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Applied Rheology

SPE Library content related to rheology
Rheological and Tensile Strength Characteristics of Polymer Melts
M. Zatloukal, P. Štach, P. Liu, J. Vl?ek, P. Sáha, May 2002

Cogswell [1] and Wagner [2] methodology was employed to determine the rheological and tensile strength properties of two LDPEs and two metallocene LLDPEs resins through capillary and Haul-off (Rheotens-like) measurements. It has been shown that the tensile strength properties obtained by both methods yield almost the same values. Moreover, these values can be correlated to the drawability in tubular film blowing for corresponding materials.

Rheological and Thermoanalytical Investigations of a Class A" LP-SMC Paste"
Marco Wacker, Gottfried W. Ehrenstein, May 2002

Because of the good light-weight potential, the good resistance against corrosion and a good permeability for electro-magnetic waves more often SMC parts will be used in european automotive applications. As a result of varying qualities of the SMC prepreg or paste there exist still problems during the compression molding process.The paper discusses the used measuring methods for quality control and the influence of aging effect, which occurs during the storage of Sheet Molding Compound (SMC), on the viscosity and the curing behavior of a LP-SMC paste.

Temperature Sensitivity of the Linear Viscoelastic Properties of Long Chain Branched Metallocene Polyethylene
Paula Wood-Adams, Stephane Costeux, May 2002

The effects of long and short chain branching on the thermorheological behaviour of polyethylene are described. Long chain branched homo -polyethylene is thermorheologically complex and is most sensitive to temperature at low frequency. A technique for determining the activation energy spectra of thermorheologically complex materials is proposed. Short and long branches in the same system synergistically increase the zero-shear rate activation energy.

Advances in Techniques to Determine Extensional Rheology from Capillary Measurements
M . Zatloukal, J. Vlcek, C. Tzoganakis, P. Sáha, May 2002

Flow through an abrupt contraction has been analyzed experimentally and theoretically through FEM simulations using the modified White-Metzner model. The results show that the 'entrance viscosity ?ENT' (entrance pressure drop divided by the shear rate) strongly depends on the shape of the steady extensional viscosity, the L/D ratio of the orifice die and it can be properly described by the newly proposed model. A Trouton Correction" was proposed and successfully tested to improve the capability of the entrance techniques to properly predict extensional viscosity at low extensional rates. It is demonstrated that the proposed improvements in this work help to more effectively evaluate extensional rheology from capillary measurements."

Aminosilane Superficial Treatment of Lignocellulosic Fillers: Composite Preparation and Mechanical Properties
O.S. Rodríguez-Fernandez, L.L. Jimenez-Valdés, May 2002

Composite preparation including plasticized PVC and different lignocellulosic fillers was carried out. Different contents of fillers were used (20, 30 and 40% in weight), without modification and also treated with a coupling agent, N-(-2-aminoethyl)-3 aminopropyl trimethoxy silane at three concentrations (1, 2 and 3 %). Mechanical and rheological properties of the composites were evaluated. Electronic and optical microscopy was used to analyze the dispersion. Dynamic mechanical analysis was carried out to obtain Tan ?, Hook´s and Newtonian´s modulus.

Computer Aided Optimization of Extrusion Dies
Stefan Kaul, Walter Michaeli, May 2002

In an extrusion process polymer is melted and conveyed through the extrusion die. In the die the form of the melt is converted from a cylindrical into a requested cross-section of the profile. The primary objective of the rheological design of extrusion dies in polymer processing is to obtain an even melt velocity distribution at the outlet of the die. For a given complex cross-section of a profile, yet no procedure is known to calculate or predict the die flow channel geometry with respect to an even velocity profile at the outlet. By designing a complex profile extrusion die an iterative process has to be performed to optimize the flow channel.In this paper a new calculation method is presented which uses a combination of the Finite-Element-Analysis (FEA) and the 'network-theory'. With the aid of this method it is possible to accelerate the iterative optimization process for the design of profile extrusion dies. Furthermore, this method is combined with an optimization scheme based on the evolution strategy. The result is an algorithm to optimize the flow channels in extrusion dies automatically.

Coupled Rheological and Mechanical Design of Stackable Spiral Dies
B. Rotter, W. Michaeli, May 2002

In recent years, the use of stackable spiral (pancake") dies in blown film extrusion has been continuously growing. One main disadvantage of this die design is the susceptibility to mechanical die deflections resulting from melt pressure which can lead to a poor melt distribution or leakage problems. In this paper a flow simulation model will be presented that is able to calculate the melt velocity and pressure distribution in the spiral section. Additionally a mechanical simulation model has been derived that can calculate the deflection of the die plates for a given pressure load. Because of the mutual influence of melt flow and die deflection the two models are coupled and iteratively solved. The impact of the die deflection on the melt distribution and experimental results will be shown."

Designing Screen Packs for Extruders on the Basis of Resin Rheology
Natti S. Rao, Günter Schumacher, Nick R. Schott, Ray Edwards, May 2002

In various extrusion processes, particularly those involving resin blends containing fillers and additives, it is often necessary to increase the melt pressure, in order to create more back mixing of the melt in the screw channel of the extruder. This can be achieved by using screen packs of different mesh sizes. They can also be used to increase the melt temperature to attain better plastication of the resin. Another application of screens concerns melt filtration, in which undesirable material is removed from the melt. In all these operations it is necessary to be able to predict the pressure drop in the screen packs as accurately as possible, as the melt pressure is closely related to the extruder output. Based on recent developments in rheology this paper presents an easy and quick method of calculating the pressure drop in a screen pack as a function of the resin viscosity, extruder throughput and the geometry of the screen. The effect of screen blocking is also taken into account. The predictions agree well with the experiments. Practical worked-out examples illustrate the design principles involved.

Determination of Molecular Weight and Molecular Weight Distribution of I-PP by Rheological Measurements - A Comparative Study
C.H. Scuracchio, R.E.S. Bretas, May 2002

Four polypropylenes of different grades were used in this study to test the reliability of the use of rheological measurements in the determination of the curve of the molecular weight distribution, MWD. For this purpose, it was used the mixing rule theory based on the double reptation. A commercial software (Rheometric Scientific Orchestrator®) and another one developed in our laboratories were used for this purpose. The final data were compared with curves obtained by gel permeation chromatography, GPC. It was found that curves obtained from the rheological tests had weak agreement with the curves of GPC. However the method showed to be reliable for a comparative study among materials.

Development and Characterization of a New Plastomer Designed for Single-Ply Roofing Membranes
T.A. Glogovsky, May 2002

The development and characterization of a new plastomer designed as the primary building block for single-ply roofing are reviewed. An improvement in mechanical properties over existing soft plastomers having similar flexibility was achieved through the incorporation of various monomers, resulting in the creation of bipolymers which provide toughness and softness performance. A higher total level of the combined bipolymers within a polypropylene random copolymer (RACO) matrix was utilized to achieve the unique properties in comparison to the existing plastomer currently used in single-ply roofing. Controlled blending of two plastomers compounded on standard single screw compounding equipment completed development of the final product. The result of the blending study was then simulated and scaled up to a continuous three-loop gas phase pilot reactor. The final mechanical, thermal, and rheological property profile of these new resins is presented.

The Development of Nanocomposites to Enhance Functionality of Materials for Rotational Molding
Darren Martin, Peter Halley, Rowan Truss, Michael Murphy, Simon Meusburger, Oliver Jackson, May 2002

The development of new composite materials with enhanced property profiles for rotational molding represents a key challenge for the industry. The prerequisite attributes of a good rotomolding resin include grindability, sinterability, thermal stability and low moisture sensitivity. This imposes very restrictive limits on the number of promising new candidates.When traditional glass fibres or other mineral fillers such as talc, mica, or calcium carbonate are used, increased stiffness is almost always achieved at the expense of impact properties, ease of processing, wear on equipment, low density and recyclability. Many mineral fillers have been used successfully in numerous high pressure plastic forming processes, however, their successful adaptation has not transposed to the low shear, low pressure environment found in rotational moulding. In addition, large fibres tend to create a natural sieving action when tumbled with plastic powder within the mold and end up lining the inside of the mold serving no useful mechanical purpose. Furthermore, surface finish is generally rougher than that achieved with just the base resin and so it is harder to achieve a glossy finish.Possibly a more successful approach to developing a rotomoldable composite with outstanding engineering properties would be to introduce the matrix and reinforcement into the mold as a curable liquid. This has been done with some degree of success using wollastonite-filled polyurethane (1), although at higher filler loadings impact properties also suffered.In this paper polymer-clay nanocomposites are presented as possible new candidates for rotational molding. Issues and choices relating to the formulation, trials and evaluation of both PE-clay (thermoplastic) and castable polyurethane-clay (thermoset) nanocomposites for rotational molding are discussed. Some key melt rheology results for the PE-based nanocomposites are reported.

Dynamic Mechanical and Rheological Properties of Ethylene/1-Octene Resins with Bimodal Structural Distributions
Colin Li Pi Shan, João B.P. Soares, Alexander Penlidis, May 2002

Ethylene/1-octene resins with bimodal molecular weight and bimodal short chain branching distributions were synthesized in a two-step polymerization process. Comparison of the dynamic mechanical (tensile) and rheological properties of these blends shows that increasing the fraction of copolymer in the reactor blend results in a decrease in its stiffness. However, the energy dampening properties of these blends benefit from the presence of the copolymer. It was confirmed that melt flow properties of polymers depend on their molecular weight distribution.

The Effect of Boron Nitride on the Rheological Properties and Processability of Polyethylene
Sang Myung Lee, Jae Wook Lee, May 2002

The processability of the polymer in capillary extrusion is closely related to the interface between the polymer melts and die wall, and wall surface energy affects the flow of polymer melts in extrusion dies. In this paper, when used Boron Nitride (BN) with low surface energy as the processing aid, we studied about changes of the rheological behavior and processability of metallocene polyethylene (m-LDPE). It also studied about the effect of the hot-pressed BN die on the instability of capillary flow. The equipment used includes a capillary rheometer with two kinds of dies, namely the tungsten carbide and hot-pressed BN dies. The rheological properties of resins with and without BN particles were analyzed by parallel-plate and capillary rheometers. Two types of BN powders with a different the agglomerated particle size and distribution, are tested at various contents. It was found that the BN powder has an influence on the processability of the polymer, depending on the BN content and particle size.Lastly, it must be underlined that it is possible to significantly delay or eliminate the melt fracture, by considering the polymer flow through the hot pressed BN die instead of the tungsten carbide die.

The Effect of Extrusion Processing Conditions on the Thermal and Mechanical Performance of Extrusion Cast Metallocene Polyethylene Films
B.G. Millar, G.M. Mc Nally, W.R. Murphy, May 2002

Cast extruded films were prepared from a range of mPE resins with various co-monomer types (hexene, octene), using different chill roll temperatures from 30 to 60°C. Mechanical analysis showed that the tensile modulus of the films increased with progressive increase in chill roll temperature. DSC analysis showed increases in crystallinity with increasing quench temperature and decreasing MFI. Rheological and molecular weight distribution analysis showed that activation energies of flow for mPE (18-28kJ/mol) were low, this is attributable to the narrower polydispersity of mPE (2.1-3.1) compared to the wider distribution of conventional polyethylenes (4.0-5.0).

The Effect of Molecular Weight and Polydispersity on the Rheological Properties of Pigmented Polypropylene
A.F. Marks, G.M. McNally, W.R. Murphy, P. Orr, May 2002

The rheological characteristics of a range of pigmented polypropylene (iPP) of different MFI values and molecular weight distributions, were investigated using dual capillary rheometry techniques, over the temperature range 190°C to 230°C and shear rate range of 10s-1 to 800s-1 . The various iPP resins were compounded with pigment masterbatch concentrations ranging from 0.2% to 3.0%, using a 38mm Killion compounding line. The pigment masterbatches investigated were iron oxide, titanium dioxide and phthalocyanine blue. The rheological data, showed that there were considerable increases in apparent viscosity of pigmented iPP even at relatively low pigment loadings. Calculation of the non-Newtonian index (n) from the rehological data, also showed the iPP with the narrower polydisperty were less shear thinning than the wider molecular weight distribution polymer resins, especially at the lower shear rates. Activation energies (Ea) calculated from the rheological data showed large increases in Ea especially for wide molecular weight distribution pigmented iPP resins, and compared favorably with crystallinity developed in the polypropylene during the low shear compounding process.

Effect of Molecular Weight on Mechanical and Morphological Properties of High Density Polyethylene Foams
Yaolin Zhang, Abdellatif Ait-Kadi, Denis Rodrigue, May 2002

Morphological and mechanical properties of linear polyethylene (HDPE) foams were investigated as function of polymer molecular weight and blowing agent concentration. The objective of this systematic study was to understanding the effect of polymer molecular weight via rheology on the final morphology of the foams. Shear and elongational properties of linear polyethylenes with a wide range of molecular weights were first measured using, respectively, a rotational rheometer (Bohlin CVO) and an elongational rheometer (RME). Azodicarbonamide (ACA) was used as the chemical blowing agent and concentrations between 1 and 3 wt% were used to produce HDPE foams. We present here the morphology of the foams and their tensile mechanical properties. The results are discussed in terms of the rheological properties of the polymer matrix which is related to their molecular weight.

The Effect of Oil Type and Content on the Rheological, Mechanical and Thermal Properties of a Polyolefinic Based Thermoplastic Elastomer
P.M. McShane, G. McNally, T. McNally, W.R. Murphy, M. Cook, A. Miller, May 2002

Thermoplastic elastomers (TPEs) based on 65 wt. % ethylene-octene copolymer (EOC)/ 35 wt.% polypropylene (PP) plasticised with two paraffinic oils of different viscosities and a naphthenic oil, were prepared using a twin screw compounder. The oil content of the thermoplastic elastomers ranged between 10 and 20 wt.%. Rheological characterisation of these blends was studied over the shear rate range of 30 to 1000 sec-1. The apparent viscosity at temperatures 197 to 237 °C was shown to be dependent on the quantity rather than type of oil. The tensile modulus, impact strength decreased and elongation at break increased with increase in oil content. The compatibility of each plasticiser was studied by measuring the change in glass transition temperature, melting point of PP phase, and enthalpy of melting of each polymer component.

The Effect of Phyllite as a Filler for PVC Plastisols
T.S. Valera, A.P. Ribeiro, F.R. Valenzuela -Díaz, A. Yoshiga, W. Ormanji, S.M. Toffoli, May 2002

Phyllites are abundant methamorphic rocks composed by fine particles of clay minerals and quartz. This paper investigates the use of a Phyllite from Itapeva, SP, Brazil, as a filler for PVC plastisols and compared the properties of the obtained plastisols with the ones obtained for plastisols containing calcium carbonate, the usual industrial filler. Four different formulations were prepared. The pastes were tested for their Brookfield viscosities, gellation and melting temperature and plate-plate rheology. Films were laminated at 180ºC and tested under tensile stress and for heat stability. PVC plastisols containing phyllite exhibited better mechanical properties and acceptable viscoelastic properties.

The Effect of Polypropylene MFI on the Rheological, Morphological and Mechanical Properties of Polypropylene/Polyethylene-Octene Copolymer Blends
P.M. McShane, G. McNally, T. McNally, W.R. Murphy, M. Cook, A. Miller, May 2002

Blends of polypropylene (PP) of MFIs 4 and 25 g/10 min with up to 30 wt. % ethylene-octene copolymer (EOC) were prepared using a Killion compounding extruder fitted with a barrier design screw. Rheological characterisation of these blends was studied over the shear rate range of 300 to 2000 sec-1. The apparent viscosity at temperatures 197 to 237 °C was shown to be dependent primarily on the MFI of the PP rather than the EOC concentration of the blend. The MFI had a significant effect on the mechanical and phase morphology properties of the various blends. Dynamic mechanical thermal analysis (DMTA), and differential scanning calorimetry analysis (DSC) would tend to indicate some degree of polymer miscibility especially at the higher EOC concentrations, with slight decreases in crystallinity and the phase transition temperature of EOC.

Effect of Viscosity on Low Density Foaming of Poly(Ethylene-Co-Octene) Resins
Caroline Vachon, Richard Gendron, May 2002

Foaming of low density poly(ethylene-co-octene) resins by injection molding is the result of various reactions occurring during the process. This includes simultaneous decomposition of the chemical blowing agent and cross-linking of the polymer matrix during curing in the mold, followed by foaming after mold opening. Dynamic rheology as well as elongational viscosity were investigated for compounds prepared from resins with different MFIs and various cross-linking agent levels, and these results were linked to the morphology and density of the corresponding foams. Rheological requirements were finally defined quantitatively for this set of conditions.

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