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High Shear Rate (high + shear_rate)
Selected AbstractsViscoelastic Properties of Clay-Containing Nanocomposites of Thermotropic Liquid-Crystal PolymerMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2009Jayita Bandyopadhyay Abstract The nanocomposites of liquid-crystal polymer (LCP) with two different weight per cents of clay were prepared via the melt extrusion method. To investigate the properties of the materials in the linear and non-linear viscoelastic regions, both oscillatory and rotational tests were carried out. The results showed that the nanocomposite with higher clay content exhibited an almost defectless partially cross-linked structure compared to the nanocomposite with lower clay content or the pure LCP. The linear stress relaxation measurements revealed that the pure LCP relaxed faster than nanocomposites after imposition of a constant strain for a specific time. During the step rate relaxation test, high shear rate modified the defects in the pure LCP very quickly and probably attained almost an equilibrium position while the nanocomposite samples showed strong shear thinning behaviour. [source] Time-Resolved Synchrotron SAXS Observations on Sheared Syndiotactic Poly(propylene) Crystallization ProcessMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2008Huiying Wen Abstract The in situ crystallization kinetics of syndiotactic poly(propylene) (sPP) has been investigated by synchrotron small-angle X-ray scattering (SAXS). The structure evolutions during the isothermal crystallization of sPP with different shear rates have been observed. The results show that shear accelerates the process of crystallization kinetics. Even under low shear rate, the lamellae can be distinctly oriented. In contrast, the lamellar parameters such as the long period, lamellar thickness, and the scattering invariant Q can change obviously only under high shear rate. A mesomorphic structure proposed by Strobl is adopted to elucidate the differences of shear effects with low and high shear rates. Based on all the analysis we are convinced that a relatively stable mesomorphic structure forms before shear is composed and the shear effects on the mesophase will be retained to a certain extent until crystallization is finished. [source] Study on Flow Induced Nano Structures in iPP with Different Molecular Weight and Resulting Strength BehaviorMACROMOLECULAR SYMPOSIA, Issue 1 2010Achim Frick Abstract Polypropylene samples in a wide molecular weight range between approx. 100,kg/mol to 1 600,kg/mol were processed by injection molding to thin walled micro specimens with respect to study shear induced crystallization phenomena under high shear rate and subsequently possible self reinforcement effects. The specimens nano structures were investigated and related deformation behavior under tensile studied. Novel morphologies have been detect and their micromechanical mechanism interpret and summarized. [source] Nano-Rheology of Single Unentangled Polymeric Lubricant FilmsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2008Qian Guo Abstract Rheology and tribology become more and more critical issues in order to satisfy the harsh requirements for ultra-small head/media spacing HDDs. In this communication, MD simulations with a bead/spring model were employed to examine the nano-rheological response of nonfunctional and functional PFPEs by analyzing the shear viscosity of nanoscale PFPE films and the relaxation processes as a function of wall interaction/separation and endgroup functionality. Our simulation results indicate that thin PFPE films show more solid-like behavior, especially under high shear rate. The film deformation and shear viscosity change by tuning the film thickness and the endgroup functionality was discussed in conjunction with the relaxation processes. [source] Nonisothermal comprehensive 3D analysis of polymer melt flow in a coat-hanger diePOLYMER ENGINEERING & SCIENCE, Issue 4 2006Tingqi Wu The nonisothermal flow of Carreau fluid in a coat-hanger die is studied. A general three-dimensional finite volume code is developed for the purpose of flow analysis. The isobars, the isotherms, and the velocity distribution are obtained. Simulation results illustrated that the highest temperature occurred by the center of manifold, rather than the die-lip region because of the combined effects of high shear rate and poor heat conduction, which is important for processing those heat-sensitive materials. In the regions where die gap is relatively small, the wall temperature plays a key role in deciding temperature distribution in the melt. The validity of simulation results is verified experimentally. POLYM. ENG. SCI., 46:406,415, 2006. © 2006 Society of Plastics Engineers. [source] Commercial taxane formulations induce stomatocytosis and increase blood viscosityBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2001Michael Mark Taxanes are antineoplastic drugs which have cardiovascular side effects of unknown mechanism. We investigated their influence on blood viscosity and erythrocyte morphology. Whole blood was incubated in vitro with increasing concentrations of Taxol®, Taxotere®, paclitaxel (0 , 100 ,M) and the vehicles Cremophor-EL and Tween 80 (0 , 5% vol) for 1 h at 37°C. Plasma and whole blood viscosity (Haematocrit 45%) were measured and erythrocyte morphology was assessed on glutaraldehyde-fixed cells. The same investigations were performed in seven patients before and after a Taxol®-infusion. Taxol® and Taxotere® induced a dose- and time-dependent stomatocytic shape transformation of erythrocytes. Paclitaxel alone had no effect, but the vehicles cremophor-EL and Tween 80, used in Taxol® and Taxotere®, respectively, induced a comparable degree of stomatocytosis. This suggests a preferential intercalation of these substances into the inner hemileaflet of the membrane lipid bilayer. Associated with this shape change a dose-dependent increase in plasma and whole blood viscosity was observed. Neither shape nor viscosity changes were reversible upon removal of the agents. After the infusion of 130 , 300 mg Taxol® in patients a slight shift towards stomatocytosis and an increase in whole blood viscosity at high shear rate from 5.09±0.30 to 5.44±0.38 mPa.s (P<0.05) were confirmed. Commercial taxane drug formulations induce stomatocytosis and increase blood viscosity, which is due to their formulation vehicles. These findings may contribute to the understanding of the cardiovascular side effects of these drugs. British Journal of Pharmacology (2001) 134, 1207,1214; doi:10.1038/sj.bjp.0704387 [source] The PFA-100Ô system for the assessment of platelet function in normotensive and hypertensive pregnanciesINTERNATIONAL JOURNAL OF LABORATORY HEMATOLOGY, Issue 2 2001Marco Marietta Platelet function was studied in 30 pregnant women: 14 normotensive (C), and 16 affected by pregnancy-induced hypertension (PIH). Platelet aggregometry (PA) on platelet-rich plasma according to Born was compared with the new PFA-100Ô System (Dade International Inc, Miami, USA). This device evaluates platelet function (expressed in seconds as closure time, CT) in anticoagulated whole blood ex vivo at high shear rates. PA (expressed as percentage of light transmission) and CT were measured at baseline and after incubation with L-Arginine (L-Arg). MANOVA for repeated measures showed that L-Arg incubation significantly decreased PA (F=7.2, P < 0.05) and increased CT (F=6.05, P < 0.05) in the whole population of pregnant women. Moreover, we analysed separately both parameters in C and in PIH subjects. No differences in PA were found in both groups, neither at baseline nor after L-Arginine incubation. In contrast, CT was significantly longer in PIH in comparison to C before (95.9 s vs. 84 s, P < 0.05) as well after (115 s vs. 92 s, P < 0.05) L-Arginine incubation. Data from PFA-100Ô confirm our previous reports that during pregnancy the L-Arginine: Nitric Oxide pathway regulates platelet function. In hypertensive patients a significant decrease in platelet function was found by using the PFA-100Ô system. [source] Lead Zirconate Titanate Particle Dispersion in Thick-Film Ink FormulationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Erik S. Thiele Diverse device applications for lead zirconate titanate (PZT) ceramics in thick-film form are currently in active development. In the present study, the particle dispersion properties of thick-film ink formulations containing PZT powder have been determined using rheological measurements. Although all of the eight commercially available dispersants tested are more effective than the terpineol solvent alone in decreasing attractive interparticle forces in suspensions, the best dispersant identified for hard and soft PZT powders is a phosphate ester oligomer. This dispersant is extremely efficient, and its use in thick-film ink formulations results in viscosity decreases of 50% at low shear rates (10 s,1) and 30% at high shear rates (100 s,1) compared with current ink formulations containing no dispersant. The effects upon rheology of the order of addition of components in the processing of inks have been studied, with the most effective processing route using a fugitive solvent that probably facilitates uniform coverage of the particle surfaces by the dispersant molecules. Modeling of the rheological profiles of inks indicates that the use of a dispersant decreases the depth of the primary minimum in the interparticle potential by a factor of 3. Demonstrated advantages of the use of a dispersant in PZT thick-film inks include improved microstructural homogeneity in the green body and the ability to formulate printable inks with higher solids loadings. No adverse effects of the dispersant upon the dielectric and piezoelectric properties of bulk PZT samples are found following burnout and sintering. [source] Time-Resolved Synchrotron SAXS Observations on Sheared Syndiotactic Poly(propylene) Crystallization ProcessMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2008Huiying Wen Abstract The in situ crystallization kinetics of syndiotactic poly(propylene) (sPP) has been investigated by synchrotron small-angle X-ray scattering (SAXS). The structure evolutions during the isothermal crystallization of sPP with different shear rates have been observed. The results show that shear accelerates the process of crystallization kinetics. Even under low shear rate, the lamellae can be distinctly oriented. In contrast, the lamellar parameters such as the long period, lamellar thickness, and the scattering invariant Q can change obviously only under high shear rate. A mesomorphic structure proposed by Strobl is adopted to elucidate the differences of shear effects with low and high shear rates. Based on all the analysis we are convinced that a relatively stable mesomorphic structure forms before shear is composed and the shear effects on the mesophase will be retained to a certain extent until crystallization is finished. [source] Influence of the processing conditions on a two-phase reactive blend system: EVA/PP thermoplastic vulcanizatePOLYMER ENGINEERING & SCIENCE, Issue 11 2002Catherine Joubert The elaboration of a TPV based on copolymer of ethylene and vinyl acetate (EVA) and polypropylene (PP) as thermoplastic phase was investigated in a batch mixer. The crosslinking reaction is carried out through a transesterification reaction between ester groups of EVA and alcoxysilane groups of the crosslinker agent tetrapropoxyorthosilicate (TPOS). The main advantage of this crosslinking reaction is that it can be well controlled and suitable for different processing conditions. The aim of the present study is to get a better understanding of the dispersion mechanism and of the phase inversion of the EVA major phase during its dynamic vulcanization into the PP minor phase. It was proved that the initial viscosity ratio, , = ,pp/,EVA, between EVA and PP plays an important part in the morphology development of the reactive blend. The viscosity ratio must be close to the critical ratio expressed by Utracki's model of phase inversion mechanism. Furthermore, the influence of different processing parameters on the variation of the morphology and on the mechanical properties of the ultimate TPV was investigated. The main conclusion of this study is that the characteristic time of crosslinking must be of the same order than the time of mixing. Indeed, better mechanical properties are obtained when a progressive phase inversion occurred and when it is controlled by rheological aspects and transient morphology equilibrium of the two phases and not by the mechanical fragmentation of the crosslinked EVA. For example, in our experimental conditions (concerning the amounts of catalyst and crosslinker reagents), high shear rates can be avoided ( < 80 s,1) as the self-heating of the blend under shear considerably increases (,T , 50°C for = 225 s,1), leading to faster kinetics and consequently to a phase inversion controlled by the fragmentation of the crosslinked EVA phase. [source] Electrical properties of structured HIPS/gamma-irradiated UHMWPE/carbon black blendsPOLYMER ENGINEERING & SCIENCE, Issue 4 2000O. Breuer HIPS/UHMWPE and HIPS/XL-UHMWPE containing carbon black (CB) are unique systems in which CB is attracted to the PE, and thus structuring takes place affecting the morphology and the resultant electrical properties. UHMWPE, having a very high viscosity, was chosen as the dispersed phase within HIPS in place of a conventional polymer in order to explore possibilities of obtaining unique structures that would induce the CB to segregate and form a conductive network. XL-UHMWPE particles also constitute an interesting dispersed phase, maintaming their highly porous and intricate structure even subsequent to melt processing. In both cases the CB is located at the interface; however, differences in resistivity values are observed. When low UHMWPE or XL-UHMWPE contents are incorporated, the HIPS/XL-UHMWPE/CB compositions have lower resistivities due to the heterogeneity of the interface, even at high shear rates. When high UHMWPE or XL-UHMWPE contents are utilized, the trends reverse: HIPS/UHMWPE/CB depict enhanced conductivity, due to the dominance of UHMWPE particle coalescence and the resultant decrease in surface area. This is contrary to what happens with the XL-UHMWPE particles, where the surface area increases with their higher contents, since they do not coalesce. [source] | |||||||||||||