Thin Inorganic Porous Hollow Fiber Membranes

Extensive research has been performed on inorganic hollow fibers by dry–wet spinning of a particle loaded polymer solution, followed by thermal treatment. Several research groups have shown this approach to be feasible for variety of inorganic particles. Various studies are available on possibilities to tailor fiber properties and dimensions by changing the spinning solution, spinning conditions, and thermal treatment strategies. In this chapter, the emphasis is on preparation of inorganic hollow fibers with exceptionally small outer diameters. The small fiber diameters are obtained through extensive shrinkage of ‘green fibers’, upon heating above the glass transition temperature of the polymer. The extensive shrinkage is attributed to viscous removal of macro voids, present in the green fiber. For different inorganic materials a particle specific range is identified in which viscous deformation is possible; below a minimal particle concentration it is not possible to sinter particles together and above a critical particle volume fraction viscous transport is hindered by a sharp increase in viscosity.