Recently, the nanofiber is attracting attention in the textile industry and being developed for various applications in such widespread fields as environment, power energy, electronics, medicine and biotechnology. One of the typical applications of the nanofiber material is a nanofiber membrane, and it is considered to be promising as an alternative to conventional membrane. The nanofiber membrane which has complex 3D network structure and higher porosity is expected to be a new filter for environmental purification with high separation performance and various separation functions since it has a nanosized effect, an extremely high specific surface area and a high porosity. In fact, nanofibers are applied to gas or air treatment such as an exhaust gas filter and a chemical and biological protective suit. For liquid treatment, however, the separation characteristics and mechanisms of the nanofiber membrane are poorly understood because few researches have been conducted.
In this study, we focused on the application of an electrospun nanofiber membrane to 1. filtration and 2. classification of fine particles dispersed in liquid.
1. Application to Filtration
The nanofiber membrane was developed for the water purification, and the water permeation and particle filtration tests were conducted to evaluate its separation performance. As a result, it was revealed that the nanofiber membrane has extremely high water permeation rate and is effective in the separation of the submicron-sized particles in liquid. Furthermore, the pore size of the nanofiber membrane decreased with a decrease in the fiber diameter, resulting in the improvement of the particle retention performance. In contrast, the influence of the deposition weight of nanofiber was considerably less than that of the fiber diameter. In conclusion, the following merits are derived from the above experimental results: (1) The nanofiber membrane has an advantage in the treatment of very dilute contaminated water because of its high permeation rate; (2) The separation performance of the nanofiber membrane is controllable according to the purpose by controlling the fiber diameter; (3) The development of thinner nanofiber than the conventional one leads to the application to more advanced separation.
2. Application to Classification
It is of importance in widely diversified fields to uniformize the particle size of particulate material, and therefore various studies on the classification methods have been conducted. One of promising methods is wet classification by using a porous membrane, in which the particles larger than the pore size are completely captured on the membrane and only smaller particles can pass through the membrane. However, the excessive deposition of larger particles on the membrane retards the passage of smaller particles, resulting in a decline in classification performance. On the other hand, if the nanofiber membrane is applied to classification of the particulate material, it is expected that the larger particles are retained by the 3D nanofiber network and the smaller particles can pass smoothly through extremely porous space. In this study, the fractionation experiments of the binary mixture of large and small particles were conducted under the various conditions of pH and particle concentrations to provide a fundamental understanding of the classification performance of fine particles by the nanofiber membrane.