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Mixing Conditions (mixing + condition)

Distribution by Scientific Domains

Polymers and Materials Science	50%
Chemistry	33%

Selected Abstracts

Mass transport and thermodynamic analysis of PAHs in partitioning systems in the presence and absence of ultrasonication

AICHE JOURNAL, Issue 10 2010
Pedro A. Isaza
Abstract Transport of PAHs from Desmopan polymers to methanol under various mixing conditions and in the presence of ultrasound was analyzed. PAH transport was influenced by external transport resistances; however, agitation greater than 800 rpm yielded PAH transport completely limited by internal resistances. Delivery rates of phenanthrene, fluoranthene, and pyrene with ultrasonication were faster than that under any mixing condition, suggesting enhanced internal transport properties. Ultrasound also induced increased concentrations of PAHs in solution at equilibrium. The model developed described PAH delivery under sonicated/non-sonicated conditions, while quantifying diffusive and thermodynamic properties. Diffusivities with and without ultrasound decreased with permeant molecular size agreeing with coefficients determined for similar aromatic compounds in polymers. Partitioning coefficients under sonicated and non-sonicated conditions conclusively differed from each other and decreased as a function of PAH molecular size. Quantitative structure-property relationship data of PAHs yielded factors predicting thermodynamic and transport behaviors, with polarizability being the best descriptor. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

Time series analyses reveal transient relationships between abundance of larval anchovy and environmental variables in the coastal waters southwest of Taiwan

FISHERIES OCEANOGRAPHY, Issue 2 2009
CHIH-HAO HSIEH
Abstract We investigated environmental effects on larval anchovy fluctuations (based on CPUE from 1980 to 2000) in the waters off southwestern Taiwan using advanced time series analyses, including the state-space approach to remove seasonality, wavelet analysis to investigate transient relationships, and stationary bootstrap to test correlation between time series. For large-scale environmental effects, we used the Southern Oscillation Index (SOI) to represent the El Niño Southern Oscillation (ENSO); for local hydrographic conditions, we used sea surface temperature (SST), river runoff, and mixing conditions. Whereas the anchovy catch consisted of a northern species (Engraulis japonicus) and two southern species (Encrasicholina heteroloba and Encrasicholina punctifer), the magnitude of the anchovy catch appeared to be mainly determined by the strength of Eng. japonicus (Japanese anchovy). The main factor that caused the interannual variation of anchovy CPUE might change through time. The CPUE showed a negative correlation with combination of water temperature and river runoff before 1987 and a positive correlation with river runoff after 1988. Whereas a significant negative correlation between CPUE and ENSOs existed, this correlation was driven completely by the low-frequency ENSO events and explained only 10% of the variance. Several previous studies on this population emphasized that the fluctuations of larval anchovy abundance were determined by local SST. Our analyses indicated that such a correlation was transient and simply reflected ENSO signals. Recent advances in physical oceanography around Taiwan showed that the ENSOs reduced the strength of the Asian monsoon and thus weakened the China Coastal Current toward Taiwan. The decline of larval anchovy during ENSO may be due to reduced China Coastal Current, which is important in facilitating the spawning migration of the Japanese anchovy. [source]

Hydrodynamic behaviour of a full-scale anaerobic contact reactor using residence time distribution technique

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2009
Isabel Capela
Abstract BACKGROUND: The knowledge of the fluid pattern of full-scale anaerobic reactors is of fundamental importance for the optimisation of biological processes. High solids concentrations often lead to inefficient mixing conditions, which may reduce treatment capacity due to heterogeneity within the biomass. RESULTS: The hydrodynamic characteristics of a full-scale anaerobic contact reactor treating evaporator condensate from a sulphite pulp mill were investigated. The methodology applied was based on the residence time distribution (RTD) technique using lithium as a tracer. Different non-ideal hydraulic flow models were tested and the best model fitting RTD data was the Gamma distribution model with by-pass. It was concluded that the full-scale bioreactor presents a good degree of mixing with about 22% of non-effective volume due to the presence of high amounts of inorganic materials. CONCLUSION: As a result of this study it was possible to both improve the full-scale bioreactor performance and decrease the running costs by changes in the plant operation strategies which allowed reduction of the huge amount of inorganic materials contributing to the non-effective volume. The methodology is simple and results from a unique RTD experiment and confirms the importance of considering mixing characteristics when assessing complex full-scale treatment processes. Copyright © 2009 Society of Chemical Industry [source]

Mass transport and thermodynamic analysis of PAHs in partitioning systems in the presence and absence of ultrasonication

Combinatorial development of polymer nanocomposites using transient processing conditions in twin screw extrusion

AICHE JOURNAL, Issue 7 2008
Arun K. Kota
Abstract A new approach is presented for combinatorial development of polymer nanocomposites with compositional gradients (CGs). The CGs were developed using transient processing conditions in twin screw extrusion with small quantities of expensive nanoscale fillers. Convolution of step input with normalized residence volume distributions (RVDs) was used to establish the processing,structure relationship for the CGs. The normalized RVD was established as a process characteristic independent of processing conditions and measured in situ using an optical probe. The CG determined nondestructively using the new combinatorial approach was validated through comparison with more time-consuming and destructive thermogravimetric analysis. The CG could also be established with relatively inexpensive microscale fillers using the normalized RVD obtained with nanoscale fillers, suggesting that transient effects of the mixing process are independent of the size of the filler. Finally, structure,property relationship of combinatorially developed polymer nanocomposites was established by characterizing their dynamic mechanical behavior (storage modulus, G,, and loss modulus, G,). The dynamic mechanical behavior of the combinatorially developed composites correlated well with the batch-processed ones, indicating that the transient mixing conditions in extrusion do not affect the material properties. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source]

Least-squares Estimation of an Unknown Number of Shifts in a Time Series

JOURNAL OF TIME SERIES ANALYSIS, Issue 1 2000
Marc Lavielle
In this contribution, general results on the off-line least-squares estimate of changes in the mean of a random process are presented. First, a generalisation of the Hajek-Renyi inequality, dealing with the fluctuations of the normalized partial sums, is given. This preliminary result is then used to derive the consistency and the rate of convergence of the change-points estimate, in the situation where the number of changes is known. Strong consistency is obtained under some mixing conditions. The limiting distribution is also computed under an invariance principle. The case where the number of changes is unknown is then addressed. All these results apply to a large class of dependent processes, including strongly mixing and also long-range dependent processes. [source]

Thermo-Mechanical Degradation of LDPE-Based Nanocomposites

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 7 2007
Nadka Tzankova Dintcheva
Abstract Thermo-mechanical degradation of LDPE-based nanocomposites was studied by mainly investigating the rheological properties. For all of the investigated processing conditions, the viscosity of the nanocomposites was higher than that of the pure-LDPE matrix, but on increasing the severity of the mixing conditions, the difference between the viscosity of the nano-filled polymer and that of the pure LDPE decreased. The X-ray traces of the nanocomposites suggest that intercalation has been achieved during the melt, when less-severe processing conditions were used. At severe processing conditions (longer mixing time, high temperature and shear stress) the thermo-mechanical degradation was accelerated, possibly due to the loss of mass from the organoclay galleries. The variations of the viscosity in the presence of two organo-modified montmorillonite (MMt) clays were compared to the ones observed with a MMt clay at different processing conditions. [source]

Continuous Soluble Ziegler-Natta Ethylene Polymerizations in Reactor Trains, 3 , Influence of Operating Conditions upon Process Performance

MACROMOLECULAR REACTION ENGINEERING, Issue 2 2008
Marcelo Embiruçu
Abstract The behavior of continuous solution ethylene/but-1-ene polymerizations through Ziegler-Natta catalysts is analyzed, based on a previously developed mathematical model. In order to do that, dynamic simulations are carried out and process responses are analyzed as functions of process operating policies and flowsheet configuration, at conditions that resemble the actual operation of industrial sites. It is shown that system responses are highly nonlinear and very sensitive to disturbances of the operating conditions and that catalyst decay is of fundamental importance for proper understanding of process behavior. Results indicate that mixing conditions inside the reactor vessels exert a significant impact upon the final polymer quality and can be manipulated for in-line control of final resin properties. Finally, it is shown that the development of feed policies, based on the use of lateral feed streams, allows the simultaneous control of melt flow index, stress exponent and polymer density of the final polymer resin. [source]

Valorization of poly(butylene terephthalate) wastes by blending with virgin polypropylene: Effect of the composition and the compatibilization

POLYMER ENGINEERING & SCIENCE, Issue 8 2008
Najoua Barhoumi
Blends of recycled poly(butylene terephthalate) (PBT) parts obtained from scrapped cars, and virgin polypropylene (PP), were prepared in a twin-screw extruder at different compositions. Selected compositions were also prepared with the presence of ethylene- co -glycidyl methacrylate copolymer (E-GMA) and ethylene/methyl acrylate/glycidyl methacrylate terpolymer (E-MA-GMA) compatibilizers. The effect of the composition and the type of compatibilizer, as well as the mixing conditions, on the morphology phase, thermal, viscoelastic behavior, and mechanical properties of the blends has been investigated. Blends PP/PBT of various composition exhibit a coarse morphology and a poor adherence between both phases, resulting in the decrease of ductility, whereas at weak deformation, PBT reinforced the tensile properties of PP. Addition of E-GMA and E-MA-GMA to the PP/PBT blend exhibited a significant change in morphology and improved ductility because of interfacial reactions between PBT end chains and epoxy groups of GMA that generate EG- g -PBT copolymer. Moreover, thermal and viscoelastic study indicated that the miscibility of PP and PBT has been improved further and the reactions were identified. The E-MA-GMA results in the best improvement of ductility. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source]

Effect of melt processing conditions on the morphology and properties of nylon 6 nanocomposites

POLYMER ENGINEERING & SCIENCE, Issue 11 2007
F. Chavarria
Nylon 6 (PA-6) organoclay nanocomposites were prepared by melt processing using three different twin screw extruders (TSEs). The effect of mixing conditions, feed port location, residence time, and number of extrusion passes on the morphology and mechanical properties of the nanocomposites were examined. Wide-angle X-ray scattering, transmission electron microscopy (TEM), and mechanical property data are reported. Particle analyses were performed on the TEM images to quantitatively characterize the extent of exfoliation. The amount of shear and the mixing conditions created by TSEs have a significant effect on the morphology and properties of PA-6 nanocomposites. Morphology and mechanical property results show that (1) melting the polymer before coming into contact with the organoclay followed by a low level of shear and (2) maintaining a medium level of shear throughout the extruder with a longer residence time lead to extremely high platelet dispersion and matrix reinforcement for PA-6 nanocomposites. Nanocomposites formed in a DSM microcompounder showed similar morphologies and modulus trends as those obtained with conventional TSEs; thus, this microcompounder is a good alternative for nanocomposite research especially when only small amounts of material are available. POLYM. ENG. SCI., 47:1847,1864, 2007. © 2007 Society of Plastics Engineers [source]

Reactive blending of poly(ethylene terephthalate)(pet)/ poly(ethylene 2,6-naphthalate)(pen).

POLYMER ENGINEERING & SCIENCE, Issue 8 2002
I: Effect of mixing conditions on chain structure
Reactive blending of poly(ethylene terephthalate)/poly(ethylene naphthalene 2,6dicarboxylate) with addition of 2,2'-bis(1,3-oxazoline) (BOZ) has been studied under various mixing conditions for the different compositions. The transesterification level, the sequence length of both PET and PEN short blocks, and the degree of randomness were estimated using1H NMR. The results indicate that both mixing time and temperature are the primary factors controlling the transesterification, while the chain extender BOZ can significantly accelerate the transesterification between PET and PEN at 275°C. The composition also, to some extent, influences the transerification level as the mixing time is increased. As a consequence of transesterification proceeding, the sequence structures of the reactive blends are also markedly changed, which corresponds to a transfer from an initial block structure to a multiblock structure with higher randomness. The change in the microstructure of the reactive blends has also been analyzed by a Bernoullian statistics model. The effect of the BOZ on the intrinsic viscosity of the reactive blends is discussed. [source]

Reactive doping of PAni,CSA and its use in microwave absorbing materials

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2009
R. S. Biscaro
Abstract Conductive coatings have been studied for static dissipation and as microwave absorbing materials. The doping process of polyaniline (PAni), which makes it conductive, is an important stage that determines the coating performance. For this purpose, polyaniline was doped by reactive processing in a torque rheometer using different molar ratios between PAni and acid (PAni:CSA) at three different temperatures (80, 90, and 100°C). Aqueous solution doping was also used in the ratio of 1:2 of PAni/CSA, with the aim to investigate the influence of different methods of PAni doping on its characteristics and, consequently, on the performance of coatings. Thermal analyses of the processed materials showed that PAni doped by both routes, reactive and solution processing, showed similar behaviors. X-ray diffraction analyses showed a semicrystalline structure for the PAni,CSA doped by reactive processing using high CSA concentrations and temperature. It was also observed that the doping process affects the dispersion of the components into the conductive coatings. Microwave absorption measurements (8,12,GHz) of PU-doped PAni blends showed the dependence of the doping type, the PAni,CSA concentration, and the mixing conditions of the components on the coating performance; it was found up to 99% of attenuation of the incident radiation for some composites in a narrow frequency range. The microwave absorption efficiency of the coating samples prepared by using the reactive doping process indicates the advantage of this methodology over solution doping. Moreover, the reactive process addresses the environmental requirements. Copyright © 2008 John Wiley & Sons, Ltd. [source]