Entry flow of polyethylene melts in tapered dies / M. Ansari in INTERNATIONAL POLYMER PROCESSING, Vol. XXV, N° 4 (09/2010)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XXV, N° 4 (09/2010) . - p. 287-296 Titre : Entry flow of polyethylene melts in tapered dies Type de document : texte imprimé Auteurs : M. Ansari, Auteur ; A. Alabbas, Auteur ; Savvas G. Hatzikiriakos, Auteur ; Evan Mitsoulis, Auteur Année de publication : 2010 Article en page(s) : p. 287-296 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Ecoulement visqueux Polyéthylène Rhéologie Simulation par ordinateur Viscoélasticité Tags : 'Polyéthylènes  fondus'  'Ecoulements  capillaires'  'Pertes  de  surpression'  'Simulations  numériques'  Visco-élasticité  'Modèle  K-BKZ Index. décimale : 668.9 Polymères Résumé : The excess pressure losses due to end effects (mainly entrance) in the capillary flow of several types of polyethylenes were studied both experimentally and numerically under slip and no-slip conditions. These losses were first measured as a function of the contraction angle ranging from 15° to 90°. It was found that the excess pressure loss attains a local minimum at a contraction angle of about 30° for all types of polyethylenes examined. This was found to be independent of the apparent shear rate. This minimum becomes more dominant under slip conditions that were imposed by adding a significant amount of fluoropolymer into the polymer. Numerical simulations using a multimode K-BKZ viscoelastic model have shown that the entrance pressure drops can be predicted fairly well for all cases either under slip or no-slip boundary conditions. The clear experimental minimum at about 30° can only slightly be seen in numerical simulations, and at this point its origin is unknown. Further simulations with a viscous (Cross) model have shown that they severely under-predict the entrance pressure by an order of magnitude for the more elastic melts. Thus, the viscoelastic spectrum together with the extensional viscosity play a significant role in predicting the pressure drop in contraction flows, as no viscous model could. The larger the average relaxation time and the extensional viscosity are, the higher the differences in the predictions between the K-KBZ and Cross models are. DOI : 10.3139/217.2360 En ligne : https://drive.google.com/file/d/13601Vu2Ol_Pr3EBCZjiZpO5y03Wizp_a/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=9825 [article]

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Extrudate swell of high density polyethylenes in slit (flat) dies / V. K. Konaganti in INTERNATIONAL POLYMER PROCESSING, Vol. XXXI, N° 2 (05/2016)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XXXI, N° 2 (05/2016) . - p. 262-272 Titre : Extrudate swell of high density polyethylenes in slit (flat) dies Type de document : texte imprimé Auteurs : V. K. Konaganti, Auteur ; E. Behzadfar, Auteur ; M. Ansari, Auteur ; Evan Mitsoulis, Auteur ; Savvas G. Hatzikiriakos, Auteur Année de publication : 2016 Article en page(s) : p. 262-272 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Caractérisation Matières plastiques -- Extrusion Mesure Modèles mathématiques Polyéthylène haute densité Rhéologie Index. décimale : 668.4 Plastiques, vinyles Résumé : Extrudate swell of industrial-grade high-molecular mass high-density polyethylenes (HDPEs) in flat/slit dies is studied using both experiments and simulations. The experimental set-up consists of an optical micrometer to measure the extrudate dimensions and a pair of radiation heaters to control the extrudate temperature outside the die attached to the capillary rheometer. The simulation of extrudate swell phenomenon is carried out by using a well-known integral K-BKZ model. The effects of several rheological characteristics, die characteristics, and processing conditions on swell measurements are studied systematically, and the corresponding two-dimensional, steady-state numerical predictions are presented in this paper. This study includes the effects of polymer molecular characteristics, apparent shear rate, die geometrical characteristics (length to die gap (L/H) and width to die gap (W/H)), and distance from the die exit. It is found that the integral K-BKZ model predicts well both the width and thickness extrudate swells. Extrudate swell measurements demonstrate that the thickness swell is predominant in comparison with width swell. Note de contenu : - EXPERIMENTAL : Materials and rheological methods - Extrudate swell measurements - MATHEMATICAL MODELING : Governing equations - Constitutive equations - Boundary conditions - Method of solution - RESULTS AND DISCUSSION : Rheological characterization - Extrudate swell measurements DOI : 10.3139/217.3215 En ligne : https://drive.google.com/file/d/1PwNvpZbFckA66bu9PWrEohRbc7-6GBU4/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=26185 [article]

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Paste extrusion and mechanical properties of PTFE / M. Ansari in INTERNATIONAL POLYMER PROCESSING, Vol. XXX, N° 5 (11/2015)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XXX, N° 5 (11/2015) . - p. 603-614 Titre : Paste extrusion and mechanical properties of PTFE Type de document : texte imprimé Auteurs : M. Ansari, Auteur ; D. Vavlekas, Auteur ; J. L. McCoy, Auteur ; Savvas G. Hatzikiriakos, Auteur Année de publication : 2015 Article en page(s) : p. 603-614 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Densitométrie Essais dynamiques Extrusion capillaire Matières plastiques -- Extrusion Matières plastiques -- Propriétés mécaniques Polytétrafluoréthylène Traction (mécanique) Index. décimale : 668.9 Polymères Résumé : The paste extrusion process of two types of PTFE has been studied in capillary extrusion using dies having different reduction ratio (RR) and die entrance angles. The extrusion pressure shows a weak increase with shear rate over a wide range of flow rates and a more significant increase with reduction ratio. Moreover, the extrusion pressure exhibits a minimum for entrance angle at around 30°. A simple analytical model based on the radial flow hypothesis (previously developed) has been found to represent the extrusion pressure adequately as a function of flow rate (shear rate) and geometrical characteristics of the capillary dies. The extrudates collected at different processing conditions were dried and tested in uniaxial extension to assess their effect on mechanical properties. The tensile modulus, yield stress and ultimate tensile strength of the obtained extrudates were found to be increasing functions of reduction ratio, although the opposite effect was found for the ultimate elongational strain. These mechanical properties are also found to be insensitive to changes in the die entrance angle although the ultimate tensile strength has shown a maximum at the entrance angle of about 60°. The PTFE paste extrudates show a Poisson's ratio equal to zero in tensile experiments, thus exhibiting expansion (significant density reduction with stretching). Finally, a simple model was derived for the density change in tensile deformation by taking into the account the Poisson's ratio and the strain recovery (recovery of the elastic energy stored upon removal of the tensile stress). Note de contenu : - Extrusion process - Tensile mechanical properties - Densitometry DOI : 10.3139/217.3130 En ligne : https://drive.google.com/file/d/1uV9BM-co2L0iZ2GiLi0Nmp1wRHQjw2-1/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=24823 [article]

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