Extension‐dominated improved dispersive mixing in single‐screw extrusion. Part 2: Comparative analysis with twin‐screw extruder

Abstract

In Part 1 of this work, the possibility of improving single-screw extruders (SSE) better dispersive mixer was explored by harnessing extensional flows provided by the hyperbolic contracting-diverging channels of extensional mixing elements (EME). Addition of the EME to the pin screw generated enhanced breakup for polymer blends and nanocomposite systems without significant penalty in flow rate. In Part 2, experiments are performed on immiscible polymer blends (low-viscosity ratio and high-viscosity ratio) and nanocomposites on both SSE and twin-screw extruder (TSE) with the same rotation speed and throughput. Morphological results show tremendous improvement in dispersive mixing capability of SSE when equipped with EME that are mainly comparable to conventional TSE that is, with kneading blocks as mixing sections, although not as good as TSEs equipped with EMEs. Mechanical results also show enhanced modulus when EME is used in SSE operations.

Recent Advances in Elongational Flow Dominated Polymer Processing Technologies

“…In the plasticizing and conveying process, the volume of materials undergoes repeated (or periodic) change owing to the synchronized movement of the moving plate and the sliding plate, endowing a dominant elongational flow. Although the specific structure of the devices differs, researchers have successfully incorporated the elongational flow elements by setting single or multiple convergence-divergence channels in the systems [ 6 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ].…”

“…Shear flows have been proven to be less energy-efficient towards both dispersive and distributive mixing when compared to elongational flows [ 6 , 7 , 8 , 9 ]. Much effort has been devoted to developing plasticizing and conveying devices that impart elongation-dominated flows, such as the introduction of extensional mixing elements (EME) into the conventional single-screw [ 10 , 11 ] and twin-screw extruders [ 12 , 13 ]. The novel non-screw devices known as vane extruders (VE) are comprised of several vane plasticizing and conveying units [ 14 ], and the later-developed eccentric rotor extruders (ERE) are dominated by a continuous elongational flow field [ 15 , 16 ].…”

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

“…Fiber spinning, film blowing, blow molding and foaming, among a few others, are typical examples of processing techniques, in which the polymer melt is subjected to elongational flow [4][5][6]. Actually, elongational deformation also occurs in some processes essentially dominated by shear flow, such as extrusion and injection molding [7]; the variation of the flow channels and the entrance in the die section in extrusion, or the injection of the melt into the mold gate, represent some examples in which the melt is subjected to components of elongation flow [8]. Moreover, during the past few decades, plasticizing conveying methods and related devices (such as vane, eccentric rotors extruders and extensional flow mixers) based on elongational flow were continuously developed, demonstrating shorter processing times and higher mixing effectiveness as compared to conventional shear-flow-dominated techniques [9][10][11][12][13].…”

Comparative computational analysis of dispersive mixing in extension‐dominated mixers for single‐screw extruders

“…The EME concept, both uniaxial (S‐EME) and biaxial (D‐EME), was recently extended to SSE and were validated computationally and experimentally. [ 22,23 ] The addition of the EME to the SSE greatly enhanced the dispersive mixing in all the tested polymer blends and composite systems with only a relatively small penalty in the flow rate. Morphological results showed tremendous improvement in dispersive mixing capability of SSE when equipped with EME, comparable to conventional TSE with KBs as mixing sections.…”

“…Morphological results showed tremendous improvement in dispersive mixing capability of SSE when equipped with EME, comparable to conventional TSE with KBs as mixing sections. [ 23 ] Since the EME and the CRD generate extensional flows in different ways, it is important to compare them for their dispersive mixing capabilities. This can be best done via three‐dimensional computational fluid dynamics (CFD) modeling.…”