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Applied Rheology

SPE Library content related to rheology
In-Situ Ultrasonic Compatibilization of Dynamically Vulcanized PP/EPDM Blends
Wenlai Feng, A.I. Isayev, May 2004

Dynamically vulcanized PP/EPDM blends were treated by high intensity ultrasonic waves during extrusion. These blends were compared with unvulcanized PP/EPDM blends that were treated by ultrasound during extrusion and then dynamically vulcanized. Die pressure and power consumption were measured. The effect of different gap sizes, ratio of components, and number of ultrasonic horns were investigated. The rheological properties, morphology and mechanical properties of the blends with and without ultrasonic treatment were compared. The results obtained indicated that ultrasonic treatment induced the thermo-mechanical degradation causing enhanced molecular transport and chemical reactions at the interfaces, thus leading to in-situ compatibilization, which is evident by the morphological and mechanical property studies. Processing conditions were established for enhanced in-situ compatibilization of the dynamically vulcanized PP/EPDM blends.

Influence of Co-Monomer Distribution Profile on the Crystallization Characteristics and Physical Properties of High Density Polyethylene
Rajendra K. Krishnaswamy, Qing Yang, May 2004

Three sets of two-component blends from various narrow-MWD (molecular weight distribution), linear (no rheologically significant long branches) polyethylenes were prepared with multiple compositions in each set of blends. These blends were deliberately prepared such that the branching (from 1-hexene co-monomer) was present exclusively on either the high or the low molecular weight blend component. The average branching content in each blend component was verified to be uniform across its MWD. In this study, the influence exerted by such selective placing of the branching on the crystallization characteristics of the resulting blends will be discussed. Further, some new observations relating to the tensile stress-strain behavior of these blends will also be described.

Evaluation of Thermoset UV Curing Kinetics by Calorimetry, Rheology and FTIR Spectroscopy
V. Tan, M.W. Young, S.H. Patel, M. Xanthos, May 2004

UV curable polymer systems are commonly characterized for degree and time of cure by thermal methods such as scanning photocalorimetry. In this work, we modified existing thermal and rheological instruments in order to apply a controllable dosage of UV radiation and compare the curing kinetics of two commercial polyester and epoxy powder coating systems differing in rate of cure. In general, there is an optimal temperature range whereby the material is completely cured. The optimal conditions are generally set for material heated above its flow temperature to cure within 5 seconds of UV radiation. Our thermal and rheological results are in good agreement with each other and with manufacturer's published data employing photocalorimetry. The data were analyzed for temperature dependence and efforts were made to correlate thermal and rheological results with time dependent structural changes monitored by FTIR spectroscopy.

The Use of Rheology to Characterize the Branching Structure in Sparsely Branched Metallocene Catalyzed Polyethylenes
Phillip J. Doerpinghaus, Donald G. Baird, May 2004

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.

Properties of Injection Moldable Blends of {Latex/Wood Flour recipes} and Polypropylene
Sophie Morneau, J.P. Ibar, May 2004

We prepare recipes of wood flour, from maple and pin tree, and latex, in various proportions, and disperse them with Polypropylene in a TekFlow processor in order to produce various conditions of disentanglement (viscosity reduction) for PP and for the blend. In particular, dispersion temperature is reduced to below wood degradation temperature.The dispersed blends are submitted to a series of rheological, mechanical and thermal analysis tests, to compare their properties with those of pure PP (controls). It is shown that for certain wood flower/ latex recipes, the blends with PP present favorable characteristics, both in terms of improved fluidity (they can easily be injection molded) and improved mechanical properties at room temperature and at -40 °C.

Modification of Nylon 6,6 and Metallocene Linear Low-Density Polyethylenes Blends Using Ethylene-Methacrylic Acid Ionomers
F. Gribben, G.M. McNally, W.R. Murphy, T. McNally, May 2004

Polymer blends of polyamides and polyethylenes are immiscible and highly incompatible. These blends are characterised by high interfacial tension, a two-phase morphology and poor physical characteristics due to reduced interaction across the phase boundaries. The focus of this work will involve the use of various amounts of ionomers based on ethylene-methacrylic acid copolymers as compatibilisers, which will physically be miscible with the polyethylene phase and will chemically bond with the polyamide phase. The use of this material was investigated for its abilities as a suitable impact modifier for these blends. The influence of the composition of the blends and the effect of the addition of the compatibiliser were both investigated for their affect on the mechanical and rheological properties.

Synthesis of Polyamide-Polyesters Base Random-Block Terpolymers in a Twin Screw Extruder via Reactive Extrusion: Process and Properties
In Kim, James L. White, May 2004

The synthesis of polyamide-polyester based random block copolymers were carried out in a modular co-rotating twin screw extruder via reactive extrusion process. These random block terpolymers have not been previously polymerized in a twin-screw extruder and these copolymers are very limited in open literatures. We used ?-lauryllactam , ?-caprolactam, and ?-caprolactone as monomers for synthesis of copolymers in a twin screw extruder. We also used sodium hydride as an initiator and N-acetylcaprolactam as a coinitiator. Simultaneously two lactams with initiator systems to make random copolymer and subsequently added the lactone without initiator to form a random block copolymers. All formation of random-block copolymers were studied in a twin-screw extruder as a chemical reactor. The thermal, mechanical, rheological, and structural properties of new synthesized random block copolymers were investigated and compared with homopolymers and Pebax® (Atofina) which consist of polyamide12- PTMEG (polytetramethyleneglycol)-polyamide12 block copolymer. It has the properties of a thermoplastic eslastomer (TPE).

On-Line Measurement of Dispersion in Nanocomposites
Rajkumar Vaidyanathan, Bhavjit S. Ghumman, Junseok Lee, Sravanthi Mallim, Changmo Sung, Joey L. Mead, Carol M.F. Barry, May 2004

Properties of polymer-clay nanocomposites depend on the degree of dispersion of clay in the polymer matrix. Currently off-line techniques such as transmission electron microscope and x-ray diffraction are used to determine dispersion. This research aimed to determine a property that is affected by dispersion and has the ability to be measured on-line. Polypropylene and Cloiste 15A (nanoclay) were melt blended with the aid of maleic anhydride grafted polypropylene compatibilizer. The mechanical, electrical, optical, and rheological properties were measured for all the trials. Transmission electron microscopy was performed to evaluate the results. The capacitance of the nanocomposites varied with change in the degree of dispersion. The mechanical properties (tensile characteristics) did not show a significant change with dispersion. The rheological properties gave a good indication of exfoliation of clay layers at low shear rates. The visible color test could not give a definite indication of dispersion as compared to the other properties.

Impact Modification of Polypropylene
Stanley P.Westphal, May 2004

Without the advent of impact modified polypropylene car batteries they would still be a heavy , black, hard rubber Product. The new commercial battery is a blend of polyethylene, EPR(ethylene propylene rubber) and isotactic polypropylene as the continuous phase. It is lighter and semi-transparent. The problem is to produce a consistant product. In a continuous process, material analysis is complicated by not knowing the precise amount of rubbery 2nd phase which was produced and what is its rheological characteristics relative to the rigid phase. It is well known that there is an optimal particle size for the best product performance. The problem is to determine the controlling polymerization and product performance factors. Microscopy can be used to observe and quantify particle size and EPR content. From this work the optimum particle size occurs at an MFR ratio slightly less than one and an average diameter of ca.0.4 microns.

Influence of Molecular Structure on Pressure and Temperature Dependent Viscosity of LDPE Melts
Tomas Sedlacek, Martin Zatloukal, Anezka Lengalova, Petr Saha, May 2004

A capillary rheometer equipped with an especially designed additional chamber ensuring various pressure modes was used to investigate temperature and pressure effects on the rheological properties of two batches of the same LDPE grade. The variation in molecular structure of the researched batches was proved by different gel permeation chromatography and elongational viscosity behavior. The magnitudes of the pressure coefficients varied more significantly than temperature ones. I.e. the pressure effect on viscosity depends strongly on the amount of long-chain branching in polymer.

The Rheological and Mechanical Performance of Commercial uPVC Formulations
W.C. Yap, A.C. Ruddy, K. Halliwell, G.M. McNally, W.R. Murphy, May 2004

Rheological and mechanical analysis of a range of virgin, recycled, and pigmented uPVC formulations used in extruded profiles for conservatory roofing applications is reported. The shear viscosity, tensile properties and dynamic mechanical thermal properties of the various formulations were shown to be dependent on stabiliser type, thermal processing history and pigment concentration. Lead stabilised uPVCs were shown to have better impact properties than Ca/Zn stabilised compounds and slight differences in Tgs, storage modulii (E’) were recorded for all formulations.

Ethylene-Butyl Acrylate-Carbon Monoxide Terpolymer as a Replacement Plastcisier for Polyvinyl Chloride
D.C. McConnell, G.M. McNally, W.R. Murphy, Y. Romeo, B. Lahuerta, E. Rodriguez, May 2004

An ethylene-butyl acrylate-carbon monoxide terpolymer (EnBA-CO) was blended with two PVCs at various compositions. Several commercially available medical grade plasticised PVCs were also tested to assess the suitability of the PVC blends as replacements for the traditional PVCs. The results are also compared to previous work on effect of ethylene-vinyl acetatecarbon monoxide (EVA-CO) as the polymeric plasticiser for PVC. The tensile and flexural modulus of the blends decreased significantly with progressive increase in EnBA-CO, while maximum elongation at break and impact strength were recorded at 30-40% terpolymer content. A single glass transition temperature (Tg) between that of the PVC and EnBACO components was recorded (DMTA), indicating complete miscibility over the range of concentrations studied. Rheological analysis showed a decrease in shear viscosity with increasing EnBA-CO content. The properties of most of the PVC/EnBA-CO blends were similar to those of commercially available plasticised PVCs.

Process Development for Molding a Medical Grade Silicone Elastomer via Rheological and Thermal Analysis Approach
Xiaoping Guo, May 2004

Both thermal analysis and rheological approaches were employed to study the cure behavior of a medical grade silicone elastomer. Isothermal cure experiments were conducted calorimetrically at temperatures from 80 to 100 °C and rheometrically at higher temperatures from 100 to 180 °C. Non-isothermal cure experiments were also performed at different heating rates from 5 to 50 °C/min. It has been observed that the glass transition temperatures for uncured and cured materials remain almost unchanged and that the rheometric measurements are more suitable for characterizing the process of curing, especially for the prolonged, later stages of cure. Based on the changes in dynamic viscoelastic properties measured under isothermal conditions, the characteristic times of cure, including the gelation and peak cure time were determined, and presented as functions of cure temperature. These results were used in an attempt to develop a robust and viable molding process. It has been found that the post-molding cure is essential for stabilizing and optimizing mechanical properties of molded silicone elastomers.

Melt Processing of Traditionally Solution-Processed Polymers with CO2
Matthew D. Wilding, Quang T. Nguyen, Michael J. Bortner, Donald G. Baird, May 2004

The effects of using near critical and supercritical carbon dioxide (CO2) to plasticize polymers that are difficult to melt process are studied, in particular acrylonitrile (AN) and methyl acrylate (MA) copolymers. Previous work with PAN/MA copolymers included differential scanning calorimetry (DSC), used to evaluate the resulting shift in the glass transition temperature (Tg) following plasticization, and pressurized capillary rheometry to evaluate the melt rheology and entry pressure effects prior to and after plasticization. A slit-die rheometer has been designed to allow the attachment of various nozzles to the exit to maintain high pressure and single-phase flow, suitable for measuring viscosity reduction with CO2 in a continuous process. Comparisons are made between capillary and slit die rheometry for quantifying the effect of CO2 plasticization on a model 65% AN, 25% MA, and 10% rubber copolymer.

Polyampholytes as Aqueous Viscosifiers: An Investigation of Stimuli-Responsive Rheology
Christopher A. Lange, May 2004

Solution rheological analyses of polyampholyte terpolymers composed of acrylamide (AM), sodium 3- acrylamido-3-methylbutanoate (NaAMB), 3- acrylamidopropyltrimethylammonium chloride (APTAC) were performed at varying polymer concentrations, solution pHs, NaCl concentrations, and molecular weights (MW). Steady-state shear sweeps and dynamic frequency sweeps of semi-dilute solutions were used to measure solution viscosity and viscoelasticity. Results are interpreted in terms of how experimental variables affect the solutions’ electrostatic charges and polymer/solvent interactions, which ultimately affect rheological properties.

High Performance Thermoplastic Vulcanizates (TPVs) for Long Term High Temperature Application
Jushik Yun, Raman Patel, Darnell C. Worley II, May 2004

New thermoplastic vulcanizates (TPVs) based on Hydrogenated Styrene Block Copolymer (HSBC) have been developed for long term high temperature applications. A comparative study using these new TPVs and conventional TPVs (Polypropylene(PP)/EPDM rubber) was performed. Standard factorial designs were used to evaluate material performance. The material characteristics under investigation were rheological properties, dynamic mechanical properties, tensile properties and morphology. These new TPV compounds showed increased solvent resistance and elastic recovery of approximately 20%, respectively relative to conventional TPVs.

Elastomeric Property Characterization of Thermoplastic Elastomers
Kevin G. Cai, Charles G. Reid, Satchit Srinivasan, Norbert Vennemann, May 2004

The elastomeric properties of polyolefin thermoplastic vulcanizates (TPV) have been characterized by compression set, recoverable strain after hysteresis, and thermal scanning stress relaxation (TSSR) analysis. Unlike a thermoset rubber, a TPV is a two-phase system with highly crosslinked fine rubber particles dispersed in a thermoplastic matrix. Compression set, which was originally designed to characterize the elastomeric properties of a thermoset rubber, does not truly characterize the unique elastomeric properties for a TPV. Compression set for a TPV is not only highly dependent on the crosslinking density and structure, but also very sensitive to the orientation of the two phases in the TPV. For the same TPV with a fully crosslinked rubber phase, the compression set value can vary substantially depending on sample preparation and thermal history. Elastomeric properties can be better characterized by the recoverable strain after hysteresis and TSSR stress-temperature curve. The thermal-mechanical properties or stress relaxation behaviors provides more useful information for designing and producing all-thermoplastic parts, such as automotive seals, from TPV.

Characterization of a Poly(Ether-Block-Amide) Copolymer and its Significance for Polymer Processing Operations
Xiaoping Guo, May 2004

Thermal and rheological properties of a poly(etherblock- amide) copolymer were characterized by means of differential scanning calorimetry (DSC) and dynamic rheological approaches. Based on the calorimetric and rheometric data, the microphase separation transition (MST) was studied, showing that upon heating the copolymer solid could be transformed into three different states: restructured solid, structured melt, and homogeneous melt. The driving force for the conversion among the three states is primarily due to crystal re-organization, crystallization, and melting. It is also found that different crystal structures in the solid state could be introduced by changing the conditions of cooling from a homogeneous molten state. The existence of a wide MST range and the conversion of the states imply a variety of proper process windows for various polymer processing operations. This knowledge is essential for understanding the processes and further assisting in rational process development.

Analysis of Tiger Striping in Injection Molded TPO
K. Jayaraman, P. Papworth, Chichang Shu, M.D. Wolkowicz, May 2002

Tiger striping in injection molded bars made of thermoplastic olefin (TPO) blends has been examined by a detailed analysis of the disperse phase morphology. This is evaluated in flow mark regions and out of flow mark regions on the part surface and near the wall, and also just behind the flow front but away from the wall. The results point to a way to control the rheology of the components for avoiding or delaying the onset of flow lines.

The Effect of Moisture on the Rheological Behavior of Calenderable Copolyesters
Eric J. Moskala, Kab Sik Seo, May 2002

The effect of absorbed moisture on the rheological behavior of a series of calenderable copolyester resins is studied. Moisture has a profound effect on the viscosity of the resins at calendering temperatures and on the glass transition temperature of the resins. However, moisture does not lead to hydrolysis of the copolyesters at the relatively low temperatures used in calendering.

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