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Elongational Flow (elongational + flow)

Distribution by Scientific Domains

Polymers and Materials Science	85%

Selected Abstracts

Morphology Modification of Polyethylene/Clay Nanocomposite Samples under Convergent Flow

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 9 2009
Francesco Paolo La Mantia
Abstract The morphology of PE/CL nanocomposite samples subjected to convergent flows is studied. Elongational flow , the typical flow involved in spinning and film-blowing processing operations , significantly increases with the reduction of the capillary diameter. The values of the convergent extensional stress (calculated by Cogswell's formula) for the PE/CL systems, for all the adopted capillary geometries, are greater than the calculated values for pure polyethylene. The applied convergent flow, at the entrance of the capillary, is able to change the clay morphology and consequently the final material properties on the PE/CL system with limited affinity between the matrix and organo-modified clay particles. [source]

Effects of microcompounding process parameters on the properties of ABS/polyamide-6 blends based nanocomposites

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
Güralp Özkoç
Abstract Melt intercalation method was applied to produce acrylonitrile-butadiene-styrene/polyamide-6 (ABS/PA6) blends based organoclay nanocomposites using a conical twin-screw microcompounder. The blend was compatibilized using a maleated olefinic copolymer. The effects of microcompounding conditions such as screw speed, screw rotation-mode (co- or counter-), and material parameters such as blend composition and clay loading level on the morphology of the blends, dispersibility of nanoparticles, and mechanical properties were investigated. Furthermore, corotating screws were modified to achieve elongational flow which is efficient for obtaining dispersive mixing. The morphology was examined by SEM analysis after preferential extraction of the minor phase. Subsequently, the SEM micrographs were quantitatively analyzed using image analyzer software. The morphology of the blends indicated that processing with counter-rotation at a given screw speed yielded coarser morphology than that of processed with corotation. X-ray diffraction analysis showed that highest level of exfoliation is observed with increasing PA6 content, at 200 rpm of screw speed and in corotation mode. Also, the effects of screw speed, screw rotation mode, and screw modification were discussed in terms of XRD responses of the nanocomposites. The aspect ratio of the clay particles which were measured by performing image analysis on TEM micrographs exhibited a variation with processing conditions and they are in accordance with the modulus of the nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Elongational Rheology of Polymer/Clay Dispersions: Determination of Orientational Extent in Elongational Flow Processes,

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2008
Eduard A. Stefanescu
Abstract The purpose of the present contribution is to provide an efficient method that would help to quantify the orientational levels occurring in polymer/clay dispersions subjected to elongational flow. The extent of internal orientation developed in salt containing montmorillonite/poly(ethylene oxide) gels is investigated, combining shear and elongational rheology methods. Entropic changes indicate that the strength of the transient network present in each gel affects the orientational ability of clay particles and polymer chains. We found that an increased Hencky strain of the hyperbolic die leads to a higher variation of the calculated entropy of the material. [source]

Morphology and Properties of Polyethylene/Clay Nanocomposite Drawn Fibers

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 1 2008
Francesco Paolo La Mantia
Abstract The influence of an elongational flow on the morphology of PE/clay nanocomposite drawn fibers was studied. An increase of the elastic modulus and the tensile strength as well as a decrease of the elongation at break are observed with increasing draw ratio. The applied elongational gradient orients the polymer chains and the clay particles along the spinning direction. When the applied flow results in the formation and the orientation of exfoliated nanoparticles, a pronounced increase of the mechanical properties is observed. The dispersed clay particles can be broken and oriented by the extensional flow, which might indicate a flow-induced intercalated/exfoliated morphology transition. [source]

Coarse-Grained Simulations of Elongational Viscosities, Superposition Rheology and Shear Banding in Model Core,Shell Systems

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2007
A. van den Noort
Abstract A recently developed coarse-grain model is used to investigate nonlinear rheological properties of model core,shell systems. The influence of several model parameters on the stresses and shear rates is investigated. Continuous planar elongational flow and superposition rheology are studied and compared to simple shear flow results. With particular values of the model parameters, an initially linear velocity profile splits into many bands with different shear rates and different densities, which finally merge into just two bands stacked along the gradient direction. With the box sizes used in our simulations, stick and Lees,Edwards boundary conditions lead to qualitatively similar results, with the stick boundary simulations showing better quantitative agreement with experiments. [source]

Influence of co-monomer structure on properties of co-polyamide packaging films

PACKAGING TECHNOLOGY AND SCIENCE, Issue 1 2002
P. Scarfato
Abstract In this work a series of co-polyamides were prepared by random polymerization of ,-caprolactam in presence of four different co-monomers at a percentage of 5% w/w, with the aim of verifying their suitability as film-forming materials. The effects of structural changes induced in the ,-caprolactam homopolymer by co-monomers were evaluated in both molten and solid states. Rheological tests in shear and elongational flow were performed to evaluate the processability of co-polyamides. Cast films were obtained and their thermal, mechanical and transport properties were evaluated to establish the performances of the co-polyamides in view of packaging applications. The results indicate that co-polyamide films having a partially aromatic structure display the best mechanical performances and show a significant improvement in barrier properties to gases compared to the homopolymer. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Morphology development during blending of immiscible polymers in screw extruders

POLYMER ENGINEERING & SCIENCE, Issue 6 2002
Sandeep Tyagi
The present work reports evolution of morphology from initial (presence of striation) to final (droplet formation) stages in a single-screw extruder. Morphology development during the blending process controls the final size of the dispersed phase, which in turn significantly affects the properties of the blends. The experiments were carried out using a 70/30 wt% polypropylene/ethylene vinyl acetate (PP/EVA) blend; samples were collected along the length of the screw, by screw pullout experiment, to analyze the size and size distribution of the dispersed phase present both as striated layers and subsequently as droplets. Average size of the dispersed phase and standard deviation were taken into account to monitor the morphology evolution along the length of the screw. Pre-breakup morphology development was studied by analyzing the sample collected from the feed zone of the extruder in terms of upper and lower layers along the cross section of screw channel. Examination of micrographs revealed the existence of pattern of ordered striations along the length of the melting zone containing striations from average size of 1000 ,m down to 50 ,m decreasing rapidly along the length of the screw. The breakup process was captured at the start of compression zone where step-up in the shear as well as elongational flow was applied due to decrease in the channel depth along the compression zone. The observed droplet size formed by the breakup of filaments is found to be in accordance with theory. The final droplet size is found to be governed by the emulsification process occurring as a result of stretching, breakup and coalescence in the metering section of the screw and is in the order of 2 ,m. [source]