Filtration Performance Against Nanoparticles by Electrospun Nylon-6 Media Containing Ultrathin Nanofibers

Figures & data

TABLE 1 Symbols for parameters used in the layered multiple zone model

	Substrate	Uniform layers, NF	NF in mixed layer	UNF in mixed layer
Fiber diameter	D sub	DNF	DNF	DUNF
Effective solidity	αsub	αuni	αNF = αuni	αUNF
Face velocity	U0	U0	UNF	UUNF
Pressure drop	Δpsub	Δpuni	ΔpNF = Δpmix	ΔpUNF = Δpmix
Penetration	Psub	Puni	PNF	PUNF

N: Number of total layers of the electrospun fibers.

q: Mixing factor between uniform and mixed layers.

A: Mean UNF coverage factor.

FIG. 1. A schematic for the layered multiple zone model composed of both NFs and UNFs on top of the polyester substrate.

FIG. 2. A schematic for (a) a unit cell of hexagonal UNF net structure and (b) the corresponding interception mechanism.

FIG. 3. SEM images of electrospun media obtained from the Nylon-6 solutions with different (a) concentrations and (b) relative humidity (RH).

FIG. 4. SEM images of the electrospun media collected with different collecting distances. The polymer solution concentration was 20% for all the samples.

FIG. 5. SEM images of electrospun media produced from freshly made or aged polymer solutions in various concentrations.

FIG. 6. SEM images that illustrate the formation mechanism: (a) a partially split ribbon-like fiber and (b) a fiber partially split in the longitudinal direction; the panel on the top right corner is a zoomed-out view of the same fiber.

TABLE 2 The structural parameters for the filter media and the corresponding operating parameters for their production and filtration tests

Operating parameters				Characteristic properties			Estimated NF/UNF properties
No.	PA concen. (w/w)	Collecting distance [cm]	Face velocity U0 [cm/s]	Mean NF diameter DNF [μm]	Mean UNF diameter DUNF [nm]	Pressure drop Δptotal [Pa]	Effective solidity αNF	Effective layers N	Layer mixing factor q	UNF covering fraction A
I	20%	15	5	0.103	20	57	0.0054	86.17	15.50%	84.61%
II	20%	15	10	0.103	20	92	0.0054	86.17	15.50%	84.61%
III	20%	15	15	0.103	20	155	0.0054	86.17	15.50%	84.61%
IV	—	—	10	—	—	3
V	10%	15	10	0.058	20	81	0.0039	82.71	12.60%	83.59%
VI	20%	15	10	0.102	19	164	0.0068	88.24	19.11%	85.12%
VII	20%	10	10	0.112	21	283	0.0169	65.38	23.39%	78.85%

FIG. 7. Modeled and experimental data of the penetration tests for Samples I, II, and III.

FIG. 8. Modeled and experimental data of the penetration tests for Samples IV, V, VI, and VII.

FIG. 9. Quality factor Q_F for Samples V–VII and three simulated mono-structure Nylon-6 fibers in 2 μm (Microfiber), 100 nm (NF), and 20 nm (UNF) filters. The velocity is 10 cm/s for all tests.

FIG. 10. The computed specific filtration performance index I_s for Samples V–VII and the simulated mono-structural Nylon-6 fibers in 2 μm (Microfiber), 100 nm (NF), and 20 nm (UNF) filters. The unit area of the assumed filters is 1.0 mg/m².