APPLICATIONS of PURE and RECYCLED POLYMERIC MICRONANOFIBER for the REMOVAL of OIL SPILLS Afra Gharib Khamis Al-Blooshi Al-Blooshi

United Arab Emirates University Scholarworks@UAEU

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5-2015 APPLICATIONS OF PURE AND RECYCLED POLYMERIC MICRONANOFIBER FOR THE REMOVAL OF OIL SPILLS Afra Gharib Khamis Al-Blooshi Al-Blooshi

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Title

United Arab Emirates University

College of Science

Department of Chemistry

APPLICATIONS OF PURE AND RECYCLED POLYMERIC MICRO- NANOFIBER FOR THE REMOVAL OF OIL SPILLS

Afra Gharib Khamis Al-Blooshi

This thesis is submitted in partial fulfilment of the requirements for the degree of Master of Science in Chemistry

Under the Supervision of Dr. Mohamed Alazab Alnaqbi

May 2015 ii

Declaration of Original Work

I, Afra Gharib Khamis AlBlooshi ,the undersigned, a graduate student at the United

Arab Emirates University (UAEU), and the author of this thesis entitled

“Applications of pure and recycled polymeric micro-nanofiber for the removal of oil spills”, hereby, solemnly declare that this thesis is an original research work that has been done and prepared by me under the supervision of Dr. Mohamed Alazab

Alnaqbi, in the College of Science at UAEU. This work has not been previously formed as the basis for the award of any academic degree, diploma or a similar title at this or any other university. The materials borrowed from other sources and included in my thesis have been properly cited and acknowledged.

Student’s Signature Date

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Advisory Committee

1) Main Advisor: Dr. Mohamed ALazab Alnaqbi

Title: Assistant Professor

Department of Chemistry

College of Science

2) Co-Advisor: Dr. Yaser E. Greish

Title: Associate Professor

Department of Chemistry

College of Science

This Master Thesis is accepted by:

Dean of the College of Science: Professor Frederick Leung

Signature Date

Dean of the College of the Graduate Studies: Professor Nagi T. Wakim

Signature Date

Copy ____ of ____

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Abstract

Cleaning oil spills is a universal concern due to its environmental impact. The aim of this study is to study the effectiveness and applications of pure and recycled polymers in clean-up and the recovery of crude oil from oil spills. In this study, micro-nanofibers of analytical-grade and commercial polystyrene samples were prepared by electrospinning technique. Fiber size distribution was shown to vary with the electrospinning parameters and type of polymer. Fibrous sorbents prepare hereafter were investigated for their efficiency in removing oil spills. Results showed a variation in the sorption capacities of the fibers to various types of crude oils with the morphology of the fibers and the conditions at which they were prepared. Results also showed a variation of the sorption capacities with the original properties of the crude oils investigated. To fine-tune the sorption process, optimization of the electrospinning process was carried out including electrospinning setup parameters as well as polymeric solution and electrospinning chamber parameters. Correlations were established between each of the parameters and the sorption efficiency of the fibrous sorbents prepared thereafter. A high potential of the fibrous sorbents in the removal of crude oil spills was, therefore, proven with experimental evidences and structure-property relationships.

Keywords: Oil spills, electrospinning, micro-nanofibers, sorption capacity, retrieval.

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Title and Abstract (in Arabic)

ﺗﻄﺒﯿﻘﺎت أﻟﯿﺎف اﻟﻨﺎﻧﻮواﻟﻤﯿﻜﺮو ﺑﻮﻟﯿﻤﯿﺮﯾﺔ ﺑﻨﻮﻋﯿﮭﺎ اﻟﻨﻘﻲ واﻟﻤﻌﺎد ﺗﺪوﯾﺮه ﻓﻲ إزاﻟﺔ اﻟﺘﻠﻮث اﻟﻨﻔﻄﻲ

اﻟﻤﻠﺨﺺ

ﺗﻌﺪ إزاﻟﺔ اﻟﺒﻘﻊ اﻟﻨﻔﻄﯿﺔ ﻣﻦ أﻛﺜﺮ اﻻﻣﻮر اھﺘﻤﺎﻣﺎ ﻋﻠﻰ اﻟﻤﺴﺘﻮى اﻟﻌﺎﻟﻤﻲ وذﻟﻚ ﻟﺘﺄﺛﯿﺮھﺎ اﻟﻮاﺿﺢ ﻋﻠﻰ اﻟﺒﯿﺌﺔ. ﯾﮭﺪف ھﺬا اﻟﺒﺤﺚ ﻟﺪراﺳﺔ اﺳﺘﺨﺪام ﻟﺪاﺋﻦ ﻣﺨﻠﻘﺔ وأﺧﺮى أﻋﯿﺪ ﺗﺪوﯾﺮھﺎ ﻓﻲ إزاﻟﺔ ﺑﻘﻊ اﻟﻨﻔﻂ اﻟﺨﺎم وإﻋﺎدة اﺳﺘﺮﺟﺎﻋﮭﺎ. ﺗﻢ اﺳﺘﺨﺪام ﺗﻘﻨﯿﺔ اﻟﻐﺰل اﻟﻜﮭﺮﺑﻲ ﻓﻲ ﺗﺤﻀﯿﺮ أﻟﯿﺎف ﻧﺎﻧﻮﻧﯿﺔ وﻣﯿﻜﺮوﻧﯿﺔ ﻣﻦ ﻟﺪاﺋﻦ اﻟﺒﻮﻟﯿﺴﺘﯿﺮﯾ ﻦ اﻟﻤﺨﻠﻖ واﻟﻤﻌﺎد ﺗﺪوﯾﺮه. وﻗﺪ أﺛﺒﺘﺖ اﻟﺪراﺳﺔ اﻋﺘﻤﺎد أﺑﻌﺎد اﻷﻟﯿﺎف اﻟﻤﺤﻀﺮة ﻋﻠﻰ اﻟﻌﻮاﻣﻞ اﻟﻤﺨﺘﻠﻔﺔ ﻟﺘﻘﻨﯿﺔ اﻟﻐﺰل اﻟﻜﮭﺮﺑﻲ وﻗﺪ ﺗﻢ اﺧﺘﺒﺎر اﻟﻤﻤﺼﺎت ااﻟﻠﯿﻔﯿﺔ اﻟﺘﻲ ﺗﻢ ﺗﺤﻀﯿﺮھﺎ ﻣﻦ ھﺬه اﻷﻟﯿﺎف ﻟﺪراﺳﺔ ﻛﻔﺎءﺗﮭﺎ ﻓﻲ إزاﻟﺔ اﻟﺒﻘﻊ اﻟﻨﻔﻄﯿﺔ.

وﻗﺪ أﺛﺒﺘﺖ اﻟﻨﺘﺎﺋﺞ ﺗﻔﺎوت ﻓﻲ ﻧﺴﺒﺔ اﻣﺘﺼﺎص ﺑﻘﻊ اﻟﻨﻔﻂ ﺑﺘﻐﯿﯿﺮ ﻧﻮع وﺧﻮاص اﻟﻨﻔﻂ وﺷﻜﻞ اﻷﻟﯿﺎف اﻟﻤﺴﺘﺨﺪﻣﺔ ﻓﻲ ﺗﺼﻨﯿﻊ اﻟﻤﻤﺼﺎت اﻟﻠﯿﻔﯿﺔ واﻟﺘﻲ اﻋﺘﻤﺪت ﺑﺪورھﺎ ﻋﻠﻰ اﻟﻌﻮاﻣﻞ اﻟﻤﺨﺘﻠﻔﺔ اﻟﺘﻲ ﺗﻢ ﺗﺤﻀﯿﺮ اﻷﻟﯿﺎف ﻋﻨﺪھﺎ. ﻛﻤﺎ ﻗﺎم اﻟﺒﺤﺚ ﺑﺈﻋﺎدة ﺗﺪﻗﯿﻖ اﻟﻌﻮاﻣﻞ اﻟﺘﻲ ﺗﻢ ﺗﺤﻀﯿﺮ اﻷﻟﯿﺎف ﻋﻨﺪھﺎ ﻟﻠﺤﺼﻮل ﻋﻠﻰ ﻧﺴﺒﺔ أﻋﻠﻰ ﻟﻼﻣﺘﺼﺎص. وﺿﻤﺖ ھﺬه اﻟﻌﻮاﻣﻞ ﻣﺎ ﯾﺨﺺ ﻣﺤﺎﻟﯿﻞ اﻟﻠﺪاﺋﻦ اﻟﻤﺤﻀﺮة ﺑﺎﻻﺿﺎﻓﺔ إﻟﻰ اﻟﻌﻮاﻣﻞ اﻟﺨﺎﺻﺔ ﺑﺘﻘﻨﯿﺔ اﻟﻐﺰل اﻟﻜﮭﺮﺑﻲ. وﻗﺎﻣﺖ اﻟﺪراﺳﺔ ﺑﺎﺳﺘﻨﺘﺎج ﻋﻼﻗﺎت ﻣﺨﺘﻠﻔﺔ ﺑﯿﻦ ﻛﻞ ﻣﻦ ھﺬه اﻟﻌﻮاﻣﻞ وﻣﻘﺪرة اﻟﻤﻤﺼﺎت اﻟﻠﯿﻔﯿﺔ اﻟﻤﺤﻀﺮة ﻋﻨﺪھﺎ ﻋﻠﻰ اﻣﺘﺼﺎص اﻟﺒﻘﻊ اﻟﻨﻔﻄﯿﺔ. واﻧﺘﮭﺖ اﻟﺪراﺳﺔ ﺑﺎﺛﺒﺎت اﻟﻤﻘﺪرة اﻟﻌﺎﻟﯿﺔ ﻟﻠﻤﻤﺼﺎت اﻟﻠﯿﻔﯿﺔ اﻟﺘﻲ ﺗﻢ ﺗﺤﻀﯿﺮھﺎ ﻋﻠﻰ إزاﻟﺔ اﻟﺒﻘﻊ اﻟﻨﻔﻄﯿﺔ وإﻋﺎدة ﺗﺪوﯾﺮ اﻟﻨﻔﻂ اﻟﺬي ﺗﻢ إزاﻟﺘﮫ.

اﻟﻜﻠﻤﺎت اﻟﻤﻔﺘﺎﺣﯿﺔ: ﺑﻘﻊ اﻟﻨﻔﻂ، اﻟﻐﺰل اﻟﻜﮭﺮﺑﻲ، أﻟﯿﺎف ﻣﯿﻜﺮوﻧﯿﺔ ـ ﻧﺎﻧﻮﻧﯿﺔ، ﻗﺪرة اﻻﻣﺘﺼﺎص، - اﻻﺳﺘﺮﺟﺎع.

Acknowledgements

All thanks and praises to Allah, the master and creator of the whole universe.

No words can express my feelings of thanks and gratitude for my supervisor, Dr.

Mohamed Alazab Alnaqbi, the Chair of the Chemistry Department and for Dr. Yaser

E. Greish, my co-supervisor, for their continuous and untiring support and help throughout my Master’s degree. Thank you!

Special thanks are also due to Dr. Ahmed Alshamsi, Dr. Muna Alfalasi,

Professor Sayed Marzouk and Professor Salman Ashraf and Mr. Bassam Hindawi for always supporting and providing encouragement whenever I would have difficulty and hardship. Thank you!

A very special thanks and love for my dear sisters and friends, at home –

Khlood, and Alanood, and at work – Mariam Al Shamisi, Mouza Al Zaabie,

Ruwaya Al Nuaimi, Khaula Al Shamisi , Leena Al Kaabi, Mariam Al Koyoumi,

Mariam Al Saedi, Zahra Al Badi, Sharifa Al Maqdi, Mouza Al Khaili, and Khaula

Al Jahoushi. I would also like to thank my dear sister and friend Aeysha Al Shehhi, as well as Hajer Al Koyoumi, Shaikha Al Neyadi, Halawa Al Shehhi and Aeysha Al

Nyadi.

I would like to express my thanks and gratitude to my external examiners,

Dr. Mahmoud Mohsin (University of Sharjah) and Dr. Dr. Nayef Ghasem (College of Chemical and Petroleum Engineering, UAEU) for their constructive review of my thesis. I would also like to acknowledge the kind support received from

Dr. Abdulmajeed Al Khajeh (Assistant Dean for Graduate Studies, College of

Science).

Lastly, I would like to express my deep and sincere thanks to my beloved university, the College of Science, and the College of Graduate Studies for allowing me to continue to study and keep improving myself.

Dedication

I dedicate this thesis to the memory of my dear late mother.

Though she is not with me physically, I always feel surrounded by her presence, prayers and support!

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Table of Contents

Title ...... i Declaration of Original Work ...... ii Copyright ...... iii Advisory Committee ...... iv Approval of the Master Thesis ...... v Abstract ...... vii Title and Abstract (in Arabic) ...... viii Acknowledgements ...... ix Dedication ...... xi Table of Contents ...... xii List of Tables ...... xiv List of Figures ...... xv List of Abbreviation ...... xxii Chapter 1: Introduction ...... 1 1.1 Physical Methods ...... 8 1.2 Chemical Methods ...... 11 1.3 Biological Methods ...... 14 1.4 Other Approaches ...... 16 1.5 Fibrous Sorbents ...... 18 1.6 Fabrication of Fibrous Sorbents – Electrospinning Technique ...... 21 Chapter 2: Objectives ...... 37 Chapter 3: Materials and Methods ...... 38 3.1 Materials ...... 38 3.2 Methods ...... 39 3.2.1 Fabrication of PS Microfibers ...... 39 3.2.2 Characterization of the Sorbents ...... 41 3.2.3 Sorption Experiments ...... 41 Chapter 4: Results and Discussion ...... 43 4.1 Characterization of the Starting Materials ...... 43 4.1.1 Crude Oil ...... 43 4.1.2 Polystyrene ...... 45 4.2 Characterization of the Polymeric Microfibers ...... 47 4.3 Oil Sorption Experiments ...... 58

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4.3.1 ADNOC Crude Oil ...... 58 4.3.2 TOTAL Crude Oil ...... 72 4.3.3 ADCO Crude Oil ...... 80 4.4 Effect of Electrospinning Parameters on Sorption of TOTAL Crude Oil on PSII Fibrous Sorbents ...... 91 4.4.1 Effect of Solvents ...... 91 4.4.2 Effect of Applied Voltage ...... 104 4.4.3 Effect of Feeding Rate ...... 112 4.4.4 Effect of Distance ...... 117 4.4.5 Effect of Humidity ...... 121 4.4.6 Effect of Needle Diameter ...... 128 Chapter 5: Conclusion and Future Directions ...... 134 Bibliography ...... 137

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List of Tables

Table 1: Recent oil spills in Australia (>100 tonnes)...... 5 Table 2: Methods for treating oily wastewater ...... 17 Table 3: Properties of the Crude oil, measured at room temperature ...... 38 Table 4: Composition of solvent mixtures of THF and DMF...... 92 Table 5: Gauge number - nominal internal diameter conversion of ...... 128 Needles used in the current study

List of Figures

Figure 1: Extent of oil pollution from different sources into the coastal and marine 4 environment worldwide each year from different sources

Figure 2: Weathering processes that change oil properties 7

Figure 3: Use a boom for oil clean up 10

Figure 4: Use skimmer for oil clean up 10

Figure 5: Schematic representation showing the principles behind the use of 12 dispersants

Figure 6: A boom filled up with polypropylene sorbent, applied to collect oil 15

Figure 7: Fibrous materials and their classification 19

Figure 8: Schematic diagram of electrospinning set-up 24

Figure 9: Effect of varying the applied voltage on the formation of the Taylor cone 26

Figure10: Variation of beaded fibers as the mass ratio of water/ethanol was changed. 28 Electric field is 0.5 kV/cm, weight fraction of PEO is 3.0%. The horizontal edge of each of the figures is 20 microns long

Figure11: images of PS fibers as a function of flow rate 29

Figure 12: Optical microscope images of PS fibers electrospun from THF as a 33 function of PS concentration: (a) 18 wt %; (b) 20 wt %; (c) 25 wt %; (d) 28 wt %; (e) 30 wt %; (f) 35 wt %

Figure 13: SEM images of spun fibers electrospun from a 30 wt % PS/DMF solution 36 under (a) 43%, (b) 37%, (c) 24%, (d) 22%, (e) 15%, (f) 11% with relative humidity (scale bar: 5 µm).

Figure 14: Density (a) and Viscosity(b) of crude oils used in the current study 44

Figure 15: FT-IR spectra for PSI, PSII, and PSCIII polymers 46

Figure 16: Weight-based Molecular weight of PSI, PSII, and PSCIII polymers 46

Figure. 17: SEM micrographs of a) PSI, b) PSII, and c) PSCIII fibrous sorbents 49 obtained by electrospinning 20 wt% solutions of each polymers in DMF

Figure 18: SEM micrographs of a) PSI, b) PSII, and c) PSCIII fibrous sorbents 50 obtained by electrospinning 30 wt% solutions of each polymers in DMF

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Figure 19: SEM micrographs of a) PSI, b) PSII, and c) PSCIII fibrous sorbents 51 obtained by electrospinning 40 wt% solutions of each polymers in DMF

Figure 20: Fiber size distribution of fibrous sorbents obtained by electrospinning of 52 (a) 20%, (b) 30%, and (c) 40% solutions of PSI polymers in DMF

Figure 21: Fiber size distribution of fibrous sorbents obtained by electrospinning of 53 (a) 20%, (b) 30%, and (c) 40% solutions of PSII polymers in DMF

Figure 22: Fiber size distribution of fibrous sorbents obtained by electrospinning of 54 (a) 20%, (b) 30%, and (c) 40% solutions of PSCIII polymers in DMF

Figure 23: High magnification SEM micrographs of fibrous sorbents obtained by 55 electrospinning 20 wt% solutions of (a) PSI, (b) PSII, and (c) PSCIII polymers in DMF

Figure 24: Adsorption Isotherms of fibrous sorbents obtained by electrospinning 57 solutions containing 20 wt% of each of the polymers in DMF

Figure 25: Pore Size distribution of fibrous sorbents obtained by electrospinning 57 solutions containing 20 wt% of each of the polymers in DMF

Figure 26: Sorption capacities to ADNOC crude oil of fibrous sorbents (a) 0.0044g, 59 (b) 0.0066g, (c) 0.05g, and (d) 0.1g prepared from electrospinning of 20 wt% solutions of the polymers in DMF

Figure 27: Maximum sorption capacities achieved after 30 seconds using various 60 weights of the fibrous sorbents that were prepared from solutions containing 20 wt% of PSI, PSII, and PSCIII

Figure 28: Steps of the sorption capacity experiments 62

Figure 29: Sorption capacities to ADNOC crude oil of fibrous sorbents (a) 0.0044g, 63 (b) 0.0066g, (c) 0.05g, and (d) 0.1g prepared from electrospinning of 30 wt% solutions of the polymers in DMF

Figure 30: Maximum sorption capacities achieved after 30 seconds using various 64 weights of the fibrous sorbents that were prepared from solutions containing 30 wt% of PSI, PSII, and PSCIII

Figure 31: Sorption capacities to ADNOC crude oil of fibrous sorbents (a) 0.0044g, 65 (b) 0.0066g, (c) 0.05g, and (d) 0.1g prepared from electrospinning of 40 wt% solutions of the polymers in DMF

Figure 32: maximum sorption capacities achieved after 30 seconds using various 66 weights of the fibrous sorbents that were prepared from solutions containing 40 wt% of PSI, PSII, and PSCIII

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Figure 33: Highest achieved sorption capacities after 30 sec of fibrous sorbents 67 prepared from electrospinning of 20, 30, and 40 wt% solutions of each of the polymers in DMF

Figure 34: Highest achieved sorption capacities after 30 min of fibrous sorbents 69 prepared from electrospinning of 20, 30, and 40 wt% solutions of each of the polymers in DMF

Figure 35: Extent of retrieval (%) of ADNOC crude oil adsorbed onto PSI, PSII, and 71 PSCIII fibrous sorbents (a) 0.0044g, (b) 0.0066g, (c) 0.05g, and (d) 0.1g prepared by the electrospin of 20, 30, and 40 wt% solutions of each of the polymers in DMF

Figure 36: Sorption capacities to TOTAL crude oil of fibrous sorbents (a) 0.005g, 73 and (b) 0.01g prepared from electrospinning of 20 wt% solutions of the polymers in DMF

Figure 37: Sorption capacities to TOTAL crude oil of fibrous sorbents (a) 0.005g, 74 and (b) 0.01g prepared from electrospinning of 30 wt% solutions of the polymers in DMF

Figure 38: Sorption capacities to TOTAL crude oil of fibrous sorbents (a) 0.005g, 75 and (b) 0.01g prepared from electrospinning of 40 wt% solutions of the polymers in DMF

Figure 39: Highest achieved sorption capacities capacities to TOTAL crude oil after 77 30 sec of fibrous sorbents (0.005g & 0.01g) prepared from electrospinning of (a) 20 wt%, (b) 30 wt%, and (c ) 40 wt% solutions of each of the polymers in DMF

Figure 40: Highest achieved sorption capacities capacities to TOTAL crude oil after 78 30 min of fibrous sorbents sorbents (0.005g & 0.01g) prepared from electrospinning of of (a) 20 wt%, (b) 30 wt%, and (c ) 40 wt% solutions of each of the polymers in DMF Figure 41: Extent of retrieval (%) of TOTAL crude oil adsorbed onto PSI, PSII, and 79 PSCIII fibrous sorbents (a) 0.005g, and (b) 0.01g prepared by the electrospinnig of 20, 30, and 40 wt% solutions of each of the polymers in DMF Figure 42: Sorption capacities to ADCO crude oil of fibrous sorbents (a) 0.005g, and 81 (b) 0.01g prepared from electrospinning of 20 wt% solutions of the polymers in DMF

Figure 43: Sorption capacities to ADCO crude oil of fibrous sorbents (a) 0.005g, and 82 (b) 0.01g prepared from electrospinning of 30 wt% solutions of the polymers in DMF

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Figure 44: Sorption capacities to ADCO crude oil of fibrous sorbents (a) 0.005g, and 83 (b) 0.01g prepared from electrospinning of 40 wt% solutions of the polymers in DMF

Figure 45: Highest achieved sorption capacities to ADCO crude oil after 30 sec of 85 fibrous sorbents prepared from electrospinning of (a) 20 wt%, (b) 30 wt%, and (c ) 40 wt% solutions of each of the polymers in DMF

Figure 46: Highest achieved sorption capacities to ADCO crude oil after 30 min of 86 fibrous sorbents prepared from electrospinning of (a) 20 wt%, (b) 30 wt%, and (c ) 40 wt% solutions of each of the polymers in DMF

Figure 47: Extent of retrieval (%) of ADCO crude oil adsorbed onto PSI, PSII, and 87 PSCIII fibrous sorbents (a) 0.005g, and (b) 0.01g prepared by the electrospin of 20, 30, and 40 wt% solutions of each of the polymers in DMF

Figure 48: Comparison between the sorption capacities to ADNOC, TOTAL, and 89 ADCO crude oils of fibrous sorbents (a) 0.005g, and (b) 0.01g /each prepared from electrospinning of 20 wt% solutions of PSII in DMF

Figure 49: Highest achieved sorption capacities to ADNOC, TOTAL, and ADCO 90 crude oils after 30 sec of fibrous sorbents (0.005g & 0.01g) prepared from electrospinning of 20 wt% solutions of PSII in DMF

Figure 50: Extent of retrieval (%) to ADNOC, TOTAL, and ADCO crude oils of 90 fibrous sorbents (0.005g & 0.01g) prepared from electrospinning of 20 wt% solutions of PSII in DMF

Figure 51: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g/each) 93 prepared by the electrospin of 20 wt% solvent of each (a) PSI, (b) PSII, and (c ) PSCIII in various solvent systems

Figure 52: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g/each) 94 prepared by the electrospin of 30 wt% solvent of each (a) PSI, (b) PSII, and (c ) PSCIII in various solvent systems

Figure 53: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g/each) 95 prepared by the electrospin of 40 wt% solvent of each (a) PSI, (b) PSII, and (c ) PSCIII in various solvent systems

Figure 54: Highest achieved sorption capacities to TOTAL crude oil after 30 sec of 96 fibrous sorbents prepared by electrospinning of 20, 30, and 40 wt% of (a) PSI, (b)PSII, and (c) PSCIII solutions in 100% DMF

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Figure 55: Highest achieved sorption capacities to TOTAL crude oil after 30 sec of 97 fibrous sorbents prepared by electrospinning of 20, 30, and 40 wt% of (a) PSI, (b)PSII, and (c) PSCIII solutions in (50:50)-(THF: DMF)

Figure 56: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% 100 solutions of PS at different solvent concentration (a) PSI (100%DMF), (b) PSI (50:50,THD:DMF), ( c) PSII (100% DMF), (d) PSII (50:50, THD:DMF), (e) PSCIII (100% DMF), and (f) PSCII (50:50, THD:DMF)

Figure 57: SEM micrographs of fibrous sorbents obtained by electrospinning of PS 101 at different solvent concentration (a) 20 w% PSII (100%DMF), (b) 20 w% PSII (50:50,THD:DMF), ( c) 30 w% PSII I (100% DMF), (d)320 w% PSII (50:50, THD:DMF), (e) 40 w% PSII (100% DMF), and (f) 40 w% PSII I (50:50, THD:DMF)

Figure 58: Extent of retrieval (%) of TOTAL crude oil adsorbed onto (a) PSI, (b) 102 PSII, and (c ) PSCIII fibrous sorbents (0.005g/each) prepared by the electrospin of 20, 30, and 40 wt% solutions of each of the polymers in 100% DMF

Figure 59: Extent of retrieval (%) of TOTAL crude oil adsorbed onto (a) PSI, (b) 103 PSII, and (c ) PSCIII fibrous sorbents (0.005g/each) prepared by the electrospin of 20, 30, and 40 wt% solutions of each of the polymers in (50:50)% -(THF:DMF)

Figure 60: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) 106 prepared by the electrospinning of 20 wt% PSI solutions (a) 100% DMF, and (b) (THF:DMF) (50:50)% at different applied voltages

Figure 61: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) 107 prepared by the electrospinning of 20 wt% PSII solutions (a) 100% DMF, and (b) (THF:DMF) (50:50)% at different applied voltages

Figure 62: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) 108 prepared by the electrospinning of 20 wt% PSCIII solutions (a) 100% DMF, and (b) (THF:DMF) (50:50)% at different applied voltages

Figure 63: Highest achieved sorption capacities to TOTAL crude oil after 30 sec of 109 fibrous sorbents prepared by electrospinning of of 20 wt% of (a) 100% DMF, (b)THF:DMF-(50:50) solutions of each of the polymers at different applied voltages

Figure 64: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% 110 solutions of PSII in DMF at different applied voltages (a) 10kV, (b) 15kV, ( c) 20kV, (d) 25kV, and (e) 30kV

Figure 65: Extent of retrieval (%) of TOTAL crude oil adsorbed onto fibrous 111 sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions (a) 100% DMF, and (b) (THF:DMF) (50:50)% solutions of each of the polymers at different applied voltages

Figure 66: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) 114 prepared by the electrospinning of 20 wt% PSII solutions at feeding rate (1ml/hr, 5ml/hr, and 10ml/hr) in DMF

Figure 67: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% 115 solutions of PSII in DMF at feeding rate at (a) 1ml/hr, (b) 5ml/hr, and ( c) 10ml/hr

Figure 68: Extent of retrieval (%) of TOTAL crude oil adsorbed onto fibrous 116 sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at feeding rate (1ml/hr, 5ml/hr, and 10ml/hr) in DMF

Figure 69: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) 118 prepared by the electrospinning of 20 wt% PSII solutions at distance (Needle to collector) at 10, 15, and 20cm in DMF

Figure 70: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% 119 solutions of PSII at distance (Needle to collector) at (a) 10cm, (b) 15cm, and ( c) 20cm

Figure 71: Extent of retrieval (%) of TOTAL crude oil adsorbed onto fibrous 120 sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at distance (Needle to collector) at 10, 15, and 20cm in DMF

Figure 72: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) 122 prepared by the electrospinning of 20 wt% PSII solutions at different Humidity % at 49% -Normal, (70-88)%, and (89-99)%) in DMF

Figure 73: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% 123 solutions of PSII at different Humidity % at (a) 49% -Normal, (b) (70- 88)%, and ( c) (89-99)%) in DMF

Figure 74: High magnification SEM micrographs of fibrous sorbents obtained by 124 electrospinning 20 wt% solutions of PSII at different Humidity % at (a) (70-88)%, and ( b) (89-99)%) in DMF

Figure 75: Extent of retrieval (%) of TOTAL crude oil adsorbed onto fibrous 127 sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at different Humidity % at 49% -Normal, (70-88)%, and (89- 99)%) in DMF

xxi

Figure 76: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) 130 prepared by the electrospinning of 20 wt% PSII solutions at different Needle diameters at 18G, 21G, 23G, and 29G in DMF

Figure 77: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% 131 solutions of PSII at different Needle diameters at (a) 18G, (b) 21G, ( c) 23G, and (d) 29G in DMF

Figure 78: Extent of retrieval (%) of TOTAL crude oil adsorbed onto fibrous 133 sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at different Needle diameters at 18G, 21G, 23G, and 29G in DMF

xxii

List of Abbreviations

DMF N, N-dimethylformamide

FT-IR Fourier Transform Infrared Spectroscopy

GPC Gel Permeation Chromatography

PSI Polystyrene Mw = 100,000 g/mol

PSII Polystyrene Mw = 350,000 g/mol

PSCIII Recycled Polystyrene

SEM Scanning Electron Microscope

THF Tetrahydrofuran

Chapter 1: Introduction

Water pollution is known worldwide to be induced directly or indirectly by humans into the marine environment. It includes estuaries, which effect and damage the living resources and marine life. In addition to directly affecting the human health, pollution is also considered an obstruction to marine activities, causes a deterioration of sea water usage and a reduction of amenities.1 Williams (1996) concluded that water pollution is not only related to hazardous materials in aqueous media but air pollutants, which eventually end up accumulated in different types of aqueous media as well. 2,3

Pollution of water has been always attributed to the increase in industrialization and human activities in the world. As a result, and according to the

World Health Organization (WHO), three billion people in the world lack access to clean water. Most of the sources of aquatic pollution are well-known, 50% of which is a direct result of the agriculture sector.1 Domestic and municipal wastes4,5 also cause massive damage to ecosystems. Such wastes may contain a broad range of the pollutants, like pathogens6, organic substances7,8, heavy metals9,10, and oil11. Due to the population growth, the amount of wastes produced by people is significantly increasing. It is supposed, that water pollution will increase at least twice over the next 20 years12,13. The environmental response of an aquatic system to pollutants greatly depends on its inherent susceptibility, i.e., a natural capacity to absorb environmental stress and still easily recover stability14,15.

Oil pollution has been receiving increasing attention since the middle of the

19th century with the increase in tanker operations, oil use, frequent marine tanker collisions and accidents resulting in oil spills. Unfortunately, every year, millions of

2 gallons of oil are being added to the coastal and marine environments from different sources, as shown in Figure 1.1 Smith (1971) reported that as many as half a million tons of persistent oils are discharged into the sea every year16. Reed (1972) suggested a similar figure and reported that the annual release of hydrocarbon is around

600,000–1,000,000 tons. Under still conditions, the oil traps silts and other suspended matters and sinks to the bottom where it is deposited. Coastal refineries institute another distinct risk of continuous oil pollution since millions of gallons of crude oil and its products are processed and stored there. Crude oil is purified and processed in refineries to produce a variety of fuels, lubricants, and solvents. During these operations, a continuous small-scale pollution occurs through leakages, spills, breakages, etc. Water is used in many processes and inevitably becomes contaminated with oil and derivatives, and when discharged, it carries appreciable fuel loads.1 Spillages et. al. (2007) reported that Australia's largest spill was the loss of 17,000 tons of light crude oil from the tanker Kirki off the coast of Western

Australia in July 1991. There have been 13 incidents involving the loss of more than

100 tons of oil in Australian marine environments since 1970 as shown in Table 1.17

In addition, the largest offshore spill in U.S history took place in spring-summer

2010, known as “Deepwater Horizon disaster”. It presented a significant threat to the coastline and the marine ecosystem of the Gulf of Mexico, and was estimated around

33,000 barrels/day.18 Moreover, the worst environmental maritime disaster took place in New Zealand in 2011. It was attributed to the rupture of one of the ship's main fuel tanks. As a result, it released between 130 and 350 tonnes of heavy oil into the water. The fresh damage was caused after the ship's hull dragged in heavy winds and swells of up to four metres.19

The United Arab Emirates is one of the word’s leading countries of oil production, and its marine environment along the Arabian Gulf and the Gulf of

Oman is subjected to increasing quantities of oil spills.20,21 Similar to most of the countries in the Arabian Peninsula, UAE registered desalination plants as the main supply for fresh water. Consequently, and being all built close to the shore, these plants are subjected to the threat of oil spills, hence introducing toxic materials, which directly affect marine life.22 Smith (1970) reported mortality and elimination of sea stars (Pisaster spp.) and sea urchins (Strongylocentrotus spp.) as a result of diesel oil pollution and reported that as little as 0.1% emulsion of the oil may inactivate the tube feet of the urchins16,1.

400

300

200

100

0 Oil volume (millions gallons) (millions volume Oil

Big spills Up in smoke Natural seeps Down the drain Offshore drilling Routine maintenance

Figure 1: Extent of oil pollution from different sources into the coastal and marine environment worldwide each year from different sources.1

Table 1: Recent oil spills in Australia (>100 tonnes):17

Ship Year Ship type Estimated oil lost

(>100 tonnes)

Kirki 1991 Oil tanker 17000

Metaxata 1999 Oil tanker 1400

Oceanic Grandeur 1970 Oil tanker 1067

Korean Star 1988 Bulk carrier 800

Sanko Harvest 1991 Bulk Carrier 700

Bethioua 1976 Oil tanker 350

Iron Baron 1995 Bulk carrier 300

Laura D'Amato 1999 Oil tanker 300

Era 1992 Oil tanker 296

Port Stanvac 1999 Pipeline 270

Al Qurain 1988 Livestock carrier 184

Esso Gippsland 1982 Oil tanker 180

World Encouragement 1979 Oil tanker 110

The rate of recovery of the ecosystem as a result of contamination with oil spills is debatable. Shriadah (1998) observed a rapid reduction in the contamination level and recovery of the ecosystem along the Gulf of Oman in one of the oil spill incidents which caused a temporary elevation of contamination levels. On the other hand, Yamamoto et al. (2003) concluded that the recovery rate is dependent on the pollution sites and the intensity of contamination.23

Consequences of oil spills have direct environmental and economical impacts. Concerning the environmental impact, oil spills cause a decrease in the concentration of dissolved oxygen in water, as it is well known that film formation of

24 oils obstructs O2 transferring between air and water . Moreover, dark oil (e.g. crude and residue fuel oil) tends to absorb more solar energy than light oil (e.g. gasoline and diesel), hence raising the water temperature, which might be cause a fire hazard.25 In addition, oil slick disturbs the amount of light reaching marine plants, algae, and planktons hence affect their photosynthesis. Figure 2 describes the changes that usually take place in the physical and chemical properties of water as a result of the presence of oil slick onto aquatic media.26

In addition to all of the above consequences, oil spills have acute-to-chronic effects on organisms, depending on the amount of oil released. Metabolic processes of the affected plants can also increase the toxicity of the well known toxic agents, such as n-paraffin, by converting it to other derivatives that are more toxic than the original.27 Reptiles and amphibians can also be killed directly by petroleum. In a temperate region, mammals (polar bear, otter, fur seal, and muskrat) that rely on fur insulation are frequently killed by oil. Seabirds are often killed by oil spills, primarily because of plumage oiling and oil ingestion. An example of a chronic biological

Figure 2: Weathering processes that change oil properties27

8 impact is the reduction in the thickness of eggshells of the next generation seabirds.

It should be also mentioned that damages caused by an oil spill will be greater if occurring near coral or mangrove areas.28 Economical impact of oil spills are difficult to assess because it depends on the type of oil, and the geographical details of the region where oil spill took place. 29

Crude oil is considered a precious commodity. Therefore, any spillage or inefficient extraction implies economic and environmental concerns. Thus, efficient systems are significantly essential for the treatment and recovery of the spilled oil.30

In addition to accidents, such as well drilling, shipping or bunkering incidents, or by deliberate discharge from the vessels, oil spills may also arise as a result of natural leakage from the sea floor. These events have encouraged environmental scientists to develop techniques to deal with oil spills, both at sea and on shorelines. Depending on the approach taken in the treatment, these techniques include physical, chemical, and biological in origin. Some of these methods were debated and as a result, significant research efforts have been devoted to this subject in the recent years.31,32 the following sections provide more details about these approaches.

I.1 Physical Methods

Some of the most common practical and environmental physical methods of the oil spill cleanup are based on mechanical recovery. This approach is the largest class of the recovery techniques, and includes a broad variety of skimmers, booms, and oil-collecting vessels. The mechanical methods do not involve chemicals and do not, therefore, require special official permission to be implemented, unlike dispersants, whose use is limited or even forbidden in many regions. The mechanical oil recovery systems are provided to the oil spill location by the specially designed

9 and equipped spill response vessels. A boom is a device used to control oil spreading and restrict discharge into a limited area. Booms can be made from various polymer- based materials which are tolerant to oil, UV light, and other handling conditions.

Examples, include nylon, polyester, polyurethane, and PVC, etc, and are variable in design and construction. A boom is made of essential components; a freeboard, a skirt, and a longtitudinal support. A “freeboard" is a top part that contains the oil and helps preventing waves from splashing oil over the top part of the boom. A "skirt" is an underwater part of the boom, and it helps collecting the oil and contributes in reducing the amount of oil lost in the boom. A "longitudinal support", which is usually a chain or cable running along the bottom of the skirt, strengthens the boom against wind and wave action, and may also serve as a weight or ballast to add stability and help keep the boom upright as shown in Figure 3.33

Skimmers are usually used together with the booms. The skimmers remove oil from the water surface without causing changes in its physical or chemical properties and transfer it to the storage tanks onboard the vessel. During severe winter conditions where ice covers is found onto the water surface, there is usually no need to use the booms because the ice serves as a barrier against oil spreading. A variety of skimmer designs have been optimized to operate efficiently in different weather conditions, as well as in the Arctic sea with a high concentration of ice.

Although designs vary, all skimmers rely on specific gravity; surface tension and a moving medium to remove floating oil from the water surface as shown in Figure

4.34

Figure 3: Use a boom for oil clean up.35

Figure 4: Use skimmer for oil clean up.36

Oil-collecting vessels are motorized vessels, which are integrated with some of the above-mentioned technologies. They perform an independent collection of the oil spill on the water, and are, therefore, considered the most reliable and possible technology in the future. This is based on the fact that they have the ability to handle large volumes of the inflow to be treated with minimal negative impact on the environment, compared to other technologies. Most of the vessels combine several oil spill response technologies onboard.37

I.2 Chemical Methods

In many cases, physical methods are not sufficient for a complete removal of an oil spill. In addition, the time used for oil spill removal is very critical. In these situations, chemical methods are suitable alternatives. However, chemical methods are relatively more expensive and have other side effects, which are considered disadvantages of these methods. Chemical methods are mainly composed of chemical solidifiers, which have chemical structure that makes it different from chemical dispersants. Their main function is to change the physical and chemical properties of an oil spill to form coagulate, which then either sinks to the bottom of the water media or floats onto the water surface then collected using special boats.

However, due to their high costs, solidifires are not so common and are only used in some countries. Chemical dispersants are chemical agents that are composed of surfactant and petroleum-based solvents. Additionally, some reagent aids may be added to control the spreading of the dispersed oil. The primary function of dispersants is to reduce surface tension of an oil slick as shown in Figure 5.38

Figure 5: Schematic representation showing the principles behind the use of

dispersants.38

Sorbents makes up another class of materials with the ability of soaking up oil spills from water. The main advantage of sorbents is the convenience of removing oil slick from contaminated area, unlike other methods. However, it is well known that oil-containing sorbents should be collected for oil recovery or for further elimination. Thus, adsorbents should be low in density to make them buoyant for long periods and be able to adsorb oil. Therefore, sorbents should be designed with high porosity for a maximum efficiency of oils spill removal.

Oleophilic materials are preferred as sorbents as they possess high affinity towards the hydrophobic oils spills, hence removal efficiency is expected to be high.

On the other hand, sorbents should not be hydrophilic to avoid the adsorption of water. An example of a polymeric boom is shown in Figure 6. Additionally, ideal sorbents should have the following properties:

1. During pick up of the saturated adsorbents, soaked oil should be

minimum.

2. Application and transportation of sorbents should be convenient.

3. Sorbents should be non-toxic and non-harmful to the environment.

4. Sorbents should be less expensive than other materials used on oil spill

removal.

I.3 Biological Methods

These methods are also known as “bioremediation”, which are usually applied as a secondary on-site treatment, after mechanical or chemical methods, especially when the oil spill layer thickness is not less than 0.1 mm. Few microorganisms are capable of digesting the petroleum hydrocarbons, such as bacteria of the genus Pseudomonas and some species of fungi and yeasts. It becomes more accessible to other types of oil-eating bacteria if the oil spill is more finely divided. Bioremediation typically involves biostimulation, which means the addition of the rate-limiting nutrients in order to accelerate the biodegradation of the oil. Namely, in order for the microorganisms to digest carbon-based materials, significant amounts of nitrogen and phosphorus, which are essential ingredients of protein and nucleic acid, are needed. Maintaining sufficient nitrogen is considered the biggest challenge.

Biological methods involve the use of living organisms such as; bacteria, yeast, algae, and fungi to degrade oil spill. The main advantage of biological metods is its low negative impact on ecology. However, the disadvantage of biological methods is the slow rate of degradation as long time is always needed for a complete degradation of the oil spill products. 39

Figure 6: A boom filled up with polypropylene sorbent, applied to collect oil.

I.4 Other Approaches

A number of other technologies may also be used such inorganic minerals, natural materials, synthetic chemical and biological materials; these include the use polymeric materials. Recently, Wang et al. have used kapok fibers for high oil absorbency.40 In another recent work by Likon et al., used seed fibers as a natural source for oil absorbents.41 Table 2 shows the advantages and limitations of each of the various treatment methods. Examples of physical and mechanical methods are skimmer, gravity separation, micro and ultrafiltration, and membrane filtration. The biological method includes the use of microorganisms to remove oil 42. Chemical treatment can be realized by coagulation and flocculation, electrocoagulation, and flotation techniques43,44,45. Granular or fibrous filter materials are used for surface and depth filtration method.46,47 Meanwhile, adsorption method utilizes booms, dispersants, and sorbents to remove oil. 48 In the following sections, more focus will be given to sorption of oil using fibrous sorbents and various methods of preparing those sorbents.

Table 2 . Methods for treating oily wastewater67

Methods Advantages Disadvantages References

Adsorption Good oil removal Labor intensive. PM efficiency, Simple operation. Low processing Poor removal of fine 48–51 cost emulsions (<100 μm)

Coagulation and Good oil removal High initial and operating PM flocculation efficiency cost, Labor intensive, Generation of a secondary 43,52,53 pollutant

Electrocoagulation High oil removal High initial cost PM efficiency, Low operating cost 42,54

Flotation High oil removal efficiency Complex operation PM (involves coagulants/ flocculants),Inadequate 44,55–57 removal of fine oil droplets (<50 μm), High operating cost

Coalescences (depth Good oil removal Oil removal efficiency PM filtration) efficiency, Simple highly depends on the operation, Low initial and quality of filter bed media. 45,46,58–62 Slow oil removal process Operating cost

Membrane filtration High oil removal efficiency Requires pre-treatment of PM wastewater, High initial and operating cost, 63–65 Premature membrane fouling

Biological treatment Good oil removal Extremely temperature and PM efficiency, Low operating pH sensitive, Requires cost skilled operator Requires 41 wide space

I.5 Fibrous Sorbents

Fibrous sorbents of different origins; natural and synthetic, have been investigated for oil spill removal. Figure 7 shows some types of fibrous materials and their classification.68 In the textile industry, fibers are considered the basic unit of textile products, which are characterized by flexibility, fineness and high aspect ratio

(length-to-thickness) of ≥100. Textile technology has evolved over millennia, and the term textile now has a very broad meaning. In general, this term applies to product forms (fiber, yarn, and fabric); either from natural or synthetic sources as well as the products derived from them. This includes all types of yarns or ropes (threads, cords, ropes and braided), all kinds of fabrics (woven, knitted and nonwoven), hosiery

(knitwear and garments), household fibrous, furnishing and upholstery, industrial and technical fibrous (e.g. geotextiles, medical fibrous and fibrous composites).

Moreover, an earlier classification of fibrous material as reinforcements was established by Scardino.69 Numerous types of synthetic inorganic and organic fibers are used for commercial, industrial, and even medical purposes. Some of the major commercial uses of fibers are for thermal and acoustical insulation, filtration, and reinforcements. Thus, fibrous products aid in energy conservation (thermal insulation) and the removal of pollution (filtration). Medical uses of fibers include blood filtration and implant reinforcements.70

Polymeric man-made fibers are fabricated from natural or synthetic sources.

The consumption of man-made fibers based on synthetic polymers, frequently referred to as synthetic fibers, has grown rapidly since their introduction into the market in the 1940s and 1950s. Today in the United States, more than 50% of the fibers used in textile applications are man-made. The worldwide production of man- made fibers amounted to about 27 million metric tons in 1996.71,72

Figure 7: Fibrous materials and their classification68

The first man-made fiber was presented in 1889 at the World Exhibition in

Paris. Developments in the polymer and chemical industries – as well as in electronics and mechanics – have led to the introduction of new types of man-made fibers, especially the first synthetic fibers, such as nylon73, polypropylene74 and polystyrene75,76. Regenerated cellulosic fibers are a class of man-made fibrous materials manufactured from wood pulp or other natural sources of cellulose.

Besides the application of unmodified cellulose products, cellulose can be converted into regenerated cellulosic materials, which have been widely applied in many fields.77

Sorption by natural fibrous materials takes place by adsorption and coalescence method. Adsorption and coalescence (via depth filtration) showed reasonable and attractive results if appropriate media are used.68 In these mechanisms, no additional chemicals are required to emulsify oil in water, and high removal efficiencies of chemical oxygen demand (COD) from wastewater were demonstrated78. In general, natural fibrous oil sorbents contain micro and macroporous structures that permit an oil attachment and entrapment within inter- and intrafiber structures. Adsorption and coalescence mechanisms are often separately studied, although there is a very high probability that both mechanisms occur simultaneously. In both mechanisms, oil adsorption performance is commonly measured in terms of oil removal efficiency (% removal) and sorption capacity (mass of oil sorbed per gram sorbent).67

A number of natural sorbents have been studied in this regard such as straw79, sawdust48, corncob80, rice81, coconut husk82, cotton83, wood84, wool85, kenaf86, cattail41, and kapok ﬁbers69. However, it has been shown that most of them have disadvantages such as poor buoyancy, relatively low oil absorption capacity, low hydrophobicity, and high affinity towards water absorption68. Considering the high hydrophobicity of oil, the most proper sorbents should possess high hydrophobic as well. Therefore, the attention of environmental scientists has been driven towards the use of synthetic hydrophobic polymers, such as polypropylene87, polyurethane foams88, and polystyrene89. These synthetic sorbents have excellent hydrophobic and oleophilic properties68, and could be further treated to enhance their hydrophobic characteristics90. In addition to high hydrophobicity, fibers with high surface area are also expected to have higher sorption capacities. When the diameters of polymeric fibers are shrunk from micrometers (e.g. 10–100 µm) to submicron or nanometers

(e.g. 10–100 nm), there appear several surprising and useful characteristics such as very large surface area to volume ratio (this ratio for a nanofiber can be as large as

100 times of that of a microfiber), flexibility in surface functionalities, and superior mechanical performance (e.g. stiffness and tensile strength) compared with any other known form of the material. These outstanding properties make the polymer nanofibers to be optimal candidates for many critical applications.91

I.6 Fabrication of Fibrous Sorbents – Electrospinning Technique

A number of processing techniques such as drawing92, template synthesis93, self-assembly94, 95, electrospinning44, etc. have been used to prepare polymeric micro- to-nanofibrous sorbents in recent years.91 Electrospinning has been recognized as an efficient technique for the fabrication of polymer nanofibers. The process of

“electrospinning’’, was first discovered in 1934 by Formhals97. Within the following

10 years (1934-44), Formhals published a series of patents describing an experimental setup for the production of polymer fibers using an electrostatic force91, 97,98,99,100,101. The first spinning method adopted by Formhals had some technical disadvantages, such as the difficulty of completely drying the fibers obtained from spinning due to the short distance between the spinning and collection area, which resulted in a less aggregated web structure. In a subsequent patent,

Formhals refined his earlier approach98, where the distance between the feeding nozzle and the fiber collecting device was altered to provide more drying time for the electrospun fibers. Subsequently in 1940, Formhals patented a method for producing composite fiber webs from multiple polymeric sources by electrostatically spinning polymer fibers on a moving base substrate.103

The major advantage of the electrospinning process is its technical simplicity and ease of adaptability.104 Electrospinning unit is simple to construct. It consists of a high voltage electric source with positive or negative polarity, a syringe pump with capillaries or tubes to carry the solution from the syringe or pipette to the spinneret, and conducting collector. The collector could be metallic in origin such as aluminum, which can be shaped as flat plates, rotating drums, etc. A schematic drawing of the electrospinning unit is shown in Figure 8. Previous researchers have used an apparatus similar to the one given in Figure 8 with modifications depending on process conditions to spin a wide variety of fine fibers.104 Electrospun fibers can be made from solutions or melts of polymers, which are then forced through a syringe pump to form a pendant drop of the polymer at the tip of the capillary. High voltage is applied to the polymer solution into the syringe through an immersed electrode, or by direct contact with the syringe metallic needle, thereby inducing free charges into

23 the polymer solution. These charged ions move in response to the applied electric field towards the electrode of opposite polarity; grounded collector.105 At the tip of the capillary, the pendant hemispherical polymer drop takes a cone-like projection in the presence of an electric field. Additionally, when the applied potential reaches the critical value required in order to overcome the surface tension of the liquid, a jet of liquid is ejected from the cone tip.106 Various instability modes that occur during the fiber forming processes are expected to occur by the combined effect of both the electrostatic field and the material properties of the polymer. It has been suggested that the onset of different modes of instabilities in the electrospinning process may depend on the shape of the jet initiating surface and the degree of instability, which efficiently produces changes in the fiber morphology107.

Figure 8: Schematic diagram of electrospinning set-up.104

In electrospinning, the charge transport due to the applied voltage is mainly due to the flow of the polymer jet towards the collector, and the increase or decrease in the current is linked to the mass flow of the polymer from the nozzle tip. Deitzel et al. (2011) have inferred that the change in the spinning current is correlated to the change in the instability mode108. They experimentally showed that an increase in applied voltage causes a change in the shape of the jet initiating point, and hence the structure and morphology of fibers107. Earlier in 1971, Baumgarten while carrying out experiments with acrylic fibers observed an increase in fiber length of approximately twice with small changes in fiber diameter with an increase in applied voltage.109 Similarly, Megelski et al. (2013) have investigated the voltage dependence on the fiber diameter using polystyrene (PS) and showed that the PS fiber size decreased from about 20 µm to 10 µm with an increase in voltage from

5KV to 12KV, while there was no significant change observed in the pore size distribution, as shown in Figure 9.110

It has also been shown that varying the applied voltage has a significant effect on the formation of the Taylor cone. At relatively low applied voltages a pendant drop (depicted in light gray in Figure 9) is formed at the tip of the capillary, where after the Taylor cone (represented in dark gray) then forms at the tip of the pendant

Figure 9: Effect of varying the applied voltage on the formation of the Taylor

cone.110

27 drop. However, as the applied voltage is increased (moving from left to right) the volume of the pendant drop decreases until the Taylor cone is formed at the tip of the capillary. Increasing the applied voltage further results in the fiber jet being ejected from within the capillary, which is associated with an increase in bead defects as shown in Figure 10.111

The structure and morphology of electrospun fibers are easily affected by the nozzle to collector distance because of their dependence on the deposition time, evaporation rate, and whipping or instability interval.112 Megelski et al. (2013) observed bead formation in electrospun PS fibers on reducing the nozzle to collector distance while preserving the ribbon shaped morphology with a decrease in the nozzle to collector distance.113

The flow rate of the polymer from the syringe is another important process parameter as it influences the jet velocity and the material transfer rate. In the case of

PS fibers, Megelski et al. (2013) observed that the fiber diameter and the pore diameter increased with an increase in the polymer flow rate. As the flow rate increased, the fibers had pronounced beaded morphologies and the mean pore size increased from 90 to 150 nm Figure 11 shows the FESEM images of these PS fibers as a function of flow rate.113

Figure 10: Variation of beaded fibers as the mass ratio of water/ethanol was changed. Electric field is 0.5 kV/cm, weight fraction of PEO is 3.0%. The horizontal edge of each of the figures is 20 microns long.111

Figure 11: FESEM images of PS fibers as a function of flow rate: (a) 0.004 mL/min (5 kV, WD 9.5 mm); (b) 0.07 mL/min (15 kV, WD 5.5 mm); (c) 0.1 mL/min (15 kV, WD 5.2 mm); (d) 0.14 mL/min (15 kV, WD 5.5 mm); (e) 0.24 mL/min (15 kV, WD 5.5 mm).113

Research activity on the electrospinning of nanofibers has been successful in spinning submicron range fibers from different polymeric solutions and melts.

Although a vast amount of literature is available on the structure and morphological properties of polymeric micro- and nanofibers, there is very little published information on the electrohydrodynamics of the electrospinning process. Polymers with attractive chemical, mechanical, and electrical properties like high conductivity, high chemical resistance, and high tensile strength have been spun into ultrafine fibers by the electrospinning process, and their potential application in areas like filtration, optical fibers, drug delivery system, tissue scaffolds, and protective textiles have been examined.107 ,115. MacDiarmid et al. (2001) have electrospun polystyrene using THF as a solvent to produce nanofibers with a minimum diameter of 16 nm and an average diameter of 30.5 nm. He observed higher temperature in fibers due to higher conductivity.116

The production of nanofibers by the electrospinning process is influenced by both the electrostatic forces and the viscoelastic behavior of the polymer. Process parameters, like solution feed rate, applied voltage, nozzle-collector distance, and spinning environment, as well as material properties, like solution concentration, viscosity, surface tension, conductivity, and solvent vapor pressure, influence the structure and properties of electrospun nanofibers. Significant work has been done to correlate fibers’ characteristics to process parameters, and to characterize the properties of fibers as a function of process and material parameters.103

In terms of materials properties effect, solution concentration has been shown to limit boundaries for the formation of electrospun fibers due to variations in the viscosity and surface tension.107 Low strength solution forms droplets due to the

31 influence of surface tension while higher concentration prohibits fiber formation due to higher viscosity. Previously published literature has documented the difficulties in the electrospinning of polymers, for example, Megelski et al. (2002) have reported on the fiber morphology and pore formation of PS in THF in varied concentrations from 18 to 35 wt %. They found that the viscosity of the solution increased as the PS concentration increased while all other spinning parameters were kept constant.

Optical micrographs showed an increase in fiber diameter from 0.8 to 20 (±10) µm with increasing solution concentration. The PS fibers form beads up to a concentration of 30 wt %, with the occurrence of beads decreasing with increasing solution viscosity. As can be seen in Figure 12, the size of the beads as well as the size of the fibers increased with higher PS concentration.114

In addition to the above, electrospinning process can also be influenced by choices in nozzle configuration (single, single with emulsion, side-by-side, or coaxial nozzles). Depending on the application, a number of nozzle configurations have been employed. Perhaps the simplest and most common configuration is the single nozzle technique. In this configuration, a charged polymer solution flows through a single capillary. This configuration is very versatile and has been used to electrospun only polymer solutions117 as well as polymer blends (with soluble polymers) in common solvent. 110

Many synthetic and natural polymers have been electrospun using a variety of solvents, and their effect on the formation of pores was briefly described only by

Bognitzki et al (2000).118 Some work has been carried out on PS membranes, where the pores were found to be either a function of solvent density or created by thermally induced phase separation techniques.119–121 In the study as mentioned earlier, the physical properties of the solvents play a significant role in this process

32 and hypothesize that the solvent volatility plays a critical role in the pore formation process. 114

Figure 12: Optical microscope images of PS fibers electrospun from THF as a function of PS concentration: (a) 18 wt %; (b) 20 wt %; (c) 25 wt %; (d) 28 wt %; (e) 30 wt %; (f) 35 wt %.114

In general, a very high density of pores was observed on PS fibers electrospun from THF, and the resulting microtexture induced at the fiber surface increases the surface area by as much as 20 to 40% depending on the diameter of the fiber.122 Substitution of THF observed the influence of the solvent vapor pressure with DMF, with the microtexture and nanopores of the PS fibers disappearing as the volatility of the mixed solvent system decreased.114

The characterization of fibers produced by the electrospinning process remains one of the most difficult tasks as the chances of getting single fibers are rare.

In order to empirically understand electrospinning process, assessment of the entire process from polymer selection to mechanical testing needs to be carried out accurately. In electrospinning, the polymers used are characterized into four distinct categories: physical, structural, mechanical, and chemical123. Presently, nanofibers have attracted the attention of researchers due to their remarkable micro and nanostructural characteristics, high surface area, small pore size, and the possibility of their producing three-dimensional structures that enable the development of advanced materials with sophisticated applications.124 Physical characterization is associated with structure and morphology of the sample and the nanofibers internal structure determines the physical and mechanical properties. Geometric properties of nanofibers include fiber diameter, diameter distribution, fiber orientation, and fiber morphology (e.g. cross-section shape and surface roughness). For the characterization of geometric properties, techniques such as scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) were used 125,126,114,127–130 . SEM has been used by many researchers to observe the morphology of the fibers produced,109,125,126,131–133 as SEM is capable of detecting

35 fiber diameters and morphologies, but the resolution is less at extreme magnifications. Figure 13 shows the typical SEM image of Polystyrene electrospun fibers. For SEM, there is a requirement for the samples to be electrically conductive, therefore, for most of the electrospun polymers produced, a gold or platinum coating must be applied that may alter the diameter readings at higher magnifications.

Nevertheless, SEM remains a quick method for observing the fibers produced, and it requires a slight sample size for its operation.124

Figure13: SEM images of spun fibers electrospun from a 30 wt % PS/DMF solution under (a) 43%, (b) 37%, (c) 24%, (d) 22%, (e) 15%, (f) 11% with relative humidity (scale bar: 5 µm).134

Chapter 2: Objectives

The following is a detailed list of objectives of the current work:

1) Prepare the appropriate polystyrene solutions with different concentrations

suitable for electrospinning

2) Fabricate fibers with micro and/or nano diameters of synthetic (pure) and

recycled polymers with variable fiber size distribution

3) Optimize the electrospinning conditions that will yield fibers with uniform

size distribution within the mm -nm scale, and to characterize the fibers

prepared there of.

4) Evaluate the electrospunfibers of all types of polystyrene polymers for the

removal of various types of oil spills from aqueous media

5) Model the process of oil spills using prepared fibers and correlate the

efficiency of oil pick-up capacity with the structure and morphology of the

prepared fibers.

Chapter 3: Materials and Methods

3.1 Materials

The starting materials included two types of polystyrene PSI (Mw = 100,000 g/mol) and PSII (Mw = 350,000 g/mol), were purchased from Avocado Research

Chemicals Ltd, and Sigma-Aldrich Companies. In addition, a recycled polystyrene

(PSCIII) was also used by using foam and Styrofoam cups. Solvents included N, N- dimethylformamide (DMF) (>99.8%), and was purchased from Fluka, while tetrahydrofuran (THF) (>99.8%) was purchased from LiChrosolv. Polymers used in the current study were designated as PSI, PSII, and PSCIII, respectively, and were all used as received. Crude oils used in the current study were supplied by ADNOC,

TOTAL, and ADCO; all in Abu Dhabi, UAE with labeled densities. The Crude oil properties investigated are listed in Table 3.

Table 3. Properties of the Crude oil, measured at room temperature.

Crude Oil Types Density (g/cm3) Viscosity cP @50RPM

ADNOC 0.869 38.5

TOTAL 0.867 7.0

ADCO 0.829 4.1

Each crude oil’s viscosity was measured using viscometer (Brookfield Viscometer by using spindle S34).

3.2 Methods

3.2.1 Fabrication of PS Microfibers

Homogeneous solutions of PSI, PSII and PSCIII containing 20, 30, and 40 w/v% were prepared by dissolving the corresponding amounts of the polymer beads in DMF, THF or a mixture of both. Polymer microfibers were made using an electrospinning technique where each of the polymer solutions was injected at a feeding rate of 10 ml/hr using an automatic syringe pump, and a voltage of 15 kV, provided by a Gama High Voltage Research power supply, towards a grounded metallic collector. The collector is located at a distance of 15 cm from the syringe needle. The electrospinning process was carried out under laboratory humidity and at room temperature. The whole electrospinning assembly was kept inside a Plexiglas box to avoid the effect of external airflow and change in temperature and humidity around the system when in use. Electrospun fibers were collected on a flat square aluminum foil sheet and were left till complete dryness before studying their morphology and before evaluating their sorption capacities.

In order to study the effect of electrospinning parameters on the sorption capacities of the fibrous sorbents, an optimization procedure was carried out in which six electrospinning parameters were evaluated. In the following sections, details about each variable will be given. It should be mentioned that each parameter was separately varied while keeping all other parameters constant, in order to carefully optimize the electrospinning process and produce fibers with maximum affinity towards crude oil collection.

Ø Effect of Solvents: Polystyrene solutions (PSI, PSII and PSCIII) of

concentrations 20%, 30% and 40% were prepared by dissolving each of them in

DMF, THF and their mixtures at volume ratios of 100/0, 75/25, 50/50, 25/75, and

0/100. All other electrospinning parameters were kept constant.

Ø Effect of Applied Voltage: Microfibers were collected at applied voltages of

10KV, 15KV, 20KV, 25KV and 30KV.

Ø Effect of Feeding Rate: Polymer solutions were fed through the syringe using an

automatic syringe pump at feeding rates of 1, 5, and 10 ml/h.

Ø Effect of Distance: As mentioned above, this is the distance between the tip of

the syringe needle and the grounded metallic collector. Distance was varied at 10,

15, and 20 cm.

Ø Effect of Humidity: The presence of humidity is known to affect the fibers’

surface topography. It should be mentioned that electrospinning setup and

experiment was all carried out in a closed plexiglass box to avoid external air

flow, temperature and humidity effects on the fibers during their formation. In

the current study, microfibers were collected under the effect of relative humidity

adjusted at 49, 70-80, and 80-90 % by using humidifier.

Ø Effect of Needle Diameter: It is known that diameter of the needle determines

the starting size of the fibers before their deposition onto the grounded collector.

In this regard, needles with gauge numbers of 18G, 21G, 23G and 29G were

used.

3.2.2 Characterization of the Sorbents

Starting polymers (as-received) were characterized for their composition using FT-IR spectroscopy to characterize the polymer composition. This was carried out on a polymer thin film cast a solution containing 20% of each of the polymers in

DMF. Electrospun PSI, PSII, and PSCIII microfibers were characterized for their morphology, BET surface area, and pore size distribution. Analysis of the fibers morphology was carried out using a scanning electron microscope (JOEL-6010) after being gold-coated. Fibers size and distribution were calculated using image analysis software (ImageJ, National Institutes of Health, Bethesda, Maryland). BET surface area, porosity, and pore size distribution were carried out using a nitrogen gas adsorption at 77 K employing a Quantochrome NOVA 1000 volumetric gas sorption instrument; Autosorb, USA.

3.2.3. Sorption Experiments

In a typical sorption experiment, 10 ml of crude oil was poured into a 250-mL beaker containing 100 mL artificial seawater (3.5% NaCl). Different amounts of each of the polymeric microfibrous sorbents (0.005, 0.01, 0.05, and 0.1g) were then evenly placed onto the oil surface. After various time intervals, namely, 0.5, 1, 2, 5,

10 and 30 minutes, the sorbent containing the adsorbed oil was collected, drained for one minute, and placed on a watch glass for weighing. All experiments were performed at ambient temperature and all weighing performed using an analytical balance with readability up to 0.01mg (5 decimal places). The oil sorption capacity

(g/g) of the sorbent was determined by following equation (Tanobe et al., 2008)135.

m -m Q = o s ms

Where Q is the oil sorption capacity (g/g), mo is the total mass of sorbent after the oil drained, and ms is the mass of the dry sorbent. Results are expressed as an average of triplicate readings.

Chapter 4: Results and Discussion

In the following sections, characterization of the starting materials will be first shown, followed by discussing the application of the fabricated polymeric microfibers in the removal of crude oil spills. In the second part of this chapter, detailed optimization of the electrospinning process will be discussed and the effect of optimizing the electrospinning parameters on the sorption capacities of the fibers prepared thereafter will be deliberated.

4.1 Characterization of the Starting Materials

4.1.1 Crude Oil

Three types of crude oils were used in the current study. These were obtained from oil companies in UAE. Studying the density and viscosity of these oils showed their variability. Figure 14 (a,b) shows densities and viscosities of the oils, respectively. Although the three oils showed minor variation in their densities, a more pronounced variation in their viscosities was found. ADNOC crude oil showed the highest viscosity, while ADCO crude oil had the lowest. It should be mentioned that variation in the densities and viscosities of crude oil depend on the composition of the oil, where crude oil is essentially a mixture of many different hydrocarbons, all of varying chain lengths and complexities.

(a) 1.4

1.2

)

3 1.0 0.8 0.6 Density (g/cm Density

0.4

0.2

0.0 TOTAL ADNOC ADCO

Type of Crude Oil

45 (b) 40 35 30 25 20 15 Viscosity, cP@50 RPM 10 5

0 TOTAL ADNOC ADC O

Type of Crude Oil

Figure 14: Density (a) and Viscosity (b) of crude oils used in the current

study

4.1.2 Polystyrene

In the current study, polystyrene of different origins were used. Analytical- grade polystyrene (PSI and PSII) were obtained from Sigmal-Aldrich, while commercial polystyrene (PSCIII) was prepared by recycling styrofoam sheets and cups. In order to confirm phase composition, all types of polystyrene were analyzed by FTIR; Figure 15. All polystyrene bands were shown at their corresponding wave numbers known in the literature. Bands such as those at 3081.2-3001.1 cm-1 and

2923.91 cm-1 and 2850.40 cm-1 corresponding to the stretching mode of aromatic C-

H and at 1943.2-1728.3 cm-1 corresponding to the aromatic CH asymmetric stretching mode were all observed in the IR spectra of all types of polystyrene. These findings indicate the high purity of the analytical-grade polystyrene and surprisingly indicate the exceptional high purity of the recycled polystyrene samples. No evidence of non-polystrene reagents, which are usually used in manufacturing polystyrene foam, was found.

Molecular weights of PSI and PSII starting polymers were confirmed by GPC analysis (University of Sharjah) to match the information of the supplier. In addition, molecular weight of PSCIII was also measured using GPC analysis. Results are shown in Figure 16.

340 PSI 320

300

PSII

280 T%

260 PSCIII

240

220

200 3000 2500 2000 1500 1000 500 Wavenumbers (cm-1)

Figure 15: FT-IR spectra for PSI, PSII, and PSCIII polymers

450

400 (350 KDa) 350 ) 3

300 X10 (

250 (216 KDa)

200

150 (100 KDa) M.Wt,*Daltons * 100

0 PSI PSII PSCIII Polystyrene*Type

Figure 16: Weight-based Molecular weight of PSI, PSII, and PSCIII polymers

4.2 Characterization of the Polymeric Microfibers

Polystyrene of different origins (PSI, PSII and PSCIII) were electrospun into fibers using a pre-organized set of electrospinning conditions. Those were voltage of 15 kV, feeding rate of 10 ml/hr, spinning distance of 15 cm and laboratory humidity (47% relative humidity). Under these conditions, solutions containing 20,

30, and 40 wt% of each of the polymers were electrospun into fibers. Those were characterized for their morphology using SEM, and surface area and pore size distribution using N2- adsorption. Figures 17-19 show SEM micrographs of microfibers electrospun from solutions containing 20, 30, and 40 wt%, respectively.

All samples showed the formation of randomly distributed micro-scale fibers with cylindrical morphology. No signs of other non-fibrous morphologies, such as beads, ribbons, islands, or films, were found. Results of the fiber size distribution of these fibrous samples are shown in Figures 20-22. An average fiber size of 3.5 mm was shown in the fibers produced from 20, 30, and 40 wt% solutions of PSI with a slight increase with increasing the initial concentration of the polymer solutions; Figure

20. On the other hand, average fiber size of 5, 7, and 10 mm were shown in the fibrous samples produced by the electrospinning of 20, 30, and 40 wt% PSII solutions; Figure 21. The relatively higher average fiber size produced from the spinning of PSII solutions than the PSI solutions could be related to the higher molecular weight of PSII than PSI (100,000 vs. 350,000 Da, respectively). Fibers produced from the spinning of solutions containing 20, 30, and 40 wt% of recycled polymer (PSCIII) showed an average sizes of 1, 4.5 and 7 mm, respectively;

Figure 22. These confirm the effect of initial molecular weight of the polymer on the average size of fibers, where molecular weight of PSCIII was midway between that of PSI and PSII; 216,000 Da. Increasing the molecular weight of the polymers is

48 known to highly affect the viscosity of solutions prepared thereof. This, in turn, is also known to be yield coarser fibers. High magnification micrographs of fibers produced from the spinning of 20wt% solutions of the three polymers are shown in

Figure 23. Micrographs confirmed the cylindrical morphology of the fibers with low surface roughness and signs of internal porosity. Surface roughness and internal porosity could be related to the immediate evaporation of the solvent as a result of fibers deposition during electrospinning.

Figure 17: SEM micrographs of a) PSI, b) PSII, and c) PSCIII fibrous sorbents obtained by electrospinning 20 wt% solutions of each polymers in DMF

Figure 18: SEM micrographs of a) PSI, b) PSII, and c) PSCIII fibrous sorbents obtained by electrospinning 30 wt% solutions of each polymers in DMF

Figure 19: SEM micrographs of a) PSI, b) PSII, and c) PSCIII fibrous sorbents obtained by electrospinning 40 wt% solutions of each polymers in DMF

14 (a)

Frequency

0 1 2 3 4 5 6 7 Size (µm) (b)

4 Frequency 2

0 1 2 3 4 5 6 7

Size (µm)

Frequency 2

0 1 2 3 4 5 6 7 Size (µ m)

Figure 20: Fiber size distribution of fibrous sorbents obtained by electrospinning of (a) 20%, (b) 30%, and (c) 40% solutions of PSI polymers in DMF

16 (a)

Frequency 6

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Size (µm) 10 (b)

4 Frequency

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Size (µm) 10 (c) 9

8 7

Frequency 4

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Size (µ m)

Figure 21: Fiber size distribution of fibrous sorbents obtained by electrospinning of (a) 20%, (b) 30%, and (c) 40% solutions of PSII polymers in DMF

54 4 (a)

2 Frequency

0 1.0 1.5 2.0 Size (µm)

2.5 (b)

2.0

1.5

1.0

Frequency

0.5

0.0 3.5 4.0 4.5 5.0 5.5 6.0 Size (µm) 3.5 (c) 3.0

2.5

2.0

1.5

Frequency

1.0

0.5

0.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0

Size (µm)

Figure 22: Fiber size distribution of fibrous sorbents obtained by electrospinning of (a) 20%, (b) 30%, and (c) 40% solutions of PSCIII polymers in DMF

Figure 23: High magnification SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% solutions of (a) PSI, (b) PSII, and (c) PSCIII polymers in DMF

Assessment of the fibers porosity was carried out by adsorption-desorption experiments using N2 adsorption. Figure 24 shows adsorption-desorption hysteresis of fibers produced from the electrospinning of 20 wt% solutions of the three polymers. All fibers showed type IV isotherms with a low extent of N2 adsorption, which is related to the low surface roughness of the fibers. As a result of the nonwoven nature of the fibers, pore size distribution was measured; shown in Figure 25.

The absence of high surface roughness of the fibers of all polymers was reflected in the presence of minor meso- and micro-porosity within the fibers. The distribution curves showed, on the other hand, macro-porosity, which could be related to the interconnected porosities present within the fibrous sorbents.

3.5 PSI PS II PSCIII 3.0

2.5

2.0

1.5 adsorbed (cc/g) 2 1.0

0.5

Amount of N 0.0

0.0 0.2 0.4 0.6 0.8 1.0

o Relative Pressure (P/P )

Figure 24: Adsorption Isotherms of fibrous sorbents obtained by electrospinning solutions containing 20 wt% of each of the polymers in DMF

1.6 PSI PSII PSCIII 1.4

1.2

1.0

0.8 adsorbed (cc/g) 2

0.6

0.4 Amount of N 0.2

0.0 10 100 1000 Pore size (A)

Figure 25:Pore Size distribution of fibrous sorbents obtained by electrospinning solutions containing 20 wt% of each of the polymers in DMF

4.3 Oil Sorption Experiments

4.3.1 ADNOC Crude Oil

Electrospun polystyrene fibers fabricated from solutions containing 20, 30, and 40 wt% PSI, PSII and PSCIII were evaluated for their efficiency in collecting

ADNOC crude oil spills in simulated salty water. In addition, sorption capacity was evaluated as a function of the sorbent weight. Figures 26 show the sorption capacity

(g/g) of the crude oil using 0.0044, 0.0066, 0.05 and 0.1 g of fibrous sorbents prepared from solutions containing 20 wt% of PSI, PSII, and PSCIII polymers.

Sorption experiments were conducted for 30 minutes. All sorption curves showed a similar pattern with an instant sorption of the crude oil by the fibrous sorbent within the first 30 seconds of the sorption experiment. Initial sorption did not take place on a gradual basis similar to the adsorption of gasses onto solid sorbents. Instead, sorption was instant and is attributed to the strong hydrophobic-hydrophobic interaction between the polymeric fibrous sorbent and the crude oil floating on the surface of an aqueous medium. Figure 27 shows the maximum sorption capacities achieved after 30 seconds using various weights of the fibrous sorbents that were prepared from solutions containing 20 wt% of PSI, PSII, and PSCIII. A general trend can be derived from this graph, where the instantaneous sorption decreased with increasing the weight of the sorbent regardless of the type of polymer. It should be mentioned that all experiments were conducted at a constant volume of the oil. This indicates that a minimum amount of each of the sorbents was essentially used for collecting the crude oil from water. In addition, the cotton-like visual morphology of the fibrous sorbents and the random distribution of the fibers indicate that increasing the sorbent weight will increase the volume-to-weight ratio, which will make it difficult for the highly

240 240 (b) (a) 220 220 PSI PSII PSCIII 200 PSI PSII PSCIII 200 180 180 160 160 140

140 120 120 100 100 80 Sorption capacity (g/g) 80 Sorption capacity (g/g) 60

60 40 0 5 10 15 20 25 30 0 5 10 15 20 25 30

Time (min) Time (min)

100 100 95 (d) 95 (c) 90 PSI PSII PSCIII 90 PSI PSII PSCIII 85 85 80 80 75 75 70 65 70

60 65 55 60 50 55 Sorption capacity (g/g) 45

Sorption capacity (g/g) 50 40 45 35 40 30 25 0 5 10 15 20 25 30 0 5 10 15 20 25 30

Time (min) Time (min)

Figure 26: Sorption capacities of ADNOC crude oil onto (a) 0.0044g, (b) 0.0066g, (c) 0.05g, and (d) 0.1g fibrous sorbents prepared from electrospinning of 20 wt% solutions of the polymers in DMF

200 PSI PSII PSCIII 180

160 140

120

100

60 40

30 seconds sorption capacity (g/g) capacity sorption 30 seconds 20

0 0.00 0.02 0.04 0.06 0.08 0.10 Sorbent weight (g)

Figure 27: Maximum sorption capacities achieved after 30 seconds using various weights of the fibrous sorbents that were prepared from solutions containing 20 wt% of PSI, PSII, and PSCIII

61 viscous crude oil to penetrate within the interconnected porosities of the fibrous sorbents. Figure 28 shows photographs taken during sorption experiments. They clearly indicates the cotton- like nature of the fibrous sorbents and strong interaction between the crude oil and the sorbent.

Fibrous sorbents prepared from 30 and 40% polymeric solutions showed a similar pattern, with overall lower sorption capacities. Figures 29 and 31 show the corresponding sorption capacities, respectively, as a function of the sorbent weight.

The highest achieved sorption capacities after 30 seconds were also recorded and plotted in Figures 30 and 32, respectively. Results also indicate that maximum sorption was achieved when 0.0044 g of sorbent was used. Figure 33 summarizes the sorption capacities of sorbents prepared from 20, 30, and 40 wt% solutions of

PSI, PSII, and PSCIII at a constant sorbent weight of 0.0044 g. It can be shown that the initial instantaneous sorption decreased with increasing the initial concentrations of the polymers. This could be attributed to the increase in the fibers dimensions as the initial concentrations of the polymer solutions were increased. This is reflected in an overall decrease in the surface area of the fibers; a major property that dictates the high sorption capacity of the fibers. On the other hand, results shown in Figure 33 do not clearly indicate the effect of molecular weight of the polymers on their sorption capacity as a function of the concentrations of the polymer solutions.

(a (b ) )

(c (d ) )

Figure 28: Steps of the sorption capacity experiments

(a) 150 140 (b) PSI PSII PSCIII 140 PSI PSII PSCIII 130 120 120

110 100 100

90 80 80 Sorption capacity (g/g) Sorption capacity (g/g) 70 60 60

0 5 10 15 20 25 30 0 5 10 15 20 25 30

Time (min) Time (min)

100 100 (c) (d) 90 90 PSI PSII PSCIII PSI PSII PSCIII 80 80

70 70 60

50 50

40 Sorption capacity (g/g) 40

Sorption capacity (g/g) 30 30 20 0 5 10 15 20 25 30 0 5 10 15 20 25 30

Time (min) Time (min)

Figure 29: Sorption capacities of ADNOC crude oil onto (a) 0.0044g, (b) 0.0066g, (c) 0.05g, and (d) 0.1g fibrous sorbents prepared from electrospinning of 30 wt% solutions of the polymers in DMF

200 PSI PSII PSCIII 180

160

140

120 100

(g/g) capacity sorption 30 seconds 0 0.00 0.02 0.04 0.06 0.08 0.10

Sorbent weight (g)

Figure 30: Maximum sorption capacities achieved after 30 seconds using various weights of the fibrous sorbents that were prepared from solutions containing 30 wt% of PSI, PSII, and PSCIII

200 200 (a) (b) 180 180 PSI PSII PSCIII PSI PSII PSCIII 160 160

140 140 120

120 100 100 80 80 Sorption capacity (g/g) Sorption capacity (g/g) 60 60 40 0 5 10 15 20 25 30 0 5 10 15 20 25 30

Time (min) Time (min)

100 100 (c) 95 (d) 95 PSI PSII PSCIII 90 PSI PSII PSCIII 90 85 85 80 75 80 70 75 65

70 60 55 65 50

Sorption capacity (g/g) 60 45 Sorption capacity (g/g) 40 55 35 50 30 0 5 10 15 20 25 30 0 5 10 15 20 25 30 Time (min) Time (min)

Figure 31: Sorption capacities of ADNOC crude oil onto (a) 0.0044g, (b) 0.0066g, (c) 0.05g, and (d) 0.1g fibrous sorbents prepared from electrospinning of 40 wt% solutions of the polymers in DMF

200 PSI PSII PSCIII 180

160

140

120

100

80 60

(g/g) capacity sorption 30 seconds 0 0.00 0.02 0.04 0.06 0.08 0.10 Sorbent weight (g)

Figure 32: Maximum sorption capacities achieved after 30 seconds using various weights of the fibrous sorbents that were prepared from solutions containing 40 wt% of PSI, PSII, and PSCIII

200 PSI PSII PSCIII 180

160

140

120 100

20 30 seconds sorption capacity (g/g) capacity sorption 30 seconds 0 20 30 40

Initial Polymer Concentration (%)

Figure 33: Highest achieved sorption capacities after 30 sec of fibrous sorbents (0.0044g/each) prepared from electrospinning of 20, 30, and 40 wt% solutions of each of the polymers in DMF

Upon initial adsorption of the crude oil onto and into the fibers, desorption of the un-adsorbed oil started to take place on a gradual basis within the following 30 minutes duration of the experiment. This pattern was observed in all experiments.

Desorption could be related to the presence of weakly adsorbed layers of oil that were not directly attracted to the fibrous sorbent through the hydrophobic- hydrophobic interaction. Therefore, it could be stated that the high cohesive forces between various hydrocarbons in the crude oil predominated in these externally adsorbed layers, leading to their desorption. In addition, the gradual desorption could be related to the high viscosity of the crude oil. Figure 34 shows the 30 minutes sorption capacities of the oil onto fibrous sorbents of the three polymers at a constant sorbent weight of 0.0044g. These results also imply the percent oil remaining into and onto the fibrous sorbent after 30 minutes of adsorption. A pattern similar to that shown in Figure 33 was observed where the amount of adsorbed oil remaining in the fibrous sorbent was directly related to that initially adsorbed after 30 seconds.

200 PSI PSII PSCIII 180

160

140

120

100 80

20 30 minutes sorption capacity (g/g) capacity sorption 30 minutes 0 20 30 40 Initial Polymer Concentration (%)

Figure 34: Highest achieved sorption capacities after 30 min of fibrous sorbents prepared from electrospinning of 20, 30, and 40 wt% solutions of each of the polymers in DMF

It should be mentioned that sorbent loaded with oil was removed from the media after 30 seconds and left for dripping in a petridish. Therefore, the desorbed oil was dripped in the petridish, and is was retrieved. This means that the removed oil spill is completely collected despite the desorption of the externally bound layers of oil. The retrieved water-free oil can therefore be recycled. To estimate the extent of retrieval of oil, the following equation was applied:

� − � % Retrieval = ! ! x 100 �!

Where:

wi: is the sorption capacity (g/g) after 30 seconds (initial)

wf: is the sorption capacity (g/g) after 30 minutes (Final)

Figures 35 show the extent of retrieval of crude oil after desorption from the fibrous sorbents of different weights electrospun from solutions containing 20, 30, and 40 wt% of PSI, PSII, and PSCIII. These results indicate that a maximum of 40% oil can be retrieved during the process of its removal from aqueous media. Despite the absence of a direct correlation between the type of polymer, its concentration or the weight of sorbent, a general trend can be derived where PSII sorbents of all percentages showed the highest percent of retrieval followed by PSCIII then PSI sorbents.

(b) (a) 40% 40 40 40% 30% 20% 30% 20% 40% 30% 30 30 30% 20% 40% 30% 30% 20% 20% 20% 40% 20 40% 20 % Retrival % Retrival 10 10

0 0 PSI PSII PSCIII PSI PSII PSCIII Type of Polymer Type of Polymer

40 (d) (c) 30% 20% 40 30% 40% 30 20% 30% 40% 20% 30 20% 40% 40% 20% 20 40% 40% 20

% Retrival 20% % Retrival 30%

10 10 30% 30%

0 0 PSI PSII PSCIII PSI PSII PSCIII Type of Polymer Type of Polymer

Figure 35: Extent of retrieval (%) of ADNOC crude oil adsorbed onto PSI, PSII, and PSCIII fibrous sorbents (a) 0.0044g, (b) 0.0066g, (c) 0.05g, and (d) 0.1g prepared by the electrospin of 20, 30, and 40 wt% solutions of each of the polymers in DMF

4.3.2 TOTAL Crude Oil

Based on the findings of the sorption of ADNOC crude oil onto PSI, PSII and

PSCIII fibrous sorbents, two weights of the sorbent were chosen for further evaluation on their performance on removal TOTAL crude oil from simulated salty water. Those were 0.005 and 0.01 g. As was previously mentioned, TOTAL crude oil was shown to have a close density to that of ADNOC crude oil, but was found to be

20% less viscous. Fluidity of the oil during the sorption experiments is, therefore, expected as compared to that of ADNOC crude oil. Figures 36-38 show the sorption capacities of 0.005 and 0.01 g – sorbents prepared from solutions containing 20, 30 and 40 wt% of PSI, PSII, and PSCIII polymers, respectively. All sorption experiments showed an initial instantaneous sorption onto the fibrous sorbents after

30 seconds of sorption. However, the maximum achieved sorption capacities were inferior to those obtained during the sorption of ADNOC crude oil onto the same sorbents. These results could be related to the difference in viscosity of the oils, hence their variation in fluidity during sorption. Highly viscous ADNOC crude oil was shown to highly adsorb onto the fibrous sorbents. As was mentioned before, viscosity is related to the presence of long chain hydrocarbons in the oil. The higher viscosity of ADNOC crude oil could be related to the presence of higher molecular weight hydrocarbons than those present in the less viscous TOTAL crude oil. This brings in an important hypothesis where higher molecular weight hydrocarbons indicate higher degree of hydrophobicity, which was reflected in higher sorption capacities onto the hydrophobic fibrous sorbent. On the other hand, the low viscosity of the TOTAL oil indicates the presence of lower hydrophobic species, which could strongly explain the lower sorption capacities of this oil onto the fibrous sorbents.

100 (a) 90 PSI P S II P S C III

40 Sorption Capacity (g/g) 30

0 5 10 15 20 25 30 Time (min)

100 (b)

90 PSI P S II P S C III

Sorption Capacity (g/g) 40

0 5 10 15 20 25 30 Time (min)

Figure 36: Sorption capacities to TOTAL crude oil of fibrous sorbents (a) 0.005g, and (b) 0.01g prepared from electrospinning of 20 wt% solutions of the polymers in DMF

70 (a) PSI P S II P S C III 60

Sorption Capacity (g/g)

0 5 10 15 20 25 30 Time (min)

70 (b) PSI P S II P S C III 60

40 Sorption Capacity (g/g) 30

20 0 5 10 15 20 25 30 Time (min)

Figure 37: Sorption capacities to TOTAL crude oil of fibrous sorbents (a) 0.005g, and (b) 0.01g prepared from electrospinning of 30 wt% solutions of the polymers in DMF

70 (a) PSI P S II P S C III

Sorption Capacity (g/g) 30

20 0 5 10 15 20 25 30 Time (min)

70 (b) PSI P S II P S C III

40 Sorption Capacity (g/g)

0 5 10 15 20 25 30 Time (min)

Figure 38: Sorption capacities to TOTAL crude oil of fibrous sorbents (a) 0.005g, and (b) 0.01g prepared from electrospinning of 40 wt% solutions of the polymers in DMF

Figure 39 (a-c) shows a comparison between the highest achieved sorption capacities of the sorbents prepared from 20, 30, and 40% solutions of the three polymers, respectively as a function of the sorbent weight after 30 seconds of sorption. An overall trend can be derived where doubling the weight of the sorbent showed a slight increase in the initial instantaneous sorption capacities in all experiments. On the other hand, there was an insignificant effect of the initial solution concentration, from which sorbents were prepared, on the sorption capacities. Moreover, the effect of molecular weight of the polymer on the sorption capacities was also insignificant.

Upon instant adsorption of the TOTAL crude oil onto the fibers, desorption of the weakly adsorbed oil started to take place during the 30 minutes duration of the experiment. This behavior was observed in all experiments involving TOTAL crude oil and is similar to that shown in the desorption of ADNOC crude oil from the fibrous sorbents. Calculations of percent retention and percent retrieval of the

TOTAL oil after 30 minutes are plotted in Figures 40-41, respectively. A direct relationship can be also derived between the remaining oil in the fibrous sorbent and the initially adsorbed oil after 30 seconds. These results also indicate the possibility of retrieving 60% of the adsorbed TOTAL oil. Compared with 40% retrieval of the

ADNOC crude oil, the difference could be related to the lower viscosity of the

TOTAL oil and the lower extent of initial adsorption with the fibrous sorbents.

100 (a) PSI PSII PSCIII 90 80 70

10 (g/g) capacity sorption 30 seconds 0 0.005 0.010 Weight of Sorbent (g)

100 (b) PSI PSII PSCIII 90 80

70 60

30 seconds sorption capacity (g/g) capacity sorption 30 seconds 10 0 0.005 0.010 Weight of Sorbent (g)

100 (c) PSI PSII PSCIII 90 80 70

(g/g) capacity sorption 30 seconds 10

0 0.005 0.010 Weight of Sorbent (g)

Figure 39: Highest achieved sorption capacities capacities to TOTAL crude oil after 30 sec of fibrous sorbents (0.005g & 0.01g) prepared from electrospinning of (a) 20 wt%, (b) 30 wt%, and (c ) 40 wt% solutions of each of the polymers in DMF

78 100 (a) PSI PSII PSCIII 90 80

50 40 30

(g/g) capacity sorption 30 minutes 10

0 0.005 0.010 Weight of Sorbent (g) 100 (b) PSI PSII PSCIII 90

70 60 50

10 (g/g) capacity sorption 30 minutes 0 0.005 0.010 Weight of Sorbent (g) 100 (c) PSI PSII PSCIII 90 80 70

40 30 20

(g/g) capacity sorption 30 minutes 10 0 0.005 0.010 Weight of Sorbent (g)

Figure 40: Highest achieved sorption capacities capacities to TOTAL crude oil after 30 min of fibrous sorbents sorbents (0.005g & 0.01g) prepared from electrospinning of of (a) 20 wt%, (b) 30 wt%, and (c ) 40 wt% solutions of each of the polymers in DMF

70 (a)

20% 20% 60

30% 40% 50 40% 30%

40 20% 30% 30 40% % Retrival 20

0 PSI PSII PSCIII Type of Polymer

40 (a) 20%

40% 30 20% 30%

20 40% 40% 20% % Retrival 30%

10 30%

0 PSI PSII PSCIII Type of Polymer

Figure 41:Extent of retrieval (%) of TOTAL crude oil adsorbed onto PSI, PSII, and PSCIII fibrous sorbents (a) 0.005g, and (b) 0.01g prepared by the electrospinnig of 20, 30, and 40 wt% solutions of each of the polymers in DMF

4.3.3 ADCO Crude Oil

Fibrous sorbents prepared from solutions containing 20, 30, and 40 wt% of

PSI, PSII, and PSCIII polymers were also used for the sorption of ADCO crude oil.

Based on the results shown in Figure 14, ADCO oil is less viscous than both

ADNOC and TOTAL crude oils. Its viscosity is around 10% that of the viscosity of

ADNOC oil but is closer to the viscosity of TOTAL oil, hence it has more fluidity than both oils. Figures 42-44 show sorption capacities of fibrous sorbents (0.005 and

0.01 g) to ADCO oil. Despite the lower viscosity of the oil than the other oils, it showed an instant adsorption onto the fibrous sorbents within the first 30 seconds of the experiment. This behavior is similar to what was shown with both ADNOC and

TOTAL.

80 (a) PSI PSII PSCIII

Sorptioncapacity(g/g) 40

30 0 5 10 15 20 25 30

Time (min)

80 (b) 75 PSI PSII PSCIII

65 60 55

35 Sorption capacity (g/g) 30 25 0 5 10 15 20 25 30

Time (min)

Figure 42: Sorption capacities to ADCO crude oil of fibrous sorbents (a) 0.005g, and (b)0.01g prepared from electrospinning of 20 wt% solutions of the polymers in DMF

80 (a) PSI PSII PSCIII 70

30 Sorption capacity (g/g) 20

10 0 5 10 15 20 25 30

Time (min)

80 (b) PSI PSII PSCIII 70

Sorption capacity (g/g) 20

10 0 5 10 15 20 25 30

Time (min)

Figure 43: Sorption capacities to ADCO crude oil of fibrous sorbents (a) 0.005g, and (b)0.01g prepared from electrospinning of 30 wt% solutions of the polymers in DMF

75 (a) 70 PSI PSII PSCIII

50 45

40 Sorption capacity (g/g) 35

30 0 5 10 15 20 25 30

Time (min)

75 (b) PSI PSII PSCIII 70 65

Sorption capacity (g/g) 35

25 0 5 10 15 20 25 30 Time (min)

Figure 44: Sorption capacities to ADCO crude oil of fibrous sorbents (a) 0.005g, and (b)0.01g prepared from electrospinning of 40 wt% solutions of the polymers in DMF

Figure 45 shows highest achieved sorption capacities after 30 seconds of experiment. Values shown in these graphs are closer to those achieved with TOTAL crude oil, where the highest achieved sorption capacity was 68 g/g. Externally adsorbed oil started to desorb from the surfaces of all sorbents within the following

30 minutes of the sorption experiment reaching a plateau after 10 minutes of sorption. This is comparable to the time at which plateau was achieved in desorption of TOTAL crude oil. On the other hand, desorption of ADNOC crude oil took place after ≤ 5 minutes of experiment. This variation is attributed to the difference in viscosity between the three oils. Figure 46 shows the lowest sorption capacities; an indication of the amount of oil remained onto the fibrous sorbent, after 30 minutes of experiment. The amount of oil remained in the sorbent was directly proportional to those initially adsorbed after 30 seconds, showing a similar pattern to what was observed on the other crude oils. As a result, the percent retrieval after 30 minutes was calculated in all experiments, and plotted in Figure 47. A maximum of 48% of

ADCO crude oil was retrieved. Compared with a maximum of 60% retrieval extent with TOTAL crude oil, the difference could be attributed to the relatively lower viscosity; hence lower hydrophobicity of the ADCO crude oil than that of the

TOTAL crude oil. These findings indicate that initial adsorption of the crude oil could be followed by higher extents of desorption in case of lower viscosity crude oils, as was observed with TOTAL and ADCO oils. On the other hand, higher initial adsorption, as was shown in the experiments involving ADNOC crude oil, was followed by a retrieval extent of 48%, which could be attributed to the higher cohesive forces between the long chain hydrocarbons which highly contribute to the elevated viscosity of the crude oil.

85 100 (a) PSI PSII PSCIII 90

(g/g) capacity sorption 30 seconds 10

0 0.005 0.010 Weight of Sorbent (g)

100 (b) PSI PSII PSCIII 90

80 70 60

30 20

30 seconds sorption capacity (g/g) capacity sorption 30 seconds 10

0 0.005 0.010 Weight of Sorbent (g)

100 (c) PSI PSII PSCIII 90

60 50

40 30 20

(g/g) capacity sorption 30 seconds 10 0 0.005 0.010 Weight of Sorbent (g)

Figure 45: Highest achieved sorption capacities to ADCO crude oil after 30 sec of fibrous sorbents prepared from electrospinning of (a) 20 wt%, (b) 30 wt%, and (c ) 40 wt% solutions of each of the polymers in DMF

86 100 (a) PSI PSII PSCIII 90

70 60 50

40 30

20 10 30 minutes sorption capacity (g/g) capacity sorption 30 minutes 0 0.005 0.010 Weight of Sorbent (g) 100 (b) PSI PSII PSCIII 90 80 70 60 50

40 30

30 minutes sorption capacity (g/g) capacity sorption 30 minutes 10

0 0.005 0.010 Weight of Sorbent (g) 100 (c) PSI PSII PSCIII 90

80 70

60 50

40 30

30 minutes sorption capacity (g/g) capacity sorption 30 minutes 10

0 0.005 0.010 Weight of Sorbent (g) Figure 46: Highest achieved sorption capacities to ADCO crude oil after 30 min of fibrous sorbents prepared from electrospinning of (a) 20 wt%, (b) 30 wt%, and (c ) 40 wt% solutions of each of the polymers in DMF

(a) 40 30% 20% 40% 30% 40% 30% 20% 30

20% 40% 20 % Retrival

0 PSI PSII PSCIII Type of Polymer

(b) 50 40% 40%

40 30%

30% 40% 30 20% 20% 30% 20%

% Retrival 20

0 PSI PSII PSCIII Type of Polymer

Figure 47: Extent of retrieval (%) of ADCO crude oil adsorbed onto PSI, PSII, and PSCIII fibrous sorbents (a) 0.005g, and (b) 0.01g prepared by the electrospin of 20, 30, and 40 wt% solutions of each of the polymers in DMF

Based on the sorption results of all crude oils with fibrous sorbents, it was observed that on average sorbents prepared from solutions containing 20 wt% of

PSII showed the highest sorption capacities among other polymers. Figure 48 shows a comparison between the sorption capacities of the three types of crude oil onto fibrous sorbents fabricated from solutions containing 20 wt% of PSII. Highest achieved sorption values were summarized in Figure 49. It is evident that ADNOC crude oil showed the highest sorption capacities than the two other crude oils. This was attributed to difference in viscosity between the oils, where high viscosity indicates longer chain hydrocarbons, hence higher hydrophobicity and as a consequence higher extent of attraction to the hydrophobic fibrous sorbents. The close sorption capacities of TOTAL and ADCO crude oils on the same fibrous sorbents confirms this hypothesis where both oils were close in viscosity and were both inferior to that of the ADNOC crude oil. It can be also shown in Figure 48 that all crude oils showed a similar plateau after 10 minutes of sorption where desorption of the weakly adsorbed oil was ceased. Figure 50 summarizes the retrieval % of all crude oils onto the PSII fibrous sorbents. The highest retrieval rate was achieved when TOTAL oil was involved.

240 (a) 220 ADNOC TOTAL ADCO 200

180

160 140

120 100 80 Sorption capacity (g/g) 60

20 0 5 10 15 20 25 30 Time (min)

240 (b) 220 ADNOC TOTAL ADCO 200 180

160

140

120

100

80 Sorption capacity (g/g) 60 40

20 0 5 10 15 20 25 30

Time (min)

Figure 48: Comparison between the sorption capacities to ADNOC, TOTAL, and ADCO crude oils of fibrous sorbents (a) 0.005g, and (b) 0.01g /each prepared from electrospinning of 20 wt% solutions of PSII in DMF

240 ADNOC TOTAL ADCO 220

200

180

160 140

120 100 80 60 40 30 second sorption capacity (g/g) capacity sorption 30 second 20 0 0.005 0.010

Weight of Sorbent (g)

Figure 49: Highest achieved sorption capacities to ADNOC, TOTAL, and ADCO crude oils after 30 sec of fibrous sorbents (0.005g & 0.01g) prepared from electrospinning of 20 wt% solutions of PSII in DMF

100

ADNOC TOTAL ADCO

Retrieval Retrieval 40 %

0 0.005 0.010 Weight of Sorbent (g)

Figure 50: Extent of retrieval (%) to ADNOC, TOTAL, and ADCO crude oils of fibrous sorbents (0.005g & 0.01g) prepared from electrospinning of 20 wt% solutions of PSII in DMF

4.4 Effect of Electrospinning Parameters on Sorption of TOTAL Crude Oil on

PSII Fibrous Sorbents

In the previous sections, it was shown that polystyrene fibrous sorbents were successfully used to collect three different types of crude oil from simulated salty water media. The main hypothesis behind this high efficiency was attributed to the high surface area of the fibers and their hydrophobic nature. Based on these findings, fine tuning of the characteristics of the fibers produced by electrospinning of 20, 30 and 40 wt% PSI, PSII, and PSCIII solutions was attempted. The main objective was to study the effect of varying the electrospinning conditions on the performance of the fibers towards the sorption of TOTAL crude oil. Results will be discussed in the following sections.

4.4.1 Effect of Solvent

It should be mentioned that fibrous sorbents evaluated in the previous sections for the removal of ADNOC, TOTAL and ADCO crude oils were prepared by electrospinning solutions of each of the polymers in dimethyl formamide (DMF).

This is one of the commonly used solvents for dissolving polystyrene136. Another common solvent; tetrahydrofuran (THF) has been studied as well136. Solvent mixtures based on formulations of DMF and THF were used to dissolve PSI, PSII, and PSCIII making 20, 30 and 40 wt% solutions thereof, and were electrospun at constant voltage15KV, feeding rate 10 ml/hr, spinning distance 15cm, humidity

(normal) 47%, and needle size 21G. Proportions of DMF and THF in the solvent mixtures are given in Table 4.

Table 4: Composition of solvent mixtures of THF and DMF

Solvent Solvent Composition (% by volume)

THF 100 75 50 25 0

DMF 0 25 50 75 100

Under these conditions, fibrous sorbents (0.005 g/each) were evaluated for their efficiencies in removing TOTAL crude oil from salty water. Results are shown in Figures 51-53 for fibrous sorbents prepared from solutions containing 20, 30, and

40% of PSI, PSII, and, PSCIII, respectively. An overall trend was shown where all fibrous sorbents showed an instantaneous sorption within the first 30 seconds of experiment, followed by a sustained desorption throughout the remaining 30 minutes of experiments. On average, sorbents prepared from pure DMF and 50:50

(DMF:THF) solvents showed the highest sorption capacities achieved after 30 seconds. A close comparison between sorption capacities after 30 seconds of sorbents prepared from pure DMF and DMF:THF (50:50) are shown in Figures 54-

55. Sorbents prepared from solutions containing 20 wt% of all polymers showed the highest sorption capacities in both solvents. The highest achieved sorption capacities in these cases reached 80, 55, and 95 g/g for polymers PSI, PSII, and PSCIII dissolved in pure DMF, while those dissolved in DMF:THF (50:50) showed 87, 60 and 84 g/g, respectively.

120 (a) THF/DMF (100 % DMF) (25:75) (50:50) (75:25) 100 (100 % THF)

Sorption Capacity (g/g)

0 5 10 15 20 25 30 Time (min)

120 (b) THF/DMF (100 % DMF) (25:75) (50:50) (75:25) 100

Sorption Capacity (g/g) 20

0 5 10 15 20 25 30 Time (min)

120 (c) THF/DMF 110 (100% DMF) (25:75) (50:50) (75:25) 100 (100% THF) 90

Sorption Capacity (g/g) 30

0 0 5 10 15 20 25 30 Time (min)

Figure 51: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g/each) prepared by the electrospin of 20 wt% solvent of each (a) PSI, (b) PSII, and (c ) PSCIII in various solvent systems

120 (a) 110 THF/DMF (100 % DMF) (25:75) (50:50) (75:25) 100 (100 % THF) 90 80 70 60

50 40 Sorption Capacity (g/g) 30 20 10

0 5 10 15 20 25 30 Time (min)

120 (c) 110 THF/DMF (100% DMF) (25:75) (50:50) (75:25) 100 (100% THF) 90 80 70 60

50 40 Sorption Capacity (g/g) 30 20 10 0 0 5 10 15 20 25 30 Time (min)

120 (b) THF/DMF 110 (100% DMF) (25:75) (50:50) (75:25) 100 (100% THF) 90 80 70 60

50 40

Sorption Capacity (g/g) 30 20 10

0 5 10 15 20 25 30 Time (min)

Figure 52: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g/each) prepared by the electrospin of 30 wt% solvent of each (a) PSI, (b) PSII, and (c ) PSCIII in various solvent systems

120 (a) 110 THF/DMF (100 % DMF) (25:75) (50:50) (75:25) 100 (100 % THF) 90 80 70 60

50 40 30 Sorption Capacity (g/g) 20 10 0 0 5 10 15 20 25 30 Time (min)

120 (b) 110 THF/DMF (100% DMF) (25:75) (50:50) (75:25) 100 (100% THF) 90 80 70 60

50 40 30 Sorption Capacity (g/g) 20 10 0 0 5 10 15 20 25 30 Time (min)

120 (c) THF/DMF (100% DMF) (25:75) (50:50) (75:25) 100 (100% THF)

40 Sorption Capacity (g/g) 20

0 0 5 10 15 20 25 30 Time (min)

Figure 53: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g/each) prepared by the electrospin of 40 wt% solvent of each (a) PSI, (b) PSII, and (c ) PSCIII in various solvent systems

120 (a) 110 100 90 20% 80 70 60 30% 50 40% 40 30

30 second sorption capacity (g/g) capacity sorption second 30 20 10 0 PSI

120 (b) 110 100 90 80 70 60 20% 50 30% 40 40% 30 20 30 second sorption capacity (g/g) capacity sorption second 30 10 0 PSII 120 (c) 110 100 20% 90 80 30% 70 60 40% 50 40 30

20 30 second sorption capacity (g/g) capacity sorption second 30 10 0 PSCIII

Figure 54: Highest achieved sorption capacities to TOTAL crude oil after 30 sec of fibrous sorbents prepared by electrospinning of 20, 30, and 40 wt% of (a) PSI, (b)PSII, and (c) PSCIII solutions in 100% DMF

120 (a) 110 100 90 20% 80 30% 70 40% 60 50 40 30 20 30 second sorption capacity (g/g) capacity sorption second 30 10 0 PSI

120 (b) 110 100 90

80 70 20% 30% 60 40% 50 40 30 20 30 second sorption capacity (g/g) capacity sorption second 30 10 0 PSII

120 (c) 110 100 90 20% 80 70 30% 60 50 40% 40 30 20 30 second sorption capacity (g/g) capacity sorption second 30 10 0 PSCIII

Figure 55: Highest achieved sorption capacities to TOTAL crude oil after 30 sec of fibrous sorbents prepared by electrospinning of 20, 30, and 40 wt% of (a) PSI, (b)PSII, and (c) PSCIII solutions in (50:50)-(THF: DMF)

Correlating these values with the SEM micrographs of these sorbents Figure

56 explains the relatively higher performance of PSI and PSCIII sorbents where their fiber size was in the range of 1-1.5 mm, while fibers produced from PSII 20% solution showed a higher size range; up to 2.5 mm. The smaller the size of the fibers the higher is their surface area, and consequently this is known to enhance their sorption capacity. The SEM micrographs of PSII sorbents shown in Figure 56 also indicates more surface roughness of the fibers, as compared with sorbents prepared from other polymers. Considering sorbents prepared from other concentrations of the

PSII polymer, Figure 57 compared SEM micrographs of sorbents prepared from 20,

30, and 40 wt% of PSII. The decrease in the sorption capacities with increasing the concentration of the solutions from which the PSII sorbents were prepared can be related to the relative increase in the size of the fibers, hence the decrease in the surface area of those fibers and their tendency towards oil sorption. It should be mentioned that surface roughness of the fibers obtained from PSII-20% solutions was not mentioned in the micrographs of sorbents prepared from 30 and 40% solutions in both solvents. These findings indicate an insignificant variation in the sorption capacities of sorbents prepared in both pure DMF and DMF:THF (50:50). Figures

58-9 show the percent retrieval of oil from sorbents of 20, 30, and 40 wt% PSI, PSII, and PSCIII polymers dissolved in pure DMF and DMF:THF (50:50), respectively.

Despite the variable % retrieval with percentage of polymer solution in pure DMF from which sorbents were prepared, sorbents made from solutions in DMF:THF

(50:50) showed an increasing % retrieval with increasing the initial concentration of the polymers solutions. This was opposite to the decreasing sorption capacity with increasing the polymer solutions after 30 seconds; shown in Figure 55. This related

99 to the relative increase in the size of the fibers, hence the decrease in the surface area of those fibers and their tendency towards oil sorption.

Based on the above findings, sorbents prepared from solutions containing 20 wt% of PSI, PSII and PSCIII in pure DMF and DMF:THF (50:50) were selected for further investigation of the effect of other electrospinning parameters on their performance in the removal of TOTAL crude oil.

100

Figure 56: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% solutions of PS at different solvent concentration (a) PSI (100%DMF), (b) PSI (50:50,THD:DMF), ( c) PSII (100% DMF), (d) PSII (50:50, THD:DMF), (e) PSCIII (100% DMF), and (f) PSCII (50:50, THD:DMF)

101

Figure 57: SEM micrographs of fibrous sorbents obtained by electrospinning of PS at different solvent concentration (a) 20 w% PSII (100%DMF), (b) 20 w% PSII (50:50,THD:DMF), ( c) 30 w% PSII I (100% DMF), (d)320 w% PSII (50:50, THD:DMF), (e) 40 w% PSII (100% DMF), and (f) 40 w% PSII I (50:50, THD:DMF)

102

100 (a) 90 80 70

60 30% 40% 50 20%

% Retrival 40

20 10 0

PSI

100 (b) 90

70 20% 60 50 40% 30% % Retrival 40

20 10 0 PSII

100 (c) 90

60 40% 50 30% 20% % Retrival 40 30

0 PSCIII

Figure 58: Extent of retrieval (%) of TOTAL crude oil adsorbed onto (a) PSI, (b) PSII, and (c ) PSCIII fibrous sorbents (0.005g/each) prepared by the electrospin of 20, 30, and 40 wt% solutions of each of the polymers in 100% DMF

103

100 (a) 90

40% 50 20% 30% 40 % Retrival 30

0 PSI

100 (b) 90

70 40% 60 30% 50 20% % Retrival 40

10 0 PSII

100 (c) 90

70 40% 60 30%

50 20% % Retrival 40

0 PSCIII

Figure 59: Extent of retrieval (%) of TOTAL crude oil adsorbed onto (a) PSI, (b) PSII, and (c ) PSCIII fibrous sorbents (0.005g/each) prepared by the electrospin of 20, 30, and 40 wt% solutions of each of the polymers in (50:50)% -(THF:DMF)

104

4.4.2 Effect of Applied Voltage

Solutions containing 20 wt% of PSI, PSII and PSCIII in pure DMF, and

DMF:THF (50:50) were electrospun into sorbents at applied voltages of 10, 15, 20,

25 and 30 kV. Fibrous sorbents prepared hereafter were evaluated for their efficiency in removal of TOTAL crude oil. Figures 60-62 show the sorption capacities for sorbents made of PSI, PSII and PSCIII polymers, respectively. It should be mentioned that non-fibrous sorbents were obtained at an applied voltage of 10 kV as a result of electrospinning solutions containing 20 wt% of PSI in DMF:THF (50:50) and PSCIII in pure DMF and DMF:THF (50:50) solvents. Therefore, their sorption capacities were not considered since the main objective of the work was to evaluate high surface area fibrous sorbents for their performance in removing oil spills.

Results shown in Figures 60-62 indicate a similar pattern to what has been observed before in the sorption experiments of crude oil. An instantaneous sorption took place within the first 30 seconds of the experiment, followed by a slow pattern of partial desorption of the weakly adsorbed oil from the fibers for the remaining 30 minutes of the experiments. The highest achieved sorption capacities after 30 seconds were plotted in Figure 63. An overall trend can be derived where increasing the applied voltage during the preparation of the sorbents led to an overall enhancement in the sorption capacities of the sorbents. Figure 64 shows SEM micrographs of sorbents prepared by electrospinning 20 wt% PSII in pure DMF at

10, 15, 20, 25 and 30 kV. Fibers prepared at 10, 15, 20, and 25 kV showed the same size and size distribution, while deformed fibers were obtained at an applied voltage of 30 kV. Variation in the sorption capacities are, therefore, related to the relative increase in the surface roughness of the fibers with increasing voltage, as shown in

105 the inserts of the SEM micrographs at different voltages. Figure 65 shows the percent retrieval of the oil after 30 minutes of sorption from all fibrous sorbents.

Despite the fact that insignificant correlation could be found between the percent retrieval and the applied voltage, percent retrieval was found to increase with increasing the applied voltage during the preparation of PSII 20 wt% solution. This could be attributed to the initial sorption performance of these samples after 30 seconds of experiment.

As a result of these findings, an applied voltage of 25 kV was selected for the preparation of PSII sorbents from solutions containing 20 wt% in pure DMF solvent.

These conditions were maintained for studying the following parameters.

106

70 (a) 65 10 KV 60 15 KV 55 20 KV 25 KV 50 30 KV

Capacity (g/g) Sorption 30

20 0 5 10 15 20 25 30 Time (min)

70 (b) 65 (THF:DMF) (50:50) 15 KV 60 20 KV 55 25 KV

50 30 KV 45 40

Sorption Capacity (g/g) Sorption 30

15 0 5 10 15 20 25 30 Time (min)

Figure 60: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSI solutions (a) 100% DMF, and (b) (THF:DMF) (50:50)% at different applied voltages

107

70 (a) 65 100% DMF

60 10 KV 15 KV 55 20 KV 25 KV 50 30 KV 45

40 35

Sorption Capacity (g/g) Sorption 30

15 0 5 10 15 20 25 30 Time (min)

70 (b) 65 THF:DMF-(50:50) 60 10 KV 15 KV 55 20 KV 25 KV 50 30 KV 45

Sorption Capacity (g/g) Sorption 30 25 20 0 5 10 15 20 25 30 Time (min)

Figure 61: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions (a) 100% DMF, and (b) (THF:DMF) (50:50)% at different applied voltages

108

70 (a) 65 100% DMF 60 15 KV 20 KV 55 25 KV 50 30 KV 45

35 30

Sorption Capacity (g/g) Sorption 25

10 0 5 10 15 20 25 30 Time (min)

65 (50:50)-(THF :DMF ) 15 K V 60 20 K V 55 25 K v 30 K V 50

30 Sorption Capacity (g/g) Sorption 25

20 15 0 5 10 15 20 25 30 Time (min)

Figure 62: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSCIII solutions (a) 100% DMF, and (b) (THF:DMF) (50:50)% at different applied voltages

109

70 65 (a) 60 10 K V 15 K V 20KV 25 K V 30 K V 55 50 45 40 35 30 25 20 15 10 5 0 Maximum Sorption Capacity after 30 sec (g/g) PSI PSII PSCIII PS

70 (b) 60 10KV 15KV 20KV 25KV 30KV

0 Maximum Sorption Capacity after 30 sec (g/g) PSI PSII PSCIII PS

Figure 63: Highest achieved sorption capacities to TOTAL crude oil after 30 sec of fibrous sorbents prepared by electrospinning of of 20 wt% of (a) 100% DMF, (b)THF:DMF-(50:50) solutions of each of the polymers at different applied voltages

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Figure 64: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% solutions of PSII in DMF at different applied voltages (a) 10kV, (b) 15kV, ( c) 20kV, (d) 25kV, and (e) 30kV

111

80 75 (a) 70 65 10KV 15KV 20KV 25KV 30KV 60 55 50 45 40

35 30

% Retrival 25 20 15 10 5 0 PSI PSII PSCIII PS 70 (b) 65 60 55 10KV 15KV 20KV 25KV 30KV 50 45 40 35

30 25 % Retrival 20 15 10 5 0 PSI PSII PSCIII PS

Figure 65: Extent of retrieval (%) of TOTAL crude oil adsorbed onto fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions (a) 100% DMF, and (b) (THF:DMF) (50:50)% solutions of each of the polymers at different applied voltages

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4.4.3 Effect of Feeding Rate

Fibrous sorbents were prepared at 25 kV from solutions containing 20 wt% of

PSII in pure DMF, while varying the feeding rate during electrospinning at 1, 5, and

10 mL/hr. Sorbents prepared here with were evaluated for their performance in removing TOTAL crude oil. Results are plotted in Figure 66. All sorbents showed a typical sorption pattern with high instantaneous sorption capacities of 29, 27, and 50 g/g for sorbents prepared at feeding rates of 1, 5, and 10 mL/hr, respectively. All sorbents also showed a sustained slow-rate desorption of the weakly adsorbed oil with time during the following 30 minutes of experiment. SEM micrographs of these sorbents are shown in Figure 67, where sorbents prepared at different feeding rates showed fibrous morphology. However, sorbents prepared at a feeding rate of 1 mL/hr showed inhomogeneous fiber size distribution and fibers were distorted.

Surface cracks are evident on the fibers in the insert of this micrograph. On the other hand, sorbent prepared at a feeding rate of 5 mL/hr showed the presence of beads as well as inhomogeneous size distribution of the fibers. Beaded morphology provides sites of low surface area which could be considered the reason for the decreased oil sorption in sorbents prepared at 5 mL/hr feeding rate, while un-beaded slightly cracked fibers (prepared at a feeding rate of 1 mL/hr) showed moderate sorption capacities. In contrast, sorbents prepared at a feeding rate of 10 mL/hr showed a non- beaded fibrous morphology with a homogeneous size distribution. This morphology explains the high performance of those sorbents prepared at 10 mL/hr as compared with sorbents prepared at other feeding rates. In addition, sorbent prepared at a feeding rate of 10 mL/hr achieved a 56% retrieval after 30 minutes Figure 68. Based on these findings, a feeding rate of 10 mL/hr was selected as an optimum parameter

113 for the following set of experiments towards the fabrication of fibrous sorbents by electrospinning.

114

50 1 ml/h 5ml/h 10ml/h

30 Sorption Capacity (g/g) Capacity Sorption

0 5 10 15 20 25 30 Time (min)

Figure 66: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at feeding rate (1ml/hr, 5ml/hr, and 10ml/hr) in DMF

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Figure 67: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% solutions of PSII in DMF at feeding rate at (a) 1ml/hr, (b) 5ml/hr, and ( c) 10ml/hr

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70 65 60 55 50 45

40 35 30 25

% Retrival % 20 15 10 5 0 1 ml/hr 5 ml/hr 10 ml/hr PSII

Figure 68: Extent of retrieval (%) of TOTAL crude oil adsorbed onto fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at feeding rate (1ml/hr, 5ml/hr, and 10ml/hr) in DMF

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4.4.4 Effect of Distance

Figure 69 shows sorption capacities of sorbents prepared at an applied voltage of 25 kV, a feeding rate of 10 mL/hr of 20 wt% solution of PSII in pure

DMF, and electrospinning distances of 10, 15 and 20 cm. Increasing the spinning distance is known to elongate the travel pathway of the fibers towards the grounded collector, hence more thinning of the fibers.112 Therefore, size of the fibers should decrease with increasing the spinning distance. However, the SEM micrographs shown in Figure 70 do not support this concept. An insignificant change in the size of the fibers was observed. In addition, more beading was shown in the microstructures of the sorbents prepared at spinning distances of 10 and 20 cm. On the other hand, a homogeneous non-beaded morphology was achieved when sorbents were prepared at a spinning distance of 15 cm. the presence of beads indicates a lowering in the surface area of the fibers, which explains the low sorption capacity of sorbents prepared at a spinning distance of 10 cm. In contrast, sorbents prepared at a spinning distance of 20 cm showed the highest initial sorption capacity after 30 seconds despite the fact that beads were also found in the micrograph of this sorbent.

This could be related to the homogeneous distribution of the size of the fibers in the sorbent. The absence of beads, and the homogeneous size distribution of the sorbent prepared at a spinning distance of 15 cm suggested this distance to be selected as an optimum spinning distance for the rest of the optimization process. Figure 71 shows a linear increased pattern for the percent retrieval of the oil with increasing the spinning distance. This pattern could be related to the difference in the initial instantaneous sorption capacities of all samples.

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10 cm 15 cm 20 cm 60

35 Sorption Capacity (g/g) Capacity Sorption

0 5 10 15 20 25 30 Time (min)

Figure 69: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at distance (Needle to collector) at 10, 15, and 20cm in DMF

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Figure 70: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% solutions of PSII at distance (Needle to collector) at (a) 10cm, (b) 15cm, and ( c) 20cm

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% Retrival Retrival % 20

0 10 cm 15 cm 20 cm PSII

Figure 71: Extent of retrieval (%) of TOTAL crude oil adsorbed onto fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at distance (Needle to collector) at 10, 15, and 20cm in DMF

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4.4.5 Effect of Humidity

In the presence of humidity, electrospinning was previously shown to produce fibers with surface roughness and internal porosity. The main objective of studying the effect of humidity was to see whether or not created surface roughness would affect the sorption capacities of the produced fibrous sorbents at different degrees of relative humidity. It should be mentioned that humidity was changed inside the electrospinning chamber by saturating it with water vapor before electrospinning was to be carried out.

Figure 72 shows the sorption capacities of fibrous sorbents formed under the previously optimized conditions and under the effect of various degrees of humidity.

Typically to what was observed in the previous sorption experiments, all sorbents showed instantaneous sorption capacities of various extents depending on the degree of humidity under which sorbents were prepared. The overall sorption capacities decreased with increasing the degree of humidity. Figure 73 show the SEM micrographs of sorbents prepared under various degrees of humidity. An overall increase in the average size of the fibers with increasing the degree of humidity can be seen. Average fiber size of 2, 3, and 5.7 µm were calculated for the fibers electrospun at 47, 70-88, and 89-99% relative humidity, respectively. These findings indicate a possibility of impregnation of the water of humidity within the fibers during their formation. In order to confirm this assumption, SEM was carried out at a high magnification of the fibers created under 70-88, and 89-99% relative humidity;

Figure 74. Both micrographs showed a maximum degree of internal porosity and a less rough surface morphology.

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70 Normal 47% (70-80)% (80-99)% 60

Sorption Capacity (g/g) Capacity Sorption 20

0 5 10 15 20 25 30 Time (min)

Figure 72: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at different Humidity % at 49% -Normal, (70-88)%, and (89-99)%) in DMF

123

Figure 73: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% solutions of PSII at different Humidity % at (a) 49% -Normal, (b) (70-88)%, and ( c) (89-99)%) in DMF

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Figure 74: High magnification SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% solutions of PSII at different Humidity % at (a) (70-88)%, and ( b) (89-99)%) in DMF

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These features were only observed when the relative humidity during preparation was increased to the said values. These micrographs, therefore, confirm the assumption that water of humidity was impregnated within the fibers during their formation and as a result of its evaporation porous fibers were created. The presence of increased porosity was expected to increase the overall surface area of the fibers, hence reflected on an increased sorption capacity. The opposite was found where increased degree of relative humidity produced fibers that showed a decreased sorption capacity. These results are attributed to the following two observations: First, the surfaces of the fibers were not as porous as their interiors, and should therefore not be expected to have elevated sorption capacities. Second, and during the sorption experiments of the sorbents produced at higher degrees of humidity, it was observed that brittleness of the fibers increased with increasing the degree of humidity. Moreover, fibers were shown to breakdown after mixing with the oil, leading to a loss of the fibrous architecture of the sorbents. These observations, therefore, explain the decrease in the sorption capacity of the sorbents with increasing the degree of relative humidity under which fibers were prepared. Figure 75 shows the percent retrieval of the oil after 30 minutes of sorption within the porous sorbents created at different degrees of relative humidity. Under normal humidity conditions, 60% of the oil was retrieved.

This high value was in accordance of its sorption behavior where a continuous desorption of the weakly adsorbed oil was observed throughout the 30 minutes of the experiment. On the other hand, the decreased percent retrieval of the sorbent prepared under 70-88% relative humidity is attributed to the low initial adsorption after 30 seconds. In contrast, the highly increased percent retrieval (> 70%) of the

126 fibers prepared at the highest degree of relative humidity could be attributed to the low mechanical stability of the fibers and their breakdown during the sorption experiments; hence oil was mechanically retrieved from the fibers. In conclusion, a normal degree of relative humidity (47%) was selected as an optimum value for the preparation of sorbents.

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100

70 60

40 Retrival % Retrival 30

0 Normal 47% (70-88)% (89-99)% PSII

Figure 75: Extent of retrieval (%) of TOTAL crude oil adsorbed onto fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at different Humidity % at 49% -Normal, (70-88)%, and (89-99)%) in DMF

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IV.4.6. Effect of Needle Diameter

Previous studies showed that needle diameter has an important effect on the diameter of the fiber emerging from the needle. In the market, syringe needles are known by gauge number where increasing the gauge number decreases the internal diameter of the needle. In the current study, needles with 4 various gauges were studies. Those were 18, 21, 23, and 29. Table 5. shows the nominal internal diameter of needles.

Table 5. Gauge number - nominal internal diameter conversion of needles

used in the current study

Gauge number 18 21 23 29

Nominal Internal Diameter (mm) 0.838 0.514 0.337 0.184

Fibrous sorbents prepared using these needles were investigated for their sorption capacities. Results are shown in Figure 76. All sorbents showed a typical pattern of sorption with time starting with initial instantaneous sorption capacities after 30 seconds of sorption, followed by a slow desorption pattern throughout the remaining 30 minutes of the experiments. Figure 77 shows SEM micrographs of fibrous sorbents prepared using these different gauge needles. It is evident from these micrographs that the average size of the fibers decreased by increasing the gauge number of the needles, which is in accordance with the conversion data shown in

Table 4. However, more beads were observed by increasing the gauge number, as pointed by arrows in the micrographs of fibrous sorbents electrospun using 23 and 29

129 gauges. On the other hand, fibrous sorbents prepared using gauge number 21 showed un-beaded fibers with a homogeneous size distribution, which was reflected on a relatively high sorption capacity; Figure 76.

130

18G 21G 23G 29G 50

Sorption Capacity (g/g) Capacity Sorption

0 5 10 15 20 25 30 Time (min)

Figure 76: Sorption capacities to TOTAL crude oil of fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at different Needle diameters at 18G, 21G, 23G, and 29G in DMF

131

Figure 77: SEM micrographs of fibrous sorbents obtained by electrospinning 20 wt% solutions of PSII at different Needle diameters at (a) 18G, (b) 21G, ( c) 23G, and (d) 29G in DMF

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In addition, fibrous sorbents prepared using gauge 21 showed the highest percent retrieval (60%) among all investigated fibrous sorbents; Figure 78. The low sorption capacity of the fibrous sorbents prepared using needles of other gauges was also reflected in low retrieval percentages within the range of 33-37%.

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70 65 60 55

50 45 40 35 30

% Retrival 25 20 15 10 5 0 23 G 29 G 18 G 21 G PSII

Figure 78: Extent of retrieval (%) of TOTAL crude oil adsorbed onto fibrous sorbents (0.005g) prepared by the electrospinning of 20 wt% PSII solutions at different Needle diameters at 18G, 21G, 23G, and 29G in DMF

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Chapter 5: Conclusion & Future Directions

This study investigated the potential of using high surface area fibrous sorbents in the removal of crude oil spills from salty water media. Three types of polystyrene with various molecular weights were investigated. Those were PSI

(100,000), PSII (350,000), and PSCIII (225,000). PSCIII was prepared by recycling polystyrene foam and coffee cups made of the same material. Three types of crude oils were investigated. Those included; ADNOC, TOTAL and ADCO with various viscosities. Polymeric solutions containing 20, 30, and 40% of each of the polymers were prepared by dissolving the corresponding amount of the polymer in THF, DMF or a combination of the two solvents. Polymeric solutions were electrospun into microfibrous sorbents, which were then characterized for their microstructure using

SEM technique and porosity as well as pore size distribution using N2-adsorption technique. Sorbents were evaluated for their efficiency in the removal of crude oil spills from simulated salty water media using a standardized ASTM method.

Results showed a strong correlation between the characteristics of the fibrous sorbents in terms of the size, size distribution and morphology of the fibers, and their sorption capacities of the crude oils spills. Results also confirmed the possibility of retrieving around 70% of the collected crude oil spills with a confirmation of absence of water in the adsorbed oil. Based on these findings, detailed optimization experiments were carried out, where the effects of varying the electrospinning conditions on the characteristics of the fibers and consequently the sorption performance of the fibrous sorbents prepared thereafter, were studied. These factors included: solvent in which polymer solutions were prepared, applied voltage, feeding rate, spinning distance, humidity inside the electrospinning chamber, and spinneret

135

(needle) gauge. The main objectives were to obtain bead-free fibrous sorbents with unified size distribution, pore size distribution, and consequently consistent sorption capacities.

Correlations were drawn between each of the electrospinning parameters and the sorption capacities and electrospnning conditions were optimized at the following:

1. Pure DMF and DMF:THF (50:50), as proper solvents

2. 25kV as an applied voltage

3. 10 ml/hr as a feeding rate

4. 15 cm as a spinning distance

5. Normal relative humidity (47%) inside the electrospinning chamber

6. 21 G (0.514 mm) as a gauge of the spinneret (needle) used in the

electrospinning

Based on the overall findings of the current work, a high potential for the removal and retrieval of the crude oil spills was proven. In addition, the study showed the possibility of solving three environmental problems via the recycling of polymeric waste, removing crude oil spills, and retrieving the collected oil spills. The author, therefore, strongly recommend the continuation of these studied with more efforts towards the maximization of the efficiency of removal and retrieval of crude oils pills from aqueous and non-aqueous as well as dry media.

Our future plane related to this study, is to scale-up the electrospinning of the

PS microfibers for possible testing under ‘real life’ conditions. We are also interested in exploring ways to possibly recycle or regenerate the sorbed oil from the PS fibers.

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In addition, we would like to test the possibility of using our PS microfibrous sorbents for oil spill clean up in non-aqueous environment such as beaches.

Finally, it will be nice to study the mechanism for oil sorption onto PS microfibrous sorbents.

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