Effect of post-drawing on the mechanical and mass transfer properties of polyacrylonitrile hollow fiber membranes

Abstract

The effects of the drawing conditions on spun polyacrylonitrile hollow fibers were investigated. The drawing conditions included draw ratio, temperature, and concentration of dimethylformamide in the drawing bath. The resulting hollow fiber was examined with a scanning electron microscope. Both the inner and outer diameters of the hollow fibers decreased with the increase in draw ratio. Microvoids were observed on the outer surface of the drawn fibers. The stress-strain behavior of the resulting hollow fibers was measured in both the dry and wet states. The breaking strength increased with the draw ratio, which was higher for the dry samples than for the wet samples. The breaking elongation of the dry sample increased with the draw ratio, whereas the wet sample showed opposite trend. The permeation performance was measured. The pore size increased with the draw ratio. The hydraulic permeability of pure water increased markedly with increase in the draw ratio. However, increasing the concentration of dimethylformamide in the drawing bath reduced the increase in the pore size and hydraulic permeability. On the basis of the analysis of variance, both the pore size and hydraulic permeability were influenced mostly by the draw ratio, and slightly by the concentration of DMF in the drawing bath and by the drawing temperature.