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Applied Rheology

SPE Library content related to rheology
Study of the PTFE Rheology During Paste Extrusion Process
Shia Chung Chen, Lei-Ti Huang, Ping-Shun Hsu, Yu-Wan Lin, James Huang, May 2006

Polytetrafluoroethylene (PTFE) is a remarkable membrane material. Due to its high melting point, PTFE fine powder cannot be processed using conventional molding methods. Instead, techniques involving paste extrusion, rolling and sintering have to be employed. This research builds a simple PTFE capillary rheometer system, with accurate extrusion speed and extrusion pressure control, and investigate the rheology of PTFE paste during extrusion process. Due to the lower constant speed, the density variation of PTFE extrudate decreases from 1.75 g/cm3 (± 5.8%) to 1.68 g/cm3 (± 0.48%). In addition, different lubricant content (18 wt%, 20 wt%, and 22 wt%) was used to monitor the pressure drop at different extrusion speeds (0.5 mm/s, 1 mm/s, 2 mm/s) and reduction ratios (RR=26.47, 47.06, 80.06). It was found that higher lubricant content and high reduction ratio result in lower pressure drop. Lower extrusion speed also results in a better performance in extrudate formation.

Linear Viscoelastic Behaviors of Polypropylene
Yeh Wang, Kai-C. Wu, Jian-Z. Wang, May 2006

Polypropylene-layered silicate nanocomposites modified with different levels of maleated polypropylene (PPgMA) compatibilizers were prepared through melt compounding. Above a threshold loading the storage modulus G’ was shown to display a low-frequency plateau. The threshold loading level was found to be strongly correlated with the exfoliation of layered silicates. The samples with higher degree of exfoliation exhibited lower threshold loading level. Such threshold behavior is attributed to the existence, in the quiescent state, of mesoscopic domains composed of correlated silicate layers. Finally, melt rheology also demonstrated that the stress level imposed during melt compounding played an important role in clay exfoliation.

Rheological Studies on Radiation Modified Polyethylene Resins
Song Cheng, Ed Phillips, May 2006

Radiation modification of polyethylene resins prior to end product conversion has brought about significant improvement of various properties of the resins and products made from them using extrusion based processes where the products are formed in the melt phase at different shear rates and extensional rates. Rheological characterizations including Rheotens measurements, capillary viscosity and melt flow stability were carried out on radiation modified HDPE and LLDPE resins and their un-irradiated base resins. It is shown that electron beam irradiation of the resins has significantly enhanced the melt strength due to long chain branching. This effect would be very beneficial to the processability of the radiation-modified resins for applications that demand higher melt strength.

In-Mold Coating for Thermoplastic Parts: Modeling, Rheology and Apparent Slip
Narayan Bhagavatula, Chuckaphun Aramphongphun, Elliott Straus, José M. Castro, May 2006

In-mold coating (IMC) is carried out by injecting a liquid low viscosity thermoset material onto the surface of the thermoplastic substrate while it is still in the mold. A computer code based on the Control Volume based Finite Element Method (CV/FEM) has been developed to predict the fill pattern and pressure distribution during the coating flow using the Sisko viscosity model and taking apparent slip into account during. Both these factors lead to a better prediction of pressure distribution. The rheological parameters and the apparent slip parameter are ascertained by using a slit rheometer. Simulation and rheology results are presented in this paper.

Modeling of Deformation Processes in Vacuum Thermoforming of a Pre-Stretched Sheet
Hosseini Hossein, Berdyshev Boris Vasilivich, May 2006

Modeling of deformation processes in vacuum thermoforming for a preliminary stretched thermoplastic sheet (plug-assist vacuum thermoforming) is investigated in this paper. The model can be used for production of polymeric articles with minor wall-thickness variation. A nonlinear rheological model is implemented for developing the process model. It describes deformation process of a pre-stretched sheet at any phase of vacuum thermoforming process. This process is described by a set of deformation processes that each on them is specified by an appropriate boundary conditions. For model validation, a comparative analysis of the theoretical and experimental data is presented. The wall-thickness distributions obtained from modeling results corresponded well with experiments. The satisfactory result establishes a method for prediction and enhancement of the final products quality in criterion of wall-thickness distribution.

Novel Metallocene Catalyst Phillips Loop-Slurry Based Polyethylene Resins for Extrusion Coating Applications
Ashish M. Sukhadia, Gary D. Jerdee, Kelly R. Frey, Michael D. Jensen, Max P. McDaniel, Youlu Yu, May 2006

Significant advances in our abilities to synthesize novel polyethylene resins for extrusion coating applications are discussed. The new resins were largely equivalent to a conventional HP-LDPE resin in impact, tear, adhesion, sealing, extruder motor loads and pressures at comparable melt index values. Some resins closely approached the neck-in and drawdown of the HP-LDPE resin. These results are discussed in terms of the molecular and rheological properties of these novel resins compared to conventional HP-LDPE resins.

Observations and Insights into Some Unusual Rheological Behavior of Metallocene Catalyst Polyethylene Resins
Ashish M. Sukhadia, Youlu Yu, David C. Rohlfing, G.L. Hawley, May 2006

The dynamic shear rheological behavior of polyethylene resins made using a single metallocene catalyst was measured and analyzed. We observed some unusual rheological behavior that, at first glance, was more reminiscent of the well-known behavior of highly filled systems. Specifically, the viscosity exhibited yield stresslike character with a sharp upturn in the low-frequency viscosity. The standard molecular weight distribution profile for these resins was generally unremarkable. The causes of this viscosity behavior were explored by further characterization of the molecular architecture and attributed to the presence of long chain branching selectively present in the highest molecular weight fractions of the polymers.

Low Temperature Impact Modifier for Clear Polypropylene Applications
Huan Yang, Dave Hansen, Jeff Southwick, May 2006

A styrene-ethylene/butylene-styrene (SEBS) block copolymer with enhanced rubber segment is used to modify homo polypropylene and random copolypropylene. The impact property of blends is analyzed based on the instrumented impact test, and the optical property is measured by haze and transmission tests. The results show that both impact strength and optical properties of blends are improved even with low addition of the unique SEBS. Another novel SEBS is also used to further improve the low temperature impact strength of random co-polypropylene without sacrificing the clarity. The findings can be applied in many packaging applications where both clarity and impact strength are desired. The mechanical, rheological and thermal properties of blends are investigated by flexural test, capillary rheometer and DSC respectively. Those results provide important guidance for optimizing the formulation.

Structure Development of Various Polyolefins in Injection Molding
Jaein Suh, James L. White, May 2006

There have been no systematic comparison studies of structures in injection moldings of the various commercial polyolefins.We have investigated crystallization and orientation development in injection molding of various polyolefins, which include high density polyethylene (HDPE), isotactic polypropylene (i-PP), isotactic polybutene-1 (i-PB1) and isotactic poly(4-methyl pentene-1) (i-P4MP1). We used both volumetric injection speed and injection pressure control as the main processing parameters with varying packing pressure and thermal condition based on injection melt and mold temperatures, similarly related to the crystalline melting points.The effort to take into account of these variations on structure development was combined with considerations of crystallization kinetics and rheological properties of raw materials.

Using sc-CO2 as a Processing Aid for Improving the Properties of Polymer Nanocomposites
Quang T. Nguyen, Donald G. Baird, May 2006

Supercritical carbon dioxide (sc-CO2) is used in this work as a processing aid for improving the dispersion of the clay nanoparticles in the melt intercalation process of HDPE-clay nanocomposites. Some preliminary experiments were performed to study the effect of sc-CO2 on the melt intercalation process. Results from the mechanical properties and rheological studies show a direct effect of the sc-CO2, suggesting that the presence of sc-CO2 in the melt blending process can enhance the degree of mixing and the dispersion of the nanoclays into the polymer matrices.

Rheological Modeling of Warpage in Polymeric Products Under High Temperature
Hosseini Hossein, Berdyshev Boris Vasilivich, May 2006

Thermoforming process is one of the most popular techniques in the polymer processing. Wide applications of thermoforming are due to its high performance, simplicity, compactness and relatively low-cost equipment. The fundamental defect inherent to the thermoforming technology is warpage of the products during their application which becomes particularly apparent under high temperatures. The warpage defect is understood as the process of non-uniform (heterogeneous) change of the geometric dimensions of products in time resulting in a change (distortion) of their original form. The results of this work allow us to find out the causes of this warpage and ascertain the conditions that give rise to this defect, thereby making it possible to work out valid recommendations for its partial and, in some cases, complete elimination.

Ultrasound Aided Extrusion Process for Preparation of Polypropylene-Clay Nanocomposites
Sergey Lapshin, A.I. Isayev, May 2006

Two methods for the fabrication of PP/clay nanocomposites using a continuous ultrasound assisted process are compared. In the first approach a two stage process was implemented. The nanocomposites were prepared using a co-rotating twin screw extruder followed by a single screw extruder equipped with an ultrasonic die attachment. In the second method a single stage process was used. The nanocomposites were compounded using a single screw extruder with mixing elements and an ultrasonic die attachment. Two regimes of feeding were realized, namely, starved and flood feeding. The gap size in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Similarities and differences of nanocomposites obtained by these two methods are discussed based on their rheological, mechanical properties, and structural characteristics.

Development of a High-Pressure Slit Rheometer
Fritz Klaiber, Ivan Dario Lopez Gomez, Tim A. Osswald, Lih-Sheng Turng, May 2006

In thin - wall injection molding processes, parts thinner than 1 mm are produced using high injection pressures and velocities. Modeling has not been successful in predicting process physics during molding. We have built a high pressure slit rheometer that enables us to measure the rheological properties of polymers at elevated pressures and temperatures. Measurements were done with polystyrene, and the results showed the effect of pressure and the effect of viscous heating on the viscosity. Results from such measurements will allow us to introduce viscosity pressure effects during mold filling of Thin-Wall Injection Molding.

Flame Retardancy and Rheological Behaviour of Acrylonitrile-Butadiene-Styrene Copolymer (ABS) Composites Filled with Magnesium Hydroxide Sulfate Hydrate(MHSH) Whiskers
Bo Liu, Yong Zhang, Chaoying Wan, Yinxi Zhang, May 2006

Flame-retardant ABS composites were prepared using MHSH whisker as a flame retardant. The morphology observation indicates that the addition of zinc stearate could lead to the uniform dispersion of the whisker and improvement of flame retardancy. With increasing whisker content, flame retardancy properties of the composites is improved, the viscosity and storage moduli of the composites increase at low frequency zone. The presence of zinc stearate leads to slight increases in the storage moduli.

Effect of Epoxy Modifier on Flame Retardancy and Rheological Behavior of Acrylonitrile-Butadiene-Styrene(ABS)/Montmorillonite(MMT) Composites
Bo Liu, Yong Zhang, Chaoying Wan, Yinxi Zhang, May 2006

ABS/MMT composites were prepared via melt intercalation to MMT with or without pretreatment of liquid epoxy resin. For the direct addition of epoxy, the composite has intercalated structure; while for the pretreatment of MMT with epoxy, the composite has exfoliated structure. Cone analysis results reveals slight difference in flame retardancy between the two composites. At low frequency zone, the composite with intercalated structure has higher storage modulus than the composite with exfoliated structure.

Rheological Characterization of Compatability & Degradation of Polycarbonate/Polybutylene Terephthalate Layered Silicate Nanocomposites
Wade S. DePolo, David W. Litchfield, Donald G. Baird, May 2006

The linear viscoelastic oscillatory shear properties of a polycarbonate PC and polybutylene terephtahalate PBT, 60/40 by respective weight, blend and its nanocomposites with various concentrations of organically modified organoclay and clay surface treatment were evaluated. The decrease in properties is attributed to a decrease in molecular weight. A 70% decrease in complex viscosity over all angular frequencies is observed. A relatively small decrease in Tg is observed and is attributed to increased compatibility.

Effect of Preparation Method on the Rheological Behavior of Waterborne Polyurethane Dispersion
Samy A. Madbouly, Joshua U. Otaigbe, Ajaya K. Nanda, Douglas A. Wicks, May 2006

Two classes of environmentally-friendly polyurethane dispersions have been prepared via prepolymer emulsification process and acetone process. Rheological behavior of these dispersions has been studied as functions of PU-concentration, degree of post-neutralization and temperature. At a critical volume fraction of PU (? ~0.43), a dramatic increase in the reduced zero shear viscosity was detected for the two dispersions. Co-occurrence of thermal-induced gelation and liquid-liquid phase separation was observed for the prepolymer process, while, only liquid-liquid phase separation was discovered both rheologically and morphologically for the acetone process.

Functionalization of Polypropylene with Sulfonyl Azide through Reactive Blending
Qing Li, Costas Tzoganakis, May 2006

The functionalization of polypropylene (PP) by 4-carboxybenzene sulfonyl azide (CBSA) was investigated in a batch mixer. The degree of grafting was studied through FTIR, 1H-NMR and XPS spectroscopy using varying levels of CBSA. Under different reaction temperatures, the grafting degree showed a maximum point at 190°C. The degree of grafting increased with feed azide content initially and then leveled off. The rheological properties of the functionalized PP were also evaluated by oscillatory shear measurements and were found to correlate with the grafting degree results. Finally, the adhesion of functionalized PP to aluminum substrates was found to increase significantly.

Rheology Studies of Two-Phase Gas-Polymer Suspensions During Mold Filling
X. Qin, M.R. Thompson, A.N. Hrymak, May 2006

In thermoplastic foaming, phase separation (i.e., bubble nucleation and growth) occurs due to a sudden change in pressure during mold filling that has significant effects on the rheology of polymer flow. An instrumented mold cavity has been designed to capture rheological measurements of the eventual two-phase gas-polymer suspensions. Experimental results for low density polyethylene (LDPE) and thermoplastic polyolefin (TPO) with two types of chemical blowing agents indicated that the rheological properties of two-phase gas-polymer suspensions were sensitive to shear rate, blowing agent concentration, melt temperature and mold temperature. The viscosity of gas-polymer suspensions was reduced in the presence of gas bubbles. A model has been proposed that yields good agreement with our experimental results for estimating the viscosity of two-phase flow in the mold cavity of the injection molding machine.

Injection Molding Simulation in Dealing with Part Quality Variance and Correlation Study
Byung Hak Lee, May 2006

Utilizing the injection molding simulation, this paper illustrates a methodology of dealing with manufacturing variance occurring in molded parts. For the simulation, the manufacturing variance is deliberately induced by a small change in processing condition variables, which consequently causes a variation in the rheological properties of the polymer melt entering into cavity. By comparing the simulation results with previously published experimental results, an attempt is made to statistically validate this methodology. In doing so, the effect of different switchover methods during the injection stage is comparatively evaluated. The part weight and dimensions are chosen as the quality characteristics. This study also investigates correlations between part weight and dimensions, as well as between the predictions and the experiments of an actual molding trial.

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