Comparative study of ziegler-natta and metallocene based polypropylenes in injection molding / Avraam I. Isayev in INTERNATIONAL POLYMER PROCESSING, Vol. XV, N° 1 (03/2000)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XV, N° 1 (03/2000) . - p. 72-82 Titre : Comparative study of ziegler-natta and metallocene based polypropylenes in injection molding : Simulation and experiment Type de document : texte imprimé Auteurs : Avraam I. Isayev, Auteur ; Y. Churdpunt, Auteur ; X. Guo, Auteur Année de publication : 2000 Article en page(s) : p. 72-82 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 668.9 Polymères Résumé : Injection molding of the isotactic polypropylenes polymerized using metallocene and Ziegler-Natta catalysts and having the same molecular weights was performed. Rheological properties and shear-induced crystallization kinetics were measured and their comparative analysis is made. These data are fitted to the equations necessary for simulation of the injection molding process. Numerous injection molding runs were carried out and pressure measurements during molding were performed. The gapwise distribution of crystallinity, spherulite size and thickness of flow-induced crystallized layer in moldings were measured. The effect of various processing conditions on these values was determined. The measured values were compared with the results obtained from the simulation of injection molding process using unified theory of crystallization proposed earlier. Comparative analysis is made between flow conditions and crystallization behavior of these polymers and their effect on the pressure development and structural characteristics of the moldings. Note de contenu : - THEORETICAL CONSIDERATION : The unified crystallization model - Microstructure and competing mechanism - Injection molding process simulation - Numerical simulation - EXPERIMENTAL : Materials - Rheological characterization - Injection molding experiments - Sample preparation - Shear-induced crystallization layer and spherulite size distribution - Crystallinity distribution - RESULTS AND DISCUSSION : Rheological properties - Process simulation and comparison with experiments - pressure traces - Shear-induced crystallization layer - Spherulite size distribution - Crystallinity distribution DOI : 10.3139/217.1571 En ligne : https://drive.google.com/file/d/1Capiy1yrjEbCnidc-HnS3pPsykbDjfOr/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=16076 [article]

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Constitutive modeling of nonlinear rheological behavior of carbon nanotube-filled polypropylene nanocomposites / S. S. Pole in INTERNATIONAL POLYMER PROCESSING, Vol. 36, N° 3 (2021)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. 36, N° 3 (2021) . - p. 233-254 Titre : Constitutive modeling of nonlinear rheological behavior of carbon nanotube-filled polypropylene nanocomposites Type de document : texte imprimé Auteurs : S. S. Pole, Auteur ; Avraam I. Isayev, Auteur ; J. Zhong, Auteur Année de publication : 2021 Article en page(s) : p. 233-254 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Cisaillement (mécanique) Matériaux hybrides Nanotubes de carbone à parois multiples Un nanotube de carbone multifeuillet est constitué de plusieurs feuillets de graphènes enroulés les uns autour des autres. Il existe deux modèles pour décrire la structure des nanotubes multifeuillets : - le modèle poupée russe: les plans de graphène sont arrangés en cylindres concentriques ; - le modèle parchemin: un seul feuillet de graphène est enroulé sur lui-même, comme une feuille de papier. Polypropylène Rhéologie Index. décimale : 668.4 Plastiques, vinyles Résumé : The rheological behavior of multi-walled carbon nanotube (MWCNT)-filled polypropylene (PP) nanocomposites with different filler loadings was experimentally studied and simulated using constitutive modeling. Rheological behavior was characterized in small amplitude oscillatory shear (SAOS) flow, large amplitude oscillatory shear (LAOS) flow, startup of shear flow, steady shear flow, and stress relaxation after the imposition of a step shear strain. Virgin PP and PP with CNT loadings of 1, 3, and 5 wt% were used. The formation of a rheological percolation network was observed at these loadings. The Leonov and Simhambhatla-Leonov models were used to simulate the rheological behavior. In the linear region, the simulations provided good predictions of the experimental data for both the unfilled and filled PP. In the nonlinear region, the simulations also provided good results for the virgin PP and satisfactory results for the PP/1 wt%CNT nanocomposite under most flow conditions. However, for the other two nanocomposites the model showed mixed results. Note de contenu : - SIMULATING RHEOLOGICAL BEHAVIOR USING THE LEONOV AND SIMHAMBHATLA-LENOV CES : Modeling SAOS - Modeling LAOS - Modeling startup and steady shear flow - Modeling stress relaxation after a step strain - MATERIALS AND METHODS : Materials - Composite preparation - Rheological testing - Model parameters - RESULTS AND DISCUSSION : SAOS - LAOS - Startup shear - Steady shear - Cox-Merz rule - Philippoff approach - Stress relaxation after a step strain - Table 1 : Matrix modes for the virgin PP - Table 2 : The parameters f, Zc, and Gp for the PP/CNT nanocomposites for the Leonov model - Table 3 : The parameters f , Zc, Gp, and r for the PP/CNT nanocomposites for the Simhambhatla-Leonov model - Table 4 : Particle modes for the PP/CNT nanocomposites for the Leonov model DOI : https://doi.org/10.1515/ipp-2020-4055 En ligne : https://drive.google.com/file/d/1klfXR0nsF7XyiVbq-SM8CCc7eIFZOJYa/view?usp=shari [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=36367 [article]

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Film casting of polycarbonate/multi-walled carbon nanotubes composites using ultrasound-assisted twin-screw extruder: experiment and simulation / Xiang Gao in INTERNATIONAL POLYMER PROCESSING, Vol. 37, N° 4 (2022)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. 37, N° 4 (2022) . - p. 357-371 Titre : Film casting of polycarbonate/multi-walled carbon nanotubes composites using ultrasound-assisted twin-screw extruder: experiment and simulation Type de document : texte imprimé Auteurs : Xiang Gao, Auteur ; Avraam I. Isayev, Auteur Année de publication : 2022 Article en page(s) : p. 357-371 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Composites à fibres -- Extrusion Composites à fibres de carbone Essais (technologie) Films plastiques Nanotubes de carbone à parois multiples Un nanotube de carbone multifeuillet est constitué de plusieurs feuillets de graphènes enroulés les uns autour des autres. Il existe deux modèles pour décrire la structure des nanotubes multifeuillets : - le modèle poupée russe: les plans de graphène sont arrangés en cylindres concentriques ; - le modèle parchemin: un seul feuillet de graphène est enroulé sur lui-même, comme une feuille de papier. Polycarbonates Viscosité élongationnelle La viscosité élongationnelle est la viscosité apparaissant lorsqu’une contrainte élongationnelle est appliquée au fluide. (Wikipedia) Index. décimale : 668.4 Plastiques, vinyles Résumé : A one-step ultrasonic film casting process to manufacture nanocomposite films was developed, in which polycarbonate (PC) was mixed with multi-walled carbon nanotubes (CNT) and cast into films in one process. Numerical and experimental investigations of necking phenomenon were carried out for film casting of PC/CNT composites. Experimental results revealed that the necking along film line decreased with imposition of ultrasound and increasing CNT content, indicating that incorporation of CNT and imposition of ultrasound restrained the elongational flow behavior of melt, resulting in film of a larger width. Isothermal and nonisothermal numerical simulations of the process were performed. In isothermal simulations, the polymer melt was assumed to be maintained at the die temperature. In nonisothermal simulations, the temperature change along the film line was determined from heat transfer calculations with the WLF temperature-dependent viscosity. The simulated and experimental results on normalized film width, defined as a ratio of cast film width to die width, as a function of the distance from the die at various extension ratios were compared. The comparison indicated that changes in film width and thickness along the stretching direction in the nonisothermal process were in better agreement with experimental results than that in the isothermal process. Both experimental and simulated results showed a decrease of film width with take-up speed. Due to the presence of edge effect, the film width in experiment was lower than the simulated one. With incorporation of CNT, a better agreement between experimental and simulated results was obtained, due to a reduced edge effect in the film. Note de contenu : - EXPERIMENTAL : Materials - Preparation of PC/CNT nanocomposite films - Testing - RESULTS AND DISCUSSION : Processing characteristics - Necking phenomenon during film casting - Mechanical properties - NUMERICAL SIMULATION OF THE FILM CASTING PROCESS : Isothermal simulation - Non-isothermal simulation - Table 1 : Parameters used in film casting simulation - Table 2 : Elongational viscosity of PC/CNT composites DOI : https://doi.org/10.1515/ipp-2021-4200 En ligne : https://drive.google.com/file/d/1l5bi0RCPdWKDKFcbCnAXkY18HhEQ806J/view?usp=shari [...] Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=37912 [article]

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Residual stresses and birefringence in injection molding of semicrystalline polymer / X. Guo in INTERNATIONAL POLYMER PROCESSING, Vol. XIV, N° 4 (12/1999)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XIV, N° 4 (12/1999) . - p. 377-386 Titre : Residual stresses and birefringence in injection molding of semicrystalline polymer : Part I : Theoretical formulation Type de document : texte imprimé Auteurs : X. Guo, Auteur ; Avraam I. Isayev, Auteur Année de publication : 1999 Article en page(s) : p. 377-386 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 668.9 Polymères Résumé : Molding - A composite model for the buildup and the relaxation of residual stresses and birefringence during the injection molding of semicrystalline polymer is proposed. This model takes into account the flow-induced crystallization occurring under non isothermal conditions. The effects of crystallization on the variations of mechanical and physical properties are considered. The viscoelastic constitutive equation due to Giesekus and Leonov is employed for the calculation of the buildup and relaxation of flow stresses, whereas the Morland-Lee constitutive equation of linear viscoelasticity is utilized for the calculation of the buildup and relaxation of thermal stresses during the molding. The overall residual stresses in the molding are determined based upon the addition of residual flow and thermal stresses. The multilayered microstructure in the moldings arising due to the flow-induced crystallization is determined. Flow birefringence is related to flow stresses according to the stress-optical rule. An expression is proposed to evaluate the overall residual birefringence based upon the resultant microstructure pattern and residual flow birefringence in the moldings. As a result, numerical simulations for idealized injection molding process are formulated to calculate the residual stresses and birefringence in molded semicrystalline polymers. Based upon the above theoretical approach, the numerical simulation schemes are formulated, and a computer program is developed. Based upon the simulations, the effects of molding conditions and molecular weights on the overall residual stresses and birefringence are further evaluated. Note de contenu : - UNIFIED CRYSTALLIZATION MODEL - GOVERNING EQUATIONS - CALCULATION OF RESIDUAL STRESSES AND BIREFRINGENCE : Introductory remarks - Residual flow stresses and birefringence - Residual thermal stresses - Overall residual stresses and birefringence - Numerical scheme DOI : 10.3139/217.1563 En ligne : https://drive.google.com/file/d/1GY5vxtBHxYOvRjEsHayJJe1gTQEcUrpy/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=16129 [article]

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Residual stresses and birefringence in injection molding of semicrystalline polymer / X. Guo in INTERNATIONAL POLYMER PROCESSING, Vol. XIV, N° 4 (12/1999)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XIV, N° 4 (12/1999) . - p. 387-398 Titre : Residual stresses and birefringence in injection molding of semicrystalline polymer : Part II : Experiment and simulation Type de document : texte imprimé Auteurs : X. Guo, Auteur ; Avraam I. Isayev, Auteur Année de publication : 1999 Article en page(s) : p. 387-398 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 668.9 Polymères Résumé : The viscoelastic process simulation of the idealized injection molding process for various isotactic polypropylenes having different molecular weights are conducted by using the theoretical formulation developed in the first part of the present study. Molding experiments are performed under a variety of molding conditions, and birefringence measurements are carried out on the molded samples. Based upon the experimental and simulated results of the residual stresses and birefringence, the effects of molding conditions and molecular weights are studied. The influences of flow-induced crystallization kinetics on the buildup and relaxation of residual stresses and birefringence in the moldings are discussed. It has been found that, due to the absence of the flow-induced crystallization in the core region, the flow stresses and birefringence introduced in that region during the filling stage relax shortly after the cavity is filled. Moreover, the flow stresses and birefringence get frozen-in due to the occurrence of the flow-induced crystallization are relatively large and located within a very narrow region close to the mold wall. The main contribution to the overall residual stresses is found to be due by the residual thermal stresses that are introduced by the progression of crystallization during the postfilling stage. The distribution of the residual birefringence in the moldings is closely related to that of the crystalline microstructure pattern and less dependent upon the level of overall residual stresses. Note de contenu : - EVALUATION OF MODEL PARAMETERS - RESULTS AND DISCUSSION : General remarks - Development of flow stresses and birefringence - Analysis of flow and thermal stresses - Overall residual stresses and birefringence DOI : 10.3139/217.1564 En ligne : https://drive.google.com/file/d/1TBZKMXXkUTGQ6LITFjnbzUAcTb_3cd8T/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=16128 [article]

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Simulation and experimental verification of crystallization and birefringence in melt spinning of PET / K. H. Kim in INTERNATIONAL POLYMER PROCESSING, Vol. XXI, N° 1 (03/2006)  

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Ultrasound assisted single screw extrusion process for dispersion of carbon nanofibers in polymers / Avraam I. Isayev in INTERNATIONAL POLYMER PROCESSING, Vol. XXIII, N° 4 (09/2008)  

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