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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Verification of Parison Shape and Diameter with Extrusion and Blow Molding Simulation Software
The objective of this study is to use results from the analysis package, an extrusion simulation software program, to determine extrusion blow molding parison shape and thickness. This comparison will be used to develop a correlation between the software and actual trials while determining the software's ability to accurately predict parison geometry. This study is being done because this information is not easily determined and is needed for accurate blow molding simulation. In this study a parison will be modeled and trials will be run using different factors. The factors used will be varying wall thickness, speed, and temperature. Actual machine trials will then be conducted using the same factors. Measurements will be taken using a laser-mic so that a comparison can be made between the software and actual results. A correlation will then be developed from the comparison data. CAE has greatly decreased time to market in the injection molding field, now this same advantage can be found in the extrusion blow molding field.
The Effects of Ultrahigh Shear Rate and Shear Duration on Mechanical Properties of Commercial Polymers
Material manufacturers are forced to theorize the maximum shear rate limit that a polymeric material can withstand. The true shear rate limit of a material is rarely known. For the study effects of high shear rates and increased time of shearing on mechanical properties have been analyzed by creating a high shear region within an injection mold. Ultrahigh shear rates were created by reducing runner thickness. The effects of shear duration were analyzed by changing the length of the high shear region in the mold. The research looks at both glass-filled and unfilled polypropylene, nylon, and polycarbonate resins.
Raising the HDT and Elevated Temperature Tensile Properties of Injection Moldable HDPE by Dry Blending with Small Amounts of Dicumyl Peroxide
Polyethylene can be modified to improve the elevated temperature properties of the polymer by three dimensional cross-linking. One method of cross-linking is by using organic peroxides. The goal of this experimental study is to raise the Heat Deflection Temperature and elevated temperature tensile properties of high density polyethylene by dry blending with small amounts of dicumyl peroxide and injection molding the resulting composite using typical process conditions for polyethylene. The peroxide will be blended with polyethylene, at different weight ratios, and injection molded into various test specimens. Mathematical models will be developed from the results of the experiment to predict the change in heat deflection temperature that occurs from the cross-linking.
The Effects of Long Term Ultraviolet Radiation on the Mechanical Properties of Wood Flour Filled Recycled HDPE
Many outdoor products made from conventional lumber can be produced using wood flour filled polyethylene as a replacement material. In these applications the effect of ultraviolet radiation from the sun on the mechanical properties of these materials is important to understand prior to the design of any outdoor product. This study will examine the impact of long term ultraviolet exposure on the mechanical properties of wood flour filled high density polyethylene. An accelerated QUV testing apparatus will be used to simulate long term exposure to the sun. Impact strength, toughness, flexural modulus, and tensile strength will all be evaluated.
Linear Shrinkage Differences in Plastic Injection Molded Parts
Shrinkage occurs in all plastic injection molded parts. This study focuses on the shrinkage differences between amorphous and semi-crystalline plastics as well the shrinkage effects of process, wall thickness, and flow direction. A specially designed modular mold was used. The mold includes a 50.8 mm by 203.2 mm cavity with adjustable wall thickness and gating. Various neat and filled materials were processed using high and low pack pressures. The plaque samples were molded at thicknesses of 2 mm and 3 mm. Conclusions were made based on the differences in material, thickness, processing parameters, and flow direction. This information will help mold designers and moldfilling analysts develop better strategies in sizing their cavities for shrinkage and positioning their gates.
Development of a Rotational Molding Machine with Integral Heating and Cooling Passages within the Mold
Rotomolding is a process that is traditionally used to make larger complex shaped parts. A mold, traditionally, attached to a spider and arm, is moved through three or four different zones for loading, heating, cooling, and unloading. The mold(s) are rotated around two axes to allow the material to strike all internal surfaces of the mold. The heating occurs in large ovens where the mold is heated by radiation and convection until the plastic melts and coats the inside walls of the rotating mold. This paper will present ongoing construction and theory behind development of a rotomolder with integral heating and cooling passages within the mold. FIGURE 1 shows the entire machine with the mold mounted.
Breaking Barriers to Higher Output Rates with Densified Ultrafine Talc during Melt Compounding on the Corotating Intermeshing Twin Screw Extruder
The melt compounding of densified and nondensified ultrafine talc into polypropylene was performed on a 40 mm corotating twin screw extruder for comparison of compounding characteristics and product performance properties. Compounding nondensified talc was found to be volume limited by the maximum quantity of talc that the machine could be fed whereas the densified talc compounding was torque limited. The plastic performance properties for both types of talc filled compounds were comparable and would be widely acceptable for these high performance grades of talc filled polypropylene. Predictions of throughput rates on larger machines with higher toque ratings are included.
Requirements for Rapid Growth of All Olefinic Automotive Interiors
TPO has seen a major growth in the exterior applications such as fascias, claddings etc. for the last decade. For automotive interiors the growth has been slow and more in the area of hard feel applications than soft touch applications. Soft interiors are still a challenge due to many reasons including overall system cost. The driving force for TPO in Europe is mainly recyclability while in the USA, it is long-term durability. This paper describes the key limitations of the current TPO systems which are: poor grain retention of TPO skin, shrinkage in-consistency of the skin, high cost of priming (or other treatments) and painting of the skin, lower process window of the semi-crystalline TPO material during thermoforming or In-mold lamination / Low pressure molding, high cost of the foam, low tear strength of the foam for deep draw ratio etc. The paper shows the different ways of manufacturing the all olefinic parts which are: thermoforming over PP substrate, different Low pressure molding with in-mold lamination techniques, expanded PP foam process, slush molding etc. The limitations for each process and suggestions to overcome the disadvantages will be discussed to make all olefinic TPO interior parts viable and cost effective. The possibility of reducing the overall system cost will also be discussed such as: general information on formulation development to reduce the skin thickness for thermoforming, how to improve the properties of foam to reduce the thickness without affecting the formability and resiliency, value added recyclability of the skin/foam offal from production, and improving the paint efficiency etc.
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."
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