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Applied Rheology

SPE Library content related to rheology
Root Cause Analysis Of Polyolefin-Based Wire And Cable Formulation Die Build-Up
Kurt Koppi, May 2018

Die build-up negatively impacted the capacity of a compounding line for the production of a polyolefin-based wire and cable formulation. This paper discusses a root cause analysis performed on the die build-up defect, the identified solution, and the resulting economic impact.

DMA – The Other Side Of Rheology
Kevin Menard, May 2018

While dynamic testing in torsional rheometers is a well known method, the use of axial or solid state DMA is often considered more of a thermal rather than a rheological technique. DMAs like the Mettler DMA 1+ allow the testing of materials from the solid state into the melt and from the uncured liquid state to a solid. This allows a fuller range of temperatures to be covered in one scan using the shear fixtures. Examples and applications will be discussed.

How Polymer Rheology Impacts The Extrusion Blow Molding Process
Todd Hogan, May 2018

Will provide once it clears the Dow internal release process

Evaluation Of Thermoplastic Polyurethane (TPU) Resins As Possible Substitues Of Current Resins For Escalator Handrails
Qingping Guo, May 2018

Two new thermoplastic polyurethanes (TPU) were evaluated in their possibility to substitute two TPUs currently used in the production of escalator handrail. The assessment is carried out through comparison of their thermal, rheological and mechanical properties. It was found that although the new TPUs show promise, changes should be carried out to make them more compatible with the current process set up and conditions.

Knowledge-Based Product Planning And Designing Of Injection-Molded Parts
Rene Andrae, May 2018

This paper presents a procedure for an integrated design process regarding injection-molded parts. The support of the designer occurs from a knowledge-based production process and material selection, throughout the designing to a rheological part optimization. Techniques of the model-based systems engineering (MBSE) were used for the acquisition of requirements as well as for the development of this supporting system. For validation, selected methods are implemented and tested in a CAD-system.

The New Discovery DMA850 From Ta Instruments
Greg Kamykowski, May 2018

TA Instruments is the world leader in rheology and thermal instruments. One of our thermal/rheology instruments is the dynamic mechanical analyzer (DMA). For several years, the Q800 DMA has been the leader among DMA instruments, but, in late 2017, TA Instruments introduced the new Discovery DMA850 as the next generation DMA. The capabilities of this instrument, along with a comparison of its performance against the Q800 DMA, will be presented.

Modification Of Pla For Improved Layer-To-Layer Adhesion In 3-D Printed Parts
Michael Thompson, May 2018

This study examines the influence that modifying the chemical structure of poly(lactic acid) can have on improving the mechanical properties of a 3-D printed part. A multi-functional chain extender was used to change the polyester such that its rheological response resembled an increasingly branched polymer chain. The modified polyesters were printed into two-layer rectangular specimens and subsequently analyzed for tensile properties as well as adhesive strength by 180 degree peel testing. With increasing chain extender content, the printed specimen exhibited increased toughness and tensile strength, along with greater adhesive strength. The more highly branched, the greater interlayer adhesion as polymer chains diffusion and entangle across the interface.

Rheological Characterization And Quality Assessment Of Commercial Abs Filaments For Fused Deposition Modeling
Cybele Lotti, May 2018

Acrylonitrile-butadiene-styrene (ABS) is the most commonly used thermoplastic used for Fused Deposition Modeling (FDM) due to its low cost and good properties. The viscoelastic behavior of five commercial ABS filaments was investigated and compared to quality features of a two-piece printed part. The results that the commercial ABS filaments differ not only with respect to viscosity, but also to relaxation time, recoverable deformation, morphology/composition, and thermal stability. Filaments with lower recoverable deformation tend to present better surface finish regardless the viscosity and relaxation time. Filaments with lower viscosities and faster relaxation times resulted in tight fit due to disproportional variations in the critical dimensions of the printed part.

Process Impact Of Elliptic Smoothness And Powder Shape Factors On Additive Manufacturing With Laser Sintering
Marc Vetterli, May 2018

As of today, polyamide 12 covers approximatively 90% of the commercially and industrially relevant Laser Sintering (LS) materials. To ensure a reasonable growth of the LS market, new materials must be developed to enlarge the material portfolio. However, the design of novel LS materials is critical as they need to fulfil several criteria. Besides suitable intrinsic properties of the polymer like correct thermal, rheology and optical behaviour, the constitution of the powder and the particles are decisive for a successful processing. This article presents the advances done in the field of particle form characterization for LS powders and their impact on LS processability. By using a trio of form factors, the powder flowing behaviour can be accurately predicted and hence enables to screen potential LS materials on a reproducible and reliable way.

Rheology of Polymer Nanocomposites
Avraam I. Isayev, May 2018

The rheological behavior of polymer nanocomposites is a field of vital importance to scientists and engineers in the plastic and rubber industry. The rheological behavior of nanocomposites is affected by type of fillers (nanoparticles, graphene, nanofibers and nanotubes) their concentration, filler-filler and polymer-filler interactions. After decades of extensive research, the theoretical description of the linear and nonlinear behavior of nanocomposites is still lacking. This presentation will discuss the rheological behavior of the polymer nanocomposites in small and large amplitude oscillatory flow (SAOS and LAOS), start-up shear flow and step-strain relaxation. Our current understanding of theoretical description of various rheological properties obtained in these flow regimes will be presented. The model parameters will be obtained from SAOS experiments. Then these parameters will be used to describe the nonlinear behavior in various flow regimes.

Investigation On The Viscosity Characterization Of The Glass Mat Thermoplastics (Gmt) In Compression Molding System
Chien Tse-Yu, May 2018

Due to its great features of lower tooling cost, better retaining fiber length and concentration, glass fiber mat thermoplastics (GMT) material has been attracting a lot of attention in modern lightweight technology development. However, some defects and unstable quality control problems are still bothering us. To overcome these troubles, people are usually applying CAE technology to assist. However, in this field, CAE is not mature enough yet due to the rheological properties of the GMT material are not measured properly. In this study, we have proposed a method to measure the rheological properties of GMT material through a compression system. Specifically, we have focused on the viscosity of the squeeze flow under the operation of compression processing. The analyzed data is further used for estimation of the rheological parameters and calculation of viscosity at various temperature settings. Moreover, the estimated rheological parameter of the GMT material is integrated into Moldex3D to evaluate the squeeze flow behavior under the compression operation through numerical simulation and experimental study. Results showed that under the higher compression speed, the loading force is increased exponentially as melt flow time is increasing. The numerical simulation prediction is consistent with that of experimental result. However, at slower compression speed, the deviation becomes more serious for simulation approach and experiment. The reason needs to be investigated later. Also, there are various conditions need to consider in the coming future.

Effect Of Molecular Weight On Dynamics Of Linear Isotactic Polypropylene Melt At Very High Shear Rates
Martin Zatloukal, May 2018

In this work, three isotactic linear polypropylenes, with weight average molecular weights between 56 250 - 75 850 g/mol, have been characterized at 230oC over a very wide shear rate range. A low shear rate primary Newtonian plateau, a pseudoplastic region and a well developed secondary Newtonian plateau were identified for all the polypropylene melts. Flow activation energy at low (E0) and high (Einfin) shear rates was found to be 56.590 kJ/mol and 25.204 kJ/mol, respectively. For the first time, it has been discovered that the secondary Newtonian viscosity, EtaInfin, depends linearly on the weight average molecular weight, Mw, in log-log scale as EtaInfin=1.19*10^(-6)*Mw^(1.084). The observed slope close to 1 between Einfin and Mw suggests that polymer chains in the melt are disentangled at the secondary Newtonian plateau region. This conclusion is supported by the experimental observation that the high shear rate flow activation energy Einfin for given PP melts is comparable with the flow activation energy of PP like oligomer (squalane, C30H62; 2,6,10,15,19,23-hexamethyltetracosane).

Visualization Of The Flow Paths In A Tangential Internal Mixer To Optimize The Mixing Behavior
Annika Lipski, May 2018

The visualization of the flow paths in a tangential internal mixer gives the opportunity to understand which kind of mixing is pronounced in dependency of process parameters. With this knowledge the mixing processes can be optimized, so that shorter mixing times and more homogenous mixing is possible. The flowing behavior between the rotor and the mixing chamber was already investigated extensively but the complex flow paths between the rotors is not well known yet. With different colored compounds, it is possible to visualize the flow paths in the mixing chamber. Hereby, the mixing process is stopped after different mixing times and the mixing chamber is completely opened to take the compounds out of it. Those compounds are sliced and photographed. The complex flow paths can be analyzed with different methods that are evaluated in this contribution. One possibility is the analysis of objects in the area between the rotors to draw conclusion on the distributive and dispersive mixing.

Rheological Method Development: Polymer Designs For Blow-Molded, Automotive Seatbacks
Mary Ann Jones, May 2018

Extrusion blow-molding of very large parts such as those used in the automotive industry can exceed the melt strength limits of the polymer or polymer blend of choice. This study was undertaken to define new rheological tests capable of defining the maximum parison weight a material can maintain in the blow-molding process at a given die dimension and temperature. In addition, this is balanced with 1) measurements of the extent of shear thinning as it relates to shear heating that reduces melt strength and 2) measurements of strain recovery that add to the parison weight required to achieve a given length. These rheological measurements are combined with the mechanical properties required to meet specific automotive material specifications as responses in a design of experiments approach to polymer development. Compositional factors associated with PC/ABS blends were defined to successfully produce a model predicting both the ability to fabricate a part from a 30 lb. parison as well as have the mechanical properties necessary to meet the requirements of the European Luggage Retention impact standard for a seatback.

Molecular Weight Distribution Prediction Of Rheology Against Gel Permeation Chromatography For Film Grade Polypropylene
Hoda Bayazian, May 2018

General purpose isotactic polypropylene (iPP) grades are not very suitable for processing operations subjected to sever elongation flow field due to their tension thinning behavior and low melt strength of their essentially linear nature. Yet, by some modification in their structure, or even changing the shaping process design, they may be readily be used in processes such as blow molding, fiber spinning, BOPP processing, etc. In this work, suitability and molecular structure requirement of two commercial PP homo-polymer film grades for slit-die extrusion were investigated. Molecular weight distribution (MWD), as the main parameter to describe the molecular structure of a linear polymer, of these resins were evaluated through measurements of GPC and rheology. From their dynamic shear data the relaxation spectra, h(τ), were calculated from which MWD was estimated using molecular viscoelastic theories and then compared with the GPC results. Generally good agreement, but with narrower MWD rheology curves was found. Exception was observed for the grade for which rheological data predicted bimodal distribution curve comprising a small shoulder of high MW, not seen in the corresponding GPC curve. A higher value of the generalized mixing parameter than that of the double reptation model which was found for this bimodal grade was attributed to an increase in the number of entanglements and better network connectivity.

Effect Of Salt Addition On Dynamic Mechanical Properties For Poly(Methyl Methacrylate)
Masayuki Yamaguchi, May 2018

The effect of the addition of a metal salt compound with low molecular weight on the glass transition temperature Tg was investigated using poly(methyl methacrylate) (PMMA). Lithium trifluoromethanesulfonate was found to be miscible with PMMA and thus the blends show excellent transparency. Furthermore, the Tg shift to high temperature as well as the modulus enhancement in the glassy region were detected by the addition of the salt. The electrostatic interaction between PMMA and the salt is responsible for the phenomenon. Furthermore, it was found from the oscillatory shear modulus measurements beyond Tg that rheological terminal region is clearly detected in the blend without a secondary plateau.

Synergistic Absorption Of Microwave Radiation In Pvdf Hybrid Nanocomposites Containing Multiwall Carbon Nanotubes And Ferrite Particles
Uttandaraman Sundararaj, May 2018

This study presents absorption driven attenuation of microwave radiation in polyvinylidene fluoride (PVDF) nanocomposites facilitated by conducting multiwall carbon nanotubes (MWNTs) and ferrite particles. Electromagnetic interference (EMI) shielding was achieved via a large dielectric loss arising from electrical conductivity (associated with networks of MWNTs) and magnetic loss stemming from ferrite particles. Two different types of ferrites (i.e., nickel ferrite and cobalt ferrite) were synthesized and employed for absorption of microwave radiation. When ferrite particles along with MWNTs were incorporated in PVDF matrix, cobalt ferrites depicted the highest shielding effectiveness. Moreover, the effect of network formation of fillers in PVDF matrix was analyzed by rheology and the correlation of rheological properties with microwave attenuation was studied. The underlying mechanism of microwave absorption in these nanocomposites was systematically assessed with the help of complex permittivity and permeability in X-band frequency, as the X-band frequency range is essential for major commercial applications.

Modification Of Rheological And Crystallization Properties Of High Performance Polymers For Thermoplastic Composite Applications
Sarah Morgan, May 2018

Continuous fiber reinforced thermoplastic composites offer many advantages over thermoset composites, including longer shelf lives of raw materials, faster processing times, design freedom, and the ability to recycle. High performance resins offer high use temperature and excellent mechanical properties in composites, however they present the challenges of high processing temperatures and melt viscosities. Polyhedral oligomeric silisesquioxane (POSS) nanostructured chemicals offer the opportunity to enhance melt flow and increase crystallization rates in polymer systems when they can be dispersed at the nano-level. We describe the rheological and crystallization performance of POSS blends with PPS and PEEK resins.

Nonlinear Viscoelastic Fluid Models With Fractal Time Derivative
Donggang Yao, May 2018

In this paper, we present a viscoelastic fluid formulation containing fractal time derivative. We demonstrate that the inclusion of fractality allows one to model multiscale effects of typical viscoelastic fluids, overcoming undesired stationary predictions and reducing or even eliminating multiple modes in data fitting. The linear version of the fractal model is scaled up to large deformation by incorporation of objective rotation in the constitutive formulation. The resulting model having five model parameters (one for degree of fractality, two for linear viscoelasticity, one for straining, and the last one for rotation) is able to fit startup shear viscosity of a high molecular weight polystyrene solution in high accuracy, and yet using only a single mode.

The Effects Of Metal Stearates On The Rheological Properties Of Powder Injection Molding Feedstocks And Resulting Molded Green Parts
Michael Shone, May 2018

The effects of adding metal stearates to a powder injection molding (PIM) feedstock prepared with a wax based binder system and silicon powder was investigated. The rheological properties and molding properties of the feedstocks were characterized. Predictive viscosity models were developed for each feedstock. The zero-shear viscosity was constant with the introduction of metal stearates while, the yield stress was seen to decrease. The molded green parts were produced with a traditional injection molding process. The surface quality of the molded green parts did not seem to change. The quality through the thickness changed as vacuum voids started to form with the introduction of the metal stearates.

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