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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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.
Extrusion/Compression of Long Fiber Thermoplastic Composites
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
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
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
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
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.
Predicting Shrinkage for Injection Molds
Shrinkage of plastics materials can be significantly affected by both process and flow induced orientation in a cavity. This paper presents a study of the factors that affect shrinkage in a variety of different types of thermoplastic materials. These include process, flow type (linear versus radial), material and material fillers. Sensitivity of shrinkage to these factors is established and can assist mold designers in more accurately sizing their cavities to account for in-mold shrinkage
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