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Applied Rheology

SPE Library content related to rheology

The Nanoporous Morphology of Photopolymerized Crosslinked Polyacrylamide Hydrogels for DNA Electrophoresis

Jian Wang, Victor M. Ugaz, May 2007

Photopolymerized crosslinked polyacrylamide hydrogels are emerging as an attractive electrophoresis sieving matrix formulation owing to their ideal range of pore size, rapid polymerization times and the potential to locally tailor the gel structure through spatial variation of illumination intensity. This capability is especially important in microfluidic systems, where photopolymerization allows a gel matrix to be precisely positioned within a complex microchannel network. The achievable level of separation performance is directly related to the nanoscale gel pore structure, which is in turn strongly influenced by polymerization kinetics. Unfortunately, detailed studies of the interplay between polymerization kinetics, mechanical properties, and structural morphology are lacking in photopolymerized hydrogel systems. In this paper, we address this issue by performing a series of in-situ dynamic small-amplitude oscillatory shear measurements during photopolymerization of crosslinked polyacrylamide electrophoresis gels to investigate the relationship between rheology and parameters associated with the gelation process including UV intensity, monomer and crosslinker composition, and reaction temperature. In general, we find that the storage modulus G' increases with increasing initial monomer concentration, crosslinker concentration, and polymerization temperature. We also find an optimal UV intensity level at which the resulting hydrogels exhibit a maximum value of G'. A simple model based on classical rubber elasticity theory is used to obtain estimates of the average gel pore size that are in agreement with corresponding data obtained from analysis of DNA electrophoretic mobility in hydrogels polymerized under the same conditions.

Nitroxide-Mediated Controlled Degradation of Polypropylene

Alexandros Psarreas, Neil McManus, Costas Tzoganakis, Alexander Penlidis, May 2007

The purpose of this work is to evaluate a new polypropylene (PP)–based nitroxyl radical generator (NOR) and offer comparisons with a commonly used peroxide in the production of controlled-rheology polypropylene (CRPP) resins. CRPP resins are produced by reactive processing in a batch mixer by using different amounts of either the NOR or a peroxide initiator at different temperatures. Molecular weight and rheological properties are determined for all CRPP produced and a comparison between the effectiveness of the NOR and the peroxide initiator is provided.

Smarter Materials Systems Designs for the Future

Clive P. Bosnyak, Alexander Chudnovsky, Shaofu Wu, Hoang T. Pham, May 2007

The term Smart Materials" has been coined to those materials which change behavior when stimulated by light pressure thermal electrical or magnetic fields. Early applications of smart materials are for example electrorheological fluids for clutches and piezoelectric sensors for airbags. The challenge is to create significant additional value to large plastics markets by bringing enhanced functionality through smart materials systems designs. Smart materials systems designs require integration of multidisciplinary skills from materials science through to fabrication and lifetime prediction. Here in this review we address the issues of advancing the technology of polymers into "smarter systems". In particular we identify the needs and challenges to create significant additional value to large plastics markets via smart materials systems designs."

Polyvinylidene Fluoride Containing Long Chain Branching for Blown Film Applications

Nafaa Mekhilef, Sara Reynaud, Lotfi Hedhli, Gilberto O. Pasquariello, May 2007

In this work the effect of long chain branching in polyvinylidene fluoride on its rheology and blown film processing is investigated. Branched samples prepared by a conventional polymerization process were compared to commercial resins in terms of their rheological properties in shear and extensional flows. The branched samples showed an enhanced elasticity allowing a higher melt strength as well as strain hardening when subjected to extensional deformation. The enhanced rheological properties in the branched samples resulted in better processing performance in a blown film application where higher blow-up ratios and thinner films were achieved.

Preparation and Melt Viscoelastic Properties Study of TPV Nanocomposite Using Peroxide Crosslinking System

A.Jalali, F.Goharpey, H.Nazockdast, A.A.Katbab, May 2007

Dynamically vulcanized thermoplastic elastomer (TPV)/organoclay nanocomposites based on EPDM/PP containing 2, 4, 6% of organically treated montmorillonite were prepared by using EPDM-g-MA and PP-g-MA as compatibilizer. Dicumylperoxide (DCP) and triallyl cyanurate (TAC) were employed as crosslinking system. X-ray diffraction (XRD) analysis has been performed to evaluate the extent of the intercalation.. In this study, attempts have been made to exclusively reinforce rubber dispersed phase. Rheological behavior and melt viscoelastic properties of the samples such as elastic modulus, and elastic response expressed in terms of relaxation time distribution, H (?) , were studied. The results were also supported by differential scanning calorimetry (DSC) and mechanical tests.

The Study of Particle Size and Surface Treatment of next Generation Radiopaque Fillers Used in Bio-Medical Device Applications

Charles J. O’Neil, Lawrence A. Acquarulo Jr., Sunil P. Mirji, Tony Listro, Stephen Burke Driscoll, May 2007

Medical tubing and catheters have revolutionized the medical industry by enabling minimal invasive surgery procedures. The trend in the medical-device industry is thinner walls, especially in critical applications. Extruding smooth surface using micron-sized radiopaque fillers forms a challenge since they can form rough surface due to non-uniform dispersion. An effort was made to study the effects of particle size and surface treatment of radiopaque fillers on the dispersion, rheological and mechanical properties of PEBA at three loading levels. New generation barium sulfate and bismuth trioxide radiopaque fillers were chosen for this study.

Understanding Melt Rheology & Foamability of PP-Based TPO Blends

F. Gunkel, A.N.J. Spörrer, G.T. Lim, D.S.B. Sampath, V. Altstädt, May 2007

Rubber-toughened PP is an important resin for many engineering applications. By structural foaming, material cost-saving and lightweight structures can be achieved. In this study, physical blends of PP and poly(ethylene/octene) with various compositions were characterized regarding their melt strength and shear viscosity. The high pressure MuCell® foaming process was used to obtain structural foams with average cell diameters of < 50 ?m and cell densities of ~ 8 × 106 cells/cm3. This study presents key correlations between material rheology and its suitability for structural foaming and elucidates how the foaming behavior is linked to blend composition and melt temperature for an optimum system.

Modeling the Rheology and Orientation Distribution of Short Glass Fibers Suspended in Polymeric Fluids: Simple Shear Flow

Aaron P.R. Eberle, Donald G. Baird, Peter Wapperom, May 2007

In this paper we present a constitutive relation for predicting the rheology of short glass fibers suspended in a polymeric matrix. The performance of the model is assessed through its ability to predict the steady-state and transient shear rheology as well as qualitatively predict the fiber orientation distribution of a short glass fiber (0.5 mm, L/D < 30) filled polypropylene. In this approach the total extra stress is equal to the sum of the contributions from the fibers (a special form of the Doi theory), the polymer and the rod-polymer interaction (multi-mode viscoelastic constitutive relation).

Ultrasound Assisted Single Screw Extrusion Process for Dispersion of Carbon Nanofibers in Polymers

Avraam I. Isayev, Changdo Jung, Kaan Gunes, May 2007

A novel method for the continuous dispersion of carbon nanofibers (CNFs) in a polymer matrix for manufacturing high performance nanocomposites was developed using an ultrasonically assisted single screw extrusion process. The effect of ultrasound on die pressure, electrical conductivity, rheological, morphological and mechanical properties of polyetherimide (PEI) filled with 1-20 wt% CNFs was studied. A reduction in the die pressure, percolation threshold and an increase in the viscosity, Young's modulus and electrical conductivity along with better CNF dispersion in nanocomposites was achieved through ultrasonic treatment.

Measurement of the High Frequency Viscoelastic Properties of Polypropylene Using a Sliding Plate Rheometer

Chelsea A. Braybrook, Jennifer A. Lee, Philip J. Bates, Marianna Kontopoulou, May 2007

A newly constructed sliding plate rheometer (SPR) is used to investigate the high frequency linear viscoelastic properties of two polypropylene (PP) resins with widely differing melt flow rates. Extrapolation of rheological measurements obtained on a traditional parallel plate rheometer to frequencies obtained on the SPR, through use of the generalized Maxwell and Cross models, was used to assess the performance of the high frequency SPR. Good agreement between the extrapolated and measured data demonstrates the ability of the SPR to measure the high frequency rheological properties of PP.

Thermal Stability and Rheological Properties of Multiwall Carbon Nanotube Reinforced Thermotropic Liquid Crystalline Polymer Nanocomposites

Sang Ki Park, Seong Hun KIM, Jin Taek Hwang, May 2007

Multiwall carbon nanotube (MWCNT) reinforced thermotropic liquid crystalline polymer (TLCP) nanocomposites were prepared by a melt compounding process. Incorporation of small quantity of the MWCNT improved the thermal stability of MWCNT reinforced TLCP nanocomposites. The rheological behavior of TLCP/MWCNT nanocomposites was dependent on the MWCNT content. The complex viscosity and storage modulus of TLCP/MWCNT nanocomposites increased with increasing MWCNT, resulting from physical interactions such as the nanotube-polymer matrix interactions and the nanotube-nanotube interactions. This increment effect was more significant at lower frequencies.

Crystalline Polymer Microgels with Surface Interactions

Gerald H. Ling, Montgomery T. Shaw, May 2007

We report one rheological and microstructural investigation of dispersions of polyethylene microgels in squalane. Emphasis in literature has mainly been limited to systems that depend largely on polymer-solvent interactions and little is known of systems that exhibit both intra- and inter-particle crystallinity. The majority of similar reported systems are prepared using a bottom-up approach while the described system is prepared from recycled bulk XLPE via mechanical grinding and fragmentation by sonic energy. Bulk rheological properties and particle surface interactions are explored using conventional rotational and oscillatory rheometry.

Ionic Liquids as Additives for Thermoplastics

K.I. Park, M. Xanthos, May 2007

In attempts to develop new process modifiers for thermoplastics, two ionic liquids with long chain hydrophobic cations and different anions were introduced in a biodegradable polymer. Methods of incorporation included melt blending, solvent casting and microencapsulation from w/o/w systems at concentrations up to 10 wt%. The modified polymers were characterized rheologically and by TGA to determine process and thermal stability, respectively, and by DSC to determine miscibility and types of the polymer-ionic liquid interactions. Potential applications in plasticization, lubrication and emulsification are discussed for selected polymer-ionic liquid combinations.

Effect of Electron Beam Radiation on the Melt Rheology of Polyvinylidene Fluoride and its Copolymers

Nafaa Mekhilef, Ramin Amin-Sanayei, Stephan Moyses, May 2007

The effect of electron beam radiation on the shear and extensional rheology of polyvinylidene fluoride and its copolymers with hexafluoropropylene is investigated. The samples were exposed to low levels of radiation ranging from 0 to 5 Mrads at room temperature. The shear rheology showed an increase in the storage modulus, as the level of radiation increased while the viscosity at high frequency remained unchanged. These results suggest the formation of chain branching and/or the formation of a second population of higher molecular weight. The results were corroborated using size exclusion chromatography combined with light scattering (SEC-MALLS), which confirmed both the presence of chain branching and the formation of a higher molecular weight tail. Extensional rheology showed strain hardening as the level of radiation is increased.

Study of Orange Peel Phenomena in Rotational Molding

E. Soos Takacs, M. Emami, D. D’Agostin, J. Vlachopoulos, May 2007

The term orange peel" describes a surface defect that is characterized by irregular grooves and pitting—much like the topography of the outer skin of an orange. Although similar phenomena have been reported for high-pressure processes such as injection molding the root causes of orange peel in rotational molding are essentially unknown. The presence of orange peel is undesirable not only for aesthetic reasons but also for its potential negative effects on the functional properties of the final product.A fundamental study was conducted to determine the root causes of the orange peel in rotational molding. The effects of material properties such as density rheological thermal and powder properties and process parameters were investigated. In addition comparisons are made between the dry blended and melt blended samples in terms of orange peel development."

Super-Critical Carbon Dioxide Assisted Melt Intercalation of Polymer Layered Silicate Nanocomposites

David Litchfield, Quang Nguyen, Donald Baird, May 2007

Preliminary experiments were preformed to study the influence of super critical carbon dioxide (sc-CO2) on the melt intercalation (platelet dispersion and mechanical properties) of polymer-nanoclay composites. A series of mixing scenarios incorporating sc-CO2 and maleic anhydride in the melt compounding of polypropylene with organically-modified nanoclay were examined and compared to a commercially available polypropylene nanocomposite. The greatest mechanical property response was a result of the novel technique of directly and rapidly injecting pre-mixed sc-CO2 and nanoclay into the polypropylene melt during extrusion. X-ray diffraction data showed no characteristic peak for the nanoclay layer spacing in this method. The invented mixing technique showed a negligible influence on the rheological response, which was dissimilar to the commercially produced nanocomposite.

Continuous Dispersion of Carbon Nanotubes in Polymers Using Ultrasound Assisted Extrusion Process

Rishi Kumar, Todd Lewis, Avraam I. Isayev, May 2007

The unique morphology and strong intertube attraction between carbon nanotubes (CNTs) makes the dispersion of CNTs a big challenge and hence limits its effective use. A novel method for the continuous dispersion of carbon nanotubes in a polymer matrix for manufacturing high performance nanocomposites was developed using an ultrasonically assisted twin screw extrusion process. The effect of ultrasound on die pressure, electrical conductivity, rheological, morphological and mechanical properties of polyetherimide filled with 1-10 wt% MWNT was studied. Ultrasonic treatment caused a reduction in die pressure with a permanent increase of viscosity of treated samples.

Effect of Die Land Length on Die Pressure during Foam Extrusion – Part I Experimental Observations

Jing Wang, Chul B. Park, David F. James, May 2007

Entrance pressures are determined experimentally for foam extrusion dies of constant cross section. These pressures are affected by the rheological properties of the polymer matrix, by the plasticizing effect of the blowing agent, and by the cell nucleation and growth. While the pressures change linearly with die land length during extrusion of pure polymer, this relation becomes nonlinear during extrusion of polymer/blowing agent mixtures. It is found that the degree of nonlinearity depends on the amount of premature cell growth and by the processing conditions, including temperature, pressure drop rate, and blowing agent content.

Effect of Multiple Shear Histories on Rheological Behavior and Devolatilization of Poly(Ether Ether Ketone)

Jeffrey Galloway, Richard Hoffman, Sanjiv Bhatt, May 2007

The effect of shear history on the properties of poly(ether ether ketone) (PEEK) was investigated by processing it through a twin screw extruder 20 times. Samples were taken at various stages in the recycling sequence for testing. The melt rheological behavior, solid mechanical properties, and total outgassing performance were monitored to evaluate the degradation of the PEEK as a function of processing history.The results of rheological testing suggest that degradation is initially dominated by chain scission with cross-linking becoming more significant with more reprocessing cycles. The rheological and mechanical behavior shows similarities to liquid crystalline polymers and filled polymer systems. The results of outgassing testing showed that the total amount of volatiles decreased with increasing processing cycles.

Controlling Morphology in Cocontinuous Polymer Blends

Joel R. Bell, Carlos R. Lopez-Barron, Christopher W. Macosko, May 2007

Cocontinuous morphologies, distinguished by the mutual interpenetration of two polymer phases, allow for enhanced mechanical properties, static charge dissipation, and barrier properties. Compatibilizers, e.g. block copolymers (bcp), are often added to hinder phase coarsening in blends of immiscible polymers and can improve adhesion at interfaces. We have studied the effect of bcp on the cocontinuous morphology of polystyrene (PS)/polyethylene (PE) and PS/poly (methylmethacrylate) PMMA model blends using scanning electron microscopy (SEM) with image analysis, 3D synchrotron x-ray microtomography, mercury porosimetry, solvent extraction, and rheology. We have shown that an optimal bcp suppresses coarsening in these blends and widens the range of cocontinuity.