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

Microstructure Development during the Injection Moulding of PET/LCP Blends
E. Turcott, K.T. Nguyen, A. Garcia-Rejon, May 1999

For several years, plastics processors have been blending two or more generally incompatible materials in order to improve physical or mechanical properties. Depending on the degree of compatibility and thermomechanical history during processing, various goals may be attained: easier processing, improved mechanical (modulus, impact strength), thermal and barrier properties. Polyethylene terephthalate (PET) enjoys wide success in industrial applications because of its outstanding mechanical, optical and barrier properties. However, the growing demands of the electronics and automotive sectors have surpassed the PET performance limits. With its outstanding barrier properties as well as mechanical properties even at high temperatures, LCP's are potential candidates as a blend component.

Transverse Permeability of Direct Glass Rovings
P.J. Bates, Danny Taylor, Michael Cunningham, May 1999

Rovings are used in a variety of polymer processes such as filament winding and compression molding. In all these processes, impregnation of the roving monofilament bundle by the liquid polymer is essential. Modeling polymer impregnation requires an estimate of the transverse Darcy's Law permeability. This study measured the transverse permeability of 2400 tex glass rovings as a function of applied compressive stress, monofilament diameter, roving thickness, fluid velocity and viscosity. The permeability was observed to depend strongly on the compressive stress, and hence void fraction. The permeability was independent of the monofilament diameter, roving thickness, fluid velocity and viscosity. Results are presented using a simple model that accounts for roving void fraction inhomogeneities.

Finite Element Modeling of the Plug-Assisted Thermoforming Process
J.F. Lappin, E.M.A. Harkin-Jones, P.J. Martin, May 1999

In the production of food packaging using the plug assisted pressure thermoforming process it is desirable to optimize costs and product properties through efficient distribution of material. Typically in industry conditions for forming are obtained by trial and error which can be very inefficient. In this paper the development of a finite element model of the process is described. Modeling was carried out using a commercial finite element package and the model encompasses both 2D axisymmetric and more complex 3D geometry. Material behavior is simulated using a viscoelastic model based on data obtained from various material tests.

Crystallization of Isotactic Polypropylene: Pigment, Nucleating Agent and Recycling Effects
Y. Mubarak, E. Harkin-Jones, P. Martin, M. Ahmad, May 1999

In order to produce thermoformed products of consistent quality, an understanding of the effect of material and process parameters on end part performance is necessary. In this investigation the effect of pigment, nucleating agent, and recycling regrind on the nucleation of homopolymer isotactic polypropylene have been studied. Differential Scanning Calorimetry was used to reveal the effect of these additives on the crystallinity, type of crystals, crystallization and melting temperatures at different cooling rates. It has been found that percentage cystallinities were increased as the concentration of the nucleating agent and first and fifth generation regrinds increase up to the saturation level. Although more hexagonal ? crystals were formed by increasing the concentration of the pigment, the enthalpy of fusion was decreased.

Influence of Extrusion Parameters on Polypropylene Sheet for Use in Thermoforming
G.W. Harron, E.M.A. Harkin-Jones, P.J. Martin, May 1999

The quality of extruded sheet for use in subsequent thermoforming operations may be defined in terms of its resistance to sag, low and consistent shrinkage, tensile properties and overall consistency of these properties with time. The sheet extrusion process has many variables such as melt temperature and output rate that may influence the properties of the sheet and it is the objective of this work to identify the critical variables in the process. To achieve this objective a series of experiments were conducted using a statistical design of experiments methodology. This investigated the effects of MFI, Melt Temperature, Chill Roll Temperature and Line Speed on the properties of the extruded polypropylene sheet which are of importance in the future thermoforming process. The sheet properties investigated included tensile properties, crystallinity, sheet sag and shrinkage. The main findings of the study were that melt temperature had the main effect on the shrinkage in the machine direction, while the chill roll temperature and line speed had the main effects on the tensile properties. Sheet sag was found to be greatest at the lower MFI value, which correlated to the lower levels of crystallinity of the as made sheet.

Correlation of the Thermal Analysis of Chemical Blowing Agents with the Cell Morphology of Extruded, Expanded Polypropylene Rod Samples
D. Dixon, E.M.A. Harkin-Jones, P.J. Martin, May 1999

This paper relates the thermal decomposition behaviour of chemical blowing agents (CBAs) with the cell morphology of EPP (expanded polypropylene) produced using those blowing agents. Correlation between decomposition temperatures and rates of the various agents and the cell morphology of extruded, EPP are reported and discussed. The research has revealed relationships between the structure of an extruded PP foam and the thermal decomposition response of the chemical blowing agent used during production. The CBAs tested showed a very wide range of cellular structures under the same processing conditions. Those with a higher temperature and rate of gas evolution generally produced foams with the smallest cell sizes and highest cell densities.

Effects of Process Conditions on Shrinkage and Warpage in the Injection Molding Process
T. James Wang, C.K. Yoon, May 1999

Polymer density increases when it cools down in the cavity. In the injection molding process, without proper packing to provide extra material to fill the void due to the density change, parts will shrink and even warp. Reducing shrinkage and warpage of injection molded parts in order to improve quality is one of the top priorities in the manufacturing process. Part design, material properties and process conditions are factors that affect part quality most significantly. In this paper, the effects of process conditions on shrinkage and warpage will be discussed. They include packing pressure, packing time, fill time and mold wall temperature. Two tools, CAE software and design of experiment, will be used in this investigation. This paper will show that these two can be used together effectively to design the process window.

Product Demonstrations via Desktop Video
Geoffrey Engelstein, May 1999

New PC-based software and peripherals are now available that allow the creation of a broadcast-quality animation and live-action video studio for under $2000. This opens up a valuable means for engineering and marketing to communicate design intent and performance via the readily accepted medium of video tape very early in the development cycle. These tools allow CAD data to be further leveraged through photorealistic computer animations of intended product usage. This paper surveys currently available software and hardware, including rendering and animation, video capture, video compositing, and video output, and discusses advantages and disadvantages of various approaches. Sample product demonstration videos will also be shown. The uses of desktop video are limited only by the imagination. However some of the more obvious possibilities include: • Animated fly-by • Product usage • Assembly procedure • Marketing and engineering evaluation • Corporate promotional video

Analysis of Mixing Inco-Rotating Twin Screw Extruders through Numerical Simulation
Th. Avalosse, Y. Rubin, May 1999

Nowadays, many materials, pigments, additives, gas or reactants, are mixed to create new products combining the characteristics of different raw materials to obtain a specific product properties. The quality of the mixing, i.e. the uniformity of the mixture, is a key issue that will determine the morphology and the properties of the resulting compound [1, 2]. An insight into those features can now be obtained through the numerical simulation of flow in extruder components. 3-D transient numerical simulations of two twin screw extruder (TSE) sections are presented and their behavior compared. A new technique, the mesh superposition method (MST), accurately determines the part of the computational domain which is occupied by the fluid with respect to the current screws position; the Navier-Stokes equations are then solved without involving any remeshing. Through the calculation of trajectories of material points, statistical information (of the RTD, deformations, dispersion, etc.) can be obtained to compare both configurations in a synthetic and quantitative way.

Improvement of the Simulation of Shrinkage and Warpage by Characterizing the Material Behaviour More Exactly
Peter Niggemeier, Walter Michaeli, May 1999

Caused by the demand on shorter development times for technical products the use of simulation programs for the rheological, thermal and geometrical mould design increases. Up to the present, the prediction of shrinkage and warpage of semi-crystalline polymers is difficult because of the complex material behavior during the crystallization [1-3]. Therefore the influence of the thermal material data und parameters on the prediction of temperature profiles is intensively discussed at the IKV. The cooling rate is also considered in the pvT-behaviour.

Numerical Simulation and Process Window Design of Injection/Compression Molding
T. James Wang, May 1999

The injection/compression molding process is a better choice than traditional injection molding process when large, thin or precision parts are produced. However, by introducing an independent press control to the polymer injection control, it becomes more difficult to find proper process conditions. In this paper two tools are discussed. The first tool is CAE software that has been developed to simulate injection/compression molding process. Second, a process window also has been developed to help the design of process conditions. This paper will show that both tools provide useful insight into the process that helps engineers make rational judgements.

The Effect of Rapid Prototype Tooling on Final Product Properties
E. Kent Dawson, John D. Muzzy, May 1999

Rapid tooling has allowed manufacturers to produce plastic injection-molded prototypes quickly and inexpensively. However, the mechanical properties of parts differ between rapid and conventional tools. The tensile and flexural properties of injection-molded parts produced in geometrically identical steel and composite molds were compared using atactic and syndiotactic polystyrene. When molded in the composite mold, both isomers exhibited an average of 17% lower ultimate tensile strength, similar Young's modulus, and 20% lower ultimate elongation than parts produced in the steel mold. The tensile stress-strain data for both isomers were found to be correlated. In flexural testing, both isomers molded in the composite mold exhibited an average of 19% higher flexural strength, 39% higher flexural modulus, and 27% lower ultimate flexural elongation than parts produced in the steel mold.

Higher Conductivity Composite Tooling
E. Kent Dawson, John D. Muzzy, May 1999

High conductivity carbon fiber was used to produce reinforced epoxy tools with unique thermal properties. When compared to epoxy and alloy backfilled stereolithography (SL) tools in identical heat conduction experiments, the fiber-reinforced epoxy tool showed an average of 17% greater conduction through the tool and 31% greater conduction across the tool's surface. These anisotropic thermal properties were speculated to be the result of preferential fiber orientation on the surface of the fiber-reinforced epoxy tool. Additionally, the fiber-reinforced epoxy tool exhibited 81% less total injection molding cycle time and 229% less production time than its backfilled SL counterpart.

A New Dispersive and Distributive Static Mixer for the Compounding of Highly Viscous Materials
Paul Gramann, Bruce Davis, Tim Osswald, Chris Rauwendaal, May 1999

In the compounding of polymers, static mixers are commonly used for distributive mixing. However, successful compounding generally requires both distributive and dispersive mixing; where the most difficult mixing involves the dispersion of materials having widely different viscosities. The best method to accomplish successful dispersive mixing is to expose the material to extensional flow. Furthermore, in terms of power consumption, extensional flows are far superior to the shear-type flows found in most mixing systems. This paper presents a new dispersive and distributive static mixer (DDSM), which exposes the fluid element to continual extensional flow for enhanced mixing.

Polymerization in a Twin Screw Extruder - Effect of Screw Configuration on MWD and Copolymer Content
J. Grenci, D.B. Todd, May 1999

A counter-rotating nonintermeshing twin screw extruder specifically designed to provide extensive backmixing was used to investigate the molecular weight distribution (MWD) occurring in the polymerization of Butyl Acrylate and the MWD and drift of copolymer content occurring in the copolymerizations of Butyl Acrylate/Styrene and Butyl Acrylate/Butyl Methacrylate. In contrast to almost plug flow characteristics observed in conventional single screw and twin screw extruders, this backmixed extruder has a residence time distribution comparable to a continuous stirred tank reactor, yet provides a positive drag flow regime for high viscosity fluids not available in stirred pots. The polydispersity (Mw/Mn) of chain addition polymerizations carried out in the backmixed extruder was cut in half when compared to those obtained in a conventional (plug flow) extruder, thus producing a more monodisperse polymer, and approached the theoretical value for a micromixed CSTR. The copolymer content of chain addition copolymerizations carried out in the backmixed extruder was demonstrated to be constant as a function of position in the reactor, whereas drift was observed in the conventional (plug flow) extruder. Acrylate/Styrene and Butyl Acrylate/Butyl Methacrylate produced in the backmixed reactor is contrasted with that from a conventional twin screw extruder, which exhibits virtual plug flow behavior. The copolymer composition is also contrasted at various locations in the extruder.

System Modelling for the Control of the Rotational Molding Process
D.I. Abu Fara, M.P. Kearns, R.J. Crawford, May 1999

In recent years the rotational molding process for plastics has become more sophisticated in terms of equipment design and the complexity of the molded parts. One of the weaknesses that remain is the lack of precise control of the process variables. Molders can now monitor in real time the temperatures inside the mould but there is a lack of a model relating machine controls and the key temperatures in the process. This paper presents for the first time the use of neural network methods to develop models to assist in the design of control systems. In this first phase of the work, deterministic step changes were used to derive a model relating oven temperature and the mold internal air temperature.

The Blending and Coextrusion of Metallocene Catalysed Polyethylene in Blown Film Applications
C.M. Beagan, G.M. Mc Nally, W.R. Murphy, May 1999

As Metallocene Catalysed Polyethylenes ( mPE's ) become more commercially available they are finding ever increasing application in the blown film industry. However, it is becoming apparent that no two mPE resins behave in exactly the same manner. This paper examines the rheological properties of a range of mPE's with different densities and MFI's. These resins were then blended with a conventional low density polyethylene ( LDPE ) to form monolayer films. The mechanical properties of these films were compared to three layer coextruded films of A:B:A structure, where A is LDPE and B is mPE.

Finite Element Analysis of Plastic Plumbing Assemblies
Y. Chen, B.D. Agarwal, L.J. Broutman, May 1999

The long term performance of household plumbing assemblies is influenced by several factors including design, installation, and field service conditions. With plastic components, different factors interact to complicate the situation. Stresses in the body of plastic components and at the interface of components (pressure) strongly affect the chemical resistance, stress cracking and leak proofing of joints. A finite element stress analysis of plastic fittings has been carried out using a special contact algorithm. This algorithm permitted free relative movements of materials in contact and thereby allowed an accurate determination of assembly stresses. Many other FEA softwares on the market impose stronger constraints on relative movements that may introduce significant errors. The long-term performance has been predicted using creep analysis. FEA results compare favorably with experimental measurements.

Analysis of Polymer Flow near Glass Transition Temperature
Yi-Je Juang, L. James Lee, Kurt W. Koelling, May 1999

In many polymer manufacturing operations, the material is processed near the glass transition or melting temperature. Examples are plastic welding, thermoforming, blow molding, film blowing, forging, and de-airing in safety glass lamination. In these processes, some of the solid-like behavior like strain hardening and yield stress may play important roles. They make material flow (or deformation) substantially different from that of a polymer melt. In order to understand the flow behavior near the glass transition temperature, polyvinyl butyral (PVB), a polymer used in safety glass lamination, was studied in this work. The material properties of the polymer were characterized by using the Rheometrics Mechanical Spectrometer (RMS) and the Rheometrics Solids Analyzer (RSA). The measured flow properties were modeled by a viscoplastic model. A finite element code, DEFORM, was applied to compare the simulation results with a compression molding experiment.

The Effect of Flight Radii Size on the Performance of Single-Screw Extruders
Mark A. Spalding, Joseph Dooley, Kun Sup Hyun, May 1999

The size of flight radii on the screw channel is important for the proper performance of a single-screw extruder. SPI guidelines state that the root radii should not be less than half the depth of the channel. Improper design or fabrication, however, often results in radii that are less than half that for the metering and transition sections, leading to regions with long residence time and material degradation. For optimal solids conveying, however, the effect of flight radii is considerably more complicated. This paper will present experimental and numerical data that indicate how to specify the flight radii for all sections of the screw.

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