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Review
. 2021 Oct 14;13(20):3529.
doi: 10.3390/polym13203529.

Effect of the Elongational Flow on the Morphology and Properties of Polymer Systems: A Brief Review

Rossella Arrigo  1   2 , Giulio Malucelli  1   2 , Francesco Paolo La Mantia  2   3
Affiliations
Review

Effect of the Elongational Flow on the Morphology and Properties of Polymer Systems: A Brief Review

Rossella Arrigo et al. Polymers (Basel). .

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.

Keywords: elongational flow; elongational viscosity; fiber spinning; film blowing; morphology evolution; multiphase polymer systems; strain hardening.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic representation of melt-spinning (A) and film-blowing (B) processing.
Figure 2
Figure 2
Isothermal shear and elongational viscosity as a function of time for an LDPE sample. Reprinted from Reference [41] under CC BY license.
Figure 3
Figure 3
Tensile stress as a function of the Hencky strain at two elongational rates for an LDPE sample at 150 °C. Reprinted from Reference [41] under CC BY license.
Figure 4
Figure 4
Rheotens curves for an LDPE sample obtained at different temperatures, and Rheotens-mastercurve. Adapted with permission from Reference [66]. Copyright (1996) WILEY-VCH Verlag GmbH & Co. KGaA.
Figure 5
Figure 5
Melt strength (A) and breaking stretching ratio (B) as a function of shear rate for linear low-density polyethylene samples with different molecular weights. Reprinted with permission from Reference [67]. Copyright (1985) The Society of Rheology.
Figure 6
Figure 6
Temporal evolution of the elongational viscosities for (A) LDPE and (B) LLDPE samples at 150 °C and different elongational rates. Reprinted from Reference [41] under CC BY license.
Figure 7
Figure 7
MS values as a function of the shear rate for HDPE, LDPE and LLDPE samples with different molecular weights. Reprinted with permission from Reference [88]. Copyright (1985) WILEY-VCH Verlag GmbH & Co. KGaA.
Figure 8
Figure 8
BSR values as a function of the shear rate for HDPE, LDPE and LLDPE samples with different molecular weights. Reprinted with permission from Reference [88]. Copyright (1985) WILEY-VCH Verlag GmbH & Co. KGaA.
Figure 9
Figure 9
(A) Tensile modulus as a function of DR for melt-spun PP fibers, (B) stress at break as function of strain at break of selected PP fibers at different DR. Adapted from Reference [109] under CC BY 4.0 license.
Figure 10
Figure 10
Stress-strain curves for as-spun spun and hot-drawn PP. Reprinted with permission from Reference [114]. Copyright (1978) WILEY-VCH Verlag GmbH & Co. KGaA.
Figure 11
Figure 11
Schematic representation of the crystalline morphology evolution in PP blown films with the increase of DR. Reprinted with permission from Reference [121]. Copyright (2010) WILEY-VCH Verlag GmbH & Co. KGaA.
Figure 12
Figure 12
(A) Tensile modulus, (B) strength and (C) elongation at break of PLA fibers drawn at various temperatures. Reprinted with permission from Reference [126]. Copyright (2006) Elsevier.
Figure 13
Figure 13
Elongation at break as a function of birefringence for a polystyrene filament. Data taken from Reference [103].
Figure 14
Figure 14
Critical capillary number as a function of the viscosity ratio in polymer blends according to the Grace’s analysis. Reprinted from Reference [143] under CC BY 4.0 license.
Figure 15
Figure 15
Schematic representation of the possible mechanism of the droplet-to-fibril transition in immiscible blends subjected to elongational flow: (A) Deformation of the original particles of the dispersed phase and (B) formation of microfibrillar structures.
Figure 16
Figure 16
Mechanisms of fibrillation process along the spin line for a PLA filament. Reprinted with permission from Reference [167]. Copyright (2014) Elsevier.
Figure 17
Figure 17
(A) Tensile modulus, (B) strength and (C) elongation at break as a function of the stretching ratio for a PET/PE blend. Reprinted with permission from Reference [172]. Copyright (2003) WILEY-VCH Verlag GmbH & Co. KGaA.
Figure 18
Figure 18
(A) Stress–strain curves of isotropic and anisotropic LDPE/PA6 samples and (B) sketch of the stress–strain test of the anisotropic film in MD. Reprinted with permission from Reference [34]. Copyright (2014) Elsevier.
Figure 19
Figure 19
CNT orientation factor as a function of DR for PET-based composites. Reprinted with permission from Reference [204]. Copyright 2013 American Chemical Society.
Figure 20
Figure 20
Proposed mechanisms (i.e., (A) tearing and (B) sliding) of elongational-flow-induced deformation of the tactoids in polymer/clay nanocomposites. Adapted with permission from Reference [218]. Copyright (2008) WILEY-VCH Verlag GmbH & Co. KGaA.
Figure 21
Figure 21
Schematic representation of debonding mechanism of exfoliated OMMT/PVDF nanocomposites in elongational flow field. Reprinted with permission from Reference [226]. Copyright (2021) WILEY-VCH Verlag GmbH & Co. KGaA.
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