Structural study on the formation mechanism of porous fibers obtained by the electrospinning technique
1)Purpose
The surface porous fibers are fibers having a lot of pores on the fiber surface. A lot of pores increase the specific surface area of the fibers. By increasing the specific surface area, the adsorption performance of fibers is enhanced. So, the surface porous fibers are used as the separation membranes or the filters. However, the formation mechanism that the fiber surface becomes porous is not yet elucidated from the thermodynamic point of view. In this study, as the first purpose, I make the surface porous fibers by using the electrospinning technique from the ternary system solution. This ternary system solution consists of a polymer, a good solvent and a poor solvent. As the second purpose, I elucidate the formation mechanism of the fibers I made from the thermodynamic point of view. 2)Describe I will explain about my experimental method. About materials, I used the cellulose acetate(CA) as a polymer, the acetone(Ace) as a good solvent and the distilled water(DW) as a poor solvent. I mixed these three materials at 25 degrees. The CA concentrations were 6wt%, 10wt% and 14wt%. The Ace/DW ratios were 2.5, 3, 4 and 5. I made the CA fibers from this ternary system solution by using the electrospinning technique. The electrospinning technique is the method that we can make the fibers from the polymer solution by using the power of electricity. I observed the CA fibers with the scanning electron microscopy(SEM). 3)Result The SEM image of fibers with CA=14wt% and Ace/DW=3 is shown below. In this experiment, we succeeded in making the fibers with a lot of pores on the surface. However, the diameters of the porous fibers were large. The solution for CA=14wt% and Ace/DW=2.5 could not form the fibers, because the amount of Ace was so small that it evaporated before CA formed fibers. Now, I will tell you about the formation mechanism of surface porous fibers. First, at the start of spinning, Ace having a higher vapor pressure evaporates. Second, CA and DW are microphase-separated and pores are generated. Finally, CA solidifies as pores remain. Thus, the surface porous fibers are formed. From now on, I would like to make the surface porous nanofibers. |
The SEM image of fibers with CA=14wt% and Ace/DW=3