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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
Design Sensitivity Analysis of Gas-Assisted Injection Molding
Florin Ilinca, Jean-François Hétu, May 2002
Gas-assisted injection molding is an increasingly used manufacturing process that allows production of parts with more uniform properties, reduced shrinkage, warpage and residual stresses. Getting the proper combination of different process parameters such as gas pressure, gas injection delay and melt temperature, makes gas-assisted injection molding more intricate than the traditional injection. Very often a successful design in gas-assisted injection comes at the end of a long trial and error process. Design Sensitivity Analysis (DSA) can help the processors improve the design and can produce substantial investment savings in both time and money. This paper compares two approaches to perform sensitivity analysis for the filling stage of the gas-assisted injection molding process. Solution of the gas-assisted process and the sensitivity of the solution with respect to different design parameters are computed in three-dimensions using a finite element method.
Design, Processing and Biological Behaviour of Starch Based Scaffolds for Bone and Cartilage Tissue Engineering
M.E. Gomes, J.S. Godinho, D. Tchalamov, A.M. Cunha, R.L. Reis, May 2002
The design and processing of appropriate porous 3-D scaffolds is one of the most important steps towards the regeneration of damaged tissues/organs using a tissue engineering approach. Work has been going on designing scaffolds from a range of starch based polymers that combine an appropriate degradation rate, with controlled porosity and adequate pore sizes, as well as tissue matching mechanical properties.Several processing techniques have been specially developed for producing the scaffolds. The developed methods include melt based processing technologies (based on injection moulding and extrusion using blowing agents), combined techniques based on solvent casting and on compression moulding associated to particle leaching, and other innovative techniques such as in-situ polymerization. It has been possible to produce scaffolds with adequate properties and structure. Some of them can be eventually used on minimally invasive surgical techniques. Furthermore, the developed methods have no negative effect on the biocompatible behavior of the starch based polymers.
Designing Screen Packs for Extruders on the Basis of Resin Rheology
Natti S. Rao, Günter Schumacher, Nick R. Schott, Ray Edwards, May 2002
In various extrusion processes, particularly those involving resin blends containing fillers and additives, it is often necessary to increase the melt pressure, in order to create more back mixing of the melt in the screw channel of the extruder. This can be achieved by using screen packs of different mesh sizes. They can also be used to increase the melt temperature to attain better plastication of the resin. Another application of screens concerns melt filtration, in which undesirable material is removed from the melt. In all these operations it is necessary to be able to predict the pressure drop in the screen packs as accurately as possible, as the melt pressure is closely related to the extruder output. Based on recent developments in rheology this paper presents an easy and quick method of calculating the pressure drop in a screen pack as a function of the resin viscosity, extruder throughput and the geometry of the screen. The effect of screen blocking is also taken into account. The predictions agree well with the experiments. Practical worked-out examples illustrate the design principles involved.
Detailed Energy Measurements in Injection Moulding
A.J. Dawson, H.S. Rajamani, R. Collis, L. Owen, D. Owen, P.D. Coates, May 2002
Growing concern for ecological issues, including international standards agreements such as ISO14001, demonstrate a clear requirement to conserve energy for both environmental and cost issues. Energy measurements on injection moulding machines both in the laboratory and in industry demonstrate the potential of process energy measurements in the development of a systematic management approach to the environmental concerns of an organization. The data gathered can also provide useful information to both the processor regarding the performance of the machine in question, and the power companies regarding the specification of supply equipment.Detailed energy measurements during the injection moulding cycle provide data regarding the energy consumption of specific machine components and/or phases of the injection moulding cycle, providing valuable data for machinery manufacturers and processors.
Determination of Molecular Weight and Molecular Weight Distribution of I-PP by Rheological Measurements - A Comparative Study
C.H. Scuracchio, R.E.S. Bretas, May 2002
Four polypropylenes of different grades were used in this study to test the reliability of the use of rheological measurements in the determination of the curve of the molecular weight distribution, MWD. For this purpose, it was used the mixing rule theory based on the double reptation. A commercial software (Rheometric Scientific Orchestrator®) and another one developed in our laboratories were used for this purpose. The final data were compared with curves obtained by gel permeation chromatography, GPC. It was found that curves obtained from the rheological tests had weak agreement with the curves of GPC. However the method showed to be reliable for a comparative study among materials.
Development and Characterization of a New Plastomer Designed for Single-Ply Roofing Membranes
T.A. Glogovsky, May 2002
The development and characterization of a new plastomer designed as the primary building block for single-ply roofing are reviewed. An improvement in mechanical properties over existing soft plastomers having similar flexibility was achieved through the incorporation of various monomers, resulting in the creation of bipolymers which provide toughness and softness performance. A higher total level of the combined bipolymers within a polypropylene random copolymer (RACO) matrix was utilized to achieve the unique properties in comparison to the existing plastomer currently used in single-ply roofing. Controlled blending of two plastomers compounded on standard single screw compounding equipment completed development of the final product. The result of the blending study was then simulated and scaled up to a continuous three-loop gas phase pilot reactor. The final mechanical, thermal, and rheological property profile of these new resins is presented.
Development of a Heat/Pressure Formable Wood Fiber Thermoplastic Composite from Recycled Paperboard
Tom Mase, Lawrence T. Drzal, Bob Jurek, May 2002
In this paper, an engineered material made from paperboard and powdered polypropylene is examined. A wet, paper process was chosen for converting paperboard waste into an engineered, cost effective composite material. Using a fourdrinier, a 30 inch wide continuous sheet of paper/plastic stock was produced for subsequent thermal molding. Tensile modulus and strength of 6,000 and 50 MPa, respectively, were obtained for a material having just less than 30 percent polypropylene. Additionally, moisture content and water absorption was examined. Testing and failure analysis indicate that increasing the percent of polypropylene will improve the mechanical properties.
Development of a High Heat, High Impact ABS for Automotive Blow Molded Spoilers
Thomas Pickett, Greg P. Reny, Tom Traugott, Michael Shoemaker, May 2002
Automotive spoilers (otherwise known as rear deck air deflectors) have been on vehicles since the mid nineteen sixties and have since made the transition from steel to plastics. Several plastic materials are used today to produce automotive spoilers, including Acrylonitrile-Butadiene- Styrene (ABS), Polyamide, Polyesters, Polyurea RRIM, Polyethylene Terephthalate (PET) and Polyphenylene Ether blend (PPE blend). A variety of fabrication techniques are in use, including blow molding, injection molding, injection/compression molding and compression molding.The utility of the spoiler, initially created as a means to reduce drag and improve fuel economy and vehicle performance, has changed over the years such that today spoilers are largely added for vehicle appearance enhancement. However, the performance requirements of spoilers are more rigorous than what one would expect from an appearance part. This paper examines the development of a new high heat, high impact, blow moldable grade of ABS for spoilers.
Development of an Integrated Computer-Aided Engineering and Optimization System for Injection Molding
Michael Peic, Lih-Sheng Turng, May 2002
Sophisticated computer-aided engineering (CAE) tools for injection molding have been available and are now widely used in industrial practices. However, a successful application of CAE typically involves numerous iterations of process simulations to evaluate various competing design options, material choices and process settings. To further enhance the effectiveness of CAE, efforts have been made in integrating the process simulation analysis with an optimization tool to automatically and intelligently search for the optimal design and/or process parameters. This paper presents the numerical implementation and experimental verification of this integrated optimization tool and the application of various optimization algorithms for an instrumented test mold.
Development of Inorganic Composites for Production of Structural Elements
Ioan I. Negulescu, Roger K. Seals, Simioan Petrovan, May 2002
The overall goal of the paper is to develop recycled plastic lumber products with improved mechanical properties using inorganic filler consisting of Louisiana residuals, such as phosphogypsum, in conjunction with recycled plastic resins. Blends have been established and samples have been prepared by mixing polyethylene derived from detergent bottles with inorganic fillers in the inner chamber of a Haake rheometer. Reactive mixtures have been made in the same way using maleic anhydride in addition to polyolefin and inorganic filler. The actual composition of blends has been calculated from thermogravimetric data. Tensile properties have been determined for each composition using both an INSTRON machine and a dynamo-mechanical spectrometer.
The Development of Nanocomposites to Enhance Functionality of Materials for Rotational Molding
Darren Martin, Peter Halley, Rowan Truss, Michael Murphy, Simon Meusburger, Oliver Jackson, May 2002
The development of new composite materials with enhanced property profiles for rotational molding represents a key challenge for the industry. The prerequisite attributes of a good rotomolding resin include grindability, sinterability, thermal stability and low moisture sensitivity. This imposes very restrictive limits on the number of promising new candidates.When traditional glass fibres or other mineral fillers such as talc, mica, or calcium carbonate are used, increased stiffness is almost always achieved at the expense of impact properties, ease of processing, wear on equipment, low density and recyclability. Many mineral fillers have been used successfully in numerous high pressure plastic forming processes, however, their successful adaptation has not transposed to the low shear, low pressure environment found in rotational moulding. In addition, large fibres tend to create a natural sieving action when tumbled with plastic powder within the mold and end up lining the inside of the mold serving no useful mechanical purpose. Furthermore, surface finish is generally rougher than that achieved with just the base resin and so it is harder to achieve a glossy finish.Possibly a more successful approach to developing a rotomoldable composite with outstanding engineering properties would be to introduce the matrix and reinforcement into the mold as a curable liquid. This has been done with some degree of success using wollastonite-filled polyurethane (1), although at higher filler loadings impact properties also suffered.In this paper polymer-clay nanocomposites are presented as possible new candidates for rotational molding. Issues and choices relating to the formulation, trials and evaluation of both PE-clay (thermoplastic) and castable polyurethane-clay (thermoset) nanocomposites for rotational molding are discussed. Some key melt rheology results for the PE-based nanocomposites are reported.
Devolatilization of Polymers in a Transparent Double-Screw Extruder
Ingo Gestring, Dieter Mewes, May 2002
Devolatilization is a key-step in polymer processing. Low-molecular-weight components are removed from a polymeric system. On of the most used equipment for devolatilization is the extruder. The mass transfer rate inside the devolatilization section of an extruder depends on the flow regime. A double-screw extruder with a transparent barrel is used for the experimental investigations to correlate the mass transfer with the flow regime. At the entrance section of the devolatilization section the polymer starts to foam. Two-phase bubbly flow exists. There the mass transfer is highest. The intensity of the foam expansion depends mainly on the rotational speed of the screws and the inlet concentration. After the foam has collapsed it may foam again under the vacuum vent. Down stream behind the vent two-phase stratified flow exists. There the mass transfer is low. The flow field along the screws is filmed with a digital video camera.
Diamine Grafted Polypropylene as an Adhesion-Promoting Agent to Layers of PC
Sofía Vázquez-Rodríguez, Saúl Sánchez-Valdes, Octavio Manero-Brito, May 2002
Polypropylene grafted with maleic anhydride (PPgMA) was modified using different diamines during the melt. Two-layered films were prepared using polycarbonate (PC) film and PPgMA modified with diamines (PPgNH2). Adhesion strength was measured using T-peel Test. FTIR data showed that the addition of the diamine caused an imide linkage, which is performed between the amine primary group of the diamine and the maleic anhydride functionality of the PPgMA. The adhesion between layers of PC y PPgNH2 was found to be improved using PPgNH2. No adhesion was found between layers of PPgMA and PC, but the adhesion was improved when using PPgNH2 instead of PPgMA.
Die Lip Build-Up in the Extrusion of Highly Filled Low Density Polyethylene
Chun D. Lee, May 2002
It is common that a highly filled master batch (MB) contains a low molecular weight (LMw) lubricant as a filler dispersion agent and compounding processing aid. Sometimes, the presence of such a lubricant in the MB creates a die build-up problem in the extrusion process of a let-down formulation. Several MBs with a laboratory Banbury mixer were produced to investigate the effect of the amount of aluminum stearate (as a lubricant) on dispersion and die build-up. When the MB containing the stearate below the critical amount is used, die build-up decreases and filler dispersion improves with increased amounts of stearate. At the critical amount of the stearate, the MB shows good dispersion as well as minimum build-up. Above the critical amount, dispersion is still good. But, build-up increases with further increase in the amount of stearate added up to 3.0%. This observation results from the different mechanisms of the die build-up, which depends on whether the stearate level is below or above the critical amount. We confirmed such a mechanism in the commercial extrusion process of the MBs. This observation leads to the conclusion that in the use of the stearate (as a dispersion agent) for highly filled MB, the amount of the stearate need to be optimized to minimize a die build-up of the MB with good filler dispersion.
Dimensional Stability Analysis of Foams Based on LDPE and Ethylene-Styrene Interpolymer Blends
Chi-Tai Yang, Shau-Tarng Lee, May 2002
This study extends our earlier work on the fundamental aspects of modeling on foaming aging and dimensional stability. The thickness change of extruded polyolefin foam to the blowing agent and air counter diffusion during the post-extrusion aging process is modeled. The blowing agent and air counter diffusion equations are coupled with more complicated Maxwell-Voigt four-parameter viscoelastic equations to model the foam dimensional change and recovery processes. The effects of blending ethylene-styrene interpolymer resin and adding aging modifier are investigated, respectively and altogether. The mathematical model is also compared with experimental data.
Dimensional Stability of Complex Shapes Manufactured by the VARTM Process
Pascal Hubert, Brian W. Grimsley, Roberto J. Cano, R. Byron Pipes, May 2002
The vacuum assisted resin transfer molding (VARTM) process is a cost effective, innovative method that is being considered for manufacture of large aircraft-quality components where high mechanical properties and dimensional tolerance are essential. In the present work, carbon fiber SAERTEX fabric/SI-ZG-5A epoxy resin C-shaped laminates were manufactured by VARTM using different cure cycles followed by the same post-cure cycle. The final part thickness was uniform except at the corner were thinning was observed. The cure cycle selected is shown to significantly affect the part spring-in and a long cycle at 66°C followed by a 178°C post-cure produced a part with negligible spring-in.
Diode Laser Microweldng of Polycarbonate and Polystyrene
David Grewell, Timothy Jerew, Avraham Benatar, May 2002
New technological developments in micro-fabrication have created the need to assemble thermoplastics components with narrow weld joints (~100 ?m wide). This paper reviews the use of fiber coupled laser diodes in conjunction with special lenses to produce spot sizes between 25 and 50 ?m in diameter. The effects of travel speed, power density and pressure on weld line width, consistency and strength were evaluated. It was found that process parameters are extremely critical in producing consistent welds. In addition, new testing techniques need to be developed to allow quantitative measurements of weld strength due to relatively small weld area.
Direct Rapid Tooling of Injection Moulds Using Electro-Discharge Machining
S.H. Masood, S. Thatiot, I. Harianton, May 2002
This paper presents a method of creating a rapid tool for injection moulding, which can produce components of higher accuracy and better surface finish. Main investigation focuses on the rapid tooling process of a complex part using high speed machining and Electro Discharge Machining (EDM) to produce an injection mould of higher accuracy and surface finish than that achieved by a rapid prototyping based tooling process. Results demonstrate how short-run injection moulds with a higher accuracy could be made in a much faster way using high speed machining and EDM with a lead-time that can match any other methods of rapid tooling process.
Distinguishing Features of the Mechanical Design of Plastic Parts - Commentaries for the Undergraduate Student
S.I. Krishnamachari, May 2002
This review paper presents certain fresh viewpoints about the already-known process-independent and intrinsic differences in the mechanical design of plastic parts, as also its complexities. This paper is motivated by the fact the mechanical design education in the schools begins from mechanics of materials - predominantly of metals - and that plastics part design education begins from specific plastics processes. The predominant process-orientation is marked by the fact that the presence of text book titles such as “Design for Injection Molding”, or “Design for Rotational Molding” stand in contrast with the absence of titles such as “Design for Turning on Lathes”, “Part Design for Milling and Grinding”, or “Part Design for Five Axes Milling”.Furthermore, it is noted that the advent of CAD/CAE has changed but only the management of the design and development, however, the intrinsic differences remain.It is emphasized that the points discussed herein are well-known, however a fresh viewpoint is presented for the student audience.
Solid Finite Elements for the Prediction of Complex Parison Distortions
D. Laroche, P. Debergue, May 2002
Significant developments in finite element modelling of the blow moulding process have been observed in the recent years. The large deformations occuring during parison formation, clamping and inflation have traditionally been modelled using membrane or shell type elements. In this paper, a 3D solid finite element approach for improving the part wall thickness predictions is proposed. A 27-node brick element with incompressibility constraint is presented for modelling large viscoelastic deformations of the parison in the consecutive stages of the process. Part wall thickness predictions using 3D simulations are compared to experimental measurements on two different blow moulding cases. The results are also compared to predictions from the membrane formulation.

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