better dynamic thermal mechanical properties. The electrical resistivity declined with the increase of bamboo charcoal contents; consequently, the EMI shielding effectiveness improved gradually. The lowest electrical resistivity, down to 0.071 Ω·m, corresponded to the best EMI shielding effectiveness of BC/CF composites, which could be above 60 dB over a frequency range of 30 MHz to 1500 MHz while the carbon fiber content was at 40 wt.%.

A Coupled Eulerian Lagrangian Model to Predict Fundamental Process Variables and Wear Rate on Ferrite-pearlite Steels

A coupled Eulerian-Lagrangian Finite Element model of the orthogonal cutting process was developed to predict the influence that ferrite-pearlite steel variants have on fundamental process variables and tool wear. As a case study, this paper is focused on two different ferrite-pearlite inclusion free alloys, where mainly the influence of ferrite-pearlite ratio was tested. Flow stress behavior based on dynamic compression tests and thermal properties function of temperature were characterized for model input parameters. The numerical model is compared with orthogonal cutting tests where the cutting and feed forces, tool temperature, chip morphology and tool wear related variables were measured. Globally, predicted tendencies match with experiments in forces and temperatures. Widest differences on predictions were found for chip thickness and tool-chip contact length. Predicted wear rates are in accordance to experimentally measured values.

The issue of thermal comfort of medical clothing in the operating room

La ropa médica tiene la función principal de protección. Sin embargo, esta función debe estar correlacionada con una buena experiencia de comodidad para el usuario. La comodidad es un tema muy importante, ya que los profesionales están expuestos a situaciones de estrés que pueden influir, negativamente, en su desempeño laboral. Más específico, el confort térmico juega un papel crucial para el mejor rendimiento de la ropa médica usado en la sala de operaciones, que implica la regulación del calor y la transferencia de masa entre un cuerpo vestido y el medio ambiente, una vez que la ropa es la interfaz entre el cuerpo y el medio ambiente. El objetivo de este trabajo fue estudiar el comportamiento de propiedades térmicas de batas quirúrgicos y trajes de aire limpio usados en la sala de operaciones. Se realizó una comparación entre estos dos tipos de prendas con equipos Alambeta, para propiedades térmicas estacionarias y un Maniquí Térmico, para propriedades dinâmicas, como el flujo de calor y el aislamiento térmico. Se encontró que el aislamiento térmico de las prendas es estadísticamente diferente, mostrando que la diferencia entre los trajes puede ser percibida por el usuario.

Effect of alcohol-acid modification on physicochemical, rheological and morphological properties of glutinous rice starch

In the present study chemical modification of glutinous rice starch was carried out using 1-Buatnol-hydrochloric acid with varying time and temperature. The changes in physico-chemical, dynamic rheological and morphological properties of starch during hydrolysis was investigated. There was a significant increase in water solubility of starch due to modification; however, swelling and sedimentation value decrease after modification. The peak, hold and final viscosity of modified starches were decreased significantly as compared to native starch. Thermal properties and dynamic rheological properties of rice starch were changed with the change in time and temperature during modification. The storage (G′) modulus, loss (G″) modulus, dynamic viscosity (η′) and complex viscosity (η*) of modified starches were varied significantly. Analysis of microstructure revealed that the hydrolysis altered morphology of starch granules. The hydrolysis was affected the surface properties and granule size of rice starch. These results suggested that 1-butanol–HCl hydrolysis of glutinous rice starch can be a preferred way of modification.

Branched polyols based on oleic acid for production of polyurethane foams reinforced with bamboo fiber

Fatty acids and bamboo fiber (BF) are abundant and renewable materials that have great potential application in the production of high-valued chemical products. In this work, polyurethane foams (PUFs) with remarkable mechanical and thermal properties were synthesized using OAPs (polyols-based on oleic acid (OA), an important fatty acid) and polymeric isocyanates. PUFs were reinforced with BF. Novel OAPs were prepared from OA through a process consisting of hydroxylation, carboxylation, and esterification. The strategy afforded branched polyols with high content of primary hydroxyls. Phthalic anhydride was used as a modifying agent to improve the properties of OAPs. Physicochemical properties of the polyols were characterized by standard methods (analyses of hydroxyl number, viscosity, acid value, density, and water content) and instrumental analysis (gel permeation chromatography, Fourier transform infrared spectroscopy, and thermogravimetry). The mechanical properties of polyurethane foams made from the OAPs were improved by applying modified BF as filler. With BF having particle sizes of 250–500 μm, the compressive strength of composite foams increased from 0.45 to 0.66 MPa, and the flexural strength increased from 0.66 to 0.77 MPa. Surface modification of BF by alkali could enhance the interfacial interaction between the reinforcing fibers and foam matrix, resulting in greater mechanical strength of the PUFs. It also improved the thermal stability and dynamic thermomechanical properties of PUFs.

Phenylethynyl-terminated polyimide, exfoliated graphite nanoplatelets, and the composites: an overview

In efforts to characterize and understand the properties and processing of phenylethynyl-terminated imide (LaRC PETI-5, simply referred to as PETI-5) oligomers and polymers as a high-temperature sizing material for carbon fiber-reinforced polymer matrix composites, PETI-5 imidization and thermal curing behaviors have been extensively investigated based on the phenylethynyl end-group reaction. These studies are reviewed here. In addition, the use of PETI-5 to enhance interfacial adhesion between carbon fibers and a bismaleimide (BMI) matrix, as well as the dynamic mechanical properties of carbon/BMI composites, are discussed. Reports on the thermal expansion behavior of intercalated graphite flake, and the effects of exfoliated graphite nanoplatelets (xGnP) on the properties of PETI-5 matrix composites are also reviewed. The dynamic mechanical and thermal properties and the electrical resistivity of xGnP/PETI-5 composites are characterized. The effect of liquid rubber amine-terminated poly(butadiene-co-acrylonitrile) (ATBN)-coated xGnP particles incorporated into epoxy resin on the toughness of xGnP/epoxy composites is examined in terms of its impact on Izod strength. This paper provides an extensive overview from fundamental studies on PETI-5 and xGnP, as well as applied studies on relevant composite materials.

Thermal and dynamic mechanical analysis of hybrid jute/sisal fibre reinforced epoxy composite

The aim of the present study is to investigate the dynamic mechanical and thermal properties of hybrid jute/sisal fibre reinforced epoxy composites. The hybrid composites were prepared by hand layup technique having total fibre loading of 30% by weight with different weight ratios of jute and sisal fibres. Dynamic mechanical properties such as storage modulus ([Formula: see text]), loss modulus ([Formula: see text]) and damping ([Formula: see text]) were investigated in the temperature range of 30–200 ℃. The thermal stability of the prepared composites was studied using thermogravimetric analysis. Other thermal properties such as glass transition temperature ( Tg), crystallization temperature ( Tc) and decomposition temperature ( Td) were also obtained by differential scanning calorimetry. The results indicated a positive effect of hybridization in terms of increase in dynamic mechanical and thermal properties. Storage modulus, loss modulus and Tg were found to be higher for hybrid composite having a higher percentage of jute fibres.

Influence of diaminobenzoyl‐functionalized multiwalled carbon nanotubes on the nonisothermal curing kinetics, dynamic mechanical properties, and thermal conductivity of epoxy–anhydride composites

ABSTRACTTo obtain advanced materials with a high thermal dissipation, the addition of multiwalled carbon nanotubes containing diverse functionality groups, that is, as‐received multiwalled carbon nanotubes (AS‐MWCNTs) and diaminobenzoyl multiwalled carbon nanotubes (DA‐MWCNTs), to epoxy–anhydride composites was accomplished. According to nonisothermal differential scanning calorimetry analysis, the reactive functional groups present on the surfaces of the AS‐MWCNTs and DA‐MWCNTs accelerated the nucleophilic addition reaction of epoxy composites. Because of the difference in the reactivities of these functional groups toward epoxy groups, the distinction of fractional conversion and the reaction rate of the curing process were remarkably evident at the early stage. A suitable kinetic model was effectively elucidated with the Málek approach. The curing kinetics could best be described by a two‐parameter autocatalytic model as a truncated Šesták–Berggren model. The DA‐MWCNTs achieved effective load transfer and active heat conductive pathways; this resulted in good dynamic mechanical and thermal properties. As a result, the diglycidyl ether of bisphenol A/DA‐MWCNTs constituted an effective system with enhanced heat dissipation of materials for electronic applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43567.

Elaboration of low viscosity and high impact polypropylene blends through reactive extrusion

In this work, a reactive high flow polypropylene, PP800 (η0 = 40 Pa s, 190°C), is extruded with a commercial compound of polypropylene and ethylene‐propylene random copolymer (η0 = 3000 Pa s, 190°C). On one hand, the fluidity of resulting blends is highly increased but, on the other hand, matrix degradation leads to a strong decrease of the impact behavior and tensile strain. Then, the addition of 10 wt% of propylene‐based copolymer (PBC) leads to a very interesting impact enhancement while keeping high fluidity. A study of morphological, thermal, and dynamical thermal mechanical properties reveal the anchoring of semi crystalline propylene segments of PBC droplets at the interface with the PP matrix. On the contrary, the addition of ethylene‐based copolymer (EBC) is not able to restore satisfactory impact properties. POLYM. ENG. SCI., 56:418–426, 2016. © 2016 Society of Plastics Engineers