Hollow fiber membranes of PVDF were prepared by isothermal wet spinning process from the
water/DMF/PVDF system at 25 C. The dope solution comprised 21 wt% PVDF in DMF, and pure
water was employed both as the inner and outer coagulants. SEM imaging of the membrane indicated
an unexpected interesting morphology: columnar macrovoids extended from the outer surface to the
central region, while cellular pores constituted the inner half of the membrane. As water was a harsh
nonsolvent, one tended to think that macrovoids shall form towards the inner surface of the hollow
fiber. Absence of macrovoids in this region was explained based on the fact that DMF would
accumulate rapidly in the inner extruding stream as it underwent mass-exchange with water in the
inner bath. Such activity rendered effectively the coagulant became effectively a soft one. As a result,
macrovoids was eliminated and the inner surface became porous.
Relation:
Journal of Applied Science and Engineering 21(1), p.89-98
