SPE Library
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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Conference Proceedings
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.
Permeability Measurement of Polymers and Layered Silicate Nanocomposites
The limited chain packing capability of polymer chains make the barrier properties of polymers significantly poor compared to other materials like ceramics and metals. However large-scale processability, flexibility and relative economy of use, make plastics the material of choice. The advent of organic LED based displays and the concomitant loss of product functionality by the exposure to oxygen and water vapor, make improved barrier substrates, a necessity. Separately, layered silicate structures have shown promise for barrier properties of nylon in particular. Its high aspect ratio (1:1000) creates a tortuous path for penetrant molecule resulting in improvement in barrier properties. More recent results indicate that chemical interactions may further improve the barrier properties of these systems. Therefore in our first paper, we determine the barrier properties using helium to determine purely tortuous path effects. Finding absolute permeability of plastic has always been the difficult task for the scientists. We have developed a system to measure the permeability of gasses through thin flexible substrates. This paper provides a background to our method and its application to three nanocomposite systems namely exfoliated nylon 6, immiscible macro-aggregated PETG-15A and intercalated PETG-20A nanocomposites. X-ray diffraction was used to study the dispersion in all the nanocomposites.
Liquid Permeation of Elastomers with a Fully Flooded Cell Test Method
A fully flooded, liquid permeation cell was developed to provide a convenient method to evaluate the barrier performance of nonporous films, membranes, and other thin sections against organic liquids. Previously established test methods for determining the resistance of nonporous materials to permeation by liquids tend either to be cumbersome or relatively slow and insensitive due to partial coverage of the test material by the liquid. This paper will describe the apparatus and method based on the complete coverage of the test material with the organic liquid challenge. Of particular interest to the Army is the permeation resistance of elastomeric materials to chemical warfare agents (CWAs) and their simulants. A simulant suitable for determining the effectiveness of a diffusion barrier should exhibit permeation directly relatable to that observed for the highly toxic CWA in a wide range of materials. This paper will also describe the criteria used in the selection of simulants and the subsequent testing of elastomers with the developed method to derive a CWA-simulant correlation for these barrier materials.
Effects of Nanoparticle Morphology on the Permeation and Physical Properties of Polymer Nanocomposites
Exfoliated graphite nanoparticles (EGN) have the potential to be a low cost, high performance reinforcement for polymers due to their platelet structure and predicted physical properties. Thermoplastic films were prepared containing different EGNs at different loading levels. Barrier and physical properties of these EGN/polymer nanocomposite films were then compared to similar nanocomposite films having either comparable filler morphology, such as smectite clays, or similar chemical composition, such as carbon nanotubes and conventional carbon black. Barrier testing included permeation of selected organic permeants, water vapor, and oxygen utilizing a number of different vapor and liquid permeation methods. Relationships between the properties of the nanocomposites and the nanoparticle composition and morphology are presented.
The Effect of Montmorillonite Layered Silicates on the Properties of Ethylene Co-Vinyl Alcohol Blown Film Nanocomposites
Ethylene co-vinyl alcohol (EVOH) nanocomposites incorporating montorillonite layered silicates (MLS) were examined in this study. EVOH with 3% MLS loading was melt compounded and later extruded into blown film. The morphology, as well as mechanical and thermal properties were examined. Morphology analysis confirms an intercalated system, with a higher degree of dispersion and alignment in the blown film as opposed to the compounded material. Thermal analysis shows an improvement in thermal stability with the addition of MLS. An increase in Young's modulus is also observed in the nanocomposite film.
Effect of Fiber Source on Cellulose Reinforced Polymer Nanocomposites
Cellulose microfibrils obtained by the acid hydrolysis of cellulose fibers obtained from different sources were added at low concentrations (2-10% w/w) to polymer gels and films as reinforcing agents. Significant changes in mechanical properties, especially maximum load and tensile strength, were obtained for fibrils derived from several cellulosic sources, including cotton, softwood, and bacterial cellulose. For extruded starch plastics, the addition of cotton-derived microfibrils at 10.3% (w/w) concentration increased Young's modulus by 5-fold relative to a control sample with no cellulose reinforcement. Preliminary data suggests that shear alignment significantly improves tensile strength. However, addition of microfibrils does not always change mechanical properties in a predictable direction. Whereas tensile strength and modulus were shown to increase during addition of microfibrils to an extruded starch thermoplastic and a cast latex film, these parameters decreased when microfibrils were added to a starch-pectin blend, implying that complex interactions are involved in the application of these reinforcing agents.
Harnessing Natural Polymers and Fibers for the Development of Biocomposites
Economic and environmental forces are providing an impetus for the development of biocomposites from renewable agricultural byproducts. In pursuit of this goal, we are developing biocomposites from wheat-, kenaf-, and corn-byproducts without external additives. Our differential scanning calorimetry (DSC) measurements suggest that micronized wheat straw and inner kenaf fibers have similar thermal characteristics at 50°C < T < 400°C, thus they can be co-processed. The flexural strength of the composites formulated from micronized wheat straw and kenaf fibers increases as the concentration of straw in the composite increases. Postcuring the composites at 190°C also decreases the strength.
Characteristics and Performance of Starch-Poly- (Vinyl Alcohol) (PVA) Blends with Agricultural Waste Fiber
The renewable polymers are environmentally friendly and naturally biodegradable, and could serve as an inexpensive source of raw material for single-use engineered products. Efforts are underway to develop ecocompatible consumer plastics by incorporating renewable polymers as an alternative to petroleum-derived chemicals. Therefore, gaining fundamental understanding of biobased polymers is critical for the design and development of consumer products. The research efforts at the USDA laboratory pertaining to the development of biopolymer blends, polymer processing, characterization and lifetime evaluation are presented.
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