SPE Library
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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Conference Proceedings
Transient in the Mold Measurements of Thermal Diffusivity Using Injection Molded Cylinders
The thermal properties of polymers such as thermal conductivity, k, heat capacity, Cp, and thermal diffusivity, ?, are important properties that affect polymer processing economics due to their critical influence on cooling time and cycle time (1). For cooling calculations one needs the physical properties of k, ?, and Cp to calculate the thermal diffusivity. These vary with each resin and also with the additives, fillers and reinforcements. The task of collecting these data is almost insurmountable since the U.S. has about 8000 resin grades recognized by UL (Underwriter’s Laboratories) and a total of about 30,000 grades are commercially available. By injection molding and experimentally determining the thermal diffusivity under actual molding conditions one can eliminate the individual measurements of k, ? and Cp and instead measure the thermal diffusivity directly. The objective of the study was to show that this is a practical approach to the evaluation of the thermal diffusivity for injection molding cooling calculations.
Optimizing the Mechanical Performance in Semi-Crystalline Polymers: Roles of Melt Temperature and Skin-Core Crystalline Morphology of Nylon
Crystalline texture and mechanical (tensile and flexural) properties of injection molded nylon 6 were evaluated to understand the influence of one of the key-processing variable, the melt temperature (Tmlt). We find that mechanical properties are sensitive to Tmlt only below ~ 250°C. Rapid quenching of the surface produces a skin with lower crystallinity than the core, which cools more slowly; this difference in the rate of cooling produces ? crystalline form in the skin and ? crystalline form in the core. Higher tensile strength at yield, lower elongation at break and higher flexural strength were observed in specimens molded at lower Tmlt. These characteristics are associated with thicker and less ordered skin, and a lower crystallinity core. The role of the Tmlt on micro-structure and mechanical properties of injection molded nylon 6, the development of skin and core morphologies, and the role of the residual stresses in the core are discussed.
Simulation, Implementation and Evaluation of the Production of a Gas-Assisted Long Part
At this paper the simulation of a gas-assisted injection molded part will be studied. Several gas injection strategies will be developed and simulated using the C-Mold software. As the Gas-Assisted injection molding is a complicated process with many parameters to tune, a detailed analysis of the effects of each processing parameter at the final product will be simulated. Furthermore, a test mould for a commercial product has been constructed and the simulated results will be compared to the real outcome of each strategy. In this way, the accuracy of the simulations according to each production strategy will be evaluated and guidelines will be drawn according to the outcome of these evaluations.
Comparison of Electrical, Thermal, and Mechanical Properties of Carbon Filled Resins
The conductive properties of polymers can be improved by adding carbon fillers. The effect of filler content on the mechanical properties must also be considered. High filler concentrations used to maximize thermal and electrical conductivity can degrade mechanical properties. In this study, chopped and milled Polyacrylonitrile PAN-based carbon fibers, nickel coated PAN-based carbon fibers, and a synthetic graphite were added to nylon 6,6 to determine filler amounts needed to obtain acceptable conductivity and mechanical properties.
Miscibility of Poly(Aryl Ether Ketone Ketone) and Thermotropic Liquid Crystalline Polymer
Poly(aryl ether ketone ketone) was melt-blended with a thermotropic liquid crystalline aromatic copolyester, Vectra 950A. A miscibility of the blend was investigated by dynamic mechanical analysis and differential scanning calorimetry. These polymer blends were found to form partial miscible blends. Glass transition temperature (Tg) and crystallization behavior of each phase in the blends were found to be affected by counterpart component. Tgs of each phase in the blends shifted toward each other compared to those of pure polymers. Slight depression of Tm of both component was observed in the blends. When the crystallization temperature is above the melt temperature (Tm) of LCP, the crystallization rate of PEKK in the blends decreased while it increased at the temperature below Tm of LCP. This result was discussed in terms of phase separated nucleation effect.
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.
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