Surface modified polyacrylonitrile/polyamide nanofibre composite for air filtration

Abstract

Polyacrylonitrile (PAN) and Polyamide (PA)-6 based nanofibrous composite were prepared for air filtration application. PAN was electrospun on spun-bonded non-woven polypropylene which acts as a collector and the samples were coated with PA-6. Box-Behnken experimental design was used to design the experimental plan. As per the experimental plan, PA-6 coated samples were treated with different concentrations of an alkali solution (NaOH) (2%, 5% and 8%) and treatment temperature (60^oC, 80^oC and 100^oC) to enhance the surface properties. As prepared nanofibrous composite was tested for its various properties such as surface morphology, particle filtration efficiency and air permeability. Fourier transform infra-red analysis and scanning electron microscope were performed to analyze the functional groups and morphology of the nanofibrous composite respectively. The air permeability of the control and treated samples was analyzed as per the standard procedure and the permeation level varies from 52.5 to 60 cm³/cm²/s for control samples, 65–195 cm³/cm²/s for treated samples. The overall filtration efficiency for treated samples varies from 36.54% to 78.56%. The sample which is treated with 5% NaOH at 60^oC has a higher overall filtration efficiency of 78.56%.

Keywords

Nanofibrous composite box- behnken design alkali treatment overall filtration efficiency air permeability

Introduction

Filtration is an effective process used to separate suspended solid particles from the air using a filter medium. The filter medium is usually a permeable material so that filtration can be achieved effectively. Thus, for better filtration, the filter media should have high permeability and efficiency.¹ For airborne particles, both fibrous and fabric filters were used to remove solid particulates from the air. Filters are classified into two types such as mechanical filters and electrostatic filters based on the principle of separation of particles. For mechanical filters, they are separated by specific filtration mechanisms such as interception, inertial impaction, diffusion and electrostatic interaction which depends upon the size of the particle and airflow velocity. As per the mechanism, 1–10 μm particles are filtered by gravitational settling and the maximum efficiency was achieved for bigger particle size. In the case of inertial impaction, the particles are filtered in the range of 0.1–1 μm, however, a bigger, particle size gives higher filtration efficiency. In the case of the interception mechanism, the particles are filtered from 0.05–0.5 μm. In the case of diffusion, the increase in particle size leads to a decrease in efficiency. However, while comparing all the mechanisms, the least filtration efficiency such as less than 50% was achieved for 0.3 μm particle, which is called as most penetrating particle.² Electrostatic filters are charged fibres that attract the particles by the application of an electric field. Synthetic polymer fibres were used as filters when the electrostatic interaction method is preferred.^3,4 The existing air filters are produced from various polymeric materials such as polypropylene,⁵ polyamide (PA),⁶ polyester,⁷ polyacrylonitrile (PAN)⁸ etc. Nanofibres are produced by several methods however electrospinning is the widely used method to produce nanofibres for air filtration application.⁹ Various surface modification methodologies are used to enhance the performance of membrane including chemical (chemical vapour deposition, alkali treatment and co-polymerization) and physical (high energy irradiation, heat and plasma treatments) methods.¹⁰ PAN is an extensively used polymer for several applications due to its high abrasion resistance, inexpensive, porous nature and easy surface modification.¹¹ By alkaline solution hydrolysis, the conversion of –CN groups of the PAN membrane surface into –CONH₂ and then into –COO– groups. Thus, the functional groups can be uniformly distributed along the PAN chain. Recently, PAN hydrolysis has been widely used for the preparation of composites for various applications.^12,13

In this research work, nanofibre (PA) was collected on polypropylene non-woven fabric and PA-6/Polyethylene glycol (PEG) solution was uniformly coated over the electrospun web to increase the stability of the web. Then the developed nanofibrous composite was surface treated with alkali to enhance the roughness of the PA surface and exposed pan nanofibre. The effect of alkali treatment on various physical and functional properties of the nanofibrous composite was studied and discussed in detail.

Materials and method

Spun-bonded polypropylene nonwoven fabric with 40GSM (grams per square meter) and 0.3 mm thickness was used as a base material to collect the electrospun web. Dimethylformamide (DMF), Sodium Hydroxide (NaOH), Formic acid as solvents and PEG (MW1000) as pore former used were of analytical grade. The electrospun PAN (MW 1,50,000) nanofibre was prepared at an applied voltage of 18kVA and 15 cm as a tip to collector distance. Initially, the PAN nanofibres were prepared by electrospinning at different time duration such as 1 h, 2 h and 3 h. PAN electrospun nanofibre was coated with PA. Then, as prepared nanofibrous composite was treated with sodium hydroxide for the period of 1 h. The concentration of NaOH and treatment temperature was varied based on the experimental plan. The experimental plan of three variables and three levels were shown in Table 1.

Table 1.

Variables for box-behnken design.

	Variables	−1	0	+1
X₁	Electrospun time of polyacrylonitrile (h)	1	2	3
X₂	NaOH concentration (%)	2	5	8
X₃	NaOH treatment temperature (°C)	60	80	100

Construction of nanofibrous composite

As per the plan, by varying the collection time, 15 samples of PAN electrospun nanofiber were prepared. Equal weight proportion (50:50) of PA-6 and PEG was dissolved in formic acid (85%) and coated uniformly on the as-prepared nanofibrous web. The samples were dried at room temperature and washed several times to remove the residual solvent and polymer. The prepared nanofibrous composite was treated with different concentrations of sodium hydroxide (NaOH) and placed in the shaking water bath at a constant period of 1 h, as per the temperature in the experimental plan. After alkaline treatment, the nanofibrous composite was washed with cold water and dried at room temperature. The construction of nanofibrous composite is represented in Figure 1.

Figure 1.

Schematic representation of the construction of nanofibrous composite.

Mass per unit area (grams per square meter)/thickness

As per the ASTM D 3776, the weight, length and width of the sample were measured and the GSM was calculated as per the below-mentioned equation.

G S M = \frac{10^{3} M}{L W} g / m^{2}

where M = mass/weight of the nanofiber sample (Kg)

L = length of the nanofiber sample (m)

W = width of the nanofiber sample (m)

Using a thickness gauge meter, the average thickness of the sample is calculated as per the ASTM D 1777.

Scanning electron microscope

The surface morphology of the nanofibrous composite was observed through a scanning electron microscope (SEM), (VEGAS TESCAN) with a magnification of 25kx and an accelerating voltage of 30 kV.

Fourier transform infra-red analysis

Fourier transform infrared spectroscopy (Shimadzu FT-IR spectrometer) was used and the spectrogram was observed in the range of 4000–500 cm⁻¹, to study the functional groups of nanofibrous composite.

Air permeability

As per the ASTM D1776-90 Standard Test Method, the air permeability of the developed samples was analyzed and it was carried out with the pressure of 125 Pa (114 cm/4.5^″) at different places in the test sample. Air permeability is calculated as per the formula given below.

R = \frac{1000 r}{3600 A} c m 3 / c m 2 / s

Where r= Rotometer reading in liters per hour

A= area of the cross-section of the ring (10 cm)

Particle filtration efficiency

As per the ASTM F2299 standard test method, the filtration efficiency was determined for the developed samples. This test method utilizes the light scattering particle counter with the capacity of 0.3–10.0 μm to find out the input and output particle sizes with numbers. In this test method, the airflow velocity is maintained at 5 cm/s. The test procedure measures filtration efficiency by comparing the particle count in the feed stream (upstream) to that in the filtrate (downstream). Filtration efficiency is calculated as per the formula given below and the schematic diagram of the filtration efficiency tester in Figure 2.

Filtration efficiency = \frac{(N o . o f p a r t i c l e s f e e d - n o . o f p a r t i c l e s c o l l e c t e d)}{N o . o f p a r t i c l e s f e e d} \times 100

Figure 2.

Schematic diagram of filtration efficiency tester.¹⁴

Results and discussion

Surface modification

Hydrolysis is to transform surface nitrile groups into carboxylic groups, which improves the web’s stability. This occurs in two phases; the first phase involves the hydrolysis of nitrile groups to produce an amide moiety. The –CONH₂ groups are removed in the second stage, and carboxylic acids are formed by adding a hydroxyl group to the amide. Overall, alkaline solution hydrolysis is to convert the –CN– groups present on the surface of PAN membrane to –CONH₂– and eventually to –COO– groups, resulting in membrane stability.¹⁵

Surface morphology of the nanofibre and surface modified filter (scanning electron microscope)

The surface morphology of electrospun web and alkali-treated nanofibrous composite was observed through SEM micrographs and given in Figure 3. The average fiber diameter of the control sample is around 250 nm and the structure has randomly oriented more uniform fibers.

Figure 3.

Scanning electron microscope images of (a) Control sample, (b) 2% NaOH at 60°C, (c) 2% NaOH at 80°C, (d) 2% NaOH at 100°C, (e) 5% NaOH at 60°C, (f) 5% NaOH at 80°C, (g) 5% NaOH at 100°C, (h) 8% NaOH at 60°C, (i) 8% NaOH at 80°C, (j) 8% NaOH at 100°C.

It was observed that the surface morphology of the alkali-treated nanofibrous composite varies based on the concentration of the alkali and treatment temperature. The pore size of treated composite with 2% NaOH varies from 0.297 to 0.649 and variation in pore size is due to an increase in treatment temperature. Further increase in NaOH concentration and temperature results in an increase in pore size and also the nanofibrous layer is exposed due to the removal of the PA-6 surface layer. The average pore size of the nanofibrous composite is mentioned in Table 2.

Table 2.

The average pore size of nanofibrous composite.

S.No	Conditions	Average pore size
1	2% NaOH at 60°C	0.297 μm
2	2% NaOH at 80°C	0.618 µm
3	2% NaOH at100°C	0.649 µm
4	5% NaOH at 60°C	0.481 µm
5	5% NaOH at 80°C	0.513 µm
6	5% NaOH at 100°C	0.940 µm
7	8%NaOH at 60°C	0.592 µm
8	8% NaOH at 80°C	1.034 µm
9	8% NaOH at 100°C	—

Fourier transform infra-red analysis

Figure 4(a) shows the FTIR spectrum of the control sample and Figure 4(b)–(d) shows the alkali-treated samples with different concentrations and different temperatures. In the control sample, the peak at 2936 cm⁻¹ and 1736 cm⁻¹ is due to stretching of C≡N and C=O of PAN respectively.¹⁶ The peak at 3294 cm⁻¹ is the N-H stretching vibration and 1635 cm⁻¹ is amide carbonyl (C=O) of PA-6 respectively.¹⁷

Figure 4.

(a) FT-IR graph of the control sample. (b) FT-IR graph of 2% NaOH at different temperatures such as 60°C, 80°C and 100°C treated samples. (c) FT-IR graph of 5% NaOH at a different temperature such as 60°C, 80°C and 100°C treated samples. (d) FT-IR graph of 8% NaOH at a different temperature such as 60°C, 80°C and 100°C treated samples. FT-IR: Fourier Transform Infra-Red Analysis.

The peak at 1536 cm⁻¹ existing in the treated sample represents the amide CONH₂ moiety.¹² When comparing the 2% alkali-treated samples for the temperature, the peak intensity is high for the 80°C treated sample. For all the bonds in this temperature, the peak intensity was observed as high. Hence, the suitable temperature for this alkali treatment is 80°C. However, while comparing the 5% alkali treatment conditions, the effect of treatment on peak intensity is not uniform and it varies based on the stretching of bonds.

In the case of 8% alkali-treated samples, the peak intensity decreases further increase in temperature. This is due to the degradation of the compounds due to alkali treatment with higher treatment time and higher temperature.

Properties of nanofibrous composite

The thickness, mass per unit area in GSM and air permeability of the control samples are given in Table 3. The thickness and mass per unit area increase due to an increase in accumulation time. The air permeability gradually decreases as the increase in thickness of the nanofibrous composite.

Table 3.

Properties of control samples.

Accumulation hour (h)	Thickness (mm)	Gram per square meter	Air permeability (cm³/cm²/s)
1	0.384	65.45	62.5
2	0.42	68.45	60
3	0.542	77.38	55

For the alkali-treated nanofibrous composite, the physical properties were tested and are tabulated in Table 4. The variation in thickness, mass per unit area and air permeability is due to variation in process parameters

Table 4.

Physical properties of alkali-treated samples.

Run	Accumulation hour (h)X₁	NaOH concentrationX₂	Treatment timeX₃	Thickness (mm)	Mass per unit area (grams per square meter)	Air permeability (cm³/cm²/s)
1	1	2	80	0.398	65.48	110
2	3	2	80	0.448	71.43	75
3	1	8	80	0.386	71.43	180
4	3	8	80	0.406	80.36	90
5	1	5	60	0.42	62.5	125
6	3	5	60	0.43	74.4	65
7	1	5	100	0.384	77.38	195
8	3	5	100	0.438	83.33	110
9	2	2	60	0.408	77.38	75
10	2	8	60	0.53	74.4	65
11	2	2	100	0.388	80.36	90
12	2	8	100	0.372	71.43	120
13	2	5	80	0.432	65.48	110
14	2	5	80	0.512	80.36	98
15	2	5	80	0.400	65.48	108

Filtration efficiency

The filtration efficiency of the control and alkali-treated nanofibrous composite were tested against the particle diameter varying from 0.3 to 3 μm and the overall filtration efficiency is represented in Table 5.

Table 5.

Particle filtration efficiency of control and treated sample.

Control sample
S.No	Filtration efficiency
S.No	0.3 µ	1.0 µ	1.5 µ	2.0 µ	2.5 µ	3.0 µ	Overall efficiency	Desirability value	Rank
C1	19.878	43.451	77.837	86.123	93.654	96.945	32.480
C2	25.196	62.967	86.899	96.630	96.331	96.823	43.383
C3	36.808	73.594	89.781	99.916	99.945	99.945	54.829
Treated sample
S1	42.12	64.32	82.00	90.59	92.56	98.43	56.12	0.889568	2
S2	65.56	92.19	93.19	96.57	98.51	99.52	78.56	0.909747	1
S3	32.56	56.23	74.56	96.96	98.58	99.47	36.54	0.804870	12
S4	45.63	68.12	89.55	94.23	97.70	99.11	72.56	0.861700	9
S5	38.15	66.45	78.56	97.64	98.88	99.39	38.37	0.816065	10
S6	52.78	78.54	97.78	98.73	99.27	99.64	68.75	0.877165	4
S7	40.94	62.45	75.12	87.49	93.53	96.88	49.88	0.863948	8
S8	23.30	77.82	82.72	88.84	94.31	97.55	65.24	0.888027	3
S9	29.20	75.86	83.12	94.84	97.76	98.83	56.23	0.000000	14
S10	29.32	64.52	66.52	69.37	83.70	91.88	39.45	0.664963	13
S11	23.29	73.21	76.54	94.01	96.97	98.49	47.90	0.811317	11
S12	13.83	53.12	69.85	94.28	97.73	98.81	41.30	0.000000	15
S13	41.01	68.45	74.32	92.22	96.74	98.50	68.45	0.876451	5
S14	51.73	67.12	76.89	91.51	96.09	98.13	69.23	0.876451	6
S15	55.34	68.54	75.24	97.29	98.86	99.41	66.29	0.876451	7

The overall filtration efficiency of control samples varies from 32.48% to 54.83%. The overall filtration efficiency of the control sample has been varied based on the PAN accumulation hour. As the accumulation hour increases, the thickness of the nanofibrous composite increases which shows significantly lower performance than alkali-treated samples.

With respect to the particle size 0.3–3 μm, the particles are filtered by the mechanism’s diffusion, inertial impaction and interception. In general, the slippage of the particles from the surface of the filter or fibre will also happen due to smoothness. Hence if the surface roughness is imparted to the filters will also help to improve the filtration efficiency. Thus, the filtration efficiency of the alkali-treated samples was improved due to surface roughness.¹⁸ The highest overall filtration efficiency was obtained for the second S2 compared to the control sample. This implies that the 2% alkali treatment is best the concentration as the pore size is minimum compared to other alkali concentrations. At lower alkali concentration and treatment temperature, the fibre swells and forms very small pores. Further, an increase in the concentration of NaOH and treatment temperature results in the degradation of PA-6 which creates a bigger size pore.

Regression analysis

Regression analysis was carried out for air permeability, individual and overall filtration efficiency for the nanofibrous composite to derive regression equations. F value and R² values were derived and given in Table 6. It was observed that the F value shows, a significant effect on air permeability, individual and overall filtration efficiency of the nanofibrous composite by the independent variables. For the particle size 2.0 μm, 2.5 μm and 3.0 μm, the filtration efficiency was insignificant. All the R² values lie between 86–99.9%. The R² value shows that the predicted values from the regression equation fit closer to the original values.

Table 6.

Regression equations, F value, and R² value.

S.No	Property	Regression equation	F	R²
1	Filtration efficiency for 0.3 μm	$\begin{array}{l} - 281.73 + 16 {. 80 X}_{1} + 13 {. 18 X}_{2} + 7 {. 33 X}_{3} + 5.96 \\ X_{1}^{2} - 0 {. 988 X}_{2}^{2} - 0 {. 041 X}_{3}^{2} - 0 {. 864 X}_{1} X_{2} - 0.403 \\ X_{1} X_{3} - 0 {. 04 X}_{2} X_{3} \end{array}$	3.67	86.9
2	Filtration efficiency for 1.0 μm	$\begin{array}{l} 60.67 - 1 {. 85 X}_{1} + 4 {. 30 X}_{2} + 0 {. 03 X}_{3} + 3 {. 41 X}_{1}^{2} - \\ 0 {. 13 X}_{2}^{2} - 0 {. 0003 X}_{3}^{2} - 1 {. 331 X}_{1} X_{2} + 0.041 \\ X_{1} X_{3} - 0 {. 0365 X}_{2} X_{3} \end{array}$	22.34	97.6
3	Filtration efficiency for 1.5 μm	$\begin{array}{l} 92.15 - 21 {. 09 X}_{1} - 5 {. 26 X}_{2} + 0 {. 499 X}_{3} + 9 {. 44 X}_{1}^{2} \\ - 0 {. 0109 X}_{2}^{2} - 0 {. 0034 X}_{3}^{2} + 0 {. 316 X}_{1} X_{2} - 0.145 \\ X_{1} X_{3} + 0 {. 0413 X}_{2} X_{3} \end{array}$	10.5	95.0
4	Over all filtration efficiency	$\begin{array}{l} - 185.78 + 17 {. 78 X}_{1} + 1 {. 406 X}_{2} + 5 {. 604 X}_{3} \\ + 1 {. 148 X}_{1}^{2} - 0 {. 910 X}_{2}^{2} - 0 {. 034 X}_{3}^{2} + 1 {. 132 X}_{1} X_{2} - \\ 0 {. 188 X}_{1} X_{3} + 0 {. 042 X}_{2} X_{3} \end{array}$	28.85	98.1
5	Air permeability	$\begin{array}{l} 17.3 - 75 {. 16 X}_{1} + 15 {. 67 X}_{2} + 2 {. 51 X}_{3} + 22 {. 33 X}_{1}^{2} \\ - 1 {. 546 X}_{2}^{2} - 0 {. 0098 X}_{3}^{2} - 4 {. 583 X}_{1} X_{2} - 0.312 \\ X_{1} X_{3} + 0 {. 166 X}_{2} X_{3} \end{array}$	11.49	95.4

Response optimization and composite desirability analysis

In the response optimization by composite desirability analysis, the input parameters are minimum and maximum values for each response, weightage and importance of each response. The obtained desirability values for each experiment are given in Table 7. The overall composite desirability value was found as 0.86674. The desirability values are ranked and sample 2 is ranked as 1 such as 3 h of electrospinning time, 2% NaOH concentration and 80°C temperature for surface treatment give better properties for air permeability and filtration efficiency. However, as per the response optimization analysis, the predicted input parameters for the targeted response are 1 h electrospinning time, 3.41% of NaOH and 64.19°C treatment temperature.

Table 7.

Input parameters for response optimization.

Response	Goal	Lower	Target	Upper	Weightage	Importance	Desirability value
FE of 0.3 µ	Maximum	13.83	65.56	65.56	0.2	2	0.85085
FE of 1.0 µ	Maximum	53.12	92.19	92.19	0.1	4	0.89701
FE of 1.5 µ	Maximum	66.52	97.78	97.78	0.1	5	0.92644
Overall FE	Maximum	36.54	78.56	78.56	0.4	1	0.60133
Air permeability	Maximum	65	195	195	0.2	3	0.8473

Effect of input parameters on various properties of nanofibrous composite

Influence of process parameters on air permeability

The effect of process variables on air permeability is shown in Figure 5(a)–(c). It was observed that the lower electrospinning time, the higher concentration of NaOH and the higher treatment temperature result in higher air permeability due to lower nanofibre content, and more surface etching of composite by alkali conditions. While comparing the independent variables, the effect of concentration of NaOH is minimum on-air permeability then electrospinning time and treatment temperature. The increase in thickness of nanofibre composite due to higher electrospinning time results in lower air permeability. However, the higher concentration of NaOH and higher treatment temperature results in higher air permeability.

Figure 5.

(a)–(c) Influence of input parameters on the air permeability of surface-treated filters.

Influence of process parameters on filtration efficiency of 0.3 μm particles

The filtration efficiency for the particle size of 0.3 μm varies from 13.83% to 65.56%. The effect of process variables on the filtration efficiency of 0.3 μm particles is shown in Figure 6(a)–(c). In the case of filtration efficiency for 0.3 μm, higher electrospinning time, lower concentration of NaOH and temperature results in higher filtration efficiency. This implies that the lower concentration and temperature for the treated samples have a small pore diameter due to the swelling of nanofibers. Hence the surface roughness of the PA layer, nanofibers and random orientation of nanofibers can trap the smaller particles. In this case, due to the roughness of the surface of the filter and fibre, the probability of capturing 0.3 μm particles by Brownian motion is high.¹⁸

Figure 6.

(a)–(c) Influence of input parameters on the filtration efficiency of 0.3 μm particles of surface-treated filters.

Influence of process parameters on filtration efficiency of 1.0 μm particles

The filtration efficiency for the particle size of 1.0 μm varies from 53.12% to 92.19%. The effect of process variables on the filtration efficiency of 1.0 μm particles is shown in Figure 7(a)–(c). The electrospinning time influences more on filtration efficiency for the particles 1.0 μm due to higher deposition of electrospun fibres. 2% NaOH concentration is sufficient to enhance the surface roughness to obtain higher filtration efficiency. Hence, higher electrospinning time, lower temperature and concentration results in higher filtration efficiency. A higher concentration of NaOH results in bigger pores and more degradation of surface layers, it reduces the filtration efficiency.

Figure 7.

(a)–(c) Influence of input parameters on the filtration efficiency of 1.0 μm particles of surface-treated filters.

Influence of process parameters on filtration efficiency of 1.5 μm particles

The filtration efficiency for the particle size of 1.5 μm varies from 66.52% to 97.78%. The effect of process variables on the filtration efficiency of 1.5 μm particles is shown in Figure 8(a)–(c). It was observed that the particle size of 1.5 μm follows the same trend as 1.0 μm particles. However, the filtration efficiency is higher due to the larger particle size. The physical phenomenon involved in the particle collection of 1.5 μm is inertial impaction. This mechanism is responsible to capture particles of size greater than 0.3–1 μm.¹⁹

Figure 8.

(a)–(c) Influence of input parameters on the filtration efficiency of 1.5 μm particles of surface-treated filters.

Influence of process parameters on overall filtration efficiency

The overall filtration efficiency for the particles varies from 36.54% to 78.56%. The effect of process variables on overall filtration efficiency is shown in Figure 9(a)–(c). From the observations, in the case of overall filtration efficiency, the smaller pore size can be achieved due to higher electrospinning time and lower concentration of alkali used for treatment. This gives higher overall filtration efficiency. When the treatment temperature increases, it leads to degradation of the surface layer. Hence, a lower concentration of NaOH, higher electrospinning time and 80°C treatment temperature treated sample give higher filtration efficiency.

Figure 9.

(a)–(c) Influence of input parameters on the overall filtration efficiency of surface-treated filters.

Conclusion

Polyacrylonitrile nanofibre web was prepared by electrospinning and PA-6 coating solution was coated on the nanofibrous surface to develop a nanofibre composite. The nanofibrous composite was treated with different concentrations of alkaline and treatment temperature as per the Box Behnken experimental plan. The alkaline treated and control nanofiber membrane surface morphology was observed through the SEM images and FTIR analyses were also carried out. Due to the alkali treatment, the variation in surface morphology was observed, it also leads to change in various properties of the nanofibrous composite such as air permeability and overall filtration efficiency. The regression equations were derived and the effect of independent variables on various properties was graphically presented and discussed.

The variation of thickness was observed as 0.384–0.53 mm and the mass per unit area is varied from 62.5 to 83.33 g/cm². The air permeation level varies from 52.5 to 60 cm³/cm²/s for control samples and 65–195 cm³/cm²/s for treated samples. The overall filtration efficiency varies from 36.54% to 78.56%. Composite desirability values for all samples are derived based on air permeability and overall filtration efficiency and the best sample is identified. As per the composite desirability value, the combination of independent variables is identified. The 5% NaOH treated sample at 60^oC having the higher filtration efficiency of 78.56% is the best for air filtration.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

N Gobi

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Jiang

, et al. Green electrospun nanofibers and its application in air filtration. Macromol Mater Eng 2018; 303: 1800336.