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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

Case Study: The Root Cause of Failure of an EPS Foam Coffee Cup
Duane Priddy, Thomas Peeler, May 2014

This study was carried out to determine the root cause of failure of a coffee cup resulting in serious personal injury. Billions of disposable coffee cups are used annually around the world. Most of the cups are molded using expandable polystyrene (EPS). EPS is a very complex material with many structural variables that affect the strength of molded parts. Lab testing and computer FEA analyses of the most common cup designs reveal that cups having a flared rim design are least robust and are thus most likely to fail during human interaction (e.g., lidding and holding/squeezing) compared with cups having a straight rim design.

Moisture Determination of Specialty Resins Using Relative Humidity Sensor Technology; A Solvent-Free Alternative to Karl Fischer Titration
James A. Moore, May 2014

The Health Care industry has increased its needs for specialized devices over the past decade, which has led to a new frontier of resin and polymer development designed to keep the quality of care high while minimizing cost. With these goals in mind, the resins being used for medical devices are scrutinized more thoroughly than other resins that require less regulatory compliance. The development of an alternative to Karl Fischer moisture analyzer, which uses a relative humidity (RH) sensor for quantifying water content has been achieved, and can be used for moisture specific analysis of medical device grade resins. The results between the two methods of detection of H2O content in TPU strongly correlate with the KF, with the KF measuring an average of 62ppm of water in the resin and the RH sensor instrument measuring 65ppm.

A Hybrid Approach for Prediction of Sheet Formation in Twin Sheet Extrusion Blow Molding (TSEBM) Process
Zohir Benrabah, Hicham Mir, May 2014

The sheet formation is the most critical stage in the Twin Sheet Extrusion Blow Molding (TSEBM) process, as the final dimensions of the blow molded part is directly related the initial extrudate sheet shape. A better understanding of the sheet swell/sag phenomena will ultimately lead to improvements in the prediction of the extrusion process, such as the optimization of both die design and processing parameters. Consequently, the development of a robust 2.5D numerical simulation tool of sheet formation in TSEBM process remains a challenging task, in order to achieve a prescribed accuracy with an optimal computational time, especially when it comes to industrial production rates featuring high Weissenberg numbers. The numerical validation, in terms of length and width distribution of the extruded sheet, is performed by comparing predicted solutions to experimental measurements obtained with different flow rates, die gap opening and extrusion time.

New Stainless Mold Base Steel with High Machinability and Improved Thermal Conductivity
Rob Esling, Valery Ngomo, Paul Britton, May 2014

An injection mold is designed to contain the polymer melt within the mold, efficiently transfer the thermal energy from the hot polymer to the cooler mold steel to provide uniform plastic parts, and eject the plastic part. In order to fulfil these primary functions, there are some main requirements for mold bases: • High machinability to provide both high productivity and longer tool life (cost reduction) • High and consistent mechanical strength and hardness • Good thermal properties to facilitate the removal of heat energy through cooling. • Good corrosion resistance to ensure mold durability and reduce maintenance costs. INDUSTEEL ArcelorMittal has developed an original patented free machining martensitic stainless steel: SUPERPLAST® Stainless (SPS). In this paper hardness and microstructure uniformity, high feed milling performance and thermal conductivity of the new grade and standard grade AISI 420FM (2085) will be compared.

Notes on Characterization of Natural Fiber Polypropylene Composites
Ahmed El-Sabbagh, Amna Ramzy, Leif Steuernagel, Stefan Kirchberg, Dieter Meiners, Gerhard Ziegmann, May 2014

Injection molding simulation of natural fiber thermoplastic composites NFTC requires material full characterization of the following parameter: density, thermal expansion, viscosity, (Pressure- Volume- Temperature) PVT-behavior, thermal conductivity, thermal degradation, polymer structure, specific heat and dynamic mechanical properties. The effect of fiber type (regenerated cellulose, sisal, hemp, wood fiber, wheat straw and kenaf), fiber content (10 and 30 wt.-%) and fiber length (0.5 and 1.5 mm for cellulose) on the mentioned material parameter as well as on their processing behavior during injection in a spiral mold was characterized. Compound viscosity and fiber type/ size were correlated. Other auxiliary results are found in this study concerning the constancy of fiber content along the injected products and the pore formation due to the inevitable gas evolution from the natural fibers.

Measurement of Transmittance and Reflectance Spectra of Edge-Lit 2-D Polymeric Light Guides
Moris Amon, May 2014

A commercially emerging type of lighting technology utilizing two-dimensional edge-lit polymeric light guide panels is described. Potential polymer-related engineering problems associated with these light fixtures are identified. One of these problems is the possibility of a color differences between panel surface regions close to and far from the light source. The theory and practice of a spectrophotometric method that can be used to assist material selection to solve this problem are described. Illustrative results are shown.

Critical Factors Affecting the Use of Finite Element Analysis for Rotomolded Parts
Hashim Bhabha, Christopher Liauw, Howard Taylor, Nick Henwood, Jason Condliffe, May 2014

Computer aided engineering (CAE) technologies, such as finite element analysis (FEA) of stresses offers the capability to optimize and validate engineering designs within a virtual environment, enabling potential problems to be highlighted and development time to be decreased. FEA has been used widely in the rotomolding industry, although it does not always appear to give an accurate prediction of behavior in the field. This paper examines several aspects with the aim of ensuring better correlation between FEA and actual part performance. Aspects considered include: Is Young’s Modulus representative of real stiffness? How important is Poisson’s Ratio? What is the effect of wall thickness variation in moldings?

4 Case Studies to Discover the Possible Automotive Applications of Glass Beads
Frédéric Juprelle, May 2014

Solid glass beads can be used in a lot of different thermoplastics in order to improve the following properties : scratch and abrasion résistances, dimensional stability, processing, ... The goal of this presentation is to show, with 4 case studies in automotive, the advantages given by the introduction of solid glass beads in different resins. The 4 case studies are : Mix of glass in Nylon compound in order to improve surface properties. Filler Pp compound with glass beads to improve scratch resistance Advantages to use glass beads in styrenic resins New solid glass bead grade to improve PC properties General conclusion will finish this presentation.

Limitations & Level of Accuracy of Tests for Rotomolding Powders
Nick Henwood, May 2014

The rotomolding industry commonly uses two connected tests to assess the quality of plastic powders: Dry Flow and Bulk Density. Industry-specific test methods are available for both parameters. Repeated measurements were carried out on five different rotomolding powders, in order to assess the influence of the various equipment and environmental parameters that are thought to affect the test. This enabled estimates to be made of the limits for the accuracy and repeatability that are achievable practically. The results obtained from the Dry Flow test suffer from significantly higher variance than those obtained from the Bulk Density test.

Effects of Temperature and Viscoelasticity on Film Die Flow Uniformity
Patrick C. Lee, Laura Dietsche, Joseph Dooley, Robert Wrisley, May 2014

This study shows the effect of die temperature distribution and resin viscoelacticity on the flow uniformity in a film die. The magnitude of the thermal affects can be significant enough to mask other rheological effects. Computational Fluid Dynamics (CFD) simulations predictions using temperature-dependent viscosity models and gradients in the die wall temperature boundary conditions agreed well with the experimental measurements of flow uniformity. When the die wall is more uniformly heated, the flow uniformity is improved in both the measurements and simulations, although the simulations showed more deviation from the experimental results as the elasticity and shear thinning of the resins increased.

Unique Rheological Properties of Polymer Melts with Flexible Nanofibers
Masayuki Yamaguchi, May 2014

Rheological response under elongational flow is studied using polymer melts with polymeric fine fibers composed of poly(butylene terephthalate) PBT and poly(4-methyl-1-pentene) PMP. Both fibers are prepared by hot-stretching of the blends with isotactic polypropylene PP or poly(L-lactic acid) PLA. The samples with 1 wt% of PBT fibers whose diameters are smaller than 1 µm show marked strain-hardening in elongational stress. On the contrary, the sample with PMP fibers with a diameter of approximately 2 ?m shows no strain-hardening, although the measured elongational stress is significantly higher than that calculated from the linear viscoelastic properties.

A Study on Void Formation in the Residual Wall Thickness of a Curved Area during Fluid-Assisted Injection Molding
Hyung-pil Park, Baeg-Soon Cha, Jae-Huck Choi, Dong-Han Kim, Byung-Ohk Rhee, Soo-Bin Park, Kye-Hwan Lee, May 2014

We analyzed the different effects on the formation of void in a residual’s wall thickness during fluid-assisted injection molding where water and silicone oil that had different thermal properties were used. For this, we conducted heat transfer analysis and injection molding analysis. We confirmed that void formation occurred due to the distribution of the temperature and volumetric shrinkage in the direction of the residual wall thickness in a curved area with a hollow section. We also found that void formation in the curved area decreased in case of using silicone oil compared to using water from simulation and experiment.

Viscoelastic Models with Logarithmic Strains
Donggang Yao, May 2014

Analysis of 3-D viscoelastic flows is of a particular interest in polymer processing. Classical approaches rely on the Finger tensor and its inverse for strain evaluation. In this paper, we present a general Maxwell model with a logarithmic tensor for strain determination. Since the logarithmic strain provides a better representation of the state of straining of the material, the resulting constitutive model is expected to have a number of advantages including more uniform straining in different directions and extended linear behavior towards moderate deformations. Model testing on simple shear with only two material constants demonstrated simultaneous prediction of shear thinning and first and second normal stress differences.

Nucleation Efficiency of Talc in the Foaming Behavior and Cellular Structure of Polyolefin-Based Foams: New Perspectives for Optimized Lightweight Materials
Parashar Dave, Gilles Meli, Frédéric Jouffret, May 2014

The research consisted in evaluating the nucleation efficiency of different types of talc (with different particle size distributions, morphologies and even surface modifications) in the foaming behavior and cellular structure of polypropylene-based materials, with the objective of developing lightweight materials with improved stiffness at lower densities. Nucleation efficiency was first evaluated in talc filled PP foamed with a physical blowing agent inside a high pressure vessel. Depending on different talc characteristics, such as particle size distribution, surface area and morphology, cell density as much as doubled. Optimized foamed PP-talc composites prepared by injection-molding using the MuCell® process displayed further weight reductions for similar stiffness values. There was some work done on polystyrene foams

Cooling Simulation for the Prediction of Quality Properties and Production Costs of Semi-Finished Extruded Products like Pipes
Patrick Weiss, Kenny Saul, Gregor Hiesgen, Martin Spitz, May 2014

When producing extruded products like pipes, the cooling process has a decisive effect on the quality and the production costs. The high potential for optimization of cooling processes is shown by a cooling simulation software that replicates the cooling stage in a virtual model, named chillWARE. Using the recommended settings for specific processes can reduce residual stresses and eliminates the need for follow-up processes like a subsequent tempering. It is possible to link the cooling process settings to the demanded product quality properties. In many cases, a positive side effect is the resulting reduction in operating costs for the cooling process.

Micromechanical Modeling of Thermally Conductive Polymer Matrix Composite Foams
Hao Ding, Yuxiao Wang, Siu Ning Leung, May 2014

A micromechanical model has been developed to study the effect of polymer matrix composite (PMC) foams’ morphology on its effective thermal conductivity (keff). Polymeric foams are commonly used for thermal insulation. This paper reveals that it is possible to fabricate light-weight thermally conductive PMC foams by tailoring their cellular structures. Their keff are governed by both the foams’ volume expansion ratios as well as the foaming-assisted alignment of thermally conductive filler. Moreover, the PMC foams’ keff would further be promoted by tailoring the aspect ratio of the cellular structures through constrained foaming. The exciting results have led to new research directions to develop novel polymeric material systems for thermal management applications.

Composites of Multi-Walled Carbon Nanotubes and Ethylene-Tetrafluoroethylene Copolymers
Yuan Rui, Brian Grady, Jeff Harwell, Tomoaki Nakanishi, Seigo Kotera, May 2014

Multi-walled carbon nanotubes (MWCNTs) were added to random copolymers of ethylene and tetrafluoroethylene. Surprisingly, the electrical percolation threshold of the resultant composites was quite low; approximately 0.9 wt. %; the same nanotubes with the same mixing procedures in polyamide 6,6 yielded a percolation threshold of 1.5%. This low percolation threshold occurred even though the polymer surface energy is quite low which should make tubes more difficult to disperse. The effect on crystallization kinetics was quite small; suggesting perhaps that a lack of transcrystallinity might explain the low percolation threshold. The dispersion was measured via optical microscopy and seemed to be excellent.

Polypropylene Block Copolymers Flame Retarded with the Blends of Poly(Pentabromobenzyl Acrylate) and Magnesium Hydroxide
Sergei Levchik, Lior Melamed, Eyal Eden, Marc Leifer, Pierre Georlette, May 2014

Flame retardant systems for polypropylene block copolymers based on combinations of poly(pentabromobenzyl acrylate) and synthetic magnesium hydroxide are reported in this paper. This combination of flame retardants allows a significant decrease of use of antimony trioxide synergist. It also helps to maintain good physical properties and significantly reduces smoke evolution. The addition of ethylene/1-octene copolymers to this combination improves Izod impact strength. Since poly(pentabromobenzyl acrylate) is a high molecular weight polymer, it will not migrate from the plastic parts and cannot penetrate through the cell membranes of living organisms and therefore it is believed to be safe in use. The high thermal stability of poly(pentabromobenzyl acrylate) and synthetic magnesium hydroxide indicates good recyclability of the flame retardant polypropylene copolymer.

Predicting the Flow Behavior of Powders, with Particular Reference to Rotomolding Materials
Nick Henwood, May 2014

The rotomoulding industry uses a simple but crude measure to assess the flowability of powders, which involves timing the discharge of powder through a funnel with a circular bottom orifice. The flow of granular materials through orifices has been the subject of considerable research elsewhere and equations exist that relate flow to the various parameters involved. The most well accepted formula was assessed for its suitability to typical rotomoulding materials, as well as a variety of other powders and granulates. The characteristics of many materials (including rotograde micropellets) showed good correlation to theoretical predictions. Polyethylene and polypropylene rotograde powders showed behaviour that could be described by a modified version of the existing equation.

Modeling of Moisture Effects on the Rheological Behavior of Polymers and Influences on the Injection Molding Process
Felix A. Heinzler, Christoph Mielicki, Jens Siepmann, Johannes Wortberg, May 2014

By processing technical polymers like polyamide or polybuthylene terephthalate, possible causes for process variations are residual moisture of the material or different conditions with respect to time and temperature. To show influences on the quality of an injection molding process, the changes have to be measured and described by a rheological model. The material behavior is measured by a rotational rheometer and a high-pressure capillary rheometer at different conditions. Effects like thermal and hydrolytic degradation or viscosity reduction by residual moisture are examined during this investigation. Combining measurements to a rheological model allows the simulation of influences on the processing and compensations. Therefore a new extension of the Carreau-model is presented. Parameters describing the material behavior are completed by a thermodynamic and calorimetric analysis of the material.

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