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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Molecular Orientation of Crosslinked Polyethylene
To achieve improved mechanical properties, crosslinked polyethylene was uniaxially stretched above the crystalline melting point, (Tm). The material was stretched at different draw temperatures, draw speeds and to different draw ratios (?). The effect of different gel contents was also examined. For the molecular oriented samples tensile strength was shown to increase with increasing gel content. Tensile stress at yield (?y) was found to decrease at ?<1.5 and to increase for ?>1.5 while tensile stress at break (?B) was found to increase linearly with increasing ?. A lower draw temperature was shown to have an increasing effect on the tensile strength.
Melt-Flow Instabilities in Metallocene Based Polyethylenes
In capillary flow surface distortion of the extrudates, know as shark-skin" has been intensively investigated for decades especially in conventional polyethylene. Few papers however have been published using metallocene catalyzed polyethylenes although this instability represents currently one of the most serious limitation for the commercial application of these new polymers. In this contribution we present dynamic viscoelastic and extrusion capillary results of a series of polyethylenes and copolymers with 1-hexene (SCB) produced by single-site catalysts. Several of the samples analyzed content also small amounts of long chain branching (LCB). We investigate the effect of the molecular weight and the molecular architecture on the appearance of shark-skin and novel methods are discussed to overcome this limitation. A new type of distortion which we call "splitting" is described."
Properties of Polylactic Acid Optical Copolymers Achieved through Stress Induced Crystallization
The use of polylactic acid for common thermoplastic applications has grown substantially in recent years. The stereo structure of polylactic acid can be varied by polymerizing controlled ratios of the D- and L- isomers of lactic acid. Cargill Dow Polymers, LLC has developed a unique manufacturing process for polylactic acid, whereby lactide, one of the intermediates of the process, can be separated by optical composition, and then polymerized with controlled stereo composition. In turn the level of crystallinity can be varied from highly crystalline to amorphous, resulting in a wide range of properties that can be optimized for many applications. Fabrication processes using stress-induced crystallization take full advantage of the semi-crystalline nature of polylactic acid. The strain hardening and shrinkage properties of various optical copolymers of polylactic acid made by stress induced crystallization have been studied.
Innovative Compounding with the RingExtruder
Current development of Twin Screw Extruders ends at the absolute physical limits of mechanical strength and process technology. Rather than pursue conventional attempts to increase speed and torque, the RingExtruder increases the number of screws. It utilizes twelve co-rotating, closely intermeshing screws, arranged in a stationary ring. This unique design creates new possibilities, especially for products requiring degassing, dispersion, and low degradation. This technology has been successfully demonstrated. The unique action of the geometrically arranged screws provides high product quality with very low degradation of the polymer as indicated in trials with polypropylene (1). The increased surface area of multiple screws, combined with a divided process section, permits exceptional degassing of polystyrene (2).
Benefits of Coextruded LLDPE/LDPE Film versus Blended LLDPE/LDPE Film
The benefits of three-layer coextrusion versus a mono-layer blend of the same resins are explored. Good design considerations of the coextruded structure can allow a processor to take advantage of the performance characteristics of the resins and the equipment. These performance characteristics can be compromised in a mono-layer blend of the same materials. Expected benefits of coextrusion can be improved physical properties and reduction in additives required for good processing. These are accomplished by eliminating blends of LDPE and LLDPE, reducing the draw-down ratio and taking advantage of the rheological differences between LDPE and LLDPE.
Blown Film Bubble Instability Induced by Fabrication Conditions
Bubble instabilities in the blown film process can take several forms. Each type of instability places limits on the maximum production rate. This paper considers process variables such as melt temperature, frost line height (FLH), blow-up-ratio (BUR), and film thickness to determine the influence of bubble stability on maximum output rate. A linear low density polyethylene (LLDPE) polymer produced three types of blown film bubble instability: 1. Periodic variations in the bubble layflat 2. Oscillation of the FLH 3. Molten bubble surface contacting the air ring Methods to monitor the on-set of bubble instability included film thickness variation, internal bubble pressure variation, bubble temperature profile, and bubble edge weave to determine the maximum output rate.
Permeation Processes in Barriers and Membranes: Complementary Differences
Permeation through polymer matrices and structures constructed from polymers determines the efficacy of both barrier packaging and membrane separation devices. Of course, membranes and barrier packaging materials typically are at opposite ends of the transport spectrum. The packaging engineer generally seeks to suppress permeation, while the membrane engineer seeks to promote it selectively. Nevertheless, barriers involving modified atmosphere packaging" are effectively permselective membranes so distinctions between barriers and membranes become blurred. In this presentation emphasis will be placed on a physical understanding of the issues that impact diffusion processes in and through glassy and rubbery polymers. The capabilities and limitations of molecular structure tailoring to achieve desired properties as compared to combination of multiple material types into higher order structures will be considered."
The Influence of Polymer Processing Additives (PPAS) on the Surface and Optical Properties of Polyolefin Plastomer Blown Film
Polyolefin Plastomer films formulated with slip and antiblock were blown on a wide die gap with and without two Dynamar™ polymer processing additives (PPAs). A wide die gap was used so that melt fracture-free film could be obtained with no PPA present for comparison purposes. The films were analyzed for the following properties: surface tension (on treated films), gloss, haze, clarity, transmittance, hot tack, heat seal, COF and block. In addition, the surface of films was examined using ESCA (Electron Spectroscopy for Chemical Analysis) and SSIMS (Static Secondary Ion Mass Spectrometry) to determine the surface chemical composition.
Experimental Determination of Optimized Vibration-Assisted Injection Molding Processing Parameters for Atactic Polystyrene
The current experimental study focused on determining optimal vibration assisted molding conditions for Polystyrene thermoplastic material. Although previous attempts at understanding the connection between applied oscillatory or vibrational motion to an injection molding process and it's affect on final product morphology has shown positive quantitative advantages to final product properties, there still exists a void in the scientific explanation on a molecular level linking these effects. Therefore, in an attempt to contribute to the development of this novel injection molding process, optimal control and mechanical vibrational molding conditions were obtained experimentally for Polystyrene.
Alignment of People to Business Goals in the INSITE Technology Development Process
Over the past several years, Dow's Polyolefin R&D department has used a philosophy called Speed Based R&D to launch several products such as ELITE™ enhanced polyethylene resins, AFFINITY™ polyolefin plastomers, ENGAGE* polyolefin elastomers, NORDEL IP* elastomers, and recently INDEX™ interpolymers in best-in-class development time. One of the important aspects of this development philosophy is the close alignment of people's goals and development to business strategy and research goals. Unlike many other aspects of Speed" this alignment is very regimented monitored and enforced. It involves employees supervisors and management links pay to performance of goals helps set development objectives and links people's goals to visible department goals."
A Knowledge-Based Tuning Method
Complexity of manufacturing processes has hindered methodical specification of machine setpoints for improving productivity. Traditionally in injection molding, the machine setpoints are assigned either by trial and error. based on heuristic knowledge of an experienced operator, or according to an empirical model between the inputs and part quality attributes obtained from statistical design experiments (DOE). In this paper, a Knowledge-Based Tuning (KBT) Method is presented which takes advantage of the 'a priori' knowledge of the process in the form of a qualitative model to reduce the demand for experimentation. The KBT Method is designed to also provide an estimate of the process feasible region (process window) as the basis of finding the optimal setpoints. Since tuning will result in new input-output data that can be used for training, the qualitative model is refined on-line to better represent the data obtained from tuning.
Prototype vs. Production Tooling in Rapid Product Development
In the course of mechanical product development, the main purpose of prototyping is to verify the integrity of the proposed design. The design engineer wants to validate the entire design and its performance prior to committing resources to production tools. In order to provide useful and meaningful results, a prototype unit needs to simulate a production unit so that the test results are valid. If a design fails during the prototype stage, the design engineer is left to determine if the failure was due to a faulty design or a prototype part" shortcoming. In the case of plastic parts the most important mechanical properties are dimensional accuracy and material performance."
Pressurization and Energy Characteristics of ZSK40 Twin Screw Elements: The Power of Spreadsheet and Good Experiments vs. CFD?
A complete study of pressurization and energy characteristics of various elements of ZSK40 with two grades of PS are presented. This work builds upon previous works [1,2,3] and identifies the differences between screw and kneading blocks and shows by appropriate factors, most of these differences can be displayed by dimensionless curves. The work compares the experimental results with CFD results developed independently by BASF and Krupp Werner & Pfleiderer researchers. In this work, we try to show that the myth created around kneading blocks (wide disc or narrow discs) and their efficient use can be answered by understanding the conveying nature of these elements.
Training Program for Troubleshooting Injection Molded Defects
The objective of this project was to develop a systematic program for teaching plastics technicians and engineers how to enhance their troubleshooting skills for solving injection molded part problems and defects. A prioritized troubleshooting procedure was first developed for 12 of the most common molding defects and their major manifestations. For each defect classification, real life molding scenarios were developed for use as the core of the hands-on practitioner training. Each of the defects had to be generated through a series of molding trials to find a combination of mold, material, and processing conditions that would create a distinct defect and appropriate case study problem for use in the training program. Below are four common defects that yielded positive case studies.
Structural Mechanics of Polymer Coated Optical Glass Fibers: Review
The paper contains a brief review of the state-of-the-art in the stress-strain analysis (Structural Mechanics) of polymer coated optical glass fibers, with an emphasis on the analytical modeling.
Kinetics of Isothermal Crystallization of Syndiotactic Polypropylene: Avrami and Urbanovici-Segal Analyses
In this paper, the Avrami and Urbanovici-Segal macrokinetic models were applied to describe the kinetics of isothermal crystallization from the melt state of syndiotactic polypropylene (sPP). Data analysis was carried out using a direct data-fitting procedure, in which the experimental data were directly fitted to each macrokinetic model using a non-linear multi-variable regression program. The results suggested that the Urbanovici-Segal model was the better of the two in describing the isothermal crystallization data of sPP.
Production of Structures from Thermoplastic Composite Towpregs
An efficient and cost effective way of producing continuous fibre-thermoplastic matrix composites relies on the use of towpregs. Equipments are being developed for the production of the towpregs and also to manufacture pultruded profiles and filament winding structures. The properties of the composite products are determined and compared with conventional alternatives. An assessment is made on the influence of the processing conditions on the output and mechanical properties of glass fibre/polypropylene (GF/PP) composites.
Friction Properties of Thermoplastics in Injection Molding
In the ejection stage of parts injection molded over cores the knowledge of the friction properties between the mould surface and the part are important to optimize the ejection system solution. The coefficient of friction depends strongly on the mould surface and the temperature at the moment of ejection. Prototype equipment was developed to measure the friction properties in as-molding conditions, and methods developed to perform the testing. Data will be presented for two thermoplastics (polycarbonate and polypropylene).
Prediction of Ejection Forces in Tubular Moldings in Amorphous Polymers
The prediction of ejection forces in tubular moldings (pipe fittings, cups, ..) is relevant for the optimization of the ejection systems in molds. An instrumented mold (pressure, temperature and force) for a tubular part was developed for measuring the actual ejection forces for two amorphous materials, polystyrene and polycarbonate. The ejection forces depend mostly on the holding pressure and the mould core temperature. The experimental data is used to validate a thermo-mechanical model that predicts the shrinkage and internal stresses.
Niche Marketing: High Temperature Nylons
As nylons 66 and 6 continue to grow in volume, they are beginning to take on the attributes of commodities, e.g., product interchangeability and price sensitivity. Producers are finding that high temperature nylons aimed at niche markets are sufficiently differentiated that they resist the trend toward commoditization while offering interesting volume potential in applications where value means more than price. This is an area where monomers make the difference and integrated producers have the field to themselves.
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