Modification of the PTT Model and its Application for the Predictions of Elongational Viscosity of Polypropylenes-Edición Única
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2004-05-01Autor
Cortés Rodríguez, Leonardo Federico
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Resumen
A comprehensive Theological study of four pairs of isotactic and syndiotactic
polypropylene resins with similar MFI was conducted. The study also includes the
standard quality properties commonly used in the industry. The Theological tests
included double bore capillary rheometry, frequency sweeps and creep and
recovery compliance. The standard quality properties tested were percentage of
Xylene Solubles (XS), Gel Permation Chromatography (GPC), Nuclear Magnetic
Resonance (NMR) and Differential Scanning Calorimetry (DSC). It was found that
the viscoelastic behavior is significantly different between these two types of
resins.
On the other hand, the PTT (Phan Thien and Tanner, 1977) and XPP (Verbeeten,
2001) models were analyzed and evaluated using the experimental data of the
resins under study. It was found that the PTT model fails to predict accurately the
elongational response of the syndiotactic resins.
In addition, a modified PTT model is proposed and evaluated with satisfactory
results. The parameters of this new model were found to be related to molecular
weight distributions features such as Mz and Me.
Additionally, an innovative approach using fractals theory is proposed for the
development of a new fundamental constitutive equation. Further study is
recommended to this topic as well as to the modified PTT model.