Crystallization in polymer melts : metamorphism of flow induced nuclei / Hermann Janeschitz-Kriegl in INTERNATIONAL POLYMER PROCESSING, Vol. XXVI, N° 4 (09/2011)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XXVI, N° 4 (09/2011) . - p. 460-463 Titre : Crystallization in polymer melts : metamorphism of flow induced nuclei Type de document : texte imprimé Auteurs : Hermann Janeschitz-Kriegl, Auteur ; E. Ratajski, Auteur Année de publication : 2011 Article en page(s) : p. 460-463 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Cristallisation Ecoulement cisaillé Etat fondu (matériaux) Nucléation Polarisation (lumière) Polypropylène vision des couleurs Index. décimale : 668.9 Polymères Résumé : As is well-known, characteristic complementary colors are obtained, if a λ-plate is introduced in white polarized light. This fact is used for an unexpected characterization of nucleation occurring during short term shearing of supercooled melts of iPP. Blue specks show up some time after cessation of flow on a red background. The blue color indicates that these tiny nuclei are oriented in the direction of previous flow. With prolonged waiting these specks extend over a large volume. At their centers spherulites start growing. DOI : 10.3139/217.2515 En ligne : https://drive.google.com/file/d/117GPNomCIqiTJe-6kqJAapV4x8LcinsE/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=12451 [article]

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A process classification number for the solidification of crystallizing materials / Hermann Janeschitz-Kriegl in INTERNATIONAL POLYMER PROCESSING, Vol. XXI, N° 5 (11/2006)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XXI, N° 5 (11/2006) . - p. 521-526 Titre : A process classification number for the solidification of crystallizing materials Type de document : texte imprimé Auteurs : Hermann Janeschitz-Kriegl, Auteur ; E. Ratajski, Auteur ; G. Eder, Auteur Année de publication : 2006 Article en page(s) : p. 521-526 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 668.9 Polymères Résumé : A critical number, which one may call a process classification number, has been introduced more than twenty years ago [1 to 3]. It has been called the Janeschitz-Kriegl number Jk [4]. It gives the ratio of two times governing the solidification process of a crystallizing material: one for the thermal equilibration and the other for the crystallization process itself. With one class of materials (mainly metals) the thermal equilibration time is usually the longest time, dependent of course on the sample thickness. With another class (glass forming minerals) always the crystallization time is the longest time. So, one obtains (as extreme cases) purely heat diffusion controlled and purely crystallization kinetics controlled processes. Only polymers (and probably also other crystallizing soft condensed matters) show an intermediate behavior, as can be characterized by the announced number. So far, however, this number could not be made operational because of a lack of crystallization kinetics data. This shortcoming could now be cleared away. It turns out that between the values of Jk for HDPE and for i-PS a gap exists of more than six decades. In their behavior all other known industrial polymers lie between these limiting cases. In this way the transition from heat diffusion controlled to crystallization kinetics controlled processes is clearly marked. For the now relevant interaction between cooling and crystallization a new mathematics was required [2]. It enables also the description of the development of structures, which are of particular interest for the quality of the product. DOI : https://doi.org/10.3139/217.0045 En ligne : https://drive.google.com/file/d/1ghx5GPHCbpApRAoM92rl-79PQf7dONWW/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=2807 [article]

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Unlimited shear as a source of information in polymer melt processing / Hermann Janeschitz-Kriegl in INTERNATIONAL POLYMER PROCESSING, Vol. XXIX, N° 3 (07/2014)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XXIX, N° 3 (07/2014) . - p. 402-411 Titre : Unlimited shear as a source of information in polymer melt processing Type de document : texte imprimé Auteurs : Hermann Janeschitz-Kriegl, Auteur ; E. Ratajski, Auteur ; G. Eder, Auteur Année de publication : 2014 Article en page(s) : p. 402-411 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Cisaillement (mécanique) Cristallisation Etat fondu (matériaux) Polypropylène Rhéologie Index. décimale : 668.4 Plastiques, vinyles Résumé : It is shown that at unprecedented (high) temperatures an extremely slow long lasting shear treatment, which requires almost an hour for its unwinding, can produce a highly oriented structure in the melt of a crystallizing polypropylene. It seems that a convection process, which is characteristic for shear flow, furthers intimate contacts between parts of passing by macromolecular coils. In this respect an inspection of the broad spectrum of crystallization speeds of quiescent melts of a variety of polymers is instructive. The conception, which is defended in the present paper, is that thread-like nuclei are the result of the straightening of assemblages of already loosely connected macromolecules. At the high temperature applied the melt must immediately be quenched after the cessation of the flow in order to preserve the obtained thread-like nuclei. Apparently, only the number of successful encounters is relevant and not the frequency of their occurrence. For a lower frequency more time is required. It is evident that even mild touches can cause permanent adhesions, if the mutual local conformations just fit. One is reminded of the click of a slot. A new apparatus for unlimited shearing is described. This apparatus uses polymer samples, which are ring-shaped, being cut from molded plates of reasonable thickness. These rings possess an unusually large radius of 18 cm, in order to keep the curvature of the flow lines low. Rectilinear unlimited shearing is approached in this way. DOI : 10.3139/217.2859 En ligne : https://drive.google.com/file/d/1FR2U0wHV4XOI3TcKCwUiGrl5XeTVFrkc/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=21738 [article]

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