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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The Effects of Directional Molecular Orientation on Tensile Stress and Elongation of Polypropylene Film
Highly oriented polymer dogbone samples were tensile tested at different angles to the machine direction to determine how tensile stress at yield and the percent elongation at yield is affected by the alignment of molecules. Theoretically, as the angle from machine direction increases, the tensile strength at yield will decrease. It is also expected that as the angle from machine direction increases, the strain will decrease. These effects are important in determining how the same material can have different mechanical properties.
Heat Transfer in Foam Plastics
Predicting insulating values in foam plastics have been difficult because of variations in process, variations in geometry, and general lack of understanding in heat transfer. With this research, an attempt will be made to develop a systematic method of characterizing foam injection molded parts so that the parts can be designed to withstand thermal-mechanical loads that they would not be able to survive in normal operating conditions. Finite element analysis techniques will be used to help map actual heat transfer results. These results will then be compared to those measured through heat transfer experiments.
Optimization of the Pultrusion Process Using Thermodynamic Analysis
In the pultrusion process, line speed is the primary measurement for process optimization. With the process being continuous, the fastest speed with no defects is seen as the production goal. Before optimal line speed can be determined, the amount of time required for commencement of the reaction must be obtained. Performing a thermodynamic analysis of the die is the first step in achieving this goal. Creating a computer simulation of this process using the results of the thermodynamic analysis is the objective of this research.
In Situ Observation of Fracturing Behavior of Polyethylenes by Transmission Electron Microscopy
In situ observation of deformation and fracturing process of polyethylenes was carried out using a transmission electron microscope (TEM). It was found that there are three kinds of fracturing behavior concerning polyethylenes. In case of linear polyethylenes, two kinds of fracturing behavior caused by Crazing" and "Elongation" were observed. On the other hand low-density polyethylenes (LDPEs) having long-chain branches (LCBs) were fractured dominantly by "Interfacial splitting" of spherulites. These results show that the molecular structure of polyethylenes effects the deformation and fracturing behavior."
The Effect of Wall Slip on the Performance of Flat Extrusion Dies
Flat extrusion dies are commonly used in a wide variety of film, sheet and coating applications. Although flat dies can be designed to produce an exit flow distribution that is very uniform across most of the width, there will usually be a region along each side where it drops gradually to zero. This often requires trimming the edges of the film or sheet downstream in order to meet product specifications. It is commonly believed that treating the land area of the die with coatings that promote a small amount wall slip will reduce the size of this edge effect and therefore improve die performance. This analysis shows that slip over the entire land region of the die will adversely affect die performance. Better performance is possible but only if the sides of the land are treated.
FFT - An Efficient Process Analytical Tool for Plastics Film and Sheet Processes
Every Plastics Film and Sheet Processor, whether using Calendering, Extrusion or Coating process, strives to manufacture the best quality product with minimal variations. The total variations in a product comprise of Cross Direction (CD) and Machine Direction (MD) variations. The Machine Direction variations can be further broken down into controllable Long-Term drift and uncontrolled Short-Term high frequency variations. Gauging Systems have been available in the Marketplace for quite a few years, which efficiently control the Profile (CD) and Long Term Machine Direction (LTMD) variations. This paper illustrates the capability of Gauging Systems that incorporate Fast Fourier Transform (FFT) feature to provide the plastics film & sheet processors with a timely and detailed analysis of the uncontrolled high frequency variations (Short Term Machine Direction (STMD) and the causes thereof. This efficient process analytical tool enables the processor to take timely action to reduce STMD, thus improving the overall product quality. The economic benefits to the plastics film & sheet processors derived from down-gauging, while meeting the specifications for end-use applications of the product can be substantial. This paper presents a case study of FFT application to a vinyl calendering process.
Optical Haze Properties of Polyethylene Blown Films: Part 1-Surface Versus Bulk Structural Considerations
In this paper we report on some recent findings regarding the factors affecting the optical (haze) properties of polyethylene (PE) blown films. The large majority of the contribution to the total haze in these blown films was a result of the surface roughness of the films, with the bulk (internal) contribution being relatively minor. Using several characterization techniques, we found, rather unexpectedly, that the surface roughness in some of these films was a result of the development of distinct spherulitic-like" superstructures formed during the blown film processing. Analysis of the rheological and molecular characteristics led us to conclude that in blown films of LLDPE-type resins the optical haze properties are adversely affected due to enhanced surface roughness caused by the formation of "spherulitic-like" superstructures in polymer melts that possess fast relaxing and low melt elasticity rheological characteristics."
Optical Haze Properties of Polyethylene Blown Films: Part 2-The Origins of Various Surface Roughness Mechanisms
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.
The Recycling of Thermoset Materials into Thermoplastic Composites
Thermoset process scrap costs companies millions of dollars annually. Specific thermoplastics could benefit from the addition of recycled thermoset material. The incorporation of thermoset regrind into thermoplastic material would provide a viable alternative for the thermoset scrap that is currently sent to the landfills.
Developing Techniques for Fabricating Aluminum Molds with Cast-In Passages
This paper will explain the development of a new method for heating and cooling rotational molds with cast in passages. The goal is to develop a technique for manufacturing these molds that is cost competitive with conventional methods while maintaining the same ease of fabrication and common timeline. The mold will be used in conjunction with a hot oil rotational mold machine built at Penn State University-The Behrend College, Erie, PA.
Verification of Parison Sag and Swell with CAE Simulation Software
Parison sag and die swell are the most theoretical part of the extrusion blow molding industry. Both factors affect the wall thickness of the parison, and will add variation to the molded part. This study is part of ongoing research at Penn State Erie. After correlating data, a comparison will be drawn between CAE calculations and the actual extruded parison data. This research will quantify the parison sag and swell, and demonstrate the need to focus on parison geometry to yield accurate blow molding simulation results.
Recovery of Post-Consumer Plastic Waste via Solid State Mechanochemistry
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
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
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
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
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
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.
Comparison of Results from a Simulated and Actual Design of Experiments
This study includes a design of experiments using a blow molding simulation software. An eight-run, four factor D.O.E. format was chosen. The response variable of interest is the variable wall thickness throughout an extrusion blow molded part. The simulation will help pinpoint the factors that have the largest effect on wall thickness variation throughout the part. The results will be implemented into an actual D.O.E. that will be completed in the future.
Study of Cast in Passages for Rotational Molds
This paper discusses the theoretical effect of cast in passages on the wall thickness of rotationally molded part. Finite element analysis was used to determine temperature differences for given passage geometry and dimensions. Testing was done to determine the relationship between surface temperatures and melt thickness versus time. This information provides a theoretical model for construction of rotational molds using cast in passages.
True 3D Flow Analysis for Designing Hot and Cold Runners in Injection Molds
The industry standard 1D beams used in current state of the art injection molding simulation software does not pick up the shear-induced imbalances created in branching runners. This imbalance requires the use of 3D simulation software, which is in its infancy, when used for injection molding. As none of the commercially available injection molding simulation programs currently provide the required solution, use of general purpose 3D flow analysis and 3D extrusion software is evaluated. This paper provides information on the accuracy of these 3D programs against actual molding.
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