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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Binary Blends of Ziegler-Natta and Metallocene Catalyzed Polyethylenes: Rheological Properties
The rheological and morphological behaviors of three binary blends of polyethylenes regarding the melt index and density, one component made by Ziegler-Natta and the other by metallocene catalysts, have been investigated to elucidate miscibility and phase behavior. If the comonomer contents are similar, then the melt viscosity is weight average value, otherwise it shows different behavior: the FA+FM blend is miscible, but the RF+EN and RF+PL blends inform immiscible. The microtomed cutting surface indicates that all the blends are not homogenous regardless the density, melt index and cooling processes, and show banded spherulites.
Cure Monitoring of Phenolic Resins Using Dynamic Rotational Rheometry
The mechanical responses of two phenolic thermoset resins during curing were monitored as a function of time and temperature using dynamic rotational rheometry. The tangent of the phase angle tan ?, the ratio of elastic to viscous modulus, was used to characterize the reactions because of foaming and emission of by-products. For resole phenolic resins, gelation was interpreted as the cross-over of the storage and loss moduli, i.e. tan ?=1. This assumption proved to be reasonable, as activation energies derived thereby agreed with those found using in-line ultrasonic measurements. The gelation time of the novolac resin was successively assumed to be the first occurrence of tan ?=1 or the minimum of tan ?. The activation energies found using these assumptions were both significantly higher than those found using ultrasonic measurements. Resolution of this discrepancy may require a knowledge of the influence of the foam structure on tan ?.
The Analytical Models for the Warpage of Integrated Circuit Devices
This paper studies thin elongated packaging for large size silicon chips and its warpage caused by temperature changes during the packaging process. An integrated circuit device is composed of several materials with various different properties, of which, differences in the thermal expansion coefficients of the materials poses the largest influence on the resulting product. In the course of IC encapsulation, as the product goes through numerous processes, temperature will rise and fall and causes the composing materials to experience repeated thermal expansion and shrinkage. Since the material layers are under perfect adhesion, if two neighboring materials have different thermal expansion coefficients, the stress from the temperature change will cause the product to deform. Current IC warpage analytical models researches base mainly on Dr. Suhir's theory of the compatibility conditions for the interfacial strains. The analytical model in Dr. Suhir's theory is constructed upon four layers of two-dimensional materials. There are two sections in the model: one is the section comprising the silicon chip and one is the section without the silicon chip. The latter section is only roughly simulated with a single homogenous material and is unable to correctly simulate the geometric shape of an actual encapsulation component. This paper, extends Dr. Suhir's analytical model to possessing unlimited layers and consisting of many sections, thus not only increases the completeness and correctness of the analysis results but also resolves the problem of accommodating models with different geometric shapes.
Rapid Prototyping of Small Injection Molded Plastic Components for Critical Medical Devices
Mallinckrodt Inc is an international company serving markets in healthcare and specialty chemicals. The Advanced Process Development Lab supports the Critical Care Division. It is staffed by four individuals who each contribute a particular specialty. • The designer is an expert in the use of solid modeler software and is responsible for the engineering design and solid modeling. • The PLC/CNC programmer is a computer science graduate, and is responsible for programming automated machinery as well as operation of the CNC equipment. • The Tool and Die Maker has over 35 years experience, and is responsible for all conventional machining. • The Plastics Processing Technician has over 25 years experience in a wide range of plastics processing, and is responsible for establishing parameters for all new tooling and dies, as well as developing processes for new equipment.
In-Line Dielectric Sensor for Chemical Composition Measurements in Molten Polymers
Resin producers and compounders use additives to extend and modify the properties of their polymers, and they increasingly use rugged dielectric sensors to measure additive concentrations in-line for automatic process control and quality monitoring. They need to control the concentrations of the additives they use as processing aids and to modify properties in plastics, elastomers, fibers, adhesives and coatings. This helps them meet demanding product quality specifications and ensure strong prices and market shares. Theory and experiments described here indicate that dielectric measurements in melts can quantitatively determine individual or total additive concentrations with an accuracy that depends on electrical contrast and can exceed 0.1 volume percent (1000 ppm) with polymers and compounds having one or possibly two dominant additives. In-line measurements of additive concentration facilitate automatic process control, which helps maintain product quality and manufacturing efficiency. In multi-component mixtures the measurements indicate on-aim conditions, provide automatic quality monitoring and accelerate transitions.
Hierarchical Assembly of Fibrous Proteins
Fibrous proteins provide useful models with which to explore self-assembly processes from the molecular scale to the macromolecular scale. Silks and collagens are under study in an effort to understand the sequence of events involved in these assembly processes, as well as to explore options to direct this process toward different paths. Model peptides, the native proteins, and recombinant versions of these proteins are studied. Interfacial and bulk solvent environments are utilized in an effort to understand and direct these processes. The interplay between primary repeat sequence and solvent is essential in fostering a specific assembly pathway. Insights into these processes will be presented within the context of pattern formation in fibrous protein materials with implications for biomaterials and tissue engineering.
An Accurate Warpage Prediction for Injection Molded Part by Using Simulation Program
This paper describes the computerized injection molding simulation of filling, post-filling, cooling and shrinkage and warpage phase analyses for an injection molded fiber-filled reinforced frame part used in a laser printer. Using C-MOLD ® simulation program, the part warpage was separately predicted by non-uniform shrinkage, fiber orientation, and unbalanced cooing effects. In the study, the frame part, as an example, the displacement components induced by different factors were investigated. The predicted shrinkage and warpage of the part are compared to the measurements of an actual production part. It was in good agreement with the actual injection molded part.
Modification of Thermoplastics for Density and Gas Permeability through Additives and Reactive Processing
Transport properties of thermoplastics such as thermal conductivity and gas permeability are usually controlled through foaming and the formation of lamellar microstructures respectively. Production of low-density foams by extrusion in the presence of physical blowing agents requires materials with particular rheological characteristics. Reactor/post-reactor branching or controlled cross-linking is commonly carried out in the presence of multifunctional additives. Low vapor/gas permeability structures may be formed through the incorporation and subsequent orientation of impermeable lamellar fillers, or the in-situ formation of lamellar microstructures during processing of mixtures of immiscible polymers. Examples of available technologies in both areas and recent research results will be presented.
Visual Research of Melting Mechanism of Polymer Pellets in Intermeshing Co-Rotating Twin-Screw Extrusion
With visualization co-rotating twin-screw extruder, the transition of polymer from solid to melt can be investigated on-line. Based on different states of polymer pellets along the screw in the experiments, several melting sub-stages, such as conduction melting, particle deformation, inter-particle friction melting and viscous dissipative mix-melting, were divided and defined in order to fully understand the melting process. Function of every stage was deeply discussed. It showed that dissipative mix-melting was an efficient way to polymer pellets melting, which depended on not only screw configurations but operational conditions and polymer properties as well.
The Formation of Supermolecular Polycaprolactone (PCL) Spherulites in Polystyrene-Polybutadiene-PCL (PS-b-PB-b-PCL) Semicrystalline Block Copolymers
The morphological behavior of polystyrene (PS), polybutadiene (PB), and polycaprolactone (PCL) semicrystalline block copolymers as a function of annealing conditions is discussed. For this study, both bulk and thin films of (PS)0.35(PB)0.15(PCL)0.5 were cast from toluene solution and the morphologies were examined using transmission electron microscopy (TEM) and polarized light microscopy (PLM). The morphology of either as-cast or annealed bulk (1 mm) specimens is a lamellar-cylindrical morphology having PB cylinders at the interphase boundaries. The block copolymer thin film (5-10 µm) from fast solvent evaporation also shows a lamellar-cylindrical microphase-separated morphology without the formation of visible PCL spherulites using PLM. After the formation of the well-defined PCL spherulites by annealing, the micromorphology is no longer lamellar-cylindrical but instead the PCL lamellar crystals dominate the system.
Structure and Processing Control of Electrically Conducting Polymers
The electrical conductivity of doped conjugated polymers is very sensitive to their in-chain and interchain structure. We present results of an integrated study of the electrical and magnetic properties. Modifications examined include the role of oligomer length, substituent group, chirality of dopant and processing-induced orientation and crystallinity. The data show a systematic variation of the room temperature conductivity and its temperature dependence. The variation of magnetic behavior supports the important role of structural order and inhomogenity. New concepts such as the role of “fractal networks” in determining the electrical properties (and industrial applicability) of these polymers are introduced.
Corrosion Protection of Aluminum and Iron Alloys Using Polyanilines
Corrosion protection capabilities of polyaniline in the emeraldine base form and self-doped sulfonated polyaniline form have been studied for aluminum and Al 3003 and Al 2024-T3 alloys. The polyaniline is applied as a coating on the aluminum coupons which were exposed to a variety of corrosive environments, including 0.1M NaCl. The oxide layers that formed were studied by X-ray photoelectron spectroscopy depth profiling using argon sputtering. Potentiodynamic polarization studies were used to determine changes in corrosion current and corrosion potential as well as pitting potential. For Al and Al 3003 there were modest indications of potential corrosion protection capability of polyanilines. The coatings of emeraldine base (EB) and sulfonated polyaniline (SPAN) on Al 2024-T3 were effective at reducing the corrosion rate when these coated coupons were exposed to 0.1M NaCl environment. The XPS study suggests a reduction in the copper concentration at the surface of the coated coupons. It is suggested that the EB and sulfonated polyaniline coatings facilitate the extraction of copper from the surface of the Al 2024-T3 thereby reducing the galvanic couple between aluminum and copper that usually leads to accelerated corrosion for the Al 2024-T3 alloys.
Single-Site Supported Catalysts for Ethylene Polymerization
The new family of single-site catalysts for ethylene polymerization are soluble organometallic compounds, which make them suitable to be used in solution or in high pressure processes. However, if they want to have an impact in the polyolefin industry they need to be heterogenized for dropping into large gas-phase and slurry production plants and to produce polyethylene with differentiated properties. In this paper we describe different approaches for the preparation of supported single-site catalysts. Special attention have been paid to the requirements of the catalysts for retaining the essential characteristics of the homogeneous analogs (e.g., single-site nature) after supporting them, as well as to the ability to control of morphology of the polymer particles (replication phenomena) and the properties of the resulting polyethylene
Estimating Permeability of Compacted Fabrics and its Use in Modeling and Control of the RTM Process
Permeability of compacted multi-layer fabric preforms is predicted by using an analytical code based on an approximated two-dimensional lubrication flow in open spaces between the fabric tows and one-dimensional transverse Darcy's flow within the tows. The distribution of microscopically measured tow architecture of compacted and resin-filled fabric samples is used in the code to predict the range of permeability and a weighted permeability. The predicted permeability values are compared with the experimentally measured values for some fabrics. The predicted value serves as input to a separate mold filling simulation code which can predict flow front location and pressure distribution. The experimental and simulation injection pressures are compared under constant injection flow rate boundary condition within molds with both uniform and non-uniform fiber volume fractions. This permeability predictor code is an alternative to the costly and time-consuming permeability measurement experiments in RTM process and empirical relations between permeability and fiber volume fraction. Besides the tow distribution analysis, the model is flexible enough to study the effects of in-plane shifting of layers of a multi-layer mat.
On-Line Measurement of Polymer Melt Specific Volume Using a Gear Pump
This paper presents a newly developed experimental system that can economically and accurately measure the pressure-volume-temperature (PVT) properties of polymeric fluids based on an extrusion system. The density or specific volume of a polymer melt is determined by measuring the mass and volume flow rates of the melt. A positive displacement gear pump mounted on an extruder is used to measure the volume flow rate of the melt. In order to reduce the leakage across the gear pump, the difference between the upstream and downstream pressures is minimized by using a variable resistance die attached to the downstream outlet of the gear pump. The positive displacement volume of a gear pump was determined in calibration experiments with water and oil with the aid of a syringe pump. A critical set of experiments was carried out to measure the specific volume of a linear polypropylene as a case example. The measured results were compatible with the known PVT data of the polypropylene material, confirming the validity of the system.
Insights Regarding the Mechanism for Interfacial Polymer-Metal Oxide Reactions
An anodic coating process for aluminum and aluminum alloy substrates has been theorized and experimentally proven which enables the formation of composite polymer-metal oxide films. Important to the process is the modification of the sulfuric acid electrolyte to include aniline monomer. The additive is made electroactive through ring substitution on the aminobenzene structure in the electrolyte [1- 4]. Autocatalytic side reactions were also noted during experiments to optimize electrochemical formation of composite metal oxide - polyaniline films. Analysis of the films formed through the electrochemical (anodizing) and autocatalytic reactions elucidated the mechanism for bonding at the polymer-metal interface. This paper discusses the reactions, analysis and the insights toward understanding the mechanism for polyaniline-metal interfacial reactions.
Comparison of Dry Blending-Based and Melt Compounding-Based Rotomolding Techniques for LLDPE Foams
This paper presents a melt compounding based rotational foam molding technique for production of fine-celled LLDPE foams in comparison with the dry blending based technique. A chemical blowing agent (CBA) is well dispersed in the LLDPE matrix in a compounder while preventing the predecomposition of the CBA. The compounded pellets are then rotationally molded to produce foams. The morphology of the LLDPE foams obtained in such a way was investigated at various processing conditions. The quality of the cell structures obtained in melt compounding based rotational foam molding was superior to that of the dry-blended based in terms of cell size, cell population density and volume expansion ratio. The results indicate that the cell nucleation mechanism in the compounding based technique is superior and that the scheme of well distributing the CBA particles in the polymer matrix by compounding is effective to achieve better nucleation of cells compared to the dry blending technique.
Dynamics of Vulcanization Induced Phase Separation in Olefinic Elastomer Blends
Blends of syndiotactic polypropylene (sPP) with ethylene propylene rubber (EPR), prepared through solvent casting, show no phase separation in the melt. Upon cooling, phase separation takes place in the vicinity of crystallization temperature of sPP. The phase diagram of the sPP/EPR blend is essentially an overlap of an upper critical solution temperature (UCST) and the melting temperature of sPP in the blends. In the case of sPP/ethylene propylene diene terpolymer (EPDM) blends, a lower critical solution temperature (LCST) was observed in the melt, i.e., about 30 K above the UCST. Vulcanization has been undertaken in the single phase using dicumyl peroxide (DCP) for EPR and DCP or phenolic resins for EPDM. Temporal evolution of structure factors and the emergence of phase separated domains in these blends have been investigated by time-resolved light scattering and optical microscopy. The temporal evolution of structure factors has been analyzed in the context of nonlinear dynamical scaling laws to elucidate mechanism(s) of vulcanization induced phase separation (VIPS) of sPP/EPR blends.
Determining Crack Growth Measurements for the Tear Resistance of Polyethylene Film
Two methods are currently used to evaluate the tear resistance of polyethylene films, the Elmendorf and Dart tests. Often times these tests yield contradicting results, leaving much information to be desired on the properties of the film. Two tests that may provide more useful information are the Single Specimen J-Integral analysis and Crack-Tip Opening Displacement method. One important area in the determination of tear resistance is the measure of crack tip growth. It is crucial to observe and measure the growth of the initial crack as it is loaded constant extension. This was one of the main focal areas in development of the proper testing protocol.
A New Approach to Determining the Boundary between the Liquid and Gelatinous Zones in a Pultrusion Die
The aim of this investigation is to propose an approach for the determination of the degree of cure at the gel point for a high reactivity amine cured epoxy pultrusion resin. To determine the gel time of the resin, two standard techniques have been adopted, with some modifications to suite the needs. The first is ASTM D-3056, Standard test method for gel time of solventless varnishes, and the second is ASTM D-4217, Standard test method for gel time of thermosetting coating powder. The results from these methods yielded a linear relationship, which is defined by kinetic theory. Secondly, the isothermal degree of cure profile's, are calculated from the kinematics equation. Using the two sets of data, the degree of cure at the gel point was found to be 54%. This result is verified using Flory's classical approach, which gave a degree of cure at the gel point of 58%. The degree of cure at the gel point can then be used as a fundamental parameter to model the pultrusion process.
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