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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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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