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SPE Library content related to rheology
PEN-Poly(ether imide) Blends: Melt Rheology and Stress Relaxation in Semi-Crystalline Films
Past studies on the stress relaxation of biaxially oriented polyester films are extended to a blend of poly(ethylene-2,6-naphthalate) (PEN) and poly(ether imide) (PEI) at a composition of 85/15 by wt. At this composition the polymers are fully miscible and the melt viscosity and flow activation energy of the blend are dominated by the PEN component. PEI plays a more important role in controlling the sub-Tg stress relaxation response of films produced from the corresponding blend. We show that the relaxation time of a biaxially oriented, semi-crystalline film is increased upon addition of PEI to the PEN matrix, consistent with the rise in glass transition temperature. Also, using stress relaxation data in combination with the concept of aging acceleration factors, we probe the kinetics of the physical aging process for the neat PEN and blend films over a temperature range spanning from ca. Tg - 5O°C to Tg + 10°C. Over this temperature interval both films eshibit thermorheological simplicity with respect to time-aging time and time-aging temperature superposition and the rate of physical aging peaks at ca. Tg - 20°C. However, the relative increase in the rate of aging is much lower for the blend, thus suggesting that the PEI component is well dispersed in the PEN matrix and is effectively retarding the segmental mobility of PEN.
Measurements and Modeling of Rheological Properties of Biodegradable PBS/CO2 Solutions
The purpose of this research is to study the pressure drop profiles of biodegradable polybutylene succinate (PBS)/CO2 solutions in a slit die and to measure the rheological properties of the solutions as a function of the blowing agent concentration. A slit die with four pressure transducers has been designed to describe the effects of shear rate, temperature, pressure, and gas content on the shear viscosity and extensional viscosity of the flowing PBS/CO2 solutions. The low shear rate viscosity of the pure polymer was measured using a cone and plate rheometer. Extensive experiments were conducted to investigate the polymer/gas solution viscosities at five different shear rates, three temperatures and five gas contents. Cross-Carreau model and generalized Arrhenius equation were used to describe the shear-viscosity behaviors of PBS/CO2 solutions. The extensional viscosity of solution was modeled based on Cogswell's equation.
Mechanical and Rheological Properties of Liquid Crystalline PHB/PEN/PET Blends
Mechanical and rheological properties of blends of a para hydroxy benzoate - ethylene terephthalate copolyester TLCP (PHB 80 / PET 20 mole%) with Poly(ethylene 2,6-naphthalate) (PEN) and Poly (ethylene terephthalate) (PET) were investigated. Torque values of blends with increasing PHB content abruptly decreased above 40 wt% of PHB content because the melt viscosity of ternary blends were decreased. Tensile strength and tensile modulus of blends containing above 30 wt% PHB were improved with increasing PHB content due to the formation of fibrous structure. The blend of 40 wt% PHB showed pseudo LC phase, and mechanical property was improved with thermal treatment. Rheological property changes with shear rate and processing temperature will be presented.
Interfacial Tensions in Polyolefin Blends
The interfacial tension between immiscible polymers is difficult to measure due to the high viscosity of molten polymers. Additionally, the lack of optical contrast that exists between two molten polyolefins renders conventional optical methods impractical. Small-amplitude oscillatory shear flow provides an indirect technique for measuring the interfacial stress between immiscible polyolefin binary blends. Based on the model of Palierne, the interfacial contribution to the measured rheological response is governed by the ratio of the interfacial tension to the average radius of the dispersed droplets. In this work we have investigated the use of amplitude oscillatory shear measurements to determine the interfacial tension in binary blends of immiscible polyolefins. The two-dimensional droplet morphology in each blend was characterized using tapping-phase AFM. True dispersion phase radii were obtained after converting the measured two-dimensional size distributions to three-dimensional size distributions through the linear transformation method of Schwartz-Saltykov. Results of measured interfacial tensions in various polyolefin blends are reported. The interfacial tension of a PP/EP blend thus obtained was in agreement with the value calculated from the SANS measurement.
Rheological Properties of in situ Organic Composites
A study to evaluate the rheological properties of organic in situ short polymer fibres (poly(butylene terephtalate) (PBT))/high density polyethylene (HDPE) and high density polyethylene/poly(ethylene-co-vinyl acetate) (HDPE/EVA9) composites has been carried out. The in situ compatibilization of the HDPE/EVA9/PBT systems with the Bu2SnO catalyst was performed. The different systems were melt blended in a twin screw extruder, drawn at the die exit and cooled. The results indicate that it is possible to produce such composites using reactive extrusion for compatibilization and post extrusion drawing to control the aspect ratio of the PBT fibres. Morphological analysis allowed evaluation of parameters such as draw ratio, PBT concentration and compatibilization on the size and shape of the fibrils. Their influence on the solid rheological behaviour is discussed.
Anisotropic Properties of Injection-Molded Short-Fiber Thermoplastics
As plastics are reinforced with short fibers to increase stiffness and strength and to reduce shrinkage and thermal expansion, fiber motion controlled by the developing flow field during molding leads to a layered microstructure characterized by different fiber orientations through the thickness. The anisotropy of material properties is determined by the fiber orientation and the thickness of each layer which depends on the gating configuration, the part geometry, the rheological properties, and the processing conditions. In this paper we report the directional elastic properties in plaques injection molded with glass fiber reinforced polycarbonate (PC), polybutyleneterephthalate (PBT), and polyamide (PA). Anisotropy plus fiber content and length strongly govern the thermomechanical properties of fiber-reinforced products, which are essential for performing CAE analyses of short-fiber-filled parts.
The Role of Interfacial Slip in Melt Rheology of Immiscible Polymer Blends
A number of researchers have reported an anomalous lowering of viscosity in immiscible polymer blends. Slip at the interfaces between the polymers has been proposed to explain these observations. Because of the complex morphology developed in melt blends it is difficult to test the slip hypothesis. However, using layer multiplication dies in coextrusion, two or more polymers can be alternatively combined into hundreds or even thousands of continuous layers generating a large amount of well-defined interfacial area. Polypropylene (PP) and polystyrene (PS) with closely matched viscosity were blended in a twin screw extruder and also coextruded into 2, 32, 128 alternating layers. The steady shear and dynamic shear viscosity of the blends was first measured in a capillary rheometer and a rotational shear rheometer using parallel plates geometry. While the steady shear viscosity of the blends was lower than that of both homopolymers, the dynamic shear viscosity of the blends was the same as that of the homopolymers. The pressure drop of the coextruded multilayer melts through a slit die was lower than that of both homopolymers and decreased with an increase in the number of layers. From these results an interfacial slip viscosity was estimated. Addition of diblock copolymer was able to suppress interfacial slip.
Benefits of Coextruded LLDPE/LDPE Film versus Blended LLDPE/LDPE Film
The benefits of three-layer coextrusion versus a mono-layer blend of the same resins are explored. Good design considerations of the coextruded structure can allow a processor to take advantage of the performance characteristics of the resins and the equipment. These performance characteristics can be compromised in a mono-layer blend of the same materials. Expected benefits of coextrusion can be improved physical properties and reduction in additives required for good processing. These are accomplished by eliminating blends of LDPE and LLDPE, reducing the draw-down ratio and taking advantage of the rheological differences between LDPE and LLDPE.
Melt Rheology and Processability of Conventional and Metallocene Polyethylenes
The melt rheology and film processing behaviours of conventional high pressure-LDPE and LLDPE are compared with both linear and long chain branched (LCB) metallocene polyethylenes. The effects of molecular structure on melt behaviours of these different types of polymers will be discussed in terms of an improved melt strength measurement. Two new parameters: ?(MS)/?P the melt strength pressure derivative and ?(MS)/?(log?), the melt strength shear rate derivative, have been defined.
Product Design with High Value Recyclable Plastic Waste Streams
As part of on-going studies on the manufacturing of re-engineered materials from waste plastic streams, rheological, mechanical and thermal characterization of recyclable plastics from old computer housings and used carpet materials were carried out, with anticipated use in thin-walled products. A combined stress and mold cavity flow analysis has been used to obtain optimum design and process parameters for the anticipated products.
Investigation of the Rheological Properties of Rotomolding Resins
There are many influential factors and processing variables that can impact the mechanical and aesthetic properties of a rotomolded part. One of the main variables is the resin being processed and its associated rheological properties. The manner by which the polymer powder sinters and fuses together needs to be understood to ensure the correct processing cycle is used to obtain an optimum cured part. The influence of bubbles that form during the sintering phase and the melt index of the material, contribute to the quality of the part being produced.
Extrusion of LLDPE through Polypropylene Coated Dies
Polypropylene (PP) coated dies were used in an attempt to decrease the die pressure and eliminate surface melt fracture during the extrusion of linear low density polyethylene (LLDPE). The investigated coatings were: controlled-rheology PP, hydrosilylated PP, amorphous PP wax, and maleic anhydride grafted PP. Extrusion stability, die pressure, and extrudate appearance were used to compare the effectiveness of the different coatings.
Prediction of Viscoelastic Behaviour of Thermorheologically Complex Polymeric Materials
A simplified numerical computational technique based on a Gaussian spectral distribution model developed by Dutta and Edward  has been used to describe the stress relaxation behavior of polystyrene (PS) and isotactic polypropylene (iPP) over a wide range of, time and temperature. An excellent fit between experimental data and the mathematical model is observed. The method may be applied generally for any linear viscoelastic property and for any polymer.
Difference in Integral Aggregate Structure for Co-Neutralized Carboxylate Ionomers
The purpose of this study was to determine the arrangement of atoms inside ionic aggregates for ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers neutralized with a combination of sodium and zinc. Significant qualitative differences were found as a function of sodium:zinc ratio. The implications of the differences in aggregate structure on the rheological behavior of these mixed-cation systems is discussed.
Effects of Lubricants on Processing of Metallocene LLDPE
Fatty acid ester and amide lubricants were evaluated as processing aids in a 1.0 MI film grade mLLDPE. The effect of the lubricants on extruder energy and output of laboratory extruders fitted with a capillary rheology die and with a two inch film die were determined. Additives were found that reduced the amount of extruder energy required to process the mLLDPE. These additives also increased the output of the extruders per unit of extruder energy.
Rheological Properties and Numerical Simulation of S-PVC Formulations in Extrusion Dies
We report effects of formulation and sample preparations on measured rheological properties relevant for constitutive modelling of die flow in PVC extrusion. Numerical simulations are performed in order to separate non-isothermal and viscoelastic effects in the extrusion experiments as well as self-consistency between constitutive models and measurements.
Processing Trends of Metallocene Linear Low Density Polyethylenes and Their Influence on Single Screw Design
New families of polyolefin resins using single site catalysis technology, are being produced to enhance resin properties. The changes to the molecular architecture of these resins effect the rheological, thermal, frictional, and elastic properties; all of which play a significant role in screw design. This paper will investigate several polyolefin plastomers and compare them to a conventional linear low density polyethylene (LLDPE) to determine their impact on screw design.
Computing an Injection Fill Speed from a Relative Viscosity Curve
On-machine rheology is a methodology of determining the flow characteristics of a material at a given temperature with a specific mold and machine.  This methodology can be used to help determine the best injection fill speed to be used for a given material, machine and mold combination. This study presents a mathematical method to obtain an injection fill speed starting point when setting up a new mold, machine and material combination.
Polymer Melt Formation and Densification in Rotational Molding
Polymer melt densification, involving particle coalescence followed by the formation and dissolution of bubbles, has been studied in order to evaluate how it is affected by powder properties, chemical structure, thermal properties and rheology. A variety of rotomolding grade resins have been tested, in an effort to understand the mechanisms involved in the melt formation and its subsequent densification.
Effect of Formulation and Processing Conditions on the Viscosity of Masterbatches
Adding colorants and additives in masterbatches may affect the rheological properties of the resins into which they are mixed, but the extent of this effect has not been fully investigated. This paper reports on a design of experiments (DOE) study of the effect of 3 common colorants, 2 lubricants, a filler, an antioxidant, and 2 processing parameters (melt temperature and screw speed), on the viscosity of a linear low-density polyethylene (LLDPE) masterbatch. The series of experiments determined that only the lubricant and filler had a significant impact on resin rheology.
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