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Rheological Behaviour (rheological + behaviour)
Selected AbstractsRHEOLOGICAL BEHAVIOUR OF CLARIFIED MANGO JUICE CONCENTRATESJOURNAL OF TEXTURE STUDIES, Issue 3 2000NGASEPPAM IBOYAIMA SINGH ABSTRACT The rheological behaviour of clarified mango juice was measured at temperatures 15,85C and concentrations 15,66 °Brix, using a rotoviscometer. Mango juice free of pectin and pulp behaves as a Newtonian fluid. The effect of temperature can be described by an Arrhenius-type equation. The activation energy for viscous flow was in the range of 1.64,8.44 kcal/g-mol, depending on the concentration. The effect of concentration was modelled better by an exponential relationship than a power-law relationship. Simple equations are proposed for describing the combined effect of temperature and soluble solids content on the juice viscosity. [source] Rheological behaviour of weaning food formulations as affected by addition of maltINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 10 2006Mamudu Halidu Badau Summary Eight weaning food formulations were prepared from the mixture of pearl millet, cowpea and groundnut in the ratio of 70:20:10. The viscosities of gruels from the eight weaning food formulations were determined at eight shear rates and five temperatures, and data obtained were subjected to power-law and Arrhenius equations. The viscosity of the weaning food gruels decreased with increase in shear rate and temperature. The gruels from the eight weaning food formulations exhibited pseudoplastic behaviour. The power-law indices (,n' values) were significantly (P < 0.05) affected by the formulations and changes in temperature. Weaning food formulations that had no malt showed the least sensitivity to temperature, while the one that had 5% ICMV-IS 94206 malt showed the highest. The correlation coefficient ranged from ,0.9993 to ,0.9524, showing that the power-law model adequately described the viscosity and shear rate characteristics of the weaning food gruels. [source] Rheological behaviour of sour pomegranate juice concentrates (Punica granatum L.)INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 2 2005Ahmet Kaya First page of article [source] Rheological behaviour and colour changes of ginger paste during storageINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 3 2004Jasim Ahmed Summary Ginger paste was prepared from fresh ginger by addition of 8% common salt and citric acid. The paste was thermally processed and packed in glass, polyethyleneterephthalate or high-density-polyethylene containers and stored at 5 ± 1 and 25 ± 1 °C for 120 days. The rheological characteristics of the paste were studied by using a computer controlled rotational viscometer over the temperature range of 20,80 °C. Samples were subjected to a programmed shear rate, increasing linearly from 0 to 200 s,1 in 3 min, followed by a steady shear at 200 s,1 for 3 min and finally decreasing linearly from 200 to 0 s,1 in 3 min. Ginger paste exhibited pseudoplasticity with yield stress and flow adequately described by the Herschel,Bulkley model. The yield stress decreased exponentially with process temperature and ranged between 3.86 and 27.82 Pa. The flow behaviour index (n) varied between 0.66 and 0.82 over the temperature range. Both consistency index and apparent viscosity decreased with increase in temperature and the process activation energies were found to be in the range of 16.7 to 21.9 kJ mol,1. The effect of temperature was significant (P < 0.05) on the Hunter colour combination value of the paste during storage; however it was not affected by type of packaging material (P > 0.05). It is recommended that ginger paste is stored at 5 ± 1 °C in polyethyleneterephthalate or glass containers. [source] Modelling the hysteresis in the velocity pattern of slow-moving earth flows: the role of excess pore pressureEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2005T. W. J. van Asch Abstract This paper describes the velocity pattern of a slow-moving earth flow containing a viscous shear band and a more or less rigid landslide body on top. In the case of small groundwater fluctuations, Bingham's law may describe the velocity of these slow-moving landslides, with velocity as a linear function of excess shear stress. Many authors have stated that in most cases a non-linear version of Bingham's law best describes the moving pattern of these earth flows. However, such an exponential relationship fails to describe the hysteresis loop of the velocity, which was found by some authors. These authors showed that the velocity of the investigated earth flows proved to be higher during the rising limb of the groundwater than during the falling limb. To explain the hysteris loop in the velocity pattern, this paper considers the role of excess pore pressure in the rheological behaviour of earth flows by means of a mechanistic model. It describes changes in lateral internal stresses due to a change in the velocity of the earth flow, which generates excess pore pressure followed by pore pressure dissipation. Model results are compared with a hysteresis in the velocity pattern, which was measured on the Valette landslide complex (French Alps). Copyright © 2005 John Wiley & Sons, Ltd. [source] The characterization of the semi-solid W/O/W emulsions with low concentrations of the primary polymeric emulsifierINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 2 2005D. Vasiljevic Synopsis Semi-solid multiple W/O/W emulsions with low concentrations (0.8, 1.6 and 2.4% w/w) of lipophilic polymeric primary emulsifier PEG-30-dipolyhydroxystearate (PDHS) have been formulated. Both emulsions, primary and multiple, were prepared with high content of inner phase (,1 = ,2 = 0.8). All the formulations differ only in the lipophilic emulsifier concentration. Evaluating several parameters such as macroscopic and microscopic aspect, droplet size, accelerated stability under centrifugation and flow and oscillatory rheological behaviour, assessed the multiple systems. It is possible to formulate the semi-solid W/O/W multiple emulsions with low concentrations of PDHS as the primary emulsifier. It appeared that the highest long-term stable multiple emulsion with the lowest droplet size, the highest apparent viscosity and highest elastic characteristic, was the sample with the highest concentration (2.4% w/w) of the primary emulsifier. Résumé Les émulsions H/L/H semi-solides ont été formulées avec les concentrations basses (0.8, 1.6 et 2.4% m/m) de l'émulsifiant lipophile polymèrique PEG-30-dipolyhydroxystearate. Les émulsions simples et multiples ont été préparées avec la teneur élevée en phase intérieure (,1 = ,2 = 0.8). La teneur en émulsifiant lipophile était la seule différence entre ces formulations. L'aspect macroscopique et microscopique, la taille de globules, la stabilité physique déterminée par le test de centrifugation ainsi que le comportement rhéologique (rhéologie d'écoulement et oscillatoire) ont permis l'évaluation des émulsions multiples. Il est possible de formuler les émulsions H/L/H semi-solides multiples avec les concentrations basses de PEG-30-dipolyhydroxystearate comme émulsifiant primaire. Il a été découvert que l'émulsion H/L/H multiple avec le plus grand pourcentage (2.4% m/m) de l'émulsifiant primaire a le diamètre de globule le plus petit, la plus grande viscosité apparente et le plus grand module élastique ainsi que la plus longue stabilité. [source] Utilisation de la méthode du cubic simplex pour l'optimisation de la formulation a froid d'une emulsion de thioglycolate de calciumINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 5 2003N. Moulai-Mostefa Synopsis The aim of this work relates to the optimization of a cold formulation of a depilatory emulsion containing thioglycolate of calcium, which presents the same characteristics as a reference product. To lead to this objective, a cubic simplex method was used. A preliminary formulation was preformed to evaluate the influence of each factor on the process formulation. The depilatory creams carried out present a rheological behaviour described by the model of Hershell,Bulkely, whose parameters are considered as responses of the optimizing system. This strategy allows both reducing and optimizing the number of experiments. The rheological measurements and the tests of stability showed that the use of an emulsifying polymer led to obtain a stable depilatory cream with a good effectiveness at a strong pH value. Résumé L'objectif principal de ce travail concerne l'optimisation de la formulation à froid d'une émulsion dépilatoire à base de thioglycolate de calcium, présentant les mêmes caractéristiques qu'un produit de référence. Pour aboutir à cet objectif, on a utilisé la méthode du cubic simplex. L'étude de préformulation a permis d'évaluer avec précision l'influence des différents facteurs sur le processus de formulation. Les crèmes dépilatoires réalisées présentent un comportement rhéologique décrit par le modèle de Hershell,Bulkley dont les deux paramètres sont considérés comme réponses du système à optimiser. Les plans d'expériences utilisés ont permis de restreindre le nombre d'essais à réaliser. Les résultats expérimentaux de l'analyse rhéologique et les tests de stabilité ont montré que l'utilisation d'un polymère émulsifiant conduit à l'obtention d'une crème dépilatoire stable possédant une bonne efficacité aux fortes valeurs du pH. [source] The rheological behaviour of low fat soy-based salad dressingINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 12 2008Chi Zhang Summary Low fat soy-based salad dressings were formulated with different oil levels (3%, 13% and 23%) and emulsifiers (whey protein concentrate, soy-lecithin and sodium caseinate) using either blender or ultra-turrax (UT) homogeniser. Results showed that the rheological behaviour of these samples were highly dependent on the oil content, emulsifiers and blending methods. The UT method produced samples with better viscosity and have droplet size of 2,100 ,m. Samples containing higher oil level have higher viscosity, smaller droplet size, larger G, and G, values. All samples show a shear-thinning effect and larger G, than G,, indicating the elastic nature of the samples. A quantity Q(t)% was applied to estimate the elasticity and the values were found to be in the range 22.8,85.2%. G, and G, were found to decrease with increased temperature. However, tan , increased slightly with temperature; the values ranged from 0.2 to 0.4 at 5 °C to 0.3,0.5 at 25 °C. Current results demonstrated that the formulated samples have good stability compared with commercial products. [source] Rheological study of ternary mixtures and pectic gels of red fruit pulpsINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 6 2007Charles Windson Isidoro Haminiuk Summary In this work, the rheological behaviour of ternary mixtures of strawberry, blackberry and raspberry pulps in steady shear was studied using the response surface methodology. In addition, the rheology of pectic gels extracted from these pulps was investigated by means of oscillatory shear tests. The flow curves were adequately described by the rheological model of Herschel,Bulkley. All the formulations analysed exhibited shear-thinning behaviour. The rheological responses were influenced by the difference in pulp proportions and also by the temperatures (20 and 60 °C). The quadratic and cubic models used to fit the response were considered suitable owing to the higher values of determination coefficient (R2). The pectic gels from strawberry, blackberry and raspberry showed a strong gel character, with strawberry presenting the stronger gel, which was confirmed by the Cox,Merz experiment, degree of esterification and average molecular weight data. [source] The effect of high pressure treatment on rheological characteristics and colour of mango pulpINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 8 2005Jasim Ahmed Summary The effect of high-pressure (HP) treatment (100,400 MPa for 15 or 30 min at 20 °C) on the rheological characteristics and colour of fresh and canned mango pulps was evaluated. Differences were observed in the rheological behaviour of fresh and canned mango pulps treated with HP. Shear stress,shear rate data of pulps were well described by the Herschel,Bulkley model. The consistency index (K) of fresh pulp increased with pressure level from 100 to 200 MPa while a steady decrease was noticed for canned pulp. For fresh pulp the flow behaviour index decreased with pressure treatment whereas an increasing trend was observed with canned pulp. Storage and loss moduli of treated fresh pulp with HP increased linearly with angular frequency up to 200 MPa for a treatment time of 30 min while a steady decreasing trend was found for processed pulp. No significant variation in colour was observed during pressure treatment. [source] In vitro percutaneous penetration of acyclovir from solvent systems and Carbopol 971-P hydrogels: Influence of propylene glycolJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2005O. Díez-Sales Abstract The mechanism underlying propylene glycol (PG) effects on acyclovir (ACV) penetration through human epidermis were studied. Solvent systems and Carbopol gels containing increasing percentage of PG (from 0% to 70%, w/w) were used. Viscosity studies of both vehicles were carried out to characterise the influence of rheological behaviour. In solvent systems skin permeation values of ACV increase as the concentration of PG increase yielding a maximum enhancement ratio (ER,=,10) for 70% PG. The release rate of ACV from gels was determined. Higuchi's model was used to estimate the apparent diffusion coefficient of the drug. These values show a decrease as the content of PG in the vehicle increases; this effect could be attributed to the increase of the viscosity in the diffusional pathway. When gels are used skin permeation values of ACV were smaller than those of the solvent systems. This could be attributed to the network structure created by the polymer that increases the length of the diffusional pathway. The maximum ER (=6.8) was for Carbopol gel containing 50% PG. Therefore, these gels can be considered candidates for further research to confirm their usefulness as delivery systems for ACV topical formulations. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1039,1047, 2005 [source] The effects of refined barley ,-glucan on the physico-structural properties of low-fat dairy products: curd yield, microstructure, texture and rheologyJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 10 2004Carmen M Tudorica Abstract The beneficial role of dietary fibre in human nutrition has lead to a growing demand for incorporation of novel fibres, particularly barley ,-glucans, into foods. Barley ,-glucans are regarded as dietary fibre ingredients that are partially soluble in water. The aim of the present work was to investigate the possibility of using barley ,-glucan in milk systems in relation to the coagulation properties of milk containing ,-glucan, and to the rheology, texture and microstructure of fresh curds. The rate of coagulation and optimum coagulum cutting time were evaluated using rheological measurements. Results show that coagulation/gelation time of the milk can be reduced significantly with the incorporation of ,-glucan; curd yield increased and the viscoelastic properties of the curd were altered with ,-glucan additions. The relationships between curd rheological behaviour and its microstructure are discussed in relation to use of novel hydrocolloids in dairy processing. The results suggest that barley ,-glucan has the potential to be used as a fat replacer in low-fat dairy systems. Copyright © 2004 Society of Chemical Industry [source] Effect of surface roughness on elastohydrodynamic traction.LUBRICATION SCIENCE, Issue 4 2005Part Abstract To investigate the performance of a traction-drive toroidal continuously variable transmission, the traction characteristics under partial elastohydrodynamic lubrication contact were calculated theoretically based on roller test results. A calculation model was constructed for considering the effects of surface roughness on performance. The model incorporated a viscoelastic and elastic-plastic model using a nonlinear Maxwell model to represent the rheological behaviour of the traction fluid. The validity of the model was confirmed by its good agreement with the experimental results described in Part 1 of this paper. Various calculations were made to investigate the effect of surface roughness on traction under the operating conditions of an actual traction drive. The results indicated that the effect of surface roughness on durability could not be ignored. [source] Study of the Segmental Dynamics in Semi-Crystalline Poly(lactic acid) using Mechanical SpectroscopiesMACROMOLECULAR BIOSCIENCE, Issue 4 2005João F. Mano Abstract Summary: The glass transition of poly(L -lactic acid) (PLLA) occurs not far above typical service temperatures (room or body temperatures) which has consequences on the material properties during its use, such as damping or the occurrence of structural relaxation. This work aims at characterising the glass transition dynamics of a semi-crystalline PLLA using both dynamic mechanical analysis (DMA) and thermally stimulated recovery (TSR). The main viscoelastic parameters have been characterised at 1 Hz using DMA and the master curve obtained after isothermal experiments at different temperatures provided a full picture of the solid-state rheological behaviour throughout a wide frequency range. The activation energies calculated from the shift factors agree with the TSR ones, exhibiting a maximum near the Tg. Above the Tg, the results can be described with the WLF model. In the glassy state, the activation energy decreases with decreasing temperatures being always higher than the prediction of the Adam and Gibbs theory, at least down to temperatures 30,°C below the Tg. This suggests the existence of non-arrested degrees of freedom in the glassy state, being consistent with the existence of a significant degree of cooperativity in the TSR results. Temperature dependence of the apparent activation energy across the glass transition. [source] Amphiphilic polyelectrolyte for stabilization of multiple emulsions,POLYMER INTERNATIONAL, Issue 4 2003Fanny Michaut Abstract Multiple emulsions are complex thermodynamically unstable systems where both types of emulsion coexist. We investigated the stability behaviour of water-in-oil-in-water (W/O/W) emulsions formulated with a hydrophobically modified poly(sodium acrylate) emulsifier at the outer interface and a monomeric surfactant (span 80) at the inner interface. Their stability was tested through release kinetics of a marker (NaCl) initially encapsulated in the aqueous droplets, and by rheology. Slow release rates and remarkably long shelf-life were obtained compared to typical multiple emulsions stabilized by two commonly used surfactants (span 80 and tween 20). In addition, we prepared stable highly concentrated multiple emulsions. Their rheological behaviour indicated that the internal interface was essentially covered with span 80. Thus, transportation of the polymer across the oil phase is limited, which in turn explains, at least partially, the stability improvement in the presence of the polymeric emulsifier. Finally, the long lifetime of the emulsions allowed study by diffusing wave spectroscopy of the interactions between the droplets and the globule surface which are important for understanding the destruction mechanisms of multiple emulsions. © 2003 Society of Chemical Industry [source] HYPERHOMOCYSTEINAEMIA AND MEMBRANE FLUIDITY OF RED BLOOD CELLS IN NORMOTENSIVE AND HYPERTENSIVE MEN: AN ELECTRON PARAMAGNETIC RESONANCE INVESTIGATIONCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 2007Kazushi Tsuda SUMMARY 1The purpose of the present study was to assess the possible link between plasma homocysteine and membrane fluidity in normotensive and hypertensive men. 2The membrane fluidity (a reciprocal value of membrane microviscosity) of red blood cells (RBC) was measured using an electron paramagnetic resonance and spin-labelling method. The membrane fluidity of RBC was decreased in hypertensive compared with normotensive men. 3Total plasma homocysteine levels were significantly higher in hypertensive men than normotensive men. In contrast, plasma levels of nitric oxide (NO) metabolites were significantly lower in hypertensive men than in normotensive men. The decreased membrane fluidity of RBC was associated with hyperhomocysteinaemia and reduced plasma levels of NO metabolites. 4The results of the present study suggest that hyperhomocysteinaemia may have a role in modulating the rheological behaviour of RBC and microcirculation in men by, at least in part, reducing NO bioavailability. [source] | ||||||||||||||||