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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A New Family of Positive Temperature Coefficient (PTC) Materials Based on Nylon 12
An experimental study has been conducted to establish factors influencing the positive temperature coefficient behavior of particulate-filled nylon 12. Fillers considered included both finely-divided nickel as well as carbon black. Resistivity of the blends was used to determine the effect of filler loading on the conductivity and percolation threshold of this new family of materials. PTC effects of up to nine orders of magnitude were observed as functions of filler fraction, type of filler, etc.
Rubber Toughening of Epoxy-Cyanate Ester Blends for VARTM Applications
Blends of cyanate ester resins and epoxies offer unique properties and performance that are midrange between the two materials alone. These blends are attractive due to the lower cost the epoxy resin imparts as well as increased toughness and resistance to crystallization. In this study, epoxy and cyanate ester resin blends were toughened using different liquid rubber modifiers. The adducting sequence of the rubber materials was found to alter the morphology and toughening efficiency of these materials.
Cryogenic Microcracking of Carbon Fiber/Epoxy Composites: Influence of Fiber Type
Cross-ply laminates were created from model prepregs and evaluated to determine their response to cryogenic cycling. The tensile modulus of the carbon fibers was varied to alter the composite material's properties. Examination of the laminates after cycling provided insight into the mechanism of thermal stress-induced microcracking. Optical microscopy revealed that increasing the tensile modulus of the fibers resulted in a corresponding increase in the degree of microcracking that occurred in the composite.
Dispersive and Distributive Mixing Characterization in Extrusion Equipment
Mixing is a key step in almost every polymer processing operation. The traditional methodology for improving machinery performance has relied more on users' experience and trial and error experiments. Recently, the fast development of advanced computing resources has enabled the use of numerical modeling as an alternative and more efficient approach in studying the influence of design and processing conditions on equipment mixing performance. In this work using numerical simulations we record the flow history of a number of tracers in the equipment and use them in conjunction with dispersion kinetics models to evaluate minor component size and concentration distributions.
Flow Balancing of Profile Extrusion Dies
In this work a methodology to automatically balance the flow in profile extrusion dies is used. For this purpose a computational code, based on the finite-volume method, was developed and used to perform the required three-dimensional numerical simulations of the flow. The methodology is illustrated using two case studies, each one leading to the adoption of a different constructive solution (with and without flow separators). In order to evaluate the quality of the automatically generated die geometries, an objective function, that takes into account the flow balancing and the ratio L/t of the parallel zone, is proposed.
Hot Plate Welding of Glass Reinforced Polypropylene
The reinforcement of thermoplastics with short glass fibers is a common way for obtaining composites with high strength and stiffness. These materials are amenable for welding by the hot plate method, although a drop in the mechanical strength is observed. In this paper 20% glass reinforced polypropylene (GRPP) was injection molded in mono-material and bi-material (PP/GRPP) ISO-type tensile testing specimens and welded using the hot-plate technique. Morphological analysis and mechanical testing were used to investigate the effect of the processing parameters and type of molding on the weld behavior. It was found that the welds made with PP/GRPP moldings are stronger than if only GRPP is used in the moldings.
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."
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