bluuebunny/crossref_metadata_2025_split huggingface dataset:
Viscoelastic Simulations of Stratified Bicomponent Extrusion through Slit Dies
Authors: Barakos G. , Mitsoulis E. 
Published: December 2013

Abstract
Numerical simulations have been performed of viscoelastic flow in double-layer coextrusion of polymer melts. The constitutive equation used is a realistic integral model of the K-BKZ type, which can describe the viscoelastic memory of polymer melts. In particular, coextrusion of a typical PS/HDPE system through a slit die has been simulated. The model constants have been determined using experimental data available in the literature. The simulation results reveal bending of the extrudate. The occurrence of bending can be justified using the relative values of the rheological properties of the melts. Bending can be eliminated for certain extrusion rate regions while it is dominant in others.
Modelling of a Viscous Non-Newtonian Polymer Melt in a List/Buss Kneader and Comparison to Experiment
Authors: Lyu M.-Y. , White J. L. 
Published: December 2013

Abstract
A theoretical and experimental study of the behavior of a viscous non-Newtonian polymer melt in a List/Buss Kneader is presented. The modelling study for viscous non-Newtonian behavior considers the dynamics of flow including the influences of screw oscillations and interrupted screw flights. Calculations are made using different methods for various individual Kneader elements which consider (i) pumping capabilities, (ii) leakage flows through the slices in interrupted flights, (iii) pressure distributions and flow fluxes. Predictions of pressure profiles, fill factors, and positions of starvation in modular machines are made. An experimental study which uses polypropylene considers the distributions of polymer in modular screws with different screw configurations. The experimental results are compared to the flow simulation.
The Extensional Flow Mixer, EFM
Authors: Luciani A. , Utracki L. A. 
Published: December 2013

Abstract
There are several reports indicating that deformation and breakup of dispersed drops is easier in extensional flow field than that in shear. This is particularly true for the systems containing the dispersed phase significantly more viscous than the matrix, e.g., blends in which the viscosity ratio λ – ηdisp/ηmatrix≥3.8. These reports led to development of an extensional flow mixer, EFM, a device in which multicomponent, multiphase system [e.g., polymer alloys, blends, master-batches, filled systems] can be hydrodynamically mixed by flowing through a series of convergent/divergent regions of increasing intensity To be effective, EFM must be attached to a machine capable of melting and pressurizing the compound, preferably a single-screw extruder, SSE.
In this paper efficiency of two compounding systems is compared, the first is made of a SSE and an EFM, while the second is a twin-screw extruder, TSE To evaluate the efficiency three types of blends, all characterized by high viscosity ratio, λ ≥ 3.8, were used: (i) high density polyethylene dispersed in polystyrene, HDPE/PS (ii) polypropylene impact-modified by addition of an ethylene-propylene elastomer, EPR/PP, and (iii) ultrahigh molecular weight polyethylene added to high density polyethylene, UHMWPE/HDPE System (i) was used to study the effect of compounding on blend's morphology – the dispersion from the SSE + EFM compounding unit was significantly finer than that from TSE. System (ii) was selected to examine usefulness of EFM for impact modification. The results demonstrated that SSE + EFM provided milder compounding conditions that less shear-degraded PP than TSE The impact strength of specimens prepared in SSE + EFM was superior to that of blends compounded in TSE. The system (iii) was studied to examine the relative merit of SSE + EFM over TSE to produce a finer dispersion of the UHMWPE domains that in turn would result in better dissolution of this ultrahigh molecular weight fraction. Again in this case the SSE + EFM compounder outperformed TSE – the dissolution of UHMWPE was significantly better without parallel degradation of the resin.
A Study on the Reactive Compatibilization of a PBT/LCP Blend: Catalyst Effect
Authors: Lee J. Y. , Jang J. , Hong S. M. , Hwnag S. S. , Seo Y. , Kim K. U. 
Published: December 2013

Abstract
The in situ compatibilization of poly(butylene terephthalate) (PBT) with liquid crystalline polymer (LCP) via catalyzed transesterification reaction was examined through thermal, rheological, morphological and mechanical studies. The addition of catalyst, dibutyltindilaurate, was found to promote the transesterification between PBT and LCP. Maintenance of high vacuum environment was required to produce the high molecular weight copolymers in the reactor, which, acting at the interface, diminished the size of the dispersed phase (LCP) and enhanced interfacial adhesion that led to an early increase of the flexural strength. Flexural strength was reduced after long time reaction due to the chain scission. Transesterification confirmed by NMR spectroscopic analysis played a major role in the interchange process.
Rheology of Layered Thermoplastic Matrix Composites during Compression Molding
Authors: Leterrier Y. , G'Sell C. 
Published: December 2013

Abstract
In view of optimizing the industrial compression molding process of thermoplastic composites, the rheological and microstructural behavior of a polypropylene/glass fiber composite is investigated in model squeeze-flow geometries. The overall stress / strain behavior of the material at various compression rates is recorded and the induced orientation of the fibers is investigated by means of a special electron microscopic characterization method. By contrast to pure polypropylene, it is shown that in the high speed range, the macroscopic flow process is controlled by both the viscous extension and the relative sliding of parallel fibrous layers, the latter becoming unstable when the flow undergoes a rapid transition from divergent to convergent. Under high pressure, voids are dissolved in the polymer melt. In the case of non-isothermal compression, the rheology of the composite is not significantly affected by the cooling of the surface layers. The multilayer plug-flow model based on the sliding mechanism of viscous layers is found to reproduce correctly the experimental stress/strain behavior.
Chaotic Features of Flow in Polymer Processing Equipment-Relevance to Distributive Mixing
Authors: Cheng H. , Manas-Zloczower I. 
Published: December 2013

Abstract
The dominant distributive mixing mechanism in polymer processing is convection. Convection, involving movement of fluid elements from one spatial location in the system to another, results in the creation of interfacial area. Length stretch distributions can be used as a measure of distributive mixing efficiency. We have studied the dynamics of distributive mixing in single and tangential twin screw extruders by means of tracking the evolution of particles originally gathered as clusters. Length stretch distributions and the dynamics of the average length stretch indicate that the tangential twin screw extruder is a better mixing device by comparison with the single screw extruder. The chaotic features of flow in these devices, studied by means of Poincaré sections and Lyapunov exponents, correlate well with the distributive mixing efficiency of the equipment.
Continuous Mixing of Low Viscosity and High Viscosity Polymer Melts in a Modular Co-Rotating Twin Screw Extruder
Authors: Lee S.-H. , White J. L. 
Published: December 2013

Abstract
Modular self-wiping co-rotating twin screw extruders have been widely used in polymer blending and compounding over the past four decades since they were first commercialized by Werner and Pfleiderer [1]. Despite its importance in the polymer processing industry, studies of the initial mixing process in a modular co-rotating twin screw extruder of binary polymer blends have received little attention until the last three years [2 to 9]. Among the various factors controlling the mixing of thermoplastic blends, the viscosity characteristics are a major determinant the degree of deformation of a disperse phase domain depends greatly upon the viscosity ratio. When one component of the mixing system has a very low viscosity, and there is an extremely large viscosity ratio, it is well known to be very difficult to mix [10 to 12].
Flow Field Analysis of Both the Trilobal Element and Mixing Disc Zones within a Closely Intermeshing, Co-Rotating Twin-Screw Extruder
Authors: Bruce D. , Wilson M. , Generalis S. 
Published: December 2013

Abstract
Of the different mixing modules contained within the closely intermeshing, co-rotating twin-screw extruder (CICo-TSE), the trilobal elements and mixing discs are of major importance to the mixing efficiency. These two types of mixing element impose contrasting mixing behaviour on the viscous melt and are thus used selectively to perform differing mixing tasks. Problems encountered when solving the flow problem within these two mixing element zones arise from both the complex 3D geometry and the time dependent flow boundaries as each respective element type rotates about its fixed axes. Following on from the 2D results reported, the computational fluid dynamics package, Polyflow, was employed to investigate the mixing mechanisms exhibited by both a set of three trilobe element pairs and by a pair of staggered mixing discs, as utilised within the Betol BTS40 CICo-TSE. The flow fields were simulated using the ideal rheological properties of polypropylene and characterised in terms of velocity vectors, shear stresses generated and a mixing parameter λ, which quantifies the elongational and rotational flow components. Each flow field exhibited different characteristics for the configurations investigated and it has been found that the average flow field parameter values for the trilobe elements change periodically, whereas minimal changes are observed as the mixing discs rotate.
Temperature Rise in the Extrusion of Highly Viscous Composite Materials
Authors: Sbarski I. , Kosior E. , Bhattacharya S. N. 
Published: December 2013

Abstract
In this paper a model has been developed for the approximate evaluation of the temperature rise in the extrusion of filled plastic materials. The model developed in this paper considers the influence of thermal and rheological properties of extrudate, operating conditions of extrusion and geometry of screw channel on the temperature of extrudate. The optimal parameters of screw channel in terms of productivity and temperature build-up are discussed. The model was tested by experimental studies in which filled plastic material was produced using ground rubber tyre particles dispersed in LDPE. The agreement between the model prediction and the experimental data is discussed.
Simulation of Free Surface Flow in Partially Filled Internal Mixers
Authors: Nassehi V. , Ghoreishy M. H. R. 
Published: December 2013

Abstract
Internal mixers used in rubber processing and other industries are always partially filled. This results in the establishment of multiple random free surfaces in the flow field generated inside these mixers. Therefore successful mathematical modelling of internal mixing process depends on the development of efficient techniques for the reliable simulation of complex free surface flows. Various interface tracking and boundary capturing methods have been used in the past to model this kind of flow regimes. In particular, in recent years the well-known volume of fluid (VOF) method has been frequently used to model a variety of processes involving free surface and moving boundary flows. Both Eulerian and Lagrangian frameworks can be adopted in the VOF scheme to simulate free surface regimes. Under realistic flow conditions, however, the straightforward application of the technique in both frameworks may yield inaccurate results unless elaborate solution strategies are used to avoid errors. In many cases the use of such elaborate schemes requires excessive computational costs and effort or the solution scheme becomes complex and inflexible. In this paper we describe a relatively simple free surface tracking method based on the application of the VOF method in an Eulerian framework. In this scheme the flow field inside a partially filled internal mixer is treated as a two-phase system consisting of incompressible and compressible phases. The sections filled with the fluid which is being mixed are always regarded as an incompressible phase. The parts which are filled with air (or voids in some applications) form the second phase in the present two-phase flow analysis. The latter phase is treated as a compressible or an incompressible fluid (or pseudo fluid in the case of voids) depending on the value of the pressure calculated at each time step for the sections which contain it. We show that free surface flow of highly viscous fluids in partially filled internal mixers can be very successfully simulated by this method.
Injection Moulding of Rubber Compounds1
Authors: Karam S. , Vincent M. , De Zelicourt Y. 
Published: December 2013

Abstract
The aim of this study is to show the relevant physical parameters related to rubber injection moulding, and especially compressibility, vulcanisation and wall slippage. Three materials are studied: an SBR compound, without and with a lubricant, and an EPDM compound. The viscosity is determined by capillary rheometry. The modified SBR exhibits wall slippage. Rheological vulcanisation kinetics are determined with a Moving Die Rheometer. Precise moulding experiments are carried out with an injection moulding machine and a mould equipped with pressure and temperature transducers. At low flow rate, the influence of the curing reaction on the pressure appears clearly especially for the fast curing EPDM. The conditions in which surface scorch defects appear are determined. The SBR with lubricant needs a lower pressure to fill the cavity than without lubircant. A model of mould filling is developed. The material is purely viscous, with a state of cure dependence of the viscosity. A Norton friction law is introduced to take into account a possible slippage at the cavity walls. A compressible calculation in the injection chamber allows a realistic evaluation of the flow rate at the entry of the cavity. The comparison with the experimental data confirms the importance of the compressibility, and the influence of the vulcanisation on the viscosity at low flow rate. In moulding conditions for which vulcanisation is not activated during the filling stage, despite uncertainties on the friction law parameters appropriate to the cavity wall roughness, the agreement with experiments is better when wall slippage is taken into account.
Fluid Mechanics of Intermeshing Counter-Rotating Twin Screw Extruders
Authors: Hong M.-H. , White J. L. 
Published: December 2013

Abstract
A simulation is presented of the flow and pumping behavior of an intermeshing counter-rotating twin screw extruder. The problem of incorporating the positive displacement characteristics of moving machine parts in a cylindrical coordinate Flow Analysis Network (FAN) analysis is presented. Screw pumping characteristic curves were determined for various elements of the Leistritz GG modular counter-rotating twin screw extruder for a Newtonian fluid. We discuss the analysis of composite modular counter-rotating twin screw extruders using these screw pumping characteristics.
Lateral and medial tibial plateau angles in normal dogs
Authors: Ocal M. K. , Sabanci S. S. 
Published: December 2013

SummaryTo measure lateral and medial tibial plateau angle values in isolated canine tibiae and to compare lateral and medial tibial plateau angle values between dogs based on sex and breed.Tibiae of 90 dogs from 24 different breeds were used. Photographs were taken of the medial and lateral aspects of the tibiae for measurement of the medial and lateral tibial plateau angles. Additionally, the medial tibial plateau angle was measured from radiographs of the tibiae. Two-way analysis of variance was used to test the effects of side, sex and breed on the medial and lateral tibial plateau angles as measured from photographs as well as the medial tibial plateal angles as measured from radiographs. The photographic and radiographic medial tibial plateau angles were compared by paired t-test, whereas the medial and lateral photographic tibial plateau angles were compared by t-test.When all dogs were included in the analysis, the difference between the mean medial tibial plateau angle (24.0 ± 3.19°) and the mean lateral tibial plateau angle (25.5 ± 3.84°) as measured from photographs was significant (p <0.05). The difference in the photographic medial tibial plateau angle between male and female dogs was significant (p <0.05), whereas the difference in the photographic lateral tibial plateau angle between sexes was not significant. There was a significant difference between the medial and lateral tibial plateau angles as measured from photographs in male dogs (p <0.05) but not in female dogs. Breed comparisons also showed significant differences for the photographic lateral tibial plateau angle (p <0.05).The axial rotation of the femoral condyles on the tibial plateau is probably affected by the discrepancy between the medial and lateral tibial plateau angles, and this difference in certain breeds might influence the prevalence of cranial cruciate ligament disease.
Rapid prototyping to design a customized locking plate for pancarpal arthrodesis in a giant breed dog
Authors: Nicetto T. , Petazzoni M. 
Published: December 2013

SummaryThis report describes the treatment of traumatic carpal hyperextension in a giant breed dog by pancarpal arthrodesis using a custom- made Fixin locking plate, created with the aid of a three-dimensional plastic model of the bones of the antebrachium produced by rapid prototyping technology.A three-year-old 104 kg male Mastiff dog was admitted for treatment of carpal hyperextension injury. After diagnosis of carpal instability, surgery was recommended. Computed tomography images were used to create a life-size three-dimensional plastic model of the forelimb. The model was used as the basis for constructing a customized 12-hole Fixin locking plate. The plate was used to attain successful pancarpal arthrodesis in the animal.Radiographic examination after 74 and 140 days revealed signs of osseous union of the arthrodesis. Further clinical and radiographic follow-up examination three years later did not reveal any changes in implant position or complications.
Um método para avaliação aproximada de coeficientes de permeabilidade em aquíferos
Authors: Carvalho Moacyr de 
Published: December 2013

o presente trabalho é uma tentativa para a obtenção de valores aproximados de coeficiente de permeabilidade de aqüíferos em cuja estrutura' ocorrem camadas .ou estratos diversos de sedimentos. O método consiste na essência, partindo de certas condições restritivas, no estabelecimento de um sistema de equações lineares utilizando-se de dados conhecidos de poços tubulares numa área limitada, sob a hipótese de que cada estrato doaqüífero se· comporte como um aqüífero individual de lençol livre. Um exemplo de aplicação é apresentado com dados retirados de 3 poços tubulares da cidade de Catanduva, porém com estratificações sedimentares imaginárias devido a inexistência de uma descrição adequada dos perfís geológicos. Observamos também que tais poços não obedecem as condições restritivas impostas no método, por receberem contribuições de rochas fraturadas subjacentes, provavelmente de água proveniente da Formação Botucatu.
The difficult, the dangerous, and the catastrophic: Managing the spectrum of climate risks
Authors: Luers Amy L. , Sklar Leonard S. 
Published: December 2013

AbstractThe notion of a threshold of dangerous climate change has been central to national and international efforts to address climate risks. However, the focus on a single target has now become an obstacle because it reinforces three key problems: it frames climate change as a distant abstract threat, it impedes integration of mitigation and adaptation, and it fails to recognize the diversity of values and risk perceptions of people around the globe. We present an alternative framework that considers both biophysical science and social values in characterizing the broad spectrum of climate risks. The framework also presents the options for managing these risks within four quadrants defined by the inherent limits to mitigation and adaptation. This quadrant‐based approach to managing the spectrum of climate risks restructures the climate change problem from avoiding a distant catastrophe to minimizing collective suffering.
The Witkop Cyclization: A Photoinduced CH Activation of the Indole System
Authors: Gritsch Philipp J. , Leitner Christian , Pfaffenbach Magnus , Gaich Tanja 
Published: December 2013

AbstractInvestigations of excited‐state redox processes have an exceptional impact on the field of organic photochemistry and its application to the synthesis of complex target molecules. In such a photochemical process a single‐electron transfer takes place to produce ion‐radical intermediates, if the reduction and oxidation potentials, as well as excited‐state energies of electron donors and acceptors are chosen appropriately. The Witkop cyclization constitutes an intramolecular variant of such a process, typically with an indole heterocycle as an electron donor. The specific synthetic value of this reaction lies in a CC bond formation without requiring any prefunctionalization of the indole system. Although this photoreaction has been applied to the total synthesis of natural products, it has still not been used to its full capacity. The following review details synthetic efforts using the Witkop cyclization, and aims to incite further applications of reaction in the synthesis of complex molecular architectures.
Fabrication and processing of polypropylene ‐ paraffin compounds with enhanced thermal and processing properties: Impact penetration and thermal characterization
Authors: Saleem Anjum , Frormann Lars , Koltermann Jan , Reichelt Claudia 
Published: December 2013

ABSTRACTThe compounds of polypropylene (PP) with paraffin wax (PR) as phase change material were fabricated by extrusion melt compounding. The compounds of PR and PP were brittle and showed PR leakage within its melting point range. The maximum 60 weight percent content of the PR was compounded with the polymer. The high amount of paraffin in the polymer plasticized and significantly decreased the melting point of the polymer. The addition of a linear triblock copolymer based on styrene and ethylene/butylene noticeably ameliorated the workability, impact penetration and paraffin retention properties of the compounds. The compounds were further reinforced by carbon fibers and carbon nanotubes that led to an enhancement of their thermal conductivity and heat transfer efficiency. The material structure and thermophysical properties were studied by microscopy and various characterization techniques. The compounds of polymer with PR show phase change effect due to the solid–liquid phase transition of PR within its melting point range. The experimental time vs. temperature curves of the compounds were recorded within the melting range of PR. The experimental curves were compared with the theoretical calculated results. The results were in agreement except small difference that can be attributed to the experimental errors and the assumptions made during theoretical calculations. The manuscript describes the fabrication of shape enduring compounds, with improved thermal, physical, and mechanical properties and their processing by standard techniques, such as extrusion and blow molding. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40164.