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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Effect of Freeze-Drying on the Glass Temperature of Cyclic Polystrenes
The calorimetric glass temperature was measured for three cyclic polystyrenes with apparent molecular weights ranging from 4.0 x 103 to 195.5 x 103 g/mol for both bulk material and for samples freeze-dried from dilute solution. Freeze-drying from dilute solution was found to reduce the glass temperature by 7 to 14 K depending on the sample. These Tg depressions are 5 to 12 K greater than those found previously for freeze-dried linear polystyrene. Annealing at 403.2 K and 443.2 K (130 °C and 170 °C) resulted in recovery of the Tg back to the bulk value with the time scales depending on both temperature and the magnitude of the Tg reduction; the low apparent activation energy dependence of the recovery of Tg precludes its being due to viscous flow.
Modeling the Yield Behavior of Glassy Networks using Molecular-Based Parameters
Recent findings suggest that the yield behavior of glassy networks is governed primarily by two molecular based parameters. The first of these parameters is the glass transition temperature, Tg, and reflects the network stiffness including backbone stiffness, crosslink density, crosslink functionality, and other inter and intra-molecular interactions. The second of these parameters is the cohesive energy density, Ecoh, reflects the cohesive strength of the network. In this paper, we present a framework to incorporate these parameters in a molecular-based yield model. We extend the framework to include alterations in temperature, strain rate, stress state, and molecular composition (through these parameters). We also outline current experiments to evaluate the limits and capabilities of the hypothetical model presented and summarize recent findings.
The Temperature Dependent Viscoelastic and Viscoplastic Properties of Nylon 12
We report the viscoelastic and viscoplastic properties of Nylon 12 by treating the polymer as an equivalent network of chains bridged by temporary junctions (entanglements, physical cross-links and lamellar blocks). The network is thought of as an ensemble of meso-regions linked with each other. Tensile tests were carried out with constant crosshead speeds (ranging from 5 to 200 mm/min) from 35 to 140°C using a tensile test machine with an oven attachment. Stress strain relations for uniaxial deformation were developed by using thermodynamic principles. These governing equations involve two material constants that were derived by fitting the experimental observations. Good agreement was obtained between the numerical simulation and experimental data. These results will be used as a basis for characterizing the bending prior to thermoforming of Nylon 12 automotive tubing.
Finite Element Analysis of Hyperelastic Materials: Elastomeric Seal
Seals are critical components in virtually all mechanical devices, which are used for closing the gap and/or to separate two liquids or gasses in static or dynamic applications. But the complexity of seals and the difficulties associated with resolving essential parameters, both material and geometric, have hindered the effectiveness of experimental and theoretical understanding of seal design. The present paper describes the axisymmetric analysis of elastomeric seals at medium strain (strain less than 100%) under static and dynamic conditions using Abaqus software. The stress strain behavior of a black filled ethylene propylene (EPDM) rubber are studied in extension over a range of temperature to examine the validity of Arruda-Boyce, Mooney-Rivlin, Neo-Hooke, Ogden, Polynomial, Reduced polynomial, Van der Waals and Yeoh models. The analytical form for strain energy density function of Arruda-Boyce model gives a very good fit to the experimental data for strains less than 100%, which cover the range of interest for most engineering applications.
Review of the Ultrasensitive Oxygen Consumption Method for Making More Reliable Extrapolated Predictions of Polymer Lifetimes
Predicting polymer lifetimes in air is often based on unconfirmed extrapolations of elevated-temperature Arrhenius behavior. To improve confidence in such extrapolations, we describe an ultrasensitive oxygen consumption approach. Measurements are made at elevated temperatures to confirm correlation between activation energies (Ea) for consumption and conventionally measured properties (e.g., mechanical). In addition, the sensitivity of the consumption approach allows measurements to be made in the lower-temperature extrapolation region, thereby testing whether the hightemperature Ea remains constant.
Real-Time Synchrotron X-Ray Techniques for Polymer Processing Research
The Advanced Polymers Beamline (X27C) at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory (BNL) was commissioned in January 1997 by Ben Hsiao and Ben Chu from the State University of New York at Stony Brook (SUNY-Stony Brook). This facility is the first synchrotron facility in the United States dedicated to chemistry/materials research (with emphasis on polymers) using combined small-angle x-ray scattering (SAXS) and wide-angle x-ray diffraction (WAXD) techniques. Today, X27C has become a major workhorse serving the U.S. polymer community for time-resolved and in-situ x-ray scattering and diffraction studies. The primary focus of the X27C beamline is to investigate polymer structures, morphologies and dynamics from atomic, nanoscopic, and microscopic to mesoscopic scales in real-time and/or in-situ using SAXS and WAXD techniques. Selected examples of studies carried out in X27C include characterizations of nanocomposites, crystallization, melting and phase transition of polymers, polymer melts and solutions during shear, fiber formation and deformation, high pressure study under supercritical conditions, biopolymers, organic/inorganic hybrid nanocomposites and supramolecular structured biological molecules. In this presentation, we will focus on the current research opportunities of using real-time synchrotron techniques to assist varying polymer processing research.
Some Recent Developments in Melt Rheometry
The linear viscoelastic behavior of the melt provides a wealth of information concerning the structure of a highly-entangled polymer and is widely used to characterize polyolefins. Long-time relaxation processes are most sensitive to molecular structure but are difficult to probe in the case of polymers with broad molecular weight distributions or long-chain branching. By combining complex modulus data with creep/creep recovery data using a continuous relaxation spectrum one can often reach the terminal zone even when this zone is inaccessible using standard techniques. Nonlinear viscoelascitity plays an important role in many melt processing operations, but the characterization of nonlinear behavior poses major challenges for the rheologist. The sliding plate rheometer has proven valuable for establishing nonlinear behavior in shear and for the study of wall slip and melt rupture. A new extensional rheometer designed as an accessory for a standared rotational rheometer has also been evaluated.
The Use of Rheology to Characterize the Branching Structure in Sparsely Branched Metallocene Catalyzed Polyethylenes
A series of six commercial polyethylenes are investigated including four metallocene catalyzed (mc) PE resins having varying degrees of long-chain branching and narrow MWD and a LDPE and a LLDPE. The degree of branching (i.e. the number of long chain branches per 10,000 carbon atoms) is estimated via dilute solution light scattering measurements. However, whether the branching in the mc PE's is random or concentrated on a few chains cannot be assessed by means of dilute solution measurements. Shear and extensional viscosity measurements along with the use of molecular theory are employed to determine which is the most likely scenario.
Real-Time Monitoring of Mass-Change during the Structural Evolution of an Epoxy Glass Subsequent to Relative Humidity Jumps through the Glass Transition
The structural recovery response of an epoxy resin subjected to relative humidity (RH) and carbon dioxide (PCO2) jumps has been investigated by the real time monitoring of the mass change. Results show that, the structural recovery phenomenon is qualitatively similar to that observed by volume change measurements and also qualitatively similar to results obtained after temperature jumps (T-jumps). In addition, sorption/desorption measurements during up- and down-jumps in relative humidity are the first demonstration of the real-time monitoring of mass-change during the structural evolution of a glassy epoxy subjected to plasticizer jumps.
Applications of Nanostructured Carbons in Polymer-Based Materials
Nanostructured carbons include carbon nanotube, carbon nanofiber and carbon black. Their incorporation in polymer matrices allows practical applications. Evaluation of the feasibility of the applications required comparison with competing materials in terms of cost and performance. The evaluation provided in this paper shows that nanostructured carbons in polymer-based materials are suitable for electromagnetic, electrochemical and thermal applications, such as shielding, battery electrodes and thermal pastes for microelectronic cooling. A limited structural application in the area of vibration reduction is also feasible.
Mechanical Properties of Multiwalled Carbon Nanotube-Epoxy Nanocomposites
Epoxy-multi wall carbon nanotube composites have been fabricated. By choosing two different curing agents, both hard, rigid epoxy and soft, flexible rubbery matrices have been investigated. Since multi-walled nanotubes have a high strain to failure originating from telescopic deformation, the influence of matrix strain was examined. The concentration dependence of the nanotubes was examined by comparing two concentrations- 1wt% and 4wt%. Dynamic mechanical tensile tests using a three-point bend geometry was utilized to probe the glass transition, and plateau modulus effects of the material. Separate tensile tests showed that increasing filler concentration increases Young's modulus and decreases percent elongation to break for both rigid and flexible samples. Both rigid and flexible epoxy/nanotube composites have higher ultimate tensile strength and lower percent elongation to break than corresponding epoxy matrices. Flexible epoxy/nanotube composites however showed a larger percent increase in ultimate tensile strength and smaller percent decrease in elongation to break than rigid matrices supporting the concept that the strain match of the matrix is vital to effect multiwalled nanotube composites. SEM of the fracture surfaces showed fiber pullout to be the dominating failure mechanism.
Investigation of Reinforcement Mechanisms of Carbon Nanotube-Polymer Composites with Numerical Simulation
The tensile modulus of carbon nanotube reinforced polymer composites was calculated with 3-D Finite Element Method. The effects of nanotube orientation and nanotube agglomeration on tensile modulus of the composites were investigated. The simulation results show that the tensile modulus of a nanotube reinforced composite drops sharply either when the nanotubes diverge from the applied load direction, or when the nanotube agglomerations are formed. This finding could explain why the predicted tensile modulus of a nanotube composite, based on the assumption that the nanotubes are fully isolated and aligned in polymer matrix, is much higher than the values obtained from experiments.
Effects of Free-Surface and Interfacial Effects and Plasticizer Content on the Distribution of Glass Transition Temperatures in Nanoconfined Polymers
A novel fluorescence/multilayer method has been developed allowing the first determination of the distribution of glass transition temperatures (Tg) in thin and ultrathin polymer films. The perturbation in polymer dynamics associated with Tg near a free surface of a polymer film, leading to a lower Tg at the surface, affects the local Tg several tens of nanometers into the film. The extent to which the Tg dynamics smoothly transition from enhanced to bulk states depends strongly on nanoconfinement. However, the impact of nanoconfinement on Tg is also a strong function of plasticizer content and attractive interactions at a polymer-substrate interface. The potential of these studies for understanding polymer nanocomposite behavior is discussed.
Effect of Montmorillonite Layered Silicate (MLS) on Crystallization Growth Rate in Semi-Crystalline PET Nanocomposites
The influence of montmorillonite-layered silicates (MLS) on the isothermal and non-isothermal crystallization and growth rates of semi-crystalline PET is investigated. The non-isothermal DSC measurements show that the cold crystallization temperature decreases with increasing concentration of MLS. A concomitant decrease in melting temperature and enthalpy shows that this decrease is not a result of the increased crystallinity in the PET. Therefore it is clear that the surface area afforded by the MLS platelet leads to changes in the metastable fraction of polymer that is more responsive to thermal energy. The isothermal Avrami analysis shows that the crystallite shape is not affected by MLS but the growth rate is significantly affected. For low concentrations, the growth rate increases but additional MLS concentration then inhibits the growth.
Epoxy + Montmorillonite Nanocomposite Processing Influences on Dispersion
Alkyl ammonium treated montmorillonite used in conjunction with polymer matrices has shown promising results for improved strength, barrier properties and dimensional stability at temperatures higher than the matrix phase. Here we investigate the effect of montmorillonite concentration and premix temperature on dispersion of the clay platelets into the matrix. It is found that for an epoxy cured by alkyl amines, a critical concentration is obtained at 2.25% montmorillonite by weight when the premix temperature is 80 degrees. If the temperature is dropped to 75 degrees the kinetics reflect an micelle like transition.
Combining Mechanics and Chemistry to Generate Controlled Nano-Scale Topography in Polymer Thin Films
We have used a plasma-mediated cross-linking process to generate patterns on polydimethylsiloxane (PDMS) thin film surfaces. The method is fast, inexpensive, and can be uniformly applied to macroscopically large areas in a single procedure. Exposure of pure spin-coated PDMS (150 – 700 nm thick) to an argon plasma leads to the formation of a siloxane network in the near-surface region, as confirmed by surface spectroscopy measurements. This silica-like surface layer is put into compressive stress when the sample cools after removing it from the plasma chamber due to differential thermal contraction, generating a wrinkling pattern to reduce the stress. The wavelength, amplitude, and pattern characteristics are controlled by modifying the plasma conditions, the initial PDMS film thickness, and the PDMS molecular weight. Atomic force microscopy is used to study the nano-scale topography as a function of these parameters.Features with wavelengths from 300 nm to ~ 5 ?m have been produced, with peak-to-peak amplitudes ranging from < 30 nm to over two microns. Comparison to recent analytic models of the wrinkling of compressively stressed films provides a theoretical framework for the results, and suggests means of achieving smaller features. We use these models to explore the lower bounds on the pattern dimensions imposed by alternate strain relief mechanisms such as plastic deformation and viscous dissipation.The relationship between wrinkle amplitude and wavelength is found to be PDMS molecular-weight dependent, suggesting that the compressive strain is larger for the siloxane networks of 3780 molecular weight PDMS than for the 116,500 molecular weight PDMS; i.e. the thermal expansion coefficient is larger for the smaller molecular weight. Also, application of a “crumpling” model to determine the total elastic energy stored in the wrinkles suggests that less energy is stored in the wrinkles of longwavelength features, indicating that energy may be dissipated during compr
Mapping Polymeric Properties using Combinatorial and High-Throughput Methods: Adhesion and Mechanical Properties
The NIST Combinatorial Methods Center (NCMC) develops Combinatorial and High-Throughput (C&HT) methods for material properties measurements. C&HT methods combine experiment design, instrument automation, and computing tools to form a new paradigm for scientific research. Through this combination of disciplines, combinatorial methods provide a faster and more comprehensive exploration of complex parameter spaces. Given this premise, the C&HT concept is being adapted by the NCMC to achieve similar benefits in materials science.The pharmaceutical and geneomics industries have benefited from utilizing combinatorial techniques for the discovery of new products. However, the C&HT methods developed for the pharmaceutical industry often cannot be applied directly to materials research since methods for generating materials libraries and for rapidly measuring properties, especially adhesive or mechanical properties, are often lacking.A current focus of the NCMC is the development of novel high-throughput platforms for both adhesion and mechanical property testing. This presentation will describe four different C&HT methods that have been developed at NIST specifically to fill the need for adhesive and mechanical properties testing platforms.
Characterization of the Transport Properties in Elastomeric Polymer Membranes by FT-IR-ATR
In order to understand membrane transport and thereby develop suitable membranes for protection and separation, there are a few characteristics of the membrane and the diffusing constituents that must be known. These include the molecular states of the diffusing components, their diffusion coefficients, permeabilities and the membrane selectivity. In general, the fundamental physical property required to design and optimize polymers used as barrier and membranes is the mutual diffusion coefficient.The FT-IR-ATR (Fourier Transform Infrared Attenuated Total Reflectance) technique offers the advantage of allowing polymer-penetrant interactions to be identified as well as allowing the transport two or more diffusing species to be monitored. The basic FT-IR-ATR Fickian diffusion model developed by Barbari and Fieldson was applied to the resultant data.In this paper, FTIR-ATR spectroscopy was used to measure the effective diffusion coefficients of acetonitrile in a series aliphatic polyurethanes and a series of sulfonated triblock co-polymer films. For the polyurethane elastomers, the effect of varying isomer structure at a fixed hard segment content on the diffusion of acetonitrile was examined with FTIR-ATR spectroscopy. The results show a clear dependence on the chemical structure of the hard segment. In the case of the sulfonated triblock co-polymer, the increasing the sulfonation level leads to the ability of the membrane to transport water and other polar molecules through the film.
Permselectivity Measurements of Ion Beam Modified Barrier Membranes for Improved Chemical/Biological Protective Clothing
Elastomeric materials have commonly been used over the years to provide barrier properties in chemical/biological (CB) protective clothing. One novel approach to reducing the weight of CB protective clothing is based on the use of selectively permeable membranes. The ideal permselective membrane for CB protective garments would provide a high moisture vapor transport rate while providing extremely low to negligible transport rates of hazardous chemicals and biologicals. The goal of the work reported in this abstract is to improve the permselectivity of membranes through the ion beam modification of their surface layers. Measurement of permselectivity was made through a vapor permeation method. A wide variety of untreated and ion beam modified commercially available membrane materials were tested as functions of activity level for water and a number of organic compounds. The variables initially investigated included ion type and irradiation energy level. Irradiation generally decreased permeation of both water and organic compounds, but measurements suggest that the organic compound permeation was decreased to a higher degree, thus increasing permselectivity. This effect is significantly more pronounced in certain modified membrane chemical structures when compared to others. This paper primarily addresses the ion beam modification process and the vapor permeation method utilized to determine permselectivity.
Ultra-Low Permeation Test Method for Fuel System Applications
The new and more stringent regulations due in the USA by 2004 call for technical development on both fuel barrier structures and on innovative fuel system designs. They also require new techniques to evaluate emissions from such high performance systems. An experimental technique is described which can measure permeability factors on material samples such as films or plates. In-depth analysis of the technique reveals significant benefits, which makes it a powerful tool to evaluate and compare complex system components such as sub assemblies or large parts such as fuel tank shells. When combined with a gas chromatography, this tool offers an additional advantage of being able to determine the hydrocarbon types permeating from the system. This can be an advantage in developing green" for fuel systems which can control the emissions of toxic and reactive hydrocarbons.
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