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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Mathematical Modeling of Three-Dimensional Die Flows of Viscoplastic Fluids with Wall Slip
The mathematical modeling of the continuous processing of filled polymers, and concentrated suspensions in screw extruders and dies of complex shapes is undertaken. The simulation of the flow of such filled systems in complex geometries is rendered complicated by the occurrence of wall slip at fluid/solid boundaries. The incorporation of wall slip in the analysis of three-dimensional flows including flows through dies, single/twin-screw extruders and other processing geometries is currently lacking. Here we present an analysis of three-dimensional flows with wall slip, and demonstrate the procedure using the flow of a Herschel-Bulkley fluid in a tapered die.
Squeeze Flow Rheometer
The squeeze flow rheometer is widely used especially for the rheological characterization of composites and polymer melts. However, since it incorporates both shear and extensional deformations its use is not straightforward. Here the two-dimensional constant-speed squeezing flow of viscoplastic fluids between two approaching surfaces in relative motion is solved using the Finite Element Method. Slip at the wall, a condition generally encountered with viscplastic fluids at solid surfaces, is incorporated in the model. The analysis is applicable to the rheological characterization and testing of parameters of constitutive equations for filled polymers and elatomers that exhibit a yield stress and will expand our understanding of the squeeze flow rheometer. The numerical analysis was focused on the determination of conditions under which 1-D analysis is valid.
Particulate Based Conductive Composites Exploiting Percolation-Range Microstructure
The electrical and tensile properties of graphite based conductive composites were investigated as a function of mixing conditions and the specific energy input incorporated during the mixing process. The microstructural features were characterized employing wide-angle x-ray diffraction. A tri-block copolymer with polystyrene end blocks and poly(ethylene-butylene) mid block was used as the primary matrix material. Graphite powders with controlled particle size distributions were used as conductive fillers. Systematic studies were carried-out varying the volume percent and mixing distribution characteristics of the filler particles. The volume resistivity of the composites exhibited a significant increase with the increased specific energy input. The increase was associated with the enhanced coating of the conductive particles and the better distribution of the matrix polymer as the specific energy input increased.
Viscoelasticity of Polyethylenes Produced with Single Site Metallocene Catalysis
Linear low density polyethylene (LLDPE) produced using metallocene catalysts is gaining prominence as a class of new polyethylenes with superior performance. Two recently commercialized metallocene-catalyzed linear low density polyethylene resins were characterized in terms of their storage and loss moduli, shear viscosity, shear stress growth, stress relaxation upon cessation of steady shear, and first normal stress difference material functions. Overall the rheological behavior reflects the relatively narrow molecular weight distributions of the resins. The oscillatory shear and relaxation moduli data were employed to determine the parameters of Wagner model. Various material functions, determined on the basis of this model in conjunction with the fitted parameters, agreed reasonably well with the experimental results. The reported data and parameters should facilitate an improved understanding of the processability characteristics of these two new LLDPEs.
3-D Analysis of Fully Flighted Screws of Co-Rotating Twin Screw Extruder
A new mathematical model of the flow and heat transfer occurring in the fully-flighted regular flighted" screw elements of the co-rotating twin screw extruder is developed. The method avoids the unwrapping of the screws and solves the conservation equations using a realistic replication of the actual channel geometry. The numerical solution of the conservation equations is accomplished using the three dimensional Finite Element Method. The technique allows a wide range of processing features including the effects of the gap thickness between the barrel and the screws to be investigated. Here typical isothermal results are presented for two generalized Newtonian fluids i.e. Bingham and Ostwald-de Waele "Power-Law" fluids."
Assessment of Particle Migration Effects in Capillary Rheometry of Filled Polymers
It is important to assess the conditions under which the migration of particles becomes important during rheological characterization of filled polymers. Such migrations may become important during nonhomogeneous flow where gradients in shear rate induce particles to move away from high shear rate regions resulting in nonhomogeneous concentration distributions and the blunting of velocity distributions. Using the mathematical model of Phillips et al., a finite difference numerical solution was developed to assess the importance of particle migration effects in pressure-driven viscometric flows.
Statistics of Mixing Distributions in Filled Elastomers Processed by Twin Screw Extrusion
Continuous processing of filled elastomers by twin screw extrusion and achievement of viable mixing distribution characteristics present formidable challenges. In this work a thermoplastic elastomer, HyTemp, was plasticized with DOA and filled with ammonium perchlorate powder and additives. It was found that the extruder geometry, the order of ingredient addition and die pressurization have profound effects on the mixing distribution characteristics of the elastomer based extruded profiles. The mixing distribution characteristics were quantitatively determined by x-ray diffraction techniques.
Elastomeric Coating of Filler Powders by Slurry Precipitation
The work presented here involves the coating of inert particles by an elastomer. The plasticized elastomer is first dissolved in an organic solvent and is mixed with water in which the inert particles are slurried. Due to the miscibility of the organic solvent and water, the elastomer gels and coats the inert particles. The coated particles further coalesce to form the molding powder of desired size range. This paper addresses the dynamics of the coating operation and the role of process parameters on the extent of coating and particle size distribution.
Hot Water Resistance of Glass Fiber-Reinforced Thermoplastics
The hot water resistances of three kinds of short glass fiber or glass bead-reinforced plastics [polyphenyleneether (PPE), polyphenylenesulfide (PPS), and polyoxymethylene (POM)] were studied by hot water immersion tests and tensile tests. It was found that the tensile strengths of these plastics decreased and that the change of the strength was most remarkable in glass fiber-reinforced PPS (GF-PPS). Scanning electron microscope (SEM) observations of the tensile fracture surface revealed that the change in tensile strength was attributable to the deterioration of the interface between the glass fiber and the matrix resin. Although the change in the tensile strength of glass fiber-reinforced PPE (GF-PPE) was small compared with that of GF-PPS, debonding between the glass fiber and the matrix resin and surface cracks were observed on the surface of the GF-PPE specimens.
Environmental Stress Cracking (ECS) of Abs (II)
Environmental stress cracking (ESC) of acrylonitrile-butadiene- styrene (ABS) co-polymer caused by two kinds of non-ionic surfactants was studied by edge crack tension (ECT) tests. The dependence of the ESC on temperature and on the kind of surfactant was investigated. The fracture surfaces were investigated by a scanning electron microscope (SEM). It was found that the rise of temperature had a different effect on each surfactant. The crack propagation behavior of each surfactant at different temperatures was understood from the change of morphology at the crack tip.
A Criterion for the Onset of Gross Melt Fracture of Polyolefins: Molecular Structure Effect
In this work, a critical extensional stress is proposed as the criterion for the onset of gross melt fracture. This stress is estimated by means of the entrance pressure drop analyses developed by Cogswell and by Binding. This criterion for the onset of gross melt fracture was evaluated for several constrained geometry catalyzed (CGC) and metallocene, linear low, and high density polyethylenes. The presence of a low level of long chain branching in CGC polyethylene enhances the critical extensional stress, as compared to purely linear polyethylene. High density polyethylene blends having large low molecular weight fractions exhibit higher critical extensional stress than blends with lower amounts of low molecular weight material. Finally, a polymer having a broad molecular weight distribution shows a higher critical extensional stress than a narrow molecular weight polymer. The critical extensional stress for the onset of gross melt fracture is independent of temperature.
Eliminating PVC Degradation during Injection Molding Using Computational Techniques
New vinyl compounds with lower viscosity and increased thermal stability have been developed for injection molding. Furthermore, more advanced and robust computational techniques allow for proper design of molds and determination of process conditions. Yet, even with all the recent advancements, there still exists a need for either expertise or a trial-and-error" approach to optimize injection molding of vinyl compounds. This is due to the limited amount of detail that can be included when designing complex parts in order to reduce computational time. Research was performed in order to gain better understanding of important parameters for injection molding of vinyl compounds. The goal of the research was to increase the level of detail in the thickness direction and include a model of the degradation kinetics by reducing the complexity of the geometry being studied. The parallel plate flow geometry was evaluated in this study using a finite difference scheme to provide detailed information about viscous heating during injection. A "stop-and-go" technique was used to simulate the filling process; the degree of degradation was evaluated by implementing a computational tracer method. The simulation results were compared to experiments performed using a spiral mold."
The Influence of Polymer Rheology on Bubble Penetration in Gas-Assisted Injection Molding
The influence of polymer rheology on the wall thickness and flow dynamics during the filling stage of gas-assisted injection molding is examined. Isothermal experiments are conducted with tailored ideal elastic fluids to isolate the influence of polymer elasticity on the hydrodynamic coating thickness formed during the bubble penetration process. The results indicate that the wall thickness increases with increasing elasticity and extensional viscosity. The results for several tube diameters are scaled onto a single master curve using the Deborah number (De). Flow visualization and particle tracking experiments are conducted to investigate the flow field in the vicinity of the bubble front. It is concluded that the extensional rheology plays an important role in determining the wall thickness in gas-assisted injection molding.
Evolution of Structural Hierarchy in Uniaxially Deformed Poly Lactic Acid Films as Followed by Spectral Birefringence Technique and Others
Polylactic acid, PLA, is a relatively new biodegradable polymer primarily used for biomedical as well as mass-market packaging applications. PLLA is a polyester comprising repeating units of the lactide residue with an asymmetric carbon atom. Because of its biodegradability to nontoxic products and good plastic properties of that polymer makes it suitable for use in film studies. De Santis and Kovacs showed that the unit cell of PLLA is pseudo-orthorhombic with dimensions of a=10.7 Å, b=6.45 Å, c= 27.8 Å and ?=?=?=90°, where the molecules assume a 10/3 helical conformation. (1).Eling et al reported the existence of another modification, which they called ?-crystal modification (2) Hoogsteen et al. studied the influence of the preparation conditions on the presence of the crystal modification (3). Fischer et al investigated solution grown crystals of lactide polymers (4). Also Kalb and Pennings estimated the crystallization of PLLA from bulk state and solution (5). Tadakazu and Masuko investigated the relationship between the fine structure of PLLA and its physical properties (6). The need for polymeric biodegradable films is well established. The use of films occurs in the packaging and disposable article industries. In light of depleting landfill space and adequate disposal sites, there is a need for biodegradable films. Currently films from nylon, polypropylene, polyethylene, polystyrene, PVC, are noncompostable, which is undesirable from an enviromental point of view (7). In this paper, we present our results on the development of structure in uniaxial and biaxial stretching of PLA and subsequent heat setting process as followed by the new spectral birefringence technique we adapted for rapid acquisition of birefringence during the course of heat setting.
Autonomous Arrangement of Cooling Channels Layout in Injection Molding
This paper deals with a methodology for designing an effective layout of cooling channels to make a desired temperature distribution on cavity surface in injection molding. A cooling channel is modeled as several Cooling Elements that remove heat from a cavity surface. These elements move in the mold according to the information that is ordained by Source Elements located on a cavity surface to estimate temperature distribution on cavity surface. A layout of cooling channels is autonomously decided through an interplay between Cooling Elements and Source Elements. Several numerical experiments assuming heat-transfer to be steady-heat conduction have been a good indication that this method can design an effective layout of cooling channels and can estimate the necessary number of cooling channels.
The Influence of Polypropylene Content on the Properties of Post Consumer Recycled High Density Polyethylene
Polypropylene (PP) from bottle caps is present in High Density Polyethylene (HDPE) in post consumer recycled resin, and it acts to reduce the overall toughness. This study is concerned with quantifying the influence of PP on the physical properties of recycled HDPE resins and evaluating toughening recycled HDPE/PP blends by the addition of metallocene catalysed linear low density polyethylene (m-LLDPE). The toughness of HDPE was found to decrease significantly with as little as 5 wt% PP, and at 20 wt% the toughness was reduced to levels comparable to that of PP alone. The addition of m-LLDPE was effective in increasing the toughness of the blends to values comparable or greater than those of recycled HDPE alone. The principal mechanism seems to arise from the suppression of crystallinity of HDPE matrix for levels of up to 20% m-LLDPE, and the introduction of amorphous phase content within the samples.
Prediction of Plasticizer Solvency Using Hansen Solubility Parameters
The solvating strength of a plasticizer for poly (vinyl chloride) resin is a measure of the interactive forces between these two materials. Hansen’s three dimensional solubility parameters provide a quantitative measure of these interactive forces. Using COACTSM service, a computer program designed for solvent systems with various resins, plasticizers were found to lie near the edge of the solvency “sphere” of PVC. The relative positions of various plasticizer structures are in the expected order, while known solvents show strong association and lubricating additives fall outside the solvency sphere of PVC.
Plasticizer Factors Influencing Take-Up by PVC Resins
The ease with which plasticizer is combined with poly (vinyl chloride) resin is a measure of processing characteristics critical in the dryblending of suspension PVC, and the gelation of plastisols. Using commercial grade plasticizers, this study developed predictive equations for the following processing parameters of dialkyl phthalates in PVC: • Relative dryblend rates in suspension PVC as a function of plasticizer viscosity. • Relative initial gelation temperatures in plastisols as a function of plasticizer molecular weight and solvating strength. • Relative final gelation temperatures in plastisols as a function of plasticizer solvating strength. This information allows one to predict the relative processing characteristics of any dialkyl phthalate plasticizer for PVC on the basis of its chemical and physical properties.
Hot Plate Welding of Blow Molded Parts: Influence of the Blow Molding Process on Weld Strength
The manufacturing process of complex blow molded parts does not only consist of the extrusion blow molding process but is finished of by hot plate welding. Especially with plastic fuel tanks more and more parts such as nipples, holders for hoses or clips, etc. are being welded on. The strength of the weld seam does not only depend on the welding parameters but also on the quality of blow molding such as wall thickness, wall thickness distribution or warpage. These characteristics result in different deformation during the heating and the joining phase. The correlation between the blow molding process, the quality of the blow molded part and the weld strength is shown.
Processing and Mechanical Properties of Co-Continuous Polymer Blends
Blending poly(ether-ester) and SEBS thermoplastic elastomers (TPEs) with ordinary pseudoplastics, at temperatures where the TPEs are microphase separated, results in stable co-continuous morphologies over a wide composition range. Processing the same blends at temperatures where the TPEs have a single phase melt, showing normal pseudoplastic behaviour, results in a much smaller range of co-continuity. Therefore, dispersed as well as co-continuous morphologies can be obtained at given compositions. The mechanical properties of dispersed blends are compared to those of co-continuous blends and it is shown that the elastic moduli of co-continuous blends are significantly higher than the moduli of the dispersed blends. No significant difference in tensile strength or impact strength was found.
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