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Applied Rheology

SPE Library content related to rheology
Effect of Formulation and Processing Conditions on the Viscosity of Masterbatches
Bob Zeller, May 1999

Adding colorants and additives in masterbatches may affect the rheological properties of the resins into which they are mixed, but the extent of this effect has not been fully investigated. This paper reports on a design of experiments (DOE) study of the effect of 3 common colorants, 2 lubricants, a filler, an antioxidant, and 2 processing parameters (melt temperature and screw speed), on the viscosity of a linear low-density polyethylene (LLDPE) masterbatch. The series of experiments determined that only the lubricant and filler had a significant impact on resin rheology.

Quality Improvement of Foamed Seals for the Automotive Industry
Annette Krusche, Edmund Haberstroh, May 1999

Automotive body seals are becoming increasingly complex. As there is still little knowledge about the manufacturing process, extensive investigations are done to analyze the influence of the rheological behavior of the materials, the parameters of the extrusion process and the foaming/vulcanization on the quality properties of the foamed seals. The evaluation allows a better process understanding which in combination with improved test methods leads to an increased product quality and reduced manufacturing costs.

Modeling of Rheological Behavior of Immiscible Polymer Blends Undergoing High Deformation Flows
Mokhtar Aouina, Mosto Bousmina, Robert Guénette, May 1999

Non linear rheology of a mixture of two immiscible viscoelastic fluids undergoing high deformation flow was considered. Using Grmela's approach of compatibility of dynamics with thermodynamics, we derived a set of highly non-linear governing equations that take into account particles breakup, coalescence and the time evolution of the complex interface between the two mixture components. The proposed model recovers previous models such as Doi-Otha, Grmela and Ait-Kadi and Lee and Park models.

Effect of Formulation Variables on Rheology of Rigid PVC
Virginia Odle Hayes, May 1999

The effect of lubricants, impact modifier, and process aid on the processing and physical properties of a rigid PVC compound have been modeled using a Central Composite designed experiment. Capillary rheology was used to evaluate the flow properties of the various formulations in the study. By modeling the rheological properties it is possible to simultaneously optimize flow, extruder conditions, and final part properties.

Rheological Study of Soy Protein-Based PRF Wood Additives
John D. Clay, Bhima Vijayendran, Jan Moon, May 1999

The gelling of soy protein-based PRF wood adhesives is studied. Soy protein isolate, in combination with phenol resorcinol formaldehyde (PRF) resins is useful in the finger joining of lumber. This unique technology has several advantages including an ability to bond green lumber, very rapid set at room temperature, excellent water resistance, and reduced formaldehyde emissions. The goal of this study is to quantify the effect of soy protein hydrolysis conditions and amine functionality on the gelling and ultimate modulus of soy-derived wood adhesives.

A New Generation of Materials for the Calendering Industry
Teresa P. Karjala, Brian W. Walther, Alastair S. Hill, Ronald Wevers, May 1999

While polyvinyl chloride (PVC) has been employed in the calendering industry for many years, other polymers have not been as widely used. Ethylene styrene interpolymers (ESI) demonstrate the requisite rheological properties and thermal stability to be successfully used in the calendering process. Commercial scale validations were performed on ESI based formulations. Examples of the applicability of ESI to calendering are discussed.

Rheology and its Relationship to Applications of Ethylene/Styrene Interpolymers
Teresa P. Karjala, Y. Wilson Cheung, Martin J. Guest, May 1999

The rheological properties of ethylene/styrene interpolymer (ESI) systems ranging in styrene content up to 80 wt% (50 mol%) and in melt index from 0.5 - 10 are discussed. Dynamic mechanical spectroscopy, melt strength, and pressure-volume-temperature data will be presented along with corresponding relationships between these data and applications of ESI.

Analysis of Halo Effects on Injection Molded Parts
Amit Dharia, May 1999

The problem of a specific type of surface defect called tiger stripes" or "halos" on the injection molded parts of the thermoplastic olefin blend is investigated. First the method to reproduce such defects on the small parts is described and then the results of a rheological method to predict materials prone to producing tiger stripes are presented. Results indicate that both the molecular weight and relaxation behavior are critical determinants. Materials with large molecular weights as predicted by very high melt viscosity at zero shear rate and short relaxation time tend to form less tiger stripes."

Analysis of Halo Effects on Injection Molded Parts
Amit Dharia, May 1999

The problem of a specific type of surface defect called tiger stripes" or "halos" on the injection molded parts of the thermoplastic olefin blend is investigated. First the method to reproduce such defects on the small parts is described and then the results of a rheological method to predict materials prone to producing tiger stripes are presented. Results indicate that both the molecular weight and relaxation behavior are critical determinants. Materials with large molecular weights as predicted by very high melt viscosity at zero shear rate and short relaxation time tend to form less tiger stripes."

Structure Versus Rheological Properties of Soft Plastics: The Case of Ep(D)M Polymers
Emmanuel G. Kontos, May 1999

In the world of polymers, EP(D)M's are considered as rubbers capable to become excellent elastomers upon vulcanization. This paper presents EP(D)M's as unique soft plastics and provides some basic relationships between molecular structure of EP(D)M and rheological properties as measured by dynamic mechanical spectrometers. The rheological properties discussed, primarily tan delta, affects greatly the processability of rubbers as well as of plastics which are not rubbers.

Influence of the HDPE Grade on the Blow Moulding of a Bottle: A Numerical Investigation
Benoît Debbaut, Gerrit Rekers, May 1999

A numerical investigation is performed on the influence of the properties of the high density polyethylene properties on the final thickness distribution of a bottle. The K-BKZ integral model with a relaxation spectrum is used for modelling the rheology of the material. A membrane element is used for performing the simulation of the blow moulding of geometrically complex objects, and is combined to a Lagrangian representation for the equations governing the motion. The simulation tool is applied for the production of a bottle with a handle. Numerical predictions on the thickness distribution of the part are compared to available experimental data.

The Effect of the Boron Mitride Type and Concentration on the Rheology and Processability of Molten Polymers
Franky Yip, Eugene E.Rosenbaum, Stuart K. Randa, Savvas G. Hatzikiriakos, Charles W. Stewart, May 1999

The influence of a new processing additive (a composition of fine particles of boron nitride) on the rheology and processability of molten polymers is studied. The equipment used includes both an Instron capillary rheometer with special annular dies (Nokia Maillefer wire coating crosshead) attached to the rheometer and a parallel-plate rheometer. A metallocene polyethylene and Teflon FEP with several types of boron nitride varying in particle size distribution are tested at various concentration levels. The additive with the finest particle size has the greatest influence in crosshead dies and tips. As a result, its use eliminates surface melt fracture and postpones the critical shear rate for the onset of gross melt fracture to significantly higher values depending on the additive concentration. The influence of the boron nitride type and its concentration on the polymer rheology is also discussed. It is found that the activation energy for flow of Teflon FEP scales with the BN concentration.

Developments in High Strength I-PP: Technology Properties, Applications and Markets
Manfred Rätzsch, Ulf Panzer, Achim Hesse, Hartmut Bucka, May 1999

In this paper the manufacture of a new family of high melt strength polypropylenes (HMS-PP), its benefits and application in the field of foam extrusion are discussed. A brief introduction into general pathways of influencing melt strength shows that it is the combination of both, a high strength and high drawability of the polymer melt (due to the introduction of some long-chain branches into the polymer structure) which is the main characteristic of these special materials. The rheological behavior is due to a special post polymerization (Daploy) process which introduces long-chain branches into the propylene polymer by comonomer bridging. The presentation of general properties resulting from the modified polymer architecture is followed by the discussion of benefits HMS-PP gives to polymer processing and to final material properties. In particular it is possible to manufacture non-crosslinked and thermoformable PP foams with a density range down to 0,1 g/cm3 and below by foam extrusion processes similar to the known from polyethylene and polystyrene. Main applications are lightweight packaging trays, beakers and containers as well as technical foams for automotive applications such as headliners, door liners, acoustic panels. In summary it is shown that the new family of high melt strength PP is a challenge and chance for PP to improve in existing and to enter into new polymer processing technologies, applications and markets.

Trade-Offs in Blown Film Processing-Structure-Property Behavior of LLDPE Type Resins from Chromium, Metallocene and Ziegler-Natta Catalysts
Ashish M. Sukhadia, May 1999

Linear low density polyethylene (LLDPE) resins are a very important class of resins for the blown and cast film industry. In this paper, the processing-structure-property behavior and trade-offs observed with three LLDPE resins made from chromium, metallocene and Ziegler-Natta catalysts were examined and critically compared. First, their basic molecular and rheological properties were examined. The blown film performance of these resins was examined with respect to the effects of film thickness and molecular orientation on film properties. The processability of these resins was compared through an examination of the typical extrusion and film blowing parameters. The extensional viscosity behavior of these resins using Cogswell's converging flow analysis was compared. Finally, an attempt was made to highlight the advantages and disadvantages of each resin type as they apply to blown film applications. The overall objective, and hope, of this work was to demonstrate that LLDPE resins from the various catalysts are dramatically different in nature, thereby resulting in different trade-offs with respect to their processing - structure - property behavior in film blowing.

Ranking of Correction Methods - How Effective Are They?
A. Goettfert, E.O. Reher, I.M. Balagula, May 1999

Capillary rheometry is the most popular rheological measurement technique for polymer melt characterization. One of the reasons it is used so frequently is the system's simplicity compared with a rotational rheometer. However, the analysis and interpretation of the raw experimental data (pressure drop as a function of piston velocity) can be time consuming, before the viscosity function can be determined in absolute terms. The Bagley-Correction to determine the entrance pressure losses and the Rabinowitsch-Weissenberg-Correction to determine the true shear rate at the wall (caused by the difference between Non-Newtonian flow and Newtonian flow), are the two classic methods for the determination of the true viscosity function. The failure of adhesion of the polymer melt at the capillary wall, encountered as slippage, asks also for correction. Viscous heating due to dissipation can be significant for high molecular weight polymers processed at high shear rates and asks also for a correction of the viscosity function. The correction methods mentioned will be analyzed with respect to their influence on the viscosity function. It is a goal of this work to provide a quantitative ranking of the methods in question for selected polymers.

The Relative Influences of Process and Resin Time-Scales on the MD Tear Strength of Polyethylene Blown Films
Rajendra K. Krishnaswamy, Ashish M. Sukhadia, May 1999

This paper is concerned with the effects of polymer relaxation time (as estimated via melt rheology) and process extension rate (as quantified via an average MD extension rate at the frost line) on the MD tear strength of various polyethylene blown films. An increase in melt relaxation time at constant process conditions or an increase in process extension rate for a given resin (constant melt relaxation time) were both observed to result in lower blown film MD tear strength. These observations were interpreted in terms of molecular orientation and deformation mechanisms in polyethylene, with preliminary data suggesting that interlamellar shear plays an important role in determining the MD tear performance of LDLPE and LLDPE blown films.

Temperature and Molecular Weight Dependence of Viscosity Revisted: New Formulations for Rheology
J.P. Ibar, May 1999

Viscosity of polymers is key to their behavior in the molten state and thus to their processing. The well known equations of rheology giving the temperature and molecular weight dependence of viscosity are reviewed and tested with two independent sets of results on Polystyrene and Polycarbonate. It is shown that the admitted view that molecular weight and temperature separate in the expression of viscosity is only an approximation. Furthermore, the classical 3.4 exponenet for the variation of Newtonian viscosity with molecular weight is shown to be temperature dependent and to represeent another curve fitting approximation of the effects of entanglements on the viscosity. Another model of melt deformation and of the influenece of entanglements is presented. Based on this new model of interactive coupling kinetics other formulations of viscosity are suggested and tested on two well characterized melts of Polycarbonate and Polystyrene. The paper gives an explanation to the reptation model dilemma. why does the theory predict a power exponent of 3 whereas viscosity behaves like 3.4?

Rheological Modification of PET by Reactive Processing with Polyepoxides
M-W. Young, M. Xanthos, G.P. Karayannidis, D.N. Bikiaris, May 1999

In attempts to produce modified PET resins with improved rheology for applications requiring high viscosity and elasticity such as foaming or extrusion blow molding, a novel diimidodiepoxide of low MW was evaluated as chain extender/branching agent; its reactivity was compared with that of an ethylene/glycidyl methacrylate copolymer. Melt modified products were characterized by end-group analysis, intrinsic viscosity and for dynamic mechanical properties. It is shown that under certain conditions, reaction with less than 1 wt% diimidodiepoxide produced materials with rheological characteristics similar to those of extrusion foamable by gas injection PET grades.

Reactive Processing of Styrene-Maleic Anhydride and Epoxy Functionalized Polymer Blends
Goknur Bayram, Ut/cu Yilmazer, Marino Xanthos, May 1999

The reaction of styrene-maleic anhydride (SMA) with polyethylene/methyl acrylate/glycidyl methacrylate (E-MA-GMA) was studied in a batch mixer and in a corotatmg twin screw extruder. Also, the mixing of a nonreactive blend of SMA with polyethylene/methyl acrylate (E-MA), with similar rheological properties to E-MAGMA, was studied under the same processing conditions. The mixing products of reactive and nonreactive systems exhibited drastically different properties. Reactive blends showed higher tensile modulus, tensile strength, strain at break and complex viscosity in comparison to non-reactive blends. The reactive blends had also finer morphology than the non-reactive ones.

Parameters Affecting Extrusion Foaming of PET by Gas Injection
M. Xanthos, S.K. Dey, Q. Zhang, J. Quintans, May 1999

The rheological properties of conventional PET resins are not particularly suitable for low density extrusion foaming with physical blowing agents and as a result modified resins with higher melt viscosity and elasticity are often used. In this work parameters affecting the monolayer flat sheet extrusion of foams having variable densities (from about 1.2 to 0.2 g/cc) are presented. Unmodified and chemically modified resins with different melt viscoelastic properties are used. The effects of variables such as type and concentration of atmospheric gases, resin rheology and choice of process conditions are related to product characteristics including density, crystallinity and thermoformability.

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