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Crystallization and Microstructure of Ziegler-Natta and Metallocene Based Isotactic Polypropylenes: Simulation and Experiment
The quiescent crystallization and microstructure of Ziegler-Natta and metallocene based isotactic polypropylenes (i-PP's) of comparable molecular weights were studied. This allowed to elucidate the differences in their crystallization behavior. In particular, the isothermal and nonisothermal rate of crystallization, induction time, and spherulite growth rate were measured. These results were used to obtain the parameters for a crystallization model. The i-PP's slabs were quenched and the gapwise spherulite size distribution in the quenched slabs was measured. Simulations of the temperature field and microstructure in slabs during quenching were performed. Simulation results were found to be in good agreement with the experimental data.
Yield Maximization in Injection Molding by the Virtual Search Method
The Virtual Search Method (VSM) is an efficient method of tuning for injection molding. The salient feature of this method is its utilization of an input-output (I-O) model as a virtual process to search for the process inputs. VSM uses learning to update the I-O model after each tuning iteration so as to improve its representation of the process. The VSM has already been tested experimentally for regulation of part dimensional and qualitative attributes. This paper focuses on extension of VSM to improving the quality of the part, where it can be used for maximization of production yield and molded part consistency. VSM's performance with two I-O models is investigated using production of optical media with six input parameters and four quality attributes.
Effects of Complexity on Tooling Cost and Time-To-Market of Plastic Injection Molded Parts
The injection molding process is increasingly being used in the manufacture of complex net shaped parts. Designers are taking advantage of improvements in the process and the development of engineering materials with superior properties by consolidating multiple parts and functions into single complex parts. However, the effects of complexity on tooling and manufacturing costs as well as time-to-market of injection molded parts are still largely undetermined. This paper proposes the use of the number of dimensions that are used in detailing a part as a measure of its complexity. The metric was tested with empirical data and found to correlate well with mold cost and to a lesser extent with tooling lead-time.
Shrinkage Study of Thermoformed Parts
Most thermoforming product development processes rely on costly and time consuming forming trials to determine adequacy of the mold and process. This paper describes the predictive capabilities, which were developed from experimental, statistical and analytical methods in order to provide estimates of shrinkage for various process conditions. On the basis of theoretical analysis, additional transfer functions have been developed to predict shrinkage for different sets of materials, process conditions, and mold geometry. A turnkey finite element analysis system utilizing commercial software is being developed and validated for commercial applications for shrinkage prediction.
Mixing Analysis of a Reactive Extrusion Process in a Co-Rotating Twin-Screw Extruder Screw Element Channel
Simulations of steady-state non-isothermal non-Newtonian reactive flow of molten polypropylene in a channel of a forward conveying screw element from a self-wiping co-rotating twin-screw extruder, performed using the commercial finite element simulation package FIDAP, are described. The reaction is peroxide-initiated controlled degradation of polypropylene. In the simulations, the screw speed, entering peroxide distribution, and pressure-to-drag flow ratio in the channel are all varied, and a mixing analysis of the flows is performed based on computed values of the flow efficiency parameter.
Utilization of the Derivatives of Fullerene (C60) Modified Phenolic Resin to Prepare Carbon/Carbon Composites (I)
The improvement on the toughness of the cured phenolic resin modified with linear PU and star C60-PU was investigated. The modified phenolic resins were utilized to prepare carbon/carbon composites. Impact strength of cured resin specimen contains 3phr linear PU is 27 % higher than that of neat phenolic resin while the impact strength of specimen contains 3phr C60-PU is 57 % higher than that of neat phenolic resin. The flexural strength of carbon/carbon composite contains 3phr linear PU is 25 % lower than that of composite contains only neat phenolic resin. The flexural strength of carbon/carbon composite contains 3phr C60-PU is 40% higher than that of composite contains only neat phenolic resin.
Syndiotactic Polystyrene Can Help Solve the 3-Piece Material Selection Puzzle: Properties, Processing, Cost
For injection molding, material selection involves three factors: properties, processing, and cost. Summing the factors determines part cost and profitability. Material properties are prerequisite to application requirements. Processing is prerequisite to part design. Cost vs. the marketable price of the application determines if and how the part should be made. A material must meet the prerequisite performance for the application but it does not need to have the highest available properties. Processing conditions, particularly cycle time, directly affect cost. Price and the forgotten property, specific gravity, directly go to the bottom line. Graphs show costs of semi-crystalline thermoplastics vs. properties, processing, and part cost. New materials like syndiotactic polystyrene provide cost effective solutions vs. established semi-crystalline polymers.
Effects of Injection Parameters on Fiber Attrition and Mechanical Properties of Polystyrene Molded Parts
Fiber degradation of injection molded fiber reinforced polystyrene has been analyzed using a statistical approach. Results showed that fiber concentration as well as injection speed are responsible for the onset of fiber degradation. The same experimental design has been used to evaluate the effects of injection processing parameters on mechanical properties of molded parts. Results have been used to generate a statistical model to predict fiber degradation and mechanical properties using the most significant parameters identified in the statistical analysis. The statistical approach has proven to be satisfactory for the analysis of fiber attrition during the injection molding process.
Fractal Description of Interlaminar Contact Development during Thermoplastic Composites Processing
Fabrication of layered thermoplastics and thermoplastic-matrix composites using processes such as tow placement, tape laying, and resistance welding, is fundamentally based on the principle of fusion bonding, which involves applying heat and pressure to contacting thermoplastic surfaces. One of the important processing steps-intimate contact-is considered in this paper. Interlaminar intimate contact development is a strong function of thermoplastic surface geometry. Profilometric measurements of thermoplastic prepreg tows show that surface roughness features can be found at several length scales, which implies that the surfaces have a fractal structure. In this paper, principles of fractal geometry are used to describe prepreg surfaces. Based on this description, an axisymmetric squeeze flow model is developed to relate degree of intimate contact to the process parameters-pressure, temperature, and time-and the fractal parameters of the surface. The model development and comparisons with available experimental data are presented and discussed in this paper.
Plastics in fuel Cell Applications: An In-Lab Developed and Fabricated Molten Carbonate Fuel Cell (MXFC) Electrolyte Matrix Support with Polyolefin-Based Binders
A low pressure compression molding, in-lab fabricating process has been used to produce crack-free, Molten Carbonate Fuel Cell (MCFC) electrolyte matrix support that are prospectively conductive and have volume resistivities much lower than those of standard insulative materials (1013 - 1016 Ohm-m). The volume resistivities of the in-lab produced MCFC electrolyte matrix support are expected to be much lower at the system's 650°C operating temperature than their currently room temperature measured resistivities (103 - 106 Ohm-m).
Injection Molding of Thermoplastic Composites Using Novel Mixing Nozzles
Injection molding of PET/PE, one of immiscible thermoplastic composites, was carried out with original novel mixing nozzles equipped with torpedoes. An ability of the nozzles to promote plasticizing and mixing of dry-blended PET/PE to achieve high performance as same as a melt mixed composite was investigated. Mixing of dry-blended PET/PE was promoted by high shear effect of the mixing nozzle with a torpedo which allowed homogeneous and fine dispersion. The dispersion structure was equal to that made using a twin-screw extruder with high ability to knead materials. When a torpedo which has barriers and grooves was used, a fine dispersion structure was also obtained by its effect of distribution and collision of materials.
In Situ Polymerization of Conducting Composite Films and Some Characterizations
Electrically conducting composite films were prepared by a vapor phase in situ polymerization of pyrrole in the methyl cellulose film containing a copper(II) perchlorate. Methylcellulose had a high affinity to pyrrole and was used as a matrix polymer. Conducting polypyrrole was embedded in the methylcellulose film forming a conducting network and the conductivity of the composite films ranged 10-1 to 10-7 S/cm. The conductivities and mechanical properties of conducting composite films were depentent showed on the concentration of oxidant and polymerization time. In situ polymerization of pyrrole was observed in the matrix polymer and confirmed by UV-vis spectra and FT-IR spectra. From the results of the thermogravimetric analysis, the chemical oxidative polymerization of pyrrole in the matrix polymers did not give any negative effect on the thermal stability of the composite films. Dynamic mechanical analysis suggested a certain degree of miscibility of the polymeric components in the composites.
Selection of Silicone Sealants for Heavy Truck and Off-Road Vehicle Applications
The unique sealing requirements encountered in Heavy Truck and Off-Road Vehicle applications warranted the investigation of silicone sealants for this marketplace. The candidate sealants were subjected to a selection protocol based on lap shear strength as a function of cure time and after immersion in water, engine wash fluid, and common automotive fluids. An acid cure silicone did not adhere well to chromate plated steel, and its adhesion to brass deteriorated after fluid immersions. A neutral cure silicone adhered well on any of the substrates, and retained adhesion after fluid immersions. Neutral cure materials were recognized as the best choice for future product performance testing.
Medical Kink-Resistant Tubing
The medical industry always prefers to employ thin-wall tubing if there is no risk of kinking. Although thick-wall tubing generally presents less kinking, the kink-resistant tubing is preferably made from a thin-wall tubing. This study employs a finite element method to identify the required quantitative characteristics of a thin-wall tubing that can match the kink-resistant characteristics of the thick-wall tubing. For a monolayer tubing, the finite element method is able to predict the need of increase in material stiffness to compensate for the reduction in wall thickness. For a double layer tubing, the model can determine the Young's modulus of each layer and its corresponding wall thickness to match the kink-resistant characteristics as a thick-wall tubing.
Synthesis of High-Molecular-Weight Elastomeric Polypropylene with Half-Titanocene/MAO Catalysts
Propylene polymerizations in the presence of various monocyclopentadienyltitanium compounds and MAOs have been investigated. It was found that the content of residual trimethylaluminum (TMA) in MAO has a determinative effect on catalytic activity for the polymerization. An excess of TMA in the catalyst systems reduces the Ti species to inactive lower valent states. By substituting hydrogen at cyclopentadienyl ring by more electron releasing methyl, the titanocene afford atactic polypropylene with increasing molecular weight by one order of magnitude. Esterified or alkylated titanocenes with appropriate -OR and -R ligands give higher molecular weight polypropylene than the corresponding halide. The produced polypropylenes with the molecular weight range of 20~100 x 104 exhibit good elasticity.
Minimizing Part Sink Marks Using C-Mold and Genetic-Optimization Algorithm
Injection molding is widely used for mass production of polymer products. One important issue is how to determine the process conditions to produce parts of the best quality. The objective of this paper is to show how C-Mold combined with an efficient optimization system can automatically predict the optimum process to minimize sink marks. C-Mold and Genetic optimization algorithm have been integrated to solve the problem. Sensitivity analysis on part sink marks with respect to process parameters (such as filling time, hold time, cooling time, packing pressure, mold temperature and melt temperature) are also presented in this paper. Simulation results show that holding time, hold pressure and gate size have the greatest effect on part sink marks. A number of examples have been tested and the results show that sink marks can be significantly reduced after optimization.
Vibrated Gas Assist Molding: Its Benefits in Injection Molding
This paper shows how air or nitrogen can be used to impart vibration and/or pressure pulses to a melt. Air is already used to blow preforms and parisons  inside of molds, and to core out hollow articles in the process of Gas Assist Injection Molding . The methods of gas assist molding have demonstrated their great usefulness in injection molding not only to hollow parts out but also to induce an excellent surface finish. Melt vibration techniques have also been reviewed [3,4] and show great potential to reduce viscosity during filling and impart optical and mechanical benefits, i.e. stiffness, strength and clarity, without resorting to processing aids such as thinning or nucleating agents. The present paper explores the processing of injection molded plastics under gas vibration. Vibrated gas can be used for several purposes. 1. Gas can be inserted and vibrated in the mold prior to melt injection to modify the filling process mechanism, fuse knit lines, heal sink lines and other defects due to flow imperfections. 2. Compressed Vibrated Gas can act like a pressurized vibrated gas spring, which helps induce orientation benefits in the short shot during filling completion. 3. Vibrated air pressure, localized in specifically designed air-runners distributed around the runners and inside the mold, helps fill and pack the mold, core out hollow parts and balance flow in multi-cavity molds. 4. Vibrated Gas can also be used to tag parts for recognition during recycling or later inspection. The paper reviews hardware and controls requirements to apply this novel technique to injection molding.
Temperature and Molecular Weight Dependence of Viscosity Revisted: New Formulations for Rheology
Viscosity of polymers is key to their behavior in the molten state and thus to their processing. The well known equations of rheology giving the temperature and molecular weight dependence of viscosity are reviewed and tested with two independent sets of results on Polystyrene and Polycarbonate. It is shown that the admitted view that molecular weight and temperature separate in the expression of viscosity is only an approximation. Furthermore, the classical 3.4 exponenet for the variation of Newtonian viscosity with molecular weight is shown to be temperature dependent and to represeent another curve fitting approximation of the effects of entanglements on the viscosity. Another model of melt deformation and of the influenece of entanglements is presented. Based on this new model of interactive coupling kinetics other formulations of viscosity are suggested and tested on two well characterized melts of Polycarbonate and Polystyrene. The paper gives an explanation to the reptation model dilemma. why does the theory predict a power exponent of 3 whereas viscosity behaves like 3.4?
A New Formulation and Inerpretation of Shear-Thinning of Polymeric Melts. Effect of Temperature, Strain Rate and Frequency
Shear-thinning of polymeric melts is analyzed in this paper from dynamic viscosity data obtained in the non-Newtonian regime. Shear-thinning is expressed as a function of (G'/G*), where G' is the elastic modulus and G* the amplitude of the complex modulus. It is shown that viscosity depreciation, i.e. shear-thinning, is due to the cooperative coupling characteristic of the interactions between the polymer macromolecules which form a network , the EKNET network. The Newtonian character of viscosity at low strain rate is interpreted with the notion of structural re-localization of the conformers, without deformation of the potential energy of their interaction. It is purely a diffusion phenomenon. New equations are provided which define the mechanisms of shear deformation of the melt under different conditions of temperature and strain rate, and relate non-Newtonian viscosity to the number of interactive conformers stretching cooperatively versus those conformers which re-localize structurally. It is stipulated that viscous and viscoelastic effects can be interpreted from the EKNET model of interactive coupling kinetics [2-7].
Viewing Entanglements as a Two-Phase System in Polymeric Materials
All past statistical theories concentrate on the macromolecular aspect of polymeric materials, and try to determine the macroscopic properties from the characteristics of the individual macromolecules. In those theories a polymer molecule is identical to a spaghetti chain" which is able to "tie" other molecules or slip against another one creating flow and hysteresis effects. By necessity there is also place in the macromolecular theories for such a concept as chain entanglement. Accordingly two macromolecules can touch each other mechanically hook around each other in a static and stable fashion or transmit a stress as if there were a little nail pinning them together. More recently macromolecules reptate through imaginary tubes which represent the constraints imposed by neighboring chains. All those concepts are entirely directed by an approach of polymer physics around the properties of the individual singularizable macromolecules. The accent is put on determining the shape of the individual macromolecules called their configuration. The presence of neighboring and interpenetrating macromolecules is perceived as a disturbance to the ideal configuration of the chain. Macromolecules are able to rearrange their multiple configurations with the change of the thermal or mechanical energy input. This also yields a change in the conformational statistics of the bonds along the chains. For instance in the treatment of rubber elasticity it is said that the elongation of the end-to-end distance of the individual macromolecules results in a preferential orientation of the bonds in the direction of stretch."
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