Modification of the PTT Model and its Application for the Predictions of Elongational Viscosity of Polypropylenes-Edición Única

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.