Rheological Characterization (rheological + characterization)

Distribution by Scientific Domains

Selected Abstracts


ABSTRACT The rheology of Carboxymethylcellulose (CMC) solutions, which are widely used as carrier fluids in aseptic processing simulations, was studied. Effects such as time dependency, recovery, and viscoelasticity were studied. A model was developed to determine the apparent viscosity of CMC solutions as a function of shear rate, temperature, and concentration. The model can be used in process design from both a fluid mechanics standpoint and a heat transfer standpoint. It was found that the solutions behaved as pseudoplastic fluids that were irreversibly thixotropic and also viscoelastic. [source]


ABSTRACT Incorporating air bubbles into foods is a technical challenge, and in all cases, the fabrication of a foam goes through a "wet foam" stage, where bubbles are diluted in the food matrix and require stabilization. Sometimes, the end product is itself a wet foam, and a popular example is ice cream. This article describes a study of structural aspects of wet foams, where the continuous phase is a fluid, by means of dynamic rheological tests. The effects of formulation and processing conditions on aerated food foams are studied, and an example is presented for ice cream mix. The incorporation of gas bubbles at volume fractions of 50% or less modifies moderately the bulk rheological properties, and their effect can be predicted by the foam limit case. The continuous phase dominates to a great part the bulk's rheological behavior, and in the case of food systems, it stems from the presence of polysaccharide thickeners. PRACTICAL APPLICATIONS This work presents an alternative approach to study the rheological properties of short life and difficult-to-sample products, such as wet food foams, in a rheo-reactor. Through the analysis of mechanical properties in oscillatory regime, the structure and stability of wet food foams can be characterized immediately after being fabricated in situ. This work presents new insights on the foaming step of ice cream mix (decoupled from the freezing step), and shows how the mechanical properties are affected by the incorporation ofbubbles, by process conditions and by the presence of thickeners and emulsifiers. This work can be a valuable guide to decide on optimal process and formulation to fabricate wet food foams (e.g., ice cream, aerated desserts) with specific mechanical properties and stability. [source]

Rheological Characterization of a Gel Formed During Extensive Enzymatic Hydrolysis

D. Doucet
ABSTRACT Extensive hydrolysis of whey protein isolate (WPI) by Alcalase 2.4L® caused a dramatic increase in turbidity and viscosity. A gel was formed after the degree of hydrolysis was , 18%, coinciding with < 16%,-lactoglobulin and < 4%,-lactalbumin remaining unhydrolyzed. Heat-induced and enzyme-induced WPI gels were compared. Frequency and strain dependence indicated that both gels could be considered as strong, physical gels. [source]

Rheological characterization of hair shampoo in the presence of dead sea salt

B. Abu-Jdayil
Synopsis In Jordan, a growing industry has been established to produce different types of Dead Sea (DS) cosmetics that have DS salt (contains mainly NaCl, KCl, and MgCl2) in their formulas. In this work, the effect of DS salt on the rheology of hair shampoo containing the sodium lauryl ether sulfate as a main active matter was studied. The effects of DS salt and active matter concentration, and the temperature and time of salt mixing, on the rheological properties of hair shampoo were investigated. The salt-free shampoo showed a Newtonian behavior at ,low active matter' (LAM) and shear thinning at ,high active matter' (HAM). The presence of DS salt changed the rheological behavior of LAM shampoo from Newtonian (for the salt-free shampoo) to shear thinning. On the other hand, the behavior of HAM shampoo switched from shear thinning to Newtonian behavior in the presence of high concentration of DS salt. The addition of DS salt increased the apparent viscosity of shampoo to reach a maximum value that corresponded to a salt concentration of 1.5 wt.%. Further addition of DS salt led to a decrease in the shampoo viscosity to reach a value less than that of the salt-free sample at high salt concentration. Changing the mixing temperature (25,45 °C) and mixing time (15,120 min) of DS salt with shampoo has no significant influence on the rheological behavior. However, the mixing process increased the apparent viscosity of salt-free shampoo. The power law model fitted well the flow curves of hair shampoo with and without DS salt. Résumé En Jordanie, une industrie croissante a été mise en place afin de produire différents types de cosmétiques à base de sels de la Mer morte (DS) contenant ces sels (pour la plupart,principalement NaCl, KCl, MgCl2) dans leurs formules. Dans ce présent travail, l'effet de ces DS sur la rhéologie d'un shampooing à base de lauryl ether sulfate de sodium comme actif principal, a étéétudié. Les effets de ce sel de DS et de la concentration en matière active ainsi que la température et le temps de mélange du sel sur les propriétés rhéologiques du shampooing ont été appréhendés. Le shampooing exempt de sel montrait un comportement Newtonien à basse concentration d'actif (LAM) et une rhéo-fluidification à haute teneur en actif (HAM). La présence de sel de DS a changé le comportement rhéologique du shampooing LAM, du Newtonien (pour le shampooing sans sel) vers la rhèo-fluidification. Par ailleurs, le comportement du shampooing HAM est passé de la rhèo-fluidification au Newtonien en présence de fortes concentrations de sels de DS. L'addition de sels de DS a accru la viscosité apparente jusqu'à une valeur maximale correspondant à 1.5% (w/w). Des additions ultérieures de sel ont conduit à une chute de la viscosité jusqu'à une valeurs inférieure à celle du shampooing sans sel. Le changement de la température de mélange du sel (25 °C à 45 °C) et du temps de mélange (15 à 120 min) du sel avec le shampooing n'a aucune influence significative sur le comportement rhéologique. Cependant, le procédé de mélange a augmenté la viscosité apparente du shampooing sans sel. La modélization par puissance a correctement ajusté les courbes d'écoulement du shampooing avec et sans sel de DS. [source]

Rheological characterization of HDPE/sisal fiber composites

Smita Mohanty
The present paper summarizes an experimental study on the molten viscoelastic behavior of HDPE/sisal composites under steady and dynamic mode. Variations of the melt viscosity and die swell of the composites with an increase in shear rate, fiber loading, and coupling agent concentration have been investigated using capillary rheometer. The shear rate , at the wall was calculated using Rabinowitsch correction applied to the apparent shear rate values. It was observed that the melt viscosity of the composites increased with the addition of fibers and maleic anhydride-grafted PE (MAPE). Die swell of HDPE also decreased with the addition of sisal fibers and MAPE. Further, the dynamic viscoelastic behavior of the composites was measured employing parallel plate rheometer. Time,temperature superposition was applied to generate various viscoelastic master curves. Temperature sweeps were also carried out to study the flow activation energy determined from Arrhenius equation. The fiber,matrix morphology of the extrudates was also examined using scanning electron microscopy. POLYM. ENG. SCI., 47:1634,1642, 2007. © 2007 Society of Plastics Engineers [source]

Rheological characterization of schizophyllan aqueous solutions after denaturation,renaturation treatment

BIOPOLYMERS, Issue 4 2004
Yapeng Fang
Abstract Schizophyllan (SPG) with a molecular weight of 2.6×106, designated SPG-1, is denatured and then renatured at a concentration of 1.8 wt % by alkalization,neutralization. The prepared denatured,renatured samples (DRSPG-1) are diluted to various concentrations and equilibrated for 10 days before rheological and intrinsic viscosity measurements. When concentration (Cp) is above 0.75 wt %, DRSPG-1 aqueous systems have weak gel-type rheological properties. However, for 0.28 wt % , Cp , 0.65 wt % and Cp , 0.19 wt %, DRSPG-1 aqueous systems behave as power law fluids and Newtonian fluids, respectively, which are attributed to the moderate isotropy degree of DRSPG-1 chains. Furthermore, a critical overlap parameter of c*[,] = 1.2 is determined for DRSPG-1 in aqueous solutions, which is close to that of 1 for intact SPG in water while far smaller than that of 4.3 for SPG in DMSO. This is considered to be due to the strong interactions of DRSPG-1 chains in water, further confirmed by the intrinsic viscosity measurements in which the DRSPG-1 aqueous solution shows an abnormally large value of Huggins constant. Regarding the structure of DRSPG-1 weak gels, multiruns of dynamic strain sweep measurements suggest that the dominant structures are aggregates formed by hydrogen-bonding associations of DRSPG-1 chains rather than the permanent three-dimensional network. In addition, the step-shear rate tests are performed to study the thixotropic properties of DRSPG-1 aqueous systems. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004 [source]

Study of pseudo-multilayer structures based on starch-polycaprolactone extruded blends

Laurent Bélard
This article is focused on the analysis of the structure-process relationships of biodegradable materials. It is mainly focused on the analysis of phase separation phenomenon occurring during the extrusion of plasticized starch/polycaprolactone blends, in a slit die. Rheological characterizations are carried out, in-line in an instrumented slit die at the exit of the extruder and, out-line with different rheometers. In certain conditions, a pseudo-multilayer structure can be generated with a polyester rich skin. Then, Electron Spectroscopy for Chemical Analysis (ESCA) and Fourier Transformed Infrared Attenuated Total Reflectance (FTIR-ATR) analyses are conducted to evaluate semi-quantitatively the polyester surface enrichment. In the range of available shear rates, the phase separation is mainly driven by the molecular weight of polycaprolactone, linked to its molten state viscosity. Three zones of surface enrichment, dependent on the molecular weights, are identified. Above 60,000 g·mol,1, no surface enrichment could be detected; below 37,000 g·mol,1, the phase separation occurs with no dependence on the processing conditions; between these two limits, the phase separation depends on both, the formulation and the processing conditions. A correlation between the rheological measurements and the phase separation is given. A predictive criterion based on the viscous behavior of the blend is established. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source]

Synthesis and rheological characterization of graft copolymers of butyl and hydroxyethyl methacrylates on starches

Mariló Gurruchaga
Abstract To study the possibility of using some acrylic-grafted polysaccharides as matrix tablets, graft copolymers of butyl methacrylate and hydroxyethyl methacrylate on starch and on hydroxypropyl starch were synthesized. In this work, the effects of the different chemical compositions of the various synthesized graft copolymers on the hydrophilicity and rheological characteristics were examined. Water absorption values that ranged from 5 to 45% were obtained. Rheological testing determined with dispersions (5% w/w) in water showed that the graft copolymers formed weak gels of high viscosity. Moreover, the synthesized powders showed good flow and good compaction. These measurements pointed toward the possibility of their application for drug release. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

A Study of the Use of Oscillatory Flow to Characterize Isotactic and Syndiotactic Poly(propylene)s

Elena Rojo
Abstract Summary: A rheological characterization of poly(propylene)s (PP) of different tacticity, monomodal and bimodal molecular distribution and long chain branching (LCB), is presented. Loss factor , plotted as a function of the complex modulus G* allows to discriminate syndiotactic from isotactic PPs, as well as syndiotactic monomodal from bimodal samples. However, using such rheological plots is not effective to investigate the broadness of the molecular weight distribution and other rheological techniques are proposed. Isotactic and syndiotactic PPs submitted to electro beam irradiation give rise to thermorheological complexity, associated to LCB. The degree of LCB is estimated using complex viscosity results. Syndiotactic poly(propylene)s are more prone to give long branches than isotactic samples. A symptom of long chain branching is detected in irradiated syndiotactic PPs. [source]

Yield stress and rheological characterization of the low shear zone of an epoxy molding compound for encapsulation of semiconductor devices

Masaki Yoshii
In encapsulation molding of IC packages, the melt flow inside the cavity is generally controlled in a low shear to prevent wire sweep, and other molding defects. Therefore, it is important to evaluate the rheological properties of epoxy molding compounds (EMC) in a low shear zone including determining the yield stress. In this study, a newly specialized Parallel-Plate Plastometer for EMCs was built up. Using this plastometer, the yield stress and its temperature dependence were clarified, and the rheological properties in the low shear zone were evaluated. As a result, the rheological properties in a low shear zone of 0.1,10 s,1 were characterized using the Herschel,Bulkley viscosity model which introduced the yield stress, the Castro,Macosko equation as a dependency model of cure, and the WLF equation as a dependency model for temperature. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source]

2165: Microplasmin as an antiscarring agent for glaucoma surgery: translation into clinical application

E VANDEWALLEArticle first published online: 23 SEP 2010
Purpose Previously Microplasmin was investigated in a rabbit model for trabeculectomy. The combination of intracameral injections and topical drops of Microplasmin improved surgical outcome. The aqueous solution of Microplasmin used, was not optimized for use as drops or injections. Microplasmin is an autocatalytic enzyme which has a short half life when it is brought in conditions of 37°C and physiological pH. Therefore there is need for a more stable and longer acting formulation. Methods Firstly we will do pharmacological experiments to determine the rheological characterization of drug carriers with Carrier-med rheometer. Then we will define the purity of Microplasmin bulk drug substance by RP-HPLC. Finally, we will check the Microplasmin activity in the new obtained solutions by spectrophotometer. Secondly we will perform trabeculectomy in a rabbit model and administer the most qualified and optimized formulations. Postoperative clinical evaluation of IOP, bleb area, conjunctival vascularity and anterior chamber assessment will be performed. The eyes will be immunohistological investigated for collagen and inflammation. Conclusion Our previous data learned that the combination therapy of Microplasmin improved surgical outcome in a rabbit model, despite the fact that the formulation of Microplasmin was not optimized for use as drops or injections. Our proposed research project will optimize the formulation of Microplasmin for extended drug delivery and determine the optimal administration route and regimen. We believe that this project will allow us to further improve the positive animal data, translate this novel antifibrotic adjunctive therapy into clinical application, and thus improve the outcome after trabeculectomy in patients. [source]