Don't you have an account?

Register now

Welcome Back

Login your account

Email*

Password*

Forgot password

No problem!

Email*

Already have an account?

Login now

Register

Create an account

Title ( Miss/Mr/Dr … )

First Name *

Last Name *

Email*

Phone

Degree ( Ph.D, MD… )

Password*

Institution Related Information

Position

Institute

Department

Address

City

Zip Code

Country/Region *

Available as a Reviewer?

Areas of Interest or Expertise

Personal Classifications*

Personal Keywords

Privacy Policy

Our staff at sciparkpub.com and its affiliated companies worldwide as well as societies whose journals we publish, if applicable, will be contacting you concerning the publishing of your article and occasionally for marketing purposes.

Previews

Thank you

Confirm your email to activate your account Please follow the instructions in the email we have sent you. If you don’t receive an email within a few minutes, please check your spam folder.

Electrospun Nylon 6 Nanofibers for Oil/Water Separation

Home / Journals / Environmental Science / Journal of Climate Change Action

Research Article

Views 533
Downloads 8
Download PDF


Received: Jan. 05, 2024; Accepted: Jul. 14, 2024; Published Online: Jul. 27, 2024

Electrospun Nylon 6 Nanofibers for Oil/Water Separation

Faten Riad1, Hesham Ibrahim1, Moataz Soliman2, Shaker Ebrahim2, Azza Shokry2,*

1 Department of Environmental Studies, Institute of Graduate Studies and Research, Alexandria University, P.O. Box 832, Alexandria, Egypt

2 Department of Materials Science, Institute of Graduate Studies and Research, Alexandria University, P.O. Box 832, Alexandria, Egypt

https://doi.org/10.62184/jcca.jccaj100020241

https://creativecommons.org/licenses/by/4.0/



To cite this article

Riad, F., Ibrahim, H., Soliman, M., Ebrahim, S., & Shokry, A. (2024). Electrospun Nylon 6 Nanofibers for Oil/Water Separation. Journal of Climate Change Action, 1–11. https://doi.org/10.62184/jcca.jccaj100020241



Keywords

Nylon 6, Electrospinning, Nanofibers, Oil spill, Removal.



Abstract

Oil-water separation is a difficult process, and many reported materials have the drawbacks of low oil absorption which limit their application. Herein, we reported nylon 6 nanofibers prepared by the electrospinning process using formic acid. The nanofibers' surface morphology, crystallinity, hydrophobicity, and sorption capacity were studied. Morphological analysis of 30 wt % nylon 6 /formic acid demonstrated uniform nanofibers that are free from beads with an average diameter varying from 30 to 90 nm. The results revealed that the contact angle of nylon 6 nanofibers is observed as 61º which refers to the nanofibers being slightly hydrophilic. The optimal preparation process was determined by 30 wt % nylon 6 /formic acid concentration, a flow rate of 0.5 ml/hr, an applied voltage of 15 kV, an immersion time of 30 min and the oil absorption capacity was 85.38 g/g. The sorption capacity of nylon 6 nanofibers is higher than some other reported adsorbents making it a promising material for water purification.




1. Introduction

Oil is a class of pollutants with very low affinity to water. The thinnest layer of oil can affect the aquatic environment by decreasing both the penetration of light and the oxygen transfer between air and water leading to the death and deterioration of the aquatic organisms. Therefore, discharge limits for oil and grease are imposed by environmental law [1]. Current methods of controlling oil spills include chemical treatment [2], physical adsorption [3], skimming [4], using booms [5], and burning the oil on the surface of the water [6].

Among these different techniques, physical adsorption is considered to be an efficient and economical cleaning method in oil pollution treatment due to its easy manufacture, low production cost, environmental friendliness, high selectivity, and recyclability [7].Up to now, polymeric nanofibers have been used as oil absorbents due to their unique physical and mechanical properties, high surface area, and small pore sizes [7,8] expelling water due to their hydrophobic and oleophilic characteristics [9-11]. There are different techniques have been used to fabricate polymeric nanofibers such as template synthesis [12], phase separation [13], drawing [14], and electrospinning [15]. The electrospinning method is used to produce continuous fine nanofibers with inner diameters of 10 μm down to 10 nm by allowing a polymer solution or melts with an electrical driving force [16,17]. The advantages of this technique are the low cost, relative easiness, and high versatility by controlling the fiber diameter [18].

In the present work, we reported the fabrication of nylon 6 nanofibers through a low-cost and simple process by electrospinning technique for the adsorption of motor oil. The effects of different electrospinning parameters on the morphology of the nanofibers are studied. These nanofibers are morphologically and structurally characterized. The hydrophilicity and the oil sorption capacities of the prepared nylon 6 sorbent for motor oil are evaluated.

2. Experimental

2.1.  Materials

Nylon 6 granules grade of Tecomid NB40 NLE with a density of 1.13 g/ cm3 was obtained from Eurotec company (Turkey), formic acid (85%) with analytical grade was purchased from Elgomhoreya chemical company (Egypt), motor oil 600/700 with a density of 0.8825 g/ cm3 according to American Society for Testing and Materials (ASTM) 4052 and molecular weight 550 g/mol according to ASTM 2502 composed of hydrocarbons chain (-C40-) was obtained from Amoc company, Alexandria (Egypt).

2.2. Preparation of nylon 6 nanofiber

Electrospinning technique employed to synthesize the nylon6 nanofiber by means of a laboratory-scale electrospinning device. The device consists of 30 kV DC power supply (Hipotronics), a syringe pump (New Era Pump Systems, Inc., NY, USA) with a conducting tip needle, spinneret, and collector plate grounded and separated from the spinneret by a defined distance. The nylon6 solution containing different amounts of nylon6/formic acid (10,20 and 30 wt%) was then electrospun using the syringe pump with a 0.5 mm diameter needle tip at a feeding rate varied from 0.2 to 1ml/hr. The applied working voltage from the DC high voltage power supply (DC-PS) varied from 5 to 20 kV, as explained later. The distance between the syringe (spinneret) tip and the collector plate was 5 cm. The collector plate was grounded and covered by aluminum foil, and the syringe needle was fastened to the positive electrode of the DC-PS before use.

2.3. Characterization of nylon 6 nanofiber

The chemical interactions and surface modification of nylon 6 nanofiber were confirmed by Fourier-transform infrared (FTIR) spectroscopy (Spectrum BX 11- LX 18–5255 Perkin Elmer). The spectra were recorded in the spectral range from 4,000 to 500 cm−1. The morphologies of the electrospun nanocomposites were assessed by scanning electron microscope (SEM) (Joel JSM 5300, Japan). The crystalline structure was evaluated by X-ray 7000 Shimadzu-Japan. The contact angle of water droplets was measured on the Rame-Hart contact angle goniometer (Rame-Hart Instrument Company, France).

2.4. Oil sorption experiments

Nylon 6 nanofibers obtained by electrospinning technique at various preparation conditions were tested for their performance in the sorption of crude oil spills. The nanofibers were cut into square pieces, dried at 70 Co for 1 hr, vacuumed for 2 hrs, and weighed. The samples were then immersed in 10 mL of motor oil. After various time intervals of up to 30 min, the mass of each sample was measured as a function of time [19]. The oil sorption capacity (Q, g/g) was calculated as follows [20]:


3. Results and discussion

3.1.  Structural analysis

FTIR spectra of nylon 6 and nylon 6 nanofiber are displayed in Figure 1 (a and b). The main characteristic bands of nylon 6 (Figure 1a) observed at 3304, 2856, 2940, 1646, 1544, 690, and 578 cm-1 are assigned to N-H stretching, CH2 stretching, CH2 stretching, amide I stretching, amide II due to carbonyl stretching, C-C bending and C-C deformation respectively [21,22]. Nylon 6 nanofiber shown in Figure 1b has similar bands of nylon 6 film, the transmittance bands observed at 2374 and 1746 cm-1 correspond to O-H and C=O refers to formic acid groups [23].

Figure 1. FTIR spectra of (a) nylon 6 and (b) nylon 6 nanofiber.

The crystalline structure of nylon 6 powder and nanofiber are shown in Figure 2 (a and b). The XRD pattern of nylon 6 film (Figure 2a) exhibits two sharp peaks at 2θ=20.5º and 2θ = 24.5º corresponding to the characteristic of the α- phase. By calculating the crystal size from the Scherrer equation, the crystal size is 3.425 nm. However, the diffraction pattern of nylon 6 nanofiber (Figure 2b) displays two smaller peaks at 2θ =20.3º and 2θ = 23.6º. The formation of small and/or defective crystals is due to the rapid vaporization of the solvent during the electrospinning process which does not allow sufficient time for the ordering of the molecules [24]. Electrospinning could also result in the formation of γ-crystalline structure for nylon 6, where the formation of γ -crystalline structures requires a rapid crystallization rate and this suggests that nylon 6 crystallization was rapid [25].

Figure 2XRD patterns of (a) nylon 6 and (b) nylon 6 nanofiber.

3.2.  Morphological analysis of nylon 6 nanofiber at different conditions

3.2.1. Effect of solution concentration

The SEM micrographs of nylon 6 nanofibers made of different concentrations of nylon 6/ formic acid wt % solutions and their diameter range distributions are presented in Figure 3. It is observed that the solution of 10 wt % did not produce nanofibers. Rather the electrospraying occurs as shown in Figure 3a with the production of beads or droplets falling on the collector target. This was reported owing to the low viscosity and high surface tensions of the solution. When an electric field is applied to any droplet, the electric charge generates an electrostatic force inside the droplet, known as the Coulomb force, which competes with the cohesive force intrinsic to the droplet [26]. When the applied Coulomb force can overcome the cohesive force of the droplet manifested in the surface tension, the droplet will undergo break up into smaller droplets in the micro- to nano-scales. This phenomenon begins at the Taylor Cone, referring to the progressive shrinkage of the unstable, charged macro-droplet into a cone from which the smaller charged droplets will be ejected as soon as the surface tension is overcome by the Coulomb force [27].

At 20 wt% nylon 6 solution (Figure 3b), the amount of the fiber increases but still contains a lot of beads. The nanofibers produced are associated with beads due to the instability of the jet under different process conditions. Beads are expected to form at times during electrospinning whenever the surface tension forces tend to overcome the forces (such as charge repulsion and viscoelastic forces) that favor the elongation of a continuous jet. This is consistent with the observation that electrospinning dilute solutions of polymers, where chain entanglement is limited, tend to result in bead formation. With the polymer solutions electrospun at a fixed electric field, some beading is invariably obtained in the critical concentration regime where the transition from electrospraying of droplets into electrospinning occurs. This is related to incipient chain entanglement gradually overcoming the surface tension forces at higher polymer concentrations.

On the other hand, at 30 wt % nylon 6 solutions, the nanofibers formed were free from the beads which formed as a thin layer as shown in Figure 3c. Thirty measurements were conducted to analyze the average diameter for using software Digimizer. A trace of fibers produced from nylon 6 nanofiber from 10 wt % in the range from 10 to 30 nm (Figure 3d). For a concentration of 20 wt % solution, the average diameters are in the range from 10 to 60 nm and the dominant diameter is in range of 30 to 40 nm (Figure 3e).  The average fiber diameter of the nylon 6 nanofiber electrospun from 30 wt % solutions is much bigger than from a 20 wt % solution, as it is ranged from 30 to 90 nm, and the dominant diameter, is in range of 40 to 50 nm (Figure 3f).

When the concentration is suitable, smooth homogeneous sheet nanofibers can be obtained [28]. For a concentration of 40 wt % nylon 6, the solution was dried very quickly when exposed to air due to the evaporation of formic acid which leads to the clogging of the syringe and prevents pumping. Consequently, the 30 wt % solution is considered the optimum concentration for the electrospinning of nylon 6.

Figure 4 (a and b) show two photographs of nanofibers formed from electrospray of 10 and 30 wt % of nylon 6, respectively.

Figure 3. SEM micrographs of (a) the beaded structures obtained at concentration of 10 wt% (b) the nonbeaded structures obtained at 20 wt % and (c) 30 wt %, and nanofiber diameter range distribution from SEM images of structures obtained at concentration of (d) 10 wt %, (e) 20 wt % and (f) 30 wt % of nylon 6 nanofibers at constant applied voltage of 15 kV.