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

Closed-Loop Viscosity Control for Injection Molding
A.S. Bakharev, R.G. Speight, P.A. Brincat, May 2002

This paper describes an automated closed-loop control system that compensates for plastic viscosity variations by directly controlling the machine parameters of an injection molding machine. Viscosity is evaluated using a primary injection pressure integral, and compensated for by changing the temperature profile settings of injection molding machine. The shrinkage changes due to the melt temperature changing are compensated for by adjusting the holding pressure. The paper discusses the theoretical basis of the algorithm and presents experimental results on testing the algorithm.

COF Analysis of POP and LLDPE Films Containing Erucamide: Effect of Repetitive Testing
Amol V. Janorkar, Douglas E. Hirt, Jeffrey J. Wooster, May 2002

Erucamide is incorporated into polymer films to reduce their coefficient of friction (COF). Such a reduction in COF is important in packaging lines where the performance of the film in contact with rollers can be governed by the frictional characteristics of the film. This research explores the COF behavior of multilayer films with either POP or LLDPE as the skin layer. Film-on-metal COF testing was performed repetitively with the same piece of film to investigate the extent of COF change with the number of runs. Film-on-film studies were also performed for comparison with the film-on-metal tests. Complementary analysis was conducted with atomic force microscopy (AFM) to investigate whether erucamide was being removed from the film surface or simply being smeared over the surface.

Co-Injection Molding of PVC with Other Thermoplastics: Processing, Properties, and Applications
Mark Parsons, Paul Toyoda, May 2002

Rigid polyvinyl chloride (PVC) was co-injected with glass fiber reinforced PVC (GFR-PVC), polypropylene (PP), acrylonitrile-butadiene-styrene copolymer (ABS), and polycarbonate (PC) using the Mono-sandwich co-injection process. Up to three through-thickness skin-core morphologies were observed along the length of the sample. Near the gate, the core was always a single, continuous layer. In some cases, the core diverged into multiple or discontinuous layers. Further from the gate, flow of the core ceased, leaving a skin-only region. The skin and core layers were more uniformly distributed through the test plaque when injection speed was low. Adhesion between PVC and PP was poor. Skin and core layers delaminated and mechanical properties were poor. PVC adhered well to GFR-PVC, ABS and PC. No layer delamination occurred and mechanical properties were intermediate between those of the skin and core components alone. Dropped dart impact energy was controlled more by the skin layer than the core. In rigid PVC/GFR-PVC co-injected samples, impact energy was 2.5 times greater when GFR-PVC was the core than when GFR-PVC was the skin.

Co-Injection Molding: Effect of Processing on Material Distribution and Mechanical Properties of Short Glass Fiber Reinforced Polypropylene Test Bars
D. Ait Messaoud, B. Sanschagrin, A. Derdouri, May 2002

The co-injection molding process involve injection of two materials sequentially to form a multilayer product with a skin and core structure. Dumbbell test specimens were molded using a 150 ton Engel co-injection machine. The effect of injection speed and skin-core ratio on material distribution was first studied. The mechanical properties of different combinations using virgin polypropylene and polypropylene reinforced with 10, 20, 30 and 40 % (by weight) short glass fiber were measured.

Cold Slug Wells in Injection Molding
Patrick Auell, Brian Martonik, May 2002

Cold slug wells are used on nearly all cold runner molds to prevent potential problems caused by cold slugs that are introduced to the runner from the nozzle tip. However, they are often used without a full understanding of what they do, how they work, were they need to be placed, and how large they must be. This paper quantifies the effectiveness of cold-slug wells and investigates design variations. The effects of location and size are examined to determine the relevance of each. By better understanding the use of cold slug wells, a molder can design and use them more successfully to help minimize related problems.

Commercialization of Gas-Assist Injection Molding or The Gas Wars""
Jack Avery, May 2002

Gas-assist injection molding was discovered in Germany 30 years ago. Even though this technology has demonstrated significant value, a relatively small number of components are manufactured utilizing this process.Since the basic technology is straightforward, why has the acceptance of gas-assist injection molding been so limited? A number of factors have played a role, including litigation, initial licensing approaches and the unfamiliarity of designer with this process.This presentation will examine a number of the key decisions made by the suppliers of this technology as well as the OEM’s and molders that impacted the acceptance and utilization and their implication on the commercialization of gas-assist injection molding.

Compact Slide Action Closure Mold Technology
Ealias C. Joseph, May 2002

The Compact Slide Action Mold Technology (CSAM) has been custom designed for tamper evident closure molds for carbonated and non-carbonated beverage bottle closures, as well as mineral water bottle closures.Existing mechanisms for opening and closing slides in a slide action mold typically include angled horn pins or delta cams mounted to the cavity plate and slide retainers to retain slides in an open position.The new compact slide action mechanism for lateral movement of slides has been developed with the use of an air driven rack and pinion arrangement. This paper discusses some of the common problems associated with the conventional mechanism and how the new mechanism overcomes these problems.

Comparative Investigations on Quasi-Simultaneous Welding on the Basis of the Materials PEEK and PC
H. Potente, G. Fiegler, F. Becker, J. Korte, May 2002

Laser transmission welding of polymers is regarded as a promising alternative in a range of industrial applications by virtue of its characteristic properties. The new variant of laser transmission welding – quasi-simultaneous welding – can be seen as a pioneering technology offering advantages such as precise local and contact-free heating, small heat affected zone, negligible warpage, high flexibility, compensation of part tolerances, high achievable weld strengths, etc.Initial systematical investigations were carried out varying the parameters: laser beam intensity, scanning velocity, joining displacement, pigment content and joining pressure. Their influence on weld strength and welding time was recorded. A T-joint was used for welding PEEK, while both T-joints and butt joints were used for the material PC. Optimum process parameters were determined for each material.

A Comparative Study of Corn Starches with Different Amylose Content
Celso L. Lotti, Elisângela Corradini, Eliton S. de Medeiros, Luiz H.C. Mattoso, May 2002

In this work, corn starches with 21% and 1 % of amylose contents, processed in the presence of 30% (w/w) of glycerol (plasticizer), were characterized by X-ray diffraction, Dynamical Mechanical Thermal Analysis (DMTA), Tensile test and Scanning Electron Microscopy (SEM). The results showed differences in the crystalline structure and mechanical properties of the starches after processing. The 21 % amylose content starch showed fragile behavior and higher tensile at rupture than 1% amylose content starch, which showed higher elongation at break and ductile behavior.

Comparing Cavity Pressure Sensor Technologies Using In-Mold Data
Michael R. Groleau, Rodney J. Groleau, May 2002

Three cavity pressure sensor configurations were used to compare data from direct and indirect, piezoelectric and strain gage sensors. The indirect button style sensors tended to read slightly lower peaks than direct flush mount sensors, and data decayed slightly later. Also, the piezoelectric sensors tended to respond approximately 5 ms faster than the strain gage sensors. However, data from all sensor types correlated very well with one another. For all practical purposes, there is no distinguishable difference in the data utility between one sensor type and another.

Comparing the Tensile/Yielding Behaviors of the New Isotactic and Syndiotactic Polypropylenes
W.R. Wheat, May 2002

PP product design and application possibilities have expanded significantly with developments in metallocene catalysis. With the large number of structural and compositional differences these resins bring to the plastics consumer, processing effects require an improved scientific understanding. A variety of isotactic and syndiotactic PP’s are described in detail regarding their tensile and (specifically) yielding behaviors, useful to predict performance characteristics, in property evaluations and as an aid for orientation processing in film and fiber applications.

Comparison between Two Different Theories for Determination of Interfacial Tension by Breaking Thread Method
Guillermo PalmerMartin, Nicole Raymonde Demarquette, May 2002

Interfacial tension between molten polymers is a key factor that helps predicting the morphology of polymer blends. In this work, the theories of Tomotika and Tjahjadi et al.[1, 2, 3] to measure interfacial tension between molten polymers using the breaking thread method are evaluated and compared. In particular, both theories were tested for PP/PS polymer pair at temperatures ranging from 200 °C to 240 °C. The results obtained using both theories corroborated. It is shown that both theories should be used in a complementary manner in order to enhance the accuracy of the breaking thread method.

Comparison of Effects of Vibration-Assisted Injection Molding on Polystyrene and Polycarbonate
Akihisa Kikuchi, John P. Coulter, May 2002

Vibration-assisted injection molding (VAIM), which involves applying mechanical vibration to polymer melts during the injection and packing stages of molding processes to control polymer behavior at a molecular level, was applied on polystyrene and polycarbonate. With optimized VAIM processing conditions, the strength of polystyrene was improved by as much as 28% without sacrificing cycle time while the strength variation was reduced by 67%. With polycarbonate, however, the strength was improved only 7% and a toughness reduction resulted in some cases. In the current paper, the findings and theoretical basis related to these seemingly incompatible results are presented and discussed.

Comparison of Energy Consumption with Two Methods of Injection Mold Cooling
Trina R. Carl, James L. Burrows, May 2002

Thermolators continually pump water through a mold and have been used for cooling since the beginning of mold cooling. Thermolators, in general, are relatively large and are not considered to be energy efficient. New technology has been used to develop a system that only pumps water as needed to maintain a consistent mold temperature.A study was conducted to demonstrate the differences between usage of a thermolator and a pulse cooling system. Cost is a main factor when comparing cooling systems. In this study the cost factors that were compared were energy usage and cycle time.This study demonstrated that pulse cooling is much more energy efficient and that pulse cooling could reduce cycle time using part warpage as the controlling factor.

Comparison of PET Chemical Modifiers for Extrusion Foaming
M. Xanthos, R. Dhavalikar, C. Wan, Q. Zhang, S.K. Dey, May 2002

The efficiency of low molecular weight multifunctional anhydride and epoxy compounds as chemical modifiers for low density extrusion foaming of low intrinsic viscosity (IV) polyethylene terephthalate (PET) was evaluated by reactive extrusion under controlled conditions. The two dianhydrides and the three epoxy compounds with different functionalities were used at concentrations based on stoichiometry derived from the measured carboxyl and hydroxyl end group contents of the base resin. Correlations of die pressure with extrudate swell during extrusion, and melt flow index with melt strength by off-line testing of the extrudates permitted the ranking of the modifiers according to their chain-extending efficiency. Extrusion foaming experiments indicate that production of low-density foams by a process involving one-step reactive modification/gas injection foaming is feasible, at conditions not significantly different than those employed in the simple reactive modification of the PET resin.

A Comparison of Proton NMR and NIR for the Online Analysis of Terpene Resin Distillate Fractions
Mark J. Sullivan, May 2002

The selection of online analyzer technology is determined by numerous practical criteria. NIR has been established as a leading technology for online process analysis due to its versatility and proven reliability. Nevertheless, the robust, multivariate calibrations that are key to the implementation of NIR analyzers can be difficult to develop or transfer and their maintenance over time can add significantly to the cost of the analysis. Recent reports have indicated that, despite the higher initial costs, process N M R m ay offer long term cost advantages over NIR for applications where global NM R calibrations have been developed.The objective of this study was to com pare the accuracy (i.e., standard error of prediction) of multivariate calibrations (PLS)for NIR and NM R on a set of process samples taken from a terpene resin still that were referenced by G C. Particular attention was focussed on whether the uniformity of NM R intensities and the discrete nature of the spectra would offer any inherent advantages over NIR with its superior signal-to-noise.The PLS calibrations on laboratory data showed better results by NIR over NM R for the same total acquisition time. The NIR advantage w as m ore pronounced for the minor components (<5% of the neat mixture) than for the major component (>90% ). The results are consistent with the higher signal-to-noise for NIR over NM R. In both cases, the PLS regression coefficients emphasized resolved spectral features that corresponded directly to functional groups in the pure components. Due to the spectral simplicity of this mixture of small molecules, the selectivity of NM R did not yield any advantage in the calibrations. Additional work would be required to determine if NM R would offer benefits in the actual online environment.

Comparison of Reactive Extrusion in Various Twin Screw Extruders and Their Roles on Mixing
Byung H . Lee, James L. White, May 2002

A comparative modeling of distributive mixing has been investigated in intermeshing co-rotating, intermeshing counter-rotating and tangential counter-rotating modular twin screw extruders. This is based on the Spencer-Wiley premise of representing mixing through interfacial area increase and its relationship to shear strain of the various modular twin screw elements. It is necessary to develop flow analyses for different modular twin screw extrusion machines. We applied this analysis to understand the reactive extrusion process in various twin screw extruders. Our approach is to compute the development of interfacial area for composite modular twin screw extruders and an internal mixer, and a mixing index was determined for each processing device.

Comparison of Structure Development in Processing Syndiotactic and Isotactic Polypropylenes
Dongman Choi, James L. White, May 2002

We investigated the crystallization and orientation development in syndiotactic polypropylene (sPP) during various polymer processing operations and also compared the results with isotactic polypropylene (iPP). This was carried out in fiber spinning, tubular film extrusion and injection molding. Melt-spun sPP fibers exhibit Form I helical structure at low spinline stress levels and zig-zag all trans structure (Form III) at high stress levels. In tubular film extrusion, sPP exhibits Form I structure and the a-axis is preferentially oriented in the film normal direction. Injection-molded sPP samples exhibit very low frozen-in orientation levels due to its slow crystallization rate.

Comparison of Tensile Properties for PET and Acetal Specimens Using Two Different Tensile Testing Units
Rhonda M. Rush, May 2002

The compiled data are for unfilled acetal and filled polyethylene terephthalate (PET) specimens. Various sample sets were evaluated using the ASTM D 638-95 method, “Tensile Properties of Plastics.” These tensile data are used to evaluate material candidates for making molded parts. It is important to determine if the tensile data are the same or if they are different so that selections can be made without repeating the data collection each time a decision is required. Sample sets were evaluated using two different instruments—a SATEC and an Instron. These data were obtained over a number of years by different operators following an iterative approach. One sample set was molded from Delrin® 500*, a medium viscosity, acetal homopolymer (POM). The three addition sets were polyethylene terephthalate (PET) specimens molded from Rynite® SST 35,* Rynite® 545, and Ticona Celstran® PETGF 20-02.

A Comparison of the Axisymmetric and Planar Elongational Viscosities of a Polymer
Peter Beaupre, Mahesh Gupta, May 2002

The elongational viscosities of a low density polyethylene in axisymmetric and planar flows are compared. The experimental data on entrance pressure loss is matched with the corresponding finite element predictions to estimate the parameters in the elongational viscosity model proposed by Sarkar and Gupta. The entrance losses in the capillary and slit rheometers are used to predict the elongational viscosities for axisymmetric and planar flows respectively. The power-law region of the axisymmetric as well as planar elongational viscosity is found to follow the time-temperature superposition principle.

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