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SPE Library content related to rheology
Rheological Characteristics of Polymer Blends
This work presents an experimental observation of the rheological characteristics of the TPE/SB blend (Thermoplastic Elastomer / Styrene-Butadiene) used in the plastic transformation industry for medical applications. The flow curves (shear viscosity x shear rate) of the blend were investigated at different temperatures and in a wide range of shear rates. During the extrusion, the instability phenomenon (melt fracture) and its relation with the shear rate and temperature parameters was also investigated. All the experiments, the flow curves and melt fracture observation, were performed in a Capillary Rheometer ( a Rosand Rh-2100 capillary rheometer) working with a 1 x 16 mm rod capillary die.
Rheological and Mechanical Properties of Recycled Polycarbonate
Polycarbonate (PC) is used in computer and electronic housings, and here it was sought to reuse this polymer after having been separated from electronic shredder residue. The separated stream was not pure PC; there was some cross-contamination. The separated polymer was characterized by rheological, thermal and mechanical methods; the measured properties were only slightly inferior to those of comparable virgin materials. Recovered plastic and virgin polymer were blended using a TSE to determine the minimum virgin content needed to mask the effects of addition of recycled material on the rheological and mechanical properties of the blend. Differences in processing behavior and mechanical performance of the blends as a function of composition are discussed in relation to potential material recycling strategies.
A Novel Ionomer for Nylon Modification
A new family of Surlyn® ionomers containing reactive functional groups is being developed for polymer modification, e.g., modifying nylon for blow-molding applications. Compared to existing ionomers, the new ionomers exhibit a higher degree of compatibility with nylon. One of the unique features of the new modifier is that the new ionomers can be dispersed in nylon in an extremely fine particle size and narrow size distribution. This has a profound effect on both the melt rheology and the mechanical properties of the modified nylon. Most significantly, the new ionomer imparts a truly shear thinning melt viscosity of the modified nylon 6. The paper discusses the dispersion of the new ionomer in nylon 6 as analyzed by SAXS and TEM and the melt rheology behavior of the modified nylon 6 and briefly highlights the effectiveness of the new ionomer to modify nylon 6 for the demanding blow-molding applications.
Mold Filling and Curing Analysis in Scrimp
In recent years, vacuum-assisted resin transfer molding (e.g. Seemann Composite Resin Infusion Molding Process - SCRIMP) has been widely used for marine, civil infrastructure, transportation and defense applications. Unsaturated polyester and vinylester resins are two major resins used in these processes. Their kinetic and rheological behaviors were investigated experimentally. A model was developed to quantify the effects of different curing agents on the gel time and reaction rate. This model, in conjunction with fluid flow and heat transfer models, was used to determine the effects of resin type and composition, curing temperature, and part geometry on mold filling and curing. SCRIMP experiments were carried out to verify the simulation results.
Isolating the Effect of Reaction on the Phase Inversion of Model PA/PS Blends
This paper aims to distinguish the effect of reaction on morphology development during polymer blending from other confounding parameters, particularly the rheological differences between the reactive and nonreactive components. Many works have focused on components that are rheologically matched at the processing temperature. However, based on previous results that have shown the importance of the melting regime in morphology development, it is crucial that the components be rheologically matched throughout the experimental temperature range. In this work, we use a model addition protocol to limit the morphology development to a temperature range where the reactive and nonreactive polystyrenes exhibit an excellent rheological match. The interfacial reaction was found to accelerate the pace of initial morphology development, where sheets are pulled off the solid pellet core during melting. Phase inversion began earlier but finished later in the nonreactive blend.
On-Line Melt Strength Enhancement of Polypropylene for Extrusion Coating
The superior performance of Montell's high melt strength branched polypropylene (bPP) resins has been well documented. Their long chain branched structure gives them high melt elasticity or melt strength, which allows very high line speeds, low neck-in, and thin coatings (high draw ratio) when extrusion coating. A concentrated but highly miscible version of branched PP has been developed which allows for the on-line addition of bPP to any linear polypropylene, including the relatively high-MFR grades used in extrusion coating. This versatile approach allows converters the flexibility to add only the quantity of bPP needed for their processing conditions and to select from a wide variety of linear PP types, depending on the desired properties of the coating. Performance data and rheology at various letdown levels into a variety of polypropylenes, heterophasic copolymers and random copolymer polypropylenes will be discussed.
Novel Ionomer for Nylon Blow Molding Applications
A novel ionomer is being developed to modify nylon for blow-molding applications. The new ionomer that contains reactive functional groups attains excellent compatibility with nylon by a combination of physical and chemical interaction. The modifier can be dispersed in small particle size as low as 50 nm in nylon 6. This report discusses the melt rheology, blow-molding evaluation and weldline strength of the nylon modified with the novel ionomer. The particle size of the ionomer dispersed in nylon is discussed to explain the unique properties of the new modifier. For comparison, a maleated ethylene polymer (EP) and a conventional ionomer are included in the study.
Thin Wall Injection Molding of Thermoplastic Microstructures
Thin-wall injection molding is a key technology allowing the low-cost mass production of microstuctures, such as devices with surface-relief microcomponents widely applied in micro-optics, micro-fluidics, medical and biotechnology. Research was performed in order to gain better understanding of important parameters in injection molding of thin-wall microstructures. A series of injection molding experiments were conducted with PC and PMMA, which are common materials in bio-MEMS (Micro Electro Mechanical System) applications. The rheological properties were characterized through dynamic, and transient shear viscosity measurement using a Rheometrics Mechanical Spectrometer. Micro-channels of different lateral and depth dimensions were obtained on thin wall substrates. The Scanning Electronic Microscope (SEM) photos were used to measure the fidelity and roughness of the replicated plastics. Birefringence was used to qualitatively examine the amount of residual stresses in the molded parts.
Magnetic Materials Based on Polymers and Magnetical Fillers
In this paper the mechanical, magnetical and rheological properties are analyzed. The influence of different magnetic powders onto a plasticized polvinyl chloride) were studied. The magnetic characterization of isotropic plastic bonded magnets, based on strontium ferrite (SrFe12O19) and plasticized polyvinyl chloride, as a function of composition was analyzed in a magnetometer at room temperature. In order to explain the dependence of the volumetric density and the saturation magnetization with composition, an additive model for these properties is considered. The intrinsic coercivity shows a decrease with increasing strontium ferrite content, which is due to the increasing interaction between the magnetic particles. The maximum energy product is lower than 1 MGOe and increases with the second power of the strontium ferrite content. The rheological properties were studied in a capillary rheometer; it was found that viscosity increased as the magnetic powder concentration increased in the composite.
Rheology of Highly Interactive Polymer-Filler Mixtures
The dynamic properties of polystyrene (PS)/silica mixtures of various concentrations were investigated as a function of frequency and strain along with the flow curves. An abrupt change in the viscoelastic properties is noticed above 1% volume concentration. Observations by means of scanning electron microscopy (SEM) indicate the creation of a 3D network through bridging of filler particles by adsorbed polymer. The rheological behavior is simulated utilizing a double network created by the entangled polymer matrix and the adsorbed polymer. Both networks are represented by a Giesekus viscoelastic constitutive equation. The dependence of rheological properties on filler concentration is taken into account through the density of polymer-filler interactions and a hydrodynamic reinforcement. The relative contribution of both networks is computed through the energy balance consistent with the thermodynamics of the chemical interactions and fluid mechanics. This self-consistent approach allows one to predict the major features of the rheological behavior of such systems.
Linearity and Non-Linearity of Mechanical Properties in Blends of Virgin and Recycled HDPE's
This paper investigates the behaviour of blends of Recycled Milk Bottle Resin (R-MBR) with Injection Moulding or Film Blowing grade HDPEs (IM-HDPE or FB-HDPE). This was done by measuring changes in mechanical and rheological properties as a function of blend composition and compounding intensity. There were three categories of compounding: bag mixing (BM), single pass single screw extrusion (EBx1) and double pass single screw extrusion (EBx2). The results were examined for linear and non-linear trends, and relationships between morphology, mechanical properties and molecular weights were proposed.
Calcium Carbonate Filled Polybutyleneterephthalates
70% of fillers used in plastic materials are calcium carbonates due mainly to availability and cost advantages. The raw material cost of polybutylene terephthalate (PBT) is relatively higher than most of polyolefins and common polyesters. It has been reported that calcium carbonate filled polyester reduces shrinkage of the product substantially. Mineral filled plastic compounds burn much more slowly than their unfilled counterparts. Lowering raw material cost without having much adverse effect on properties by blending calcium carbonates is the objective of the current study. Rheological, thermal and mechanical analyses were carried out with virgin and up-to 15 weight percent of calcium carbonate filled PBTs. Rheological and thermal properties of filled PBTs comparing with virgin PBT had not changed noticeably while the percent elongation to break decreased and the modulus increased with increasing filler content.
Predicting Molding Forces in SMC Compression Molding
Much attention is now being given to improving the economy of Sheet Molding Compound (SMC) compression molding by reducing the cycle time required to produce acceptable parts in steady production. The longest stage of the molding cycle is the cure cycle. However, the filling stage does play an important role. The shorter the filling time, the more reactive an SMC can be used and thus the shorter the cure time. In particular for truck parts, due to their large size, being able to predict the press force needed to close the mold at a given speed is extremely important. The long-term goal of our research is to develop a model to predict closing forces as a function of raw material parameters - paste rheology, glass length and concentration - without the need to make the SMC. Here we present a simple model describing our approach and propose a preliminary procedure that can be used to obtain the closing force. This preliminary procedure still requires measurements to be obtained from the already made SMC. The results from this approach are compared to experimental results for a typical automotive grade SMC.
On-Line Viscosity Measurement during Poly(ethylene terephthalate) Extrusion
The effects of various processing parameters (temperature, pressure and drying time) during extrusion of poly(ethylene terephthalate) (PET) were examined using a commercial on-line process control rheometer mounted on a twin-screw extruder. Particular attention was addressed to the effect of the moisture content. Moisture left in the resin pellets due to an incomplete drying reacts with the polyester to break down the molecular weight, which is reflected by a significant decrease of the viscosity. Since the PET resin is highly hygroscopic, off-line melt viscosity characterization may yield erroneous estimates of the rheological behavior. As in-line drying is recommended to achieve optimal properties, on-line viscosity characterization is required to provide an unbiased viscosity measurement and a true estimate of the performance of the drying step.
Modelling of Bubble Formation in Rotational Molding
Polymer sintering and heat transfer are fundamental phenomena in rotational molding. In the heating stage of the molding cycle, the powder particles melt, adhere to each other and sinter. During this stage, pockets of air are entrapped between the particles and form bubbles. This work aims at determining the relative effects of material properties and molding temperature on the initial sintering and bubble formation in rotational molding. The molding temperature varies strongly with the oven temperature and molded part thickness, and is determined using a lumped parameters heat transfer model (Gogos et al., 1998). The initial sintering of powder is predicted using a two-particle sintering model (Pokluda et al, 1997). The sintering model is used together with the heat transfer model to predict the level of sintering reached when an additional powder layer adheres to the melt and thus entraps air pockets which in turn will form bubbles. Results show that the initial size of the bubbles formed does not vary significantly when changing molding conditions. The polymer rheological properties seem to dominate the bubble formation process. Further results will be compared with experimental work.
Edge Effects in Film Casting of Molten Polymers
In most analyses of the film casting process, edge effects such as necking in and edge beading are usually neglected. In this work, we investigated the significance of these effects and their dependence on the rheological properties of the melts, the draw ratio, and the extrusion rate. Two linear low-density polyethylene melts and a low-density polyethylene melt were considered. The rheological behaviors of these melts were characterized under shear and elongational flows. Streamlines from the die exit to the chill roll, velocity profiles, film tension, neck-in profiles, thickness profile of the solidified film, and edge bead thickness profile were examined.
Chemo-Rheology and Structure Development of a Solventless System for Manufacturing Electronic Pre-Pregs
Current processes used to manufacture electronic pre-pregs and laminates use solvent based systems. Solvents are environmentally unfriendly and add no value to the final product. We are developing a new solventless process, based on the concept of continuous Resin Transfer Molding or Injection Pultrusion. The first step in designing the process is to select a suitable chemical system. The viscosity of the system should be such that it allows proper impregnation at a temperature at which not much reaction takes place. To predict the required pulling force, the friction at the wall as the material solidifies needs to be truly understood. A potential resin system has been identified and its chemo-rheology and structure formation will be discussed.
Blends of Ethylene/Styrene Interpolymers and Other Polymers: Rheology and Morphology during Processing
Ethylene/styrene Interpolymers produced via INSITE* Technology exhibit compatibility with a wide range of polymers due to their inherent combination of olefinic and styrenic functionality. Blends of Interpolymers with polyethylene and polystyrene are discussed in terms of rheology, morphology, and observations from injection molded products. Dispersion of the minor phase is predicted by a rheological model, and these predictions are compared with the morphology of the blends.
New Dialkyl Peroxide for Improved Controlled Rheology Polypropylene Used in FDA Applications
The use of polypropylene for food contact applications such as specialty packaging films has increased dramatically over the last decade. Much of the polypropylene resin used in this industry has rheology characteristics imparted by a reaction extrusion process. The modification of low melt flow resins is accomplished by an extrusion reaction of the polymer with an organic peroxide. The decomposition of the organic peroxide yields a radical species which modifies the molecular weight profile of the resin. The decomposition of the organic peroxide is known to lead to the formation secondary products (organoleptics) such as alcohols and ketones, which can impart disagreeable odor and taste characteristics to the resin. The US Food and Drug Administration (FDA) regulates the allowable concentration of potentially hazardous materials in food grade applications. The formation of hazardous decomposition products can be eliminated by employing an organic peroxide that does not yield regulated decomposition products. This paper reports the use of a new dialkyl organic peroxide in controlled rheology processes. The new peroxide combines improved odor and taste characteristics with ease of processing and cost advantages.
Evaluation of a Wood Fiber-Based Compound by Torque Rheometry
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.
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