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Title On the correlation of rheology and morphology of bimodal polypropylene reactor blends synthesized by homogeneous binary metallocene/metallocene catalysts
Date 21.07.2017
Number 53347
Abstract In this study, morphological and rheological characteristics of bimodal polypropylene (PP) reactor blends, synthesized by binary catalysts based on I: rac-Me2Si(2-Me-4-PhInd)2ZrCl2 and II: (2-PhInd)2ZrCl2 at different molar ratios were investigated. Gel permeation chromatography (GPC), scanning electron microscopy (SEM) and rheometry analysis were performed in order to evaluate the effect of the molar ratio of catalyst II, responsible for formation of the elastomeric stereoblock (sb) PP with low molecular weight (MW), to catalyst I, responsible for production of high MW isotactic (i) PP, on the MW, molecular weight distribution (MWD), morphological characteristics and rheological behavior of the synthesized products. The GPC results indicated that once a hybrid of the two catalysts is used, a broad and bimodal MWD would be obtained, and the molar ratio of the catalysts governs the values of MW and MWD. 13C NMR results suggest that the different PP tacticity resulting from the two catalysts (stereoblock vs. isotactic) is hardly influenced by using a binary system. The effect of MW enhancement and MWD broadening was confirmed via the linear rheological data (G’ at lower frequencies, cross-over modulus and cross-over frequency) due to the impeded molecular motions of chains with high MWs which play an important role in the elasticity of the chains. The zero-shear-rate viscosity and relaxation time, determined by fitting the Carreau-Yasuda model, are in great conformity with the experimental data at low-frequency region. Likewise, the miscibility and increased level of heterogeneity of microstructure, which is a result of changing the molar ratios of catalysts II/I, are confirmed via the Cole-Cole and Han plots, and were further corroborated via the obtained SEM results.
URL http://dx.doi.org/10.1080/03602559.2017.1354220
Publisher Polymer-Plastics Technology and Engineering
Identifier 0
Citation Polymer-Plastics Technology and Engineering ? (2017) ID1354220
DOI http://dx.doi.org/10.1080/03602559.2017.1354220
Authors Vaezi, J. ; Nekoomansh, M. ; Khonakdar, H. A. ; Jafari, S.H. ; Komber, H. ; Mojarrad, A.
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