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SPE Library content related to rheology
Representation of Polymer Melt Rheology Data
Polymer melt Rheology data is often represented as a power law function or as a 6 constant polynomial when used in various flow or extrusion simulation packages. Both representations are inaccurate at various shear rates due to the functionality of the representation. With the introduction of more polymers showing broad Newtonian regions, the need for better constitutive representation is needed to accurately estimate viscosity as a function of shear rate and temperature in simulation packages. This paper will compare the fit of various equations and constitutive relations to capillary rheometer data for polymer melts to determine an efficient representation of the Newtonian and power law regions
Extrusion of HDPE-Wood Blends
In previous studies1-3, both rheological and extrusion characteristics of a 50% wood-HDPE composite as well as its virgin HDPE resin were investigated. In this paper, the extrusion characteristics of the blends made up of these two materials were studied. It was found that for a screw which has the higher compression ratio, for all the blends, the pressures increased with increasing RPM with the exception of 50% HDPE-wood composite at 50RPM; whereas for a screw with lower compression ratio, for the 36% and 50% wood-HDPE blend, there was no pressure generation at any RPM even though the output increased in a nearly linear fashion. The effect of temperature on pressure generation was also looked at and will be presented here. Similar to the previous studies, the experimental results were compared to those simulated using a commercially available computer program, Flow 2000™.
Characterisation of Reactive Extruded Recycled Poly(Ethylene Terephthalate)
Recycled poly(ethylene terephthalate) (R-PET) was chain extended with pyromellitic dianhydride (PMDA) in an industrial scale twin-screw reactive extrusion system. Reactive extruded recycled poly(ethylene terephthalate) (RER-PET) samples at different PMDA concentrations were characterised in terms of rheological properties; thermal transitions and crystallinity. The results confirm the increase in molecular weight with an increase of PMDA concentration, and the formation of branching at concentrations above 0.25 wt.% PMDA. Structural changes due to PMDA addition affect the Tm, Tc and the crystallinity; however, no significant change was observed for the Tg.
The Effect of Texture on the Shear Rheology of a Thermotropic Liquid Crystalline Polymer
The effects of annealing time and temperature on the transient shear rheology of a thermotropic liquid crystalline polymer are reported. During flow startup, the first shear stress maximum and shear stress minimum was found to depend on annealing time, temperature, whereas the second shear stress maximum, a true overshoot, depends on the temperature, but not on annealing time. In situ rheo-optical characterization revealed that the evolution of the melt texture depends on the annealing time and temperature. We confirm that the threaded texture leads to the generation of the local shear stress maximum and shear stress minimum during shear flow startup.
SER Universal Testing Platform - The Ultimate in Physical Material Characterization Technology
The SER Universal Testing Platform marks a revolutionary breakthrough in the field of physical material characterization technology. Designed as a detachable fixture for a rotational rheometer host system, the SER design incorporates dual windup drums that ensure a truly uniform extensional deformation during uniaxial extension experiments. Although originally developed as an extensional rheometer to be used for the rheological characterization of uncured polymers, this remarkably versatile miniature test platform can be used in characterizing a host of physical properties on a variety polymer melts and solid state materials over a very wide range of temperatures and kinematic deformations and rates. This single instrument is capable of converting a conventional rotational rheometer host system into a single universal testing station capable of performing experiments from extensional melt rheology to solids tensile, tear, cut fracture, peel/adhesion and friction testing all within a controlled environment. Experimental results demonstrating some of these testing capabilities are presented for polyethylenes of varying macrostructure.
RCR- A Fast Rheological Testing with Higher Selectivity of Elastomer Compounds and Thermo Sets
Quick tests of elastomer compounds are usually done at low shear rates far from processing. A rheological characterisation of thermo sets under curing conditions like in the later processing is so far not possible.A new device, the RCR" a further development of the "Rheovulkameter" concept is described. The selectivity is compared to a standard Mooney and rheometer measurement for elastomer compounds. A model to estimate entrance pressure loss to characterize elongation behaviour from the simple extrusion test is introduced and compared to capillary rheometer data. Finally the determination of rheological parameters of thermo set material under process like conditions is introduced."
Shear Rheology and Melt Compounding of Compatibilized Polypropylene Nanocomposites
Melt compounding was employed to prepare nanocomposites of exfoliated organophilic montmorillonite (o-mmt) clay dispersed in a maletaed poypropylene (PPgMA) and PPgMA compatibilized composites of clay and polypropylene (PP). Several grades of PPgMA of different melt flow indices (MFI) were analyzed for the effectiveness of melt exfoliation of organoclay. The extent of clay exfoliation in the nanocomposites was confirmed by X-ray diffraction and transmission electron microscopy. The thermal effect on the rheology and compounding was also investigated. The shear viscosities of the PPMA compatibilizers are highly dependent on the processing temperature. The experimental results indicated that the high mixing temperature causes easier diffusion of polymer into clay galleries, and more complete wetting of clay stacks, however, the mixing torque exerted on the clay particles becomes lower. Thus the mixing temperature had to be varied according to different grades of PPMA in order to achieve desirable level of torque and yield extensive exfoliation of organoclay in the nanocomposites.
A Rheological Model for Quantitative Prediction of Die Swell: Effect of Shear Rate and Temperature
During the last three decades a progress has been made in modeling of the die swell by the introduction of the so-called first normal stress difference and shear stress. Initially developed by Tanner, the model has undergone several improvements or alterations, leading to the development of new formulations. The purpose of the present investigation is to review the formulation of the die swell models proposed by Tanner, Bagley and Duffy, Mendelson and Finger, White and Roman, Vinogradov and Malkin, Macosko and Kumar et al. Next, an alternative formulation is proposed, which does not appear to exhibit mathematical defects, and an attempt is made to explore its modeling performance by comparing the predictions with the experiments of low density polyethylene, polypropylene and polystyrene under a steady shear mode over the wide range of shear rates and processing temperatures.
Morphology-Rheology Relationships in Coalescence of Polypropylene Droplets in Polyamide 6-Polypropylene Blends Induced by Simple Shear Flows
A mechanistic model for coalescence was developed by considering ballistic approximation for the kinetics of approach of the droplets. The collision frequency was corrected to take into account hydrodynamic interactions and the effects of drainage between partially mobile interfaces. A semi-quantitative agreement was observed between the model and the experimental results obtained using isotactic polypropylene (PP) and polyamide-6 (PA6) blends sheared in a cone and plate rheometer at low shear sates (0.1 s-1). Model predictions were combined with the phenomenological model of Lee and Park and predictions of the rheological behavior of the blend during coalescence were obtained.
Numerical Simulation of Laser/IR Assisted Micro-Embossing
The use of hot embossing for fabrication of polymeric microfluidic devices is gaining a great deal of attention in recent years because it is a relatively simple and low-cost process. Conventional microembossing is a relatively slow process that requires both the mold and the polymer substrate to be heated during embossing and cooled before de-embossing. In order to shorten the cycle time, a laser/IR-assisted microembossing (LIME) process was evaluated in this study. Since laser/IR heats the substrate rapidly and locally, the heating and cooling time can be substantially reduced. Experimental results have shown that both shorter cycle time and good replication accuracy can be achieved. In order to better understand this process, a commercially available FEM code DEFORM® was used for process simulation. Because the temperature distribution inside the polymer substrate is affected by the penetration of radiation energy flux from laser/IR heating, the relationship between penetration energy flux and temperature distribution was implemented into the FEM code. Rheological properties of selected amorphous and crystalline polymers were characterized and incorporated into the FEM code. Two different modes of IR embossing were simulated, in which either a transparent mold or transparent substrate was used. The flow patterns observed in the experiments agreed reasonably well with the DEFORM-3D simulation and a quantitative comparison between experimental and simulation results was made using DEFORM-2D.
Effects of Stress on the Exfoliation of Polystyrene Nanocomposites
Polystyrene/organoclay nanocomposites have been prepared by melt blending in a vertical co-rotating twin-screw mixer. Monodisperse polymers having molecular weights of 18k and 49k were investigated. Low molecular weight polystyrenes were chosen to take advantage of the high viscosities near Tg, allowing temperature variation to provide for several orders of magnitude of viscosity and to correspondingly change the shear stress. Melt rheology was the primary tool used to determine the extent of exfoliation in the nanocomposite samples. The highest amount of exfoliation at low clay loading was present in samples with an 18k matrix favoring low temperature. A bimodal polystyrene matrix facilitated dispersion, but the low molecular weight chains compromised the final moduli.
Mix Models for Analysis and Optimization of Natural Rubber/Carbon Black Batches
Models based on kinetic, thermodynamic and rheological equations have been developed to compute dispersion extent, batch temperature and rotor torque/power consumption at discrete intervals during a mix cycle in an internal mixer. Evaluating the models over successive time intervals allows the computation of dispersion, temperature, and torque/power profiles for a complete mix cycle. The mix models are found to describe experimental torque and temperature curves for mixing natural rubber with carbon black fillers over a range of particle sizes and loadings (0 to 50 phr) for rotor speeds ranging from 40 to 70 RPM in lab-scale internal mixers. Rate constants for filler dispersion, incorporation and erosion can be extracted from baseline mixes and subsequently used to simulate mixing at a variety of different operating conditions. The models thus permit convenient analysis and optimization of mixing protocols on a desk-top computer.
Thermo-Kinetic Compounding of Polypropylene and Clay
Polypropylene (PP)/Montmorillonite (MMT) clay nanocomposites have been prepared by melt mixing PP and different levels of a predispersed organoclay masterbatch (PP/clay concentrate). Melt mixing was achieved using a Gelimat, a high-speed thermo-kinetic mixer. The Gelimat system is designed to handle difficult compounding and dispersion applications and can achieve mixing, heating and compounding products within a minute. Therefore, the thermal history of the compounded polymer is short, which limits degradation. The structure and properties of the nanocomposites prepared with a Gelimat were compared to ones prepared with a twin screw extruder. The structure and properties of PP/clay nanocomposites were compared by X-ray diffraction, mechanical testing and rheological analysis. Results indicate that a better exfoliation of the clay can be achieved with thermo-kinetic mixing when compared to extrusion, resulting in better mechanical properties.
In-Situ Wide-Angle X-Ray Scattering (WAXS) Analysis of Electrically Activated Polypropylene(PP)/Clay Nanocomposites
Recently we have invented a novel method for fabricating polypropylene (PP)/clay nanocomposites by applying the electric field. Electric field was found to facilitate destruction of the layer-stacking and separation of the silicate layers by the penetration of polymer chains into silicate galleries. This was evidenced by rheological measurements, X-ray diffraction and Transmission electron microscopy. From this observation, we could find that the microstructural change of PP/Clay nano-composites induced by the electric field is a very important factor to control the performance and morphology of the material. In this study, real-time evolution of PP/clay nanocomposites under electric field using in situ wide-angle X-ray scattering (WAXS) analysis will be presented. We designed a heating block equipped with electric circuits to apply electric field on the molten state of PP/clay composites. The real-time microstructural changes of PP/clay nanocomposites under AC electric field of 1kV/mm and 60 Hz were analyzed by the result of 2D WAXS data. This will be compared with that under DC electric field. We will present the kinetics of melt intercalation process under electric field.
Rheological Characterization of Polystyrene-Clay Nanocomposites as they Relate to the Degree of Dispersion
Polymer nanocomposites with as little as 2-vol. percent of layered silicate can dramatically improve tensile modulus, strength, and heat distortion temperature without significant loss of impact strength. Such improvements will have major impact in the material industry and technology. Because viscoelastic measurements are highly sensitive to the nanoscale and mesoscale structure of polymeric materials, when combined with X-ray Scattering, electron microscopy, thermal analysis, and mechanical property measurements, they will provide fundamental understanding of the state and mechanism of exfoliation of layered silicate in polymer matrix. In addition, understanding rheological properties of polymer nanocomposites is crucial for application development and understanding polymer processability.The degree of intercalation, exfoliation, and dispersion has been traditionally characterized by XRD and TEM. While both of them are very effective tools, both are limited by only probing a small volume of the sample and are too costly for routine characterization of nanocomposites. Melt rheology can quantify via a global average on the degree of intercalation/exfoliation/dispersion across whole nanocomposite test specimens usually around 2 grams of samples. It will be less ambiguous than other techniques (e.g. TEM) in quantifying exfoliation/dispersion. In addition, it will be easier to perform than TEM and XRD thereby opening up the possibilities of performing routine studies to better understand the influence of material options and processing conditions for improving nanocomposite exfoliation/dispersion. In this report, the effects of clay dispersion/exfoliation on the viscoelastic properties of polymer/clay nanocomposites are investigated using dynamic mechanical measurements, dynamic shear measurements, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Polystyrene/clay hybrid materials with different degree of dispersion/exfoliation were prepared by solve
Melt Rheology of Polylactides
Polylactides (PLAs) have been known for several decades and have recently gained considerable commercial significance. This development makes it urgently desirable to have the rheological properties of these materials well-characterized. In this study, rheological and thermal measurements were made on a comprehensive and well-characterized set of homopolymers and copolymers spanning wide ranges of molecular mass and stereoisomer proportions. Temperature dependencies of the time-temperature superposition curves were obtained. Data were correlated utilizing a viscoelastic model enabling the development of a simple Excel spreadsheet for predicting linear viscoelastic properties as a function of molecular weight and temperature.
Compositional Heterogeneity of Ethylene-Acrylate Copolymers: Effect on Melt Rheology
A new technique, Interaction Polymer Chromatography (IPC), was used to characterize ethylene/methyl acrylate (EMA) copolymers for chemical composition variation. This technique can be used to determine chemical composition heterogeneity (CCH) of copolymers. The CCH, molecular weight distribution (MWD) and long chain branching of tubular process EMA's are measured and compared with autoclave process EMA's. The tubular EMA has a much higher CCH and a narrower MMD compared with the autoclave EMA. It also has a lower degree of branching. It is found that the significant CCH of tubular EMA attributes to its unusual high melt elasticity. The discussion also highlights the correlation between CCH and some other polymer properties.
Rheology, Processing and Electrical Properties of Multiwall Carbon Nanotube/Polypropylene Nanocomposites
Dispersal of a relatively small concentration (about 1 % volume fraction) of multiwall carbon nanotubes (MWNT) into polypropylene (PP) is found to cause large and complex changes in nanocomposite transport properties. Specifically, both the shear viscosity ? (?) and electrical conductivity ? (?) of the MWNT nanocomposites decrease strongly with shear rate and, moreover, these dispersions exhibit impressively large and negative normal stresses. Additionally, when extruded, MWNT nanocomposites shrink rather than swell. We associate these flow-induced property changes with the formation of non-equilibrium, percolated nanotube network structures.
Characterization of Polypropylene Composites at Low Micro-and Nano- Filler Content
Polypropylene/nanoclay (PP/clay) and polypropylene (PP) containing traditional mineral fillers (talc, mica, GF and wollastonite) are used in a comparative study encompassing structure, mechanical, rheological and thermal properties. At equal filler loadings, PP/clay nanocomposites exhibit a higher flexural modulus and melt viscosity, and enhanced thermal stability, as compared to the microcomposites studied. The structural differences between nano and microcomposites are demonstrated by rheometry, microscopy and thermal stability. Significant differences in behavior result from the much higher surface area of delaminated plates and their higher aspect ratio.
In-Situ Ultrasonic Compatibilization of Dynamically Vulcanized PP/EPDM Blends
Dynamically vulcanized PP/EPDM blends were treated by high intensity ultrasonic waves during extrusion. These blends were compared with unvulcanized PP/EPDM blends that were treated by ultrasound during extrusion and then dynamically vulcanized. Die pressure and power consumption were measured. The effect of different gap sizes, ratio of components, and number of ultrasonic horns were investigated. The rheological properties, morphology and mechanical properties of the blends with and without ultrasonic treatment were compared. The results obtained indicated that ultrasonic treatment induced the thermo-mechanical degradation causing enhanced molecular transport and chemical reactions at the interfaces, thus leading to in-situ compatibilization, which is evident by the morphological and mechanical property studies. Processing conditions were established for enhanced in-situ compatibilization of the dynamically vulcanized PP/EPDM blends.
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