Capillary flow of sodium and zinc ionomers

Abstract

The capillary flow properties of several commercial ionomers (sodium and zinc) were studied to assess their processability in terms of instabilities such as wall slip and melt fracture. Using capillary dies of various diameters and lengths to control capillary extrusion pressure, it was found that the viscosity of these polymers exhibits a relatively small dependence on pressure, more importantly at relatively smaller pressures. Using capillaries of various diameters at fixed length-to-diameter ratios, it was also found that the no-slip boundary condition is a valid assumption for these polymers due to the strong ionic associations and strong interactions with the capillary wall. All ionomers were found to exhibit gross melt fracture (no sharkskin), a phenomenon more dominantly observed at lower temperatures. The occurrence of gross melt fracture and the absence of surface (sharkskin) melt fracture is a characteristic of extensional strain-hardening polymers, noting that all ionomers examined exhibit this phenomenon. The critical shear stress for the onset of gross melt fracture was found to depend on the lifetime of associations, τS (τS∝ZE/ZS21/5, where ZE is the number of entanglements and ZS is the number of associations), independent of temperature, molecular weight, and type of ion (zinc or sodium).

Rheological Properties Related to Extrusion of Polyolefins

“…The importance of the extensional viscosity on the entry pressure was studied extensively for the case of ionomers [ 40 , 41 , 42 , 43 ]. Results are presented in Figure 3 for two polymers, one ionomer (19.2-Na65) and its corresponding copolymer (19.2-Na65).…”

“…Unlike Newtonian fluids, polymer melts slip over solid surfaces when the wall shear stress exceeds a critical value [ 13 , 14 , 15 , 16 , 17 , 18 ]. In particular, slip effects have been reported in the capillary flow of molten polyethylenes [ 44 , 45 , 46 , 47 , 48 , 49 ], polydimethylsiloxanes [ 50 ], polystyrenes [ 51 , 52 , 53 ], polybutadienes [ 54 , 55 ], polypropylenes [ 56 , 57 , 58 ], fluoropolymers [ 59 ], polylactides [ 60 ], polyisobutylenes [ 61 ], ionomers [ 40 , 41 ] and other viscoelastic fluids [ 62 , 63 ]. Thus, in a comprehensive study of any melt, possible slip effects should be studied to be used as boundary conditions in high shear rate flows.…”

“…On the other hand, the use of the K-BKZ model is capturing adequately well the entrance pressure as a function of the contraction angle for all three polymers. As the con- The importance of the extensional viscosity on the entry pressure was studied exten-162 sively for the case of ionomers [40][41][42][43]. Results are presented in Fig.…”

Flow-induced birefringence study of secondary flow in entrance region of rectangular slit channel for long-chain-branched polyethylene melt

“…Understanding the flow behaviour of viscoelastic fluids in confined geometries is essential for applications in polymer melt/solution processing [1][2][3][4], processing of biological/medical systems [5][6][7], enhanced oil recovery [8][9][10], dampers [11][12][13] and many others. Historically, Tordella [14] in 1957 was the first to attempt to visualize the die entry flow region during his original work on melt fracture research.…”

Melt fracture and wall slip of thermoplastic vulcanizates

“…Moreover, these highly elastic systems exhibit melt fracture phenomena that manifest themselves as distortions on the surface of extruded TPV samples. [ 31 ] While several melt fracture studies exist for polymer melts such as polyethylenes, [ 32‐34 ] polypropylenes, [ 35,36 ] polystyrenes, [ 37 ] polydimethylosiloxanes, [ 38 ] polylactides and polycaprolactones, [ 39‐41 ] fluoropolymers, [ 42 ] polybutylenes, [ 43 ] ionomers [ 44 ] as well as polymer blends and composites, [ 45‐48 ] specific studies focused on TPVs are rare. The single study by Wu et al [ 31 ] on TPV melt fracture reported that by increasing the time of TPV extrusion via performing the extrusion twice and with increasing the extrusion temperature, more smooth extrudate surfaces are achieved.…”