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

Integrating Thin-Wall Molder's Needs into Polymer Manufacturing: Part II
W.G. Todd, T.J. Schwab, D.L. Wise, May 2000

Polyethylene (PE) injection molded rigid containers are widely used for food packaging and promotional drink cups. Molders of these containers have well-defined processing needs and molded part requirements. Likewise, the polymer manufacturer has well-defined manufacturing and analytical methods for characterizing resin properties. This paper presents a predictive model that was developed from molded part testing versus PE resin physical properties. Utilizing this information, the resin producer and the injection molder can work together to improve molded part performance.

A Study of the Tensile Creep Behavior of Recycled High Density Polyethylene in Aqueous Mediums
John Raybuck, Daniel Heuer, Paul Koch, May 2000

Recycled polymers are currently being used in the design of commercial products for the maritime structure industry. Marine pilings, pier fenders, and pier support elements are just some of the products being designed with recycled polymers. Understanding the effect of submersion in salt and fresh water on the mechanical properties of the material used in these products is important. This study will examine the tensile creep behavior of recycled HDPE in ocean water, fresh water from Lake Erie, distilled water, and air. A specially designed apparatus for aqueous creep testing was utilized to obtain the data for this study.

Model-Free Kinetic Analysis of Epoxy Cures
Sergey Vyazovkin, Nicolas Sbirrazzuoli, May 2000

The application of the model-free isoconversional method to differential scanning calorimetry data allows one to study the mechanism and kinetics of epoxy cures. The method yields a dependence of the effective activation energy on the extent of cure. This dependence can be effectively used to draw certain mechanistic conclusions as well as to predict the reaction kinetics outside the region of experimental temperatures. The applications are illustrated by simulations as well as by epoxy-anhydride and epoxy-amine cures.

Broad Shear Rate Viscosity Measurements via Reconstruction of Fluid Velocity Profiles in Contaminant Melts
David W. Riley, Jim Reilly, Andrew H. Schall, May 2000

A method of building velocity profiles from through the thickness, in situ, optical observations in polymer melts is discussed. It is shown that it is not necessary to know particle position across the thickness of the slit to allow for accurate shear rate determination. Coupled with a pressure drop measurement, the accurate velocity profile is transformed in a broad band viscosity vs. shear rate curve. Controversial resolution limitations are discussed along with experimental data.

Cover Part as an Application Example for Gas-Assisted Injection Molded Parts
Michael Hansen, May 2000

The gas-assisted injection molding process is in use now for several years offering new technical and creative possibilities for injection molding. After a brief survey of the principle sequence of the process and basic process physics this paper comments on an application example for a cover part and provides solutions for the problem s found during the process of fixing existing issues on this tool.

Magnetic Resonance Imaging of Polymer Melt Flows
Yusuf Uludag, Michael J. McCarthy, Robert L. Powell, Geoffrey Barall, May 2000

A tubular rheometry that is based on obtaining velocity profiles by nuclear magnetic resonance imaging (NMRI) and measuring pressure drop of the flow is used for the polymer melts. This technique allows one to get viscosity data potentially over many decades of shear rate region in a single measurement. In this study, we examined polyethylene melt as the flow medium. Despite the low shear rates attained, our results reveal that this non-invasive and non-destructive method is promising for constructing an on-line polymer melt rheometer.

Transient Viscoelastic Simulation of Coextrusion Flows in Coat-Hanger Dies
Alberto Rincon, John Vlachopoulos, Joseph Dooley, May 2000

A 2-D transient finite element model of two-layer coextrusion has been developed with the Criminale-Erikson- Filbey (CEF) constitutive equation to study the problem of interfacial instability. Experiments were done with LDPE 132I™ (Dow Chemical Co.) in a coat-hanger die using two extruders, under well controlled temperature and flow conditions, where stable and unstable interface profiles were observed. Cross-sections of the frozen heel were taken and compared to transient simulations by quantitatively examining the position of the interface between the two layers.

Welding of Plastics: Introduction into Heating by Radiation
C. Bonten, C. Tüchert, May 2000

For welding of plastics, various procedures of heat transfer are presently in use. Non-contact heating by radiation allows heating e.g. without contamination of a heated tool and makes heating faster by volume-absorption of the material. Presently infra-red lamps and infra-red laser beams are in use for welding of plastics. This paper wants to give an introduction into the physical principles of heating by infra-red radiation, wants to divide between surface and volume absorption of different materials and wants to give a survey about the advantages and disadvantages of infra-red lamps and lasers.

A Comparison between Open Flame and Hot Air Heating Methods for the Rotational Moulding of Plastics
M.P. Kearns, R.J. Crawford, N. Corrigan, May 2000

In the 1940's when rotational moulding of plastics was first developed, open flames were used to heat the mould. In the 1950's there was a switch to hot air ovens as a cleaner method to heat biaxially rotating moulds. Today hot air ovens dominate the market due to the convenience that they offer the user, although it is widely recognised that they are relatively inefficient as a means of heating. This paper presents results from an experimental investigation to assess the relative merits of open flame and hot air oven rotational moulding machines. Polyethylene mouldings of varying thickness were produced on both types of machine and cycle times were compared by using ROTOLOG to record mould internal air temperatures. It is shown that significant cost savings are possible using the open flame heating method. These savings arise from both lower energy consumption and reduced cycle times.

Evidence for a Master Curve Behavior for Polypropylene (PP) Degradation and Durability
Samuel Ding, Craig L. Sandford, Michael T.K. Ling, Atul Khare, Lecon Woo, May 2000

We have studied material degradation and durability in a broad based program in selecting medical materials. In addition, the specific requirement that medical devices and packaging must have specified shelf-lives supported by real time data also prompted for quantitative evaluation. A large number of PP types and samples were studied under diverse conditions. These included high temperature oxidative stability by oxidation induction time (OIT), high oxygen pressure OIT, oven aging, aging and oxidative stability after ionizing radiation and real time ambient storage. The activation energies from the surface embrittlement processes were also found to have a striking similarity to the thermal processes. To overcome the difficulties in generating long term ( greater than 10 years) data, well characterized historic samples of up to 23 years in age were included in this study. When all data were combined, a striking feature was apparen very few data points at higher temperatures could allow a reasonable determination of the shift factor and quite accurate estimates for lower temperature durability. This methodologyt: that for PP, a self-similarity existed among all systems examined. This allows a simple vertical shift of data to construct a master curve" similar to rheological master curves. The implication being if the master curve can be constructed when supported by further studies could lead to broader applications and deeper understandings on polymer degradation"

Effect of Electron Beam Irradiation on Medical Packaging Materials
Sherwin Shang, Tahua Yang, Craing Sandford, Michael T.K. Ling, Lecon Woo, May 2000

Medical devices industry differs from other polymer applications in one major aspect: that the products frequently need to be sterilized. Recently, sterilization by ionizing radiation has become increasingly popular, due to simplicity and cost effectiveness. In particular, the beta or electron beam (E-beam) irradiation has been adopted along with the traditional gamma radiation from radioactive Cobalt or Cesium sources. Of course, the ionizing radiation that disrupts bio-macromolecular structures in bio-burdens can and also frequently do damage polymer chains. We have conducted a study on material degradation due to E-Beam irradiation and compared with treatment with gamma. Similarity of the two processes as well as significant differences will be presented.

Relaxation Model for FE Analysis of Plastic Product Behavior
Ihor D. Skrypnyk, Jan L. Spoormaker, May 2000

The non-linear creep-based models cause numerical instabilities during FEA calculations because of the necessary inversion of stress-strain relations. From this point of view, the relaxation-based models are preferable for use within FEA. On the other hand, engineers avoid such models, due to complicated tests. Therefore, the goal was to develop the non-linear relaxation model, which uses the data of creep-recovery tests. In this way the model would be comparatively inexpensive and unconditionally stable in FE calculations.

Warpage Analysis of Solid Geometry
Z. Fan, R. Zheng, P. Kennedy, H. Yu, A. Bakharev, May 2000

The requirement to create a shell model on the midplane of the part for warpage analysis is at odds with the trend toward solid modeling. A method is introduced that enables warpage analysis without the midplane model. This ensures that the user interacts only with the solid geometry. In this paper we present results obtained with the new technique and compare them to those obtained on a midplane model.

Assessment of Opportunities to Produce Distributed Multilayer Film Microstructures in Thermoplastic Blends by Chaotic Mixing
O. Kwon, D.A. Zumbrunnen, May 2000

Chaotic mixing of binary components has been recently used to produce and distribute fibers, multi-layer films, and fragmented sheets in melts. Formation mechanisms and means to promote one type over the other remain uncertain. In this study, in situ film formation and breakup in PS/LDPE blends was examined for differing extents of mixing. Results demonstrate new opportunities to develop distributed multi-layer films during blending processes.

Single Fiber Composites: A New Methodology for Determining Interfacial Shear Strength
Gale A. Holmes, Donald L. Hunston, Walter G. McDonough, Richard C. Peterson, May 2000

One of the critical factors controlling the long-term performance and durability of composites in structural applications is the interfacial shear strength (IFSS). The single fiber composite (SFC) test has been viewed by many as the best test for determining this parameter. Although the SFC test has been extensively researched, the micro-mechanics models used to obtained IFSS values are based on simplifying assumptions that are not realized under experimental conditions. Thus, results from this test often violate the known strength of the constituent materials. Therefore, a new methodology is presented that utilizes realistic assumptions.

Degradation during Long Term Storage for Post Gamma Polypropylenes
Craig Sandford, Samuel Y. Ding, Michael T.K. Ling, Lecon Woo, May 2000

Medical devices differ from other polymer applications in one major aspect: that the product frequently needs to be sterilized. Due to simplicity and cost effectiveness, sterilization by ionizing radiation has become increasingly popular. Of course, the ionizing radiation that disrupts biological macromolecular structures (bio-burden) can and frequently does damage synthetic polymer chains. We have examined several polypropylenes (PP) subjected to long term ambient storage for up to 18 years after gamma irradiation at different doses. Many of the samples in thin film form have completely disintegrated. However, in many cases the degradation reaction was not homogeneous, with an apparent distinct skin-core structure and very different properties. These results and interpretations with an oxygen diffusion limited degradation reaction model will be presented.

Influence of Processing Conditions on Medical Material Degradation/Failures
Michael T.K. Ling, Craig Sandford, Adel Sadik, Henk Blom, Samuel Y. Ding, Lecon Woo, May 2000

In the medical packaging and devices industries, products are subjected to numerous converting and other downstream processing steps. For example, a vigorous drying step must be in place to minimize the reverse depolymerizing hydrolysis reaction before melt processing for condensation polymers. Another major downstream process for medical products is the sterilization. For medical devices, ionizing radiation has become increasingly popular. Of course the ionizing radiation which disrupts bio-macromolecular structures in bio-burdens can and frequently does damage polymer chains. In this presentation, we will report on case histories of processing modality and severity and their influence on material degradation and subsequent failures. In addition, situations where control limits can be created on manufacturing procedures can be put in place to prevent (minimize) failures due to processing degradation.

3-D Curing Simulation of Thick Thermoset Components
John Viego, Richard P. Theriault, Tim A. Osswald, May 2000

Thick components or sections such as ribs and bosses require a 3-D simulation to fully determine final properties due to the curing reaction and vitrification effects. A finite element simulation has been developed to model curing of thermoset parts, including compensation for diffusion control effects and varying boundary conditions. For diffusion control, the glass transition temperature (Tg) was related to conversion by the DiBenedetto equation. The simulation considers parts molded under realistic industrial processing conditions and has shown that non-uniform curing and thermal gradients occur during processing. These gradients depend on part geometry, cure kinetics, and processing conditions. This paper presents the models used, along with the results of the simulation applied to a sample geometry molded under various conditions.

Investigation of Rotational Moulding Characteristics and Mechanical Properties of Metallocene Polyethylene
X. Wang, R.J. Crawford, A.M. Fatnes, E. Harkin-Jones, May 2000

Metallocene grades of polyethylene offer exciting opportunities for the rotational moulding industry. However, as they have only become commercially available in the last few years, their full potential has yet to be exploited. This paper reports on the results of an experimental investigation in which processing conditions are related to the microstructure and mechanical properties of three grades of metallocene polyethylene. The materials have been characterised by dynamic parallel plate rheological tests, NMR spectra and DMTA. The results obtained from equivalent standard grades of polyethylene are used as a basis for comparison. It is shown that the metallocene materials possess many rheological and physical properties that are desirable in rotational moulding. A detailed understanding of the unique nature of these materials is necessary in order to take full advantage of their properties in rotational moulding.

A Novel Additive for PP Fiber
Olga I. Kuvshinnikova, Robert E. Lee, Nick A. Favstritsky, May 2000

The purpose of this paper is to present the data on UV stabilization of flame retarded polypropylene fiber. The evaluation was conducted by exposure in the xenon arc weatherometer @ 63°C under dry conditions. Proprietary additives provided unique physical property retention for flame retarded polypropylene fiber.

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