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SPE Library content related to rheology
Elastomeric Modification of an IR Cured Unsaturated Polyester Resin to Improve Mechanical Properties
An elastomeric modification of the “core layer” in an Unsaturated Polyester Resin reinforced with two fiber glass chopped strand mats, was used to improve impact resistance. Stress-strain and rheological properties were also measured to evaluate overall performance. Prior to resin-modifier mixing, either cis-polybutadiene or 1,7 octadiene were prereacted (10 min. or 20 min.) with styrene. The reinforced three layer samples were cured in a medium wave IR oven. Results show that both modifiers impart a considerable increase in impact resistance, with a small decrease in Young´s and storage moduli.
Elongational Viscosity as a Tool to Predict the Foamability of Polyolefins
The foaming of Polyolefin’s (PO) by direct gas injection is a delicate balance between the melt strength of the expanding polymer and the pressure of the blowing gas in the growing cells.Important parameters in this process are: melting and crystallization temperature of the polyolefin grade, viscosity in the crystallization temperature range and elongational viscosity in the crystallization temperature range. In particular the increase in elongational viscosity or so-called strain hardening is vital for a successful foam structure.This paper shows how the elongational viscosity is measured according to the Rheological Melt Extension (RME) method. The experimental conditions for LDPE, LLDPE, mPE Plastomers and PP are defined and used for a series of 25 PO grades.These experiments show that the strain hardening ratio (SHR) is influenced by the average molecular length, Molecular Weight Distribution (MWD) and the Long Chain Branching (LCB).
Flow Based Manipulation of Conductivity in Nanotube Composites
Nanotube composites are finding applications due to their ability to enhance the electrical conductivity of polymeric materials. They exhibit a percolation threshold in both rheological and electrical properties at concentrations of ~1/2 % by volume nanotube. We study the interrelationship between these two coupled transport properties by dielectric spectroscopy and rheology. We study an extruded rod and find that the nanotube network and the electrical conductivity become highly anisotropic. We find that the conductivity is quite sensitive to the shear field and becomes highly anisotropic.
Simulations of Grafting Monomers and Associated Degradation of Polypropylene in a Modular Co-Rotating Twin Screw Extruder
Kinetic models of grafting MAH and MMA on polypropylene(PP) were developed for screw extrusion. However the kinetic models are insufficient to explain the grafting reactions along the length of modular co-rotating twin screw extruders, because rheological properties and the residence time of PP changed by degradation of PP during the grafting reaction. In order to model this for a modular co-rotating twin screw extruder, the kinetic model of grafting reaction and models of degradation of PP are combined with fluid mechanics and heat transfer. Given the geometrical configurations of the screw and the operating conditions and the physical properties of the polypropylene, the simulations predict variation of molecular weight and mean residence time by degradation of PP. The weight percent of grafted MAH or MMA on PP profiles along the screw axis are also calculated in the simulation. These predictions are compared with experimental data for various operating conditions.
Study of Polypropylene Morphology to Obtain Porous Membranes by Stretching
Four different polypropylene resins were extruded using the tubular and the cast film processes. The morphology of the films was observed by SEM and the effect of extrusion processing variables on the morphology was investigated. Melt rheological experiments were carried out to characterize the behavior of the polymers. It was found that the molecular weight distribution and the chain structure as well as the processing conditions had important effects on the morphology. Efforts focused on obtaining a lamellar crystalline morphology by controlling the processing conditions. The possibility of generating a porous membrane from the initial morphology using a stretching technique was evaluated. The initial lamellae arrangement of the precursor film is shown to play a significant role in obtaining a porous structure.
Investigating Flow Behavior of Wood-Plastic Composites
The trend toward increased usage of renewable resources has led to the growing popularity of wood-filled materials. These emerging materials require extensive testing – beginning with formulation and ending with the final manufactured product. In the early stages of development, it is possible to acquire data comparing differences between recipes utilizing a Mixer/Measuring Head. The given blend can be compounded with a customized twin screw extruder and torque rheometer. Finally, a single screw extruder can quantify the rheology of the compound using a capillary die. The objective of this work is to investigate the behavior of a polyolefin based wood-filled compound using a torque rheometer.
Fundamentals of Melt Fracture Elimination Using Fluoropolymer Process Aids
Fluoropolymer process aids are widely used in polyolefin blown films to eliminate melt fracture. These process aids function by depositing a thin fluoropolymer layer on internal die surfaces, and promoting slip at the fluoropolymer – polyethylene interface. The present work describes how the morphology of fluoropolymer – polyethylene blends can be controlled to increase fluoropolymer deposition rate by using a new, rheology-modified fluoropolymer in combination with an interfacial agent.
Polytetrafluoroethylene (PTFE) Paste Preforming: The Effects of Viscosity and Surface Tension of Lubricants
Conventional processing methods are not applicable to PTFE due to its high melting point (342°C). Therefore, PTFE is processed by means of paste extrusion (extrusion of a mixture of PTFE powder with a lubricant). The physical properties of this new phase (lubricant) influence both the preforming stage as well as the rheology of the paste. In this paper, the effects of the physical properties of lubricant (viscosity and surface tension) on the preforming and extrusion pressure of PTFE paste are examined.
Automatic Injection Velocity Initialization for Computer-Assisted Injection Molding Setup
Modern systems for computer-assisted injection molding use data acquired from sensors and feedback from operators to setup the injection-molding process, to automate optimization of process parameters and to provide a statistical process control. A good initial starting point greatly streamlines injection molding setup and increases its robustness. Here we describe an algorithm for initial determination of injection velocity based on rheological calculations of the melt flow inside the mold cavity.
Effect of Overdrying Hygroscopic Resins and a Technological Solution for its Prevention
Hygroscopic resins are dried before processing. Most polymers are blended with low molecular weight additives as heat stabilizers, processing aids and/or other specialty additives. If the resin is dried for an extended period of time, these additives tend to break down causing deterioration properties. Moisture can play an important role in the melt rheology. Experiments were done to study this effect with the help of thermal analysis and evaluation of physical properties. A technological solution to prevent overdrying is presented.
Thermoformability of ABS Grades
Relationships between the rheological properties of different material grades with their processability are often difficult to make. In this work, a parameterization technique of the rheological properties is proposed to quantify the variations from grade to grade, within the same family. The impact of the identified parameters on the thermoformability of different ABS grades was investigated with the use of finite element simulation of the thermoforming process.
Challenges in Characterizing Sealant
Sealant is one of the very few major consumer products valued primarily for its rheological and adhesive properties. While, these materials may appear to be simple elastic solids, upon further examination, their behavior can be extremely complex. In this research, reasonable simplifications are developed to model the non-linear viscoelastic properties of cured sealant. Also included are modifications of the traditional instrumental design to allow for high throughput evaluation of a cured sealant’s mechanical properties.
Rheological Properties of HDPE-Wood Composites
A comparison of the rheological properties of HDPE-wood composites as measured by both capillary and rotational rheometry was made. The blends studied ranged from 0% (pure HDPE) – 50% 40-mesh size maple wood flour. The elastic behavior of these materials was studied through the measurement of storage and loss moduli, creep data and Bagley correction factors. The Cox-Merz rule was found to be invalid for these HDPE-wood composites. The effect of processing behavior on the rheological properties was also investigated.
Dynamic Rheology of Amorphous Poly-Alpha-Olfeins (APAOs) as Hot Melt Adhesives
Amorphous poly-alpha-olefins based on propylene were characterized over a wide temperature range by dynamic rheology. The rheological characteristics were useful in correlating Brookfield viscosity, ring-and-ball softening point, needle penetration, and open time with molecular structure and comonomer content.
Oxidized Polypropylene and Ionomers Thereof as Compatibilizers for Polypropylene/Nylon-6 Blends
Oxidized polypropylene and ionomers thereof were evaluated as compatiblizers for polypropylene/ nylon-6 (PP/PA-6) blends. For these blends, the ionomer of oxidized PP provided better morphology and physical properties than the oxidized PP. The change in morphology was also reflected in the rheological behaviors that the compatibilized blends showed an increase in melt elasticity. With improvement in flowability and yellowing resistance, the ionomer of oxidized PP also, for the most part, yielded mechanical properties comparable to commercially available maleated PP.
Oxidized Polypropylene as Compatibilizer/Dispersion Agent for Flame Retardants
Oxidized polypropylene has been produced with a controlled level of functionality. Applications of this new polymer in both halogenated and non-halogenated flame retardant (FR) formulations were studied. Benefits include enhancement of flame retardance performance and improvement in mechanical properties, processability, and surface appearance. In the melt stage, rheological measurements of G’ indicate that relaxation time decreases significantly when adding oxidized PP, confirming the improvements in PP-FR interfacial interaction and FR dispersion in the PP matrix.
Controlled Rheology Polyolefins- New Concepts in Stabilization
This paper deals with controlled rheology (vis-cracked) polyolefins and new concepts in stabilization to reduce peroxide consumption and retain color and other performance criteria. Recently, non-phenolic stabilizer systems have been introduced for improved gas fade resistance but increased peroxide consumption drove up systems cost. Therefore, new concepts must balance total requirements for rheology control and stabilization.
Computer Simulation of the Film Blowing Process Incorporating Crystallization & Viscoelastic Effects
A detailed two-dimensional simulation of the film blowing process is developed based on a mathematical model that incorporates the Phan-Thien Tanner (PTT) and Neo-Hookean constitutive equation with crystallization effects. The PTT constitutive equation is employed in the hot region, while the Neo-Hookean constitutive equation is used in the cold region to describe the rheological behaviour of the film. The model predicts bubble shape dimensions, temperature distribution, crystallinity, and orientation.
A Dielectric Slit Die for In-Line Monitoring of Polymer Compounding
The dielectric slit die is a new in-line instrument that is designed as a multipurpose sensing device to measure dielectric, rheological, and optical properties during extrusion. The instrument is mounted at the exit of an extruder and consists of a slit with dimensions 2 mm high by 28 mm wide by 15 cm length along which are situated dielectric, pressure and optical sensors. A flexible design permits interchanging of sensor locations and the addition of new sensors.
Monitoring Polymer/Clay Nanocomposites Compounding Using a Dielectric Slit Die
A new in-line process monitoring instrument, a dielectric slit die, was used to examine the compounding of polymer/clay nanocomposites. The instrument is a multipurpose sensing device for measuring dielectric, rheological, and optical properties during extrusion compounding. We report results of compounding nylon 12 and polyethylene ethyl vinyl acetate copolymer with organo modified clays.
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