Time-temperature Superposition Technique Research Articles

Erroneous or Arrhenius: A Degradation Rate-Based Model for EPDM during Homogeneous Ageing.

To improve the predictive capability of long-term stress relaxation of elastomers during thermo-oxidative ageing, a method to separate reversible and irreversible processes was adopted. The separation is performed through the analysis of compression set after tempering. On the basis of this separation, a numerical model for long-term stress relaxation during homogeneous ageing is proposed. The model consists of an additive contribution of physical and chemical relaxation. Computer simulations of compression stress relaxation were performed for long ageing times and the results were validated with the Arrhenius treatment, the kinetic study and the time-temperature superposition technique based on experimental data. For chemical relaxation, two decay functions are introduced each with an activation energy and a degradative process. The first process with the lower activation energy dominates at lower ageing times, while the second one with the higher activation energy at longer ageing times. A degradation-rate based model for the evolution of each process and its contribution to the total system during homogeneous ageing is proposed. The main advantage of the model is the possibility to quickly validate the interpolation at lower temperatures within the range of slower chemical processes without forcing a straight-line extrapolation.

Temperature fractionation, physicochemical and rheological analysis of psyllium seed husk heteroxylan

Psyllium husk is a source of natural dietary fibre with marked water absorbability and gelling properties, which makes it an attractive functional ingredient for applications in the food industry, such as gluten free bread and breakfast cereals. The main functional component of psyllium husk is a complex branched heteroxylan. In this study, a straightforward sequential fractionation of hydrated psyllium seed husk powder based on temperature-dependent behaviours was applied. The F20 (20 °C fraction) showed the highest yield followed by F60 while 13.5% of the husk is unextractable (residue).The obtained fractions showed unique rheological properties as analysed using small amplitude oscillatory shear rheometry and the time-temperature superposition (TTS) technique. The results indicate that: 1) only F20 was influenced by heat treatment, 2) high temperature fractions showed stronger gel properties, 3) a three-step softening/melting was observed, 4) F60 has longest relaxation time as shown in TTS master curves. The four fractions were also characterised using the monosaccharide analysis, FTIR and 13C NMR. The arabinose/xylose ratio was found to increase with the increase in fractionation temperature. FTIR and 13C NMR spectra supported that low temperature fraction is less branched.Two hypotheses were therefore proposed: The first one based on models by Haque, Richardson, Morris, and Dea (1993) and Yu et al. (2019) focusing on chemical and structural properties of the molecules. The second hypothesis highlights differences in hierarchical molecular conformations of polysaccharides which is proposed by Diener et al. (2019). Sidechain substitution and composition and length of sidechains are critical and significantly influence the properties of each fraction.

Dynamic mechanical response of plasticizer-laden acoustic polyurethanes extrapolated to higher frequencies using time–temperature superposition technique

Acoustically transparent elastomers are the windows through which the US Navy views the ocean. For acoustic clarity and sensitivity, it is important that these elastomers operate well outside damping conditions as dictated by the temperatures and frequencies of interest. Damping behavior is characterized by a peak in the loss tangent and is associated with transitions in molecular mobility, such as the primary glass–rubber or alpha transition. However, the temperature and frequency location of this peak can shift in response to absorbed plasticizing fluids. This material characteristic is under investigation using dynamic mechanical analysis to assess its dependence on the plasticizer and polyurethane component chemistry. In this second stage of the research, the time–temperature superposition technique was employed to extrapolate storage modulus and loss factor to frequencies beyond the limits of the equipment. The technique appears to be valid for plasticized primary transition behavior but becomes circumspect when applied to secondary transition behavior.

Creep analysis of bamboo high‐density polyethylene composites: Effect of interfacial treatment and fiber loading level

AbstractThe effect of chemical treatment at fiber–plastic interface and fiber loading level on creep property of bamboo fiber high‐density polyethylene (BF/HDPE) composites was investigated. For single modifier systems, the use of maleic anhydride grafted polyethylene (PE‐g‐MA) as a coupling agent helped reduce the creep and achieved the optimum effect at the 5.7% loading level. The addition of either a semicrystalline or an amorphous MA grafted ethylene propylene rubber (sEPR‐g‐MA or aEPR‐g‐MA) as an impact modifier increased the creep. For the combined modifiers, the use of PE‐g‐MA in EPR‐g‐MA modified composites gradually improved creep performance. Four‐element Burgers model was shown to fit measured creep data well only within the specified test period. However, both partially stretched Burgers (PSB) model and fully stretched Burgers (FSB) model could be applied for characterization and prediction when the stretching exponent was fixed at certain given values. The FSB model offered a better long‐term prediction based on the short‐term creep data. Time‐temperature superposition technique produced smooth master creep curves through horizontal shifts, but it slightly over‐predicted the long‐term creep for most composite systems. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Role of rheological characteristics in amorphous food particle-wall collisions in spray drying

A gap in knowledge exists in modeling particle-wall collision of amorphous food particles in spray drying. Most work uses a stick-upon-contact or glass transition criterion which tends to over-predict the deposition. This communication introduces a new idea in relating viscoelastic rheological characteristics to modeling of amorphous food particle-wall collisions. A time–temperature superposition technique was employed. This approach allows the effect of impacting velocity and particle size as well as the effect of particle rigidity to be incorporated in determining the impaction outcome. Trends obtained from the case study undertaken showed good qualitative agreement with past reports. Suggestions are included on possible extension to model particle–particle collisions.

Broadband Viscoelastic Spectroscopy: A New Technique for Characterizing Rheological Behavior of Solid Foods

The broadband viscoelastic spectroscopy (BVS) is a new technique for characterizing rheological behavior of solid foods. Conventional methods to obtain rheological behavior of materials over a broad range of frequencies are time-temperature superposition (TTS) technique and direct method using specific instruments. TTS technique works only for materials that are thermorheologically simple and over a limited range of about three decades of time or frequency. Materials for which the measured curves do not overlap by making a horizontal shift on the frequency axis are thermorheologically complex. Food systems are inherently complex with multiple constituents rendering them thermorheologically complex. Thus, it is necessary to acquire data directly over a wide frequency range in a single test to truly characterize such complex materials. The problems associated with TTS can be circumvented by using the BVS, which is capable of directly measuring viscoelastic properties over an extended frequency range. Applications of the BVS are introduced for characterizing viscoelastic behavior of food materials. Some advantages of the BVS technique over the TTS and other available instruments are also discussed.

Effect of temperature on hydration kinetics of sesame seeds ( Sesamum indicum L.)

Hydration kinetics of sesame seeds (SS) in plain water was determined at temperatures of 27–60 °C. A new model was proposed to describe the hydration kinetics of SS. A novel alternative technique, time–temperature-superposition technique (TTST), was also introduced for modeling the effect of temperature on water absorption kinetics of SS. The diffusion coefficient values calculated using two different forms of Fick’s second law were all of the order of 10 −11 m 2/s. The new introduced model was able to adequately describe the hydration kinetics of SS with RMSE of less than 5%. Moisture absorption in SS was an endothermic process with a heat of absorption of 7.37 kJ/mol. The TTST found to be an adequate technique for modeling the effect of temperature on water absorption data. The soluble solid losses after 225 min soaking were found to be between 0.26% and 2.85% for temperatures of 27–60 °C. An exponential relationship ( R 2 = 0.949) was obtained between solids losses and electrical conductivity of leak water.

A Novel Alternative Method for Modeling the Effects of Air Temperature and Slice Thickness on Quality and Drying Kinetics of Tomato Slices: Superposition Technique

The effect of air temperature (AT) and slice thickness (ST) on the quality and drying kinetics of tomato slices were studied. The drying period of tomato slices to reach the moisture content of 15% (wb) ranged from 2.6 to 18.7 h. The water diffusivity, activation energy, and resistance to diffusion ranged from 1.4 × 10−10 to 2.8 × 10−9 m2/s, 21.25 to 23.4 kJ/mol, and from 939 to 4590 m2 s/kg, respectively. Drying had a significant effect on ascorbic acid, soluble solid, acidity, and pH (P = 0.01). The ascorbic acid degradation was greatly influenced by ST. The results show that time-temperature superposition technique (TTST) was very efficient in the modeling of the drying process. The proposed TTST provides a novel alternative in curve-fitting exercise of drying data. Neural networks also showed favorable performance in estimating the drying functions.

Application of Superposition Technique for Modeling Drying Behavior of Avishan (Zataria multiflora) Leaves

Drying curves of agricultural products at different air temperatures and air velocities are often identical in shape, but shifted along the abscissa. The shift distance for each curve measured relative to a chosen reference curve is called the shift factor. This allows the drying curves to shift horizontally along the time axis through a time multiplier (shift factor) until a smooth master curve is created. The master curves can be used to address air temperature and air velocity effects on the drying kinetics through the use of the shift factors. The purpose of the present work was to test the validity of this method, called the time-temperature superposition technique (TTST), in order to model the effects of air temperature (AT) and air velocity (AV) on drying kinetics of avishan (Zataria multiflora L.) leaves (AL). The drying data at three AT (30°C, 40°C, and 50°C) as well as three AV levels (0.5, 0.8 and 1.2 m/s) were used for the modeling. The results showed that the TTST was adequate to generate a moisture ratio master curve for AL. The resulting master curves represented by the Page model (R2 > 0.996) and its validity to predict the moisture ratio of AL were compared with a regression model. The master curve model performed better than the regression model in predicting the moisture ratio of AL as a function of AT and AV. The result confirmed the applicability of the TTST for determining the activation energy of avishan leaves.

Inferring Viscoelastic Dynamic Material Properties From Finite Element and Experimental Studies of Beams With Constrained Layer Damping

Viscoelastic materials are often used to add damping to metal structures, usually via the constrained layer damping method. The added damping depends strongly on material temperature and frequency, as do the underlying material properties of the viscoelastomer. Several standardized test methods are available to characterize the dynamic material properties of viscoelastomers. However, they rely on limited test data which is extrapolated using the time—temperature superposition technique. The authors have found that the different testing methods typically produce significantly different dynamic material properties, or “master curves.” An approach for inferring viscoelastomer dynamic moduli with better accuracy is suggested here. Several metal bars are treated using constrained layer damping. Experimental modal analyses are conducted on the bars at different temperatures to produce sets of system resonance frequencies and loss factors. Corresponding finite element (FE) models of the treated bars are analyzed using assumed viscoelastomer material properties based on master curves generated using a standardized test technique. The parameters which define the master curves are adjusted by trial and error until the FE-simulated system loss factors match those of the measurements. The procedure is demonstrated on two viscoelastomers with soft and stiff moduli.

Viscoelastic characteristics of plasticized cellulose nanocomposites

AbstractThe plasticization effects of cellulose diacetate composite systems including nanoparticles (montmorillonite, MMT) and plasticizers(diethyl phthalate, DEP) were investigated by the time–temperature superposition technique and viscoelastic modeling. Exhibiting the highest modulus value in the glass state, the viscoelastic modulus of the MMT nanocomposite rapidly decreased above the glass‐transition temperature (Tg). The Arrhenius‐type activation energy of pristine cellulose acetate showed the lowest value of activation energy and both DEP‐plasticized and MMT‐reinforced systems exhibited increased values of activation energy. Although the free volume fraction at the Tg decreased with the plasticizer content, it increased with the incorporation of MMT, seemingly preventing the polymer chains from being arranged in an ordered structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 59–65, 2005

Continuous and intermittent stress relaxation studies on foamed polysiloxane rubber

Stress relaxation studies of foamed polysiloxane rubber samples have been conducted using a thermomechanical analyser (TMA). The data were assessed using the principle of time–temperature superposition and also by a kinetic study of the experimental results. The time–temperature superposition technique produced acceleration factors that showed good adherence to the Arrhenius relationship and showed two distinct regions where processes with different activation energies dominate. Our kinetic studies showed that the stress relaxation isotherms between 21 °C and 100 °C showed poor correlation to both first- and second-order rate equations. In comparison, the stress relaxation isotherms at elevated temperatures between 120 °C and 175 °C showed good conformity to second-order kinetics. The second-order rate constants for the isotherms at elevated temperatures showed good adherence to the Arrhenius relationship yielding an apparent activation energy of 63 ± 4 kJ/mol. These values are in close agreement to that derived using time–temperature superposition (65 ± 5 kJ/mol). The simple kinetic approach adopted here could not be used to assess the stress relaxation data below 120 °C because a suitable rate function could not be identified. Intermittent stress relaxation studies allowed compression set data to be obtained as a function of time and temperature. Comparison of intermittent and continuous stress relaxation profiles at a number of different temperatures shows that the foamed polysiloxane rubber exhibits significant physical relaxation or spring back during the recovery process. To assess the physical contribution to compression set, samples showing set were swollen in toluene for 1 day and then dried in air to constant weight. All samples with set showed significant solvent-induced recovery suggesting reversible physical relaxation processes contribute significantly to compression set in these polymers. This suggests that possible compression set damage in real-time aged foamed polysiloxane rubbers may be partially reversible using the toluene swell procedure reported here, opening up the possibility of component re-use.

Annealing effect on semi-crystalline materials in creep behavior

Three glass reinforced polymers of Nylon 66, PET and HT-Nylon with glass transitions of 58, 72, and 132°C are selected for checking the necessity of high temperature annealing and degree of its impact on creep strains. The improvement after annealing depends on the polymer type of whether it is fast or slow crystallizing at molding process and whether it has hydrogen bonded sheets. The physical property changes observed of these materials before and after annealing support the explanation of crystal reorganization through crystallization, free volume reduction through densification and crystal perfection through better chain packing. The prediction of long-term creep strains up to 10 years using time-temperature superposition technique has been the practice for last 13 years in our laboratory. The accuracy of the prediction are shown in confidence level of about 90%.

The Combined Influence of Molecular Weight and Temperature on the Physical Aging and Creep Compliance of a Glassy Thermoplastic Polyimide

The effect of molecular weight on the viscoelastic performance of anadvanced polymer (LaRC™-SI) was investigated through the use of creepcompliance tests. Testing consisted of short-term isothermal creep andrecovery with the creep segments performed under constant load. Thetests were conducted at three temperatures below the glass transitiontemperature of five materials of different molecular weight. Through theuse of time-aging-time superposition procedures, the material constants,material master curves and aging-related parameters were evaluated ateach temperature for a given molecular weight. The time-temperaturesuperposition technique helped to describe the effect of temperature onthe timescale of the viscoelastic response of each molecular weight. Itwas shown that the low molecular weight materials have higher creepcompliance and creep rate, and are more sensitive to temperature thanthe high molecular weight materials. Furthermore, a critical molecularweight transition was observed to occur at a weight-average molecularweight of $${\bar M}$$ w ∼ 25,000 g/mol below which, the temperature sensitivity of thetime-temperature superposition shift factor increases significantly. Theshort-term creep compliance data were used in association with Struik'seffective time theory to predict the long-term creep compliance behaviorfor the different molecular weights. At long timescales, physical agingserves to significantly decrease the creep compliance and creep rate ofall the materials tested. Long-term test data verified the predictivecreep behavior. Materials with higher temperature and lower molecularweights had greater creep compliance and higher creep rates.

Generalized Maxwell model for the viscoelastic behavior of a soda-lime-silica glass under low frequency shear loading

The linear viscoelastic behavior of a soda-lime-silica glass under low frequency shear loading is investigated in the glass transition range. Using the time-temperature superposition technique, the master curves of the shear dynamic relaxation moduli are obtained at a reference temperature of 566°C. A method to determine the viscoelastic constants from dynamic relaxation moduli is proposed. However, some viscoelastic constants cannot be directly measured from the experimental curves and others cannot be precisely obtained due to non-linearity effects at very low frequencies. The generalized Maxwell model is investigated from the experimental dynamic moduli without fixing the viscoelastic constants. A set of parameters is shown to be in good agreement with the experimental dynamic relaxation moduli, but does not give the correct values of the viscoelastic constants of the investigated glass. The soda-lime-silica glass exhibits a non-linear viscoelastic behavior at very low stress level which is usually observed for organic glasses. This non-linear behavior is questioned.

Determination of the piezoelectric properties of piezoelectric composite materials by laser Doppler velocimetry

Measurement of the piezoelectric coefficients of a commercial piezoelectric composite material and their temperature dependence was made using a complex electrical admittance-fitting technique. The results were reported previously [J. Acoust. Soc. Am. Suppl. 1 83, S81 (1988)]. In order to extrapolate these measurements to lower frequencies, the time-temperature superposition technique as described by Ferry was successfully applied to direct measurements of the dielectric and elastic constants [Proc. 6th Int. Symp. Appl. Ferroelectr.]. In order to measure the piezoelectric coefficients over an extended frequency range, laser Doppler velocimetry was employed. The technique is shown to be useful for nonresonant determination of piezoelectric coefficients over extended ranges of frequency and temperature. [Work supported by the Office of Naval Research.]

Rheology of Cold-Recycled Pavement Materials Using Creep Test

Abstract The recycling technique of asphalt pavement materials has been used in the past decade, however, unsolved problems still exist such as rutting or instability. The slow reaction of the softening agents or the new binders or both may be responsible for this phenomenon. The viscosity of the binder in the cold-recycled pavement materials mixed with emulsified asphalts is experimentally analyzed by evaluating certain rheological characteristics of the mixture using the creep test at three temperatures. The properties of the recycled mixture are determined at both early and accelerated long-term aging and the results are compared with the properties of virgin materials. Master creep curves are developed using the time-temperature superposition technique. The creep behavior of the recycled asphalt mixture used in this study does not support the hypothesis of the long-term reaction between the emulsified asphalt and the reclaimed materials. In addition, the bulk specific gravity and the retained moisture in the compacted recycled mixture were evaluated at various ages.