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Applied Rheology

SPE Library content related to rheology
Chemical Structure Effects on the Performance of TPUs
A.C. Ruddy, G.M. McNally, May 2005

This work studied the effect of polyurethane chemical structure (i.e. polyester or polyether soft segments) on the rheological, mechanical and thermal properties of four commercial medical grade polyurethanes of similar Shore hardness. The results showed significant differences in melt viscosity, tensile properties and phase transition temperatures (tan ?) with particular polyurethane chemical structure.

Morphology and Rheology of Polycaprolactone/Thermoplastic Starch Blends
Gang Li, Pierre Sarazin, Zhenhua Yuan, Basil D. Favis, May 2005

Polycaprolactone (PCL)/thermoplastic starch (TPS) biodegradable blends were prepared via a one-step extrusion system over the entire range of composition at different viscosity ratios. A detailed morphology analysis of the PCL/TPS blends was investigated by electron microscopy after selective extraction. Through a judicious combination of concentration control and processing conditions, the volume average diameter of TPS droplets can be closely controlled from 0.5 to 16?m. The rheological behavior of these blends is also examined in depth.

Rheometric Properties Based Model for an Improved Solid Contents CIM Feedstock
Hélio R. Jorge, António M. Correia, António M. Cunha, May 2005

A new formulation for Ceramic Injection Molding (CIM), based on a high-grade alumina powder bound with a water debinding system, composed by a mixture of a low molecular weight polyethylene and a polyethylene glycol, has been developed.The present paper reports the determination of the critical powder concentration of the developed feedstock by rheological model fitting. Semiempirical models were discriminated in order to establish the optimum ceramic powder concentration window.

Compounding of Conductive Polypropylene/Graphite Composites
P.E. Poirier, D.J.Y.S. Pagé, P.J. Bates, May 2005

Polypropylene (PP) and Natural Graphite Flake (NGF) composites were prepared by three methods using a high-speed thermo-kinetic mixer. The electrical conductivity of the materials was measured as a function of NGF content. Mechanical and rheological properties were characterized to assess the composite's potential to be processed for applications such as fuel cells.

The Effect of Compatibilisation on the Rheology of Polyamide Blends
F. Gribben, G.M. McNally, W.R. Murphy, A.H. Clarke, May 2005

Blends of Nylon 6.6 with metallocene catalysed polyolefins have previously demonstrated phase separation and component immiscibility. This work investigates the effect of blend composition and of the addition of ethylene copolymer based physical and reactive compatibilisers on the rheological performance of these blends. The results demonstrate that the viscosity of the blends showed negative deviations from a simple log additivity rule but was dependent on both blend composition and compatibilisation.

Rheological and Morphological Properties of VARTM (Vacuum Assisted Resin Transfer Molding) Epoxy Resins/Clay Nanocomposites
R. Peila, S.S. Sangari, T. Karaki, J.C. Seferis, G. Parker, May 2005

Three types of modified organoclay were incorporated into VARTM resins at various concentrations. A Rheometric Dynamic Analyzer was used to analyze the flow behavior of the resins, while the morphology of the clay was examined by X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM). It was found that the viscosity of the resins increased after the addition of the clays and the clays were exfoliated into the matrix.

Geometry Dependent Flow Properties of Long Glass Fiber Reinforced Polypropylene
Peter J. Farrington, Russell G. Speight, May 2005

Long glass fiber (LGF) reinforced resins have established a strong presence in the injection molding industry. Optimising the mechanical properties requires control of fiber orientation during molding. CAE simulations have proven beneficial in mold design; however these simulations depend on the quality and relevance of the rheological properties. The flow behaviour of LGF grades measured in a variety of rheometric geometries is presented.

QC of Polyolefin Manufacturing by Rheology and Multivariate Analysis
Svein Eggen, May 2005

The paper will focus on explaining some of the fundamental techniques of multivariate analysis (principal component analysis) and show examples on how such techniques can facilitate use of rheological measurements in offline and online QC of polyolefin manufacturing.

Impact of Rheological Properties on Melting Rate Calculations
Eldridge M. Mount III, May 2005

Melting rate calculations have been shown in the literature to be strongly effected by the temperature dependent effects (flow activation energy) of polymer viscosity, especially for amorphous polymers1. And this is an important factor in explaining the poor model results for polymers relative to semicrystalline polymers observed in the literature2. Over the years a great number of changes in catalyst systems have occurred in the polymerization of “standard” polymers such as polypropylene and polyethylene. These new catalyst systems have appreciable changed the temperature response of the polymers which can have a significant impact on melting rate calculations. This paper will examine the cause of many melting models general failure with amorphous polymers in relationship to existing experimental melting rate calculations which clearly highlight the importance of the temperature sensitivity of the viscosity to accurate melting rate calculations.

The Effect of Recycle History and Processing Temperature on the Weld Line Strength of a Polypropylene Homopolymer
Robert Simas Jr., Robert A. Malloy, May 2005

This investigation focuses on the inherent recyclablility of a polypropylene homopolymer by characterizing the mechanical and rheological properties of a multiprocessed resin. The investigation studied molded samples both with and without the presence of a weld line. Several blends of virgin and reground polypropylene homopolymer (consisting of 5 recycle histories) were prepared. The tensile properties (including weld strength) and melt flow rate tests were performed on all molded samples from each of the blends.The results of the study showed that regrind did not affect the tensile modulus, tensile strength at yield, or elongation at yield for samples molded without the weld line to any significant degree. The presence of a weld line had a negative effect on the mechanical properties of the molded sample. The weld line strength also decreased significantly as regrind concentration increased. Melt flow rate tests of the various blends showed the melt flow rate increased by a total of 29% over the entire range of regrind percentages studied. Increasing the processing temperature did have a positive effect on the weld line strength. The addition of regrind did not affect the first stage injection pressure or cavity pressure observed during the molding of the test samples.

Numerical Simulation of Deformations for Injection Molded Parts
Chang-Yu Shen, Hai-Mei Li, Shia-Chung Chen, Li Shi, Ching-Hsin Hu, May 2005

Thermally induced stress and the relevant warpage cause by inappropriate mold design and processing conditions are problems that confounded the overall success of injection molding. A thermorheologically simple thermoviscoelastic material model is used to simulate the residual stress and warpage within injection molded parts generated during the cooling stage of the injection molding cycle. The initial temperature field corresponds to the end of the filling stage. The fully time-dependent algorithm is based on the calculation of the elastic response at every time step. Numerical results are discussed with respect to temperature and pressure.

The Investigation of the PTFE Wall Slip Effect in Paste Extrusion
Lei-Ti Huang, Shia Chung Chen, Ping-Shun Hsu, Chun-Yin Kuo, Juin-Yih Lai, May 2005

Polytetrafluoroethylene (PTFE) is a remarkable material having high melting temperature, high chemical resistance, low frictional and dielectric coefficients. However, PTFE fine powder cannot be processed without understanding the rheological behavior of paste powder. In this study, a simple PTFE rheometer was built and the PID control technology used to control the extrusion pressure and extrusion speed (from 2mm/s to 0.5mm/s). Different extrusion length from 45mm to 94mm to change the L/D ratio were also utilized. After analysis of measured data, it was founded the viscosity of PTFE paste basically follows the power law with shear thinning behavior similar to thermoplastics melt. Because of wall slip effect, the pressure drop was one order of magnitude less than that without wall slip and wall slip becomes more significant at high extrusion speed. Lower extrusion speed also results in a better performance in extrudate.

Structure-Property Relations in Visbroken (Peroxide Treated) Impact Polypropylene Copolymers
Chun D. Lee, May 2005

Impact polypropylene (PP) copolymer (reactor blend) or a postreactor blend of PP and ethylene-propylene rubber (EPR), is an immisible two-phase system consisting of PP as a matrix and EPR as a dispersed phase. When the amount and the molecular weight of EPR in such a blend exceed certain limits, then visbreaking of such a blend leads to an unusual melt rheological behavior – namely, a viscosity up-turn at low frequencies as seen in the dynamic measurements of the molten polymer. We attribute this unusual behavior to the formation of an “interacting network structure” between the two immisible phases via grafted molecules created during the visbreaking process.This melt network structure is carried over into the solid state as evidenced from the optical micrographs of the isothermally crystallized samples. The control of this network structure is important because it affects such properties as stiffness, impact strength and bruise resistance. This paper describes the relation between the extent of viscosity up-turn with the impact resistance and flex modulus of the injection molded samples.

Extrusion Rheology of Glass-Fiber-Filled Polypropylene Melts
Natti S. Rao, N. Subramanian, S.R. Nanguneri, Günter Schumacher, May 2005

The advantages of glass-reinforced plastics in various branches of the industry such as automotive and aircraft industries, and also in the manufacturing of furniture and sports goods are well-known. In all these applications knowledge of the melt flow of the composite material is required, in order to design machinery for processing the filled polymer. This paper is a contribution to the quantitative description of the rheology of glass-fiber-filled polypropylene melts. The effect of shear rate, melt temperature and fiber concentration on the melt viscosity have been studied by means of a high-pressure capillary rheometer. A novel equation has been presented to correlate the melt viscosity with the fiber content, using a modified shift factor taking the melt temperature and the fiber content into account. The proposed modeling can be applied to any filled thermoplastic melt.

On the Three-Dimensional Modeling of Polymer Processes
W.A. Gifford, May 2005

The accurate modeling of polymer processes for prediction or design purposes requires many considerations. These include defining the problem, determining the necessary physics the model should include, determining the equations needed to be solved, determining the rheological parameters important in the particular problem being solved, running rheology experiments to determine these parameters, deciding on the best" rheological model to represent the rheological data creating a 3-D representation of the flow domain volume on which the equations are to be solved determining and specifying all necessary boundary conditions obtaining or writing a 3-D flow code which incorporates all the preceding information running the program and finally determining and displaying the output data for which the modeling process was performed. Each of these considerations is discussed to some extent in this paper."

Effect of Compatibilizer Molecular Weight on the Rheology of Polypropylene Nanocomposites
Yeh Wang, Kai-C. Wu, Jian-Z. Wang, May 2005

Melt compounding with a twin-screw extruder was used to prepare exfoliated polypropylene (PP) nanocomposites of organophilic montmorillonite clay compatibilized with maletaed polypropylene (PPgMA). Several grades of PPgMAs of different melt flow indices (MI) and molecular weights were analyzed for the effectiveness of melt exfoliation of organoclay. The extent of clay exfoliation in the nanocomposites was confirmed by X-ray diffraction spectroscopy. It was found that the nanoscale dimensions of the dispersed clay platelets led to significantly increased oscillatory shear flow properties. At a clay loading of 5 wt%, which is much smaller than that of conventional macrocomposites, the hybrid materials exhibited unbound increase of shear viscosity at low frequencies; and nonterminal low-frequency plateau in the linear storage modulus. The relative dynamic properties revealed a systematic trend with the state of exfoliation and dispersion in the nanocomposites.

Rheology of Polystyrene/Carbon Nanofiber Composites
Jianhua Xu, Yingru Wang, Kurt W. Koelling, Stephen E. Bechtel, May 2005

Polystyrene/carbon nanofiber (CNF) composites with various CNF concentrations are prepared using melt blending and solvent casting techniques. Size and dispersion of the CNF are characterized using SEM, TEM, and optical microscopy. Linear and non-linear rheological behavior at elevated temperatures was measured to be very sensitive to the CNF aspect ratio, concentration and temperature. Orientation of the CNFs in shear and extensional flow is characterized using TEM micrographs in 2 perpendicular directions. A full 3D thermo-mechanical model is used to couple the rheology and the CNF orientation.

Description of the Foaming Process during the Extrusion of Foams Based on Renewable Resources
Helmut Potente, Wolfgang Ernst, Jörg Oblotzki, May 2005

Some polymers based on renewable resources like starch containing materials can be plasticated by extrusion processing. Foams based on theses materials have an increasing importance in packaging applications, but also insulation materials have been developed. Starch contains water, which can work as a physical blowing agent for processing of these foams. The foaming process depends on process parameters like the pressure gradient in the die as well as on material properties like rheology. The main target is the production of foams with low density, high expansion ratio and a homogenous cell structure.The foaming process starts in the flow channel of the die. The cell nucleation process can be investigated by a die design with transparent inserts in the flow channel. The influence of process parameters on cell nucleation was determined. It could be shown that a higher pressure gradient in the die leads to a higher expansion ratio and thus to a later cell nucleation.Furthermore, the rheological properties also have an impact on the foaming behavior of molten starch. Shear viscosity is influenced by melt temperature, water content and mechanical energy input during the extrusion process. In this work, the dependency of the flow properties on process parameters was investigated in order to quantify the differences in pressure build-up caused by changes in screw speed and the resulting consequences on viscosity.

A Comparison of Rheological and Thermal Measurements of Cure in Three Epoxy Resins
Mitch Hargis, Levent Aktas, Cengiz Altan, Brian P. Grady, May 2005

Cure kinetics of 3 different thermosetting resins were investigated using differential scanning calorimetry (DSC) and oscillatory rheometry, with smooth and grooved plates. For the latter, a fractional conversion was defined based on the maximum storage modulus achieved at a given temperature, and compared to the fractional conversion calculated from enthalpy measurements. As expected, the rates of reaction for the DSC measurements were much factor than those calculated from rheometry, while the rate of reactions were identical with smooth and grooved plates. However, our measurements showed that the torque for the grooved plates was independent of sample thickness, indicating that the grooves were being deformed rather then the whole resin.

Study on the Rheological Behavior of Polymer Melt for Micro Molding
S.C. Chen, R.I. Tsai, T.K. Lin, R.D. Chien, May 2005

Determination of polymer melt rheological behavior within micro structured geometry is very important for the accurate simulation of micro molding. Yet its investigation is difficult due to the lack of commercial equipment. In this study, melt viscosity measurement within micro channel was established using a micro channel embedded mold operated at a mold temperature as high as the melt temperature. From measured pressures drop and volumetric flow rate both capillary flow model and slit flow model were used for the calculation of viscosity utilizing Rabinowitsch and Walters corrections. It was found that the measured viscosity values in the test ranges are significantly lower (about 30% to 90% lower) than those obtained from macroscopic rheometer. As micro channel size decreases, the derivation in viscosity is increases. This may be attributed to the melt slip occurs on the micro channel wall and the extend of wall slip increases when size of micro channels decreases. In addition, the higher the melt temperature, the effect of wall slip also becomes more significant. The result indicates that current simulation packages are not suitable for micro molding simulation without considering this effect.

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