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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Design of Extrusion Screws Using an Optimisation Approach
The design of a screw for polymer extrusion based on scientific principles is still a challenging task, which has received relative little attention in the literature. Prior to the definition of the geometric parameters of the screw, the designer has to decide about general features, such as the type and location of mixing zones, which is mainly based on empirical knowledge. Once the main process criteria are identified (e.g., pressure generation capability, mixing efficiency, power consumption), the design is then carried out on a trial-and-error basis. In the present work we consider screw design as an optimisation problem where the aim is to maximise the value of an objective function that describes quantitatively the process performance. A design methodology incorporating this approach is presented. The relevance of the solutions and the sensitivity of the method to changes in the criteria considered are demonstrated with various examples.
Polyethylene Die Deposit-Measurement, Formation Mechanism and Routes to Reduction
Die deposit (sometimes known as die drool, die lip build-up, etc) occurs in melt extrusion of polyolefins. It is an undesirable build-up of material, normally on the lip or open faces of extrusion dies. In commercial scale polyethylene extrusion processes (e.g. blown or cast film, fibre spinning, etc), die deposit can have a significant influence on productivity, through the need to shut down processing line periodically to clean the die, and on the end-product quality. There are a wide range of factors or sources that lead to the formation of die deposit as its mechanism is not understood, these include low molecular weight species and volatiles, die swell, die design and polymer structure. This paper investigates, through laboratory-scale extrusion and rheology evaluations, some of the key relationships in the die deposit formation process. A deposition mechanism is thus proposed from these studies, with some suggestions for its reduction.
Microporous Polyolefin Film for Battery Separator
An experimental study was performed on how microporous polyolefin film was made and how it could be used as battery separator. Effect of various processing variables on the microporous film properties was investigated. To get better microporous film various conditions were to be optimized. Microporous film having smaller pore size, higher porosity and shut down capability was obtained.
Thermal Effusivity as a Void or Delamination Measurement
Thermal effusivity has been measured on materials that include carbon-carbon aerospace composites, air ship fabric and thin rubber materials. The effusivity, which multiplies thermal conductivity, density and heat capacity, was found to be sensitive to the presence of voids or delamination in the products. The presence of air in the delamination lowers the effusivity as the air has lower thermal conductivity, density and heat capacity when compared to the sample. This triple sensitivity has applications for on-line QC detection during production.
Polymer Kit Project for Grades K-12
A 5-year Polymer Kit Project (PKP) to bring the story of polymers into the precollege curricula is nearing conclusion. The goals, concepts, guidelines, and problems have been reported previously [1-3] and are briefly reviewed here. The progression in the treatment of five basic concepts as the lesson plans proceed from grade K to 9 is described in this paper.
New Advances in Torque Rheometry
The torque rheometer has been an essential instrument for a wide spectrum of research and development and quality control testing laboratories throughout the years. The torque rheometer has evolved just as quickly as advances in material chemistry. Highly sophisticated software and hardware technologies have now been introduced to better serve the needs of a modern laboratory. New challenges in such areas as plastics recycling and environmentally friendly fillers for plastics are some of the needs being met by using this multifunctional instrument. This paper intends to discuss how these changes have made the instrument more relevant than ever.
Studies on the Foamability of Rigid PVC/Wood-Flour Composites
Solid state microcellular foaming technology was employed to investigate the influence of impact modification on the foamability of neat rigid PVC and rigid PVC/wood-flour composite samples. The effects of impact modifier types (crosslinked versus uncrosslinked) and concentrations on the void fraction of foamed samples were examined. The influence of impact modification on the sorption behavior of CO2 in the samples was also studied. The experimental results indicate that impact modification accelerates the rate of gas loss during foaming process, which impedes the growth of nucleated cells, independent of modifier type. Due to this accelerated gas loss, impact modification inhibits the potential of producing foamed samples with void fractions similar to those achieved in unmodified samples. Consequently, impact modifiers are an unnecessary ingredient in the formulation of foamed neat rigid PVC and rigid PVC/wood-flour composites.
Foaming of Rigid PVC/Wood-Flour Composites through a Continuous Extrusion Process
The effects of chemical foaming agent types (endothermic versus exothermic) and concentrations, as well as the influence of all-acrylic processing aid on the density and cell morphology of extrusion-foamed neat rigid PVC and rigid PVC/wood-flour composites were studied. Regardless of the CFA type, the density reduction of foamed rigid PVC/wood-flour composites was not influenced by the CFA content. The cell size, however, was affected by the CFA type, independent of CFA content. Exothermic foaming agent produced foamed samples with smaller average cell sizes compared to endothermic counterparts. The experimental results indicate that the addition of an all-acrylic processing aid in the formulation of rigid PVC/wood-flour composite foams provides not only the ability to achieve density comparable to that achieved in the neat rigid PVC foams, but also the potential of producing rigid PVC/wood-flour composite foams without using any chemical foaming agents.
Hybrid Thermoplastic-Thermoset Molding
A new molding technology is described which makes use of blends of thermoplastic polymers and reactive monomers (thermosetting polymer). In this way the viscosity is reduced and a low pressure processing is achieved. Due to polymerisation of the monomer during molding phase separation occurs with the thermoplastic polymer as the continuous phase in order to retain the desired properties of the thermoplastic. The behavior of such hybrid blend systems needs to be understood before an industrial process can be established. Here the reaction and diffusion kinetics of blends of epoxy and amine in PMMA are investigated. It is found that the reaction is slowed down initially by the presence of PMMA. In the second stage, after phase separation, the reaction rate increases in the polymer-poor dispersed phase. Since in the molding process the reaction is started by mixing the blends of polymers containing the respective monomers, diffusion has to establish a stoichiometric balance in the matrix after a certain extent of distributive mixing. By FT-IR microscopy in layered systems the diffusion coefficients are determined in the absence of reaction and concentration distributions are determined in the case of reaction. It is concluded from the model systems that in layers of 100 µm thickness stoichiometric balance is not achieved due to limited rate of diffusion.
Mass Transfer between a Slender Bubble and a Variable Diffusion Coefficient Liquid in an Extensional Flow
Mass Transfer between a slender bubble and a Newtonian liquid in a simple extensional and creeping flow has been theoretically studied. The liquid is a solvent-polymer solution, having a variable diffusion coefficient, which depends exponentially on the solvent concentration. Assuming a thin concentration boundary layer thickness and applying the method presented by Levich for a constant diffusion coefficient, the differential binary mass balance was transformed into an ordinary differential equation, which was numerically solved. The final result was also compared with an approximated analytical solution developed by Polyanin and Dil'man.
Can DSC Fractionation Be an Alternative Technique to CRYSTAF for Determination of Comonomer Distribution in Polyethylene?
The use of differential scanning calorimetry (DSC) fractionation techniques as a possible alternative to temperature rising elution fractionation (TREF) and/ or crystallization analysis fractionation (CRYSTAF) technique for the determination of comonomer distribution in polyethylene has been a topic of enduring interest in the polymer literature over the last ten years. In this paper, we demonstrate a surprisingly good correlation between CRYSTAF and the two most popular DSC fractionation techniques, the segregated fractionation technique (SFT) and the successive self nucleation and annealing (SSA) Technique for metallocene based polyethylenes.
Composite Tooling for Injection Molding
Aluminum, ceramic, and high conductivity carbon fiber have been used to cast composite injection molds with superior thermal and mechanical properties. Heat transfer and dynamic mechanical analysis experiments showed improved conduction and glass-transition temperature compared to traditional epoxy and stereolithography-based tooling. The master pattern was produced using stereolithography and multijet prototyping technologies. In injection molding experiments, the composite tools required less total cycle time than a comparable stereolithography tool.
Fracture of a TPE Catheter
A nylon/polyether TPE catheter fractured during the final stages of childbirth in a British hospital. The catheter supplied an epidural anaesthetic to the patient, and part of the tip was left in her spinal fluid. She sued the hospital and manufacturer. The catheter showed brittle behaviour, and research showed that it was probably caused by a combination of UV and gamma radiation of the polymer, initiating chain degradation. ESEM of the fracture surface showed no cut marks, as suggested by another expert witness. FTIR microscopy showed traces of esters near the fracture, confirming degradation.
Double Foam-In-Foam Polymer Materials
Reticulated 100% open-pore low density (20 kg/m3) flexible polyurethane (PUR) foams with various pore sizes (1-8mm) were used as three-dimensional fillers to reinforce low-density closed-cell PUR flexible foams. The final materials represent the double foam-in-foam" structures where one foam "impregnates" another one. Compared to the "single" closed-cell PUR foam the double material exhibit considerable improvement of mechanical properties: for the same low density the compressive modulus increased up more than 10 times. Marketing aspects of a new family of the developed foams are discussed such as cushioning and packaging application."
3D Solid Brick Element Injection Molding Simulation - A Time Effective Solution
The model preparation for the current mid-plane shell element type flow/pack/shrinkage/warpage and cooling analysis is time consuming and tedious. Many attempts have been made to automate the process, but most have proven to be inadequate. The obvious solution of moving to solids based analysis programs was limited by unacceptably long calculation times. This paper describes the results of three years of experimentation, to develop a proprietary technique to quickly and easily create a user controlled hexahedral mesh from STL files and reduced the solid model calculation times.
Perspectivies of the East European Plastics Food Packaging
This paper is an attempt to analyze, in the limits of available space, the existing situation and development tendencies of the plastics food packaging, i.e. raw material resources, market structure and forecast for seven former Soviet influence zone states from Eastern Europe, not enough known to the American plastics market. Also presented here are the opportunities for American and Western European investors, with emphasis on the small and medium size production units already in place, benefiting from skilled work force, low production costs and increased market demand. Recommendations for changes in the western trade policy are also made.
Effect of Maleic Anhydride Content on the Rheology and Phase Behavior of Poly(Styrene-Co-Maleic Anhydride)/Poly(Methyl Methacrylate) Blends
The thermo-rheological properties of lower critical solution temperature (LCST) poly(styrene-co-maleic anhydride) (SMA)/polymethyl methacrlylate (PMMA) blends, with varying amounts of maleic anhydride (MA) content (8%, 14% and 32% by weight) in the SMA component have been investigated, using differential scanning calorimetry and small amplitude dynamic oscillatory rheological methods. The effect of MA content on the phase behavior of SMA/PMMA blends has been determined. The resulting phase diagrams have been modeled using Flory-Huggins theory.
Processability Studies of Silane Treated Silicas and Carbon Blacks in EPDM Matrix
Treated silica particles with different silane chain lengths were compounded in ethylene-propylene-diene terpolymer (EPDM) using an internal mixer, and their viscosity, agglomerate sizes, and extrudate swell were investigated and compared to carbon black filled systems. The treated silica compounds exhibited lower viscosity, smaller agglomerate size, and lower swell reduction than untreated silica compound after equivalent mixing times. The silica treated with shortest aliphatic chain length silane exhibited smallest agglomerate size compared to other silane treated systems. Silane acted as dispersing and processing aids in silica/EPDM compounds. Treated silica systems exhibited higher agglomerate size and viscosity than carbon black filled systems.
The Influence of Screw Design on the Stability of a Reactive Twin-Screw Extrusion Process
The pressure fluctuations that occur during the reactive twin-screw extrusion of polymers that contain solvents or solvent-borne reactants can be suppressed by closing off the reaction zone with low-pitch, reverse (so-called left-handed") screw elements. We suspect that the average down-channel velocity of the melt inside these screw elements is so high that the destabilizing effects of melt foaming occur only after the pressure is reduced. The time elapsing between the pressure drop below the boiling pressure and the end of the left-handed screw elements is the crucial parameter for controlling the stability of the process."
Rheological Characterization of the Molecular Weight and Molecular Weight Distribution of Linear Polyethylenes
It has been known for many years that the rheology of linear single phase polymer melts depends strictly upon their molecular weight and molecular weight distribution. Recently, theoretical relationships have been developed that permit transforming rheological data into molecular weight information. Rheology has several advantages over GPC or LC in determining the molecular weight distribution of linear polymers. For one, rheology is highly sensitive to the high molecular weight tail, which is usually excluded in chromatographic separations. These fractions dominate the elasticity of the polymer melt, which greatly affects processing behavior. Generally, in order to determine the entire molecular weight distribution of a polymer, the rheological data must characterize the complete range of relaxation times between the plateau and terminal regions. In practice, such measurements are very tedious and time consuming, and can involve multiple tests run at several different temperatures, with different sets of conditions. A solution to this problem has been developed by Mead et. al. that allows incomplete rheological data to be combined with appropriate mathematical models to produce the molecular weight distribution curves. This paper reports on the transformation of the frequency dependent viscoelastic material functions to molecular weight and molecular weight distribution curves of LLDPE samples using this method. These results are compared with the molecular weight distribution curves obtained from GPC.
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