Separation of Water from Ultralow Sulfur Diesel ... - ACS Publications

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Separation of water from ultra-low sulphur diesel using novel polymer nanofiber-coated glass fiber media Stuti Rajgarhia, Sadhan C Jana, and George G. Chase ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b07364 • Publication Date (Web): 03 Aug 2016 Downloaded from http://pubs.acs.org on August 7, 2016

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ACS Applied Materials & Interfaces

Separation of water from ultra-low sulphur diesel using novel polymer nanofiber-coated glass fiber media Stuti S. Rajgarhia 1, § and Sadhan C Jana 1* and George G Chase 2 1 2

Department of Polymer Engineering, University of Akron, Akron, OH 44325

Department of Chemical and Biomolecular Engineering, University of Akron, Akron, OH 44325 §

Currently at Donaldson Company, Corporate Technology, Bloomington, Minnesota *Corresponding author email: [email protected]

Abstract: Polymer nanofibers with interpenetrating network (IPN) morphology are used in this work for development of composite, hydrophobic filter media in conjunction with glass fibers for removal of water droplets from ultra-low sulphur diesel (ULSD). The nanofibers are produced from hydrophobic polyvinyl acetate (PVAc) and hydrophilic polyvinyl pyrrolidone (PVP) by spinning the polymer solutions using gas jet fiber (GJF) method. The nanofibers coat the individual glass fibers due to polar-polar interactions during the spinning process and render the filter media highly hydrophobic with water contact angle approaching 150°. The efficiency of the

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resultant filter media is evaluated in terms of separation of water droplets of average size 20 µm from the suspensions in ULSD.

Keywords: hydrophobic and hydrophilic polymers; interpenetrating network morphology; coalescing filtration; nanofibers; coating. Introduction Separation of finely dispersed minor phase immiscible liquids is an important step in wastewater treatment1,2 and in efficient burning of diesel fuels in engines3, and therefore has great implications on human health and maintaining cleaner environment. Specifically, the presence of suspended water droplets in diesel fuels can have detrimental effects on engine performance as water can promote microbial growth and form acids by reacting with the chemicals present in the fuel leading to corrosion of fuel system parts, plugging of the orifices and filters, thereby reducing the life of fuel injection systems3–5. Poor engine performance results in emissions that exceed the limits set forth by the United States Environmental Protection Agency (EPA) for diesel engines4,5. High emissions of pollutants adversely affect human health and the environment due to the presence of particulate matters, oxides of nitrogen, carbon monoxide and incompletely combusted hydrocarbons6–9. The advanced emission control systems have less tolerance for sulphur in diesel fuels5,10. Consequently, regulatory agencies demand low sulphur content diesel fuels4,11. Ultra-low sulphur diesel (ULSD) is the hydro-sulfurized petroleum fraction that also has less heteroatoms and conjugated aromatic compounds. However, ULSD loses its lubricity because of the removal of the aromatic compounds3,5,12,13. The lubricity is maintained by adding synthetic lubricant additives, which in turn act as surfactants and reduce the interfacial tension between the fuel and suspended water droplets. This makes separation of 2


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the emulsified water droplets more difficult as the droplets are stable in the fuel at small sizes, ~20 µm3,5,13.

Water in diesel fuel originates from precipitation, humidity, and condensation of atmospheric moisture5,14 and exists as free water, emulsified water, and dissolved water. The free water is typically separated by gravity settling4,5,14,15 while dissolved water is removed by distillation. The emulsified water as droplets of sizes less than 100 µm are removed using coalescing filters16,17. During coalescence, two small droplets merge into a bigger droplet by overcoming the surface tension force. Coalescing filter media are commonly formed of glass, metal, or polymer fibers with hydrophilic surface properties that promote attachment of water drops onto the fiber surfaces. The coalesced drops are dragged through the filter media by the pressure-driven flow of the emulsions and finally settle out in the downstream section of the filter media. The resultant liquid holdup in the filter media causes an increase of the pressure drop and a reduction of permeability of the filter. The mechanical integrity of water droplets in ULSD may be poor as the synthetic additives can reduce the interfacial tension. Consequently, coalesced water droplets deform during the flow of diesel through the filter media, and can break due to shear at high flow rates thus producing little or no net increase in drop size under some operating conditions4,18,19. Hydrophobic filter media are also not efficient in removing water from ULSD. In this case, water droplets coalescing upstream into larger drops are rejected. Some other water droplets are easily deformed and squeezed due to weak interfacial tension between water and diesel and pass through the pores of the filter media upstream especially if the drops are smaller than or about the same size of the pores of the filter media4.

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The separation efficiencies of coalescing filter media depend on the properties of the dispersion and the fiber bed. The fiber bed properties include the diameter of the fibers, the volume of the filter, the orientation of the fibers, and the wetting properties of the filter media18,20–22. The surface tension of the liquid and the flow rate of emulsion through the filter are also important parameters. Separation efficiency (E) of the filter media is a measure of the separation performance of the filter. It is calculated by the expression23 E=

(1)

In equation (1), Cin is the mass concentration of water upstream of the filter and Cout is the outlet mass concentration of water. The mass concentrations are calculated from droplet size distribution data by the expression =

Ʃ

(2)

where Ci (i=in, out) is the mass of water per unit volume of ULSD, Ni is the number of water drops of diameter di per unit volume, and ρ is the density of water. The overall performance of the filter media can be represented by a lumped parameter such as the quality factor24 figure of merit21 (QF) or filtration index25 (FI) that takes into account the separation efficiency and the pressure drop (∆P) across the filter media as given by =

() ∆

(3)

The aim of the filtration industry is to fabricate filters with higher filtration efficiency and lower pressure drop, which implies that filter media with higher FI are desired.

The fiber surface wettability influences the performance of filters in water-oil separation. The wettability of a flat surface is inferred from the value of contact angle. A surface is considered 4


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hydrophilic if the liquid contact angle is less than 90° and hydrophobic when the contact angle is greater than 90°. Superhydrophobic surfaces with water contact angle 150° or greater usually have rough structures with micro-or nanoscale asperities

26–28

and produce higher water contact

angle either due to homogeneous or heterogeneous wetting29,30. Glass fibers coated with different surface energy silanes show better performance in separation of water from oil than uncoated glass fibers15,31,32. The addition of sub-micrometer size polystyrene or polymeric nanofibers into glass fibers improve oil droplet capture efficiency due to changes in wetting characteristics14,24,33. Layered filter media based on alternate layers of hydrophilic and hydrophobic components produce different wettability values and produce better filter performance in oil-water filtration compared to micrometer size glass fibers23. A number of superhydrophobic materials were found useful in water-oil separation such as stainless steel meshes coated with fluorinated compounds34, carbon nanotube meshes35,

microphase-separated rough surfaces36, and filter

papers produced from porous films and polytetrafluoroethylene (PTFE) nanoparticles37. Polyvinylidenefluoride (PVDF) films fabricated using a solvent-induced phase inversion process are also used in separation of water from emulsion in oil 38. Table S1 summarizes the studies to date on oil-water separation.

In this study, filter media with water contact angles close to 150° were prepared and their performances in separation of water suspended in ULSD were evaluated. The effective filter media were prepared by coating glass fibers with nanofibers of interpenetrating network (IPN)39 morphologies. IPN nanofibers were produced by spinning homogeneous solutions of two immiscible polymers polyvinyl acetate (PVAC) and polyvinyl pyrrolidone (PVP) and two mutually miscible solvents chlorobenzene and 1-butanol using gas jet fiber process (GJF)39–42 . 5



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The nanofibers of IPN morphology have co-continuous PVAc and PVP domains present with characteristic domain dimensions less than 10 nm. Figure 1 presents a schematic of how the polymers are intermingled with each other in the same nanofiber. The cross-section of the nanofibers sliced along the plane P1 show random placement of the polymer domains in the cross-sectional area. This shows the fiber surfaces in some places had the hydrophobic properties of PVAc and in other places the hydrophilic properties of PVP.

P1

P1

Figure 1: Schematic of interpenetrating network (IPN) morphology formed by two polymer domains. In the GJF process39–42 shown schematically in Figure 2, the polymer solutions were extruded via a syringe pump through a single nozzle into a rapidly thinning liquid jet due to stretching by the high velocity gas jet. Solid fibers were formed as the solvents evaporated. In this work, PVP and PVAc formed phase separated domains due to evaporation of the solvents39.

Syringe pump Needle tip nozzle Solidification

Liquid jet stretching

Fiber mat

6

Gas jet Gas flow meter

Pressure regulator

Collector box

Figure 2. ACS Schematic of Plus the GJF process. Paragon Environment

Compressor

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Experimental Section Materials PVAc (Mw=500,000 g/mol) and PVP (Mw=1,300,000 g/mol) were used as the hydrophobic and hydrophilic polymers respectively and were purchased from Sigma Aldrich along with the solvents chlorobenzene and 1-butanol. B-glass fibers with an average diameter of 6 µm were obtained from Hollingsworth and Vose Company (Walpole, MA).

Filter media preparation It was recognized that the filter media could not be fabricated based only on nanofibers. Nanofiber mats by themselves do not have sufficient mechanical strength to sustain high flow rates of ULSD emulsions in the filtration test setup. In view of this, glass fiber mats were used to impart mechanical integrity and to support the nanofibers, while the nanofibers of IPN morphology served as the active surfaces promoting coalescence of water droplets from the emulsions. We note that glass fibers also contribute as a coalescing medium. In view of this, glass fiber mats without the nanofibers were used in this work to obtain reference data.

Spinning nanofibers on glass fiber mats by the GJF process The polymer nanofibers were deposited onto glass fiber mats by spinning the polymer solutions of 5 wt. % PVP and PVAc with PVP and PVAc in a pre-defined ratio by weight (Table 1). The polymer solutions were prepared in a mutually miscible solvent pair, 1-butanol and 7



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chlorobenzene. Clear, homogeneous polymer solutions were prepared at room temperature by dissolving the polymers in the solvent mixture over a period of half an hour in a THINKY® mixer. The glass fiber mats of desired dimensions were attached onto a wire-mesh collector and the nanofibers were spun onto the glass fiber mats by spinning the homogeneous polymer solutions using the GJF process39–42. The temperature and the relative humidity during spinning were maintained at respectively 23-26°C and 16-23%, as listed in Table 1. The glass matnanofiber media were prepared by spinning 60 mL of polymer solutions over a period of 2 hours. A blunted needle-tip nozzle manufactured by Jensen Global Inc. with internal diameter 0.8 mm was used for the delivery of polymer solutions. Compressed air passed through a rigid pipe of internal diameter 5.5 mm to establish the gas jet. Other experimental parameters were as follows, solution flow rate ~ 0.5 mL/min, air pressure ~20 psi, and the distance between the needle-tip nozzle and the exit of the compressed air ~ 2 cm. A more detailed description of the GJF process is presented elsewhere39–42. Table 1 lists the weight fractions of nanofibers in the filter media.

Table 1. Spinning temperature, relative humidity, and weight fraction of nanofibers added onto glass fibers. Weight ratio, PVAc/PVP

Temperature (°C)

1:1 2:1 1:2 1:0 (Only PVAc) 0:1 (Only PVP)

23 24 26 23 23

Relative humidity (%) 16 21 21 23 22

8


Weight fraction of nanofibers in the filter media 0.01±0.0008 0.01±0.001 0.008±0.0003 0.003±5.06×10-5 No measurement

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Characterization of nanofibers and filter media Nanofiber diameter and morphology The morphologies of the nanofibers were studied using transmission electron microscope (TEM) images. The fiber samples collected on 300-mesh copper grids were imaged using a JEOL 1230 microscope. The average fiber diameters were obtained from the analysis of scanning electron microscope (SEM) images of representative fiber samples. SEM model JEOL JSM5310 under accelerating voltage of 5-10 kV and emission current of 20 mA was used to capture the SEM images. The fiber diameter distributions were determined using Fiber Quant 1.3 software (nanoScaffold Technologies LLC). SEM and AFM (Dimension, ICON, Veeco) were used to characterize the surface morphologies of the nanofibers once coated onto glass fibers.

Porosity and contact angle of filter media Porosity () was calculated using skeletal density (ρs) and bulk density (ρb) as in equation (4). The values of skeletal densities were obtained using a helium pycnometer (AccuPyc II 1340, Micromeritics Instrument Corporation GA) and the bulk densities were calculated from the mass and volume of the filter media. = 1 −

!

"

# × 100

(4)

A sessile drop method was used to measure water contact angle on filter media using a RameHart goniometer model 100 at ambient condition of temperature, 22 ± 2°C.

Coalescing filtration experiments Filtration experiments were performed using deionized water dispersed finely in ULSD. ULSD and 0.2% (by volume) water were mixed for 10 minutes using an impeller and subsequently 9



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pumped into a recycle flow loop (Figure 3) to generate a dispersion of fine water droplets with mean diameter 20 µm. Figure 3 presents the flow diagram showing sampling points positioned upstream and downstream and split flow of ULSD into a recycled stream and a stream directed to the filter medium. Recycling stream

Pressure transducer

ULSD+ water

Pump

Sample holder Upstream sample

Downstream sample

Figure 3: Schematic of the ULSD-water separation experiment. The size distributions of water droplets in the upstream flow and downstream flow were obtained using a particle counter, Accusizer 780, PALS -Particle Sizing Systems (Florida, United States). The pressure drops across the filter media were measured using an electronic pressure gauge with pressure taps positioned upstream and downstream of the filter medium. The flow rates of the dispersions during the experiments were maintained at 210 mL/min and the corresponding filter face velocities were 2 cm/min. All measurements were performed in triplicate.

Results and Discussion Morphology and diameter of nanofibers The TEM images in Figure 4 and SEM images in Figure 5 show that the nanofibers were of average diameters 246 ± 70 nm and 280 ±82 nm obtained respectively from spinning of 10


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homogeneous solutions with 1:1 and 2:1 wt/wt ratios of PVAc and PVP in chlorobenzene and 1butanol. The PVP domains should appear darker in TEM images due to higher electron density compared to PVAc. The resolution of JEOL 1230 microscope used in imaging is greater than 10 nm. One can infer that the images in Figures 4 (a, b) show no electron density difference along the length of the fiber. This implies that the domains of PVP and PVAc were present in these fibers at length scales smaller than 10 nm. We refer to such nanofibers as having interpenetrating morphology, schematically depicted in Figure 1. We verified such morphology using water dissolution test. For this purpose, non-woven nanofiber mats of size 1 cm×1 cm weighing a few tens of milligrams were kept in 20 mL deionized water at room temperature for 6 hours and their weight loss was recorded after drying in a vacuum oven at 60 °C for 6 hours. The average weight loss based on three specimens was less than 10 wt%, although PVP was present at 50 wt% in the nanofibers. This indicates that only a small fraction of the original PVP dissolved in water. This low value indicates that the PVP domains in the fibers were not easily accessible by water and that hydrophobic PVAc domains present at a scale smaller than 10 nm deterred penetration of water into single nanofibers and thus prevented dissolution of the PVP phase.

Figure 5(c) presents SEM images of fibers obtained from polymer solutions with 1:2 wt/wt ratio of PVAc/PVP. It is evident that these nanofibers contained significant fractions of beads. The fibrillar fractions, however, had an average diameter 296 ± 72 nm.

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(a)

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(b)

100 nm

200 nm

Figure 4: TEM images of nanofibers produced from blends of PVAc and PVP in weight ratios (a) 1:1 and (b) 2:1.

(a)

(b)

1 μm

10 μm

(c)

10 μm

Figure 5: SEM image of nanofibers produced from PVAc and PVP in weight ratios (a) 1:1, (b) 2:1, and (c) 1:2.

Morphology of filter media 12


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Figures 6a and 6b show SEM images of bulk quantities of nanofibers with 1:1 wt/wt ratios of PVAc/PVP and glass fibers respectively. The image in Figure 6(c) clearly indicates that the polymer nanofibers adhered well onto the glass fibers. It is noted here that typical diameters of glass fibers and nanofibers were respectively 6 µm and ~300 nm. Higher magnification images in Figure 6(d-e) show thin sheet-like coatings of the nanofibers on the glass fibers. Recall that the fiber collection distance from the liquid nozzle exit was the same in each case and that the nanofibers were dry before they arrived at the collector. In view of this, we discount the possibility that the sheet-like nanofiber coatings on glass fibers seen in Figure 6(d-e) originated from spraying of the liquid jet onto glass fiber surfaces. Instead, we attribute the formation of sheet-like coating on glass fibers to polar-polar interactions between the surface functional groups on glass fibers and the PVP component of the nanofibers.

The polar functional groups on glass fiber surfaces quite possibly originated from the chemical sizing agents. X-ray photo-electron spectroscopy (XPS) was performed to determine the nature of polar functional groups present on glass fibers. Atomic spectra obtained from XPS show the presence of various elements (Figure S1a and Table 2). High resolution XPS of C1s and O1s peaks and their curve fitting established the presence of various functional groups, such as hydroxyl, carbonyl, isocyanate, and esters on glass fiber surfaces as presented in Figure S1b and S1c.

The role of polar-polar interactions on nanofiber adhesion onto glass fiber surfaces was further verified by spinning the nanofibers of PVP and PVAc onto glass fibers. The images in Figure 6(c-e) and Figure 7(a) show that nanofibers of both PVP and PVAc/PVP blend adhered 13



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onto glass fibers, but PVAc nanofibers did not form coating layers on glass fibers as seen in Figure 7(b) due to non-polar nature of PVAc. The total surface energy (γ) of a material is the sum of the dispersive (γd) and polar (γp) components where γd represents the surface energy of non-polar interactions sites and γp represents the surface energy of polar interactions sites. Lee et. al43 reported the total surface energy γ for PVP is 48.4 mJ/m2 with γd eqauls to 5.1 mJ/m2 and γp equals to 43.3 mJ/m2. In comparison, the total surface energy of PVAc is 42.8 mJ/m2 with γd equals to 27.4 mJ/m2 and γp equals to 15.4 mJ/ m2 44.

(a)

10 µm

(b)

(c)

100 µm

(d)

(e)

10 µm

1 μm

10 µm

Figure 6: SEM images of (a) 1:1 wt/wt PVAc/PVP nanofibers, (b) glass fibers, (c) 1:1 wt/wt PVAc/PVP nanofibers spun onto glass fibers (Filter C), (d) High magnification image of (c) showing nanofibers adhered onto a glass fiber, (e) sheet composed of nanofibers adhered onto glass fiber.

14


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Table 2: The atomic percentage of various elements in the sizing agent of glass fibers obtained from XPS data. Elements Si

Atomic % 10.1

Weight % 18.80

C

53.3

42.53

O

35.3

37.55

N

1.2

1.12

(a)

(b)

10 µm

10 µm

Figure 7: SEM images of polymer nanofibers spun onto glass fibers. (a) PVP nanofibers, (b) PVAc nanofibers.

Prior research reports on separation of water from ULSD considered hydrophobic materials in the form of coatings of silanes on the glass fibers15,31,32, addition of hydrophobic poly(styrene) fibers into hydrophilic fiber media14,24,33, or stacking of alternate layers of hydrophobic and hydrophilic components23. In the present work, however, the IPN nanofibers contained both the hydrophobic and hydrophilic polymers in single strands of nanofibers. The nanofiber coating

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layers seen in Figure 6(c-e), therefore, obviated the need for secondary incorporation method of the hydrophobic materials.

Contact angle and porosity of filter media Five different filter media specimens (Filter A-E, Table 3) were prepared for evaluation of ULSD-water separation performance. The values of water contact angles and porosities of these filter media are listed in Table 3. The glass fiber mats (Filter A) without nanofibers were hydrophilic with water contact angles of 9° while the water contact angle on PVAc-glass fiber composite (Filter B) was 131° indicating that the addition of PVAc rendered the fiber mat hydrophobic. The IPN nanofibers, with significant content of hydrophilic polymer PVP, in Filter C and Filter D, however, produced highly hydrophobic surfaces with water contact angles greater than 140°. The material in Filter C provided water contact angles of ~147°, rendering this material close to superhydrophobic in nature. The data in Table 3 show all five filter media had comparable porosities in the range of 96%-97%. Water contact angles on Filter E were not measured. In this case, the hydrophilic PVP polymer produced strong capillary action and the test water droplets were absorbed rapidly by the filter media. Table 3: Water contact angles and porosities of filter media based on nanofibers with different weight ratios of PVAc and PVP. Filter media

Composition

A B

Glass fibers PVAc fibers deposited onto glass fibers 1:1 wt/wt PVAc/PVP nanofibers onto glass fibers

C

Contact angle of filter media (degree) 9 ±1 131. 4±2

Porosity

146.6±1

96.5%

16


97.1% 96.8%

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D

E

2:1 wt/wt PVAc/PVP nanofibers onto glass fibers 1:2 wt/wt PVAc/PVP nanofibers onto glass fibers

142.1±2

96.3%

Could not measure; high capillary force

96.5%

Evaluation of performance of the filter media The fiber mats made up of only the glass fibers (Filter A) were used as the control material. All filtration tests were conducted at the liquid flow rates of 210 mL/min and face velocities of 20 mm/min. The values of separation efficiencies, pressure drops, and the Filtration Indexes of filter media are presented in Table 4. We see that the efficiencies of Filter C were almost twice as much as Filter A. The FI of Filter C was 3.05±0.06 1/kPa compared with a value of 0.74±0.02 1/kPa for Filter A. We attribute such increase in filter media performance to close to super hydrophobic nature of the media surfaces contributed by the coating layers of IPN nanofibers.

A question arises about the role of the hydrophobic PVAc component in the nanofibers. To understand this, we changed the ratios of PVAc and PVP contents in the nanofibers to 2:1 (Filter D) and 1:2 (Filter E). From the data listed in Table 4, we infer that the performance of Filter D and Filter E were much higher than that of Filter A but lower than that of Filter C. We see a direct correlation between the wettability and the performance of the filter media. For example, the filtration performance was higher for filter media with larger water contact angle values. It is still not clear why the contact angle values and the wettability were different when different ratios of PVAc and PVP were used. SEM and AFM images were examined to obtain an insight.

Table 4: Filtration efficiencies, pressure drops, and Filtration Indexes of filter media. 17



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Filter media

Glass fibers (Filter A) PVAc onto glass fibers (Filter B) 1:1 PVAc/PVP onto glass fibers (Filter C) 2:1 PVAc/PVP onto glass fibers (Filter D) 1:2 PVAc/PVP onto glass fibers (Filter E)

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Filtration efficiency (%) 48.5±0.8

Pressure drop (kPa)

Filtration Index (1/kPa)

0.896

0.74±0.02

81.8±1.2

0.919± 0.04

1.86±0.08

96.6±0.2

1.1

3.05±0.06

95.3±0.2

1.448

2.11±0.02

64.5±0.2

0.827

1.25±0.01

SEM images in Figure 8 (a, b) show that the nanofibers in Filter D also adhered onto the glass fiber surfaces. In this case, the individual nanofibers were seen adhering onto glass fibers without forming a thin sheet as seen in the case of nanofibers obtained from 1:1 PVAc/PVP system. We attribute this to smaller proportions of PVP. In the case of Filter E, the beaded nanofibers were seen adhered onto the glass fiber surfaces as shown in Figure 8c. The polar-polar interactions were highest in this case due to presence of higher fractions of PVP on the nanofiber surfaces to interact with the functional groups of the sizing agents on the surfaces of glass fiber mats.

a)

b)

100 µm

1 µm

c)

d) 18

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Figure 8: SEM images of (a-b) 2:1 wt /wt ratios of PVAc/PVP nanofibers on glass fibers, (c-d) 1:2 wt/wt ratios of PVAc/PVP nanofibers on glass fibers. Filter C and D were analyzed using AFM to determine the roughness of the filter media which in turn would affect the wettability. Figure 9 (a, b) show the height plots and Figure 9 (c, d) the phase plots obtained from AFM. The height plots showed variations in the thickness of the filter media on a scale of a few micrometers. The phase plots showed sheet-like structures of the polymer nanofibers formed onto the glass fibers in the case of 1:1 wt ratios of PVP and PVAc whereas in the case of 2:1 wt ratios of PVP and PVAc, the nanofibers adhered onto the glass surface but did not form sheet-like coating layers. The line cut of the height plots gives information about the roughness of the filter media. Figure 10 shows that the roughness was higher in the case of Filter C in comparison to Filter D. These microstructures on the glass fibers yielded higher water contact angle values compared to nanofibers alone (seen in Table 5). We attribute lower contact angle values in the case of 2:1 PVP/PVAc nanofibers to its lower surface roughness.

Table 5: Contact angles of 1:1 IPN nanofiber filter media comprising of 1:1 and 2:1 IPN nanofibers 19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Different nanofiber systems 1:1 IPN nanofibers 1:1 IPN nanofibers onto glass fibers (Filter C) 2:1 IPN nanofibers onto glass fibers (Filter D)

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Contact angles of filter media (degree) 123.6±1 146.6±1 142.1±2

b)

a)

c)

d)

Figure 9: AFM images. Height plots of (a) Filter C and (b) Filter D and phase plots of (c) Filter C and (d) Filter D.

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Filter C Filter D Roughness, µm

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Distance along the plane, µ Figure 10: Roughness profiles of filter media Filter C and Filter D.

Conclusions The data presented in this paper establish that nanofibers of IPN morphology containing a hydrophobic polymer (PVAc) and a hydrophilic polymer (PVP) can easily coat and form thin sheets of polymer nanofibers around the glass fibers although no such coating is observed for only the hydrophobic polymer nanofibers. The sheet-like nanofiber coating originated from the polar-polar interactions between the functional groups on glass fibers and the hydrophilic polymer present in the nanofibers. The sheet-like coatings of the IPN nanofibers on glass fibers rendered the filter media highly hydrophobic with surface roughness of the order of a few micrometers and water contacts angle close to 150°. The increase in hydrophobicity leads to higher separation efficiencies and higher filter index values for separation of water droplets from

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ULSD. The filter index of the composite filter media reach values as high as 3.05 (1/kPa) compared to 0.74(1/kPa) for filter media comprising of only the glass fibers.

Supporting Information. Observations from prior work on media for water-oil separation and glass fiber XPS data supplied as Supporting Information.

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Separation Of Water From Ultra-low Sulphur Diesel Using Novel Polymer Nanofiber-coated Glass Fiber Media Stuti S. Rajgarhia, Sadhan C. Jana, George G. Chase

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Separation of Water from Ultralow Sulfur Diesel ... - ACS Publications

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