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Conference Proceedings

Effect of Clay Surface Modification on the Polymer Nanocomposite Foam Structure
Xiangmin Han, Changchun Zeng, Maxwell J. Wingert, L. James Lee, Kurt W. Koelling, David L. Tomasko, May 2004

Nanoclay can work as a nucleation agent to control foam cell structure and reinforcement to enhance foam properties. In this paper, the clay surface is modified by a reactive quaternary ammonium surfactants and grafted with either poly(methyl methacrylate) (PMMA) or polystyrene (PS). The polystyrene and the polymer modified clay nanocomposites are synthesized by in-situ polymerization and extrusion compounding. By using CO2 as the foaming agent, the nanocomposite foams are prepared in a single screw extruder. It is found that the surface modification has a great influence on the foam morphology. The presence of more CO2-philic PMMA on the clay surface leads to a lower melt viscosity.

Graphene Nanoplatelet Reinforced Polymer Coatings
Shing-Chung Wong, Eric M. Sutherland, Fawn M. Uhl, Suchitra Yerramaddu, Dean C. Webster, Bor Z. Jang, May 2004

Fabrication of carbon nanotubes is expensive, particularly for the purifying process required to make useful nanotube polymer composites. Instead of trying to discover lower cost processes for nanotubes, we seek to develop an alternative nanoscale carbon material with comparable properties that can be produced cost-effectively and in larger quantities for composites applications. This new class of nano material is herein referred to as nanoscale graphene plate (NGP). This paper introduces the novel processing ideas for NGP and some mechanical and electrical properties of the NGP reinforced polymers.

Melt Rheology of Polylactides
John R. Dorgan, Jay Janzen, Dan Knauss, Birgit Braun, May 2004

Polylactides (PLAs) have been known for several decades and have recently gained considerable commercial significance. This development makes it urgently desirable to have the rheological properties of these materials well-characterized. In this study, rheological and thermal measurements were made on a comprehensive and well-characterized set of homopolymers and copolymers spanning wide ranges of molecular mass and stereoisomer proportions. Temperature dependencies of the time-temperature superposition curves were obtained. Data were correlated utilizing a viscoelastic model enabling the development of a simple Excel spreadsheet for predicting linear viscoelastic properties as a function of molecular weight and temperature.

Novel Controlled Drug Release Biodegradable Polymers Systems
Freddy Y.C.Boey, Subbu S.Venkatraman, J. Pan, L.P. Tan, May 2004

Biodegradable polymers, in particular polylactide and polyglycolide systems, having started out predominantly in the degradable sutures market, are now finding increasing use for controlled drug delivery and tissue engineering, where their use as temporary substrates or devices provides significant therapeutic advantages. The idea of using them as micro particles to prolong delivery of drugs have already been commercialized. This paper describes some work focusing on using these polymers as novel structures for localized and multiple drug delivery. The development of a dual drug eluting stent will be described to treat stenosis of coronary blood vessels, pulmonary airways or urological passages. The stents are inserted non invasively into and anchored to be resident in the body for a prescribed period to release drugs according to a prescribed profile and bio-erosion rate, hence eliminating the need for a second surgical procedure. Another application presented is the development of novel copolymers of PLA particles with stealth ability to evade the immune system and hence achieve protracted blood lifetimes, allowing efficacious therapy in especially cancer treatment. With suitable modifications, such nanoparticles may also be made to act as non-viral gene vectors to be used in delivering gene payloads to the nucleus.

Mechanical Responses in Biomimetic Polymer Hydroxyapatite Nanocomposites
Kalpana S. Katti, Phanikumar Turlapati, May 2004

In situ composites of hydroxyapatite (HAP-the mineral component of natural bone) were synthesized in our previous work. The in situ composites exhibit improved recovery and smaller plastic strains than the ex situ composite systems. The role of synthetic macromolecules in controlling the mineralization of HAP is shown to be the primary reason for the improved mechanical responses in these material systems. The control of macromolecules on mineralization of HAP and resulting bulk properties of the composite are similar to that of collagen in natural bone. This process thus represents a biomimetic method for control of mechanical responses in polymer-HAP composites. Mechanical responses of the composite after soaking in a simulated body fluid (SBF) are investigated using X-ray diffraction, scanning electron microscopy and infrared spectroscopy. Superior response of the composites (higher modulus and strength) is observed under SBF as compared to soaking in water. Response of these composites under strain rates typical for human bones is also investigated

Degradation Studies of PLA Films Grafted with Hydrophilic Polymers
Amol V. Janorkar, Douglas E. Hirt, May 2004

Poly(lactic acid) (PLA) is being investigated vastly due to its biodegradable and biocompatible nature. However, the degradation of PLA is slow, often leading to a long life-time in vivo. The major objective of this research is to modify PLA film surfaces with the ultimate aim of making a bioactive surface that will show faster degradation. The PLA film was solvent cast and the film surfaces were grafted with poly(acrylic acid) (PAA) using a UV induced photopolymerization process. The films were incubated in different pH solutions, viz., pH = 4, 7, and 10, for a specified time period. The film resulting from each treatment was analyzed using Transmission-FTIR spectroscopy and Atomic Force Microscopy (AFM). The molecular weights of the films were measured using gel permeation chromatography (GPC). Results established that faster degradation of the PLA film when incubated in different pH solutions could be achieved by surface modification of the PLA film by grafting PAA.

The Comparitive Role of Relaxation and Forced Retraction on the Structural Organization Processes in Uniaxially Stretched PLA Films from Amorphous Precursors
Jake H. Mulligan, Miko Cakmak, May 2004

Extrusion cast poly(lactic acid) (PLA) films were stretched uniaxially in the rubbery state while their optical and mechanical behavior were monitored with our on-line stretch birefringence instrumentation.If the films are stretched fast they exhibit nematic order as also reflected in the negative deviation from linearity in stress optical behavior. This structure was found to eventually convert to oriented ?-phase crystalline form if sufficiently long time is allowed for relaxation If, on the other hand, a rapid slight retraction is employed, this conversion form nematic order oriented crystalline order is accelerated. This significant behavior strongly supports the use of retraction stages in processes that utilize uniaxial and biaxial stretching.

Deformation Processes of Single-Wall Carbon Nanotubes in Composites
Robert J. Young, Marcel Lucas, May 2004

Raman spectroscopy is a technique widely used to study the vibrational modes of carbon nanotubes. The low-frequency Radial Breathing Modes (RBMs) are frequently used to characterize carbon nanotube samples. We report a Raman spectroscopic study on the strain-induced intensity variations of the RBMs of Single-Wall Carbon Nanotubes (SWNTs) in epoxy/SWNT composites. The RBM intensities have been found to vary significantly over a range of strain between -0.3% and 0.7%. The trend (increase or decrease) as well as the magnitudes of the intensity variation depends on the nanotube diameter and its chirality. Using tight-binding calculations, we have shown that these intensity variations can be explained entirely by resonance theory. Electronic density of states calculations confirm that the energy separation between the Van Hove singularities shifts with strain. The nanotubes are thus moved closer or further away from resonance, causing the intensity variations. It is demonstrated that through the use of resonance theory, a tentative chirality can be assigned to each type of SWNT from knowledge of its RBM position and the effect of strain upon the RBM intensity, thus determining its entire structure.

On the Tearing Toughness and Permeability Modelling of Polymer Nanocomposites
Y.-W. Mai, J.S.S. Wong, R.K.Y. Li, C. Lu, May 2004

This paper presents preliminary studies on two aspects of nylon-based nanoclay composite films: their out-of-plane tearing fracture resistance and moisture diffusion characteristics. Attempts to analyze the out-of-plane tearing fracture based on the essential work of fracture analysis will be presented. Also, theoretical modelling of the permeability of these polymer nanocomposites is also presented which takes into account the degree of exfoliation, orientation, aspect ratio and volume fraction of the nanoclay sheets; crystallinity of polymer matrix; and the affinity of polymer and clay with the diffusing species. Comparisons with published permeability data are given.

Remote Strain-Sensor Coatings Based upon Carbon Nanotube-Polymer Composites
Robert J. Young, Jérôme Halary, John L. Stanford, Peter A. Lovell, May 2004

Nanocomposites and nanostructured polymers with unique opto-mechanical properties have been developed as smart coatings for use in a novel, high resolution, and non-contact strain-measuring application. Remote polarized Raman spectroscopy has been used to monitor optical strain sensitivity of deformed coatings (deformation micromechanics), and determine local strains on the micron scale directly from stress/strain induced Raman band shifts. The research is aimed at providing a novel high-resolution non-contact technique for the determination of surface stresses and strains in a wide variety of engineering components used in both laboratory and in-the-field (external) applications.

Some Studies on Montmorillonite (MMT) Filled Polypropylene Composite Systems
Robert K.Y. Li, Dean Shi, May 2004

In this presentation, two aspects of PP/MMT composite systems will be addressed. In the first part, the effect of using MMT particles as the initiator carrier in the melt grafting reaction of maleic anhydride (MAH) onto polypropylene backbone will be presented. It was found that using this method; the degradation of the PP molecular chains can be significantly reduced. In the second part, a method of improving the dispersion of MMT particles in PP/MMT nanocomposites will be presented. This new method involves the pretreatment of MMT particles with PVA, and our results show that the method is effective in improving the dispersion of MMT particles in PP matrix.

Importance of Concomitant Strengthening and Toughening in Nanoclay-Reinforced Polymers
Shing-Chung Wong, Ling Chen, Chaobin He, Xuehong Lu, May 2004

Fracture properties and deformation mechanisms of nanoclay reinforced polypropylene (PP) modified with maleic anhydride were investigated. Elastic-plastic fracture mechanics was employed to characterize the toughness in light of substantial post-yield deformation for the reinforced maleated PP. Upon introduction of 2.5 wt% clay loading, it was observed that tensile strength, modulus and fracture initiation toughness concomitantly increased substantially. Continued increase in clay loading only led to stiffening and strengthening effects to the detriment of fracture toughness. Deformation mechanisms were examined using electron microscopy and small angle X-ray scattering.

Drawing of Nylon 66 Fibers in the Presence of Supercritical Carbon Dioxide
Xianbo Hu, Alan J. Lesser, May 2004

The drawing behavior and mechanical properties of as-spun and highly oriented nylon 66 fibers drawn in supercritical carbon dioxide (SCCO2) were studied. Conditions including different temperature, CO2 pressure and plasticizers with different polarity were systematically investigated. Results show that CO2 is an efficient plasticizer for as-spun Nylon 66 fibers as shown by decreases in the draw stress. In contrast, CO2 shows only a slight influence on the drawability of highly oriented nylon 66 fiber. The effect of other plasticizers such as water, methanol, and ethanol on the drawability of nylon 66 fibers is very similar to that of CO2. Tenacity and modulus of one-stage drawn fibers are less than 0.8GPa and 5.0GPa. Fibers with highest tenacity and modulus 0.96GPa/5.04GPa, 1.06GPa/5.04GPa were obtained by two-stage drawing in SCCO2 from as-spun and drawn nylon 66 fibers respectively. The main reason for the extremely low draw ratio (less than 6.0) of nylon 66 fibers is the hydrogen bonds in crystalline phase.

Shear-Induced Migration of Glass Beads during Injection Molding in Filled Polymer Compound and its Effect on Mechanical Properties and Electrical Conductivity
Chang Min Hong, Sadhan C. Jana, May 2004

Filler particles tend to migrate in non-uniform shear fields such as during mold filling of polymer compounds from the regions of high shear stress to low shear stress. In this paper, the extent of shear-induced migration during injection molding was studied in polymer compounds of polypropylene and polystyrene with glass beads of 42 and 203 ?m average diameter. The distribution of particles in the cross-sectional planes of injection molded specimens presented evidence of significant migration of glass bead particles from the surface to the interior. Tensile, impact, and flexural properties and surface and volume conductivity values were evaluated and compared with compression molded specimens to assess the effects of migration.

Comparative Structure Development in Injection Molding of Various Polyolefins
Jaein Suh, James L. White, May 2004

We have investigated crystallization and orientation development in injection molding of polyolefins. These include high-density polyethylene (HDPE), isotactic polypropylene (PP), isotactic polybutene-1 (PB1) and isotactic poly(4-methyl pentene-1) (P4MP1).Isothermal and non-isothermal crystallization kinetics of these materials were investigated to understand and predict heterogeneous structure through the thickness direction of injection-molded articles. The heterogeneity of the molded articles was characterized by birefringence and crystallinity measurements using differential scanning calorimetry (DSC) technique.Considerations were made on the effects of cooling rate and thermal history in injection molding process by varying melt and mold temperatures as well as volumetric injection speeds and packing pressures.Comparison between semicrystalline polyolefins and polystyrene as an amorphous material was also made to study the effect of crystallization on orientation distribution.

Compositional Heterogeneity of Ethylene-Acrylate Copolymers: Effect on Melt Rheology
Richard T. Chou, Yefim Brun, Michael T. Pottiger, May 2004

A new technique, Interaction Polymer Chromatography (IPC), was used to characterize ethylene/methyl acrylate (EMA) copolymers for chemical composition variation. This technique can be used to determine chemical composition heterogeneity (CCH) of copolymers. The CCH, molecular weight distribution (MWD) and long chain branching of tubular process EMA's are measured and compared with autoclave process EMA's. The tubular EMA has a much higher CCH and a narrower MMD compared with the autoclave EMA. It also has a lower degree of branching. It is found that the significant CCH of tubular EMA attributes to its unusual high melt elasticity. The discussion also highlights the correlation between CCH and some other polymer properties.

On-Line Birefringence Measurement in Film Blowing Process
Hiroshi Ito, Ken-ichi Suzuki, Takeshi Kikutani, Ho-Jong Kang, Toshitaka Kanai, May 2004

On-line measurements of velocity, bubble diameter, temperature and three principal birefringences were performed during the tubular film extrusion of polypropylene at various draw ratios and blow-up ratios. Birefringence increased rapidly in the vicinity of the frost line height where the crystallization started. Birefringence between MD and ND showed the maximum value near the solidification position, and then it decreased with increasing distance from the die, and eventually the obtained PP film showed almost uniaxial molecular orientation.

Influence of Blend Composition on Structure Development during Uniaxial Stretching of Melt Miscible PVC/PCL
Mayela Ramirez-Huerta, Miko Cakmak, May 2004

Polymer blends are increasingly replacing homopolymers, because they synergistically combine the properties of the parent's polymers. In order to improve its processability, PVC is often mixed with plasticizers or blended with other polymers. In this study we investigate the effect of blend composition on the development of orientation, crystallization, and relaxation mechanism that occurs during the uniaxial stretching of miscible PVC/PCL blends studied by real time birefringence measurements system. By varying the blend composition we obtained two sets of materials one amorphous and the other crystalline blends. Stress optical behavior at large deformation from these from these precursors were determined.

Flow-Induced Crystallization and Birefringence in High-Speed Spun Pet Fibers
Kyuk Hyun Kim, A.I. Isayev, Keehae Kwon, May 2004

A novel approach for the simulation of the development of crystallinity and birefringence on the spinline including neck-like deformation was proposed using a nonlinear viscoelastic constitutive equation with crystallinity dependent viscosity and relaxation time. The approach was based on the calculation of melting temperature elevation, elastic recovery and crystalline and amorphous orientation function frozen when the flow-induced crystallization occurred. The predicted temperature, diameter, density and birefringence profile in both low- and high-speed spun PET fibers were in good agreement with the experimental data from literature.

Computational Materials at NASA Langley Research Center
Thomas S. Gates, Jeffrey A. Hinkley, May 2004

The paper provides details on the structure and implementation of the Computational Materials Program at the NASA Langley Research Center. Examples are given that illustrate the suggested approaches to predicting the behavior and influencing the design of nanostructured materials such as high-performance polymers, composites, and nanotube-reinforced polymers. Primary simulation and measurement methods applicable to multi-scale modeling are outlined. Key challenges including verification and validation of models are highlighted and discussed within the context of NASA's broad mission objectives.







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