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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

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.

Portals to the Millenium: Internet '99
Geoffrey Engelstein, May 1999

Portals have replaced Push as the hot Internet buzzword of the moment. A Portal Site is one that provides a variety of services to surfers, including a search engine, discussion groups, and editorial content. They also host extensive corporate advertising. By providing a one-stop entry point portals aim to maximize hits and make it more attractive to advertisers. While portals are typically associated with ‘mega-sites’ like Yahoo and Infoseek, industry-specific portals are springing up. Internal intranet portals are also becoming popular in larger companies. This paper reviews the portal concept and looks at how it fits into a marketing plan on all three levels: mega, industry-specific, and internal.

The Development of Polyolefin Based Oriented Glass Fiber Building Materials
Thomas J. Nosker, Richard W. Renfree, Kenneth E. Van Ness, May 1999

In 1994, Rutgers University’s Plastics and Composites Group, formerly the Center for Plastics Recycling Research, was grant funded by the New Jersey Commission on Science and Technology to develop and test composite railroad ties made from recycled plastic. Since the inception of this project, the major participants have been Rutgers University, US Plastic Lumber Corporation (formerly Earth Care Products, Inc.), Conrail, Norfolk Southern, Washington and Lee University, and the US Army Corps of Engineers. Though the main goal of this research was to produce plastic lumber with properties required of railroad ties for substitution with creosote treated oak, the project participants knew that many other applications could utilize this material as a direct substitute for wood. A direct result of this research was the discovery of a way to orient a high percentage of short, random length glass fibers along the axis of flow in a mold. U.S. Patent 5,789,477 was granted August 4, 1998 for this discovery, and we are sharing the information here.

Synthesis and Characterization of Poly(Butyl Acrylate-Co-Styrene)/PMMA with Gradient Composition
C.F. Jasso-Gastinel, J.M. Martinez-Chavez, G. Spence, L.J. Gonzalez Ortiz, May 1999

Formerly, gradient polymers made by sequential polymerization have been studied for systems having a rigid matrix. There, the gradient structure has raised performance compared to material of global equivalent composition with homogeneous structure. In this work, a converse material was synthesized, preparing a Butyl acrylate (54 mol %) - Styrene photocopolymer to use it as matrix. MMA was then diffused at low temperatures and photopolymerized in situ to obtain a certain composition with homogeneous or gradient structure. Chemical composition throughout the slabs was established by IR. Stress - Strain and dynamic mechanical properties showed the performance superiority of the gradient materials.

Mechanical Behavior of Fabric-Film Laminates
Magdi A. Said, May 1999

Inflatable structures are gaining wide support in planetary scientific missions as well as commercial applications. For such applications a new class of materials made of laminating thin homogenous films to lightweight fabrics are being considered as structural gas envelops. The emerging composite materials are a result of recent advances in the manufacturing of lightweight, high strength fibers, fabrics and scrims. The lamination of these load-carrying members with the proper gas barrier film results in a wide range of materials suitable for various loading and environmental conditions. Polyesterbased woven fabrics laminated to thin homogenous film of polyester (Mylar) are an example of this class. This fabric/film laminate is being considered for the development of a material suitable for building large gas envelopes for use in the NASA Ultra Long Duration Balloon Program (ULDB). Compared to commercial homogenous films, the material provides relatively high strength to weight ratio as well as better resistance to crack and tear propagation. The purpose of this paper is to introduce the mechanical behavior of this class of multi-layers composite and to highlight some of the concerns observed during the characterization of these laminate composites.

Eliminating Density and Heat Capacity Requirements in Transient Thermal Conductivity Measurements
Nancy Mathis, May 1999

Transient thermal conductivity methods have benefited from the rapid nature of the testing. The drawback has been the need to measure density (?) and heat capacity (cp) for the materials in order to calculate thermal conductivity. For speed, nominal values of ? and cp have been used, producing questionable thermal conductivity results. If ? and cp are measured, the increase in time reduced the benefit of the transient measurement. This difficulty has now been removed. A new technique has successfully been demonstrated which produces thermal conductivity directly. The only additional parameter that is necessary is material thickness. This new technique uses existing instrumentation without the need for hardware modification.

Stress Relaxation of Poly(Ethylene Naphthalate): Isothermal, Isochromal and Isostructural Responses
Maria L. Cerrada, Gregory B. McKenna, May 1999

The physical aging response of polymers is generally examined in isothermal conditions by following the viscoelastic behavior as a function of aging time. It is then often asked if time-aging time superposition applies at a single temperature. If so, it can then be ascertained if time-temperature superposition applies to the aging time reduced curves obtained at different temperatures. In prior work from this laboratory we showed that isothermal time-aging time superposition did not apply to amorphous PEN. In this work we describe the surprising result that samples aged at 100 °C and then tested at 30 °C, 50 °C, 70 ° and 90 °C, that is iso-structurally (constant fictive temperature) seem to follow time-temperature superposition.

Low-Temperature Toughening Behavior of Polyolefin Blends and Composites
Joo Seok Oh, Yong Lak Joo, May 1999

The low temperature impact properties of glass fiber reinforced Polypropylene and polyolefin blends with two different rubbers are investigated. Our results reveal that the impact strength increases with decreasing temperatures when glass fibers are highly loaded. The thermomechanical analysis over a wide range of temperatures is employed to elucidate the possible cause of the pronounced temperature dependence of the impact strength. It is found that the average thermal expansion coefficient of the highly filled composites significantly deviates from the linearity of a simple mixing rule. This significant reduction in the thermal expansion coefficient caused by the addition of glass fibers can provide a useful strengthening of the bond between fiber and matrix by increasing the compressive pressure exerted on the fibers by the matrix at low temperature. Meanwhile, the increase in the impact strength of polyolefin blends with some rubbers was also observed below room temperature. The examination of fractured surfaces of these blends clearly demonstrates the different toughening behaviors at low temperatures. We suspect that the difference in thermal expansion coefficient between rubber and matrix possibly causes the increase in the interfacial stress between rubber and matrix at low temperature.

Membrane-Inflation Rheometry - A New Way of Measuring Biaxial Deformation Behaviour at Process-Relevant Conditions
C. Detrois, E. Haberstroh, May 1999

In blow-moulding, film production and other processes, polymers are biaxially stretched. For the layout of those processes, for Finite-Element Analysis (FEA) and for raw material development, the mechanical material behaviour of the polymer materials must be known. Therefore, the stress/strain behaviour of the material at forming temperatures and high strain rates is investigated in this paper. A new measurement device is described called the Membrane-Inflation Rheometer. It is capable to measure stress/strain behaviour of polymers under equibiaxial deformation and process relevant conditions concerning temperature and strain rate. The algorithm for data evaluation is explained. Some results for different polymer materials are presented.

Fast Design of Mixing Sections by Means of Network Theory
Jochen Hennes, Walter Michaeli, May 1999

Single-screw extruders make use of mixing and shearing sections to ensure good thermal and mechanical homogeneity at high mass throughput rates. Nowadays, these sections are usually designed empirically or with very simple estimation formulas. Therefore, important interpretation criteria, like pressure loss, temperature increase, average shear rate or residence time profile are only determined very inaccurately. The 3D finite-element analysis (FEA) can determine these parameters very precisely, but with very long computation times. The network theory allows an economic calculation with a sufficient accuracy of the aforementioned data. This paper describes the modelling of extruder mixing sections and the solution of these models by means of the network theory.

Quality Control of the Discontinuous Compounding Process in a Rubber Internal Mixer by Regression and Neural Networks Process Models
P. Ryzko, E. Haberstroh, May 1999

The discontinuous processes in the rubber manufacturing are sensitive to low deviations in the processing method. The main reasons for these deviations are the fluctuations into the process parameters or deviations of the quality of raw materials or the manual operations. The on-line quality prediction of rubber compounds based of the mathematical models for the mixing process in an internal mixer is an important step in direction of quality control. For most applications the models based on regression or neural networks lead to quality predictions of over 90% for various compounds and machine sizes. Such a measure and control unit has been successfully tested at a laboratory mixer.

Optimization of the Wall Thickness Distribution of Pharmaceutical Press-Through Blisters
Joachim Wolf, Walter Michaeli, May 1999

The wall section of medical press-through blisters may reduce the stability of the packed medicine. A homogeneous wall thickness over the entire capsule chamber enables the manufacturer use a thinner starting foil without a lack of quality, which leads to the saving of raw material and other expenditures. Three thermoforming methods are tested on an industrial form-fill-seal" line. the temperature profile of the raw film before forming the friction coefficient between films and molds or plugs and the biaxial rheological properties of the foil influence the resulting wall thickness distribution."

The Centrifuge - An Alternative to the Filter for Highly Contaminated Polymer Melts
Frank van Lück, Walter Michaeli, May 1999

The recycling of thermoplastics gains more and more importance. For removing the contamination one-or-two step filtration units are state of the art, but due to high material loadings or running costs they often reach their limits. Therefore IKV examines whether a centrifuge, which is fed with polymer melt, might be an alternative. In preliminary tests IKV showed that centrifuges built for low-viscosity materials can also be used for polymer melts. A centrifuge was installed into an extrusion line. Up to 10 weight-% of contamination could be removed out of the polymer melt successfully.

Combining Liquid-Silicone-Rubbers with Thermoplastics to Rigid-Flexible Combinations Using 2-Component-Injection-Molding
Christoph Ronnewinkel, Edmund Haberstroh, May 1999

Since multi component injection molding techniques are well established, the development of rigid-flexible combinations is increasing. Besides combinations between thermoplastics and thermoplastic elastomers (TPE) which are used in various applications, the combination of Liquid-Silicone-Rubbers (LSR) and thermoplastics becomes more important because of their better thermomechanical and mechanical properties in comparison with TPE. Concerning the adhesive strength of these combinations which depends on the properties of the materials, the process parameters in the molding process and the mold-technique there is only insufficient knowledge. To solve this techniques are developed to improve the adhesive strength between the materials.

Process Analysis and Machine Technology for the Injection Molding of Microstructures
Alrun Spennemann, Walter Michaeli, May 1999

In micro injection molding two different tasks can be distinguished: These are the injection molding of small parts (> 1 g) with microstructured details and the direct production of micro parts, i.e. parts with a part weight down to milligrams (mg). Until now there are no suitable injection molding machines available for the production of single micro parts, so injection molders produce big, but precise sprues to achieve the necessary shot weight. To solve this problem, the IKV is developing a micro injection molding machine that meets the molder's demands. First, the injection molding process with differently manufactured micro cavities is analysed.










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