The impact of flow on semi-crystalline polymer transformation is crucial, influencing crystallization kinetics, final structure, and part properties. In injection molding, a commonly used polymer transformation process, molten polymers undergo intense shear flow fields. These conditions alter crystallization and morphology, leading to morphologies distinct from quiescent crystallization and thus to peculiar material properties in the final product. The highly non-linear nature of flow-induced crystallization poses scientific challenges, and a comprehensive predictive modeling approach is still lacking. Experimental work has focused on understanding morphological development during stress-induced crystallization, varying temperature, velocity, and shear time, along with rheo-optical measurements. This study investigates the effects of shear flow on isotactic polypropylene (iPP) using a Multi-Pass Rheometer (MPR), aiming to understand the relationship between processing conditions and final polymer morphology. The MPR reproduces flow conditions encountered during injection molding and enables the study of shear-induced crystallization kinetics. Experiments at 138 °C with varying shear rate and time are monitored on-line by using birefringence measurements. Optical microscopy images reveal a morphological transition based on shear conditions.

Effect of isothermal shear flow on morphology evolution of an isotactic polypropylene

Speranza Vito
;
De Santis Felice;Pantani Roberto
2024-01-01

Abstract

The impact of flow on semi-crystalline polymer transformation is crucial, influencing crystallization kinetics, final structure, and part properties. In injection molding, a commonly used polymer transformation process, molten polymers undergo intense shear flow fields. These conditions alter crystallization and morphology, leading to morphologies distinct from quiescent crystallization and thus to peculiar material properties in the final product. The highly non-linear nature of flow-induced crystallization poses scientific challenges, and a comprehensive predictive modeling approach is still lacking. Experimental work has focused on understanding morphological development during stress-induced crystallization, varying temperature, velocity, and shear time, along with rheo-optical measurements. This study investigates the effects of shear flow on isotactic polypropylene (iPP) using a Multi-Pass Rheometer (MPR), aiming to understand the relationship between processing conditions and final polymer morphology. The MPR reproduces flow conditions encountered during injection molding and enables the study of shear-induced crystallization kinetics. Experiments at 138 °C with varying shear rate and time are monitored on-line by using birefringence measurements. Optical microscopy images reveal a morphological transition based on shear conditions.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11386/4859897
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