Temperature Sweep Research Articles

Microwave Sensitivity Enhanced Asphalt Mastic with Magnetite Powder and Its Performance after Microwave Heating

Microwave heating technology is a promising method for asphalt pavement maintenance and de-icing; however, it requires the material to have a good microwave-absorbing ability and can also result in asphalt aging. It is therefore important to develop microwave-sensitive materials used for asphalt pavement maintenance and study the effects of microwave heating on asphalt aging. This study evaluates the electromagnetic characteristics of limestone powder and magnetite powder and explores the influence of microwave heating on the high-temperature rheological and fatigue properties of microwave sensitivity enhanced asphalt mastic with magnetite powder. A vector network analyzer was used to measure the electromagnetic characteristics of limestone powder and magnetite powder. The magnetite filler asphalt mastics were prepared and subjected to microwave heating for 1 h, 2 h, 3 h, and 4 h. Temperature sweep tests, frequency sweep tests, and linear amplitude sweep (LAS) tests were conducted for magnetite filler asphalt mastics before and after microwave heating. LAS experimental results were analyzed based on viscoelastic continuum damage (VECD) theory. The results show that magnetite powders have better electric field energy storage ability, higher dielectric loss and magnetic loss, and better microwave heating efficiency. The complex shear modulus (G*) and rutting factor (G* × (sin δ)−1) rapidly decrease with the increase in temperature, indicating that the mastics’ ability to resist deformation decreases sharply. The longer the microwave heating time for magnetite filler asphalt mastics, the faster the high-temperature rheological properties decreased as the temperature rose. The fatigue life of magnetite filler asphalt mastics significantly decreases with the increase in strain and microwave heating time. It is suggested to add anti-aging agents into asphalt materials to reduce the aging effect in the process of microwave heating. This study provides a reference for the application of microwave heating technology in asphalt pavement maintenance.

Research on high-temperature rheological performance of fiber reinforced high-viscosity asphalt mastics

High-temperature performance of high-viscosity asphalt mastic containing fiber additive were studied by means of rheological analysis. The effects of two types of asphalt, two types of fillers, and two types of fibers with three fiber contents on the high-temperature rheological properties of asphalt mastic were evaluated by temperature sweep test, multiple stress creep recovery test, and frequency sweep test using a dynamic shear rheometer. The master curve of fiber reinforced high-viscosity asphalt mastic and phase angle were constructed using 2S2P1D model. The results show that the nature of asphalt plays a leading role in improving the resistance to deformation of asphalt mastic at high temperature, compared with the type of mineral powder. For the short-term aging asphalt mastic, with temperature increasing, the unrecoverable creep compliance gradually increases and the differences between asphalt mastic with different fiber contents also become greater. The creep recovery rate of mastic with basalt fiber is much higher than that of polyester fiber under the same conditions. For long-term aging asphalt mastic, compared with increasing fiber content, the fiber type has more significant influence on the storage modulus. 2S2P1D model can well fit the master curve of the complex modulus of fiber reinforced high-viscosity asphalt mastic, but poorly fit with the phase angle. From master curves, it finds that the enhancement of the fiber to mastic is prominent in the low frequency which is corresponding to the extreme high-temperature condition.

A PVT tolerant low power wide tuning range differential voltage controlled oscillator design in 90 nm CMOS technology

This paper presents a three-stage low power and wider tuning range differential ring-oscillator with dual control voltages. This design permits lower tuning gain using dual control voltage (VTUNE 1 and VTUNE 2) to achieve high operation frequency. The dual voltage control enables a large bias current into the circuit. The proposed DRO has been implemented in 90 nm CMOS technology, whose performance results show a very high output frequency range which includes lower frequency band (LFB) and higher frequency band (HFB) from 0.007 GHz to 13.48 GHz. This DRO shows power consumption from 0.001 mW to 2.307 mW and phase noise of −92.27 dBc/Hz @ 1MHz offset. The figure of merit (FoM) for this DRO turns out to be −179.98 dBc/Hz. In addition, process corner analysis, Monte Carlo analysis, temperature sweep analysis, and stability analysis has been performed to find the robustness of the circuit.

Effect of pressure treatment duration on the rheological characteristics of dry-heated alocasia starch in the presence of monosaccharide and disaccharide

The current work investigated the impact of different pressure processing times (5, 10, and 15 min) at 120 psi on the rheological behavior of a mixture of dry-heated Alocasia macrorrizhos starch with monosaccharide and disaccharide. Shear-thinning behavior was exhibited by the samples in steady shear evaluation and the highest viscosity was observed in the 15 min pressure treated samples. In the initial phase of amplitude sweep measurement, samples exhibited strain dependency but later they remain unaffected with applied deformation. The greater value of Storage modulus (G′) than loss modulus (G″) (G′ > G″) indicating the weak gel-like behavior. Increasing in pressure treatment duration enhanced the value of G′ and G″ with applied frequency and found maximum at 15 min. In temperature sweep measurement the G′, G″ as well as complex viscosity curves increased initially and then decreased after achieving peak temperature. However, the rheological parameters of the samples treated under long pressure processing time were found to be improved during temperature sweep measurements. The resulting extremely viscous, pressure-treated dry-heated Alocasia macrorrizhos starch-saccharides combination has a variety of uses in different pharmaceuticals as well as in food industries.

Thermal Behavior of Pea and Egg White Protein Mixtures.

The partial substitution of animal protein by plant protein is a new opportunity to produce sustainable food. Hence, to control the heat treatment of a composite protein ingredient, this work investigated the thermal behavior of mixtures of raw egg white (EW) and a laboratory-prepared pea protein isolate (PPI). Ten-percentage-by-weight protein suspensions prepared with different PPI/EW weight ratios (100/0, 75/25, 50/50, 25/75, 0/100) at pH 7.5 and 9.0 were analyzed by differential scanning calorimetry (DSC) and dynamic rheology in temperature sweep mode (T < 100 °C). The DSC data revealed changes in the thermal denaturation temperatures (Td) of ovotransferrin, lysozyme, and pea legumin, supposing interactions between proteins. Denaturation enthalpy (∆H) showed a high pH dependence related to pea protein unfolding in alkaline conditions and solubility loss of some proteins in admixture. Upon temperature sweeps (25-95 °C), the elastic modulus (G') of the mixtures increased significantly with the EW content, indicating that the gel formation was governed by the EW protein. Two thermal sol-gel transitions were found in EW-containing systems. In particular, the first sol-gel transition shifted by approximately +2-3 °C at pH 9.0, probably by a steric hindering effect due to the presence of denatured and non-associated pea globulins at this pH.

Gelling and rheological properties of a polysaccharide extracted from Ocimum album L. seed

In this study, a new polysaccharide was isolated from Ocimum album L. seed (OA), and its physicochemical and rheological properties were investigated. Ocimum album polysaccharide (OAP) was an acidic heteropolysaccharide with a molecular weight of 1935 kDa, and it was composed of five types of sugars: mannose (32.95 %), glucose (27.57 %), galactose (19.29 %), rhamnose, (15.96 %) and galacturonic acid (4.23 %). According to the results obtained from Huggins and Kraemer equations, the intrinsic viscosity was 6.9 dL/g in distilled water. The OAP solutions at a concentration between 0.1 and 1.5 %, showed shear-thinning behavior, and the Herschel–Bulkley and Cross models exhibited a high ability to describe the flow behavior of OAP solutions. The apparent viscosity of 1 % OAP solution was decreased in the presence of different concentrations of NaCl (0.1, 0.3, and 0.5 M), at different pHs (3−11), and in temperatures between 5 and 100 °C. Also, the pseudoplastic behavior was observed in all samples. In OAP solutions (0.1–1.5 %), the up and down curves in the shear stress-shear rate diagram did not coincide, which indicated time-dependent (thixotropic) behavior. Although, the thixotropic properties of 1 % OAP solution were weakened with adding NaCl (0.1–0.5 M) and at different pH (3–11). The results obtained from the dynamic oscillatory test showed that the OAP solutions at concentrations higher than 0.1 % had a gel-like behavior, and the viscoelastic moduli (G′ and G″) were weakened in the presence of salt and with a change in pH. Also, in the temperature sweep test, the 1 % solution showed the behavior of thermally irreversible gels.

Extraction of asphalt mastic from mixture without chemical agent

A mechanical method is presented which helps to recover asphalt mastic from asphalt mixture without any chemical agent. It may be used as a surrogate to the current chemical extraction method when asphalt mastic shall be recovered from the asphalt mixture. The presented approach is based on granulation and sieving techniques. For the purpose of validation, the method is compared to the standard chemical extraction method which uses a chemical agent to recover the asphalt binder from the mineral aggregates. Both methods are compared in terms of recoverable amount of mastic, and of filler/binder ratio, of reproducibility, and of suitability of the recovered mastic sample for subsequent temperature and frequency sweep (T-f sweep) tests using a Dynamic Shear Rheometer (DSR).

Zein improves desirable melt-stretch properties in plant-based cheeses made from pea protein

Plant-based model cheeses made from pea protein isolate (PPI), zein and zein/PPI blends, were made in combination with corn starch, sunflower oil, different levels of κ-carrageenan (κC) and CaCl2 (CC), and glycerol as a zein-plasticizer. Their viscoelastic properties at ambient temperature and upon heating, as well as their lubrication properties were analyzed. The properties of all plant-based formulations were compared to two dairy cheeses of reference: mozzarella and raclette. Formulations containing PPI formed a gel, whose network structure did not weaken upon heating. In contrast, zein-based cheeses showed potential for structure weakening during heating, as observed during the rheological temperature sweep. The latter observation increased in zein/PPI-combinations with increasing zein content, even though the melting behaviour of any of the plant-based formulations was not fully comparable to the one of raclette cheese. All of the examined formulations reduced the friction coefficient by a factor between 2 and 10 in the boundary regime, compared to HEPES-buffer. In zein-containing formulations, the friction coefficients decreased to a lesser extent the higher the zein proportion was. Finally, the inclusion of κC or CC did not have a significant influence in the lubrication properties of PPI-formulations. In summary, particularly zein/PPI-combinations made of a total protein content of 30% in the formulation showed good potential in mimicking the melting of conventional cheese, opening prospect for the development of formulations with improved sensory characteristics in future works.

Asphalt mixture performance deterioration in the salty environment based on theoretical calculation

In a salty environment, the asphalt mixture is exposed to the effect of sodium chloride which can affect its performance. Using less energy and raw materials, a model was effectively created in this study to predict the influence of sodium chloride on the performance of the asphalt mixture (rutting resistance and fatigue damage) in a salty environment. To ascertain the physical characteristics of the asphalt binder at various salt solution proportions, fundamental tests such as the penetration test, softening point, and ductility test were performed. Additionally, the Dynamic Shear Rheometer (DSR) was used to conduct the temperature sweep test in order to assess the rheological characteristics of asphalt binder samples before and after immersion in different salt solutions. Based on the DSR results and mixture volumetric parameters, the Hirsch model and the Asphalt Institute (ALI) model were used to forecast the performance of the asphalt mixture. The test results indicated that the asphalt mixture with the highest complex modulus (G*), lowest voids in mineral aggregate (VMA), and highest voids filled with asphalt binder (VFA) had the highest value of dynamic modulus, which is preferable to increase the asphalt mixture's resistance to rutting. The maximum rate of deterioration was estimated to be 45% at 15% salt content, followed by that of 10% salt content (26.76%), and 5% salt content (22.8%). However, the findings from the ALI model revealed that the fatigue life of the asphalt mixture in the presence of salt solution significantly decreased when compared to the specimen soaked in plain water, indicating that salt was detrimental to the mixture's resistance to fatigue cracking. The largest rate of deterioration was 37.11% at 15% salt content, and it was followed by rates of 22.35% at 10% salt content and 19.13% at 5% salt content.

Effect of chemical warm-mix additives on asphalt binder rheological and chemical properties in the context of aging

Warm-Mix Asphalt (WMA) has achieved gradually increasing popularity among researchers and agencies because of the environmental and economic benefits associated with lower production temperatures. An ongoing research study sponsored by the Oklahoma Department of Transportation (ODOT) is focusing on evaluating how different chemical WMA additives and the associated lower production temperatures impact asphalt binder and mixture properties and exploring potential relationships between asphalt rheology and chemistry in the context of chemical WMA and various aging conditions. This manuscript presents partial findings from this study that involved testing of two binder types (modified and unmodified binder) and four different WMA additives (chemical additives). Different aging conditions were simulated by changing the Rolling Thin Film Oven (RTFO) temperature, and by subjecting the binder to different cycles of Pressure Aging Vessel (PAV) aging. Frequency and Temperature Sweep tests by a Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) tests were performed for rheological characterization, while Fourier Transform Infrared Spectrometer (FTIR) test was conducted for chemical characterization. Analysis of the test results indicated that while all the WMA additives can improve the rheological and chemical properties of control binders at original and RTFO conditions, two additives cause inferior properties after 20 h, 40 h, and 60 h of PAV aging, indicating possible higher aging susceptibility and long-term performance concerns. Good correlations (R2 greater than 0.8) observed between binder rheological parameters and chemical indices indicate the existence of fundamental relationships between asphalt binder’s engineering properties and chemical make-up, which also supports the possibility of using FTIR as a quick screen or fingerprint tool for binder selection and comparison. Two new rheological parameters have been proposed for evaluation of the polymer-modified binder in this study. This was important to address the presence of multi-transition behavior in modified binders. These two parameters show consistent trends with increasing aging conditions.

Evaluation of Thermal and Rheological Properties of Phase Change Material-Incorporated Asphalt Mastic with Porous Fillers

Incorporating phase change material (PCM) into paving materials can regulate the pavement temperature, improve the pavement durability, and mitigate the heat-island effects. In this research, porous fillers were used as the PCM carrier, and the thermal and rheological behaviors of the asphalt mastic with the PCM were evaluated. Two different carrier materials (diatomite and expanded perlite) and four types of PCMs were used in the study. The candidate filler, PCM, and proper blending ratios were determined based on the results of scanning electron microscope image analysis, the filter paper test, and the temperature sweep test. The thermal and rheological behaviors of the mastics with PCMs were further evaluated with different filler replacement ratios. Thermal analysis through a differential scanning calorimetry test, thermal conductivity and volumetric heat capacity test, and real-time temperature performance test were performed on the asphalt mastics. Rheological tests, including the complex shear modulus test, the bending beam rheometer test, and the linear amplitude sweep test, were also conducted. The modified mastics were found to have high heat capacity with the latent heat storage ability. The rheological analyses showed that with the addition of polyethylene glycol, while the low-temperature performance of the asphalt mastics was improved, the performance at intermediate and high temperatures was not adversely affected by the PCM.

Melting properties of vegan cheese: Effect of emulsion and protein addition on the thermal behaviour of starch gels

The aim of this study was to understand the effect of emulsion and protein incorporation on the structural and melting properties of starch gels designed as model systems for specific types of vegan cheese, and to explore the potential of using these ingredients to mimic the melting properties of dairy cheese. To characterise the melting properties of the gels, temperature sweep tests were conducted. In addition, pictures were taken to visualise changes in appearance upon increasing temperature. The microstructure of the gels was investigated with confocal laser scanning microscopy (CLSM). Whereas gels of native maize starch did not melt, those made from oxidised potato starch melted completely at temperatures above 70 °C, resulting in a fluid with a viscosity much lower than that of molten dairy cheese. With the addition of a protein-stabilised sunflower oil emulsion, at oil contents >10%, an oil droplet network was formed in the starch matrix, which partly inhibited the melting of the gel. The addition of pea protein that was subsequently heated together with the starch also resulted in the formation of a network that limited melting. However, due to the high degree of pea protein aggregation, an inhomogeneous appearance was obtained. At low protein contents syneresis occurred. When protein was added without heat treatment, the melting degree was inhibited already at low contents, a more homogeneous appearance was obtained, and syneresis was prevented due to the high-water holding capacity of the protein. When emulsion and protein were added together at high contents, the appearance was also more homogeneous, and the melting degree of the composite gels was further limited. When comparing the relative inhibiting effect of oil and protein content on melting, protein was found to be more effective. By changing both oil and protein content, samples with melting properties similar to those of processed cheese were obtained, which shows that the design of multi-component starch-protein-oil gels is a promising approach in optimising the functional properties of dairy cheese substitutes.

Physicochemical properties of cricket (Gryllus bimaculatus) gel fraction with soy protein isolate for 3D printing-based meat analogue

Cricket (Gryllus bimaculatus) gel was fractionated and mixed with different soybean protein isolate (SPI) concentrations, and its characteristics were evaluated to determine its potential use as a meat analog. Crushed crickets were separated into the filtrate, supernatant, and pellet fractions by centrifugation and freeze-drying, and powdered and mixed with 18% SPI at different concentrations (5%–20%). The filtrate fraction had the lowest protein content and the highest fat and carbohydrate content among the nutrient fractions. Conversely, the supernatant and pellet fractions had high protein, low fat, and low carbohydrate content. SDS-PAGE detected relatively low-molecular weight proteins. Numerous muscle proteins were identified, including actin, myosin, and hemocyanin, a protein that transports oxygen in insects. Regarding the rheological characteristics of the cricket fraction, the entire fraction exhibited G'>G" in both the frequency and the temperature sweep tests, revealing a tendency for gel-like viscosity. In all cricket fractions, both G' and G" increased with increasing fraction powder concentration. When printed, supernatant fractions had no structural stability, pellet fractions had 5%–15% stability, and filtrate fractions had 5%–20% stability. The three interval thixotropy test revealed that the pellet fraction had a recovery rate of over 90% after high shear deformation. Texture profile analysis showed an increase in both hardness and chewability. After heat treatment, cohesiveness was higher than adhesiveness, indicating greater elasticity. Field-emission scanning electron microscopy results revealed that the pellet fraction was denser than the other fractions, particularly at higher concentrations. Based on the overall characteristics, 15% pellets were found to be the most appropriate fraction and concentration.

Investigation on the Short-Term Aging Scheme for High Viscosity Modified Bitumen.

Due to the highly viscous characteristics of high viscosity modified bitumen (HVMB), the commonly used short-term aging schemes are not suitable for it. As such, the objective of this study is to introduce a suitable short-term aging scheme for HVMB by increasing the aging period and temperature. For this purpose, two kinds of commercial HVMB were aged via rolling thin-film oven test (RTFOT) and thin-film oven test (TFOT) at different aging periods and temperatures. At the same time, open-graded friction course (OGFC) mixtures prepared using HVMB were also aged via two aging schemes to simulate the short-term aging of bitumen at the mixing plant. With the aid of temperature sweep, frequency sweep, and multiple stress creep recovery tests, the rheological properties of short-term aged bitumen and the extracted bitumen were tested. By comparing the rheological properties of TFOT- and RTFOT-aged bitumen with those of extracted bitumen, suitable laboratory short-term aging schemes for HVMB were determined. Comparative results showed that aging the OGFC mixture in a 175 °C forced-draft oven for 2 h is suitable to simulate the short-term aging process of bitumen at the mixing plant. Compared with RTOFT, TFOT was more preferable for HVMB. Additionally, the recommended aging period and temperature for TFOT was 5 h and 178 °C, respectively.

Aging behavior of polyphosphoric acid/styrene-butadiene-styrene-modified bio-mixed asphalt based on high-temperature rheological properties and microscopic mechanism

This study investigates the performance of polyphosphoric acid/styrene–butadienestyrene (PPA/SBS)-modified bio-mixed asphalt after thermo-oxidative and ultraviolet (UV) aging, based on its high-temperature rheological properties and microscopic characteristics. The temperature sweep test results revealed that long-term thermo-oxidative aging significantly increased the dynamic shear moduli of the composite-modified asphalts, where the maximum increment in composite-modified asphalts reached to 425 %. However, the dynamic shear modulus of the composite-modified asphalt decreased owing to the degradation of aromatic aldehydes to fatty aldehydes after ultraviolet aging, leading to softer composite-modified asphalts. In addition, the multiple-stress creep recovery (MSCR) test revealed that the maximum increment in the recovery rate of composite modified asphalt reached to 37.4 %. Moreover, the increasing rate of Jnr was significantly lower than that of the control asphalt after long-term aging, particularly at a stress level of 3.2 kPa. Finally, the microstructures of each asphalt sample before and after aging were observed using atomic force microscopy. The surface morphology of the composite modified asphalt after aging was relatively smoother, indicating that the molecular homogeneity of the aging residue of the composite-modified asphalt sample was better than that of the control asphalt sample.

Assessment of the effect of straw lignin-based synthetic resin as a modifier on the rheological properties of asphalt binder towards better utilization of straw biomass

PurposeTo extend the reuse method and rate of straw biomass, this paper investigated the effect of lignin synthetic phenolic resin (LPF) on the rheological properties of asphalt binder.Design/methodology/approachFour LPFs with 25%, 50%, 75% and 100% substitution rates were prepared by replacing phenol with lignin in synthetic resins and using it as a modifier to prepare a bio-asphalt binder. Temperature sweep tests were conducted to evaluate aging resistance and temperature sensitivity of the bio-asphalt binder. The rutting resistance of the bio-asphalt binder was evaluated by frequency sweeps and multiple stress creep recovery (MSCR) test. Linear amplitude sweep (LAS) tests were conducted to evaluate the fatigue resistance of the bio-asphalt binder. A master curve was constructed to further analyze the rheological properties of the bio-asphalt binder at different frequencies. The low-temperature cracking resistance of the binder was evaluated by G-R parameters, critical temperatures and ΔTc. Fourier transform infrared spectroscopy (FTIR) was performed to investigate the changes in the functional groups of the binder before and after aging.FindingsThe results indicated that adding LPF could improve the high-temperature rutting resistance, fatigue resistance, aging resistance of asphalt and the binders are less affected by temperature. Additionally, LPF slightly prohibited the low-temperature performance of the asphalt binder, which, however, was significantly lower than the base asphalt degradation during aging. Compared with base asphalt binders, the bio-asphalt binder showed no new absorption peaks generated after adding LPF, identifying that the improved asphalt binder performance by LPF was a mainly physical modification.Originality/valueThe main objective of this paper is to further improve the substitution rate (i.e. the mass substitution ratio of lignin to phenol) of lignin and broaden the application of biomass resins, thus realizing resource sustainability.

Application of plasma modified pyrolytic carbon black in improving mechanical properties of natural rubber composite

AbstractIn this work, the Argon (Ar) plasma technology is adopted for pyrolytic carbon black (CBp) modification and the N330/Modified‐CBp (MCBp) hybrid is then incorporated into the Natural Rubber (NR) matrix. Compared with CBp, the MCBp has smaller particle size, lower ash content, higher specific surface area, and surface activity based on the results of laser diffraction method, transmission electron microscope (TEM), thermogravimetric analysis, gas sorption analysis (Nitrogen), acetone solvent, and X‐ray photoelectron spectroscopy. Among them, Dv (90) is found to have reduced by 20% while the specific surface area increased by 4%. According to the bound rubber content experiments, the equilibrium swelling experiments as well as the temperature and strain sweeps, the bound rubber content, filler‐filler bond strength, and cross‐linking density of NR/N330/MCBp are all superior to those of NR/N330/CBp, resulting in an outstanding comprehensive performance of NR/N330/MCBp composite. In particular, the 300% modulus and the tear strength rise by 43% and 14% respectively, surpassing even the system filled with N330. Finally, the mechanism of mechanical properties improvement in the NR/N330/MCBp composite is proposed: the strong filler‐filler bond is formed between the MCBp and N330 aggregates via molecular chains, and they are anchored on the MCBp and absorbed on the N330 simultaneously.

Porous Chitosan Hydrogels Produced by Physical Crosslinking: Physicochemical, Structural, and Cytotoxic Properties.

Chitosan hydrogels are biomaterials with excellent potential for biomedical applications. In this study, chitosan hydrogels were prepared at different concentrations and molecular weights by freeze-drying. The chitosan sponges were physically crosslinked using sodium bicarbonate as a crosslinking agent. The X-ray spectroscopy (XPS and XRD diffraction), equilibrium water content, microstructural morphology (confocal microscopy), rheological properties (temperature sweep test), and cytotoxicity of the chitosan hydrogels (MTT assay) were investigated. XPS analysis confirmed that the chitosan hydrogels obtained were physically crosslinked using sodium bicarbonate. The chitosan samples displayed a semi-crystalline nature and a highly porous structure with mean pore size between 115.7 ± 20.5 and 156.3 ± 21.8 µm. In addition, the chitosan hydrogels exhibited high water absorption, showing equilibrium water content values from 23 to 30 times their mass in PBS buffer and high thermal stability from 5 to 60 °C. Also, chitosan hydrogels were non-cytotoxic, obtaining cell viability values ≥ 100% for the HT29 cells. Thus, physically crosslinked chitosan hydrogels can be great candidates as biomaterials for biomedical applications.

Prediction of viscoelastic properties of epoxy/graphene oxide nanocomposites: Time-temperature-water ageing superposition

Graphene-based fillers are promising candidates for improving the long-term dimensional stability of structural epoxy resins. The development of reliable accelerated test methods is critical to predicting their durability. Herein, the viscoelastic behaviour of the industrial-grade amine-epoxy and corresponding nanocomposites with modified graphene oxide (up to 1.72 wt%) is studied using dynamic mechanical thermal analysis (DMTA) in both temperature and frequency sweep modes. Time-temperature (TTSP), time-water ageing (TWSP), and coupled superposition principles (TTWSP) are used to predict the long-term storage moduli of nanocomposites. The temperature and water shift functions, determined by curve shifting, agree well with the Arrhenius calculations based on data from independent tests. A methodology for constructing master curves from DMTA temperature scans is developed, and the results are well correlated with the predictions made from traditional isothermal multifrequency test data. The temperature and time dependences of the storage moduli are well fitted by known relaxation models, and their parameters are analysed in terms of the filler and water-ageing effects. The results can be applied in the development of the material model and the prediction of macromechanical properties and the service lifetime, which are relevant to examined epoxy/GO composites and other water-sensitive glassy polymers.

Room temperature giant magnetocaloric effect in Pd doped FeRh and the effect of martensitic transition

FeRh 0.8 Pd 0.2 is known to exhibit near room-temperature first-order antiferromagnetic (AF)–ferromagnetic (FM) transition, typical of chemically ordered FeRh system. In addition, it is also reported to show martensitic transition at a lower temperature. In this work, the effect of sample history on transition temperature (Tt) and the magnetocaloric effect (MCE) have been studied. The experimentally determined MCE parameters across FM to AF transition induced either by isothermal magnetic field sweep or by temperature sweep showed a large isothermal change in entropy around room temperature, i.e., 14 J/kg K for 50 kOe magnetic field change, whereas MCE corresponding to AF–FM transition depends on cooling history. Our study shows that in the presence of martensite phase, the peak value of MCE is shifted to higher temperatures but with significantly reduced magnitude.