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SPE Library content related to rheology
Sepiolite fibers improve the mechanical and shape-memory properties of polyurethane
Sepiolite fibers are incorporated in a simple and practical method to achieve increased tensile strength characteristics and shape fixity ratios of polyurethane composites.
High-performance polylactide biocomposites reinforced with cellulose nanofibers
Rheological, optical, mechanical, and thermomechanical investigation of the properties of cellulose-nanofiber-reinforced polylactide demonstrates the solution method for achieving good fiber dispersion.
Using elongational flow to enhance the properties of polypropylene nanocomposites
Different nozzle geometries were investigated to find the optimum injection molding strategy for the production of polymer nanoclay composites.
Polylactic acid biocomposite filaments with improved mechanical properties
Fully biodegradable polylactic acid/microcrystalline cellulose composites, with surface-modified reinforcing cellulose, are suitable for 3D printing applications.
Correlation between filler concentration and viscosity power-law for polymer slurries
A new predictive relationship that is based on percolation theory concepts has been verified with tubular flow experiments.
Shear viscosity of fast-reacting aqueous polymer solutions
A power-law function is used in a simple empirical approach to describe the shear viscosity of acrylic acid in water during polymerization.
Numerical simulation and experimental validation of the dip-coating process
A comprehensive investigation involved the direct measurement of the thickness, free surface, and flow field of non-Newtonian fluids and polyacrylic acid solutions.
High-molecular-weight polyvinylidene difluoride binder for high-capacity cathodes
Slurries prepared with optimized binders exhibit good rheological characteristics and are a cost-effective option for lithium-ion battery applications.
Frictional heating of extruded polymer melts
Rheo-particle image velocimetry and thermal imaging results show that frictional and viscous heating act synergistically to produce significant temperature increases when a melt is extruded under slip conditions.
How to Add Value to Capillary Rheometers
Capillary Rheology has been around for many years. As technology moves on, this has opened doors to use the capillary rheometer as a base on which to build a sophisticated R&D platform to perform a wide range of other tests, which help rheologists and their colleagues. We look at extensional rheology, elasticity, pressure- volume-temperature (PVT), thermal conductivity (TC), sharkskin analysis and the effects of counter pressure measurements. Those are but a few of available options to lab managers who try to squeeze out extra capabilities from their budgets.
The Effect of Viscous Encapsulation on Layer Uniformity and Rheology in Multilayer Coextrusion
Multilayer coextrusion is a process in which two or more polymers are extruded and joined together in a feedblock or die to form a single structure with multiple layers. This paper will discuss the effect of viscous encapsulation especially in a flow channel with a noncircular cross-section on layer re-arrangement and rheology of a coextruded structure.
Viscosity Measurement of Multilayer Structures via Parallel Plate Rheology
Parallel plate rheometry has been used to characterize the viscosity of multilayer polymer structures. It has been demonstrated that this technique is not a good substitute for performing such measurements using a coextrusion slit die rheometer. For the purpose of designing dies for producing multilayer structures, one needs good viscosity data that correctly represent the behavior of the intended structure under flow and for this reason, a coextrusion slit die rheometer is recommended.
Effects of Viscoelasticity on Film Die Flow Uniformity
This study shows the effect of viscoelasticity on the flow uniformity in a film die. Flow simulations were conducted on flat die geometries based on the rheology of different resins with different viscoelasticity characteristics. The results have shown that viscoelasticity can have a significant influence on flow uniformity and flow distribution becomes less uniform as the elasticity of the resins increases.
Characterizing the Rheological Behavior of Liquid Silicone Rubber Using a High Pressure Capillary Rheometer
The injection molding process of liquid silicone rubber (LSR) imposes high demands on the injection molding machines and the tools due to the low viscosity of silicone rubber. There is very little data which describes the rheo-logical behavior of LSR and its influencing factors across a range of shear rates.
In this study, the rheological behaviors of different types of LSR were characterized using a high pressure capillary rheometer with an apparent shear rate that ranged from 350 to 4000 1/s. In order to identify the temperature-dependent behavior, the test temperatures were varied between 27 and 42 °C. The behavior of the material at a high pressure was evaluated by analyzing the pressure profile of each measurement.
All types of LSR displays a low level of viscosity from approx. 150 to 30 Pa s. As the shear rate and temperature rise, the viscosity of LSR decreases by at least 25 %. Ad-ditionally, we discover that the viscosity of LSR-materials with the same shore hardness differ strongly depending on which producers had made the materials. It was able to be shown that LSR displays homogenous material behavior across a wide range of shear rates.
The low viscosity of LSR makes it well-suited for applica-tions with complex structures, which require long flow paths in the injection molding process. If the viscosity sinks too low, the requirements for the tool construction increase, and, consequently, also the costs.
Using Ultrasonic Technology to Prepare Well-Dispersed Polycarbonate/Carbon Nanotubes Composites at High Flow Rate
Polycarbonate (PC)/carbon nanotubes (CNTs) composites were prepared using ultrasonic twin screw extruder at two different flow rates. During the extrusion of PC/CNTs composites, both the shearing and ultrasonic treatment helped dispersing CNTs into the polymer matrix. At low flow rate and longer residence time, CNTs can be well dispersed, but this may induce more degradation of polymer and low production throughput, which is not good for industrial production. At high flow rate, the dispersion of CNTs is worse than that in low flow rate and thus worse properties. Regarding to this problem, ultrasonic technology stands out and shows superior capability in improving the dispersion of CNTs and increase the throughput at the same time, which is especially beneficial for industrial production of polymer/nanofiller composites. The electrical, morphological, rheological and mechanical properties of the untreated and ultrasonically treated samples were investigated. The results supported the conclusion that ultrasonic technology is exceptionally efficient on improving the dispersion of CNTs and preparing welldispersed polymer composites at high flow rate.
Origin of Strain Hardening in Branched Metallocene Polyethylenes
The occurrence of strain hardening during extensional flow is known to be dependent on the molecular structure, in particular long-chain branching and molecular weight, based on studies on model polymer systems. However, commercial branched metallocene polyethylenes (BMPs) often present little or no strain hardening. The variety of molecular structures and distribution of molecular weight make it difficult to identify which species are needed for strain hardening to be observed in extension. We investigate a series of BMPs made by solution polymerization, in which the branching level vary in a systematic way, and in which only the most highly branched members of the series exhibit mild strain hardening. By use of polymerization and rheological models along with new data on the extensional flow behavior of the most highly-branched members of the set, we conclude that in spite of their very low concentration, tree-like molecules with branch-on-branch structures that provide a large number of deeply buried inner segments are essential for strain hardening in these polymers.
Control of Rheological Resposes under Elongational Flow for Polyolefin Melts
Rheological responses under elongational flow play a crucial role in processability of a molten polymer at various processing operations. Therefore, the elongational viscosity has been evaluated. In industry, instead of elongational viscosity, the drawdown force, defined as the force required to stretch a molten polymer, is often evaluated, which is sometimes called melt tension or melt strength. In general, the drawdown force measurement is performed at non-isothermal condition, as similar to actual processing operations. Therefore, crystallization and/or glassification processes affect the value. Here, we proposed several methods to enhance the drawdown force for polyolefins with linear structure, such as isotactic polypropylene (PP) and high-density polyethylene (HDPE), considering the crystallization behavior. The results indicated that the drawdown force increases with the die length in the wide range of draw ratios and shear rates at die. Furthermore, this phenomenon was pronounced for a melt having long relaxation time at low extrusion temperature. The mechanism of the drawdown force enhancement was found to be attributed to rapid crystallization owing to the reduction in the density of entanglement couplings after passing through a long die. In fact, marked molecular orientation was confirmed by 2D-XRD measurements. Furthermore, the drawdown force of PP was enhanced by the addition of a nucleating agent. Blending with other polymeric materials such as high-density polyethylene (HDPE) and poly(methyl methacrylate) (PMMA) having low viscosity is also effective to enhance the drawdown force.
Development of a Predictive Power Law Relationship for Concentrated Slurries, Part 1: Theory
All polymer slurries that have a high concentration of filler are shear thinning. This can include the starting materials for sheet molding compound, polymer based inks, many reactive extrusions systems, and polymer concentrates that are let down in extrusion systems as color concentrates or opacifiers. Several sizes of calcium carbonate were initially investigated because of their extensive use in the polymer industry as fillers. The investigation focused on developing an analytical tool that would lead to understanding and the prediction of the flow characteristics of slurries that have a Newtonian continuous phase but have high enough filler concentration to exhibit shear thinning or power law characteristics. This work’s focuses on concentrations where the initial yield behavior is not dominant A new function was found that linearly correlates the power law constant, n, to the concentration of the filler. The behavior of this function suggests that the Newtonian to Power-law behavior may be dominated by percolation processes. We present here a theory that predicts the characteristic of the power law constant, n, as a function of filler concentration and is based on observing and modeling the well-known plug formation in the center of a tube as the material flows down the tube. The plug was experimentally shown to be a non-dissipating volume in the flowing slurry. This percolation based rheological analysis was then extended to a highly filled Polyethylene resin.
Production of Controlled Rheology Polypropylenes from Metallocene and Ziegler-Natta Resins
Peroxide induced controlled degradation of polypropylene has been well studied for commodity Ziegler-Natta based polypropylene (ZN-PP) resins and it is practiced industrially for producing resins of controlled rheological properties with accompanying narrower molecular weight distribution (MWD). In the present work, this technique was also tested on metallocene-based polypropylenes (mPP), possessing an initial narrow MWD. Kinetic model simulation results indicate that the polydispersity index (PDI) of the mPP remains almost unchanged while reducing molecular weight (MW) with increased peroxide concentration. Based on this observation, experiments were carried out to demonstrate the possibility of producing controlled rheology polypropylenes (CRPP) having targeted weight-average MW but varying PDI from different commodity resins of mPP or ZN-PP type.
Study of the Preparation and Superiority Properties of the Novel Propylene-Based Elastic HMAs
The novel propylene-based elastic hot melt adhesives (HMAs) with improved adhesive and elasticity were first reported and prepared by styrene-assisted melt free-radical grafting of maleic anhydride. The changes in chemical composition, thermal property, melt viscosity, and adhesive performance were measured by FTIR, GPC, TREF, rheology, TEM, melt flow indexer, and Intron universal testing machine, respectively. Compared to the commercial HMAs, the propylene-based elastic HMAs with special continuous phase distribution exhibited 20% increasing in peel strength, and doubled 100% tensile deformation recovery rate, which achieved a consistent of high degree of adhesion and elasticity. Meanwhile, the weather resistance test results also indicated that the propylene-based elastic HMAs had excellent resistance with high and low temperature shock, which alleviated the interface delamination caused by the different thermal shrinkage between the steel interface and plastic interface, further benefitting and extending the service life of steel composite pipe.
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