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Effect of sparse long-chain branching on the film-casting behavior for a series of well-defined HDPEs / C. D. McGrady in INTERNATIONAL POLYMER PROCESSING, Vol. XXIV, N° 5 (11/2009)
[article]
Titre : Effect of sparse long-chain branching on the film-casting behavior for a series of well-defined HDPEs Type de document : texte imprimé Auteurs : C. D. McGrady, Auteur ; C. W. Seay, Auteur ; D. G. Baird, Auteur Année de publication : 2009 Article en page(s) : p. 428-438 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 668.9 Polymères Résumé : The effect of sparse long chain branching, LCB, on the film-casting process is analyzed using a molecular model for the rheological behavior for a series of well-characterized, high-density polyethylene (HDPE) resins and a low-density polyethylene (LDPE) resin at various drawdown ratios. A full rheological characterization in both shear and shear-free flows is also presented. At low drawdown ratios, the LDPE exhibited the least degree of necking at distances less than the HDPE frostline. The sparsely-branched HDPE resins films had similar final film-widths that were larger than those of the linear HDPE. As the drawdown ratio was increased, film width profiles separated based on branching level. Small amounts of LCB were found to reduce the amount of necking at intermediate drawdown ratios. At higher drawdown ratios, the sparsely-branched HDPE resins of lower LCB content had film-widths that mimicked that of the linear HDPE, while the sparsely-branched HDPE resins of higher LCB content retained a larger film width. Molecular structural analysis via the Pom-Pom constitutive model suggested that branching that was distributed across a larger range of backbone lengths served to improve resistance to necking. As the drawdown ratio increased, the length of the backbones dominating the response decreased, so that the linear chains were controlling the necking behavior of the sparsely-branched resins of lower LCB content while remaining in the branched regime for higher LCB content HDPEs. Other processing variables such as shear viscosity magnitude, extrudate swell, and non-isothermal processing conditions were eliminated as contributing factors to the differences in the film width profile. DOI : 10.3139/217.2291 En ligne : https://drive.google.com/file/d/1Pb5a1KuePCmq0916W3J6UgkiB-hrU5Eu/view?usp=drive [...] Format de la ressource électronique : Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=6366
in INTERNATIONAL POLYMER PROCESSING > Vol. XXIV, N° 5 (11/2009) . - p. 428-438[article]Réservation
Réserver ce documentSparse long-chain branching's effect on the film-casting behavior of PE / C. W. Seay in INTERNATIONAL POLYMER PROCESSING, Vol. XXIV, N° 1 (03/2009)
[article]
Titre : Sparse long-chain branching's effect on the film-casting behavior of PE Type de document : texte imprimé Auteurs : C. W. Seay, Auteur ; D. G. Baird, Auteur Année de publication : 2009 Article en page(s) : p. 41-49 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Polyéthylène
Polyéthylène basse densité
RhéologieIndex. décimale : 668.9 Polymères Résumé : The degree of film-width reduction or necking during film-casting is analyzed for three metallocene-catalyzed linear low density polyethylenes, LLDPE, with varying degrees of sparse long-chain branching, LCB. The resins included three sparsely LCB polyethylene, PE, materials with varying LCB content ranging from linear to 0.57 LCB/10000 CH2 along with a Ziegler-Natta polymerized LLDPE and a tubular free-radical polymerized low density polyethylene, LDPE. The last two resins are used as reference materials. The primary objective of this analysis is to evaluate whether uniaxial extensional rheological characteristics, in particular strain-hardening, that are a result of LCB influence the film-necking properties. At the lowest drawdown ratio, necking is observed to be reduced with increasing LCB, and thus strain-hardening characteristics. At the higher drawdown ratios it is observed that LCB no longer reduces necking and the curves merge to the results found for linear PE, except in the case of LDPE, which shows reduced necking at all drawdown ratios. Furthermore, comparisons of film necking are also made to separate the effects of molecular weight distribution, MWD, and LCB. The results indicate that both broadening the MWD and the addition of sparse LCB reduce the degree of necking, but to a lesser degree in the case of broadening the MWD. Analysis of the uniaxial extensional and dynamic shear rheology with the pom-pom constitutive model reveals that a distribution of branches along shorter relaxation time modes is important in reducing necking at higher drawdown ratios. Factors such as shear viscosity effects, extrudate swell, and non-isothermal behavior were eliminated as contributing factors. DOI : 10.3139/217.2184 En ligne : https://drive.google.com/file/d/128DiYLbM-4iB7WfOUniXlU19J7Yy-cA9/view?usp=drive [...] Format de la ressource électronique : Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=4206
in INTERNATIONAL POLYMER PROCESSING > Vol. XXIV, N° 1 (03/2009) . - p. 41-49[article]Réservation
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