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Rheology
SPE Library content related to rheology
Rheology-Based Pore Size Estimation in Polyacrylamide Hydrogels for DNA Analysis
The physiochemical properties of polyacrylamide hydrogels have made them important in a variety of biomedical applications including drug delivery, tissue engineering, and electrophoresis of charged biomolecules. In this paper, we perform 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. These results are then combined with a simple model based on classical rubber elasticity theory to obtain estimates of the average gel pore size.
Organoclay Networking in Polypropylene-Clay Nanocomposites
This report discusses the networking of organoclays and its influence on the rheology of polymer-clay nanocomposites. Small amplitude (SAOS) and steady state rheological experiments are systematically performed to study the effect of flow and thermal history on solid-like formation dynamics in a 3wt% polypropylene-clay sample. Results indicate that the kinetics of network formation increase with temperature, while the application of a sufficiently large deformation will irreversibly weaken the clay network.
Rheology and Properties of Linear and Branched Polypropylene Blends
The rheological, thermal and mechanical properties of linear and branched polypropylene blends with varying melt flow rates are characterized. These blends are miscible in the melt state and have high melt elasticity while retaining good flow and mechanical properties.
Scale Up of Polypropylene Vis-Breaking for Industrial Application
A statistical experimental design was used to find the required concentration of a novel additive in order to obtain the same rheological behavior of higher priced, commercial controlled-rheology polypropylenes. A lab extruder was used to perform the experimental design, minimizing the amount of material needed. According to the results, recommendations were given to process two different lower priced polypropylenes with the additive in an industrial extruder with very good agreement with lab predictions.
Rheology of High Molecular Weight Polyethylenes with SCCO2
The effects of using supercritical carbon dioxide (SCCO2) to melt process high molecular weight polyethylene are studied. High molecular weight polyethylene (HDPE) is studied in an effort to produce high strength fibers and materials in a melt extrusion process. Dynamic, capillary, and slit-die rheometry are used to quantify the effect SCCO2 has on the melt viscosity of high Mw HDPEs. Carbon dioxide uptake is quantified using mass flow measurements.
Using sc-CO2 as a Processing Aid for Improving the Properties of Polymer Nanocomposites
Supercritical carbon dioxide (sc-CO2) is used in this work as a processing aid for improving the dispersion of the clay nanoparticles in the melt intercalation process of HDPE-clay nanocomposites. Some preliminary experiments were performed to study the effect of sc-CO2 on the melt intercalation process. Results from the mechanical properties and rheological studies show a direct effect of the sc-CO2, suggesting that the presence of sc-CO2 in the melt blending process can enhance the degree of mixing and the dispersion of the nanoclays into the polymer matrices.
Reactive Extrusion of PBT for Low Density Foaming
Branching or partial cross-linking of polybutylene terephthalate (PBT) resins by reactive modification with multi-functional epoxides was investigated. The rheology of the PBT products could be controlled by varying material and operational conditions of the reactive extrusion process. The modified PBT was adaptable to low density foam extrusion, where higher melt strength is necessary.
Shape Memory Binary Blends: Compositionally Tailored Fixing and Recovery
Semicrystalline-amorphous blends exhibit shape memory due to (1) the elastomeric nature imparted by crystallites that act as physical crosslinks and (2) temporary shape fixing made possible by the vitrification of a continuous, miscible amorphous phase. PVDF-containing binary blends were studied using calorimetry and rheology in order to characterize the morphological control afforded by subjecting such materials to different thermal histories. The sensitivity of the aforementioned techniques to changes in blend morphology will also be discussed.
Film-Casting Behavior as a Function of Molecular Structure and Rheology
Polyethylene resins with different molecular structures and rheological properties are investigated in terms of their performance in film-casting. Four metallocene catalyzed polyethylene resins with different degrees of long-chain branching and two conventional polyethylene resins are analyzed in terms of their dimensional changes during film production. With an increase in long-chain branching, and thus strain hardening-behavior, an increase in the necking phenomenon is observed during film-casting.
Measurement of Surface Properties of Polymeric Materials Using Nanosphere Embedment Measurements
Here we report results from our ongoing investigation of the surface properties of polymers using a nanoparticle embedment method that was originally pioneered by Teichroeb and Forrest. We describe a viscoelastic contact mechanics solution that includes surface adhesive forces and a time dependent Poisson's ratio. The results show that, with properly designed experiments, both the surface adhesion properties and the surface rheological properties can be extracted from nanosphere embedment measurements.
Modeling the Transient Rheology of a Polypropylene Melt Reinforced with Long And Short Glass Fibers
In this paper we investigate the transient shear rheology of a polypropylene containing long fibers (2.75 to 11 mm, L/D > 150) and short fibers (1 mm, L/D < 50). The objectives of this work are to determine the relationship between stress growth and relaxation behavior of fiber orientation and determine the feasibility of extending Doi's theory for the rheology of rod-like molecules to fiber reinforced materials.
Effect of Epoxy Modifier on Flame Retardancy and Rheological Behavior of Acrylonitrile-Butadiene-Styrene(ABS)/Montmorillonite(MMT) Composites
ABS/MMT composites were prepared via melt intercalation to MMT with or without pretreatment of liquid epoxy resin. For the direct addition of epoxy, the composite has intercalated structure; while for the pretreatment of MMT with epoxy, the composite has exfoliated structure. Cone analysis results reveals slight difference in flame retardancy between the two composites. At low frequency zone, the composite with intercalated structure has higher storage modulus than the composite with exfoliated structure.
Structure and Performance of ABS-Clay Nanocomposites by Melt Compounding
ABS layered-silicate nanocomposites were manufactured by melt compounding. X-ray diffraction and transmission electron microscopy analysis confirmed the achievement of hybrid intercalated and exfoliated structures, giving significant improvement in the mechanical, thermal and rheological properties.
Rheology Phenomena of Nano-Extrudate Flow
The purpose of this paper is to study the die swell phenomena in a nano-extrudate flow from the molecular dynamics simulation. We have studied a polyethylene (PE) melt extruding into vacuum surrounding through a 4-to-1 nano-extrusion die. The results indicate the extrusion velocity has a strong influence on the stability of extrudate with the die swell. Also, there is a particularly noteworthy surface effect that some molecules are adsorbed on the outer surface of capillary under the lower extrusion velocity.
Partially Oxidized Graphite in Polypropylene Grafted Maleic Anhydride
Natural graphite flakes (NGF) were partially oxidized with potassium permanganate (KMnO4) in order to increase their dispersion during melt mixing in polypropylene (PP) grafted maleic anhydride (MA) (PPg- MA). Electrical conductivity of the composite, as well as X-ray diffraction, Fourier transform infrared spectrometry, and rheological properties were assessed against the level of oxidation.
Rheology and Thermoforming of Rigid Medical Packaging Materials
Rheological properties were measured on two materials to evaluate their behavior in the thermoforming process. An impact-modified acrylic-based terpolymer compound displayed higher extensional viscosity and melt strength measurements versus a copolyester. The findings in this study showed that lower extensional viscosity and melt strength led to higher molded-in-stress and thinner walls of thermoformed parts.
Electrorheological Properties of Carbon Black Filled PDMS
The electrical conductivity and rheological properties under steady shear flow of carbon black-filled PDMS are measured as a function of filler loading, matrix viscosity and shear rate, upon application of an AC electric field. The effects of electric field are most notable at low filler loadings and low matrix viscosities.
Pressure Profile in Annular Die Using PP/CO2 Solution Viscosity
In this paper, a rheological die with a slit channel was designed to determine the solution viscosity of supercritical CO2 in non-crosslinked high-melt-strength (HMS) polypropylene (PP). The shear viscosity was modeled as a function of temperature, pressure, gas content, and shear rate. With interest in producing highly expanded foam sheets using an annular die, an analysis of the annular die pressure profile using the measured viscosity data was also conducted.
Compatibilization of Natural Fibers/PP Composites
The effect of maleic anhydride grafted polypropylene (PP-g-MA) as a compatibilizer on mechanical, rheological, and morphological properties of rossells/PP and sisal/PP composites was investigated. The fiber loading was 20wt% and the compatibilizer contents were varied from 1-10 phr. The tensile strength and unnotched impact strength of the composites increased with increasing the compatibilizer content.
The Processing and Performance of Nylon 12/PEBAX Blends
This work studied the effect of a polyether block amide (PEBA) on the rheological, mechanical and thermal properties of nylon 12 polymers. The results showed significant differences in melt viscosity, tensile properties and phase transition temperatures (tan ?) with varying PEBA concentration.
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