Microlayer and nanolayer tubing and piping via layer multiplication coextrusion. II. Rheologically mismatched systems

Abstract

An advanced technology, presented in Part 1, was utilized with a custom annular die to produce structures having 9–129 layers. Two material systems were chosen to produce layer structures of viscosity and elasticity stratified type both with/without the application of a rotating boundary wall within the annular land. A maximum rotation window for nine‐layer structures was determined to maintain the layer structure while minimizing the appearance of the weld lines and achieving concentric layers. ANSYS Polyflow was utilized in conjunction to study trilayered systems of generic material properties in stratified forms, along with replication of the experimental systems. Combination of experimental and simulation approaches herein are allowing for the achievement of high layer number, low layer thickness, systems in annular form for the first time. The continued development of this technology can lead to application areas of tubes/pipes with advanced properties such as optical filtering, pressure resistance, and permeation reduction. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48684.

Producing Microlayer Pipes and Tubes through Multiplication Coextrusion and Unique Annular Die: Simulation and Experiment

“…23 However, scarcely are these new products outside of MPS (multilayer sheet or film) geometries, even though the multilayered annular structures (MAS) with thousands of layer numbers are also highly desired, due to that they theoretically show outstanding performance. 8,24,25 One possible solution to produce the MAS with large layer numbers is shaping the MPS into MAS via an elaborately designed annular die. Dow Chemical Co. designed a crosshead annular die in 2016, which can transform MPS into MAS with layer numbers up to 32 when a polymeric sheath is incorporated.…”

“…With use of such die, the MAS with concentric layers up to 129 has been successfully achieved. 8,24,25 Undoubtedly, transforming the MPS into MAS via a custommade annular die provides a possible solution to produce MAS with layers from tens to hundreds, even to thousands. However, this solution is severely hindered by two aspects: one is nonuniformity on both the individual layer thickness and the total thickness of the MAS caused by the unstable flow behaviors in coextrusion, such as the interfacial instability, viscous encapsulation, and elastic layer arrangement; 29−31 while the other is a "weld line" that forms at the region where the separated multilayered melt stacks join into a full annulus, which causes the discontinuity of the layer structure and thus the potential mechanical defects.…”

“…Because the total thickness of the MPS is constant, increasing the layer numbers from tens to thousands will decrease the thickness of the individual layers from micrometers to nanometers, some even to the radius of gyration of polymer chains (about 10 nm) in the case that such an ultrathin layer does not break up spontaneously. − With controllable layer thickness and layer interface, such a multilayered structure has been extensively used to develop new products with superior performances, such as the robust and barrier films for packing, , iridescent films for decoration, optical filters for electronic devices, shape-memory materials for actuators, , dielectric films for capacitors, shielding materials for neutron radiation, , among others . However, scarcely are these new products outside of MPS (multilayer sheet or film) geometries, even though the multilayered annular structures (MAS) with thousands of layer numbers are also highly desired, due to that they theoretically show outstanding performance. ,, …”

“…In 2019, an elaborate annular die was also designed by Maia et al; this unique annular die only includes two channels with each cross-section transformed from a rectangle into a half annuli channel, and then these two half annuli channels combine and contract into a full annulus. With use of such die, the MAS with concentric layers up to 129 has been successfully achieved. ,, …”

“…Undoubtedly, transforming the MPS into MAS via a custom-made annular die provides a possible solution to produce MAS with layers from tens to hundreds, even to thousands. However, this solution is severely hindered by two aspects: one is nonuniformity on both the individual layer thickness and the total thickness of the MAS caused by the unstable flow behaviors in coextrusion, such as the interfacial instability, viscous encapsulation, and elastic layer arrangement; − while the other is a “weld line” that forms at the region where the separated multilayered melt stacks join into a full annulus, which causes the discontinuity of the layer structure and thus the potential mechanical defects. ,, Until now, strategies such as overlapping in jointing regions , and applying angular deformation by rotation die ,, have been proposed to eliminate the negative effects of the weld line. As for the nonuniformity of the layer thickness, it is still challenging because the unstable flow in coextrusion, especially in coextrusion with large layer numbers, is still a hard nut to crack.…”