Page 600 - Polymer-based Nanocomposites for Energy and Environmental Applications

Nanofibrous composite air filters 20

*
*
Y. Akgul * ,† , Y. Polat * ,‡ , E. Canbay , A. Demir , A. Kilic *
†
*Istanbul Technical University, Istanbul, Turkey, Karabuk University,
‡
Karabuk, Turkey, Marmara University, Istanbul, Turkey

20.1 Introduction

Increasing population, intensifying human activities, development of industry, and
the rise in agricultural production are booming the demand for air purification. The
traditional nonwoven air filters such as melt-blown filters, spunbond filters have
diameters in the range of micrometers. From the aspect of filtration performance,
nanofibers are more efficient than microfibers at the same pressure drop in the inter-
ception and inertial impaction regimes. As shown in Fig. 20.1, when the average fiber
diameter is low enough, the velocity of air over the fiber surface does not drop to zero,
which is named as slip flow. That provides a significant advantage in terms of pressure
drop on the contrary to the microfiber-based filters [1]. Nevertheless, their mechanical
strength is not sufficient to withstand against the airflow. Due to that, nanofibrous
air filters are mostly used with a substrate, as in the form of composite structure in
sandwich form. Such composite nanofibrous air filters may also provide antibacterial
properties.
Slip flow regime is explained with the Knudsen number (Kn) [2], which is a dimen-
sionless number that can be defined as the ratio of the mean free path length to fiber
diameter. Kn is calculated by the following formula [3]:

2λ
Kn ¼
d f

where λ is a mean free path length of carrier gas (λ¼0.065 μm for air at standard
conditions) and d f is the fiber diameter. Slip flow effect is very considerable for
sufficiently large Kn. The slip flow effect will prevail when Kn>0.1, but it needs
to be considered when Kn is around 0.25.

20.2 Nanofibrous air filters: Structure—process—
property

Balgis et al. [3] have produced and evaluated straight and bead-free nanofibers for
aerosol filtration application. The electrospinning technique was used to produce
bead-free straight nanofibers with diameters lower than 100 nm. During the
electrospinning, ambient conditions like temperature and humidity were set to control
the size and the morphology of webs. Used potassium iodide was blended into
Polymer-based Nanocomposites for Energy and Environmental Applications. https://doi.org/10.1016/B978-0-08-102262-7.00020-9
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