Isotactic polypropylene (iPP) is one of the commodities used in the largest quantity today. Its good mechanical properties and relatively low price result in continuous growth of pro-duction and expansion of its market. The continuously increasing application accelerates research on all related fields, including the preparation of iPP-based composites and blends. The preparation of polymer blends is an important technique in order to modify the target property of an individual polymer according to the requirement of the application field. Since the features of semi-crystalline polymers depend on the crystallinity degree and crystallite morphology, studies about the effects of fillers on the crystallization behavior of composites are of great interest. Nucleated crystallization has been the subject of several studies over the last 50 years or so [Cormia et al. 1962, Binsbergen 1970, Mercier 1990]. In the relative simple case of isothermal crystallization, the presence of a nucleating agent (NA) shortens the induction time as well as enhances the overall rate of transformation from the molten state to the crystalline solid state. A shortening of the induction time due to a NA is obviously understandable since the polymer melt does not have to form its own seeds to initiate crystallization (self-nucleation being a time-dependent phenomenon as it results from the statistical fluctuations in the local order). In the processing of polypropylene, a nucleating agent is usually used for reducing the size of the iPP spherulites, improving the optical clarity, decreasing the cycle time of the process and enhancing the mechanical properties. Therefore, the main goal of this work is the investigation of the effects of different mi-cro- and nano- fillers on the isotactic polypropylene crystallization behavior, both in quies-cent and in flow-induced conditions. To this aim, two types of isotactic polypropylene were mixed with maleic anhydride grafted polypropylene (PP-MA) as compatibilizer and various micro- (talc, carbon fibres) and nano- (montmorillonites, carbon nanofibres and carbon nanotubes) fillers were added. In order to keep the same matrix, the micro- and nano- composites were prepared by in-creasing the filler loading at a fixed iPP/PP-MA ratio (13.2). Structural characterization was carried out by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses and the materials behavior in the molten state was studied by means of rheological measurements in small-amplitude oscillatory shear (SAOS) with a rotational rheometer (plate-plate configuration). Differential Scanning Calorimetry (DSC) was employed to investigate the crystallization in quiescent conditions of the prepared micro- and nano- composites. Both the quiescent and flow-induced crystallization were evaluated using SAOS techniques (dynamic time sweep tests).

Polymer Crystallization: Micro- and Nano- Filler Effects on Isotactic Polypropylene / Gioffredi, Emilia. - STAMPA. - (2012).

Polymer Crystallization: Micro- and Nano- Filler Effects on Isotactic Polypropylene

GIOFFREDI, EMILIA
2012

Abstract

Isotactic polypropylene (iPP) is one of the commodities used in the largest quantity today. Its good mechanical properties and relatively low price result in continuous growth of pro-duction and expansion of its market. The continuously increasing application accelerates research on all related fields, including the preparation of iPP-based composites and blends. The preparation of polymer blends is an important technique in order to modify the target property of an individual polymer according to the requirement of the application field. Since the features of semi-crystalline polymers depend on the crystallinity degree and crystallite morphology, studies about the effects of fillers on the crystallization behavior of composites are of great interest. Nucleated crystallization has been the subject of several studies over the last 50 years or so [Cormia et al. 1962, Binsbergen 1970, Mercier 1990]. In the relative simple case of isothermal crystallization, the presence of a nucleating agent (NA) shortens the induction time as well as enhances the overall rate of transformation from the molten state to the crystalline solid state. A shortening of the induction time due to a NA is obviously understandable since the polymer melt does not have to form its own seeds to initiate crystallization (self-nucleation being a time-dependent phenomenon as it results from the statistical fluctuations in the local order). In the processing of polypropylene, a nucleating agent is usually used for reducing the size of the iPP spherulites, improving the optical clarity, decreasing the cycle time of the process and enhancing the mechanical properties. Therefore, the main goal of this work is the investigation of the effects of different mi-cro- and nano- fillers on the isotactic polypropylene crystallization behavior, both in quies-cent and in flow-induced conditions. To this aim, two types of isotactic polypropylene were mixed with maleic anhydride grafted polypropylene (PP-MA) as compatibilizer and various micro- (talc, carbon fibres) and nano- (montmorillonites, carbon nanofibres and carbon nanotubes) fillers were added. In order to keep the same matrix, the micro- and nano- composites were prepared by in-creasing the filler loading at a fixed iPP/PP-MA ratio (13.2). Structural characterization was carried out by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses and the materials behavior in the molten state was studied by means of rheological measurements in small-amplitude oscillatory shear (SAOS) with a rotational rheometer (plate-plate configuration). Differential Scanning Calorimetry (DSC) was employed to investigate the crystallization in quiescent conditions of the prepared micro- and nano- composites. Both the quiescent and flow-induced crystallization were evaluated using SAOS techniques (dynamic time sweep tests).
2012
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11583/2500104
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