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

Solid State Shear Orientation of Polymers via Equal Channel Angular Extrusion

Zhiyong Xia, Chris K.-Y. Li, Hung-Jue Sue, Alex J. Hsieh, Jack Chu, May 2000

The effect of large strain, simple shear deformation induced by the Equal Channel Angular Extrusion (ECAE) process on semi-crystalline poly(ethylene terephthalate) (PET) and amorphous polycarbonate (PC) has been investigated. A through-thickness shear strain of approximately 190% after one ECAE pass is induced in the extrudates. Mechanical tests revealed that the extrudates are anisotropic, indicating that the process is capable of generating highly oriented microstructures. Improved fracture toughness can also be achieved via the ECAE process.

Best Practices: Looking beyond Benchmarking to Develop Your Business Strategy

Margaret Baumann, May 2000

Real breakthroughs in strategy and business development come from looking beyond your in-kind competitors for a process view of customer-focused solutions. A company's basic operations are first level processes and cross over industry type. Best practices is the study of identifying the companies which have developed superior processes in product development, manufacturing, customer service and market segmentation regardless of the industry they are in. This paper discusses the benefits of the study of Best Practices in addition to competitive intelligence and benchmarking in business planning. Examples of companies in the plastic industry who have distinguished themselves by their best practices will be presented.

The Impossible Part-On the Verge of Failure?

Jerry Golmanavich, Barry Hofmaster, May 2000

There have been several occasions in the past where part designs have been proposed which require non-traditional approaches to manufacturing. Even with run-of-the-mill designs it seems prudent to do computer flow simulations to verify that a part is manufacturable. The case history described below details how a product was deemed impossible"; the flow simulation verified that it was "impossible" and yet the project was pursued and has now passed the prototyping stage. This paper describes a project where some risk was taken and may provide the drive to explore new limits."

Studies on the Rotomolding of Liquid Crystalline Polymers

P. Rangarajan, J. Huang, D. Baird, May 2000

This paper is concerned with the rotomolding of thermotropic liquid crystalline polymers (TLCPs) for the purpose of generating tank liners with excellent barrier to oxygen. The major issues involved include whether the TLCPs can be ground to provide resins suitable for rotomolding (~40 mesh size powder) and their ability to fuse together to provide adequate strength and barrier properties. With the use of appropriate grinding techniques, the TLCPs were found to fuse well to provide strength and stiffness significantly greater than that of HDPE.

Critical Conditions for the Onset of Unstable Flows of Molten Polymers

Kolapo P. Adewale, Arkadii I. Leonov, May 2000

A simple method to predict the critical shear stress and the critical shear rate for the onset of melt flow instabilities in capillary flow is presented. The method, earlier reported for polyisoprene, employed a bulk stable viscoelastic constitutive equation that contains a hardening parameter ?. The parameter ? is solely determined by the molecular characteristics of the polymer. Below we compare predictions of the critical shear stress with experimental data for some common polymers.

Effects of Twin Screw Compounding Conditions on the Mechanical Properties of Nylon-6/Glass Fiber Composites

Murat Cansever, Ulku Yilmazer, May 2000

The effect of processing conditions on fiber length degradation was investigated in order to produce higher performance composites. For this aim, Nylon-6 was compounded with glass fibers in a twin screw extruder for various combinations of screw speed and feed rate. Collected samples were injection molded and izod impact and tensile strength tests were performed in order to observe the effects of fiber length on mechanical properties. Also, by using the extruded and injection molded samples, fiber length distribution curves for all experimental runs were obtained. Results show that when the shear rate is increased through the alteration of screw speed and feed rate the average fiber length decreases.

Polymer Raw Material, Process and Production Fingerprints in Injection Moulding

A.J. Dawson, A. Key, P.D. Coates, May 2000

In-process monitoring of polymer melts is found to provide a fingerprint of the: • polymer (process-relevant polymer rheometry); • the process (injection pressure-time curves which reflect the material-machine-mould combination, including polymer batch to batch variation and machine dynamic repeatability); and • production trends, with 'process indices' offering an efficient basis for 100% automatic inspection, Statistical Process Control, and even insight into factory housekeeping. Specific pressure indices in an indentified low noise region of the primary injection stage of injection moulding have been found to provide a sensitive indicator of changes in a polymer, including batch to batch changes and process-induced changes, as such measurements are closely related to the rheology of the polymer melt. The same information has also been found to provide sensitive indications of variation in the processing operation for a given polymer-mould combination, and also consequently to allow meaningful statistical analysis of trends in the injection moulding process. Laboratory and factory data for raw material, process and production trend analysis (the latter involving data from substantial production runs) are presented.

Novel Small and Large Scale Flow Visualisation of Polymer Melts

P.D. Coates, M.T. Martyn, M. Kamala, C. Parminter, May 2000

A novel small scale (<30g of polymer) recirculating flow visualisation cell has been designed and built. The unit comprises a single screw extruder, gear pump and variable geometry inserts making a flow recirculation loop. The recirculation flow cell is capable of being used with a range of entry geometries, including abrupt entry and hyperbolic, with a polariscope for stress birefringence, and a CCD camera and image processing system for particle streak velocimetry. This new facility complements existing larger scale flow visualisation cells in our laboratory, fitted to a single screw extruder. Information from flows in both scales of flow cell are presented for an LDPE melt.

Viscoleastic Properties of Reactive and Non-Reactive Styrene-Maleic Anhydride / Olefinic Blends

G. Bayram, U. Yilmazer, M. Xanthos, May 2000

Reactive blends of styrene-maleic anhydride (SMAH) with polyethylene/methyl acrylate/glycidyl methacrylate (PE-F) and non-reactive blends of SMAH with polyethylene/methyl acrylate (PE-NF) were produced and characterized in terms of morphology and viscoelastic properties in order to understand the reaction characteristics between anhydride/epoxy functional groups. Storage modulus, G', loss modulus, G and complex viscosity ?* of reactive blends at 25 % and 50 % PE-F were higher than those of non-reactive ones. At 25 % PE-F a maximum in complex viscosity was obtained for the reactive blends. In morphological analysis the reactive blends showed finer morphology than the non-reactive ones."

Simultaneous Measurement of Torque, Axial Normal Force and Volume Change in the NIST Torsional Dilatometer-Experiments and Analysis

Carl R. Schultheisz, Gregory B. McKenna, May 2000

The NIST Torsional Dilatometer measures simultaneously the torque, axial normal force and volume change in response to a torsional deformation. While the torque is a linear function of the angle of twist per unit of length, the normal force and volume change are effects of geometrical nonlinearities. In stress-relaxation experiments with an epoxy cylinder near its glass transition temperature, the torque and normal force decay monotonically, but the volume change associated with the torsion shows a significant non-monotonic decay at lower temperatures. The measurements are investigated with a series solution for torsion of an elastic, compressible material [Murnaghan, F.D. (1951) Finite Deformation of an Elastic Solid. Wiley, New York.].

A Unique Benzoate Plasticizer for Reducing Viscosity and Fusion Temperature

T. Bohnert, B. Stanhope, K. Gruszecki, S. Pitman, V. Elsworth, May 2000

Plastisol viscosity reduction and control is an important property specification in many vinyl plastisol formulations. A unique benzoate plasticizer is under development that functions as a viscosity reducer. It also is a high solvating plasticizer in standard plastisol systems. Data will be presented on the effect of the new benzoate plasticizer on phthalate and benzoate containing plastisols and vinyl sheet properties.

Using Branched Polypropylene as a Melt Strength Modifier-Improvement in Sheet Sag Resistance

V.V. DeMaio, D. Dong, A. Gupta, May 2000

Blends of conventional polypropylene (PP) and branched PP (bPP) enable PP to perform well in applications where extensional flow dominates, such as blow molding, thermoforming and foaming. Sag resistance tests shows a significant improvement in sag time of extruded sheet as the content of bPP increases, up to 30-wt.%. These blends (PP/bPP) show synergistic increases in melt tension while providing excellent processability by maintaining low viscosity.

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.