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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Characteristics of the Vitrification in the TTT Diagram
Vitrification corresponds a solidification of a polymeric thermosetting material when the glass transition temperature Tg of the material precedes the experimental temperature T. Relating the vitrification progress at various isothermal temperatures to the cure time builds the Time- Temperature Transformation (TTT) diagram for thermosets. There are a number of possible routes in this diagram that could lead the material to a representative glass state, including the isothermal cure route, continuous heating route, cyclic heating route, and temperature cooling route after allotted cure. However, the glass transitions involved in the different routes are different in nature, even though the material may have the identical chemical conversion (?) and the same Tg. Such a behavior may lead to interesting density profiles of the thermosetting material upon curing that might introduce potential richness of other chemical/physical responses in the glassy state.
pCBT: A New Material for High Performance Composites in Automotive Applications
Cyclic oligomers of butylene terephthalate (CBT®) represent a new chemical route to semicrystalline thermoplastic polybutylene terephthalate (PBT). The oligomers of interest melt completely at about 150°C to produce a low viscosity fluid that is ideal for wetting and dispersing fibrous fillers and reinforcements thereby enabling the development of composites that were previously not possible when working with high viscosity commercial PBT. Introduction of catalyst to undiluted molten cyclic oligomer leads to rapid ring opening polymerization and the formation of high molecular weight thermoplastic PBT without the generation of volatile organic compounds. The polymer resulting from this polymerization will be hereby referred to as pCBT. Treatment of cyclic oligomers in this fashion results in pCBT thermoplastic resin with a high melting point (230°C) and physical performance similar to that of other commercially available PBT resins. The low viscosity oligomers enables the selection of processing technologies that are typically reserved for thermosetting systems that work in conjunction with easy flowing monomers or pre-polymers. The combination of excellent mechanical performance and the ability utilize processing techniques typically reserved for thermosets enables broad uses for these oligomers in a range of applications including; interior, exterior and structural automotive components. Additionally, the thermoplastic nature of pCBT holds promise to provide a low capital route to a new family of pCBT based recyclable materials made using a range of plastic processing technologies.
Flow Based Manipulation of Conductivity in Nanotube Composites
Nanotube composites are finding applications due to their ability to enhance the electrical conductivity of polymeric materials. They exhibit a percolation threshold in both rheological and electrical properties at concentrations of ~1/2 % by volume nanotube. We study the interrelationship between these two coupled transport properties by dielectric spectroscopy and rheology. We study an extruded rod and find that the nanotube network and the electrical conductivity become highly anisotropic. We find that the conductivity is quite sensitive to the shear field and becomes highly anisotropic.
High Clarity Linear Low Density Polyethylene for Packaging Applications
As packaging applications become more demanding, film extruders are searching for resins with a combination of properties, including strength, clarity and stiffness. Many conventional resins, such as high-pressure low density polyethylene are clear, but lack the overall balance of toughness and stiffness that many applications require. Linear low density polyethylenes provide increased toughness and stiffness, but most lack the high gloss and low haze required for clarity applications. To achieve better film clarity, some extruders use lower density linear polyethylenes or blend with high pressure polyethylenes, thus sacrificing stiffness and toughness. A new polyethylene that combines good stiffness, clarity and toughness is now available for these demanding applications. This polyethylene, a 0.926 g/cc density linear low density based polyethylene can be used to produce stiff, clear films that can be used in a variety of applications including shrink wrap, and form, fill and seal applications.
Effect of Electric Field on Alignment Behavior and Conductivity of Composite Membranes
Composite membranes of sulfonated crosslinked polystyrene particles have been made by aligning the particles under an electric field in a crosslinked poly(dimethyl siloxane) matrix following a procedure described by Oren et al. (2004). The purpose of this work, however, was to investigate the effects of electric field amplitude and frequency on alignment behavior. As expected, the particles aligned only by application of a certain minimum electric field for a given frequency. Impedance measurements indicated that the unaligned membranes showed capacitive behavior up to 8 wt % particles, which transformed to conductive behavior on alignment.
An Overview of Innovative Technologies based on 2004 Automotive Innovation Awards
This paper provides technical detail of key technologies selected as finalist during the 2004 Automotive Innovation Awards Ceremony. Process related innovations such as SIB Fuel Tank Assembly, Running Board, Simultaneous Shot Injection Molded Instrument Panel, Gas-Assist Towing Package and Material related innovations such as Static Dissipative Non-Slip Truck Bed liner, 3.7L V-6 Engine Valve Cover, Two-Shot Load Bearing Touch-Off Molding are discussed are discussed first. Exterior Applications such as Body Color Blow Moulded Running Board, Carbon Fiber Rear Deck Assembly, and Hybrid Plastic/Steel Truck Front Step Bumper are described followed by Interior applications such as Door Trim with Integrated Acoustic Chamber and Subwoofer, Low Density Glass Mat Soft Touch Interior and Instrument Panel Carrier are discussed in detail.
Three-Dimensional Simulation of Gas-Assisted Injection Molding
Gas-assisted injection molding has established itself as a successful injection molding technique. The flow behaviors in this process are dominated by three-dimensional effects that are not yet completely understood. Consequently, much process and part design in gas-assisted injection molding is accomplished heuristically. Accurate simulations of the flow behavior will both assist part manufacturers to obtain optimal part designs and aid understanding of this process. This paper presents three-dimensional simulation results of gas-assisted injection molding and compares results with experimental data.
Corner Effect in Warpage Simulation
This paper discusses additional “spring forward” or “corner effect” considerations that influence the warpage simulation of parts with corners or sharp curvatures. Incorporating these terms into warpage simulation may significantly improve the accuracy of the deflection prediction if the polymer shrinkage is anisotropic and the part geometry has prominent corners or curvatures.This corner effect must be explicitly modelled when the warpage analysis is performed on “mid-plane” and “dual domain” shell geometry representations; however, no special considerations are required when using true 3D warpage analysis.
Online Adaptive Injection Molding Process and Quality Control
An online adaptive control methodology was developed to control the process and quality variables in injection molding. A process variable, such as the cavity pressure or mold separation, was selected for the process control, which adaptively changed the fill-to-pack switchover point from shot to shot, and adjusted the hydraulic pressure during the pack/hold phase within one shot. Further, a more sophisticated online adaptive quality control scheme was investigated that incorporated direct online quality control and neural network models in the feedforward loop. The neural network models were extracted from computer-aided engineering (CAE) predictions. Incorporating CAE results in the online quality control fills the gap between a science-based product/process design and an empirics-based process/quality control on the shop floor. This methodology can also be applied to monitor and control other quality variables such as part dimensions.
Warpage Comparison between Microcellular and Conventional Injection Molding
This research investigated the effects of processing conditions on the shrinkage and warpage (S&W) behavior of a box-shaped part using conventional and microcellular injection molding. Two sets of 26-1 fractional factorial DOE were employed to perform and analyze the experiments. After the machine and material reached the steady state condition, molded samples were collected and measured using an optical coordinate measuring machine (CMM). The results suggest that the supercritical fluid (SCF) content (in terms of SCF dosage time) and the injection speed affect the S&W of microcellular injection molded parts the most, whereas hold pressure and hold time have a greater influence on the S&W of conventional injection molded parts. This study also quantitatively showed that, within the processing range studied, an increase in dimensional stability could be achieved with the microcellular injection molding process.
Biobased Polylactide (PLA) Nanocomposites
Three types of polylactide (PLA) composites, namely, PLA/nanoclay, PLA/core-shell rubber, and PLA/nanoclay/ core-shell rubber were melt compounded via a co-rotating twin-screw extruder. The effects of two types of organically modified nanoclay (i.e., Cloisite®30B and 20A), two types of core-shell rubber (i.e., Paraloid EXL2330 and EXL2314), and the combination of nanoclay and rubber on the mechanical properties of the composites were investigated. In comparison with pure PLA, both types of PLA/5wt% nanoclay composites showed an increased modulus, a slightly reduced tensile strength, a similar impact strength, and a significantly reduced strain at break. PLA/EXL2330 composites with a rubber loading level of 10wt% or higher exhibited much higher impact strength but lower modulus and strength when compared to pure PLA. The simultaneous addition of 5wt% nanoclay (Cloisite®30B) and 20wt% EXL2330 resulted in a PLA composite with a 134% increase in impact strength, a 6% increase in strain at break, a similar modulus, and a 28% reduction in tensile strength as compared to pure PLA.
Simulations of Grafting Monomers and Associated Degradation of Polypropylene in a Modular Co-Rotating Twin Screw Extruder
Kinetic models of grafting MAH and MMA on polypropylene(PP) were developed for screw extrusion. However the kinetic models are insufficient to explain the grafting reactions along the length of modular co-rotating twin screw extruders, because rheological properties and the residence time of PP changed by degradation of PP during the grafting reaction. In order to model this for a modular co-rotating twin screw extruder, the kinetic model of grafting reaction and models of degradation of PP are combined with fluid mechanics and heat transfer. Given the geometrical configurations of the screw and the operating conditions and the physical properties of the polypropylene, the simulations predict variation of molecular weight and mean residence time by degradation of PP. The weight percent of grafted MAH or MMA on PP profiles along the screw axis are also calculated in the simulation. These predictions are compared with experimental data for various operating conditions.
Compounding Wood Polymer Composites with In-Line Drying Technology
Composite decking has moved into the mainstream of commercialization. Manufacturers must have a process that can achieve high rates for a reasonable capital investment. The equipment must also be able to process a variety of materials so as to take advantage of formulation changes that increase quality and/or reduce costs.A single step process will be discussed that converts nondried cellulosic fibers and polyolefin resins into finished retail decking. The effect on process conditions, particularly moisture removal, will be presented. Technical as well as commercial issues will be addressed. The focus of the presentation will be the need for an integrated manufacturing system to provide the maximum economic return on investment.
First Principles Cause of Melt Fracture in LLDPE
Ever since the introduction of LLDPE, the industry has had to deal with problems caused by melt fracture in many processing situations, with the worst problems typically occurring in the production of blown film. Over the years, many mechanisms have been proposed in an attempt to explain the cause and therefore possible cures for melt fracture, but none of these mechanisms has been able to adequately explain the observed phenomena or provide sufficient insight to develop a cure for the problem. Based on experimental observations, a new mechanism based on volatile induced flow defects has been proposed that explains many of the observations that could not previously be explained. This mechanism has allowed us to predict new methods for reducing melt fracture, and tests have proven these predictions to be correct. SEM photos of film samples provide additional evidence in support of this proposed mechanism.
Novel Gauging Technology for Contact-Sensitive Blown Films
There are many challenges to on-line thickness measurement for blown films, some of which are:Getting data fast enough to make timely thickness profile corrections. This can be a problem with down stream stationary gauges.Measuring soft, tacky films or high optic films with gauges that ride in contact with the filmMeasuring films containing polyamide (nylon) with an “on-the-bubble” capacitance gauge. The capacitance of nylon changes rapidly in the temperature range of the cooling bubble just above the frost line (60 – 100°C / 140 – 210°F) causing inaccurate thickness readings. This precludes the use of capacitance gauges until the film is cooled below 40°C (100°F). (Fig. 1)To address these issues, a relatively new on-line technology utilizes a non-contact scanning gauge mounted downstream of the primary hauloff to measure the layflat web (double sheet). A novel software algorithm separates the double sheet measurements into full circumference profile scans. The data can then be used to take corrective action on average thickness or thickness profile variation. European patent EP 1 207 368 A2 provides a description of one of several possible methods used to implement this technology.1By measuring the layflat with a scanning gauge head, data collection rate becomes nearly independent of the process oscillation time. This addresses the first challenge. NOTE: the oscillating die or hauloff must be moving for the technology to work. Also, the oscillator must traverse far enough to generate sufficient variation in the data to perform the separation function (this distance varies according to each supplier’s experience).Using a non-contact transmission gauge (e.g. nuclear, X-Ray, IR, or capacitance) handles the second challenge -- problems associated with contacting the film.Measuring nylon films downstream of the hauloff, where the web is cooler, allows the use of a capacitance gauge in addition to nuclear, X-Ray or IR gauges. This addresses the third issue.
Study of Polypropylene Morphology to Obtain Porous Membranes by Stretching
Four different polypropylene resins were extruded using the tubular and the cast film processes. The morphology of the films was observed by SEM and the effect of extrusion processing variables on the morphology was investigated. Melt rheological experiments were carried out to characterize the behavior of the polymers. It was found that the molecular weight distribution and the chain structure as well as the processing conditions had important effects on the morphology. Efforts focused on obtaining a lamellar crystalline morphology by controlling the processing conditions. The possibility of generating a porous membrane from the initial morphology using a stretching technique was evaluated. The initial lamellae arrangement of the precursor film is shown to play a significant role in obtaining a porous structure.
New Approach to Noise Reduction in Plastic Gears
The Gear noise was studied in an individual gear mesh for a two shot molded gear. The two layers comprised of a hard core and softer tooth of the gear. PBT, PA 66 and POM were used as the hard core and TPE for the softer skin. This experiment was limited only to the noise of the gear mesh using a sound meter and not the wear of the gear teeth. The “softer” teeth demonstrated smoother and quieter gear meshes with straight PA 66 and POM parts. It was found that the noise levels reduced as much as 25% when one of the driver/driven gear had softer teeth. The sound of the driving motor was isolated from the test gears using the acoustical fiberglass shield.
Preparation and Characterization of Polyimide Nanocomposites
Electrical conductivity needed to dissipate electrostatic charge (ESC) build-up that occurs on polymeric surfaces in the space environment can be achieved through the use of single-walled carbon nanotubes (SWNTs). This study presents two samples of SWNTs prepared by two different processes and their effect upon macroscopic polyimide properties. The neat SWNTs were characterized by ultraviolet/visible (UV/Vis) and fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), and thermogravimetric analysis (TGA) prior to addition to the polymer through a surface coating process and bulk inclusion. The nanocomposites were evaluated for nanotube dispersion, electrical conductivity, mechanical, and optical properties.
Investigating Flow Behavior of Wood-Plastic Composites
The trend toward increased usage of renewable resources has led to the growing popularity of wood-filled materials. These emerging materials require extensive testing – beginning with formulation and ending with the final manufactured product. In the early stages of development, it is possible to acquire data comparing differences between recipes utilizing a Mixer/Measuring Head. The given blend can be compounded with a customized twin screw extruder and torque rheometer. Finally, a single screw extruder can quantify the rheology of the compound using a capillary die. The objective of this work is to investigate the behavior of a polyolefin based wood-filled compound using a torque rheometer.
"Reach-RS:" A Model Outreach Program
The pilot “REACH-RS” program was implemented in the summer of 2004. The PSU “REACH-RS” program is the culmination and result of the interactions between the director of the PSU/NSFREU/ RET program and high school science teachers, counselors and administrators. This interaction identified the need for an academically-oriented summer program for talented high school juniors and seniors. Selected high school students are invited to participate in a series of seven-day, hands on-oriented workshop with in-lab activities in such subject areas as “SMET of Materials Identification,” “Computerized Materials Selection Techniques,” “Toy Manufacturing Via Rotational Molding,” “Foam Production Technology,” “Ultra-sonic Bonding Techniques,” “Injection Molded Electrically Conductive Plastics In EMI Applications,” etc. Each experiment is designed to inculcate and reinforce in the student the practical applications of scientific, mathematical, engineering and technological concepts. Program sponsorship was accomplished via funding provided by 3M Foundation. Program outcome include but not limited to: preview and introduction to college life, improvement of communication and inter-personal skills, acquisition of technical proficiency in the areas of materials, nanomaterials and processing for the participants, and the development of academia-industry partnerships.
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