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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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.
Novel Solvent-Free Method for Functionalization of Polyhydroxyalkanoates: Synthesis and Characterizations
Functionalization of PHB was successfully achieved by free radical grafting of maleic anhydride using a peroxy initiator by reactive extrusion processing. The crystallization behavior and morphological changes in the PHB upon maleation were followed from the DSC, TGA, FTIR and Optical Microscopy measurements. The presence of succinic anhydride groups was substantiated by stretching vibration at 1782 cm-1 in FTIR. For maleated sample the Tm and Tc decreased up to 20 degree celsius and 10 degree celsius, respectively, indicating a decrease in its crystallinity and rate of crystallization. Decrease in the crystallinity was quantified from the enthalpy of melting (Tm endotherms). These trends were further substantiated by reduction in the crystallinity sensitive peak at 1185 cm-1 in the FTIR spectrum. Moreover, larger the graft degree smaller is the spherulite size and slower is their growth rate as observed in the optical micrographs. Disordered spherulite structure upon maleation also implies the structural changes in the polymer backbone, imperfect crystal formation. These functionally modified PHB can be used as modifiers for variety of applications.
Effect of Heat-Sealing Temperature on Mechanical Properties at Heat-Sealed Parts in Biodegradable Plastic Film
The heat-sealing machine is a vital tool in plastic bag manufacture. Processing conditions such as heat-sealing temperature and pressure greatly affect mechanical properties of the heat sealed part. In this study, the mechanical properties of the heat sealed part of a biodegradable plastic film were examined. Based on the results obtained from peeling test, circular notch tensile test and DSC measurement, the optimum heat sealing was established at 130-135 °C. The mechanical properties of the heat seals decreased with increasing heat sealing temperature.
Morphological and Functional Properties of Acetylated Starch Foams Extruded with Cellulose
Starch acetates with degrees of substitution (DS) of 1.68 and 2.3 were extruded with 10, 20 and 30% (w/w) cellulose and 20% (w/w) ethanol in a twin screw extruder at 150, 160 and 170 °C barrel temperatures with 170, 200 and 230 rpm screw speeds. X-ray diffractogram (XRD), differential scanning calormetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the morphological properties of extruded foams. A central composite response surface design was applied to analyze the effects of starch type, cellulose content, barrel temperature and screw speed on specific mechanical energy requirement of extruding foams and the radial expansion ratio and compressibility of the extruded foams. XRD showed losses of DS starch and cellulose crystallinity and the formation of new complexes. FTIR spectra revealed that functional groups and chemical bonds were maintained after extrusion. Melting temperatures changed significantly when higher DS starch acetate was used. Cellulose content, barrel temperature and screw speed showed significant effects on thermal, physical and mechanical properties of extruded foams and the specific mechanical energy requirement.
Synthesis and Characterization of Nanopolymer: High Density Polyethylene
Here, we have reported the successful preparation of the smallest nanopolymer, high density polyethylene, which has a diameter of about 0.17 ?m (but the number average molecular weight is greater than 1,00,000). The success of obtaining very small nanopolymer opens the door to unprecedented applications of this fascinating material as a true 1D material. This nanopolymer is characterized using particle size analyzer, scanning electron microscopy, infrared spectroscopy, X-ray diffraction, viscoelastic properties, etc. Similar synthesis strategies, involving careful selection of desired conditions and smart manipulation of favorable thermodynamic properties could be extended for the preparation of various nanopolymers: low density polyethylene, polypropylene, polystyrene, etc. To the best of our knowledge, this is the first demonstration for a preparation of nanopolymer in the literature.
Synthesis and Characterization of Nano Polystyrene: Effect of Temperature, Shear Rate and Solvents
Polystyrene nanopolymer (Number average molecular weight greater than 1,00,000), which has a diameter of about 0.17 ?m is prepared for the first time. This observation is confirmed using scanning electron microscopy. Infrared spectroscopy, X-ray diffraction, viscoelastic properties, etc are used to characterize it. The novel technique produces nanopolymer within a range of 0.17 to 51 ?m measured by particle size analyzer. BET surface area shows its minimum surface area of 17.7 m2/gm. We have elucidated the thermodynamic parameters for formation of nanopolymer.
Scanning Electron Microscopy, Spectroscopy and Viscoelastic Studies of Nano Low Density Polyethylene
Low density polyethylene nanopolymer is characterized by scanning electron microscopy, particle size analyzer and BET surface to prove the formation of nanopolymer over a range of diameter from 0.17 to 70 ?m. BET surface area reveals that its mimimum surface area is 17.0 m2/gm. The findings prove that the small diameter low density polyethylene nanopolymer is proved to be able to show good properties without any confinement that limits its material dimensions. Infrared spectroscopy and X-ray diffraction studies are also used to characterize it.
Kinetics of Gas Sorption and Diffusion in Polymer-Clay Nanocomposites
Gas solubility and transport properties control cell structure during polymer foam processing. This study reports the sorption and diffusion kinetics of sub and supercritical CO2 gas in nanocomposites of poly(methyl-methacrylate) containing organically modified smectite clay. Various methods for preparing the PMMA-clay nanocomposites were investigated and a solution co-precipitation method was selected. PMMA-clay nanocomposites containing 2, 4 and 6 wt. % nanoclay loadings were prepared. Using wide-angle X-ray diffraction (XRD) and scanning electron microscopy (SEM) the resulting materials were found to have well dispersed intercalated clay structures. CO2 solubility studies at 45°C and pressures up to 60 atm using an in situ gravimetric technique were performed on compression molded films. From the results diffusion coefficients were determined using the appropriate transport models for these test conditions.
Moisture Resistant Nylon - Dimensional Stability
The effects of moisture absorption on dimensional stability and mechanical properties of various polyamide/polyolefin blends are being studied. The morphology of the blends has also been investigated by using transmission electron microscopy (TEM). Furthermore, the correlation between the morphology of the blends and their moisture absorption rate and dimensional changes upon absorbing moisture has been examined as well.Results of this investigation indicate the moisture absorption rate, dimensional stability and mechanical property retention of polyamide and polyolefin blends are strongly affected by the degree of compatibility of the blend. The finer the dispersion polyolefin particles, the slower the water absorption rate, and the lower the dimension changes after being equilibrated at 50%RH or 100%RH.
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