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non-Newtonian Behavior (non-newtonian + behavior)
Selected AbstractsNumerical simulation of the microscale impregnation in commingled thermoplastic composite yarnsADVANCES IN POLYMER TECHNOLOGY, Issue 2 2010R. Gennaro Abstract The impregnation of a glass woven fabric with an amorphous polyethylene terephthalate copolymer (PET- g) matrix was investigated using a finite element (FE) model for interbundle and intrabundle flow of the matrix. Micrographs of samples obtained by film stacking of PET- g to impregnate the glass fabric have confirmed the occurrence of interbundle and intrabundle flow, taking place as separate steps. On the basis of this evidence, two different mechanisms for the fiber impregnation were postulated. The first flow process is associated with a macroscale interbundle impregnation, whereas the second is associated with microscale intrabundle impregnation. Two different FE models were developed to simulate the microscopic and macroscopic flow of the matrix, considering a large number of different random fiber arrangements. Both models could account for the non-Newtonian rheological behavior of the thermoplastic matrix. The microscale impregnation of fibers was simulated by using randomly spaced and nonoverlapping unidirectional filaments. The effect of the number of filaments and the number of random distributions necessary to achieve an adequate accuracy of the method was assessed. The results obtained from the simulation showed that at low pressures, the polymer melt exhibits Newtonian behavior, which makes it possible to predict the tow permeability by the Darcy law. A more difficult situation arises at high pressures because of the non-Newtonian behavior of the melt. This requires the introduction of a value for the permeability that is also dependent on the rheological properties of the melt. The same non-Newtonian behavior of the matrix was observed for macroscale impregnation of bundles. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:122,130, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20179 [source] Effects of ,-Glucan Addition to a Probiotic Containing YogurtJOURNAL OF FOOD SCIENCE, Issue 7 2007T. Vasiljevic ABSTRACT:, This study investigated the effects of addition of ,-glucan from 2 different cereal sources (oat and barley) on growth and metabolic activity of Bifidobacterium animalis ssp. lactis (Bb-12Ô) as determined by plating on a selective medium in yogurt during prolonged cold storage. These yogurt batches were compared to unsupplemented and inulin supplemented controls. All batches were also assessed for syneresis. Oat ,-glucan addition resulted in improved probiotic viability and stability comparable to that of inulin. It also enhanced lactic and propionic acid production. The barley ,-glucan addition suppressed proteolytic activity more than that from oat. These improvements were hindered by greater syneresis caused likely by thermodynamic incompatibility. Small amplitude oscillatory measurements of acidified model mixture of ,-glucan/skim milk solids showed formation of casein gel within the ,-glucan network. Binary mixtures of ,-glucan and skim milk solids had apparent pseudoplastic and non-Newtonian behavior governed mainly by ,-glucan contribution. Above critical concentrations, the mixtures underwent phase separation with the lower phase rich in protein. The phase diagram also showed that the addition of ,-glucan may be possible at or below 0.24 w/w%. [source] High-Temperature Rheology of Calcium Aluminosilicate (Anorthite) Glass-Ceramics under Uniaxial and Triaxial LoadingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001Balakrishnan G. Nair The high-temperature creep behavior of two fine-grained (,3 ,m) anorthite-rich glass-ceramics was characterized at ambient pressure and under a confining pressure of ,300 MPa. Experiments were done at differential stresses of 15,200 MPa and temperatures of 1200°,1320°C. Of the two materials, one had a tabular (lathlike) grain structure with finely dispersed second phase of mullite, mostly in the form of ,3,5 ,m grains comparable to that of the primary anorthite phase, whereas the other had an equiaxed grain morphology with fine (,400 nm) mullite precipitates concentrated at the anorthite grain boundaries. The results of creep experiments at ambient pressure showed that the material with the tabular grain structure had strain rates at least an order of magnitude faster than the equiaxed material. Creep in the tabular-grained material at ambient pressure was accompanied by a significant extent of intergranular cavitation: pore-volume analysis before and after creep in this material suggested that >75% of the bulk strain was due to growth of these voids. The equiaxed material, in contrast, showed a smooth transition from Newtonian (n= 1) creep at low stresses to non-Newtonian behavior at high stresses (n > 2). Under the high confining pressure, the microstructures of both materials underwent significant changes. Grain-boundary mullite precipitates in the undeformed, equiaxed-grain material were replaced by fine (,100 nm), intragranular precipitates of silliminate and corundum because of a pressure-induced chemical reaction. This was accompanied by a significant reduction in grain size in both materials. The substantial microstructural changes at high confining pressure resulted in substantially lower viscosities for both materials. The absence of mullite precipitates at the grain boundaries changed the behavior of the equiaxed material to non-Newtonian (n= 2) at a pressure of ,300 MPa, possibly because of a grain-boundary sliding mechanism; the tabular-grained material showed Newtonian diffusional creep under similar conditions. [source] Model filled polymers: The effect of particle size on the rheology of filled poly(methyl methacrylate) compositesPOLYMER ENGINEERING & SCIENCE, Issue 3 2004Joshua Qingsong Li The effect of size of crosslinked monodisperse spherical polymer particles on the steady shear and dynamic rheology of filled poly(methyl methacrylate) (PMMA) composites was studied for PMMA and polystyrene (PS) particles in the range from 0.1 to 1.3 micron particle size. For PMMA matrices filled with crosslinked PS particles, reduction in filler size increases non-Newtonian behavior. Particle size effects on the rheology of filled PMMA were much less pronounced for PMMA filler. The rate of growth of steady shear viscosity with aging time was much larger for PMMA filled with PS particles than with PMMA particles. The apparent yield stress of filled PMMA composites was estimated from Casson plots. The yield stress was negligible for PMMA filler but increased with decreasing particle size for PS filler. We suggest that PS particles are rejected by the PMMA matrix and form clusters, causing large enhancements in viscosity and moduli. Polym. Eng. Sci. 44:452,462, 2004. © 2004 Society of Plastics Engineers. [source] Experimental Results and Models for Solid/Liquid Fluidized Beds Involving Newtonian and Non-Newtonian LiquidsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2004M. Aghajani Fluidization technology relies almost solely on fluid/particle interaction wherein the liquid phase may exhibit Newtonian or non-Newtonian behavior. The steady motion of particles and the velocity-voidage relationship are the most important design parameters for fluidization, providing the basis for the prediction of heat and mass transfer coefficients and information on hydrodynamic conditions. A summary of the literature on particle settling velocity, minimum fluidization velocity and velocity voidage relationship is supplemented by new experimental results, which extend the range of investigated solid and liquid phase physical properties. Correlations for particle settling velocity and velocity-voidage relationship are developed and verified against experimental data. [source] New milliliter-scale stirred tank bioreactors for the cultivation of mycelium forming microorganismsBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2010Ralf Hortsch Abstract A novel milliliter-scale stirred tank bioreactor was developed for the cultivation of mycelium forming microorganisms on a 10 milliliter-scale. A newly designed one-sided paddle impeller is driven magnetically and rotates freely on an axis in an unbaffled reaction vessel made of polystyrene. A rotating lamella is formed which spreads out along the reactor wall. Thus an enhanced surface-to-volume ratio of the liquid phase is generated where oxygen is introduced via surface aeration. Volumetric oxygen transfer coefficients (kLa),>,0.15,s,1 were measured. The fast moving liquid lamella efficiently prevents wall growth and foaming. Mean power consumption and maximum local energy dissipation were measured as function of operating conditions in the milliliter-scale stirred tank bioreactor (V,=,10,mL) and compared to a standard laboratory-scale stirred tank bioreactor with six-bladed Rushton turbines (V,=,2,000,mL). Mean power consumption increases with increasing impeller speed and shows the same characteristics and values on both scales. The maximum local energy dissipation of the milliliter-scale stirred tank bioreactor was reduced compared to the laboratory-scale at the same mean volumetric power input. Hence the milliliter impeller distributes power more uniformly in the reaction medium. Based on these data a reliable and robust scale-up of fermentation processes is possible. This was demonstrated with the cultivation of the actinomycete Streptomyces tendae on both scales. It was shown that the process performances were equivalent with regard to biomass concentration, mannitol consumption and production of the pharmaceutical relevant fungicide nikkomycin Z up to a process time of 120,h. A high parallel reproducibility was observed on the milliliter-scale (standard deviation,<,8%) with up to 48 stirred tank bioreactors operated in a magnetic inductive drive. Rheological behavior of the culture broth was measured and showed a highly viscous shear-thinning non-Newtonian behavior. The newly developed one-sided paddle impellers operated in unbaffled reactors on a 10 milliliter-scale with a magnetic inductive drive for up to 48 parallel bioreactors allows for the first time the parallel bioprocess development with mycelium forming microorganisms. This is especially important since these kinds of cultivations normally exhibit process times of 100,h and more. Thus the operation of parallel stirred tank reactors will have the potential to reduce process development times drastically. Biotechnol. Bioeng. 2010; 106: 443,451. © 2010 Wiley Periodicals, Inc. [source] Comparison of Physicochemical Properties of New Ionic Liquids Based on Imidazolium, Quaternary Ammonium, and Guanidinium CationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2007Prashant Abstract More than 50 ionic liquids were prepared by using imidazolium, quaternary ammonium, and guanidinium cations and various anions. In these series, different cationic structures such as 1-benzyl-3-methylimidazolium [Bzmim]+, 1,3-dibenzylimidazolium [BzmiBz]+, 1-octyl-3-methylimidazolium [C8mim]+, 1-decyl-3-methylimidazolium [C10mim]+, tricapryl-methylammonium [Aliquat]+, benzyltriethylammonium [BzTEA]+, phenyltrimethylammonium [PhTMA]+, and dimethyldihexylguanidinium [DMG]+ were combined with anions, p -toluenesulfonate [TSA],, dicyanoamide [DCA],, saccharine (2-sulfobenzoic acid imide sodium salt) [SAC],, trifluoroacetate [TFA],, bis(trifluoromethanesulfonyl)imide [Tf2N],, trifluoromethanesulfonate [TfO],, and thiocyanate [SCN],. Important physical data for these ionic liquids are collated, namely solubility in common solvents, viscosity, density, melting point and water content. Apart from the viscosity, the Newtonian and non-Newtonian behavior of these ionic liquids is also disclosed. Stability of these ionic liquids under thermal, basic, acidic, nucleophilic, and oxidative conditions was also studied. The features of the solid,liquid phase transition were analyzed, namely the glass transition temperature and the heat capacity jump associated with the transition from the non-equilibrium glass to the metastable supercooled liquid. A degradation temperature of each ionic liquid was also determined. Comparisons of the properties of various ionic liquids were made. [source] | |||||||||||||