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SPE Library content related to rheology
Study on the Rheological Behavior of Polymer Melt for Micro Molding
S.C. Chen, R.I. Tsai, T.K. Lin, R.D. Chien, May 2005
Determination of polymer melt rheological behavior within micro structured geometry is very important for the accurate simulation of micro molding. Yet its investigation is difficult due to the lack of commercial equipment. In this study, melt viscosity measurement within micro channel was established using a micro channel embedded mold operated at a mold temperature as high as the melt temperature. From measured pressures drop and volumetric flow rate both capillary flow model and slit flow model were used for the calculation of viscosity utilizing Rabinowitsch and Walters corrections. It was found that the measured viscosity values in the test ranges are significantly lower (about 30% to 90% lower) than those obtained from macroscopic rheometer. As micro channel size decreases, the derivation in viscosity is increases. This may be attributed to the melt slip occurs on the micro channel wall and the extend of wall slip increases when size of micro channels decreases. In addition, the higher the melt temperature, the effect of wall slip also becomes more significant. The result indicates that current simulation packages are not suitable for micro molding simulation without considering this effect.
The Effect of Gamma Sterilisation on Colour and Mechanical Performance of Medical Rigid PVC Compounds
P. McShane, B. Mayoral, D. McLaughlin, K. Hill, I. Kenny, G. Mc Nally, W.R. Murphy, M. Pritchard, May 2005
A range of commercially available gamma sterilisable medical rigid PVC (clear) compounds were characterized for hardness, specific gravity, Vicat softening, heat stability and rheological properties. In addition, the effect of exposure to gamma irradiation at 25 and 40 kGy on the colour, mechanical performance and dynamic mechanical response of the various PVC compounds was investigated. The results show no significant difference in hardness of the materials tested. However, significant differences in heat stability, Vicat softening temperature and rheological properties were evident. The results showed that exposure to gamma irradiation had only a slight effect on the mechanical performance of the PVC compounds tested. However, the results show exposure to gamma irradiation had a significant effect on the colour of PVC compounds B, C and D. All three compounds showed significant increases in b-value (yellowness/blueness index) following exposure to gamma radiation. PVC compound A showed superior gamma resistance, with only slight changes in b-value recorded after exposure to gamma irradiation.
Influence of Branching Distribution on the Physical Properties of High Density Polyethylene
Rajendra K. Krishnaswamy, Qing Yang, May 2005
Three sets of two-component blends from various narrow-MWD (molecular weight distribution), linear (no rheologically significant long branches) polyethylenes were prepared with multiple compositions in each set of blends. These blends were deliberately prepared such that the branching (from 1-hexene co-monomer) was present exclusively on either the high or the low molecular weight blend component. In this study, the influence exerted by such selective placement of branching on the physical properties of the resulting blends is discussed. We find that while the instantaneous tensile properties depend exclusively on crystallinity, the ultimate tensile properties depend strongly on branching distribution. Resistance to slow crack growth, impact toughness and the ductile-brittle transition temperature were all noted to depend strongly on branching distribution, with preferential placement of branches along the longer molecules being beneficial. Lastly, the tear resistance and impact toughness of oriented cast films produced using the above blends were also observed to depend on branching distribution.
3D Finite Element Modeling of the Blow Molding Process
Cedric Champin, Michel Bellet, Fabrice M. Schmidt, Jean-François Agassant, Yannick Le Maoult, May 2005
In this work, both the heating stage and the blowing stage of the blow molding process are numerically modeled. The heat transfer between the infrared oven and the preform is modeled using a ray tracing method. The cooling fan effect is taken into account thanks to a forced convection coefficient. Regarding the blowing step, a Mooney-Rivlin hyperelastic model has been implemented in Forge3® software in order to account for the rheological behavior of the polyester. The numerical finite element model is based on velocity pressure formulation and tetrahedral elements. In order to validate the implementation of the hyperelastic behavior, computations are compared to Mooney-Rivlin analytical model results for tube free inflation. Finally, the global blow molding process of a PET bottle is studied.
Viscoelastic Behavior of Highly Filled HDPE/Wood Flour Composites
Velichko Hristov, Elizabeth Takács, John Vlachopoulos, May 2005
Dynamic and steady shear viscoelastic properties of highly filled (50-70%) HDPE/Wood flour composites have been investigated by parallel-plate and capillary rheometers. The concentration effect of a new lubricant and coupling agent on the melt rheological properties of the composites was explored as well. The results showed that addition of both lubricant and coupling agent to the 70% filled HDPE composite considerably improved its flow behavior. An increase in the complex viscosity and storage modulus of the wood filled systems at low concentration of both modifiers was observed in case of 50% filler loading. Higher concentrations of modifiers resulted in a decrease of the complex viscosity. In capillary flow, it was observed that the lubricant improved the processability to a great extent. It was also found that all wood filled composites did not obey the Cox-Merz rule. It was concluded that dynamic and steady shear viscosity measurements by parallel plate rheometer did not correspond to capillary measurements at elevated wood flour loadings.
Flexible Thermoplastic Elastomer (TPE) Based on Ionomer Technology
J. McCoy, T. McQuaide, A. Montalvo, M.R. Sadeghi, A. Puttarudraiah, May 2005
Ionomer products have been in the marketplace for more than 30 years. These products offer outstanding toughness, high melt strength, excellent abrasion resistance with hardness values greater than 40 Shore D. This new class of patented flexible ionomer alloy thermoplastic elastomers (TPEs) have been developed with lower hardness and lower modulus for both Consumer and Automotive applications. These products have hardness values in the range of 70 to 90 Shore A with high toughness and tear strength, high mar/abrasion resistance, good chemical resistance, superior stain resistance, and controlled gloss.This paper will address the polymer science and technology for these new ionomer-based TPEs with respect to morphology, physical properties, rheological properties and aesthetics, as compared to traditional TPEs, including thermoplastic vulcanizates (TPV).
Rheology of Carbon Nanofiber-Modified Thermotropic Liquid Crystalline Polymers
Sungho Lee, Myung-Soo Kim, Amod A. Ogale, May 2005
A series of carbon nanofiber-modified thermotropic liquid crystalline polymers (TLCP, Vectran V400P) were investigated for their rheological properties. Steady shear viscosity at 250 °C revealed that incorporation of nanofibers led to a higher steady shear viscosity and a narrowed plateau region, implying a different microstructure for TLCP composites from that of a pure TLCP. Complex viscosity increased with increasing CNF content (0 ~ 15 wt%) for all frequencies at 230 °C. Shear thinning behavior in complex viscosity plot was observed for pure TLCP and all composites; there was no plateau in the dynamic viscosity even for a pure TLCP, indicating that this TLCP does not obey Cox-Merz rule. In a G? versus G ? plot, the slope for pure TLCP was different from those of composites.
The Effect of Ingredients and Processing Conditions on the Extrusion Processability of Halogen-Free Flame Retardant Thermoplasitcs
Seok Joong Hwang, Gi Joon Nam, May 2005
Inorganic flame retardants, such as aluminum trihydrate(ATH) and magnesium dihydrate(MDH), are most widely used fillers in halogen-free flame retardant polyolefin materials, especially for cable. These inorganic fillers, as they used in great amount, influence the rheological properties and extrusion characteristics of resin. During processing, they sometimes raise a problem such as die lip buildup, which refers to the resin accumulation on the open faces of extrusion dies. It commonly deteriorates the processability. The mechanism of die lip buildup is not fully understood, though there are many proposed explanations. The effects of resin composition and processing aids on the rheological and processing performance, including die lip buildup characteristics, were studied here. Also, processing conditions on the extrusion processability were investigated.
Modification of Polypropylene by High Intensity Ultrasonic Wave and its Characterization of Rehological Properties
Sang Myung Lee, Kyung Yl Kim, Gi Joon Nam, Jae Wook Lee, May 2005
A new method using high intensity ultrasonic wave, instead of peroxide-aided reactive extrusion, was applied to modify a linear polypropylene to a branched structure. To enhance and control the recombination reaction during sonication, multifunctional agent and antioxidant were used. From the rheological property measurements, it was confirmed that the modified polypropylene has nonlinear branched structure. Also, adequate use of antioxidant could control the degradation or recombination of polypropylene by stabilizing the structure during sonication.
Viscoelastic Properties of Acrylic-Based Copolymer Blends with Thermoplastics
Nafaa Mekhilef, Sheng Hong, May 2005
In this work, the viscoelastic properties of acrylic-based copolymer blends with poly (methyl methacrylate) and polycarbonate are investigated in the molten and solid states. Copolymers of MMA-BA with varying molecular weight and composition are used to enhance the rheological properties in shear and extension. The blends were prepared at 200°C using a DSM micro-compounder for up to 15 wt.% copolymer. The samples were characterized by size exclusion chromatography (SEC), dynamic mechanical analysis (DMA). The rheological properties were determined using small amplitude oscillatory measurements (SAOM) in shear and using a Rheotens device for melt strength determination. The results showed that depending on the nature of the copolymer used, the glass transition temperature (composition) and molecular weight, the rheological properties can be fine-tuned to enhance melt strength without a significant change in the shear rheology.
Reduced Fiber Breakage in an Injection Molding Machine
G. Zhang, M.R. Thompson, May 2005
An experimental investigation of the flow behavior of a glass fiber reinforced polypropylene in an injection molding machine revealed that it was possible to reduce the extent of fiber breakage occurring through the addition of a blowing agent. With the increased addition of a chemical blowing agent, from 0 to 5 wt%, the fibre length distribution was found to increasingly resemble the virgin resin. Rheological study of this phenomenon with an inline rheometer showed that the blowing agent changed the pseudoplasticity of the composite. As a result of the change in pseudoplasticity, less glass fibers were exposed to shear flow and therefore did not experience rotation normally leading to fibre breakage.
Continuous Process for Melt Intercalation of PP-Clay Nanocomposites with Aid of Power Ultrasound
Sergey Lapshin, A.I. Isayev, May 2005
A continuous ultrasound assisted process using a single screw extruder with an ultrasonic attachment was developed to prepare PP/clay nanocomposites of varying clay concentrations. The feed rate that controls the residence time of the polymer in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Rheological properties, morphology and mechanical properties of the untreated and ultrasonically treated nanocomposites were studied. An intercalation of polymer molecules into clay galleries and a partial exfoliation, which occur at short residence times (on the order of seconds), were observed as evident from measurements by X-ray diffraction and transmission electron microscopy. The obtained results indicate a possibility of the rapid intercalation and partial exfoliation of PP/clay nanocomposite without the matrix being chemically modified.
A Study on the Extrusion of Open Cell Polystyrene Mixed Foams
Chih-Chen Chang, Mu-Li Chang, Pen-Chang Tseng, Chih-Hung Ying, May 2005
This current study mixes two polystyrene resins with different rheology properties, PS-1 and PS-2, to present the resin with other property, and finds that the adequate mixing proportion of PS-1 and PS-2 is better between 18~25%, and perlite additive is added to carry out the minute change of property, where 1-2% difference of perlite application quantity will cause changes in complex viscosity. For the application of formulation after property changes plus difluoromethane / pentafluoroethane 50/50Wt% foaming agent, we directly adopt continuous extrusion foaming method to execute the experiment, which shows such formula combination is capable of achieving better balance in simultaneously reducing average cell diameter of foam body and maintaining the open-cell content. Via the above mentioned formula combination and process condition, the foam body produced can possesses about 30?m of average cell diameter and open- cell content higher than 90%.
The Effect of Volume Fraction and Particle Size of Polystyrene onto Magneto-Rheological Properties of Inverse Ferrofluid
Ruben Saldivar-Guerrero, Reinhard Richter, Ingo Rehberg, Nuri Aksel, Lutz Heymann, Oliverio S. Rodriguez-Fernández, May 2005
Inverse ferrofluids are prepared using microsized polystyrene particles dispersed in a ferrofluid. The magnetorheological properties were measured as a function of the particle size, and polydispersity. The measurements are performed in a plate-plate rheometer applying a vertically oriented magnetic field. The obtained flow curves show, that under shear a ”solid” to “liquid” transition take place, which is presumable due to the destruction of chains of the non-magnetic particles. This transition is characterized by an apparent yield stress and compared with theoretical predictions. In the oscillatory mode, the storage and loss moduli reveal, that also the viscoelastic behavior is affected by the particle size and the particle size distribution of the non-magnetic particles in inverse ferrofluids.
Enhanced TPO Thermoforming Using High Melt Strength Polyolefin Elastomers
Kim L. Walton, Michael K. Laughner, Lawrence J. Effler, E. Scott Gisler, May 2005
Hard TPOs have grown rapidly in the automotive industry due to their favorable cost/performance characteristics and injection molding processability. Other plastics processes are now either currently used or under investigation. Processes such as blow molding and thermoforming offer the potential to manufacture large parts with much lower tooling costs than injection molding. However, it is well known that conventional polypropylene exhibits poor melt strength. This deficiency has limited its use in either large part extrusion blow molding or thermoforming.Recently, polypropylene producers have introduced high melt strength polypropylene into the market. These polypropylenes have much higher melt strength than conventional materials. They are being promoted for use in hard thermoplastic olefin (TPO) applications requiring high melt strength.However, other components, particularly the impact modifier, can now play an important role in the thermoforming characteristics of hard TPO compounds. In a series of experiments, significant changes in TPO rheology were observed, depending on the level and type of impact modifier used. The characteristics of ethylene/alpha olefin copolymer impact modifiers and their effect on hard TPO thermoforming performance will be discussed.
Single-Step Foaming of Polypropylene in Rotational Molding
David D’Agostino, Elizabeth Takács, John Vlachopoulos, Eric Maziers, May 2005
It is well known within the plastics industry that foaming of polypropylene is a very challenging process. A new generation of polypropylene, offering improved processability, has been produced recently by using a metallocene catalyst technology. A fundamental study of single-step foaming of the newly developed polypropylene in rotational molding was conducted, using polymer microspheres as a blowing agent. The influence of polymer rheology on tensile properties, flexural modulus, and cell morphology of the foamed polypropylene parts was investigated. Comparisons are made between conventional and metallocene polypropylene materials.
Melt Fracture of Polyethylene and the Role of Extensional Flow Behavior
Martin L. Sentmanat, Edward B Muliawan, Savvas G. Hatzikiriakos, May 2005
The melt fracture and extensional flow behaviors of a series of linear polyethylenes were characterized from capillary extrusion and uniaxial extension melt rheology experiments with the SER Universal Testing Platform. Based on the experimental results it was determined that the critical shear rates for the onset of both sharkskin and gross melt fractures were found to correlate with the highrate extensional flow behavior of the polymer melts. These findings were found to mechanistically support the generally accepted observations of melt fracture phenomena occurring at the exit (sharkskin) and entrance (gross) regions of the capillary die. In addition, it was found that the presence of a small amount of boron nitride (BN) filler behaves as an energy dissipater that acts to suppress the rapid increase of extensional stress associated with gross melt fracture, and enables the BN to act as an effective processing aid in postponing the onset of gross melt fracture.
Optimise Organoclay Exfoliation in Polymer Nanocomposites by Customising the Extrusion Temperature Gradient
C.Y. Lew, I.M. Major, W.R. Murphy, G.M. McNally, May 2005
This is a communication article describing a novel and simple approach to optimise the exfoliation and dispersion of organoclay layered-silicate in the extrusion processing of polymer nanocomposites. A range of HDPE nanocomposites were processed by configuring the extrusion temperature gradient in a single-screw compounder. Wide-angle X-ray diffraction (WAXD) analysis showed that the degree of organoclay exfoliation, which is directly associated with the various property improvement in nanocomposites, was influenced by the extrusion temperature gradient. These nanocomposites exhibited significant difference in their rheological flow characteristic and mechanical properties, owing to the difference in the resultant organoclay structures. Regardless of the level of organoclay exfoliation, all the nanocomposites exhibited better processability and improved mechanical properties compared to the virgin HDPE. The elongation at break of all the nanocomposites was considerably greater than the virgin HDPE despite recording an increase in crystallinity.
An Investigtion of Metallocene and Ziegler-Natta Catalysed LLDPE/Clay Nanocomposites
C.Y. Lew, W.R. Murphy, G.M. McNally, D.C. McConnel, I. Moore, J.E. Godinho, May 2005
The influence of controlled-chain branching in a metallocene-catalysed LLDPE (mPE) and random chain branching in a conventional LLDPE (zPE) on the exfoliation behaviour of an organoclay was investigated. Both X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies showed the clay exfoliation level to be significantly higher in the metallocene LLDPE. Rheological analysis suggested that higher shear stress during the processing of metallocene polyethylene, attributed to the narrower molecular weight distribution was responsible for this phenomenon.
Impact of Titanium Dioxide Surface Characteristics on Extrusion Processing
Rajath Mudalamane, Philipp M. Niedenzu, William T. Sedar Jr., May 2005
Interfacial interactions between the titanium dioxide pigment surface and the polymeric matrix have a significant impact on the energy requirements for incorporation and the rheology of the resulting compound. This study investigated the effect of screw geometry and operating conditions on dispersion performance and torque loading during twin-screw compounding of three different grades of titanium dioxide pigments with different surface treatments into highly loaded polyethylene masterbatches. It was found that the screw design and operating conditions where the pigments performed best were quite different for the three grades. It was found that low intensity mixing sections and cooler barrel temperature settings seemed to favor the pigment with a compatibilizing hydrophobic surface treatment and high intensity mixing sections and hotter barrel temperature settings favored the pigments that did not have such a surface treatment. It was also found that by optimizing screw designs, much higher throughputs and better dispersion could be achieved.

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