Effect of Viscosity Ratio of Two Immiscible Polymers on Morphology in Bicomponent Melt Spinning Fibers

Abstract

Bicomponent fibers were melt spun to investigate the effect of individual component viscosity on the cross section morphology. Two couples were tested, polypropylene MFI 18 (PP 18 ) with polyamide 6 (PA6) and, polypropylene MFI 25 (PP 25 ) with polyamide 6 (PA6). Viscosity versus shear rates was evaluated by both rotational and capillary rheometers to cover a large range of shear rates. Higher viscosity of PA6 compared to PP 25 and PP 18 at the theoretical shear rate resulted in the encapsulation of PA6 by PP 25 and PP 18 at the periphery of the bicomponent fiber cross section. Interfacial instability from the center to the periphery fiber was explained as a result of non-uniformity of shear rates across the fiber cross section. Interface shape dependency on the viscosity ratio of the two polymers has been clearly demonstrated: lower viscosity component wrapping around the higher viscosity one whatever the initial configuration, that is, side-by-side or segmented pie structure.

Tuning gradient microstructures in immiscible polymer blends by viscosity ratio

“…Once the PS domains are shaped under the effect of converging flow in the entrance zone and flow into the capillary, PS domains in different radial positions of the die will experience different shear rates. In general, the low viscous PS phase migrates to the die wall where the shear rate is highest . These PS domains near the surface region will subsequently coalesce into larger domains and form irregular shapes.…”

“…The increasing Ca * from the centerline to the wall increases the probability of droplets to deform into fibrils and break up near the wall. Moreover, the phase with lower viscosity can also migrate to the surface of the polymer blend during melt processing and undergo coalescence processes due to the higher shear rates . As for the blend with a high viscosity ratio, the Ca * is larger than one in most radial positions of the capillary and reaches values larger than four near the surface region.…”

“…In general, the low viscous PS phase migrates to the die wall where the shear rate is highest. 33 These PS domains near the surface region will subsequently coalesce into larger domains and form irregular shapes. The PS domains near the capillary center with weak shear rates merely experience weak deformations.…”

“…In most experimental cases, the dispersed phase was found to be finer for viscosity ratios less than one ( p ≤ 1) than that for viscosity ratios larger than one ( p > 1) . In addition to the droplet deformation and breakup differences in low and high viscosity ratio polymer blends, the migration of components, which also depends on the viscosity ratio, is of significance for controlling the polymer morphology . In a study on cellulose/aromatic polysulfonamide (PSA) alloy fibers with core‐sheath structures, the low viscosity PSA phase was found to migrate to the outer layer of a filament during spinning .…”

“…[27][28][29][30] In addition to the droplet deformation and breakup differences in low and high viscosity ratio polymer blends, the migration of components, which also depends on the viscosity ratio, 31 is of significance for controlling the polymer morphology. 32,33 In a study on cellulose/aromatic polysulfonamide (PSA) alloy fibers with coresheath structures, the low viscosity PSA phase was found to migrate to the outer layer of a filament during spinning. 32 This migration facilitated the concentration of flame-retardant PSA in the surface region and improved the flame-retardant properties of blend fibers.…”