Recycling waste plastics by ‘Electrospinning’

Key words: electrospinning, oily-wastewater, polystyrene, recycling, water remediation

Since the beginning of polymer production from petrochemical sources, the production and

consumption of plastics has increased. Polystyrene (PS) foam is a widely used polymer for insulation

and packing materials. Unfortunately, PS foam waste is generally discarded after one use and poses

a serious problem due to volume it occupies within landfills. Incineration of PS is not an appropriate

approach for the waste management, meaning alternative methods for polymer waste disposal are

desirable 1.

Polystyrene electrospun nanofibrous membranes

Recently, electrospun nanofibrous membranes have gained a great attention due to their high

surface area, diversified morphology (shape), and durability. The interconnected webs and porosity

of electrospun fibres (think cotton wool with thinner fibres) create a suitable material structure for

the filtration and adsorption applications 2-4. Electrospinning is as an efficient method that has been

recognised for the fabrication of continuous polymer fibres with diameters down to a few

nanometres (1 nm = 1 x 109 m). When the diameters of fibre materials decrease from micrometres to

nanometres, several characteristics show up:

very large surface area to volume ratio,

flexibility

good mechanical performance 5.

In a typical electrospinning set up, there are three basic components: a high voltage supplier, syringe

pump with a conductive needle, and a metal-grounded collector (Figure 1).

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Figure 1. Diagram of electrospinning set up 1.

The polymer solution is pumped through the needle, which serves as an electrode, and a high

voltage is applied to create charged jet on the tip of the needle. Generally, a high electric field of 1.0

– 5.0 kV cm-1 is applied and the tip to collector distance is between 10 – 25 cm. The current ranges

from a few hundred nanoamperes to microamperes. Once the electrospun fibre has landed on the

earthed collector 6 the solvent evaporates and the polymer solidifies. When electrospinning is

completed the fibres look a bit like candy floss. Not all polymers create the fibre network,

polyvinylalcohol (PVA), for example, just forms a thin homogeneous layer on the collector.

Nanofibre property adjustments

The properties of the polymer solution (concentration, viscosity, solvent vapour pressure, and

surface tension) have the biggest influence on the morphology of the fibres during the

electrospinning. Figure 2 shows the surface texture of polystyrene (PS) fibres with respect to

polymer solution concentration and solvent composition. The solvents used are THF (Figure 3a) and

DMF (Figure 3b). DMF refers to N,N- dimethylformamide (N,N-dimethylmethanamide) and THF

refers to tetrahydrofuran (oxacyclopentane). The polymer solution concentration, and the difference

between the vapour pressure of DMF and THF results in different surface textures (smooth,

wrinkled, beads on string, ribbon shaped fibres or polymer cups) on PS fibres7.

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Figure 2. Dependence of the surface texture on DMF:THF composition versus PS solution concentration 1.

Figure 3. Molecular structures of (a) THF 8 and (b) DMF 9.

Fibrous polystyrene – can it be used in water remediation?

Water pollution is a huge global problem and its significance is increasing gradually due to

anthropogenic (human) activities releasing many substances such as oils into water sources. Reusing

the waste polymers (like PS wastes) as oil adsorbents from wastewaters is a promising approach

from the environmental point of view.

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The investigation

We tried to use these surface-tailored electrospun fibres for the remediation of oily-wastewaters.

Figure 4. Photographic image of water and oil droplets on a piece of (a) PS foam waste before

electrospinning and (b) PS fibres after electrospinning. Photographs of oil-water mixture (c) before

immersing the fibre in solution, (d) during the fibre application and (e) after the oil adsorption by

fibre1.

The photographs in Figure 4(a-b) show the oil (red) and water (blue) droplets on the PS waste before

electrospinning and the fibres fabricated after electrospinning, respectively. It is clearly seen that red

oil droplet quickly wets the surface of fibres while the same volume of oil droplet stays on the

surface of the PS without being adsorbed. In addition, the blue water droplet stays on the fibre

surface in a nearly round shape whilst it spreads out and wets on the surface of the PS. Moreover,

Figure 4(c-e) indicates that oil can be removed from the water through immersing the fibrous PS into

the solution, the red oil adsorbing to the fibrous surface and not remaining in the water, leaving a

cleaner water solution behind.

The disappearance of the red colour demonstrates that the electrospun fibres made of PS waste are

effective for the removal of oil from water.

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Dr. Tugba Isik obtained her PhD in Materials Science and Engineering in 2019 at

İzmir Institute of Technology, Turkey. Her thesis focused on the separation of

macromolecules (proteins, dyes, heavy metal ions, oils, etc.) from aqueous

systems using electrospun fibres fabricated from waste plastics. She is currently

doing her second masters degree in School of Chemistry, University of Bristol

(UK) under the supervision of Dr Ian Bull (in OGU) where she is investigating the

soil nutrients and microbial communities by using GC-MS, LC-MS and ICP-

OES/MS analytical techniques.

Bibliography

1. T. Isık, PhD, Izmir Institute of Technology, 2018.2. T. Isik and M. M. Demir, Sustainable Materials and Technologies, 2018, 18, e00084.3. T. Isik, N. Horzum, U. H. Yildiz, B. Liedberg and M. M. Demir, Macromolecular Materials and

Engineering, 2016, 301, 827-835.4. T. Isık and M. M. Demir, Fiber and Polymers, 2018, 19, 767 - 774.5. A. Greiner and J. H. Wendorff, Angew. Chem.-Int. Edit., 2007, 46, 5670-5703.6. Z. M. Huang, Y. Z. Zhang, M. Kotaki and S. Ramakrishna, Composites Science and Technology,

2003, 63, 2223-2253.7. P. vandeWitte, P. J. Dijkstra, J. W. A. vandenBerg and J. Feijen, Journal of Membrane Science,

1996, 117, 1-31.8. Sbrools, https://commons.wikimedia.org/w/index.php?curid=1988298) (accessed

08.04.2020).9. C. Sim, https://commons.wikimedia.org/w/index.php?curid=77542203, (accessed

08.04.2020).

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Recycling waste plastics by ‘Electrospinning’

Questions

1. What is electrospinning? (2 marks)2. Give 2 reasons why ‘Incineration of PS is not an appropriate approach for the waste

management’. (2 marks)3. Figure 1 shows a SEM micrograph. For what does abbreviation ‘SEM’ stand? (1 mark)4. Using Figure 2, what conditions are required to make the surface texture of polystyrene (PS)

fibres wrinkled beads on a string? (4 marks)5. What is the mass of 1 mole (RMM) of (a) THF and (b) DMF? (2 marks) C=12; H=1, O=16 N=146. Figure 4e uses the term adsorption. What is the difference between adsorption and

absorption? (2 marks)7. What does ‘water remediation’ mean? (2 marks)

Extension (mathematics problem)

surface area to volume ratio.

(a) Assuming the particle is a spherical drop and the surface area was 1 unit2 what is the volume Hint. What is the formula for the surface area of a sphere and What is the formula for the volume of a sphere?

(b) If the particle was a cube and the surface area was 1 unit2, what is the volume?

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Recycling waste plastics by ‘Electrospinning’

Questions

1. What is electrospinning? (2 marks)

2. Give 2 reasons why ‘Incineration of PS is not an appropriate approach for the waste management’. (2 marks)

3. Figure 1 shows a SEM micrograph. For what does abbreviation ‘SEM’ stand? (1 mark)

4. Using Figure 2, what conditions are required to make the surface texture of polystyrene (PS) fibres wrinkled beads on a string? (4 marks)

5. What is the mass of 1 mole (RMM) of (a) THF and (b) DMF? (2 marks) [C=12; H=1, O=16 N=14]

6. Figure 4e uses the term adsorption. What is the difference between adsorption and absorption? (2 marks)

7. What does ‘water remediation’ mean? (2 marks)

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Extension (mathematics problem)

surface area to volume ratio.

(a) Assuming the particle is a spherical drop and the surface area was 1 unit2 what is the volume Hint. What is the formula for the surface area of a sphere and What is the formula for the volume of a sphere?

(b) If the particle was a cube and the surface area was 1 unit2, what is the volume?

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