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Applied Rheology

SPE Library content related to rheology
Time-Scales of Coalescence in Polymer Processing: Study on Polypropylene/Polyamide-6 Blends
Jairo E. Perilla, Sadhan C. Jana, May 2004

The effects of shearing time, volume fraction, shear rate, and viscosity ratio on coalescence of isotactic polypropylene (PP) and polyamide-6 (PA6) blends were studied in simple shear flow. A simple model for coalescence developed to provide characteristic times in coalescence in polymer processing operations was used to analyze experimental results. The pre-coalescence droplet morphology was created by melt blending the polymers in a twin-screw extruder at several compositions and was subjected to a simple shear flow in a cone and plate rheometer at low shear rates (0.1 and 0.5 s-1). The rheological data was analyzed after removing the effects of viscosity mismatch to leave only the interfacial effects on coalescence.

Interfacial Area and Rheological Measurements of Cocontinuous Poly(Ethylene Oxide)/Polystyrene Blends
Jeffrey A. Galloway, Christopher W. Macosko, May 2004

Blends of poly(ethylene oxide) and polystyrene were analyzed using scanning electron microscopy with image analysis and rheological measurements to determine the region of cocontinuity. Local maxima in the amount of interface in the blends and in the elastic modulus at low frequency correspond to the boundaries of the region of cocontinuity. Annealing of the samples caused some blends near the boundaries of the region of cocontinuity to break up into dispersed morphologies, while other blends remained cocontinuous, despite dramatic increases in the size scale.

The Processing and Performance of Polyvinyl Chloride / Ethyl-Vinyl Acetate Copolymer Blends
D.C. McConnell, G.M. McNally, W.R. Murphy, May 2004

Two grades of ethyl-vinyl acetate (EVA), each containing 26% (modified with 1.2% methacrylic acid) and 27% vinyl acetate (VAc) respectively, were blended at various compositions, with two grades of PVC. Mechanical analysis of these blends showed that the tensile and flexural modulus decreased and impact strength increased, with increasing EVA content. Rheological analysis for the blends showed only slight changes in shear viscosity with increasing EVA content, even at lower shear rates. DMTA showed a shift in glass transition temperatures of the PVC and EVA components within the blends, suggesting partial miscibility over the range of concentrations studied.

The Suitability of Polyvinyl Chloride / Ethylene Vinyl Acetate-Carbon Monoxide Terpolymer Blends for Medical Devices
D.C McConnell, G.M. McNally, W.R. Murphy, May 2004

An ethylene vinyl acetate-carbon monoxide terpolymer (EVA-CO) (Elvaloy® by Du Pont) was blended with two PVCs at various compositions. Several commercially available medical grade plasticised PVCs were also tested to assess the suitability of the blends for the current market.Mechanical analysis showed that the tensile and flexural modulus of the blends decreased significantly with increasing EVA-CO content, with the impact strength greatly improved. DMTA showed a single glass transition temperature (Tg) between that of the PVC and EVA components indicating complete miscibility over the range of concentrations studied. Rheological analysis showed only slight changes in shear viscosity with increasing EVA-CO content. The properties of most of the PVC/EVA-CO blends were similar to those of commercially available plasticised PVCs.

Coextrusion of TPU and BaSO4 Filled Medical-Grade TPU
Guangyu Lu, Dilhan M. Kalyon, Iskender Yilg?r, Emel Yilg?r, May 2004

Coextruded products for the medical device industry, involving layers of filled and unfilled polymers, are difficult to fabricate, especially due to the various degradative processes taking place especially when various stabilizers are not included in the medical-grade formulations. Significant differences in the degradation behavior and the subsequent rheological behavior of unfilled and BaSO4 filled TPUs generally give rise to severe fluctuations at the interfaces and poor coextruded products. It is shown here that the shear viscosity values of the filled and unfilled TPU need to be matched under the extrusion conditions to obtain acceptable coextruded medical products.

Modification of Biodegradable Polyesters with Inorganic Fillers
G. Chouzouri, M. Xanthos, May 2004

Composites produced by solution mixing of a biodegradable thermoplastic polyester based on butylene adipate / succinate, as well as a commercial polylactic acid, with surface coated and uncoated hydrotalcite inorganic minerals were studied. Materials were also melt-mixed in a twin screw extruder for comparison. Significant structural and morphological differences were noted following characterization of the composites by DSC, TGA and melt rheology. Results varied depending on the materials and the processing methods. Biodegradability and biocompatibility were evaluated by performing tests “in vitro” in the presence of a phosphate buffered saline solution.

The Mechanical and Rheological Characterisation of Implantable Medical Devices Formulated from Binary Mixtures of Cellulose Derivatives
G.P. Andrews, D.S. Jones, A.D. Woolfson, May 2004

This study highlights the potential associated with utilising multi-component polymeric gels to formulate materials that possess unique rheological and mechanical properties. The synergistic effect* and interaction between hydroxyethylcellulose (HEC) and sodium carboxymethylcellulose (NaCMC), polymers which are commonly employed as drug delivery platforms for implantable medical devices, have been determined using dynamic, continuous shear and texture profile analysis. * The difference between the actual response of a binary mixture and the sum of the two components comprising the mixture.Increases in polymer concentration resulted in an increase in G’, G’’ and ?’ whereas tan ? decreased. Similarly, significant increases were also apparent in continuous shear and texture analysis. All binary mixtures showed positive synergy values which may suggest associative interaction between the two components.

Micromoulding: Consideration of Processing Effects on Medical Materials
M.T. Martyn, B. Whiteside, P.D. Coates, P.S. Allan, G. Greenway, P. Hornsby, May 2004

New medical technologies are driving demand for smaller plastic components. In response, micro-injection moulding has evolved as a technology for the mass production of minute, intricate, polymer and composite components for medical and MEMS applications. There has been significant growth in the technology but little understanding of the effects of process dynamics on product properties. To address this knowledge gap a program of work with the objectives of enhancing the understanding of polymer processing-property interaction has been implemented in our laboratories. The impact of micro-scale processing on the rheological, mechanical and tribological properties of polymers and composites are being explored. Process conditions are potentially more severe on melts than those encountered in conventional moulding. This is especially pertinent when considering process sensitive biomaterials used in medical applications. A novel micro-injection compounding (MIC) machine has been developed minimising process stages and reducing material exposure to excessive residence times. This paper gives brief details of the effects of micromoulding process conditions on component surface morphology and mechanical properties measured using atomic force microscopy.

Study of Phlogopite Mica as Fillers for Polyethylene and Polypropylene
Rakshit Amba, Ivan Javni, Paul Herring, Jeff Dyer, Zoran Petrovic, May 2004

Phlogopite mica is an abundant micaseous mineral being experimented of its usage as reinforcement in plastics. In this study the mechanical and rheological modifications due to phlogopite mica as filler in polyethylene and polypropylene materials were determined. And relative comparison was made with the fillers: talc and calcium carbonate, which are currently standard fillers for plastics.The phlogopite mica filler showed better tensile strength, and flexural modulus properties than calcium carbonate but lower than talc as filler. The cost of this mineral is lower than talc and CaCO3 (calcium carbonate) depending on the purity and particle size of the mineral.Phlogopite mica is hygroscopic, nontoxic and even has nutritious value, has light brown color and due to its higher aspect ratio gives higher shear stress and apparent melt viscosity than other fillers at the same concentration.

Melt Processing of Thermally Unstable Polymers Plasticized with CO2
Michael J. Bortner, Matthew D. Wilding, Donald G. Baird, May 2004

The effects of plasticizing acrylic copolymers, in particular a 65% (molar) polyacrylonitrile/ 25% (molar) methyl acrylate/ 10% rubber (PAN/MA/rubber) copolymer, with carbon dioxide (CO2) are studied. Previous work 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 prior to and after plasticization. A series of capillaries is used to evaluate the entry pressure effects and to observe the pressure effects of CO2 on the copolymer. The plasticizing effects of CO2 on the AN copolymer are observed to have a nonlinear pressure dependence, possibly indicating a higher plasticizing effect at higher pressures.

Use of Recycled Polymer Modified Asphalt Binder in Asphalt Concrete Pavements
Ioan I. Negulescu, Codrin Daranga, Zhong Wu, William H. Daly, Louay M. Mohammad, Chris Abadie, May 2004

Since polymer modified asphalt cements (PMAC) have been employed for a decade, the lifetime and wear on of some of these roadbeds are reaching a stage where resurfacing will be necessary. This paper considers the potential problems associated with recycling of polymer modified asphalt cements, PMAC's, in particular blending aged PMAC with tank PMAC. A standard PMAC was selected and characterized using typical asphalt binder qualification techniques, i.e., the Superpave Strategic Highway Research Protocol. Procedures were developed to separate the PMAC into its asphalt resin and polymer additive components as well as to characterize the relative concentrations of each component. Infrared and chromatographic techniques were used to identify changes in the components as a result of aging. The impact of the extraction and recovery process on binder properties has been ascertained and found to be minimal.The standard PMAC was aged under accelerated aging conditions in a Pressure Aging Vessel (PAV) that produced a material equivalent to 5-8 years in the field. The aged PMAC was then reanalyzed both chemically and rheologically and all changes in its properties due to aging were noted. Finally blends of the PAV aged PMAC with fresh PMAC, as well as blends where the PAV aged PMAC was replaced with road-aged binder, were prepared and analyzed. Our initial results indicate that aged PMAC can be blended successfully with fresh PMAC. Thus we anticipate that resurfacing of aging PMAC roadbeds can proceed, but further tests will be required to establish the precise conditions necessary to conduct this process.

Phase Reinforcement Effects in TPV Nanocomposites
Hemant Thakkar, Keun Yong Lee, Lloyd A. Goettler, May 2004

Thermoplastic vulcanizates (TPV’s) have been extensively studied and gained wide acceptance because of their rubber-like properties and thermoplastic processability. Polymer / layered silicate nanocomposites of various types have similarly received much attention as promising high performance materials. Combining these two complementary technologies to form a TPV nanocomposite generates interesting properties that significantly depend on the phase location of the silicate nanoclay reinforcement – whether it lies in the dispersed rubber phase or in the continuous plastic matrix.Our objective is to selectively reinforce either the plastic phase or the rubber phase in some typical TPV’s and observe the distinctive effect of reinforcement partitioning on mechanical and rheological properties.

Rheological and Chemical Modification of Polypropylene with Inorganic Clays
Keino Hamilton, Carlos Monzon, May 2004

Polymer composites were produced by mixing an inorganic clay hydrotalcite (HT), stearate coated (HTC) and uncoated (HTU) at 5 and 30% by weight with polypropylene and modified polypropylene. Torque profiles from blending in a batch mixer indicated significant viscosity changes depending on the type of the particular clay/polymer components. FTIR, MFI, DSC and TGA data suggested corresponding structural changes in the composites. The results showed that coated hydrotalcite produced the highest melt viscosity when added in the modified polypropylene. Tests are underway on flammability and rheology to shed more light into the interactions of the clay and the polymers.

Cross-Linked LDPE as a Rheological Modifier for LLDPE
Hyun Jung Jun, May 2004

Melt strength tests were conducted for blends of linear low density polyethylene (LLDPE) with cross-linked low density polyethylene (xLDPE) to study the effect of rheological modification on the development of low density, LLDPE foam with improved processability during extrusion foaming. Blends of LLDPE containing various concentrations of xLDPE, cross-linked with peroxide, were prepared in a Brabender batch mixer. Melt strength tests of the prepared blends were conducted through a capillary rheometer. It was found that melt strength increased with respect to increasing concentrations of xLDPE, suggesting optimum foamability at specific xLDPE content.

Morphology Development and Rheology of HDPE/PBT Blends
Joung Sook Hong, Jeong Woo Shon, Kyung Hyun Ahn, Seung Jong Lee, May 2004

High density polyethylene and a small amount of poly (1,4-butylene terephthalate) (PBT) have been blended in a twin screw extruder, and its rheology as well as morphology has been investigated as a function of extrusion condition. When the blend was extruded slightly below the melting temperature (Tm) of PBT, the dispersed phase forms a curved sheet morphology, and turns into fibril and finally into droplet structure as more shear is applied. On the contrary, when the material was blended at the higher temperature, the dispersed phase forms only droplet structure.Even though the blend contains as small as 5wt% PBT, the moduli as well as shear viscosity of the blend with the sheet structure increases significantly. However, the droplet structure does not show enhancement of rheological properties unlike the case of curved sheet. This means that we can control the blend morphology as well as its rheology, and can enhance the rheological properties by inducing the microstructure like a curved sheet.

The Effect of Different Batches of the Same Polymer on the Flow in Flat Coextrusion Dies
M. Zatloukal, W. Kopýtko, J. Vl?ek, May 2004

Rheological and molecular characteristics (MWD) were experimentally determined for different batches of LDPE. The results show that extensional viscosity may significantly vary for different batches even if shear viscosities and MWDs are very similar. FEM analysis was consequently performed to determine the stability of the coextrusion flow in the flat die for different batches of the material and the effect was found considerable. A recently proposed ‘TNSD sign criterion’ (Zatloukal et al, Int Polym Proc., 16(2) 198-207 2001), which quantifies the relative stretching of the layers in the merging area, was used for this purpose.

Characteristics and Properties of Metallocenic Syndiotactic Polypropylene
Érica Gervasoni Chaves, Hélio Scarpelli Jr., Sabrina Saraiva Mafra, Maria de Fátima V. Marques, May 2004

This work investigates the characteristics and properties of syndiotactic polypropylene produced by Ph2C(Flu)(Cp)ZrCl2/MAO metallocene catalyst system. The obtained s-PP presented melt temperature around 120°C, being more amorphous as the polymerization temperature increased. From the data obtained through HAAKE mixture chambers we could carry out the rheological characterization of the polymer, which presented a non-Newtonian pseudoplastic behavior, as expected. The polymer also had a good mechanical performance compared to conventional i-PP.

Analysis of Permeability and Weld Line Integrity in Multi-Layer Blow Molded Automotive Fuel Tanks
E. Grald, C. Gomez, T. Marchal, May 2004

In this study, numerical simulation is used to analyze the blow molding process of an automotive fuel tank. In a first step, 3D simulations employing a shell approximation are used to investigate the deformation of a multi-layer parison as well as the thickness variation for each layer. Next, 2D simulations are used to study the details of the welding line formation. Locally, the shear flow across the parison thickness can no longer be neglected. The position of the interface between the layers is calculated using adaptive meshing to handle the very large deformations. The influence of the rheology on the position of the interface is investigated.

The Influence of Melt Rheology on the Specific Output Rate of Broad Molecular Weight Distribution Polyethylenes in Single Screw Extrusion
Rajendra K. Krishnaswamy, David C. Rohlfing, Ashish M. Sukhadia, Kevin R. Slusarz, May 2004

The extrusion (single-screw) characteristics of four broad molecular weight distribution (MWD), linear polyethylene resins are discussed with an emphasis on the output rate. Despite the high molecular weights of the subject polyethylenes, their broad MWD (Mw/Mn range: 10 to 60) does not limit the pressure and torque developed during extrusion. However, the specific output of the four polymers was quite varied. The dependence of the specific output on the melt rheology of the polymers is addressed; specifically, the shear-thinning extent of the melt in the metering section was found to influence output rate. The unique and counter-intuitive temperature-dependence of the shear-thinning character of one of the four polymers will also be addressed in relation to its extrusion characteristics. Lastly, a simple and quick method to evaluate the relative solids conveying efficiencies for various polyethylenes will be presented.

Rheological Evaluation of the Processability of Polyethylenes for Extrusion Coating
Choon K. CHAI, May 2004

The two key processability characteristics of low-density polyethylenes (LDPE) in extrusion coating applications are principally concerned with the degree of neck-in (NI) and the drawdown ability (DD). Molecular structures like long chain branching (LCB) and molecular weight distribution (MWD) have strong influence on these processability parameters, which, in turn, can be correlated with the melt elasticity of the polymer at processing conditions. These molecular structures effects on melt elasticity can suitably be studied by shear and extensional rheologies. A range of extrusion coating LDPE grades have been rheologically characterised and two models relating their extrusion coating processability parameters (NI and DD) and their melt elastic properties have been established. These new rheological parameters and models enable rapid quality controls and evaluation of potential materials, from catalyst development to products scale-up, for extrusion coating applications, with the desirable processability in terms of NI and DD.

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