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SPE Library content related to rheology
Rheological Analysis of Branched-Polypropylene Produced through Reactive Extrusion
Joel Carr, Marcelo Farah, Ana Paula de Azeredo, May 2014

Traditionally, polypropylene (PP) has not performed well in polymer processing dominated by extensional flow due to a lack of melt strength. High melt strength (HMS) can be achieved in PP through the introduction of long chain branching (LCB). These branches introduce a large amount of chain entanglements, enabling PP to perform well in extensional flow processing. The characterization of long chain branched PP is not trivial and requires some expertise and advanced analytical analysis. This work will briefly review a variety of rheological techniques, both shear and extensional, that can be used to detect varying levels of LCB in PP.

The Effect of Isomer on the Thermal and Rheological Properties of Polyetherimides
Manojkumar Chellamuthu, May 2014

Thermal and rheological properties of poly-(ether-imides) with Meta and Para monomer isomer types were investigated using oscillatory rheology and thermal characterization techniques. The poly-(ether-imide) synthesized from Para based isomer showed an improved Tg with superior chemical resistance while still maintaining at least 90% of the flow properties. The observed shift in Tg and minimal differences in shear thinning index were most likely due to differences in entanglement density and relaxation dynamics between the polymers. Additionally, we have attempted to show-case the predictive capabilities of non-linear vs linear rheology in differentiating the structure-property relationship between isomer types.

Internal and Free-Surface Viscoelastic Flow Simulations Using the Corotational Maxwell Constitutive Model
Christian Schäfer, William Aquite, Jovani L. Favero, Tim A. Osswald, May 2014

Understanding and modeling of viscoelastic fluid flows is essential for several industrial applications. Simulations of internal viscoelastic flows as well as of viscoelastic free-surface flows are quite complex and it is necessary to utilize advanced material models. This work focuses on the study of the Corotational Maxwell constitutive model which is implemented in the viscoelasticInterFoam solver developed with the OpenFOAM computational fluid dynamics package. Simulations of viscoelastic secondary flows in a square channel are presented and validated with experimental results. This is followed by a viscoelastic free-surface flow application to simulate a process developed within the Polymer Engineering Center that uses a microcapillary die for the production of micropellets.

Layer-Multiplying Co-Extrusion of High Viscoelasticity Ratio Polymers
Rongzhi Huang, Jessica Patz, Jorge Silva, Joao Maia, Benjamin A. Huntington, Roger T. Bonnecaze, Mark Cox, May 2014

Traditionally, viscosities of co-extruded polymers are required to match to obtain decent multilayer structures, which severely narrows the processing window. In this study, we introduce a way to improve the non-uniform multilayered structure in rheologically mismatched polymers during layer-multiplying co-extrusion. Both high viscosity ratio (PS/PMMA) and high elasticity ratio (TPUs) polymers were used in this paper. The solution to this problem was broken into Engineering and Material approaches. In the Engineering solution a 9-layer feedblock and a new design of multiplier die are combined to start layering with more (and more uniform) layers and lower the pressure drop. In the Material approach, external lubricants are applied to provide the system with maximum wall-slip effect, thus reducing second normal stress difference (N2) responsible for the development of elastic instabilities. Finally, finite element method simulation (FEM) via ANSYS POLYFLOW® is used as a comparison tool to validate the accuracy of predicting the formation and development of flow instabilities.

Ratio Function of Dynamic Moduli and its Application in Consistency Check
Jianhua Huang, May 2014

A new type of functions – a ratio of linear combination of dynamic moduli at different frequencies – and their bounding properties were studied. It was shown that these functions have an important feature, that is, if f represents a given ratio function for a Maxwell model whereas F represents the same function for a generalized Maxwell model, then f and F have exactly the same bounds. So the bounding properties of F can be known by analyzing simple function f only. The study showed that all four ratio functions proposed are bounded for a linear system, which means the dynamic moduli at different frequencies are not independent. Given any dynamic data, one can check the data by calculating the value of ratio function and comparing it with the bounds. If the value breaks the bounds and the violation cannot be attributed to normal experimental errors, then the data must be inconsistent. If the violation exists in the shifted data but not the original ones, then the shifted data might contain artificial errors. The method worked well as it was used to check the real G’, G” data reported in the literature.

Understanding Processability of PA11 via Rheology
Chuanchom Aumnate, John Puentes, Tim A. Osswald, Steve Schick, Jake Mulligan, C. Herrild, K. Smith, May 2014

Polymers are continuously being introduced in applications where metals have been traditionally utilized. For example, PA11 is now being used in the oil and gas industry in underwater flexible pipelines. There are some challenges that are presented when using these nontraditional materials of construction, and likewise, there are interesting challenges that arise during processing. Due to molecular weight growth from shearing and thermal history, the rheological behavior of this resin is a function of time. The molecular weight increase leads to viscosity increase, which reduces sag after extrusion, but hinders flow inside the die. These competing mechanisms must be controlled during processing. This experimental study will help in the understanding of the rheological changes during processing by showing the influence of time, temperature, thermal history and moisture content on the rheology of PA11. Modeling the change in viscosity, which affects production parameters and throughput in extrusion processes, is part of the future work of this study. Beside the temperature-shifting factor, the thermal history and moisture content were identified as playing a critical role in processing tuning. Conventional shear thinning models fail to predict the behavior of this type of material. It is necessary to investigate modeling strategies to assess the appropriate processing conditions of PA11.

Multilayer Co-Extrusion of High Viscosity Elastomer Systems
Patrick J. Harris, Sidney Carson, Jesse L. Gadley, Joao M. Maia, May 2014

This research work presents the first developed multilayer co-extrusion system for high viscosity elastomer materials. Three unvulcanized rubber materials were chosen; two butyl rubbers and a polyisoprene. The elastomers were characterized under oscillatory shear conditions and placed into either a rheologically ‘matched’ or a ‘mismatched’ category. Multilayer co-extrusion was achieved at a total of 8 layers then 32 layers; with two different extrusion rates. Results show good layering performance for both systems; however, interestingly, the rheologically mismatched systems showed a better layer quality as well as a more stable variation coefficient with an increasing amount of layers.

In-Situ Characterization of Thermoplastic Polyurethane Reaction Kinetics Using Rheo-FTIR
Jesse L. Gadley, Joao M. Maia, May 2014

Understanding polymerization kinetics during reactive extrusion maintains the potential to improve processing efficiency. This study focused on understanding the kinetics and mechanical development of aromatic thermoplastic polyurethanes (TPU). The results indicate that rheology coupled with spectroscopy techniques provides a means to capture chemical and physical property development. Information on the development of materials during controlled reactions may then be applied to scenarios in extrusion of reactive systems. This study noted a significant change in both reaction rate and storage modulus as the hard segment content of the system increased from 26.4% to 55.6%.

Hydrogels for Arterial Modelling and Tissue Scaffolding
Austin Coffey, Aimee Dunne, Niall Murphy, Philip Walsh, Rachel Walsh, Seán Lyons, May 2014

Models of human blood vessels have many potential applications as aids in continuing research on new medical devices. The work detailed herein describes the development of a hydrogel material to mimic the mechanical and biological response of a range of human arteries. The developed hydrogels were characterized via swelling studies, differential calorimetry and spectroscopic techniques, while viscoelastic property measurement was investigated primarily using rheological testing methods. A range HEMA/NVP hydrogel materials were successfully developed with properties comparable to a range of arteries, namely, the thoracic and abdominal aorta with storage moduli (G’) varying from 43kPa to 64kPa depending on the formulation. This paper also describes the construction of a mathematical model for the viscoelastic properties of these materials, representing the time-dependent behaviour of the simulated areterial material when subjected to loading and unloading phenomena.

Thermotropic Liquid Crystalline Polymers and Their Fiber Reinforced Composites for Hydrogen Storage Applications
Chen Qian, Craig Mansfield, Donald G. Baird, May 2014

Thermotropic liquid crystalline polymers (TLCPs) are attractive candidates for manufacturing hydrogen fuel storage vessels because of the combination of their outstanding mechanical, barrier, and thermal properties. In this paper, basic mechanical properties of both unfilled and fiber reinforced TLCPs are reported. Significant enhancement in stiffness is observed by incorporating glass fiber and carbon fiber into TLCP matrices. Solidification behavior of TLCPs was studied by rheological experiments in an effort to establish processing conditions. Results reported in this paper build a solid foundation for understanding TLCPs' behavior and help establish parameters for processing these materials via extrusion blow molding.

Thermal, Mechanical, Rheological and Dielectric Properties of Clay-Containing SEBS Nanocomposites: Effect of Morphology
Emna Helal, Nicole Demarquette, Eric David, Danilo J. Carastan, Leice G. Amurin, Michel F. Fréchette, May 2014

In this paper, intercalated vs. exfoliated structures of clay-containing nanocomposites of polystyrene-b-poly (ethylene-co-butylene)-b-polystyrene are studied. The morphology of the nanocomposites, characterized earlier by microscopy and Small Angle X-Ray Scattering, is confirmed through the study of the thermal, mechanical, rheological and dielectric behavior. In particular, the improvement of the thermal stability of the polymer matrix was induced by the intercalated structure while the viscoelastic behavior and the mechanical and dielectric relaxation phenomena were more sensitive to the exfoliated structure.

Reproducible Relaxation Spectrum of Polyethylene via Global Log-Polynomial Kernel
Tieqi Li, Wen Lin, Joo Teh, May 2014

Discrete relaxation spectrum of an HDPE sample has been calculated using two different approaches modified from the original BSW spectrum. The spectrum with the global kernel consisting of two log-polynomial components appears to provide a good representation of the experimental data. It results in a more reasonable prediction of properties on the experimentally unreachable frequency range than a truncated 6-point spectrum does. The global kernel approach also shows the potential of predicting inflection points on VGP plots, which are useful to quantify LCB and other molecular or morphological features.

Thermo-Sensitive Copolymers for the Treatment of Arterial Aneurysms
Anup Poudel, Austin Coffey, Shane McGrath, Damian Kelly, Sean Lyons, Niall Murphy, Philip Walsh, May 2014

Aneurysms (blood filled bulges in the wall of a blood vessel) are among the most common of all lethal cardiovascular conditions. While open surgery and minimally invasive techniques can be used to treat the condition, treatment efficacy, follow up treatment and subsequent management of the healing process is often hindered by the occurrence of endoleaks; leakage into the aneurysm sack after endovascular repair. Furthermore, accessing specific treatment sites located in regions of complex tortuosity remains extremely challenging. The premise of this research is to determine the feasibility of deploying smart, thermo-responsive hydrogels as ‘filler’ materials which can be applied to the affected site using a novel, minimally invasive, catheter delivery technique; with a particular focus on the mechanical and thermo-responsive properties of said hydrogel materials. Different concentrations of poly(poly(ethylene oxide) and poly(propylene oxide) tri-block copolymers, with varying solution-solvent ratios, were studied using calorimetric and rheological techniques. Results show that specific solute-solvent concentrations have potential for use when coupled with a temperature controlled catheter delivery system. However, optimal temperature control remains challenging.

The Role of Rheology in Non-Pressurized Polymer Foaming Systems
Maryam Emami, John Vlachopoulos, Michael Thompson, May 2014

This work explores the influence of rheological properties on polymer foam development in non-pressurized systems. To understand the complex contributions of rheology on different stages of the foam processing in such systems, visualization studies were conducted using a polymer-foaming microscopy setup. Morphological analysis was used to determine the rheological processing window in terms of shear viscosity, elastic modulus, melt strength and strain-hardening, intended for the production of foams with greater foam expansion and more uniform bubble size distribution.

Effect of organoclay content in solid-state polymerization of poly(ethylene terephthalate)
Minh-Tan Ton-That, Musa R. Kamal, Babak Esmaeili, Pierre J. Carreau, Maryam Dini, April 2014

Solid-state polymerization increases the extent of molecular weight reduction of the PET matrix in PET-organoclay nanocomposites.

SPE Applied Rheology Division April 2014 Newsletter
SPE Applied Rheology Division, April 2014

Read the latest issue of the SPE Applied Rheology Division newsletter.

Recycling peroxide-crosslinked polyethylene
Keyuan Huang, Avraam I. Isayev, March 2014

An ultrasonic single screw extruder produces melt-processable decrosslinked high-density polyethylene with good mechanical performance.

Effect of kaolin and calcined kaolin loading on styrene butadiene rubber composites
Salwa Hassan El-Sabbagh, Nivin Ahmed, February 2014

Filling styrene butadiene rubber with untreated and calcined kaolin improves the mechanical properties of the composite.

To optimize nanofabrication, consider unique traits
Helin Zou , Zhifu Yin, E Cheng, January 2014

With optimized parameters, nano hot embossing can create high-quality patterns again and again.

Rheological investigation of the elasticity of polymeric systems
Esmaeil Narimissa, Rahul Gupta, November 2013

Shear rheological analysis has led to a new insight into the relationship between the first normal stress difference, the dispersion of filler material, and the applied shear stress on polymer nanocomposites.

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