Page 606 - Polymer-based Nanocomposites for Energy and Environmental Applications

Nanofibrous composite air filters 559

Fig. 20.5 Schematic illustrating formation of a free nanomat in a hole by neutralization of
electrospun nanofibers with gas-phase counterions generated by electrospraying a volatile
solvent ([14], p. 6).

(a) nanomats are not affected by electrode profile, (b) nanomats are free of defects
produced by microscopic sparks, and (c) there is no need to remove nanofibers from
collector or substrate. Results revealed that freestanding nanomats performed low
aerosol penetration with a low resistance to airflow. Also, these nanomats have high
optical transparency that enables direct observation of the captured particles and
formed cake layer (Fig. 20.5)([14], p. 6).
Wang et al. [1] studied on the filtration properties of superamphiphobic
nanofibrous membranes using fine particles, which have an aerodynamic diameter
smaller than 2.5 μm. They synthesized fluorinated polyurethane (FPU) and incorpo-
rated into polyacrylonitrile (PAN) and polyurethane (PU) nanofibers separately.
The composite structures provided water contact angle of 154 degrees classified as
superhydrophobicity and 151 degrees oil contact angle, which is in the range of super-
oleophobicity. PAN/FPU and PU/FPU solutions fed from different syringes at
the same time as seen in Fig. 20.6 (b) [1]. PAN solutions were prepared with 7
(PAN-7), 9 (PAN-9), 11 (PAN-11), and 13 (PAN-13) wt% concentrations. After
nanofiber production for each PAN solution, it is seen that the higher the concentra-
tion, the larger the fiber diameter. The average fiber diameters for PAN-7 and PAN-13
samples were found to be 175 and 558 nm, respectively. NaCl aerosol particles with
diameter range of 300–500 nm were used for filtration tests. The filtration efficiency
decreased with the increase of polymer concentration from 98.89% to 40.80% for
PAN-7 and PAN-13, respectively. The fact behind this phenomenon is that an increase
in concentration causes an increase in fiber diameter; thus, average pore size also
increases. Furthermore, the pressure drop decreased from 53 to 3 Pa with the increase
in pore size. In order to choose the best concentration, the tensile strength and Young’s
modulus of the samples were tested. It is seen that PAN-11 is the most acceptable for
air filtration (Fig. 20.7) [1].