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

Optical Haze Properties of Polyethylene Blown Films: Part 2-The Origins of Various Surface Roughness Mechanisms
Ashish M. Sukhadia, David C. Rohlfing, Matthew B. Johnson, Garth L. Wilkes, May 2001

In continuation of our associated report here (see Part 1, ANTEC 2001), we have now found that high haze in PE blown films can be caused by very different surface roughness mechanisms having unique origins. The total haze % exhibits a complex parabolic relationship with the logarithm of the recoverable shear strain parameter, ??. At low ??, spherulitic superstructures are formed. As ?? increases, an oriented, row-nucleated stacked lamella texture is developed. However, at even higher ??, fine-scale surface roughness due to high melt elastic instabilities is induced. We believe that this is the first time that both very low and very high melt elasticity have been shown as primary causative factors in yielding high haze in PE blown films, albeit for fundamentally very different reasons.

Recovery of Post-Consumer Plastic Waste via Solid State Mechanochemistry
Klementina Khait, Erin G. Riddick, John M. Torkelson, May 2001

A new solid-state mechanochemical technology is being developed to create value-added materials from post-consumer plastic waste. The process, called solid state shear pulverization (S3P), can recycle various mixtures of ordinarily incompatible plastics, including post-consumer film waste, by subjecting the polymers to high shearing forces in the solid state. This produces uniform, light-colored powders of variable fineness suitable for processing by all conventional plastic fabrication techniques. The resulting materials consistently exhibit high elongation and impact strength. Northwestern University and Material Sciences Corporation are transitioning S3P from the laboratory to the commercial scale.

Confocal Laser Scanning Microscopy of Pigmented Polypropylene Systems for Dispersion Evaluation
Erik C. Nielsen, May 2001

Determining the level of dispersion of pigments in polyolefins is a critical quality control issue in the production of color concentrate masterbatches. Confocal laser scanning microscopy (CLSM) can be used to identify the presence of agglomerates in the pellet form rather than diluting the material and blowing a film. This technique requires minimal sample preparation and is non-destructive in nature. Micrographic images can be correlated with traditional dispersion tests to develop a repeatable protocol. Four commonly used high performance pigments are investigated in a polypropylene carrier.

VOCs Emissions and Structural Changes of Polypropylene during Multiple Melt Processing
Q. Xiang, M. Xanthos, S. Mitra, S.H. Patel, May 2001

Polypropylene, as a commodity recyclable thermoplastic, is studied in this research to evaluate the potential environmental impact resulting from volatile organic compounds (VOCs) emitted during multiple reprocessing. Unstabilized commercial polypropylene (PP) grade was processed several times by injection molding. Samples were examined after each cycle for total VOCs emissions with a flame ionization detector (FID) and cumulative VOCs emissions were obtained after each processing step. Corresponding structural changes were investigated with Fourier Transform Infrared (FTIR) Spectroscopy and results were correlated with rheological data that showed decreasing viscosity particularly after the 7th processing cycle.

Extrusion Foaming of PET/PP Blends
C. Wan, M. Xanthos, S. Dey, Q. Zhang, May 2001

In order to develop new applications for recyclable commingled resin streams, blends containing PET and PP resins with different rheological characteristics were dry blended or compounded at different ratios and subsequently foamed by using PBAs and CBAs. Properties of the foamed blends were compared with those of similar products obtained by foaming the individual PET and PP components in the absence of compatibilizers/rheology modifiers. Foamed polymer blends with fine cell size and low density could be produced in the presence of suitable compatibilizer systems consisting of functionalized polyolefins or their combinations with reactive coagents

Compression Molding Tooling for Thermoplastic Composites
Harold F. Giles, Jr., May 2001

Tooling requirements for compression molding continuous glass mat, long fiber glass, or other types of reinforced thermoplastic composite products is presented along with critical tooling aspects. Emphasis is placed on the general tooling concepts associated with cooling lines, shear edges, guidance systems, ejectors and stop blocks. Basic product design issues that can lead to poor part performance i.e. weld lines, tabs and mounting holes, ribs and bosses, sink marks, multiple cavity molding, and venting are discussed. The relationship of prototype tooling and the requirements to go from design to production is discussed briefly.

A Physical-Mathematical Model for the Description of the Process Behavior of Mixing Elements
H. Potente, K. Kretschmer, J. Flecke, May 2001

Tightly intermeshing, co-rotating twin screw extruders are commonly used 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. Physical-mathematical models enable the process engineer to predict the process behavior of a chosen extruder configuration and to optimize existing compounding processes. We will present physical-mathematical models for the prediction of the pressure-throughput relationship of grooved conveying and grooved reconveying elements. The models are based on an analytical approach for the description of the flow patterns within the investigated screw elements. Experimental investigations were performed with varying geometry, material and process parameters. Finally the developed model was compared to the experimental results.

Extrusion/Compression of Long Fiber Thermoplastic Composites
Klaus Gleich, May 2001

It is becoming common for long fiber-reinforced thermo-plastics (LFT) to replace existing GMT-type applications as well as to capture new applications. This is especially true in the European automotive industry, where the market for parts made from LFT is experiencing tremendous growth. The following paper discusses the available materials, the mechanical and physical properties, machine techniques and processing details of the LFT process. It will also discuss potential applications for LFT. The paper will cover different process techniques such as direct processing and make comparisons with other processes. An explanation on the effects that LFT has on properties and economics will be made. It will show how the economics can be improved by adding recycled material to the process. This paper will provide a better understanding of the LFT-process and how you could get benefits from this process.

Interaction in PC/ABS Blends Prepared in a Dynamic Melt Mixer
Károly Belina, Péter Juhász, Desi Csongor, Nick R. Schott, May 2001

Polymer blends are more and more important materials in polymer technology. Their role increases due to the recycling processes of mixed plastic waste. One of the key problems of polymer blends is the interaction between the components as they determine the properties. Commercial polycarbonate (PC) and ABS were blended in a dynamic melt mixer in 80/20 and 70/30 ratios. Homogeneity of the blends was characterized by SEM method. Glass transitions of the blends and the pure materials were measured by calorimetric and dynamic mechanical analysis. The interaction and the partial miscibility between the components were determined from the shift of the glass transition temperatures. It was found that the homogeneity of the blends was uniform. The shifts of the glass transition temperatures show some interaction between the components.

Melt Modification of PET with Reactive Glycidyl Compounds
R. Dhavalikar, M. Xanthos, May 2001

Melt strength of polyesters for foam extrusion and extrusion blow molding is controlled by weight-average molecular weight, molecular weight distribution, and the degree of branching. This paper describes the chemical modification of polyethylene terephthalate (PET) as a technique to improve its melt strength using compounds containing the reactive glycidyl (epoxy) group. The effect of addition of di-, tri-, and tetra- functional epoxy compounds to the PET resin in the melt state was studied using a batch mixer. Changes in the torque and temperature in the mixer resulting from the addition of modifier(s) were followed in order to relate to the kinetics of the reactions.

Barrier Screws in Helically Grooved Barrels: Operating Characteristics and Implications for Simulation Models
Daniel Schläfli, Yves Zweifel, May 2001

Grooved feed zones in single screw extruders have been used in many variations over the years, mostly axial grooves in many sizes and shapes. The lesser known helically grooved feed zone permits, when properly designed, an operating mode where flow rate becomes a function of geometry only, practically independent of friction coefficients. Therefore, it has a linear behaviour with screw speed and is virtually independent of backpressure over a wide operating range, as shown by experimental evidence gathered over many years. The high flow rates obtained require barrier screws for adequate melting capacity. In the barrier zone, considerable pressure differentials are observed between the primary and secondary channel, where the melting occurs, at higher screw speeds. This effect is associated to the melting mechanism.

Effects of Material and Process Parameters on the Degree of Groove Replication in DVD Disks
W.C. Bushko, I. Dris, A. Avagliano, May 2001

Information storage devices such as re-writable DVD (DVDRW) disks require high degree of groove replication to achieve desired readability. Higher levels of replication are typically achieved by increasing mold temperature, packing pressure, and filling speed. These extreme molding conditions are often on the border of the material processing window. A simple groove forming process model is presented. The model is shown to predict well groove replication for wide ranges of mold and melt temperatures and two different radial locations. The model is useful in assessing replicability of new materials in new formats.

Design of Experiments to Optimize the Weldline Strength in Injection Molded Thermoplastics
Shih-Jung Liu, Jun-Yu Wu, Jer-Haur Chang, May 2001

The forming of weldlines wherever polymer flow fronts meet is one of the problems that confound the overall success of injection molding technology. An L'18 experimental matrix design based on the Taguchi method was conducted to optimize the weldline strength of injection molded thermoplastics. Experiments were carried out on an 80 ton injection-molding machine. A plate cavity with an obstacle at the center was used to create a weldline. After molding, the weldline strength of the parts was measured by a tensile tester. For the factors selected in the main experiments, melt temperature and mold temperature were found to be the principal factors affecting the weldline property of injection molded thermoplastics. In addition, weldline strengths of injection molded parts increase with the size of the obstacles.

Practical New Applications for an On-Line Rheometer
Donald De Laney, Steven Oliver, May 2001

On-line rheometers have been around for over 30 years. They have been used in many different applications in R&D, polymerization processes, product development, and compounding. However, their main application has been in large volume resin production, mainly in the polyolefins industry. Applications in the processing and compounding industries have been almost non-existent because of the large size of the rheometers and the need to modify the extruders or compounders in order to use them. This paper discusses applications of a new rheometer, developed to address these problems, in the monitoring of a production PET sheet extrusion line. The real time" monitoring of viscosity and its application to the control of the resin moisture level and the consistency of a virgin/regrind blend is demonstrated and discussed."

A New Method of Rheological Analysis for Polymer QA and Product Development
Donald De Laney, Jeffry Sweinhart, May 2001

For many years the capillary rheometer has served as an important tool in R&D and product development laboratories. It has even gained in popularity in the QA laboratory as a tool for assuring the processability of a resin. More recently two and even three barrels designs of the capillary rheometer have become more generally available. The main applications of these instruments have been for providing directly corrected viscosities and for doing measurements of extensional properties. However, very little has been said about the opportunity these rheometers provide for applications in QA and product development. This paper discusses the capabilities of the dual barrel rheometer for direct comparisons of materials in QA and for the fast and easy observation of changes in the flow properties of a new product, as it is modified in the development process.

Accuracy of Filling Analysis Program
Keita Ainoya, Osamu Amano, May 2001

In order to verify the accuracy of the filling analysis program (C-MOLD) for injection molding, pressure losses across four characteristic segments (Nozzle & Sprue, Runner, Gate, and Cavity) of the flow channel in the test mold were measured for the HDPE under various molding conditions regulated exactly. Without the additional assumptions in the simulation, the flow properties with the pressure-dependent viscosity and the juncture loss measured actually were added to the indispensable pvT-data, thermal conductivity, specific heat for simulation. After confirming good agreement between the observation and the simulation at the flow segment wherein thermal properties affected weakly on the pressure loss, the effects of the heat transfer coefficient between the polymer and the mold metal on the simulation were examined. By introducing the heat transfer coefficient of 1,200W/m2-K, instead of the default value of 25,000 W/m2-K, we found that the difference between the simulated and the observed pressure losses at the four segments were reduced to less than 20%.

Water Structure in Hydroxyethyl-Co-Glycerol Methacrylate Materials
G. Gates, J. Harmon, J. Ors, P. Benz, May 2001

Differential scanning calorimetry was used to analyze the state of water in crosslinked glycerol methacrylate and hydroxyethyl methacrylate hydrogel polymers. Glass transition temperatures were obtained for the dry materials and for the materials equilibrated at room temperature (23°C) and humidity (55% relative humidity). The total crystallization enthalpy was determined for these hydrogels equilibrated in water and at several states of partial hydration. The enthalpic information was used to quantitatively determine the fraction of nonfreezing water in the hydrogels. The integrated areas of the crystallization exotherms were reported to qualitatively access the freezing-bound and free water contents.

Integrated Design Environment Enhancing Concurrent Engineering Approach in Plastic Injection Molds Design
A. Pipino, E. Indino, A. Franz, M. Thornagel, R. Curado, May 2001

As the injection mold market increases, Time and Costs Reduction will be important aspects for mold makers. A detailed analysis of todays workflow in the mold making industry has pointed out the need for tailored tools in an integrated environment. The COSMOS project, (a pre-competitive European Union founded project) wants to enhance CAE integration and data exchange in CAD-based mold design. A PDM-based (Product Data Management) environment is being tuned on the basis of a new Concurrent Engineering-based approach. The expected results will lead to a reduction in time-to-market by about 30% and cost of about 40% as compared to the traditional injection mold design and manufacturing paradigm.

A Physics Based Approach to Determining Filled Volumes within a Corotating Twin Screw Extruder
Paul Elkouss, David Bigio, Gregory Walsh, May 2001

Determination of filled regions in extruders is important to the understanding of the operation of the extruder. This information can be useful to predict various performance measures for unit operations such as mean residence time and chemical conversion. A model is proposed that predicts the filled volume length for the extruder, based on the pressure drag flow model. This model is dependent on the system geometry in addition to the conveyed fluid's properties. Experiments have been performed that shows the ability of this model to predict the filled length in Co-rotating Twin-Screw Extruder (CoTSE) based upon a determined channel percent drag flow and specific throughput.

The Effect of Liquid Cooling of Gas Channel in the Gas-Assisted Injection Molding Process: Overview
Jun Seok Lee, Sooyoung Cha, Francis Lai, May 2001

In Gas-Assisted Injection Molding, gas channels are usually utilized as a gas transfer system. However, the gas channel can be considered to have dual purposes; it can be used as inner cooling channel to improve fast cooling and to reduce cycle time without losing part quality. In this study, a simple plastics part with an open gas channel is used for prediction of cooling effect when gas channel is acting as a cooling channel by introducing the mixture of gas and liquid. Results can be drawn on how fast the part cooling is and how much the fingering effect reduces. Most importantly, we can compare how the quality differs between the gas-injection molded part with and without internal cooling.

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