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Applied Rheology

SPE Library content related to rheology
Acid-free preparation of natural rubber/clay nanocomposites
Woothichai Thaijaroen, Norbert Vennemann, Uraiwan Sookyung, Charoen Nakason, June 2015

Preparing natural rubber/clay nanocomposites by a drying rather than acid coagulation method improves the thermal resistance, tensile strength, and modulus of the rubber vulcanizates.

Monitoring polymer melt rheology during injection molding
Chien Liang Wu, Chung Chih Lin, June 2015

Monitoring the rheological properties of a polymer under different processing parameters gives insight into its melt state and allows the quality of injection-molded parts to be predicted.

Estimate of Astm Melt Flow Rates from Oscillatory Shear Rheology
Ching-Tai Lue, May 2015

ASTM Melt Flow Rate is one of the most common product specifications and is widely used by resin manufacturers and users. Small Amplitude Oscillatory Shear (SAOS), on the other hand, is the preferred rheology data for researchers. A one-to-one correlation between these two kinds of rheology data has not been observed or reported in the past. With a new approach of applying the Cox-Merz Rule, excellent estimates of ASTM melt flow rates were obtained from the SAOS data for a wide range of linear polyethylene resins.

Polypropylene Impact Copolymers for Improved Tiger-Marking Resistance in Large Part Injection Molding
Joel M. Carr, Jeffrey Salek, Mark Chappell, Mois‚s Werlang, Jake Fallon, May 2015

This work will focus on Polypropylene Impact Copolymers (ICPs) aimed at reducing the surface aesthetic defect known as tiger-marking which is formed during large part injection molding of compounded thermoplastic olefins. Emphasis will be placed on rheological predictive testing and how this translates to the final part aesthetic performance.

Determination of the Zero Shear Viscosity of Polyethylene
Joo Teh, Wen Lin, Padmini Popuri, May 2015

The zero shear viscosity (ZSV) of 10 commercial polyethylene resins has been determined with a creep test and the traditional oscillatory frequency sweep test. Identical results were obtained from the two different test methods. The obtained ZSV by either method can be used to evaluate the long chain branching content of polyethylene resins.

Capillary Rheometry Transient Data Analysis
Amir M. Moshe, David Kazmer, Stephen P. Johnston, Shmuel Kenig, Robert Malloy, May 2015

A transient rheological analysis method is presented with investigation of three modeling effects: shear rate dependence, relaxation spectrum, and melt compressibility. Results are presented for Cross-WLF shear-viscosity model, two relaxation spectrum models and two compressibility conditions. The Cross-WLF viscosity model together with a power-law relaxation spectrum and melt compressible conditions yield the highest correlation between the modeled and observed viscosity.

Analysis of the Rheological Behavior of EPDM Rubber with Blowing Agent
Nora C. Restrepo Zapata, Benjamin Eagleburguer, Travis Saari, Tim A. Osswald, Juan P. Hern ndez-Ortiz, May 2015

An experimental investigation is made to study the rheological behavior of an Ethylene Propylene Diene Terpolymer rubber (EPDM) compound for extrusion containing blowing agent. The variation of the viscosity with time has been determined using a plate-plate rheometer at constant frequency. The obtained data is modeled using the Castro-Macosko model and the methodology to develop it uses a nonlinear least-squares regression method following the protocol proposed by Hernandez-Ortiz and Osswald. A good agreement between the data and the theoretical values is found and the values of constant viscosity are superposed in the TTT diagram to determine the operational window for the compound. The effect of the vulcanization and the temperature of processing on the rheological properties have also been studied.

Non-linear Rheology in Shear and Extensional Flows of Maleated PP-Clay Nanocomposites
Tanmay J. Pathak, Krishnamurthy Jayaraman, May 2015

The strain dependence of large amplitude dynamic shear moduli and the transient extensional viscosity were investigated for model polymer nanocomposites with organoclays. A linear maleic anhydride grafted polypropylene copolymer was compounded with 5 wt% each of two different organically modified clays that had different onium ion surfactants and different aspect ratios. The non-linear storage modulus for the compound with the higher aspect ratio particles showed a two stage drop with increasing strain which highlights the breakup of two structures at different rates?an entanglement network of particle attached chains with free chains and another entanglement network of free chains alone. The same nanocomposite melt also displayed a greater extent of strain hardening in uniaxial extensional flow. Both effects may be attributed to a stronger polymer mediated entanglement network in this nanocomposite.

Chemorheological Behaviors of a Reactive Epoxy-Amine System during Isothermal Curing
Xiaoping Guo, Alan Fredrick, May 2015

For a typical reactive epoxy-amine system, the initial (Tg0) and ultimate glass transition temperatures (Tgì) prior to curing and after full cure were measured, respectively, by nonisothermal differential scanning calorimetry (DSC). The chemo-rheological behaviors during isothermal curing of the system were investigated at various temperatures below, near and above the ultimate Tgì by means of dynamic rheometry. According to the characteristics of the time-evolving viscoelastic material functions of the curing system, physical transformations, such as gelation and vitrification, occurring during isothermal curing are identified and analyzed. The dependences of such transformations are then presented in terms of a cure temperature-time-transformation (TTT) diagram, which is of critical importance to providing a practical guidance for the relevant process development in manufacturing a medical device.

Aging Behavior of Polyamide 12 during Selective Laser Melting Process ? Influence on Mechanical Properties
Katrin Wudy, Dietmar Drummer, May 2015

Selective laser melting is a well-established manufacturing technique in prototype construction. In recent years a tendency to rapid manufacturing applications and the production of ready to use components with this technology can be observed. If components made by laser melting are desired to be applied in technical series products, their achievable properties play a major role. The high process temperatures in combination with long build times during laser melting process lead to chemical and physical aging mechanisms on the polymeric feed material. The unmolten partcake material, which acts as a supporting structure, can be removed after each building process and reused for further processes. To achieve part properties which endure the necessary mechanical loads, refreshing of partcake powder with 30 up to 50 % by weight virgin material is necessary. However, constant refreshing strategies will lead to varying component properties due to an undefined aging state of the basic partcake material. Therefore, a fundamental understanding of the correlation between the feed material aging state and resulting mechanical properties is alienable.
This paper deals with the analysis of the relationship between the aging state of the feed material focused on rheological behavior, mechanical part properties and deformation behavior. Therefore, polyamide 12 powder is used for at least five processing cycles without refreshing. Before and after each build process, bulk and material characteristics like bulk density, hausner ratio, viscosity number, melt volume rate and average molecular weight were determined. Tensile tests were conducted in order to study the mechanical material and deformation behavior. Finally, mechanical behavior as a function of feed material can be evaluated. On this basis, powder life cycles in dependency of mechanical properties can be derived.

Linear and NonLinear Rheology of Poly(Butylene succinate)/Fumed Silica Nanocomposites
Xun Chen, Bin Tan, Margaret J. Sobkowicz, May 2015

In this work, the role of shear deformation on the microstructure of nanocomposites formed by compounding poly(butylene succinate) (PBS) with neat and surface functionalized fumed silica is explored by melt state rheology. The rheology results uncover a unique structural evolution from shear start-up in nanocomposites, including formation of a physical network under steady shear. The linear viscoelastic responses show that the shear-induced network can result in increased elasticity and a second shear thinning regime at low frequency. The materials compounded with hydrophobic organically modified silica display shear-induced reinforcement at lower particle loadings than those with hydrophilic fumed silica. These results indicate that reinforcement in nanocomposites can be controlled by filler surface functionality and shearing effects. This method enables improved mechanical properties with low filler loadings.

Rheological Characterization on Thermal Stability and Flow Instability of Ethylene-Tetrafluoroethylene Copolymer
Seigo Kotera, Masayuki Yamaguchi, May 2015

Viscoelastic properties of ethylene-tetrafluoroethylene copolymer (ETFE) in the molten state are evaluated in detail considering the thermal stability during the measurement at high temperature with/without oxygen. It is found that random chain scission reaction occurs without crosslinking even under a nitrogen atmosphere at 300 §C. The steady-state shear compliance Je0, which is affected by the molecular weight distribution strongly, is unchanged during the chain scission, suggesting that the chain scission occurs with keeping the molecular weight distribution. According to the classical theory on the random scission reaction, this result demonstrates that the polydispersity (Mw/Mn) of the virgin ETFE sample, prior to the exposure to thermal history, is closed to 2. On the other hand, ETFE shows crosslinking reaction under air condition even in the cone-and-plate rheometer. The degree of crosslinking is estimated by the plateau modulus G?plateau in the low frequency region.
In addition, flow instability at the capillary extrusion is evaluated. ETFE shows several types of melt fracture over a critical shear stress, e.g., shark-skin, slip-stick and wavy melt fracture. It is interesting to note that quasi-stable flow region is observed between slip-stick and wavy melt fracture regions. It suggests that ETFE can be processed at a high out-put rate condition by the steady slip.

Development of a Relaxation Model for Annealing of Plastic Films and Sheets
Wenyi Huang, Michael D. Read, Todd A. Hogan, May 2015

Controlling shrinkage levels during converting is one of the most important critical customer requirements for many applications of plastic films and sheets. Shrinkage levels of 40-60% are common for cast films and calendared sheets. Shrinkage reduction can be accomplished by a subsequent annealing process after the extrusion casting/calendaring process. In this paper, we established a relaxation model for predicting the shrinkage level of plastic films/sheets upon the completion of the annealing process. Specifically, this model correlated shrinkage level of plastic films/sheets after annealing with the relaxation time of a polymer obtained by dynamic rheological measurement as well as the annealing conditions such as temperature profile and residence time. This relaxation model is very useful for determining the design parameters of an annealing process as well as for optimizing the annealing conditions such as annealing temperature and line speed.

Numerical Simulation of Expandable Polystyrene Microsphere Expansion
Yifeng Hong, Xudong Fang, Donggang Yao, May 2015

In this work, a continuum mechanics model is developed to simulate the expansion process of expandable polystyrene (EPS) microspheres both in air and in partially cured epoxy resin. The model is formulated to take into account various kinetic and dynamic parameters involved in gas bubble nucleation and growth in EPS, including nucleation rate, bubble number per EPS microsphere, rate of bubble radius growth, and bubble pressure drop. For expansion in air, the model is able to quantitatively predict the actual experimental growth rate of EPS microspheres. For expansion in partially cured epoxy resin, the model prediction shows that the retardation effects on EPS expansion only becomes significant in the late stage of the expansion process.

Using Molecular Stress Function Theory to Evaluate Strain Hardening of Polyethylene
Tieqi Li, Wen Lin, Paul Tas, May 2015

Strain Hardening of polyethylene in uniaxial extensional flow is evaluated with a focus on its strain rate dependency. The stress growth function data of LDPE and HDPE by a rheometer with dual drum fixture was evaluated with the Molecular Stress Function (MSF) Theory. The model provides evidence that the MSF fit on the data at the lowest available strain rate may be used to obtain reasonable semi-quantitative characterization of the long-chain branching content of LDPE. The rate dependent strain hardening behavior of the LDPE and HDPE samples, on the other hand, is well characterized with the maximum Trouton ratio (Tr) predicted by MSF. All three resins studied show a decreasing Tr with increasing strain rate. The rate dependence is strong when Weissenberg number Wi ó1.

Rheological Characterization of Highly Filled Composite Systems for Injection Molding Applications
Kurt A. Koppi, Xiaofei Sun, Colleen Southwell, Ellen C. Keene, Diana K. Deese, Tammy K. Fowler, Hunter Woodward, Charles F. Broomall, May 2015

The focus of this study is to characterize the rheological properties of boron nitride (BN) composites. A series of boron nitride composites with varying filler loading level were prepared using two different forms of BN fillers blended with polystyrene (PS). The rheological properties of these composites were characterized using a parallel plate rheometer and a capillary rheology. The structure and thermal conductivity of these composites were also characterized. These data were used to identify structure-property relationships for PS/BN composites.

Effect of Rheology on the Morphology of Coextruded Microcapillary Films
Wenyi Huang, Joseph Dooley, Kurt A. Koppi, Deb Bhattacharjee, Rudolf J. Koopmans, May 2015

This paper reports, for the first time, the successful implementation of microcapillary coextrusion technology with an emphasis on the fundamental understanding of the effect of rheological properties of polymers in both film matrix and microcapillaries on the morphology of coextruded microcapillary films. Four different polymer pairs were judiciously selected for coextruded microcapillary films, indicating that the microcapillary shape may be circular, oval, or even rectangular depending on the viscoelastic properties of the respective polymer pair as well as the processing conditions. The area percentage of microcapillaries in the film cross-section was dependent on the screw speed (i.e., extrusion rate) of the extruder. The average film thickness decreased with increasing line speeds, while the aspect ratio of microcapillary dimension held the reverse trend.

Thermal and Rheological Analysis of Nucleated LLDPE Resin. Determination of Crystallization Kinetics Parameters
Said Fellahi, T. Ahmed, S. Al-Theeb, I. Aloush, May 2015

The effect of a commercial nucleating agent i.e HPN20E on the thermal and rheological properties of LLDPE M500026 resin was successfully studied. The crystallization temperature increased by about 7§C and the crystallization % decrease when a NA is added. Non-isothermal crystallization parameters were determined. The lower Ea value for LL50-NA indicates easier crystallization in the presence of a nucleating agent.
Time sweep rheological experiment proved to be a powerful technique to evidence the effect of a nucleating agent. Hot stage microscopy confirmed the role of a NA in reducing the size of crystallite

Flow Behavior of Thermoplastic Starch-Blends
Matthias Musialek, Kalman Geiger, Christian Bonten, May 2015

In this study a polyethylene modified with thermoplastic starch (TPS) is investigated and its rheological behavior is shown. The unmodified polyethylene has a common shear thinning behavior whereas the thermoplastic starch presents a typical elastomeric flow property. The complex viscosity shows a strong dependence of the TPS volume fraction. To describe the flow properties over a broad range of shear rate, a new empirical approach was created, based on the Carreau and the Ostwald de Waele equation. The approach shows very good consistency with experimental results compared to other models from the literature. The parameters of the approach can be explained physically and show strong dependence of the TPS concentration. Furthermore the maximal force acting between the particles can be calculated based on the model parameters and the structure of particle network can be quantified by the fractal dimension. Futhermore an improvement in the mold construction can be achieved through a better modelling.

Investigating the Influence of Filler Type, Particle Size and Weight Fraction on Rheological and Thermal Behavior of Polypropylene/Blast Furnace Slag Microcomposite
Abdelhamid Mostafa, Stephan Laske, Elke Krischey, Helmut Flachberger, Clemens Holzer, May 2015

The aim of this study is to assess the rheological and thermal performance of polypropylene (PP) composites filled with blast furnace slag (BFS) filler. Two filler types, crystalline and amorphous, were ground into three micro-sized batches: 71, 40 and 20æm and each introduced without treatment to BB412E-grade PP via melt kneading. So composites with 10, 20 and 30 wt% filler were prepared, formed into plates by means of compression molding and then subjected to rheological and thermal investigation. Type of filler did not show any noticeable effect on rheological and thermal behavior, while particle size and content did. As expected, complex viscosity, storage modulus and loss modulus curves slightly shifted to higher values with increasing filler content. Composites with 40æm filler size showed best rheological performance regardless of filler type. Slight shifting to lower and higher temperature values was observed for crystallization and melting peaks. In addition, decrease of filler size and/or increase in filler amount lead to a decrease in enthalpy and crystallization degree

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