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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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?
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].
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."
Entanglement is responsible for the high viscosity of polymer melts and the molecular weight dependence of viscosity as M3.4. Disentangled polymers, at identical molecular weight, would have a much lower viscosity, proportional to M, providing a maximum viscosity reduction of (Mw/Mc)2.4. The objective of this work is to study methods to disentangle polymeric melts in order to achieve large viscosity reduction without breaking the polymer chains. We are also interested in the reverse process of re-entangling polymer melts which have been disentangled, in order to recover fully their mechanical performance after molding is performed. We first present the new concepts of interactive coupling kinetics of conformers, which naturally lead to the definition of an interface of penetration between adjacent macro-coil molecules in the melt, which we assign to entanglements". The stability of the entanglement phase depends on the potential energy of interaction between conformers. It can also vary with macroscopic variables such as temperature strain rate frequency and amplitude of melt deformation. We present a new method to increase cooperativeness between conformers in the melt to the extent that deformation occurs no longer by "reptation of the entanglement phase" which is dominated by entropic effects but by stretching resulting in disentanglement. We present viscosity reduction results for Polycarbonate and a metallocene PE obtained with a laboratory rheometer which might be proof that controlled disentanglement is indeed possible with potentially a large variety of applications for the plastic industry."
Knowledge of the permeability tensor in liquid composite molding is important for process optimization. Unfortunately, experimental determination of the permeability is difficult and time consuming. A rapid, non-destructive technique called optical coherence tomography (OCT) can image the microstructure of a composite in minutes. In this work, binary images were generated from the OCT data and input into a lattice Boltzmann model for permeability prediction. Calculated permeabilities agreed well with experimental values for the same fiber volume fraction.
Injection molding optimization is unique since the injection molding process is a multifaceted process offering a number of technically feasible designs for the same optimum part quality. These solutions will vary in their quality robustness to the uncontrollable process variation. Therefore, it is of great importance to consider both response improvement and solution robustness. This paper introduces a methodology for automated search of the optimal robust design against process variability. Part warpage is chosen as the quality of interest. The warpage characteristics obtained from the proposed model are compared with those from other conventional optimization models. Each optimized design is then simulated for small plausible process fluctuations. It is seen that the optimal robust design obtained in this study exhibits the best warpage characteristics in terms of warpage mean and deviation against this mean.
At the IKV a concept has been developed to describe the material behavior by means of spring/damper combinations using the time-temperature-shift principle and short-term test data. The concept called deformation model" has been used successfully to predict the uniaxial long term behavior of filled unfilled or reinforced thermoplastic polymers. In order to stimulate the dynamic material behaviour without the necessity of high speed tensile tests the deformation model is calibrated based on short-term tensile data at very low temperatures and common strain rates. To reduce the testing expenditure a concept has been developed to calibrate substitute spring/damper combination based on creep-curves from material databases (CAMPUS)."
In the two-stage stretch blow molding process for the manufacture of PET bottles, injection molded preforms are placed in an infrared oven, with axially profiled heating lamps. The subsequent inflation of the PET preform is strongly dependent on the preform geometry and the temperature profile, as hot zones will blow out faster and thin out more than colder and stiffer zones. In this work, the reheat and blowing stages of the process are both modeled and experimentally validated. The part considered is a water bottle produced at the Husky Bottle Development Center. The simulations were performed at the Industrial Materials Institute. Four oven operating settings are studied. The heat transfer in the oven is modeled by combining radiation and air convection. The preform stretching and inflation are modeled with a non-isothermal hyperelastic constitutive equation. Simulations are performed using experimentally measured temperature profiles as input.
Highly filled CaCO3/PP blends (up to 60% wt) were compounded using an intermeshing corotating twin-screw extruder. The effects of screw configuration (4 geometries) and operating conditions such as RPM, total flowrate, filler feed position, temperature profile on the dispersion were investigated. A rapid and reliable method for evaluating the state of dispersion in the composites was developed. Falling weight impact and tensile tests were carried out. Composites' toughness and tensile properties (modulus, yield stress and strain), which are very sensitive to the dispersion, were correlated to the compounding conditions and to a dispersion index calculated by image analysis.
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