Abstract
Polymer-processing operations with dominating elongational flow have a great relevance, especially in several relevant industrial applications. Film blowing, fiber spinning and foaming are some examples in which the polymer melt is subjected to elongational flow during processing. To gain a thorough knowledge of the material-processing behavior, the evaluation of the rheological properties of the polymers experiencing this kind of flow is fundamental. This paper reviews the main achievements regarding the processing-structure-properties relationships of polymer-based materials processed through different operations with dominating elongational flow. In particular, after a brief discussion on the theoretical features associated with the elongational flow and the differences with other flow regimes, the attention is focused on the rheological properties in elongation of the most industrially relevant polymers. Finally, the evolution of the morphology of homogeneous polymers, as well as of multiphase polymer-based systems, such as blends and micro- and nano-composites, subjected to the elongational flow is discussed, highlighting the potential and the unique characteristics of the processing operations based on elongation flow, as compared to their shear-dominated counterparts.
Highlights
A large number of processing operations for polymeric materials having high industrial relevance are dominated by elongational flow, i.e., a stretching deformation that, depending on the specific process, can be uniaxial or biaxial [1,2,3]
Fiber spinning and foaming are some examples in which the polymer melt is subjected to elongational flow during processing
Elongational flow is a particular kind of flow involved in many industrially relevant processing operations of thermoplastics, such as fiber spinning, film blowing, foaming and thermoforming
Summary
A large number of processing operations for polymeric materials having high industrial relevance are dominated by elongational flow, i.e., a stretching deformation that, depending on the specific process, can be uniaxial or biaxial [1,2,3]. In some cases, a kind of “compatibilizing effect” has been reported, since the results obtained for blends processed through the application of the elongational flow were very similar to those obtained with the traditional methods employed for improving the compatibility between the polymer components [34,35] It has been documented the effectiveness of the extensional flow in ameliorating the state of dispersion of micro- and nano-fillers in polymer-based composites. The effect of the elongational flow in modifying the microstructure and the morphology of homogeneous and multiphase polymer systems are elucidated, highlighting the processing–structure–properties relationships of polymeric-based materials processed through different operations with dominating elongational flow
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