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Applied Rheology

SPE Library content related to rheology

Screw Design for Ultra-High-Speed, Quad-Screw Extrusion

Carol Barry, May 2020

The effect of screw programming on the performance of an ultra-high-speed, 15 mm quad-screw extruder was investigated by processing low-density polyethylene with four screw programs, no active barrel cooling (to evaluate viscous dissipation), and screw speeds of 500-2000 rpm. Observations indicated that kneading blocks were needed for timely melting of polymer pellets. Large increases in barrel temperature occurred with mixing, rather than melting, kneading blocks. Kneading block design had limited effects on power consumption but significantly affected residence time, melt temperature, and drive torque. All designs produced significant reductions in the viscosity of the extrudate, which previously has improved mixing.

The Use of Multi-Wave Oscillation To Expedite Testing and Provide Key Rheological Information

Gregory Kamykowski, May 2020

Dynamic oscillatory testing is usually performed in a point-by-point fashion. For example, in a frequency sweep, the test material is subjected to oscillation at a particular frequency, equilibrium conditions are attained, and the experiment progresses to the next, discrete frequency. With isothermal tests or temperature ramps, testing is performed at 1 particular frequency, e.g., 1 Hz (6.28 rad/sec). The method discussed in this paper, Multi-wave oscillation, allows one to impose multiple frequencies simultaneously. This enables testing at multiple frequencies in less time than by the conventional method and is particularly useful in characterizing curing systems in isothermal time sweeps or temperature ramps. With some curing systems, especially where there is no Storage Modulus – Loss Modulus crossover point in the experimental timeframe, this enables one to determine an objective gel point, which is defined as the point where tan delta (= Loss Modulus/Storage Modulus) is independent of frequency.

Using a Micro Blown Film Line for Formulation Screening

Jin Wang, May 2020

A LabTech Ultra Micro Combi line (Microline), the smallest blown film line in the world, was used to conduct blown film formulation screening with a set of LLDPE/LDPE blends. A sample cutting pattern was developed to enable preparation of crease-free test specimens from the small layflat made on the Microline. Haze, dart A, tear (MD, TD) and tensile (MD, CD) were tested using the film made by the Microline. By carefully controlling the time to frost line on the Microline to match the time to frost line on the larger scale lines, it was found that dart A, tear (MD, TD) and tensile (MD) of the Microline film were correlated with those of the larger scale lines films. These film properties can be used for formulation screening with minimal consumption of materials (~150 g per film sample). Haze and tensile (CD) properties did not correlate with those of the larger scale lines films. Future work will investigate the cause of these deviations.

Viscoelastic Measurement and Injection Molding Simulation of Amorphous Polymer: From Liquid to Solid

Chen-Chieh Wang, May 2020

The viscoelastic properties under wide temperature range (from viscous to glassy state) and various flow field are studied in this work for a commercial amorphous polymer. It is found that multi-mode EPTT model can describe all measured properties well including dynamic modulus, steady shear viscosity, first normal stress difference, and transient extensional viscosity. 3D flow VE simulation are conducted to validate the applicability of the fitted model and parameters by comparing with the injection pressure in filling and packing stages.

Viscosity Characterization and Transient Flow Simulation and Visualization of Ptfe Paste Extrusion

George Schmidt, May 2020

The shear viscosity of polytetrafluoroethylene (PTFE) paste and its flow behavior during paste extrusion were investigated. Frequency sweeps using a parallel plate rheometer were performed on compression molded samples of PTFE paste made from fine powder PTFE mixed with ethanol as a lubricant. Various grits of sandpaper were used to reduce slip of PTFE paste on the walls. A viscosity model was generated and COMSOL Multiphysics was used to create a time-dependent flow simulation of PTFE through a paste extruder. The simulated results were compared to experimental data of actual paste extrusion. Due to simplifications used in the model, the simulated extrusion pressure over time differed in both magnitude and slope when compared to the experimental data. The simulated velocity profile was compared to flow visualization experiments, showing good agreement in wider regions of the extruder. Despite these drawbacks, the experiments and simulated model provided useful information about the flow within the paste extruder.

A MultiDrive Rheo-DMA Platform for Extended Polymer Analysis

Abhishek Shetty, March 2020

Dynamic mechanical analysis (DMA) is a well-established technique for characterizing mechanical properties of all kinds of materials, particularly polymers or polymer-based products such as thermoplastics, thermosets, elastomers, adhesives, paints and coatings, films and fibers, as well as composites. A new measuring device concept is introduced which combines an electronically commutated (EC) motor as rotational top drive and a moving magnet linear drive or another EC motor, as bottom drive to enable rheological measurements and DMA on one single device. The concept enables various modes of operation by using different combinations of the bottom drive. Besides working in the rheological modes such as separate motor transducer (SMT), combined motor transducer (CMT), counter-rotation and counter-oscillation the device is suitable to perform dynamic mechanical analysis in bending, tension, compression, and torsion. DMA can provide quantitative and qualitative data regarding:     Viscoelastic moduli and damping
    Material structure and morphology
    Relaxation behavior (Primary, secondary)
    Influence of fillers and fibers in polymers
    Crystallization/melting processes
    Curing behavior In this webinar, you will learn how DMA can be used to gain a better understanding of the viscoelastic and thermal properties of your material. The theoretical basics of DMA measurements will be covered along with the test methods and the information gained from those. Various DMA applications ranging from polymer plastics, rubbers to composites will be discussed and the flexibility and versatility of such a 2 in 1 device concept will be demonstrated for extended polymer characterization.

Improving Physical Properties in Sustainable Thermoplastic Elastomers through Incorporation of a TRA

Megan Robertson, February 2020

Thermoplastic elastomers (TPEs) are widely used in electronics, clothing, adhesives and automotive components due to their high processability and flexibility. ABA triblock copolymers, in which A represents glassy endblocks and B the rubbery midblock, are commercially available TPEs. The most commonly used triblock copolymer TPEs contain glassy polystyrene endblocks and rubbery polydiene midblocks. However, commercial TPEs are derived from petroleum. The manufacturing and disposal of petroleum-derived products have undesired environmental impacts, which promotes development of TPEs from sustainable sources. Vegetable oils and their fatty acid derivatives are attractive alternatives to petroleum due to their abundancy and low cost. Our group has previously reported replacing polydienes in commercial TPEs with sustainable polyacrylates derived from fatty acids. However, polymers with bulky constituents, such as the long alkyl side-chains of fatty acid-derived polymers, typically exhibit poor mechanical performance due to lack of entanglements in the rubbery matrix. To improve the mechanical properties, a transient network was incorporated into the fatty-acid derived midblock through hydrogen bonding. Specifically, triblock copolymers containing polystyrene endblocks and a midblock composed of a random copolymer of poly(lauryl acrylate) (derived from lauric acid) and acrylamide (which undergoes hydrogen bonding) were synthesized. Quantitative FTIR analysis confirmed the formation of a transient network. The polymers exhibits disordered spherical morphologies, desirable for application as TPEs. Rheological measurement revealed the order-disorder transition temperature reduced with increasing acrylamide content, beneficial for high temperature melting process. Importantly, triblock copolymers with hydrogen bonding in the matrix exhibited significantly higher modulus, strain at break, and tensile strength as compared to comparable polymers in the absence of hydrogen bonding.

Fundamentals of Twin-screw Compounding - Effective Mixing, the Key to Product Quality

Justyn Pyz, February 2020

The process for compounding thermoplastic formulations, both highly filled fiber or mineral products as well as color and additive MB, is comprised of several unit operations. These typically include: feedstock introduction, polymer or polymer/pigment melt-mixing, distributive/dispersive mixing of pigments/minerals/additives, removal of volatiles, and pressurization for die discharge. However, at the end of the day, if the fiber, mineral or pigment is not properly mixed into the polymer matrix, the product is not saleable. While the above list denotes a specific unit operation associated with mixing, mixing occurs along the entire length of the screw configuration in the co-rotating fully intermeshing twin screw extruder. It can range from dispersive mixing (i.e. wide disc kneading block combinations as part of, for example, titanium dioxide incorporation) to distributive mixing (that occurs during melt conveying as a result of rotation of screw bushings). Mixing in the screw bushings results from material reorientation in the apex region and circulatory flow induced by drag forces in the screw channel. The magnitude of the resultant mixing at any point along the screw depends upon the extruder barrel and screw configuration, characteristics of the materials being processed, and operating conditions. The required type and intensity of mixing depends on 1) the process task (talc filled vs. carbon black based MB), and 2) the relative physical and rheological properties of the materials being mixed. Independent of material parameters, mechanical energy input will vary according to basic extruder geometry characteristics (2 lobe vs. 3-lobe, outer diameter/inner diameter ratio [Do/Di]), element configuration, as well as operating conditions such as RPM, throughput rate, degree of fill, and barrel temperature profile. Material parameters such as viscosity, viscosity differential, elasticity, interfacial surface tension, thermal stability, as well as imposed discharge constraints, such as material temperature, particle size, and particle size distribution will dictate as well as limit the type and intensity of mixing necessary (or allowed) to accomplish the unit operation. This presentation provides a further discussion of the issues noted above as well as associated examples especially considering Polyolefins.

SPE Applied Rheology October 2019 Newsletter "Novel Trends in Rheology VIII" Edition

SPE Applied Rheology Division, October 2019

Read the October 2019 issue of SPE Applied Rheology Division newsletter. Meeting Report by Jeffrey Giacomin of Queen’s University, Canada. The meeting began on Monday afternoon with an enjoyable bicycle ride first following the river, and then crossing over the hills from village to village, to return to Zlin before dark. Led by Martin Stenicka of Tomas Bata University and Wannes Sambaer of Donaldson in Leuven, participants enjoyed unforgettable vistas of the stunning Czechian countryside.

Rotational Rheometry on PVC Materials

G. Kamykowski, October 2019

Rheology: The study of the flow and deformation of matter. Flow: Fluid Behavior; Viscous Nature: F = F(v); F ≠ F(x). Deformation: Solid Behavior Elastic Nature: F = F(x); F ≠ F(v). Viscoelastic Materials: Force depends on both Deformation and Rate of Deformation and vice versa.

On-Line Processability Characterization Of Thermoplastic Formulations During Injection Molding

Christopher Thurber, March 2019

Processability is a critical performance parameter when developing thermoplastic formulations for injection molding applications. This paper describes various on-line methods for quantifying processability and compares the results with off-line rheological methods.

Melt Index And Extensional Rheology Combined

tim haake, March 2019

Using two established measurements, the combination thereof rolled into one instrument and one measurement, is herewith covered. A Melt Indexer and an Elongation Tester put together, greatly enhance the usefulness of each test result by itself, while saving much time compared to running tests individually. GOETTFERT has many years of experience with both individual tests and developed the D-MELT in close cooperation with a customer, who has many years of experience with a similar design mix. Introduction

Pellet Heat Transfer Model With Crystallization Kinetics Using Finite Element Method

Vinod Kumar Konaganti, March 2019

An advanced Finite Element Method (FEM) based transient pellet heat transfer model with crystallization kinetics is developed to better understand the cooling requirements for a clean pellet cut during polyethylene manufacturing. This model considers conduction/convective heat transfer in and around a polymer pellet with enthalpy changes, considering a pellet of spheroid shape surrounded by a cooling water off constant temperature. The model further accounts for the changes in stiffness or elastic modulus obtained from rheological measurements using multi-wave oscillatory test during cooling/crystallization stages of the polymer. A series of simulations were performed to understand the effects of several parameters such as resin architecture/formulation, crystallization kinetics, initial molten pellet temperature, water inlet temperature, water to pellet ratio (i.e., water flow rate) and pellet dimensions. It was found that for resins of similar Melt Index (MI) and density, the differences in structural characteristics can significantly affect the pelletization process and pellet cut. This model may serve as a strong tool for efficient design, operation and troubleshooting of downstream equipment (e.g. pelletizer, cutter, Pellet Conveying Water (PCW) system, stripper etc.) through understanding of the effects of molecular architecture of the resins and/or optimization of various processing and operating conditions.

Study On The Viscoelasticity Properties Of The Glass Mat Thermoplastics (Gmt) In Compression Molding System

Chao-Tsai Huang, March 2019

Compression molding is one of the lightweight technologies able to provide efficient way to retain fiber length for better mechanical property comparing to injection molding. In compression molding development, materials such as glass fiber mat thermoplastics (GMT) are often applied. However, due to the complicated micro-structure of the reinforced material, and the interaction of fiber-resin matrix, it is still challenge to have uniform compressed GMT product. In this study, we have developed a method to measure the rheological properties of GMT material through a compression system. Specifically, we have utilized compression molding system to estimate the rheological parameters of GMT. Those rheological parameters are then integrated into CAE (Moldex3D) to evaluate the flow behavior under the compression operation. Results showed that the trend of the loading force is increased exponentially against displacement at various compression speeds. However, some significant differences between simulation and experiment are observed. Specifically, at the early compression stage, the volume of long fiber-resin matrix is expanded by 50% in real experiment. This causes the loading force difference at the beginning between simulation and experiment. On the other hand, at the middle to the end stage, due to the fiber-resin matrix separation, the more the resin left the matrix, the higher the resistance generated. This results in the jump up of the loading force in the real experiments comparing to the simulation prediction. This deviation can be validated through the measurement of fiber content through TGA.

Flow Behavior And Polymer-Particle-Interaction In Highly Filled Polylactides

Johannes Benz, March 2019

Adding fillers to polymers allows highly functional materials and thereby properties like electrical conductivity that are not achievable by polymers themselves. But higher amounts of fillers cause an increase in viscosity and thus a change in flow behavior which in turn induces difficulties in plastic processing. Above a certain value (percolation threshold) there is a flow restriction which has to be overcome by a higher pressure in plastic processing. Besides the amount of filler the flow behavior of highly filled polymers depends on the filler itself and its particle shape. Especially the aspect ratio plays an important role. Another important factor is the combination of the polymer and the filler and whether there are any interactions between each other. By differing the amorphous phase of polymers into a rigid amorphous and a mobile amorphous fraction, predictions about interactions are possible. The objective is the generation of such a flow restriction and the combined investigation of a polymer-particle-interaction. Polylactide (PLA) was used as matrix whereas minerals were used as filler material in different amounts up to 50 vol.-%. SiO2 was chosen because it is available in different spherical sizes and clay because of its platelet geometry. Rheological investigations were done on a plate-plate rheometer while the interactions were investigated using differential scanning calorimetry. The results show that a higher aspect ratio leads to a faster increase in viscosity achieving the rheological threshold. As a result of the caloric investigations the highly filled plastics show only a minor interaction between polymer chains and filler surface. This leads to the conclusion that the change in flow behavior is mainly caused by a direct interaction between the particles.

The Effect Of Graphene Nanoplatelets On The Complex Viscocity Of High Density Polyethylene

Yue Xu, March 2019

In this paper, we investigated the rheological properties of high density polyethylene (HDPE) based composites filled with different amounts of graphene nanoplatelets. The composites samples were prepared in the form of films by the method of melt mixing. A parallel-plate rheometer was used to measure the rheology properties, including the complex viscosity, storage modulus and viscous modulus. The LVE range of all the samples was determined firstly, and then we studied the rheological properties of pure HDPE and graphene/HDPE composites. The effect of graphene content on the rheological properties of the graphene/HDPE composites at 150 °C was especially investigated. The results showed that the complex viscosity of the graphene/HDPE composites was decreased and then increased with increasing the content of graphene from 0.25 to 1.0wt%. However, increased graphene content did not exhibit distinct effect on storage modulus and viscous modulus of graphene/HDPE composites.

Rheological Material Characterization Within The Injection Molding Process

Alexander Geyer, March 2019

A new evaluation method for inline viscosity measurements in injection molding is presented, which allows characterizing the pressure dependence of a plastic melt within one cycle. A viscosity measurement die in combination with a flow spiral mold was used. A fit of the increasing pressure curves allows selecting various counter pressures that can be used to calculate the pressure coefficients. This method exemplarily is demonstrated for Polypropylene (PP). The resulting pressure coefficients show a good accordance to literature values, but are slightly lower in comparison to the data calculated with other methods.

Morphology Development In Lldpe Stretch Films Prepared With Different Cast Film Process Parameters

Hoda Bayazian, March 2019

Linear low density polyethylene (LLDPE) cast stretch films were produced to evaluate the effects of line speed, air gap, frost line and film thickness on the morphology of the prepared films. Surface morphology of the films were observed using scanning electron microscopy (SEM). It was found that the most effective parameter on the surface morphology of the films is line speed followed by air gap. In addition, relaxation behavior of LLDPE resins was investigated using rheological measurements. For the films with similar thicknesses but prepared at different line speeds the time scale for the melt to relax was correlated with the crystal phase development in the films, which affected the microstructure and crystalline morphology of the films.

Development Of Polypropylene Nanocomposites Reinforced With Cellulose Filaments

Julie GENOYER, March 2019

In this work, polypropylene (PP) reinforced with cellulose filaments (CF) nanocomposites were studied. Nanocomposites with CF loadings ranging from 0 to 30 wt% were produced by melt extrusion and characterized. Rheology using Carreau-Yasuda with yield stress model was used to estimate the dispersion state of CFs and showed that a suitable dispersion was achieved. Tensile tests were conducted to study the mechanical behavior of the materials. Results showed that nanocomposites with a higher rigidity can be obtained when a suitable dispersion is achieved, however, those nanocomposites are consequently more brittle.

Performance Of Minerals In Polyamide 6

Saied Kochesfahani, March 2019

A study has been conducted to evaluate the performance of wollastonite, talc and mica minerals in comparison with chopped glass fiber in Polyamide 6. The results reveal special attributes to minerals that could be beneficial depending on the specifications required for desired applications. These include the best balance of properties for HAR wollastonite in specimens with melt flow weldline, and for HAR mica and talc where isotropic properties and best cross-flow performance are desired. Talc also significantly increases PA6 crystallization temperature, while both talc and wollastonite improve the melt rheology of PA6 formulations compared to chopped glass fiber.