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

Exploiting Refractometry to Calculate the Density of Polyethylene: The Lorentz-Lorenz Approach Re-Visited
Rajendra K. Krishnaswamy, Jay Janzen, May 2001

The Lorentz-Lorenz equation is a fundamentally sound theoritical equation that relates refractive index and density. In this study, refractive index measurements were used in combination with the Lorentz-Lorenz equation to determine the density of various polyethylene specimens. Excellent agreement was observed between the specimen density calculated from the Lorentz-Lorenz equation and as measured using a density gradient column. Further, calculating polyethylene density from refractometry experiments using a Metricon Prism Coupling device was noted to be more accurate, more reproducible, simpler and consumes far less time compared to the traditional density gradient column technique.

Rheo-Optical Studies of the Effect of Shear Flow on the Structure of Elastomer Blends
Tao Xu, Montgomery T. Shaw, R.A. Weiss, May 2001

The effect of shear flow on the structure of near critical composition blend of 50/50 (w/w) blend of poly(styrene-co-ran-butadiene) (SBR) and polybutadiene (PBD) was studied using two different custom-built rheo-optical instruments that combined polymer melt flow and small angle light scattering (SALS). One instrument (Rheo-SALS) was based on a commercial parallel plate rheometer that was modified with an optical path for laser light scattering. For the second instrument (Extrusion-SALS), a commercial normal-stress extruder was redesigned to allow light to be directed down the rotor shaft and to include an optical window in the header for SALS. Turbidity measurements indicated that SBR/PBD blends exhibited upper critical solution temperature(UCST) phase behavior. At relatively low shear rates, the characteristic length of the phase separation in the flow direction increased exponentially with shear strain while the characteristic length perpendicular to the flow direction remained constant. No evidence of a phase transition induced by flow was observed for any shear rate.

In-Line Dielectric Monitoring during Extrusion of Filled Polymers
Michael McBrearty, Anthony Bur, Steven Roth, May 2001

Dielectric measurements were made on clay filled polyethylene-ethyl vinyl acetate (EVA) copolymer nanocomposites during processing by extrusion. The results show that, at processing temperatures, composites containing chemically treated clays display significant dielectric dispersions. The addition of natural clay to the EVA copolymer increased the dielectric constant (relative permittivity) above that of the EVA copolymer but did not increase the conductivity or cause any dispersion. The chemically treated clays, which are known to exfoliate when compounded with EVA copolymer, gave substantially higher relative permitivity and conductivity having distinct variations with frequency consistent with dielectric relaxations at frequencies below 3000 Hz. One clay treatment gave a larger dielectric dispersion than the other.

The Use of Ethylene/Styrene Interpolymers in Crosslinked Foams for the Footwear Industry
Robert Dubois, Seema Karande, David P. Wright, Felipe Martinez, May 2001

Ethylene/Styrene Interpolymers (ESI) currently under development by The Dow Chemical Company can be effectively crosslinked using current commercial equipment to produce extruded sheets, bun foams, and injection molded foams (IMF) for footwear parts providing properties that enhance and/or outperform current foams of crosslinked ethylene vinyl acetate copolymers (EVA). Crosslinked EVA foams with density ranging from 0.12 to 0.35 g/cc are becoming increasingly popular in many athletic, ladies high heel, and casual shoes, for the fabrication of insoles, midsoles, and unisoles where light weight, comfort, aesthetics, low cost, and performance are the key. ESIs can be blended with EVA or used pure to give light weight, softer foams with better compression set while maintaining or improving on resiliency, heat shrinkage, and split tear.

Plasma Polymerized Films for Optoelectronic Applications
Jennifer Conley, Rachel Gahn, May 2001

Photovoltaic devices and light emitting diodes are now being developed from thin films of conjugated polymers and other organic systems. The potential to create lightweight, flexible, and inexpensive structures are the main advantages of using conjugated polymers over the conventional inorganic systems. However, the challenge is to create organic devices that are more efficient than inorganic devices already in existence. Currently, we are conducting research at the University of Cincinnati using plasma polymerization to produce optical quality thin films of Benzene, Furan, and other polymers for photovoltaic devices and light emitting diodes (LEDs).

Environmental Lining Systems - Raising the Standards
Ian D. Froment, May 2001

Annually, the United Kingdom deposits around 20 million tonnes(1) and the United States around 2 billion tonnes(2) of waste into landfill. To protect the environment from the harmful effects of leachate from the waste, landfill sites are protected using a system of thermoplastic liners, typically made from polyethylene. Due to manufacturing limitations on the size of the lining sheets, welding is employed to join adjacent sheets at the landfill site. This paper reviews current welding practices, the industry approach to quality, and discusses the moves towards certification of welding personnel in order to raise standards across the industry.

Improved Part Quality Using Cavity Pressure Switchover
Birju Sheth, Carol M.F. Barry, Nick R. Schott, Richard D. Higdon, Brady Davison, May 2001

This study examined the improvements in injection molded part quality using cavity pressure to initiate switchover from injection pressure to holding pressure. Cavity pressure produced more controllable and uniform part dimensions than the time and position switchover typically employed in older, point controlled injection molding machines. The controller was relatively easily incorporated into an older machine. When the cavity pressure set point was determined from the position switchover conditions, the pressure may not have been optimized, but provided better parts than the other transfer techniques. Direct determination of the cavity pressure set point is still being evaluated.

Improving the Fracture Resistance of Short Glass Fiber Composites under Impact
Rabeh H. Elleithy, Martin E. Woods, May 2001

The impact behavior of short glass-fiber composite was reported earlier by the authors. It was found that the first failure was a longitudinal crack followed by a perpendicular crack on the tensile side. The objective of the current work is to evaluate a method for improving the impact properties of these materials. The primary focus will be on the addition of ductile polymer layer to the extruded composite. Instrumented drop weight impact technique was extensively used to evaluate the impact properties of the composite. This work showed that the addition of the ductile layer improved the impact properties significantly.

An Advanced High Modulus (HMG) Short Glass-Fiber Reinforced Nylon 6: Part I-Role and Kinetic of Fiber-Glass Reinforcements
Val A. Kagan, Rowena McPherson, Jerry S. Chung, May 2001

Resent developments were oriented on two high-flow, high-modulus fiber-glass reinforced nylon 6 (HMG series) grades for automotive and other industrial applications requiring high stiffness and high strength. These materials combined the following improved technological (injection molding, vibration welding, etc.) and mechanical performance properties such as greater dimensional stability, higher short-term (strength and stiffness) and long-term (fatigue and creep). The current and possible applications of these plastics includes auto mirror housing brackets, clutch pedals, clutch master cylinders, ski bindings, steering wheels, levers, auto seat frames, door handles and door lock mechanisms. In Part I of this paper, we are presenting results of reinforcement analysis with the influence of level of loading and geometrical parameters of used fiber-glass.

The Effect of Three-Lobe, Off-Set Kneading Blocks on the Dispersion of Calcium Carbonate in Polystyrene Resin
Martha J. Rogers, Kurt W. Koelling, Michael D. Read, Mark A. Spalding, May 2001

Resin suppliers and compounders often add fillers to resin base stocks to form high-value filled resins. These resins are typically used for automotive injection molded applications and color concentrates for in-house coloring. Materials are generally compounded on co-rotating, intermeshing twin-screw extruders using a variety of kneading block types. The goal of this work is to describe the effect of three-lobe kneading block configurations on the dispersion of calcium carbonate into polystyrene resins.

A Study on the Bottom Design of Petaloid Carbonated PET Bottle to Prevent Bottom Crack
Min-Young Lyu, Hak Cheol Kim, Hee Cheol Shin, Jae Sik Lee, Sung-Taek Joo, Yong Hwan Kim, May 2001

Petaloid shape in bottom design for carbonated PET bottle is wide spread. Through this paper we investigated the causes of bottom crack. We then redesigned petaloid bottom to prevent bottom crack. We examined the material property variations according to the stretch ratio of PET and analyzed stretches of bottom in blowing processes. We also performed crack test to observe a crack phenomena. The effective stress and maximum principal stress were examined by computer simulation. We concluded that the bottom crack occurs because of not only insufficient strength of material due to the insufficient stretch of PET but also coarse design of petaloid shape. The crack in bottom of bottle occurred through crazing. The highest maximum principal stress occurred at valley in petaloid bottom of bottle and this strongly affected the crack in bottom. We redesigned petaloid shape to minimize maximum principal stress, and this result in increasing the crack resistance.

Comparison of the Stabilizing Efficiencies of Metal Carboxylate and Tin Stabilizers of PVC
Béla Iván, May 2001

In order to obtain detailed understanding of the mechanism and action of PVC stabilizers, a new exact method has been developed for the determination of the stabilizing efficiency of these compounds. This is based on the separation of the direct chemical stabilization, i. e. blocking according to the reversible blocking mechanism of PVC stabilization, and the HCl-scavenging capacity of stabilizers. This new method has been applied to investigate the stabilizing efficiency of different stabilizers, such as metal carboxylates and tin compounds. In this study, the stabilizing efficiencies of these stabilizers will be compared by carrying out PVC degradation under inert and oxidative conditions. The stabilizing efficiencies allowed setting an efficiency order for a variety of stabilizers. These studies also led to surprising findings for thermooxidative stabilization under the applied conditions.

In-Situ Polyamide 6/Polysulfone-Alloys
Martin Weber, May 2001

In order to develop a cost effective way to new Polyamide 6 (PA 6)-alloys and blends, solutions of Polysulfone (PSU) in ?-Caprolactam have been polymerized by the widely used hydrolytic process. The resulting materials have been characterized by various analytical techniques. Compared to melt blended PA 6/PSU-samples, materials prepared by the polymerization process reveal a unique morphology with dispersed PSU-particles having average particle diameters below 100 nm. This morphology is a consequence of in situ created copolymers, therefore these samples were designated as in situ PA 6/PSU-alloys. The in situ alloys offer improved heat distortion temperature and excellent toughness.

Influence of Low Molecular Weight Compounds on the Morphology of PSU/PA-Alloys
Piyada Charoensirisomboon, Martin Weber, May 2001

In order to develop a new polymeric material with a nice combination of high heat resistance, chemical resistance and flow, polysulfone (PSU)/ polyamide (PA) blends have been investigated. The incompatibility of these polymers can be overcome by the addition of functionalized PSU, especially anhydride terminated PSU (PSU-PhA). Since PSU-PhA sometimes contains traces of low molecular weight compound, the influence of such reactive impurities was investigated with phthalic anhydride (PhA) as model compound. The amount of in situ created PSU-PA-copolymers is significantly reduced by the addition of PhA during the extrusion process resulting in a coarsening of the morphology.

Wood Filled High Crystallinity Polypropylene
Philip Jacoby, Richard Sullivan, William Crostic, May 2001

Over the past decade wood filled polyolefins have gained acceptance as a replacement for lumber in high value outdoor applications, especially decks [1-2]. Most of the products offered have used post consumer polyethylene as the polymer matrix, with wood flour as the typical filler. Polypropylene offers specific benefits over polyethylene in terms of higher stiffness, strength, heat deflection temperature (HDT), and better creep performance. In this paper we compare the properties of wood flour (WF) filled polypropylene and polyethylene at various WF levels. The polypropylene resins include both standard Zeigler-Natta homopolymer (HPP) and high crystallinity (ACCPRO) homopolymer, as well as an impact copolymer (ICP) resin. The polyethylene resins include high density polyethylene (HDPE) and low density polyethylene (LDPE). The effect of different levels of a maleated polyolefin coupling agent were also examined. A substantial improvement in stiffness, strength, and high temperature performance was observed for all of the PP based resins relative to that of the polyethylene based materials, and the ACCPRO based composites gave the highest level of performance.

Impact Enhancement of Clarified Polypropylene with Selected Metallocene Plastomers
Thomas C. Yu, Donald K. Metzler, Manika Varma-Nair, May 2001

The addition of selected metallocene plastomers can improve the drop impact strength of parts molded from clarified polypropylene with slight effect on haze and gloss. This paper demonstrates the effects of plastomer structure (melt index, density and comonomer type), on the optical, physical and impact properties of clarified PP. A thermal segregation experiment shows the preferred methylene sequence length to minimize haze. Crystalization half-time experiments show that the addition of plastomer does not seem to hinder the polypropylene crystallization process. Finally, SEM micrographs are provided showing the dispersion of plastomer in an injection molded container.

Shear Stress Nucleation in Microcellular Foaming Process
Lee Chen, Kent Blizard, Xiang Wang, May 2001

The effect of shear stress on the foaming process has been studied using the Foaming Process Simulator developed previously. The polymer samples were saturated with gas in the test chamber. A rotor was used to apply shear stress to the polymer samples. Foams were obtained by releasing the pressure quickly. Polystyrene, filled and unfilled, was used as the material. The cell density was analyzed with a scanning electron microscope. It was found that the cell density was significantly increased by introducing shear stress. The higher the shear stress the more significant the effect. A cell stretch model has been developed to explain the cell nucleation enhancement with shear stress. The nucleation sites are stretched under the shear stress. The stretched nuclei are much easier to expand for cell formation due to their larger surface areas and non-spherical shapes. The model prediction shows the same tendency of the effect of shear stress observed in the experiment. The key issue with shear stress nucleation is the transformation of mechanical shear energy into surface energy.

Application of the Time Temperature Shift Principle to the Material Behaviour of Rubber under High Deformations
Andreas Grambow, Edmund Haberstroh, May 2001

For the finite element analysis, the stress/strain behaviour of the material has to be given in mathematical formulations (material models). These material models include parameters, which have to be determined by material testing. The material testing has to be carried out at time/temperature conditions, which correspond to those of the rubber part. Depending on the number of different time/temperature conditions, this can lead to a time and costs consuming test effort. This paper describes the possibility of test effort reduction for a wide range of time/temperature conditions with a new method, which uses the time temperature shift principle (TTS-principle). Examples are presented for three rubber materials (NR, ACM and NBR/NR) using this new method in conjunction with the WLF-equation and the van't Hoff-equation.

Introducing New Injection Molding Technologies into Small and Medium-Sized Enterprises
Andreas Franz, Walter Michaeli, May 2001

Special injection molding techniques are well-suited to provide small and medium-sized injection molders with a technological advantage over their competitors. On the other hand the introduction of special processes demands careful and detailed planning in order to be successful, a requirement that often overburdens these enterprises, whose reduced personnel resources often do not permit the elaboration of a thorough concept. This contribution shows a systematic approach of how the project of implementing a new injection molding technology can be structured, regarding not only the technological, but also organizational and personnel-related aspects and the interconnections between them. A choice of these aspects is listed in Fig. 1.

Thermoforming Low Density Glass Reinforced Thermoplastic Sheet
Valérie Bertrand, P.J. Bates, Christian de Grandpré, Abderrahmane Meddad, Enamul Haque, May 2001

Experimental studies were performed to assess the thermoformability of low-density polypropylene sheets reinforced with long discontinuous glass fibers. The effects of material parameters (glass fiber loading and sheet basis weight), mold parameters (cavity depth), and processing parameters (sheet temperature, and pressure) on part thickness, and glass fiber distribution were evaluated. The results indicate that, for the parts studied, pressure assist is required for thermoforming. Part characteristics were observed to be reproducible and constant over a wide range of sheet temperatures and pressure assist levels. Part dimensions were compared with those obtained using a thermoforming simulation package developed at the National Research Council's Industrial Materials Institute. Simulation results show that volume is not conserved when this low density material is thermoformed.










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