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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Die Swell Estimation for HDPE Blow Molding Grade Resins Using the Wagner Model Constitutive Equation
A polymer flow analysis inside a concentric annular die of an extrusion blow-molding machine was conducted using momentum and continuity balances coupled with the Wagner rheological constitutive equation for six high density polyethylene (HDPE) resins and then used to determine the thickness swell. The rheological measurements included oscillatory behavior, relaxation modulus, steady state behavior, and capillary flow.
Polyethylene Powder Characteristics: Impact on Polymer Sintering and Rotational Molding
The effect of powder characteristics on the rotational molding and sintering performance was investigated. The six LLDPE resins showed comparable rheological and thermal properties. Resins with poor powder quality produced parts with lower density and impact strength. The irregularities in shape due to grinding influenced the sintering results. To eliminate this effect on the sintering experiments cylinders were used. Variations in the sintering results, however, were also observed when using cylinders.
Blends of Polypropylene (PP) and Polyamide 6,6 (Pa 6,6) with Functional Polyolefin Elastomer (FPOE) as a Compatibilizer
The objective of this study is to evaluate the effects of functional polyolefin elastomer (FPOE) on the morphology, and mechanical properties of the blends of polypropylene (PP) and polyamide 6,6 (PA 6,6). PP was blended with different weight concentration of PA 6,6 and functional POE. All blends were carried out in a reactive twin-screw extruder. The mechanical properties of the blends, such as tensile strength at yield (?y), modulus of elasticity (E), and elongation, were examined. Moreover, their morphological behavior was investigated through scanning electron microscopy (SEM). It is clearly indicated that the morphology structure can be controlled through functional POE. It was found that the morphology of the cryogenic fracture surface of the blends was dramatically changed, from micron fibers in the mechanical blending to sub-micron fibers in the reactive blending. The tensile strengths at yield (?y), and modulus of elasticity (E) of the blends with functional POE are increased relative to mechanical blends. However, the elongation of the reactive blends is decreased. These results illustrated that the functional POE can be employed as a effective compatibilizer in the blends of PP and PA 6,6. It stands to reason that functional POE can reduce interfacial tension preventing the blends from agglomerating as well as leading to smaller domain size and better dispersion of PA 6,6 phase in the PP matrix.
The Blends of Polypropylene (PP) with Functional Polyolefin Elastomer (FPOE) for Recycling of Xerographic Toners
This paper presents experimental results on the blends of polypropylene (PP) with functional polyolefin elastomer (FPOE) for recycling of xerographic toners. All experiments were carried out in a co-rotated reactive twin screw extruder. The investigation of the mechanical properties and morphology for different blends consist of PP, xerographic black toners and functional POE (FPOE) through reactive compounding. It is of interest to note that the notched Izod impact resistance of the blends with functional POE (FPOE) is significantly improved relative to physical blends. However, tensile strength at yield (?y) and modulus of elasticity (E) of the reactive blends are reduced. The reason why the impact properties should be so is clearly shown by the stress-strain behavior of the blends. Morphology of the cryogenic fracture surfaces of the blends was studied through scanning electron microscopy (SEM). The results of morphological studies indicated that not only the domain size of the phase of black toners could be reduced but also the interfacial adhesion could be enhanced through proper functional POE (FPOE). The phase morphology of the blends also illustrated that better dispersion of black toners could be obtained through using FPOE whereas serious agglomeration of black toners was found in the physical blends. It is elucidated that the functional POE could be an excellent candidate of compatibilizer for recycling xerographic black toners.
Training of Operators in Extrusion and Stretch Blow Molding
The current lack of qualified operators in the blow molding industry and its effects on blow molding operations is described. The need for the training of blow molding operators is illustrated. Different methods of training are described and evaluated with respect to their effectiveness. The reasons for the lack of trained operators are shown and from there new training methods are developed overcoming some of the shortcomings of other methods. It is shown that only training material closely resembling the actual plant conditions is well accepted by trainees. Engineering concepts need to be translated into understandable training materials. Retention levels are improved by giving short tests challenging the trainees into thinking about the material presented. Given the right methods, one can teach more complex relationships between material properties, machine functions, and settings.
Reciprocating-Screw Injection Molding Machine for Microcellular Foam
The reciprocating-screw (RS) injection molding machine for microcellular foam has been successfully developed. It creates the necessary conditions for a single-phase solution with a specially designed plasiticizing unit. An overall system is the key for successfully implementing a microcellular foam process. The important components for the microcellular foam molding machine system including a plasticizing unit, injection unit, hydraulic unit, clamp unit, gas unit, are discussed in this paper. The general guidelines to design an injection molding machine for microcellular foam are listed as the conclusions.
CD Case Design Using a Simulation Software for Injection Molding Processing
The objective of this work was to design an injection mold for a CD case. A commercial case design has been analyzed and led to the proposal of a new one. The study was made using the mold filling/cooling simulation program for the injection process, and a three-dimension solid modeler program for planes accomplishment. The results showed that the actual design presented stress concentration in specific areas of the part. A new case design was proposed with optimized performance and with enhanced final part quality.
Non-Isothermal Melt Densification in Rotational Molding
The numerical simulation of the non-isothermal melt densification in the rotational molding process is presented. The simulation combines heat transfer, polymer sintering and bubble dissolution models, and is based on an idealized packing arrangement of powder particles. The predictions are in agreement with experimental observations presented in the literature. The simulation allows for systematic and quantitative studies on the effect of molding conditions and material properties on the molding cycle and molded part density.
Effect of Dynamic Cross-Linking on the Foaming of PP/EMA Thermoplastic Elastomers
The foaming of PP/EMA thermoplastic elastomers with CO2 during dynamic cross-linking has been investigated. The cross-linking of the EMA phase was obtained through an alcoholysis reaction with 1,5-pentanediol. The cross-linking extent was controled by changing processing parameters and chemical composition (diol content). PP/EMA foams were obtained in different conditions. Results on foam density, cell morphology and cross-linking extend are presented. The effect of cross-linking extend on foamability is discussed.
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.
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