Polyaramide hollow fibers for H2/CH4 separation

Increased Molecular Weight of a Cross-Linkable Polyimide for Spinning Plasticization Resistant Hollow Fiber Membranes

“…20,21 In previous studies using these cross-linkable polymers, higher spinning speeds were not achieved due to low viscosity of the polymer solutions used in making the fibers. 14 There are ways that may alleviate this problem, such as with the use of viscosityenhancing salts, e.g.…”

Semianalytical solution for power‐law polymer solution flow in a converging annular spinneret

“…However, the parameters controlling the spinning process of hollow fiber membranes are complicated, and many of these parameters have been investigated to date. In addition to finding the appropriate materials and methods to spin membranes, another key issue is the determination of the effect of flow conditions within the spinneret on the membrane morphology and properties . Aptel et al introduced the spinning number, an empirical dimensionless coefficient, to correlate several spinning variables that strongly influence the hydraulic permeability of hollow fiber membranes.…”

The rheology of Torlon® solutions and its role in the formation of ultra-thin defect-free Torlon® hollow fiber membranes for gas separation

“…In terms of the role of spinneret design, it is found that spinnerets with a smaller annular channel would induce a higher shear rate and stress onto the dope solution and favor the formation of macrovoid-free morphology [15,21], while spinnerets with a larger dimension would induce a lower shear rate and stress which help offset the shear-thinning effect and may enhance both permeance and permselectivity for gas separation [15]. When a dope solution is extruded out of the spinneret, the elongational stress on the nascent fiber can be monitored by changing the air-gap distance or the take-up rate [15,22,23]. Though different polymers may exhibit different elongational viscosities with respect to elongational rate as reported by Ekiner and Vasilatos [23], a proper increase in air-gap distance or elongational rate would generally result in better polymer chain packing, remove the polymer chain relaxation caused by die swell, and hence increase the permselectivity [15,19,22].…”

“…When a dope solution is extruded out of the spinneret, the elongational stress on the nascent fiber can be monitored by changing the air-gap distance or the take-up rate [15,22,23]. Though different polymers may exhibit different elongational viscosities with respect to elongational rate as reported by Ekiner and Vasilatos [23], a proper increase in air-gap distance or elongational rate would generally result in better polymer chain packing, remove the polymer chain relaxation caused by die swell, and hence increase the permselectivity [15,19,22]. Some other factors that may also affect the dope rheological properties are temperature, viscoelasticity, molecular weight, molecular coil size in the solution, as well as the flow stability within the spinneret channel [24].…”