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Applied Rheology

SPE Library content related to rheology
Modeling and Analysis of Spin Coating on Spherical Surfaces
Xudong Fang, Donggang Yao, Hao Zhang, Allen Yi, May 2013

A formulation for modeling the spinning coating process on spherical surfaces is presented in this paper. The model can be adopted to predict film thickness profile on spherical surfaces with large central angles. The simulation results showed that the uniformity of final film thickness is not ideal with uniform initial film thickness distribution. The film thickness evolution and uniformity of film thickness were studied using this model and compared with literature to determine potential advantages of the new model.

Reliable Damping Parameters for Simulating Flow of High Molecular Weight HDPE
Tieqi Li, Wen Lin, Tracy Li, May 2013

Determination of damping parameters from uniaxial extensional flow data per K-BKZ/PSM model are evaluated for high molecular weight HDPE resins. It was found that the damping properties depend on strain rate. The strain dependence, however, cannot be represented reproducibly as the relaxation mode-dependent ?k per Luo-Tanner from SER data. More efficient description of the strain dependency remains to be further explored.

Influence of the Endgroup Nature on the Rheological Behavior of Branched Polycarbonate Resins
Jean-Francois Morizur, May 2013

Branched polymer rheology represents a very active field of research with important challenges, both from the scientific and technological point of view. A study of the rheological properties of branched polycarbonate resins is presented. The effect of the endgroup nature on the polymer melt viscosity was investigated.

Liquid Crystal Polymer Films for Use in Food Packaging Applications
Gregory Pigeon, Jo Ann Ratto, May 2013

Liquid Crystal Polymers (LCPs) melt processing remains a challenge. Blown and cast films were processed byextrusion with a counter rotating mandrel die. The die rotation varied from 0 to 30 rpm with the oxygen and water barrier properties being influenced by rotation. Oxygen barrier values as low as 0.057 cc/m2- day was obtained and meets the military specification for oxygen barrier. Thermal, rheological, and mechanical testing were also performed to fully characterize the films.

Evaluation of Planar and Uniaxial Extensional Viscosities for Linear and Branched Polyolefins
Martin Zatloukal, May 2013

In this work, planar and uniaxial extensional viscosities for linear and branched polyolefins has been determined through entrance pressure drop technique on conventional twin bore capillary rheometr by using novel circular and rectangle orifice dies and the capability of two different constitutive equations to describe the measured experimental data has been tested.

Hybrid TPEs: Combining the Strengths of Olefin Block Copolymers with SEBS
Jeff Munro, Greg Li, Lisa Madenjian, Laura Weaver, May 2013

Olefin Block Copolymers (OBCs) are used in a broad range of applications and markets, including soft compounds. Recently, a new grade, INFUSE™ 9010 OBC, was introduced specifically for use in oil- extended compounds. The benefits of this OBC grade on the properties of oil-extended thermoplastic elastomers (TPEs) have been presented previously [1]. Styrenic block copolymers, such as poly(styreneethylene/ butylene-styrene) (SEBS), are frequently used in TPEs with a broad range hardness and other physical properties. The focus of this paper is on the physical and rheological properties that can be obtained in TPEs formulated using both OBC and SEBS elastomers. In general, these hybrid TPE compounds have properties intermediate between that of TPEs formulated with OBC or SEBS alone.

Effects of Clay Loading on the Structures, Mechanical, Rheological Properties of Microcellular Foams of PLA/MMT Nanocomposites
Shyh-shin Hwang, Ching-hsin Hu, May 2013

This study investigated the effect of clay loading on the properties of conventional/microcellular injection molded Poly-Lactic-Acid (PLA) nanocomposites. The results showed that addition of MMT decreases the tensile/impact strength of PLA/Clay nanocomposites. The XRD results showed that with the addition of clay which increased the crystallinity of the PLA/MMT nanocomposites. The thermal properties results showed with the addition of clay which increased melting temperature, degradation temperature and thermal conductivity of the nanocomposites. The clay helps the nanocomposites on having small size cell on the foamed nanocomposites. For the rheological test, with addition of clay into PLA which decrease the viscosity of the nanocomposites. The decreased tensile strength and viscosity is caused by the degradation of the PLA/MMT nanocomposites.

Effective Blending of Ultrahigh Molecular Weight Polyethylene with Polythylene Via Solid-State Shear Pulverization
Mirian F. Diop, John M. Torkelson, May 2013

Blending ultrahigh molecular weight polyethylene (UHMWPE) with high-density polyethylene (HDPE) via conventional processing methods is challenging; as a result of the vast viscosity mismatch between UHMWPE and HDPE, blends prepared via melt processing contain UHMWPE agglomerates dispersed in HDPE. We demonstrate the utility of solid-state shear pulverization to effectively blend 20 wt% UHMWPE with HDPE. Using rheology, differential scanning calorimetry, and tensile testing we studied the effect of UHMWPE composition on blend properties.

Shear and Extensional Rheological Evaluation of Polylactide-Nanographite Platelet Nanocomposites through Constitutive Equations
Esmaeil Narimissa, Rahul Gupta, Nhol Kao, Sati Bhattacharya, May 2013

Polymer based nanocomposites are fabricated through the incorporation of nanoscale inorganic solids into polymeric matrix. The focus of this research was on the production and rheological investigation of polylactide (PLA) and nanographite platelets (NGP) based bionanocomposites. In the current study, the linear viscoelastic behaviour of the samples was investigated in order to study the effects of the enhanced dispersion of NGP fillers on the rheological properties of the nanocomposites. Uniaxial extensional experiments were also carried out to analyse the impacts of the nanofillers on linear viscoelastic envelope (LVE) and non-linear viscoelastic behaviour (strain hardening region) of the nanocomposites. Furthermore, in order to provide an accurate prediction of the extensional viscosity behaviour of PLA/NGP nanocomposites, the modelling of strain-hardening behaviour of neat PLA and its nanocomposites was investigated using steady shear viscosity, relaxation spectrum and damping function based on Papanastasiou-Scriven- Macosko (PSM) version of Kaye-Bernstein-Kearsley-Zapas (K- BKZ) model.

Properties of clay nanocomposites based on PETG by twin-screw extruder using supercritical CO2
Kwangho Jang, Jong Han Choi, Sangmook Lee, Jae Wook Lee, May 2013

A twin-screw extrusion process for PETG/clay nanocomposites using supercritical carbon dioxide was studied. Well-dispersed nanocomposites enhance the superior properties of the PETG/clay nanocomposites. So, we studied to achieve a good dispersion of the individual silicate layers of the clay. For even more enhancement of the dispersion of the clay in polymeric phase, supercritical CO2 can be employed in the processing of the nanocomposites due to the fast diffusion into the clay particles. The properties of PETG/clay nanocomposites are investigated by rheometer, thermal analyzer, permeability tester, and mechanical tester. The effects of clay contents and CO2 feed rate on the rheological and barrier properties of PETG/clay nanocomposites are presented. The results show that the rheological and thermal properties of the nanocomposites increase with the addition of clay. From the permeability test of nanocomposites, the barrier properties also increase. Moreover, the analysis of the nanocomposites also reveals that the use of supercritical CO2 leads to an increase of the rheological and barrier properties. From the results above, we strongly suggest that the use of supercritical CO2 assisted twinscrew extrusion is an effective way to improve the superior properties of PETG/clay nanocomposites.

Polymerization of Lactide to Polylactic Acid and Co-polymers of Polylactic Acid using High Viscosity Kneader Reactors
Boyd T. Safrit, George E. Schlager, Ziang Li, May 2013

Polymerization of lactide to polylactic acid (PLA) can be performed using conventional reactor technology such as stirred tank reactors, but the conversion and/or final molecular weight may have to be controlled to a lower level. At higher conversion and/or molecular weight, the reaction mass will become very viscous, which limits the ability of conventional reactor technology to provide adequate mixing, minimize mass transfer effects on reaction kinetics, remove exothermic heat of reaction and ensure proper heat transfer in order to eliminate hotspots/thermal degradation. Kneader reactor technology has been used over 60 years in many high viscosity applications such as reactions and polymerization, devolatilization, and drying. This technology can handle the higher conversion and molecular weight polymerizations of lactide and other copolymers of lactide, while also providing the heat transfer required for proper temperature control. Using model kinetics and rheology data, a study was performed that shows the capability of kneader reactor technology for lactide polymerizations as well as other copolymers. Kneader reactor technology can also be used to remove the unconverted monomers from the polymer and expected results from the continuous operation of a polymerizer and finisher will be shown.

In Mold Coating of Thermoplastic Parts: Electrical Conductivity Versus Injection Pressure
Seunghyun Ko, May 2013

In Mold Coating (IMC) has been applied to Sheet Molding Compound (SMC) as an environmentally friendly alternative to make the surface conductive; for subsequent electrostatic painting operations. Due to its successful application to exterior body panels made from compression molded SMC, the application of In Mold Coating for injection molded thermoplastic parts is being developed. In order to make the coating conductive, the filler used in IMC is carbon black (CB). However, the injection pressure needed to coat the part is significantly affected by the amount of CB in the coating material. Predicting injection pressures for IMC of thermoplastic parts is more critical than for IMC of SMC. To predict the coating pressures we need to measure the effect of CB on the IMC viscosity. In the present work, we studied the effect of CB on electrical conductivity and viscosity. The pressures needed for coating a typical IMC part with the required conductivity level are estimated.

Transformation of Measured Viscosity Data of Special Plastic Materials Into Moldflow Software
Ruben Schlutter, Thomas Seul, May 2013

Special applications in plastic engineering require new different polymers. Therefore new polymers and additives are constantly being developed. A lot of these special polymers are not available in databases and cannot be used in simulation software. But it is becoming more and more important to know as much as possible about polymers in order to avoid problems in product development and the manufacturing process. So the polymers have to be tested. This paper shows a possibility of measuring points of flow curves and transforming them into a mathematic model to do molding simulation with the specific material afterwards.

Crystallization of Polypropylene: The Effect of Shear and Temperature
Savvas Hatzikiriakos, Maziar Derakshandeh, Mahmoud Ansari, Antonios Doufas, May 2013

The final mechanical properties of a plastic product which is made of semi-crystalline polymers depend significantly on the molecular properties and the applied processing conditions. Particularly, the formation of flow induced structures via polymer crystallization plays a major role in defining the final attributes of the product. In this paper, the effects of shearing and temperature on the flow induced crystallization of several polypropylenes are examined using rheometry. Generally, strain and strain rate found to enhance crystallization in simple shear at temperatures between the melting and crystallization points. The effects of molecular weight and its distribution are also examined and observed to have a strong influence on flow induced crystallization structures.

Controlled Rheology Polypropylenes for Processes and Applications Requiring High Melt Strength
Mike Starsinic, Jessica Fischer, May 2013

Polypropylene (PP)-based materials find limited use in applications requiring high melt strength, but chemical branching overcomes this deficiency. This work demonstrates that combining branching and controlled rheology (CR) technologies results in PP-based resins with unique combinations of rheological and material properties. PP resins ranging from 1-12 MFR and exhibiting improved melt strength at low stress combined with viscosity responses comparable to CR PP under high stress will be presented. The ability to control PP melt strength at constant MFR while maintaining high stress viscosity comparable to PP is presented. HMS-PP with PP homopolymer tensile properties and PP random copolymer flexural properties is demonstrated.

The Influence of Compatibilizer Type and Concentration on the Properties of Immiscible Polymer Blends
Christoph Burgstaller, Bernhard Riedl, Wolfgang Stadlbauer, May 2013

The aim of this work was to investigate the effectiveness of industrially available additives (with different chemical nature) for compatibilization of HDPE – PA6 blends in terms of mechanical and rheological properties. Furthermore, the morphology of the samples should be assessed to get deeper insights into the interaction of the compatibilizer with the two immiscible polymers. We found, that it is possible to compatibilize immiscible blends via the addition of industrially available additives, as well as that the chemical nature of said compatibilizers and the concentration in the blend influence the various investigated properties, like impact strength and morphology.

Effect of Extensive Recycling on Flow Properties of LDPE
Huiying Jin, Joamin Gonzalez-Gutierrez, Pavel Oblak, Barbara Zupan?i?, Igor Emri, May 2013

Low density polyethylene (LDPE) was exposed to one hundred (100) consecutive extrusion cycles to simulate the process of mechanical recycling. Collected samples were characterized by means of melt flow index measurements and small amplitude oscillatory measurements to investigate flow properties. The results suggest that thermal degradation and gelation of LDPE occur after extensive extrusion which leads to simultaneous chain scission and crosslinking of the polymer chains. However, after 40 extrusions crosslinking is more dominant than chain scission. Rheological observations were confirmed by solubility studies that showed a pronounced increase in insoluble fraction after 40 extrusion cycles. This indicates that the technological parameters should be modified when processing recycled LDPE, particularly after 40 extrusion cycles.

The effect of particle size and shape of the nucleating agent on the foaming behavior of a styrene butadiene block copolymer
Bernd Geissler, Anna Uray, Stephan Laske, Clemens Holzer, Guenter R. Langecker, May 2013

In this study the physical foaming of a styrene butadiene block copolymer (SBC) using different grades of mineral fillers as nucleating agent was examined. The aim was to determine, how the mean particle size and shape of the filler influence the foam morphology and the processing of styrene butadiene block copolymer foam. Therefore, several compounds were prepared with a twin screw extruder using calcium carbonate (CaCO3), talcum and glass bubble grades with distinct mean particle sizes. The different filler types were used to investigate the effect of the particle shape on the foam morphology of the SBC polymer. In this study spherical (glass bubbles), cubical (calcium carbonate) and plate-like (talcum) particle shapes were examined. All compounds were characterized with a cone plate rheometer to compare the influence of the different filler grades on the rheological properties. Their foaming behavior was investigated by using a single screw extruder with a screw diameter of 45 mm and supercritical CO2 as foaming agent. The different mineral fillers were compared, due to their effect on the maximum cell density, in terms of cell size and the foam density.

High Performance Thermoplastic Vulcanizates Based on Natural Rubber by Electron Induced Reactive Processing
Manas Mondal, Uwe Gohs, Udo Wagenknecht, Gert Heinrich, May 2013

Electron induced reactive processing (EIReP) – an eco-friendly and sustainable reactive processing method based on the use of high energy electrons - was used for cross-linking of the elastomeric domain during melt mixing in order to prepare natural rubber (NR) and polypropylene (PP) based thermoplastic vulcanizates (TPVs). The electron treatment with various absorbed dose values showed a prominent effect on mechanical, rheological, and morphological characteristics of the PP/NR TPV. SEM and TEM studies confirmed that these TPVs can exist across the co-continuous or discrete phase morphology. The maximum set of mechanical properties (tensile strength of 15 MPa and elongation at break of more than 500 %) were obtained at an absorbed dose of 100 kGy for a 50/50 blend ratio of NR and PP without any addition of compatibilizer or chemicals. At higher absorbed dose values the degradation of polypropylene showed a negative impact on the mechanical properties of the TPVs. Depending on the morphology and the results of tensile test a structure-property co-relationship is drawn on the basis of common phenomenological understanding of the TPVs.

The bending curvature of an elasto-viscoplastic beam under three-point flexion solicitation
Mohamed Hadid, Guerira Belhi, Saadallah Younès, Guerrah Ayoub, May 2013

The thermoplastic polymers have a very narrow range in which their behavior can be assumed to be elastic linear. When a thermoplastic is loaded, it rapidly exhibits a clear nonlinear behavior due to its viscous character, or to its plastic character or to both. However, the contribution of those two characters may be linear or nonlinear. The problem becomes more challenging when the material is subjected to a non-uniform stress field such us in the case of the flexion solicitation. In this case, the same material may have different behavior from one area to another according to the local stress state. The objective of this paper is to develop a rheological model to represent the behavior of an elastoviscoplastic and homogeneous beam, with straight and constant cross section, subjected to a three-point flexion solicitation. It is assumes the Bernoulli and Saint-Venant conditions are met in order for the strain field to be considered uni-dimensional. The work starts with the presentation of the analogical model followed by the mathematical formulation of the model established according to the elasticity, the viscoelasticity and the viscoplasticity laws. The aim of the work is to deal mainly with one specific geometrical parameter of the flexion which is the beam bending curvature. This parameter allows the determination of the deformation field and the stress field in the beam. It is found that in the elastoviscoplastic area of the beam the differential equation of the curvature requires numerical integration performed using the implicit Euler method. This theoretical modeling approach is supported by creep tests results carried out on samples of polyamide 66. The actual test results are qualitatively consistent with the predicted behavior of the rheological model.

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