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Applied Rheology

SPE Library content related to rheology
A Mechanistic Model For Nanocavity Filling
Donggang Yao, May 2018

In this paper, we present an analytical study on the influences of different competing factors on the nanocavity filling process. Particularly, various dimensionless groups are defined to gauge into the size effects in nanocavity filling. A mechanistic model for nanochannel flow is formulated on the basis of disentanglement between molecular layers. The focus was placed on determining the major enabling factors for achieving cavity fill in an extremely short imprinting period on the order of 1 second. It is found that a high-energy mold surface is necessary in roll-to-roll imprinting where the contact time is extremely short and a high imprint pressure is difficult to apply. Additionally, in-mold solidification must be incorporated in precision replication, suppressing shape distortion caused by elastic recovery.

Connecting Rheology Of Polyolefin Elastomers To Dispersion In A Polypropylene Matrix Via Modeling And Experiments With Simple Flow Fields
Jeff Munro, May 2018

Controlling the dispersion of polyolefin elastomers in polypropylene is critical for applications requiring low temperature impact toughness, such as for automotive TPO compounds. To better understand the role of polyolefin elastomer design and rheology on dispersion in polypropylene resins, a computational fluid dynamics model was developed to study the effect of viscoelastic behavior on particle breakup in simple flow fields. This model was applied to breakup of polyolefin elastomers with different rheological features in a high flow polypropylene matrix. Experiments were conducted with similar blends under comparable simple flow fields to validate the results of the model. The learnings were then applied to a simple TPO compound produced with typical twin screw extrusion and injection molding, demonstrating the benefits of a particular elastomer rheology on dispersion and impact toughness properties, and validating the utility of the computational fluid dynamics model to help guide polyolefin elastomer resin design.

Study Of Biodegradable Polybutylene Succinate/Poly(Butylene Adipate-Co-Terephthalate) Blends
Manjusri Misra, May 2018

With increasing interest towards biobased and/or biodegradable polymers that generate high performance composites, instead of petroleum based products, creates new opportunities and research challenges. Poly (butylene succinate) (PBS) is supposed to be one of the most promising biodegradable polyesters because of its good mechanical strength and high heat deflection temperature. However, the low impact strength of poly (butylene succinate) (PBS) has limited its application in some fields. Therefore, poly (butylene adipate-co-terephthalate) (PBAT) and poly (butylene succinate) (PBS) were melt-compounded to fabricate a novel PBS/PBAT blend to improve the impact strength of PBS. The effect of PBAT on the properties of the final binary blends, including mechanical properties, thermal properties and rheology properties, is studied in this research. Rheological properties revealed a strong shear-thinning tendency of the blend resulting from the high compatibility between PBAT and PBS. The partially compatibilized PBS/PBAT blends show high tensile strength (~50 MPa), high impact strength (~200 J/m) and a moderate tensile modulus (~500 MPa). A PBS/PBAT system can be a good candidate to fabricate high impact biodegradable products.

An Investigation Of Rheological Properties Of Polypropylene Single-Polymer Composites
Mingxing Yu, May 2018

Polypropylene single-polymer composites (PP SPCs), whose matrix and reinforcement came from identical type of polymers, were fabricated by an approach of applying undercooled polymer melt. The undercooling method could enlarge the processing temperature windows thus realize the fabrication of SPCs without destroy the reinforcement structures. Rheology could be used in the processing of the SPCs, however there is little investigations. This work was done with the aim to investigate the effect of undercooling compaction temperature from 125 oC to 145 oC on rheological properties of PP SPCs by dynamic rheological measurements. The linear viscoelastic range (LVE) was measured for strain sweep. And it was found that complex viscosity of PP SPCs increased as the temperature increased, whereas the storage modulus decreased during frequency sweep. Moreover, the photography of morphology before and after tests revealed a positive correlation between the degree of shrinkage and the compaction temperature. Overall, the effects of temperature on rheological and morphology properties of PP SPCs are strictly dependent upon the molecular structure parameters.

Isolating The Effect Of Polymer-Filler Interaction On Polymer Composite Property Enhancement: The Example Of Polypropylene/Halloysite Hybrids
Tong Wei, May 2018

We prepare polypropylene (PP) composites with both pristine halloysite nanotubes (p-HNT) and PP grafted halloysite nanotubes (PP-g-HNT) using two processing techniques, solid-state shear pulverization (SSSP) and melt mixing. We address the role of isolated polymer-filler interaction effects on polymer nanocomposite property enhancement at similar, high levels of filler dispersion. As demonstrated by microscopy and rheology, nanocomposites prepared by SSSP with different fillers have very similar, well-dispersed states, eliminating differences in dispersion as a factor in property enhancements. The well-dispersed PP/PP-g-HNT nanocomposites exhibit a broad range of properties that are superior to those of PP/p-HNT, including tensile strength, PP non-isothermal crystallization onset temperature, and isothermal PP crystallization half-time. However, the Young’s modulus is the same regardless of filler modification. Only superior filler dispersion contributes to Young’s modulus enhancement in nanocomposites.

In-Situ Vitamin C Reduction Of Graphene Oxide For Preparing Flexible Tpu Nanocomposites With High Dielectric Permittivity
Han-xiong Huang, May 2018

Flexible thermoplastic polyurethane/reduced graphene oxide (TPU/rGO) nanocomposite sheets are prepared via in situ vitamin C reduction. X-ray photoelectron spectroscopy spectra suggest a successful reduction of the GO by vitamin C, which can enhance the interfacial polarization ability of the resultant rGO layers. X-ray diffraction patterns and transmission electron microscopy image indicate a well exfoliation of the rGO layers in the TPU matrix. This results in the formation of a rheological percolation structure in the nanocomposite with 0.75 vol% rGO, as suggested by the rheological properties. The enhanced interfacial polarization ability and the formed percolation structure of the rGO layers in the TPU matrix allow for constructing a large network of micro-capacitors. Thus high dielectric permittivity (ε′ = 151 at 1 kHz) is obtained for the nanocomposite sample with only 0.75 vol% rGO.

Composition Dependent Charge Storage And Emi Shielding Performance Of Thermoplastic Elastomer Nanocomposites Containing Mwnts
Uttandaraman Sundararaj, May 2018

This study demonstrates the charge storage and electromagnetic interference (EMI) shielding performance of thermoplastic polyurethane (TPU) based nanocomposites containing various amounts of conducting multiwall carbon nanotubes (MWNTs). The functional properties of TPU nanocomposites were systematically designed by generating various degrees of interconnected networks of MWNTs in the TPU matrix. The dispersion and interconnected networks of MWNTs were assessed using rheology and direct current (DC) conductivity measurements. An enhanced charge storage (i.e., high real permittivity) and extremely small loss (i.e., loss tangent) were achieved at a low fraction of MWNTs (5.0wt%) in X-band frequency, whereas, large elimination of incoming microwave radiation was achieved via highly interconnected networks of dielectrically lossy MWNTs.

Practical Simulation Of Liquid Crystal Polymer Directionality During Processing
Anthony Sullivan, May 2018

Liquid crystal polymers (LCP’s) make up a class of performance materials that derive favorable mechanical, chemical, and electrical characteristics from their long-range molecular ordering. This unique microstructure gives rise to anisotropic bulk behavior that can be problematic for industrial applications, and thus the ability to model this directionality is essential to the design of manufacturing processes for isotropic material production. Previous efforts to model LCP orientation have typically been restricted to structured grids and simple geometries that demonstrate the underlying theory, but fall short of simulating realistic LCP manufacturing methods. In this investigation, a methodology is proposed to simulate the director field in practical LCP process geometries for the prediction of the bulk material orientation state. The polymer flow is first simulated using a commercial CFD software and the rheological results are input into post-processing calculations of the polymer directionality. It is shown that the model predicts the expected change in anisotropy as the mold cavity thickness is changed for an LCP injection molding process.

Experimental Study On The Melt Encapsulation: An Analysis Of Die Pressure And Rearrangement Effects
Christopher Höfs, May 2018

A central challenge in the extrusion process is the interaction of the melt with the metallic die wall. These interactions, such as friction and adhesion, lead to a limitation of mass throughput due to high pressure drop and long material and color changeover times. Since raw material costs are price-determining with a percentage of up to 80 %, it is imperative to reduce these interactions. Extrusion dies in particular offer a very large contact area for these interactions, as the melt is formed out there with usually a large surface area. A possible solution to reduce these interactions is the encapsulation of the melt with a low viscous thermoplastic melt before entering the extrusion die. Hereby, the parabolic flow profile with wall adhesion is converted into a block-like flow profile. The pressure drop and material and color changeover times can be reduced, in this way.In this paper, the influence of the melt encapsulation with two low viscous LDPE resins on the flat film extrusion process with focus on the reduction of pressure drop and rearrangement effects is investigated. Therefor the low viscous encapsulation material, the processing temperature and the layer thickness of the low viscous encapsulation material are varied. For example, the pressure drop of the reference process at 200 °C can be significantly reduced from 47 bar to 12 bar for LDPE65 at a melt pump speed of 0.2 rpm. However, due to rheological effects a rearrangement of the low viscous material appears. This means the low viscous material accumulates in the edge area of the rectangular flow channel. As a result, the usable film width is reduced.

Effect Of Die Exit Stress State, Deborah Number And Extensional Rheology On Neck-In Phenomenon
Martin Zatloukal, May 2018

In this work, effect of the second to first normal stress difference ratio at the die exit, uniaxial extensional strain hardening, planar-to-uniaxial extensional viscosity ratio and Deborah number has been investigated via viscoelastic isothermal modeling utilizing 1D membrane model and a single-mode modified Leonov model as the constitutive equation. Numerical solutions of the utilized model were successfully approximated by a dimensionless analytical equation relating the normalized maximum attainable neck-in with all above mentioned variables. Suggested equation was tested by using literature experimental data. It was found that approximate model predictions are in a very good agreement with the corresponding experimental data for low as well as very high Deborah numbers. It is believed that the obtained knowledge together with the suggested simple analytical model can be used for optimization of the extrusion die design, molecular architecture of polymer melts and processing conditions to suppress neck-in phenomenon in production of very thin polymeric flat films.

Modeling Of A Simple Numerical Calculation Methodology To Implement Cross Flows In Extrusion Die Design Based On Network Theory
Bianka Jacobkersting, May 2018

Extrusion dies exert influence on later final product quality. Therefore it´ll make a point the dimensional and die design by using programs for calculation and simulation frequently. For the implementation of product design, it is significant to understand the flow conditions and to be able to predict the flow behavior accurately. Special rheological flow phenomena in the plastic melt as cross flows, which flow perpendicular to the main flow, should be taken into account. This phenomenon is caused by pressure gradients transverse to the direction of extrusion and both the flow distribution and the pressure consumption are influenced in the die. Network theory is a simple numerical method for a holistic one-dimensional representation (GEB) in a spreadsheet program (p.e. Excel), which can design an optimal uniform flow rate distribution and low pressure drop. The cross flow behavior can´t be described with this method as yet. Therefor a linear equation system according to the Gauss algorhythm was developed, which can calculate the cross flows in the die with rectangle cross-section. In this network crosslinks are implemented to take into account the cross flows. The equation system is set up from the network, which corresponds to the number of the desired partial volume flows in the number of established equations. Furthermore the technical measurement entry of cross flows was conduced about the evaluation of ellipsoid shape according to the flow direction and the alignment according to the flow direction. Dead-stop experiments were performed by adding a blowing agent to the extrusion process. Negatives of die with gas-filled bubbles were prepared and evaluated with image analysis software across the half width of die. Afterwards the network theory was validated by Computational Fluid Dynamics (CFD).

Thermo-Rheological Modeling And Simulation Of Heat Sealing Process For Multi-Layer Flexible Packaging Applications
Vinod Kumar Konaganti, May 2018

Heat sealing processes are the most widely used sealing technique in form-fill-seal packaging applications. This process involves the optimization of sealing temperature, dwell time and sealing pressure to achieve a hermetic seal between two monolayer/multilayer polymer films. During this process, the heat transfers through the film structure, melts the resin at the interface and allows the polymer molecular chains to diffuse across the interface to develop the required seal strength. In order to develop strong seals at the interface, it is important to understand the interactions between thermal and rheological behavior of each layer in the multilayer structure as well as the dynamics of melting and crystallization at the seal interface.A novel phenomenological model based on thermo-rheological properties of polymers in the sealing regime has been developed to describe the heat sealing behavior of multilayer polymer films as a function of processing/operating conditions and resin architectural characteristics. In this modeling framework, a dynamic model combining heat transfer and deformation during the squeeze flow has been implemented to understand the coupled effects of phase change (melting/crystallization) and polymer rheology on the heat sealing behavior. The present model is capable of predicting the temporal variations of the interfacial temperature and seal behavior by considering the effects of: (a) non-isothermal squeeze flow of polymer films; (b) processing conditions (seal pressure, seal bar temperature, and dwell time); (c) resin molecular characteristics; and (d) phase transitions (melting/crystallization). The predicted seal characteristics are compared with the experimental data to validate simulation results. This model may serve as a robust tool for efficient multilayer film structure development and optimization of various processing/operating conditions.

Changeover Time For A Lab-Scale Blown Film Line
Christopher Thurber, May 2018

Accurate understanding of changeover time (i.e., the time it takes to change formulations) in a blown film line can minimize waste and maximize production. Previous work examined changeover time in extruders, and residence time distribution for blown film [Wang et. al., ANTEC Tech. Papers, 2015, Wang et. al., ANTEC Tech. Papers, 2017]. This work uses transmission UV-Vis spectroscopy with a copper phthalocyanine tracer to examine the factors affecting changeover time for a blown film line. Our results show that throughput is the strongest factor influencing changeover time, and material rheology is a weaker but potentially important factor.

Effect Of Stress Relaxation On Shrinkage And Warpage Of Injection Molded Parts
Zhiliang Fan, May 2018

The residual stresses in the injection molding process are built up due to the restriction of thermal contraction during the process, coupled with the frozen layer growth with varying pressure history. The stress relaxation behavior of plastic materials complicates the stress field. A three-dimensional linear anisotropic thermo-viscoelastic residual stress model is developed for predicting the effect of stress relaxation on shrinkage and warpage of injection molded parts. Thermo-rheological simplicity is assumed for the material, and the viscoelastic master curve is fitted with a generalized Maxwell model. A time-temperature shift factor table over the range of temperatures which occur during the injection molding process is preferred over the WLF equation and Arrhenius equation due to its general applicability. Two numerical examples are given, and the simulation result comparison between the thermo-viscoelastic model and thermo-viscous-elastic model shows that stress relaxation reduces the molded-in residual stresses slightly, and has a modest impact on shrinkage and warpage. The validation cases also confirm that the simple thermo-viscous-elastic residual stress model is generally able to give a good qualitative and reasonable quantitative prediction of the final shrinkage, warpage and molded-in residual stresses.

Effect Of Injection Molding Condition On Mold Adhesion During Thermoplastic Polyurethane Injection Molding
Jian-Yu Chen, May 2018

Injection molding is one of popular approach for the mass-production of plastic products with complex geometries. Although it is convenient and cost-effective to manufacture goods, some issues such as warpage, quality fluctuation of injection molded part, surface defects, insufficient physical properties are still needed to overcome. During ejection stage, one of annoying issues called mold adhesion, which happens to the interface between molded part and cavity surface, makes molded part difficult to release from mold surface, and the defects such as distortion and crack also occur as serious mold adhesion effect arises. This phenomenon is familiar during thermoplastic polyurethane (TPU) injection molding process. There are numerous factors affected the mold adhesion level, including injection molding conditions, surface morphology, surface modification, rheological properties of molten polymer. In order to understand the effect of molding conditions on mold adhesion level, tensile mode mold adhesion tester was proceeded to quantitatively evaluate mold adhesion level. In addition, surface free energy measured on molded part surfaces was carried out to better understand the wettability. In experiment results, mold temperature and melt temperature both effect on mold adhesion level. Moreover, the responses of SFE on different mold adhesion level are apparent.

Mechanical And Rheological Characteristics Of Pp/Pet Blend With Maleic Anhydrite And Jute Fibre
Abul Saifullah, May 2018

This paper presents an investigation of the effect of mixing natural Jute fibre and Maleic Anhydrite compatibilizer with recycled Polypropylene (PP) and Polyethylene terephthalate (PET) blends. Recycled plastic has a significant contribution to reduce the environmental issues and encourage the economic benefit. PP and PET polymers are commonly used in the industrial fields, however, they are immiscible and it is difficult to be blended. Two different PP & PET (65/35 and 78/22 v/v %) samples have been blended with 0.5% wt (2 g) Jute fibre and 5% wt (20 g) Maleic anhydride (PP-g-MAH). The mechanical mixing has been done by using twin-screw extruder to get pellets of PP/PET/jute/Maleic Anhydrite, which were used to make test samples with injection moulding machine. The comparative result shows that blend of PP/PET with and without any addition of Maleic anhydride and Jute fibre has enhanced tensile and flexural properties significantly.

Improved Processability Of Ultra-High Molecular Weight Polyethylene Via Supercritical Nitrogen And Carbon Dioxide In Injection Molding
Galip Yilmaz, May 2018

The processability of injection molding ultra-high molecular weight polyethylene (UHMWPE) was improved by introducing supercritical nitrogen (scN2) or supercritical carbon dioxide (scCO2) into the polymer melt, which decreased its viscosity and injection pressure while reducing the risk of degradation. When using the special full-shot option of microcellular injection molding (MIM), it was found that the required injection pressure decreased by up to 30% and 35% when scCO2 and scN2 were used, respectively. The mechanical properties in terms of tensile strength, Young’s modulus, and elongation-at-break of the supercritical fluid (SCF)-loaded samples were examined. The rheological properties of regular and SCF-loaded samples were analyzed using parallel-plate rheometry. The results showed that the use of scN2 and scCO2 with UHMWPE and MIM retained the high molecular weight, and thus the mechanical properties of the polymer, while regular injection molding led to signs of degradation.

Rheological Methods For Characterizing The Degree Of Long Chain Branching In Polyethylene
Greg Kamykowski, May 2018

Branching in polymers contributes many unique rheological properties in polymer processing. Polymer branching enhances chain entanglements, increases relaxation times, and increases the extensional flow viscosity as evidenced by the strain hardening phenomenon. For many years, researchers have used different rheological methods to quantify the degree of branching in polymer chains. The most commonly used rheological techniques for differentiating linear and long chain branched polymers include traditional small amplitude oscillatory shear testing (SAOS), such as frequency sweeps at multiple temperatures, followed by time-temperature superposition (TTS), extensional viscosity testing, and large amplitude oscillatory shear testing (LAOS). However, polymer chain entanglement and relaxation are not only affected by branching but also by molecular weight (Mw) and molecular weight distribution (MWD). The common rheological methods may not be able to distinguish whether the rheological property contributions are from long chain branching or Mw and MWD effects. In this paper, we describe commonly used melt rheological methods for studying polymer long chain branching and their respective benefits and limitations.

Open-Cell Foaming Of Pp/Ptfe Fibrillated Composites
Yu Guang Chen, May 2018

In the study. PP/PTFE composites with different degree of fibrillation were prepared. Crystallization and rheology behavior was investigated. The presence of PTFE fiber enhanced the kinetics of isothermal crystallization of PP. The second modulus plateau at the low ω and a tan δ peak indicates the existence of a three dimensional networks. Extrusion foaming results shows that addition of PTFE increase a 2 orders increase in cell dencity and 10-fold decrease in expansion ratio due to addition of PTFE compared to that of PP. With PTFE nanofiber, open-cell content of the composites was increased.

The Importance Of How Online Rheometers Accurately Indicate Melt Flow Rate In An Extruder
Catherine Lindquist, May 2018

TITLE: The Importance of How Online Rheometers Accurately Indicates Melt Flow Rate in an ExtruderCOMPANY: Dynisco Azadeh Farahanchi, Rheological Scientist, PH. D.Bill Desrosiers, Vice President, Business DevelopmentCatherine Lindquist, Marketing Communications Manager1Dynisco Inc. 38 Forge Parkway, Franklin, MA 02038ABSTRACTAmong the various methods for developing new polymeric systems, the extrusion process has been increasingly used in the thermoplastics industry in complex applications such as continuous reactors for melt compounding, mixing, and a variety of reaction applications. In any extrusion system precise testing and analysis is necessary in order to maximize the processing efficiency. The rheological testing measurements on extrudate materials are commonly performed by processors to ensure that their products are meeting the desired qualities and understand the effect of adding various components to their materials. A newly designed on-line rheometer has been developed to continuously monitor the rheological parameters of in-process compounds namely melt flow rate (MFR), intrinsic viscosity (IV), and apparent viscosity. This helps compounders to have a real-time quality control on their products and reduce the failure rates or scraps. The present work aims to describe the design of the on-line rheometer and how it can be easily connected to the extruders using existing ports and flexible adaptors. It also has been explained how the proposed on-line rheometer can duplicate the test conditions of an off-line melt flow rate tester on an extruder in any compounding or manufacturing process. Furthermore, through calculation of activation energy in a specific material and introducing a temperature correlation, it has been investigated how the on-line rheometer considers the temperature dependency of material`s MFR and accurately measures this parameter at various operating temperatures.

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