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Die Swell (die + swell)

Distribution by Scientific Domains

Polymers and Materials Science	76%
Chemistry	23%

Selected Abstracts

The Effect of Orientation on Extrusion Cast Metallocene Polyethylenes and the Role of Processing Conditions in the Die Swell of Metallocene and Conventional Polyethylenes

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1-2 2004
B.G. Millar
Cast films were prepared from a range of metallocene polyethylenes (mPEs) of varied co-monomer types (hexene, octene) using a Killion single-screw extruder, using different haul off speeds (8,4 m/min) and die gaps (700,250 m,m). Samples with greater orientation in one direction had increased tensile strength and shrinkage in that direction. DSC analysis showed crystallinity to decrease with decreasing haul of speed. Extrusion of mPEs and conventional linear low density polyethylenes (LLDPEs) by single capillary rheology showed that die swell increased with increasing extrusion rate and decreasing melt temperature. Increased die swell was found for the broader molecular weight distribution (M.W.D.) LLDPEs and in the higher molecular weight resins. Furthermore, long chain branching was found to increase die swell. [source]

Rheological characterization of HDPE/sisal fiber composites

POLYMER ENGINEERING & SCIENCE, Issue 10 2007
Smita Mohanty
The present paper summarizes an experimental study on the molten viscoelastic behavior of HDPE/sisal composites under steady and dynamic mode. Variations of the melt viscosity and die swell of the composites with an increase in shear rate, fiber loading, and coupling agent concentration have been investigated using capillary rheometer. The shear rate , at the wall was calculated using Rabinowitsch correction applied to the apparent shear rate values. It was observed that the melt viscosity of the composites increased with the addition of fibers and maleic anhydride-grafted PE (MAPE). Die swell of HDPE also decreased with the addition of sisal fibers and MAPE. Further, the dynamic viscoelastic behavior of the composites was measured employing parallel plate rheometer. Time,temperature superposition was applied to generate various viscoelastic master curves. Temperature sweeps were also carried out to study the flow activation energy determined from Arrhenius equation. The fiber,matrix morphology of the extrudates was also examined using scanning electron microscopy. POLYM. ENG. SCI., 47:1634,1642, 2007. © 2007 Society of Plastics Engineers [source]

Effects of diatomite on extrudate swell behavior of polypropylene composite melts

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010
J. Z. Liang
Abstract Extrudate swell (i.e., die swell) is an important parameter for characterization of melt elasticity during extrusion of polymeric melts, and die swell ratio (B) is usually used to describe quantitatively the melt swell degree. The B of the polypropylene (PP) composites filled with diatomite particles was measured by means of a melt flow rate instrument to investigate the effects of the filler content and size on the die swell behavior of the composite system melts under the experimental conditions with temperature from 210 to 230°C and load varying from 1.2 to 7.5 kg. The particle diameters were 5, 7, and 13 ,m, and the filler volume fractions were 5, 10, and 15%, respectively. The results showed that the B of the composites decreased nonlinearly with an increase of the filler volume fraction, whereas it increased as a quadratic function with an increase of the particle diameter when the load and temperature were fixed. It might be attributed to the interaction between the inclusions and the matrix, leading to blocking the recovery of the elastic deformation as the composite melts left from the die exit. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Effects of quasi-nanogel particles on the rheological and mechanical properties of natural rubber: A new insight

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
Suman Mitra
Abstract The influence of sulfur-crosslinked, quasi-nanosized gels on the rheological and mechanical properties of raw natural rubber (NR) was investigated. Latex gels with different crosslink densities were prepared through the variation of the sulfur-to-accelerator ratio. These gels were characterized by dynamic light scattering, solvent swelling, and mechanical properties. The gels were mixed with raw NR latex at concentrations of 2, 4, 8, and 16 phr, and their effect on the rheological properties of NR was studied by Monsanto processability tester. The presence of gel in raw NR reduced the apparent shear viscosity and die swell considerably. Initially, the viscosity decreased up to a 8 phr gel loading and then increased with an increase in the gel loading. However, the change in the viscosity was related to the crosslink density of the gels. A new empirical equation relating the viscosity, volume fraction of the gels, and crosslink density was proposed. The die swell of gel-filled raw NR was at least 10% lower than that of unfilled raw NR and decreased with an increase in the gel loading. The effect of the gels on the die swell properties was explained through the calculation of the principal normal stress difference of gel-filled NR systems. Scanning electron photomicrographs of the extrudates revealed much better surface smoothness for the gel-filled virgin rubber systems than for the unfilled rubber. The addition of the gels to raw NR increased the modulus and tensile strength, whereas the elongation at break decreased. The effect of the gels on the dynamic mechanical properties of NR was also investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Simulation of particle migration in free-surface flows

AICHE JOURNAL, Issue 10 2010
Kyung Hoon Min
Abstract The migration of particles in free surface flows using the diffusive flux model was investigated. As the free-surface flows, a planar jet flow and a slot coating flow were chosen. The suspension was assumed to be a Newtonian fluid with a particle concentration dependent viscosity. The governing equations were solved numerically by the finite volume method, and the free-surface problem was handled by the volume of the fraction model. The result shows that even though the velocity profile is fully developed and becomes flat, the particle distribution never reaches the uniform distribution for both of the cases. It is also shown that the die swell of the free jet is reduced compared to the Newtonian fluid and when the particle loading is 0.5, die contraction is observed. The change in die swell characteristics is purely due to particle migration since the suspension model does not show normal stress differences. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

Development of a bulgur-like product using extrusion cooking

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 7 2003
Hamit Köksel
Abstract In this study we (1) developed a new bulgur-like foodstuff using a durum wheat cultivar and an extrusion technique, (2) investigated the physicochemical properties of the extrudates produced and (3) sensorially evaluated the end-product after cooking. Durum wheat was processed in a laboratory-scale co-rotating twin-screw extruder with different levels of moisture content of the feed (367, 417 and 455,g,kg,1), screw speed (150 and 200,rpm) and feed rate (2.4 and 2.9,kg,h,1) to develop the bulgur-like product. The effects of extrusion conditions on system variables (die pressure and specific mechanical energy (SME)), physical properties (die swell and bulk density), pasting properties (peak, trough and final viscosities) and cooking and sensory properties of the bulgur-like products were determined. The results indicated that increased feed moisture content resulted in significant decreases in the die pressure and SME values of the extruded durum wheat products. As the moisture content and screw speed increased, the changes in die swell values were not significant. The lowest die swell and highest bulk density values were obtained at the highest feed moisture content. The extrusion variables also affected the pasting properties of the extrudates. Significant increases in each of the pasting properties occurred when the moisture content of the feed was increased. Some of the sensory properties (bulkiness, firmness, stickiness and taste,aroma) improved significantly as the feed moisture content increased, indicating better quality. Increased feed moisture content significantly improved cooking quality as determined by a decrease in colorimetric test results. Extrusion seems to be promising for the production of dry, relatively inexpensive bulgur-like products with acceptable sensory properties. © 2003 Society of Chemical Industry [source]

Investigation of the relationships between die build up and die swell

POLYMER ENGINEERING & SCIENCE, Issue 2 2009
Todd A. Hogan
Die build up (DBU) is a common problem encountered during extrusion of polymers where material accumulates around the die exit and may cause defects in the surface of the product. This study was initiated to better understand the fundamental relationships between DBU and die swell. The study was conducted on a strand die extrusion system using an ethylene-octene polyolefin elastomer resin. This study demonstrated that die swell is not a root cause of DBU. It was shown that at constant shear rate, increasing the die L/D ratio results in an increase in DBU, while die swell decreases. The important variables influencing DBU for the resin used in this study were: the shear rate or shear stress in capillary portion of the die, the nominal residence time that the resin is exposed to the high shear stress in the die capillary, and the concentration of oligomers present in the resin or generated during processing. These data support the conclusion that DBU is due to the shear-induced migration of oligomeric species in the polymer to the die surface. Higher shear rates and stresses in the die promote this migration and result in a higher concentration of oligomeric species near the die wall. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers [source]

Rheological characterization of HDPE/sisal fiber composites

A parallel coextrusion technique for simultaneous measurements of radial die swell and velocity profiles of a polymer melt in a capillary rheometer

POLYMER ENGINEERING & SCIENCE, Issue 10 2004
N.-T. Intawong
This article proposes a new experimental technique to simultaneously measure radial die swell and velocity profiles of polystyrene melt flowing in the capillary die of a constant shear rate rheometer. The proposed technique was based on parallel coextrusion of colored melt-layers into uncolored melt-stream from the barrel into and out of the capillary die. The size (thickness) ratio of the generated melt layers flowing in and out of the die was monitored to produce the extrudate swell ratio for any given radial position across the die diameter. The radial velocity profiles of the melt were measured by introducing relatively light and small particles into the melt layers, and the times taken for the particles to travel for a given distance were measured. The proposed experimental technique was found to be both very simple and useful for the simultaneous and accurate measurement of radial die swell and velocity profiles of highly viscous fluids in an extrusion process. The variations in radial die swell profiles were explained in terms of changes in melt velocity, shear rate, and residence time at radial positions across the die. The radial die swell and velocity profiles for PS melt determined experimentally in this work were accurate to 92.2% and 90.8%, respectively. The overall die swell ratio of the melt ranged from 1.25 to 1.38. The overall die swell ratio was found to increase with increasing piston speed (shear rate). The radial extrudate swell profiles could not be reasoned by the shear rate change, but were closely linked with the development of the velocity profiles of the melt in the die. The die swell ratio was high at the center (,1.9) and low (,0.9) near the die wall. The die swell ratio at the center of the die reduced slightly as the piston speed was increased. Polym. Eng. Sci. 44:1960,1969, 2004. © 2004 Society of Plastics Engineers. [source]

Compensating for die swell in the design of profile dies

POLYMER ENGINEERING & SCIENCE, Issue 10 2003
W. A. Gifford
Because of the effects of die swell, the final shape of an extrudate is often substantially different from that of the exit opening of the die. As a result, the design of profile dies producing complex shapes often involves more than just "balancing" the die but also compensating for the effects of die swell. Typically, a successful design of such dies is achieved only through much "cut and try," However, with the use of a fully three-dimensional finite element flow algorithm along with quick mesh generating capabilities, the usual cut and try involved in the design of many profile dies can be greatly reduced, if not eliminated. This paper demonstrates how the effects of die swell can be compensated for in the design of profile dies. For profiles with one plane of symmetry, this includes compensating for the sideways translation of the extrudate as well as the change in shape that the extrudate experiences. Completely asymmetric profiles undergo a "twisting" downstream of the die. This twisting, which appears not to have been reported in the literature (at least for isothermal extrusion), is also accounted for here, along with the change in shape that the extrudate undergoes. The translation or twisting of profiles downstream of a die is often attributed to non-Newtonian or non-isothermal effects. Only isothermal Newtonian examples are considered here. These results clearly show that asymmetry of the profile will result in a translation and twisting of the extrudate even in the isothermal Newtonian case. [source]

Nonisothermal two-dimensional film casting of a viscous polymer

POLYMER ENGINEERING & SCIENCE, Issue 8 2000
Spencer Smith
A model is presented for simulating two-dimensional, nonisothermal film casting of a viscous polymer. The model accommodates the effects of inertia and gravity, and allows the thickness of the film to vary across the width, but it excludes film sag and die swell. Based on the simulation results, three factors are shown to contribute to reducing neck-in and promoting a uniform thickness: the self-weight of the material, for low viscosity polymers; nonuniform thickness and/or velocity profiles at the die; and cooling of the film, especially when localized cooling jets are employed. [source]

Rheological behavior of highly filled ethylene propylene diene rubber compounds

POLYMER ENGINEERING & SCIENCE, Issue 5 2000
M. G. Markovic
The rheological behavior of highly filled ethylene propylene diene rubber (EPDM) compounds was studied with respect to the effect of curative system, grafted rubber, shear rate, temperature and die swell using a Monsanto Processability Tester (MPT) to gain an understanding of the molecular parameters that control the surface finish. All systems show pseudoplastic behavior. At a particular shear rate, shear viscosity increases with blend ratio. The dependence of flow behavior on extrusion velocity indicates a surface effect. The extrudate die swell and maximum recoverable deformation are related by a linear relationship, which is independent of sulfur/accelerator ratio, extrusion temperature and shear rates and blend ratio. The principal normal stress difference increases nonlinearly with shear stress. Activation energy decreases with shear rate in most cases. The faster relaxing system produces extrudate of better surface quality. [source]

Melt viscoelasticity of polyethylene terephthalate resins for low density extrusion foaming

POLYMER ENGINEERING & SCIENCE, Issue 3 2000
uintans
The rheological properties of conventional polyethylene terephthalate (PET) resins are not particularly suitable for low density extrusion foaming with physical blowing agents; as a result, chemically modified resins through chain extension/branching reactions are often used. Such resins have overall higher melt viscosity and higher melt strength/melt "elasticity" than unmodified materials. In this work, following a review of the prior art on PET chemical modification, an unmodified and a chemically modified resin were selected and characterized for their melt viscoelastic properties including shear and dynamic complex viscosity over a broad shear rate/frequency range, storage and loss modulus, and die swell. Certain rheological models were found to provide better fits of the entire viscosity curve for the unmodified vs. the modified resin. Foamed extrudates having variable densities (from about 1.2 to 0.2 g/cc), were prepared by carbon dioxide injection in monolayer flat sheet extrusion equipment. Foams with increasingly lower density, below 0.5 g/cc, were obtained by increasing gas pressure only in the case of the chemically modified resin. The effects of variables such as concentration of the physical blowing agent, resin rheology, resin thermal properties and choice of process conditions are related to product characteristics including density, cell size and crystallinity. [source]

The Effect of Orientation on Extrusion Cast Metallocene Polyethylenes and the Role of Processing Conditions in the Die Swell of Metallocene and Conventional Polyethylenes