SPE Library

The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.

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Conference Proceedings
Wave Interfacial Instabilities at Coextrusion in Flat Dies: Simulation and Experimental Research
M. Zatloukal, M.T. Martyn, P.D. Coates, P. Sáha, May 2004
The work presents both, simulation and experimental findings of the research of two LDPE melts using a flat coextrusion flow visualization cell. The simulation is performed by FEM analysis with full u-v-p-? numerical scheme employing viscoelastic constitutive equations. The predicted stresses, velocities and interface location have been found to be in a good agreement with the measurements. The experimental analysis shows that pronounced wave instabilities are caused by the minor layer break at the merge point of the layers, and extensional viscosity is a driving parameter here. Finally, recently proposed ‘TNSD sign criterion‘ has been successfully tested for the prediction of the onset of wave interfacial instabilities in this type of the die geometry.
Experimental Observations and Analysis of LDPE Melt Flow in Coextrusion Geometries
M.T. Martyn, T. Gough, R. Spares, P.D. Coates, M. Zatloukal, May 2004
The study of two low density polyethylene melt flows in slit coextrusion flow cells with 30° and 90° confluent geometries is presented. The stream flows and polymerpolymer interface in the confluent region and die land are observed through side windows of the cell. Birefringence and image processing techniques are used to quantify stress and velocity fields in the upstream and down stream melt flows. Interfacial instabilities were observed in the LDPE melt flows in both geometries. Instabilities occurred at certain stream mass flow ratios. Digital image processing shows the wave type extrudate instabilities have the same periodicity as perturbation in the flow field in the die land. A recently proposed “TNSD sign criterion” reasonably predicted the onset of the interfacial instabilities in these die geometries.
A Non-Isothermal 3D FEM Study of Spiral Mandrel Dies with Non-Symmetrical Input
Petra Škabrahová, Ji?í Švábík, John Perdikoulias, May 2004
The design of an optimal spiral mandrel die suited to given requirements is quite a complicated task for the die designer. Even for a properly designed spiral section, there is always a question how variations in the flow prior to the spiral channels can influence the melt distribution at the exit of the spiral distribution section. This study uses 3D FEM analysis to investigate an effect of having uneven inputs. Specifically, the influence of uneven mass and temperature input distributions are studied. The influence of the die distributive system is investigated by analyzing the temperature and velocity fields at the exit.
Sensitivity of Flow Distribution and Flow Patterns in Profile Extrusion Dies
J.M. Nóbrega, O.S. Carneiro, P.J. Oliveira, F.T. Pinho, May 2004
Fluctuations of the operating conditions or slight variations of the polymer rheology may occur during longterm productions, affecting the performance of the die in an extent dependent on its flow distribution sensitivity. In this work, four extrusion dies are optimised (balanced) using different design methodologies. These are compared in terms of their performance and stability to some operating conditions and polymer rheological properties. A finite-volume based computational code is used to perform the required simulations of the non-isothermal three-dimensional flows, under conditions defined by a statistical Taguchi technique. Correlation between the flow patterns developed and flow distribution sensitivity is also investigated.
Method for Measuring the Kinetics of Isometric Crystallization of Thermoplastic Sheets and Patient Fixation Devices
Bogdan Bogdanov, May 2004
A new method for crystallization kinetics of stretched polymer samples and real size polymer articles under isometric conditions is developed. The internal shrinkage force caused by the volume contraction of the sample during crystallization is measured incessantly. The kinetics parameters of isometric crystallization are calculated by the Avrami equation and discussed in terms of controlled molecular structure and design of large polymer sheet samples and of patient fixation devices for medical application in radiation therapy.
Viscosity of Blowing Agent Laden Polymer
Subir K. Dey, David B. Todd, Chen Wan, May 2004
The viscosity of a blowing agent laden polymer was measured using a Helical Barrel Rheometer (HBR). Temperature, pressure and shear rate dependence of viscosity at a fixed blowing agent concentration was computed from the experimental data. Technique was developed to identify the onset of bubble nucleation by measuring the shear viscosity as function of hydrostatic pressure.
Structure-Property Relationships in Coextruded Foam/Film Microlayers
Aditya Ranade, Anne Hiltner, Eric Baer, David Bland, May 2004
It has been demonstrated for the first time that microcellular foam structures can be produced using the microlayer coextrusion technology. Cell size can be reduced considerably by increasing the number of layers without adversely affecting the density. Unique mechanical properties can be achieved through material choice and layer structure. The cell morphology and the compressive response of these multilayered foam/film structures are similar to that of cork.
Simulation of Polymeric Flow in a Twin Screw Extruder: An Analysis of Elongational Viscosity Effects
A. Shah, M. Gupta, May 2004
Flow of a polymer in an intermeshing co-rotating twin-screw extruder is simulated. Effect of elongational viscosity on the flow is analyzed using independent power-law models for the shear and elongational viscosities. Axial component of the velocity is found to be maximum in the intermeshing region of the extruder. Axial component of velocity, which determines the throughput of the extruder, decreased as the elongational viscosity of the polymer used for the flow simulation was increased. The pressure in the extruder decreased from a very high positive value on the leading edge to a very large negative value on the trailing edge of the screw. For the same rotational speed the pressure build-up in the twin-screw extruder increased as the elongational viscosity of the polymer was increased.
Plastic Energy Dissipation (PED) of Uncompatibilized and Compatibilized Polymer Blend Systems
Bainian Qian, Costas G. Gogos, Byeong Joon Jeong, David B. Todd, May 2004
It has been demonstrated experimentally, that Plastic Energy Dissipation (PED) is the most important heating/melting mechanism, especially in the initial stage of heating of compacted solid polymer particulates in polymer compounding equipment, where forced particulate deformation takes place. Our previous work has also found that the melting of multi-component polymer blends is totally different from that of the individual blend component. The difference has been correlated to the different PED response of individual blend components in the deformation of polymer blends. In this work, we study the PED behavior of model polymer blends (PE/PS) at different compositions as well as the effect of a compatibilizer on the blend PED. The Specific Mechanical Energy (SME) input associated with PED of both uncompatibilized polymer blends and compatibilized polymer blends during uniaxial compressive deformation is calculated and compared.
Simulation of the Fluid Flow of Deeper Screw Flights for Co-Rotating Twin Screw Extruders
Olaf Wünsch, Ralf Kühn, Peter Heidemeyer, May 2004
Co-rotating twin-screw extruders are frequently used in the field of polymer compounding processes. The extruders are build in a modular design with different conveying and mixing elements to be adapted of specific processes. The user operating the machines often has an optimization problem: On the one hand a gentle mechanical treatment during the flow through the extruder are required. Otherwise there is the desire for a flow rate as much as possible. Therefore Coperion Werner & Pfleiderer has developed a new model series with deeper screw flights, because the ratio of outer versus root diameter is one of the characteristic dimensions of a screw extruder.To estimate and evaluate the success of the new model series, numerical simulations have been carried out of the three dimensional fluid flow in such twin-screw extruders. The approximation based on a finite volume method with contour-adapted meshes. The calculations are made in a relative system, where the flow appears in a steady state.In this paper we present results of numerical investigations of single- and double-flighted screw elements and compare these with calculated values of an old model range with smaller diameter ratio. We discuss not only the conveying- and power-characteristics for Newtonian and nonnewtonian highly viscous materials but also the distribution of shear rate and shear stress. It is shown that the deeper screw flights are a good choice to take care of the polymer material and reduce the energy consumption of many processes.
Development and Verification of a Method to Optimize Individual Screw Elements for Co-Rotating Twin Screw Extruders
H. Potente, A. Müller, K. Kretschmer, May 2004
Tightly Intermeshing, co-rotating twin screw extruders are commonly employed for tasks requiring good mixing. The modular constitution of both barrel and screw makes it possible to optimize the extruder configuration for a given task. This research focuses on the optimization of individual screw elements, thus the development of an optimized geometry for different materials and operating conditions.We calculated the pressure profile, the temperature development and the power consumption using one-dimensional models. A non-linear optimization algorithm was used to vary the geometrical data of the screw elements of interest. The goal was to find a geometry that shows an optimum between the contradicting goals of a minimum temperature increase, a minimum power consumption and a capability to build up a certain pressure with in a minimum distance (i.e. maximum pressure gradient). The quality of the geometry was characterized and evaluated by quality functions. We verified the optimization method by systematic experimental investigations.
Processing and Properties of Foamed HDPE/PP Blends by Extrusion
E. Herrera Tejeda, C. Zepeda Sahagún, R. González Núñez, D. Rodrigue, May 2004
This paper presents a study on the processing condition and characterization of foamed HDPE/PP blends. The blends were foamed with different blowing agent concentrations using a twin-screw extruder. A chemical blowing agent (azodicarbonamide) and activator agent (ZnO) were selected and the morphological, rheological and mechanical properties of the resulting foams are presented.
Effect of the Filler Content on the Specific Properties of Syntatic Foam
Erwin M. Wouterson, Freddy Y.C. Boey, Xiao Hu, Shing-Chung Wong, May 2004
In this study we assessed the specific properties including tensile, compression and flexure strengths and moduli for syntactic foam as a function of various microstructures. Preliminary results revealed that the specific compressive strength and the specific tensile, compressive and flexural moduli depended on the type of microsphere, which varied in density. Mechanical properties are critically evaluated in light of their microstructures.
Capillary Rheometry Studies on Wall Slip Flow of Ceramic Pastes
A. González-Álvarez, J. Graczyk, H. Buggisch, May 2004
The extrusion behavior of ?–aluminium oxide– silicone oil pastes were investigated via capillary rheometry. Several parameters affecting the paste behavior were considered, including the viscosity of the fluid phase, the solids concentration (35 to 55 Vol. %), the extrusion rate (10-2 to 103 mm/s) and the addition of pigment. The flow curves and wall slip behavior were determined under the extrusion conditions.
Synthesis of Blocky Copolymers via Ring-Opening Polymerization Using L,L-Lactide and MBC
Adam J. Pesek, May 2004
A semi-crystalline copolymer was synthesized with block-like structures by ring-opening polymerization (ROP) using L,L-lactide (LLA) and 5-methyl-5- benzyloxycarbonyl-1,3-dioxan-2-one (MBC). Analysis of the copolymer revealed retention of crystallinity and melting transition temperatures. The copolymer exhibited an upper limit to compositional incorporation of MBC before crystallinity was disrupted. The physical properties (Tg, Tc, Tm) were increased after hydrogenation.
Effects of Molecular Structure of Polyethylenes on Their Processabilities in Film Blowing Extrusion Process
Seungoh Kim, Pierre G. Lafleur, Pierre Sammut, Huneault A. Michel, May 2004
In this work, bubble instabilities of metallocene and Ziegler-Natta catalyzed polyethylenes (PEs) were studied by using an in-line scanning camera. Levels of long chain branching (LCB) and breadth of molecular weight distribution (MWD) of PEs were systematically varied to study their effects on bubble instabilities. Gel permeation chromatograph traces and small amplitude oscillatory shear data were used to verify the molecular structure of PEs. In addition, tensile stress growth coefficients and apparent uniaxial extensional viscosities were also determined by using Meissner type rheometer and converging die techniques. It was found that LDPE shows the most stable working windows confirming the previous arguments that the polymer showing strong strain hardening has the broader working window. It was also found that two branched metallocene catalyzed PEs show better bubble stability than PEs with broad MWDs implying that the presence of LCB plays a much more important role than the broadening of the MWD. The order of bubble instabilities can be properly evaluated based on a plot of normalized tensile stress growth coefficient vs Hencky strain or normalized extensional viscosities vs extensional stress.
Cluster Computing in Numerical Simulation of Extrusion Flow
Rong-Yeu Chang, Hung-Chang Hsu, Chao-Sheng Ke, Chih-Chung Hsu, May 2004
In this research, a parallel finite volume method was developed to simulate non-isothermal non-Newtonian steady flow in a coat-hanger extrusion die on PC clusters. We implemented the algorithm by domain decomposition methods that distribute the computational parts equally among the PCs and balance the loading of each PC to the utmost. Each PC exchanged data and information according to MPI (message passing interface) standard, and the governing equations were solved by using the three-dimensional collocated cell-centered finite volume method. In this approach, the extrusion flow can be predicted efficiently and accurately. Moreover, the effects of interconnect network were also discussed in this paper. The present numerical approach proved to be a promising solution for complicated extrusion problems.
Evaluation of Variability in Injection Molding (IM) Molds
Athirad Jantharawong, Mauricio Cabrera-Ríos, Blaine Lilly, José M. Castro, May 2004
The use of injection molding (IM) in high precision manufacturing relies upon the capability of the process to deliver parts consistently conforming to specifications. Characterizing such capability is a matter of understanding the most important sources of variation in IM and to find ways to provide robustness to the process. In this study, a statistical analysis of several sources of variability in IM is presented to precede a future optimization task in which the aim will be to find variable settings that provide the balance between high performance in selected measures as well as low variability around these indicators. The results presented here are meant to be an evaluation of IM molds for use in high precision manufacturing. A method that capitalizes on the strengths of statistical analysis is demonstrated here through two case studies where the variability in parts produced by different molds is assessed. The adequacy of these molds for high-precision manufacturing is determined.
Identifying the Best Compromises between Multiple Performance Measures in Injection Molding (IM) Using Data Envelopment Analysis (DEA): Preliminary Results
Carlos Castro, Narayan Bhagavatula, Mauricio Cabrera-Ríos, Blaine Lilly, José M. Castro, May 2004
Injection molding (IM) is considered to be the most important mass production process for plastic products. A substantial amount of research has been directed towards finding settings for the IM process variables as well as the optimal location of the injection gates. These objectives have been mostly approached through the optimization of performance measures (PMs) as functions of the process’ variables. The use of computer-aided engineering (CAE) has played a pivotal role in trying to achieve these objectives. The aim of this work is to demonstrate a method based on CAE, artificial neural networks (ANNs), and data envelopment analysis (DEA) to find the optimal compromises between multiple PMs to prescribe the settings of IM process variables and the location of the injection gate. Two case studies are presented for this purpose. The first case refers to the production of a cylindrical canister where part shrinkage plays an important role for an effective mold release. The second case analyzes the production of a generic part with cut-outs such as a window frame where the location of weld-lines is critical. Also in this second case flatness is considered an important measure.
Novel Impact Modification in Olefin Systems
Anna P. Andrews, Vicky Bryg, Anthony Dean, Paul DeFranco, Ann Panek, May 2004
Unique additives enable increases in the Gardner impact strength of polyolefins by a factor of 10 while maintaining up to 90% of the material flexural modulus. The effects of resin and additive loading level are addressed in a statistically designed experiment. Physical performance, rheological effects, thermal characterization, and morphological characterization are reported.

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