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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

The Establishment of a Processing Window for Thin Wall Injection Molding of Syndiotactic Polystyrene
Martha Coxe, Carol M.F. Barry, David Bank, Kevin Nichols, May 2000

This study examined the effects of injection molding conditions and critical design parameters on the filling, dimensional stability, and crystallization of syndiotactic polystyrene (sPS) parts. Part wall thickness was the primary factor affecting filling, shrinkage, and crystallization. While injection velocity was secondary influence during, mold temperature was the minor factor for crystallization and shrinkage. Melt temperature and gate dimensions had little or no effect on filling or part properties.

Standard Reference Materials: Non-Newtonian Fluids for Rheological Measurements
Carl R. Schultheisz, Gregory B. McKenna, May 2000

NIST develops Standard Reference Materials for calibration, quality assurance and research into improved measurements. Two fluid standards are being developed to exhibit shear thinning and normal stresses typical of polymeric fluids. SRM 2490 is a solution of polyisobutylene dissolved in 2,6,10,14-tetramethylpentadecane. At this time, SRM 2491 is expected to be a poly(dimethylsiloxane) melt, giving less temperature dependence than SRM 2490. NIST will certify linear viscoelastic behavior and the shear-rate dependence of the viscosity and first normal stress difference at 0 °C, 25 °C and 50 °C. A round robin with the fluids will investigate variability in rheological measurements. We report progress on the project.

Surface Delamination of an Injection Molded Medical Device Using Flexible PVC
Tahua Yang, Sherwin Shang, John Booras, Michael T.K. Ling, Henk Blom, Lecon Woo, Ho-Seon Jin, Dan Marcquenski, May 2000

An autoclavable medical device was designed using flexible PVC. The device was injection molded and subsequently was exposed to steam autoclaving. Surface delamination was observed in the adjacent area of the gate. Investigations on material properties, pigment dispersion, and residual stresses were conducted. It appeared that by simply controlling the molded-in stresses, the defect could be minimized. In a Design of Experiment (DOE) study, the key molding parameters were identified.

Comparing the Long Term Behaviour of Tough Polyethylenes by Craze Testing
K.C. Pandya, J.G. Williams, May 2000

The initiation, growth and final failure of a craze at the site of a flaw is known to precede slow crack growth under low constant load in polyethylene pipe. Most established slow crack growth tests rely on being able to generate high constraint at the crack tip in order to promote damage and micro-voiding. However, for recently developed PE80 and PE100 type grades of polyethylene, such methods cannot achieve constrained brittle fracture due to extensive crack tip blunting and the formation of large crack tip craze zones, thus invalidating the use of a conventional fracture mechanics analysis. An experimental method is described here wherein deep notched tensile specimens are used to analyse craze behaviour in tough polyethylenes under plane strain conditions. Under constant load conditions, stress - time characteristics of the craze provide good discrimination between various grades within acceptable times. Under constant speed conditions, traction - separation properties of the craze have been measured directly, yielding a rate and temperature dependent work of separation(?) which may be thought of as equivalent to Gc. Rate dependent trends in ? distinguish well between the grades allowing assessment of long term properties. The intrinsic physical justification of the method lies in the measurement and analysis of separation properties locally at the craze interface. A cohesive zone modelling technique using the 'Finite Volume' method is introduced indicating how the results may be applied to the prediction of slow crack growth in other geometries.

Degradation of an Acetal Plumbing Fitting by Chlorine
P.R. Lewis, May 2000

It has been known for many years that both types of acetal plastic are susceptible to oxidative attack, or stress corrosion cracking (SCC) when in contact with chlorine. It was thought that high levels (>30ppm) of free chlorine in cold water are needed to initiate attack, so that acetal injection moulded fittings could be used quite safely in potable water supplies where free chlorine levels are very much lower (<1 ppm). The case study to be described here of a fracture in a water supply which caused substantial damage, indicates that attack probably can occur at such levels, especially if the fittings exhibit extensive weld lines near stressed zones. High chlorine concentrations can arise due to chlorine surges in the water supply, especially when the water company overdoses the supply after a major leak.

Rheology of Randomly Branched Polymers
Ralph H. Colby, Charles P. Lusignan, Jay Janzen, May 2000

The molecular structure of randomly branched polymers is understood using percolation theory. Once the chain length between branch points and the extent of reaction relative to the gel point are specified by synthesis, both the molecular structure and the linear viscoelastic response can be determined using simple models. We demonstrate these ideas using randomly branched polymers with known chain lengths between branch points. Then we exploit this finding to characterize the chain length between branch points for polyethylenes from knowledge of their weight-average molecular weight and zero-shear-rate viscosity.

Extruder Analysis Utilizing a Transparent Extruder and Simulation Software
Weining Song, John Perdikoulias, Mirek Planeta, May 2000

Experiments using a glass window extruder are presented. These provide direct observation of the different melting behavior among various polymers. Simulations performed using commercially available software showed good correlation with the observations. The data obtained provides valuable insight into the melting behavior which, can be used to evaluate and ultimately improve the capabilities of simulation software as well as screw designs.

How to Add Value and Solve Mold Problems - With Steel
Frederick T. Gerson, May 2000

Mold designers and mold builders know many different ways to solve mold problems.. Yet a surprising number of our colleagues have not yet used the wide variety of proven mold steel on offer in to-day's market place. This paper reviews the range of available grades of steel; it cites examples of mold problems that have been solved by selecting better and more appropriate alloys; it lists the worldwide availability of innovative mold steels, and finally, it shows that better steel adds value to a mold at very modest cost.

Melt Processed Polymer-Clay Nanocomposites: Properties and Applications
Sam J. Dahman, May 2000

The melt compounding route is a powerful approach in the preparation of polymer-clay nanocomposites as existing technologies can be utilized and easily scaled to commercial quantities. Polymer-clay nanocomposites have been developed via melt compounding. Dramatic increases are exhibited in heat distortion, stiffness, and barrier properties compared to the neat resin. Other benefits include low specific gravity, processing ease, surface appearance, etc.

3D Numerical Simulation of Gas-Assisted Injection Molding Process
Florin Ilinca, Jean-François Hétu, May 2000

This paper presents a finite element algorithm for solving gas-assisted injection molding problems. The solution of the three-dimensional (3D) equations modeling the momentum, mass and energy conservation is coupled with two front-tracking equations, which are solved for the polymer/air and gas/polymer interfaces. The performances of the proposed procedure are quantified by solving the gas-assisted injection problem on a thin plate with a rib. Solutions are shown for different ratios polymer/gas injected. The effect of the melt temperature, gas pressure and gas injection delay, on the solution behavior is also investigated. The approach is then applied to a thick 3D part.

3D Simulation of the Packing-Cooling Stage in Polymer Injection Molding
Florin Ilinca, Jean-François Hétu, May 2000

This paper presents a finite element algorithm for solving polymer injection molding problems. The methodology consists in solving for the three-dimensional (3D) equations modeling the momentum, mass and energy conservation. The packing and cooling stages of the injection molding process are modeled by including the compressibility effects. The procedure is aimed by problems in which three-dimensional effects are important but is also effective for thin parts. The performances of the proposed approach are quantified for the injection of a thin plate for which experimental data are available. The procedure is then applied to a thick 3D part. The method results in accurate solutions and it proves to be a useful tool to quantify the solution behavior on cases otherwise difficult to investigate.

Compaction of Fillers, Flame Retardants and Other Additives to Improve Flowability and Accelerate Compounding Rate
George C. Hawley, May 2000

A process has been developed to compact fillers commonly used in plastics to improve mechanical properties - mica, nanoclays and wollastonite -and flame retardance - magnesium and aluminum hydroxides. Such fillers are produced in very fine particle size or high aspect ratio. They are fluffy, entraining much air, which must be removed. Aerated fillers do not flow well and require special feed devices. Voluminous filler takes up machine capacity, limiting the production rate of filled compounds. Entrained air reduces thermal conductivity and thus the flux rate of the polymer. Compaction improves the handling, feeding and incorporation rate of such fillers into compounds.

New Boron Nitride Processing Aids for the Extrusion of Molten Polymer
Franky Yip, Savvas G. Hatzikiriakos, Thomas M. Clere, May 2000

It is already known that the use of Boron Nitride (BN) in the extrusion of molten polymers may eliminate surface melt fracture and postpone the critical shear rate for the onset of gross melt fracture to significantly higher values depending on resin type and additive content. In this work several new Boron Nitride powders (Carborandum Co.) are tested that exhibit superior behavior from the previous studied ones. Critical parameters for this unique behavior (elimination of gross melt fracture) are good dispersion, small average particle size and free of agglomeration. The equipment used for the testing of the new powders include both an Instron capillary rheometer with special annular dies (Nokia Maillefer wire coating crosshead) attached to the rheometer, and a parallel-plate rheometer. A metallocene polyethylene with all types of boron nitride is tested at various additive concentrations. The additive having the finest particle size and that is free of agglomeration was found to have the greatest influence on the gross melt fracture performance of the polymer tested in crosshead dies and tips. Moreover, one of the additives was found to enhance melt slippage and as a result relieved internal shear stresses. This action is believed to eliminate surface melt fracture and postpone the critical shear rate for the onset of gross melt fracture to significantly higher values depending on the additive concentration. The influence of the boron nitride type and its concentration on the polymer rheology is also discussed.

Pressure Dependent Viscosity of Polymer Melts
Osamu Amano, Keita Ainoya, May 2000

Pressure dependent viscosity and juncture loss were measured by means of a new capillary rheometer developed at pressure up to 100 MPa and over wide shear-rate range from 5.0E+02/s to 5.0E+05/s for four polymer melts (HDPE, GPPS, HIPS, and PC) through simultaneous measurement of pressure at the entrance and exit of the capillary during applying counter pressure to the exit by means of a needle valve located in the downstream. Pressure dependent viscosity and juncture loss play an important role to improve the accuracy of simulation with a CAE program. However, there are few data in high shear-rate range corresponding to actual molding. Pressure loss in the flow path increases unexpectedly with increase of hydraulic pressure applied. The most adequate equation for fitting viscosity seems to be the Cross-WLF equation. The magnitude of the pressure parameter D3 lies in the range of 10E-07 K/Pa for these polymers.

A Study of Surface Haze Formation in Polypropylene/Acrylic Alloys
S.P. Bistany, D. Dong, C.Y. Han, L.A. Struzik, M.D. Wolkowicz, May 2000

Haze is a cosmetic defect that occasionally appears on injection molded part surfaces. This defect is especially noticeable in dark colored, high gloss parts. A study was performed to identify and understand the underlying causes of surface haze formation in unfilled PP/PMMA alloys. Four different Polypropylene resins with varying amounts of PMMA were evaluated. The formation of haze was found to correlate with the amount of PMMA included in the formulation and the melt elasticity as indicated by tan ? at low frequency.

Light Stabilization for Black and White Glass-Filled Nylon-6
Hui H. Chin, James H. Botkin, May 2000

Light stabilization of polyamides for automotive applications remains a challenge. In this paper various stabilization systems (hindered amine light stabilizer, antioxidant, phosphite) were evaluated in black and white glass-filled nylon-6. The properties being examined were color change and gloss retention of injection molded plaques during exposure in a xenon arc weatherometer under exterior automotive conditions per SAE J1960 and interior automotive conditions per SAE J1885. Light stabilization systems meeting the interior automotive requirements were identified.

Analysis of the Flow Front Profile by In-Line Visualization of the Filling Stage
G.R. Dias, A.M. Cunha, M. Cinvent, May 2000

Using a special tool designed with the purpose to visualize the melt flow across the thickness dimension of the mold cavity [l], an experimental investigation was made to assess the polymer melt behavior in specific processing conditions. The aim of the work is to visualize some unexpected flow front behaviors in the selected injection molding conditions. The design of the mold enables to adjust the location of a special glass window along the material flow path. The mold feed is based on a hot runner system. The results presented are direct visualization images of the melt front.

How to Organise a Modern Plastic Company to Have Success in a Turbulent Environment?
G. Baric, I. Catic, May 2000

Today's conditions in business activities, only short-term planning possibilities, necessity for everyday adaptation to situations within the company, require new organisational forms, new ways of managing the companies and, in a way, new people. Since today's companies are the target of constant selection, comparable to the one in nature, and their environment is unpredictable, it is no wonder that knowledge acquired by natural sciences is being increasingly implemented in the field of organisation. Modern business conditions have forced the managers to search for similarities with those scientific fields that have just begun to develop, and that try to establish some kind of order in the haphazard phenomena. Recognising similarities between the world of nature and an enterprise have led to the creation of numerous new organisational concepts, which have found their application also in plastic companies.

Measuring Viscosity of Filled Polymer Systems
Vinod B. Warrier, David B. Todd, May 2000

This paper investigates the use of a Helical Barrel Rheometer to measure the viscosity of filled polymer systems. A Helical Barrel Rheometer is an online rheometer developed at the Polymer Processing Institute. The HBR allows us to measure the viscosity of polymer systems under conditions close to that encountered in processing. The viscosity measurement does not require measuring either the torque or the flowrate. The rheometer does not require an entrance correction, avoids bridging of filler particles during measurement and also takes care of the orientation of fillers encountered in processing. This paper uses polypropylene/talc as a filled polymer system. Three different concentrations of three different grades of talc were used to measure the viscosity and a comparison with conventional capillary viscometer was made.

A Study of the Effect of Chlorinated Water on Engineering Thermoplastics at Elevated Temperatures
Steven W. Bradley, Jamal El-Hibri, Bruce H. Bersted, Walter L. Bradley, May 2000

Hot water plumbing applications can often be a severe environment for both metals and plastics. Continual exposure to elevated temperature as well as the oxidative effects of disinfectants such as chlorine can reduce the lifetime of plumbing components. A study was recently conducted to determine the potential degradation effects of hot chlorinated water on several engineering thermoplastics. Weight loss, tensile strength and elongation properties, burst strength retention and microscopy were used to examine the material behavior as a function of exposure time. This data will provide a basis for determining which engineering thermoplastics will be suitable for long-term exposure in hot, potable water.







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