Small Amplitude Oscillatory Shear Tests Research Articles

Hydrocolloids as a tool for modulating the expected satiety of milk-based snacks

The objective of this study was to discover which rheological profiles are related to greater expected satiety in semi-solid milk-based snacks. Chocolate flavoured snacks were prepared with four different hydrocolloids (alginate, carrageenan, hydroxypropyl methylcellulose -HPMC- and xanthan gum) at three different concentrations. Rheological measurements were carried out in a controlled stress rheometer using a parallel-plates sensor system. Flow curves were obtained at increasing shear rates (0–200 s−1) and viscoelastic properties were measured using small amplitude oscillatory shear tests. The results showed that, in general, increasing the hydrocolloid concentration resulted in greater yield stress, viscosity, thixotropy and viscoelastic moduli, with differences depending on the type of hydrocolloid. For HPMC and alginate, increasing the concentration mainly increased the viscosity, thixotropy and yield stress, while for xanthan gum and carrageenan the most important changes were rises in elastic modulus values and decreased tan δ. The expected satiety delivered by the different samples was evaluated by 50 participants. The snacks were presented physically, sampled and assessed in relation to picture scales of four “comparison foods”: apple, chocolate bar, sandwich (ham and cheese) and doughnut. The results indicated that the effect on expected satiety of increasing the thickness of the snack differed according to the type of thickener used. Expected satiety increased with higher concentration in the alginate and HPMC samples but not in those prepared with carrageenan or xanthan gum. PLS regression showed that viscosity, not solidity (elasticity), determined the expected satiety of semi-solid milk-based snacks.

Mechanics of Soft PSAs (Pressure Sensitive Adhesives)

The adhesive performances of a PSA (Pressure Sensitive Adhesive) are attributed to their viscoelastic properties. In this paper we analyze the viscoelastic behavior of different PSAs having substantially similar adhesive performance. Linear and non linear analyses were performed using small amplitude oscillatory shear tests and tensile stress-strain tests, respectively. It is shown that linear viscoelastic tests are useful to qualitatively characterize the adhesive performances. However, deeper knowledge can be achieved by non linear viscoelastic tests. The true stress - true strain curves are modeled by using a theory accounting for the interpenetration of micro-network and the linear polymer. It is shown that the same substantial in-service properties can be achieved with adhesives showing different fingerprints in terms of viscoelastic spectra.

Comparison of concentration dependence of mechanical modulus in two biopolymer gel systems using scaling analysis

Concentration dependence of mechanical modulus of two biopolymer systems, i.e., xanthan-locust bean (X/L) mixture and fish muscle protein (surimi) was evaluated and compared at a wide range of polymer concentrations. A small amplitude oscillatory shear test was performed to measure changes in storage (G') modulus during gelation and after gelation. Critical concentration (Cc) of the X/L mixture and surimi gel was determined to be 0.15 g/100 mL of solvent and 2.04 g/100 g of solvent, respectively. Reduced concentration (CR=CL/Cc) was used to compare the power-law dependence of modulus of the two systems. The elasticity exponent of the X/L mixture and surimi gel was determined to be 2.4 and 1.97, respectively. The concentration dependence of two biopolymer gel systems such as physical gels (X/L) and chemicals gels (fish muscle protein) theoretically demonstrated that the difference of flexibility of junctions in the networks might distinguish the elasticity of each gel.

Rheological characteristics of EVA modified bitumen and their correlations with bitumen concrete properties

Polymer modified bitumens (PMBs) were prepared by mixing bitumen from two different sources with an EVA copolymer. The rheological characteristics of the PMBs were analyzed using small amplitude oscillatory shear and steady shear tests. Data were analyzed with rheological models developed for particle suspensions and with Palierne’s model for polymer blends. Results indicate that such models cannot account for the EVA modification of the bitumen in the whole range of temperatures, frequencies and shear rates studied. The effects of EVA on the PMBs viscoelastic properties and morphology depend on the type of bitumen considered. However, power law relationships between the rheological functions of PMBs and the Young complex modulus and the rut depth of corresponding mastics are identified.

Investigation of Elastic Modulus of Xanthan and Locust Bean Gum at Different Concentrations of Mixture Using Cascade Model

Small amplitude oscillatory shear tests were performed to measure the elastic modulus of 1:1 xanthan–locust bean gum (X/L) mixed gels prepared with different total polymer concentrations (C = 0.1% to 3%). The critical concentration of X/L mixture was determined to be 0.15%. Based on the elasticity exponent (t) values, the concentration–modulus power–law relationship suggested the existence of two concentration regimes – a low concentration regime (0.15 ≤ C ≤ 0.5%) with tlow = 3.88 and a high concentration regime (0.5 ≤ C ≤ 3.0%) with thigh = 1.47. The elastic active network chain of X/L mixed gels was determined by the cascade model, and compared with the similar calculation based on the classical rubber elastic theory. The cascade model clearly showed the existence of nonideality parameter and enthalpic contribution to the X/L mixed gel. Practical applications The concentration dependence at the highest interaction might be useful for developing highly concentrated xanthan and locust bean gum mixture gels. Most studies of xanthan and locust bean gum mixtures focused only on the lower concentration regime. In this study the modulus at a higher concentration increased but eventually saturated.

Effect of Nano-Particles on Flow and Recovery of Polymer Nano-Composites in the Melt State

Abstract The effect of nano-particle geometry on flow and recovery of polymer melts based on ethylene vinyl acetate (EVA) was investigated. Two nano-particles, calcium carbonate (CaCO3) and montmorillonite clay, were used with concentrations between 2.5 and 15% by weight. First, by using small amplitude oscillatory shear and transient step shear tests, the linear and non-linear response of the nano-composites was studied. Then, to examine the structure recovery, the same behavior was studied on pre-sheared samples. The linear and non-linear data revealed that the effect of nano-particles in material flow is more important for anisometric particles which can be attributed to their ability to form a fractal structure controlling the rheological properties while spherical particles are not able to form such networks. Recovery experiments revealed that while nano-composites containing spherical particles have relatively similar response in subsequent tests, the rheological properties decreased significantly for platelet particles. The recovery results were also interpreted based on a filler-network mechanism and the reduction of the nano effect for anisometric particles was related to the breakdown of the filler network. These observations were validated by morphological investigations.

Semi‐empirical Relationship between Rupture Properties of Surimi Pastes and Failure Shear Stress of Surimi Gels at Different Moisture Contents

AbstractRupture properties, such as yield stress (YS) and the limit of linear viscoelastic region (LLVER), of Alaska pollock surimi pastes and failure shear stress (FSS) of Alaska pollock surimi gels were measured at various moisture contents. The stress‐stain behavior of surimi paste was measured by the small amplitude oscillatory shear test using a dynamic rheometer. The YS values and the applied stress at LLVER (ASLLVER) of surimi paste were analyzed based on the stress‐strain behavior during stress sweep test at 0.1 Hz. The FSS of surimi gels measured by the Hamann Torsion Gelometer showed a strong correlation with the moisture content (r2 = 0.95). YS and ASLLVER showed strong correlations with the moisture contents (r2 = 0.94 and 0.94, respectively). Such good correlations found at varied moisture contents suggest that the rupture properties of surimi paste may help estimate the texture properties of gel products.Practical ApplicationTexture properties play a major role in evaluating the quality of final products of surimi seafood, such as kamaboko and crabsticks. Failure shear stress from the torsion test is known as the most reliable value to reflect the hardness of surimi gels. Although the torsion test generates good correlations with sensory results, there are a few inevitable disadvantages: it possesses the complexity of measurements and the laborious sample preparation. Generally, the torsion test requires 1 day for gels and about 2 h for the testing specimen. Our study discovered a strong correlation of FSS of surimi gels with the rupture properties of surimi pastes, such as YS and the LLVER. Since the rupture properties of surimi pastes do not require gelation, it saves the testing time dramatically. Our new finding can be used to partially estimate the gel properties based on the paste properties, when enzymatic reactions in fish proteins are not considered.

Synthesis, surface characteristics, and electrochemical capacitance of Cu-doped carbon xerogel microspheres

Small-amplitude oscillatory shear tests were used to determine the rheological properties of a copper acetate-doped resorcinol–formaldehyde mixture at between 30 and 40°C. The apparent activation energy of the sol–gel transition was 76.6±0.6kJ/mol. Organic gel microspheres were only obtained when the sol was emulsified immediately before the gelation point and not at the gelation point itself, due to the fast gelation kinetics of the copper acetate-doped resorcinol–formaldehyde mixture. The microspherical shape was preserved after carbonization. Cu-doped carbon xerogel microspheres were steam-activated at 840°C. All samples comprised isolated well-formed microspheres, whose size increased with higher degree of activation. The surface area and porosity varied with the activation degree. Copper was detected as CuO, which acted as gasification catalyst during activation, and its size increased with higher activation degree. Electrochemical measurements were conducted with a three-electrode cell in 1M H2SO4. A very large volumetric capacitance, 146F/cm3, was found for the 30%-activated Cu-doped activated carbon xerogel, attributable to the high particle density resulting from the very compact packing of the microspheres. This sample also showed the lowest equivalent series resistance, due to its pore texture and high surface Cu content.

Correlation of chemical and physical properties of an Alaska heavy oil from the Ugnu formation

Physical properties and chemical components of an Alaska heavy oil from the Ugnu formation were studied by viscosity measurements, molecular beam mass spectrometry (MBMS), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR). The viscous samples rheology was measured between −10°C and 60°C using small amplitude oscillatory shear tests for viscosity, which generally decreases with increasing temperature. An activation energy of viscosity was measured as between 85 and 92kJ/mol. The screening method by combined use of FTIR, NMR and a time-resolved MBMS identified several component classes: water, cyclo/straight alkanes, alkenes, mono and multi-ring aromatic molecules, as well as small fractions of other organic molecules. Azeotropic behavior was observed between 100 and 250°C. The partial least squares correlation between molecular masses and the viscosity shows that water, alkylbenzene, and molecules with higher masses have positive correlations to the viscosity, but that the aliphatic molecules were anti-correlated.

Influence of some processing variables on the rheological properties of lithium lubricating greases modified with recycled polymers

This work deals with the effect that some processing variables and type of mineral lubricating oil (naphthenic and paraffinic) used exert on the rheological properties of lubricating greases modified with recycled polymers. In particular, the optimisation of recycled polymer addition at different lubricating grease processing stages and cooling profiles were studied. The influence of processing variables was evaluated by performing small-amplitude oscillatory shear (SAOS), viscous flow and thermal analysis tests. From the experimental results obtained, it may be concluded that the addition of recycled polymer significantly increases the values of linear viscoelasticity functions, especially when added immediately after the saponification reaction, during the heating stage, or at the beginning of the cooling stage (180°C). A combined stepwise cooling ramp, first at a high rate and then at a low rate, is more effective to achieve higher values of the rheological functions than the application of constant cooling rates in the final processing stage. The values of the rheological functions decrease as base oil viscosity increases and increase when using a naphthenic instead of a paraffinic oil of similar viscosity.

Influence of gellan gum concentration on the dynamic viscoelasticity and transient flow of fluid gels

Start-up at the inception of shear and flow interrupted experiments were carried out to illustrate the transient flow properties and thixotropic recovery of low-acyl gellan gum fluid gels prepared by a low-energy mechanical treatment. Small amplitude oscillatory shear tests were conducted to illustrate the rheological response under non-destructive conditions. Confocal laser scanning microscopy revealed the occurrence of a dispersion of gel-like domains in a continuous phase. Rheological methods were used to check that the samples characterised were free of thermo-mechanical history effects prior starting the transient flow tests. Start-up shear flow experiments at 10 s −1 resulted in a nearly instantaneous sharp rise of viscosity until a peak value was reached before it dropped following a sum of two first-order kinetic equations. The kinetic coefficients as well as the relative fall in viscosity were found to increase with gellan concentration. The equilibrium modulus as well as the peak and steady-state viscosities scaled with the gellan concentration following a power law equation with a characteristic exponent of about 2.0. Conversely, the degree of thixotropic recovery after a rest time of 10 s went down as gellan concentration increased, emphasising the need to balance both effects when formulating gellan fluid gels as stabilisers. The results obtained do a better job of highlighting the importance of peak viscosity than steady-state viscosity when data for pump selection and calculation are required.

Bulk and interfacial viscoelasticity in concentrated emulsions: The role of the surfactant

The aim of this study was to investigate and compare bulk and interfacial viscoelasticity of emulsions stabilized with two surfactants of a markedly different nature: the ionic phospholipids mixture Epikuron 145V and the steric emulsifier Pluronic F68. Emulsions of olive oil in water were prepared by high-pressure homogenization using only one of these surfactants. The impact of the surfactant used on the final linear viscoelastic properties was investigated by means of small-amplitude dynamic oscillatory shear tests, obtaining the values of the storage and loss moduli as a function of frequency, as well as by retardation and relaxation essays. Our results show that for concentrated emulsions, the viscoelastic properties are considerably different depending on which surfactant is used, i.e., the employed surfactant influences to a major extent the bulk rheological properties. In order to explain these differences, an interfacial study of the adsorbed surfactant layers has been carried out, measuring interfacial tension and dilatational viscoelasticity by means of the pendant drop technique. A correlation between the results obtained in bulk and interface has been found.

RHEOLOGICAL PROPERTIES OF RICE STARCH-MESONA BLUMES GUM MIXTURES

The effects of Mesona Blumes gum (MBG) at 0, 0.1, 0.35, 0.5, 0.7% (w/w, d.b.) on rheological properties of rice starch pastes (6%, w/w) were investigated. Rice starch–MBG mixtures had pseudoplastic flow behaviors (0.17 ≤ n ≤ 0.24). The effect of temperature (25–65C) on apparent viscosity (η50) was described by Arrhenius equation. Ea values (16.8–22.3 kJ/mol) of rice starch–MBG mixtures varied considerably, indicating a temperature-dependence. Small amplitude oscillatory shear tests at 25C have been modeled by natural logarithm of storage modulus, loss modulus and angular frequency. It was found that rice starch–MBG pastes displayed true gel like behavior. The dynamic (η*) and steady shear (ηa) viscosities at different MBG concentrations followed the Cox–Merz superposition rule with the application of shift factor (0.0307 ≤ α ≤ 0.114) (R2 = 0.99). Scanning electronic micrographs of these mixtures revealed that the thickness of the network wall increased and the porosity of the network decreased with MBG addition. PRACTICAL APPLICATIONS Rice starch and Mesona Blumes gum mixtures might be used as a fat-replacer, meat binder or jelly food. Therefore, it is necessary to investigate the rheological properties of such a mixture. Through steady and dynamic shear rheological experiments, the regularity of MBG and rice starch interaction will be used to guide our application. Also, it might be predicted by Cox–Merz superposition rule to show what would be the optimal ratio between these two macromolecules. Therefore, the microstructure of these macromolecular mixtures was investigated by scanning electronic micrographs to further understand their rheological properties.

Use of Konjac glucomannan as additive to reinforce the gels from low-quality squid surimi

This paper reports a study of the influence of a Konjac glucomannan aqueous dispersion ( KAD) as ingredient, at different alkalinity levels, on the thermal stability of low-quality squid surimi ( Dosidicus gigas) and the viscoelastic properties of its gel. An increase in elastic ( G ′) and viscous ( G ″) moduli at T < 50 °C, reflecting protein aggregation, and a strong decrease at T > 50 °C, reflecting structural damage, were observed in thermal gelation profiles of low-quality squid surimi. The contribution of 1% KAD (10%) to enhancement of gelation ability was assessed by evaluating the viscoelastic properties of the gels, with and without KAD, at increasing alkalinity levels. Gels with KAD at high-pH had the best rheological properties. Small amplitude oscillatory shear (SAOS) tests showed a significant decrease in rigidity, an increase in strain amplitude and a decrease in the frequency-dependence of G ′ and G ″. These results were in agreement with instrumental texture analyses, meaning that KAD may be used to overcome the negative effect of the poor protein functionality of low-quality squid surimi and achieve better gels from them.

Nonlinear Viscoelastic Response of Thermoplastic-Elastomer Melts

Observations are reported on thermoplastic elastomer (ethylene-octene copolymer) melt in small-amplitude shear oscillatory tests and start-up shear tests with various strain rates in the interval of temperatures between 120 and 210 - C. Based on the concept of heterogeneous non-affine polymer networks, constitutive equations are developed for the thermo-mechanical behavior of a melt at three- dimensional deformations with finite strains. Adjustable parameters in the stress- strain relations are found by fitting the experimental data. The model is applied to the analysis of Poiseuille flow. The effects of temperature and pressure gradient on the steady velocity profile are studied numerically.

Influence of water content, time, and temperature on the rheological behavior of polyethylene terephtalate

AbstractIn this work, the main factors affecting the rheological behavior of polyethylene terephtalate (PET) in the linear viscoelastic regime (water content, time delay before test, duration of experiment, and temperature) were accessed. Small amplitude oscillatory shear tests were performed after different time delays ranging from 300 to 5000 s for samples with water contents ranging from 0.02 to 0.45 wt %. Time sweep tests were carried out for different durations to explain the changes undergone by PET before and during small amplitude oscillatory shear measurements. Immediately after the time sweep tests, the PET samples were removed from the rheometer, analyzed by differential scanning calorimetry and their molar mass was obtained by viscometry analysis. It was shown that for all the samples, the delay before test and residence time within the rheometer (i.e. duration of experiment) result in structural changes of the PET samples, such as increase or decrease of molar mass, broadening of molar mass distribution, and branching phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Influence of low calcium and low pH on melting characteristics of model Raclette cheese

The aim of this study was to demonstrate the influence of calcium (Ca) reduction on model Raclette cheese meltability using different technological and chemical methods. Analysis was carried out on the detailed chemical, textural and rheological properties of six different model Raclette cheeses: control Raclette cheese manufacture (CON); pre-ripening (PRE) of the cheese milk; and addition of either 50 or 25 g of citric acid to the wash water (CA50 and CA25) and addition of either 70 or 35 g of lactic acid to the wash water (LA70 and LA35). The compositional analysis of the samples was carried out within the first 24 h of manufacture and after 14 weeks of ripening. In particular, total calcium, insoluble calcium (Insol Ca), nitrogen fractions and pH were examined as they were considered important parameters for meltability. Total Ca and Insol Ca were both remarkably reduced in CA50 and CA25, and were increased in PRE, LA70 and LA35 compared to the CON. The results of this study suggest that citric acid in the wash water lowered the pH value of the Raclette cheese and chelated Ca from the colloidal calcium phosphate, but also changed the rheologically determined melting properties. Various parameters of the small amplitude oscillatory shear test as well as the increase in the force in the compression test and the elevated softening and dropping points all indicated a firmer texture of the CA50 and CA25 cheeses. However, the sensory data for CA50 revealed good “viscous”, “ropy” and “gummy” properties of the melted cheese. The apparent discrepancy between the sensory sensation and the rheological data seems to be related to changes in the water-binding capacity of the protein matrix.

Engineering investigations on the potentiality of the thermoformability of HDPE charged by wood flours in the thermoforming part

AbstractA dynamic finite element method is used to analyze the thermoformability of composites containing wood and a thermoplastic matrix for five different proportions of wood flour. Linear viscoelastic properties can be obtained by small amplitude oscillatory shear tests and the viscoelastic behavior is characterized using the Lodge model. To account for enclosed gas volume, which inflates the thermoplastic composite membrane, a thermodynamic approach is used to express the external work in terms of a closed volume. Pressure load is deduced by thermodynamic law using the Redlich–Kwong gas equation. The Lagrangian method together with the assumption of membrane theory is used in the finite element implementation. In addition, the influence of air flow on thickness and stress and the energy required to form a thin polymeric part in the thermoforming process are analyzed for five different proportions of wood flour in the HDPE material. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Dynamic Rheological Behavior of Isotactic Polypropylene Filled With Nano-Calcium Carbonate Modified by Stearic Acid Coating

2 wt% and 6 wt% stearic acid (SA)-coated calcium carbonate (CaCO3) nanoparticles were compounded with isotactic polypropylene (iPP). Small-amplitude oscillatory shear tests were used to study the linear viscoelastic properties of the nanocomposite melts. The filler loading at which the composites exhibited the terminal modulus plateau was found to be much lower in the 6 wt% SA-coated particle composites than in the 2 wt% counterpart, and at the same filler content, apparently higher dynamic moduli and complex viscosities at low frequencies were shown in the former. The characteristics of pseudo-solid-like behavior almost disappeared in the 2 wt% SA-coated particle composites as the gap distance increased but were still observed in the 6 wt% counterpart. The results indicate that the dispersion of nanoparticles played a critical role in the motion of the macromolecular chains. At the same filler loading, the mobility of the iPP melts was more severely restricted by properly coated and well-dispersed nanoparticles than by aggregates due to insufficient coating.

Influence of granulometry and organic treatment of a Brazilian montmorillonite on the properties of poly(styrene‐co‐n‐butyl acrylate)/layered silicate nanocomposites prepared by miniemulsion polymerization

AbstractThe influence of granulometry and organic treatment of a Brazilian montmorillonite (MMT) clay on the synthesis and properties of poly(styrene‐co‐n‐butyl acrylate)/layered silicate nanocomposites was studied. Hybrid latexes of poly(styrene‐co‐butyl acrylate)/MMT were synthesized via miniemulsion polymerization using either sodium or organically modified MMT. Five clay granulometries ranging from clay particles smaller than 75 μm to colloidal size were selected. The size of the clay particles was evaluated by specific surface area measurements (BET). Cetyl trimethyl ammonium chloride was used as an organic modifier to enhance the clay compatibility with the monomer phase before polymerization and to improve the clay distribution and dispersion within the polymeric matrix after polymerization. The sodium and organically modified natural clays as well as the composites were characterized by X‐ray diffraction analysis. The latexes were characterized by dynamic light scattering. The mechanical, thermal, and rheological properties of the composites obtained were characterized by dynamical‐mechanical analysis, thermogravimetry, and small amplitude oscillatory shear tests, respectively. The results showed that smaller the size of the organically modified MMT, the higher the degree of exfoliation of nanoplatelets. Hybrid latexes in presence of Na‐MMT resulted in materials with intercalated structures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009