Marine Pollution Bulletin xxx (2015) xxx–xxx
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Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water Li Peng a,⇑, Qiao Ying a, Zhao Lili a, Yao Dahu b, Sun Haixiang a,⇑, Hou Yingfei a, Li Shuo c, Li Qi d a
State Key Laboratory of Heavy Oil Processing, China University of Petroleum (East China), Qingdao, Shandong 266580, China School of Chemical Engineering & Pharmaceutical, Henan University of Science and Technology, Luoyang, Henan 471023, China c Shandong Hi-tech Chemical Group, Dongying, Shandong 257105, China d Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, Jiangsu 215123, China b
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: PS/PAN fiber Electrospinning Oil sorption capacity Mechanical property
a b s t r a c t A mechanically robust and high-capacity oil sorbent is prepared by electrospinning a blend of polystyrene (PS) and polyacrylonitrile (PAN). The morphology, oil sorption capacity and mechanical property of the fibers formed in different compositions are investigated in detail. It is shown that the oil sorption capacity is a result of both the chemical composition and the specific surface area which related to diameter size. The addition of PAN as a component in fibrous sorbents can significantly improve the mechanical properties of PS fibers. Moreover, the oil sorption capacity increases with decreasing fiber diameter. The results also show that the maximum sorption capacities of the PS/PAN sorbent for pump oil, peanut oil, diesel, and gasoline were 194.85, 131.70, 66.75, and 43.38 g g1, respectively. Additionally, the sorbent exhibits quick oil sorption speed as well as high buoyancy, which make it a promising candidate for use as an oil spill cleanup sorbent. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Oil spill accidents often take place during transportation and storage of oil, causing huge economic losses as well as environmental pollution. In recent years, with the frequent occurrence of oil spills (Singh et al., 2013) at sea, such as the Exxon Valdez oil spill (1989), the Gulf of Mexico oil spill (2010) and the ConocoPhillips Bohai oil spill (2011), it is imperative to find a reliable method for cleaning up spilled oil at sea. There are a variety of methods for dealing with oil spills, such as situ burning (Buist et al., 2011), dispersion (Roulia et al., 2003), mechanical collection (Broje and Keller, 2006), bioremediation (Boopathy et al., 2012), and the use of sorption materials (Li et al., 2013; Ceylan et al., 2009; Choi et al., 2011; Wu et al., 2014; Chu and Pan, 2012). Among these existing methods, there has been extensive research on oil sorption materials because they are efficient, economical, and provide for easy oil recovery. Currently, oil sorbent materials are divided into three types: inorganic mineral products, organic natural products, and synthetic organic products (Choi and Moreau, 1993). These materials include zeolites (Choi and Cloud, 1992), activated carbon (Bayat et al., 2005), organoclays (Adebajo et al., 2003), straws (Sun et al., ⇑ Corresponding authors. Tel.: +86 18754277990. E-mail addresses: [email protected] (P. Li), [email protected] (H. Sun).
2002), fibers (Annunciado et al., 2005), sponges (Zhou et al., 2013), and alkyl acrylate copolymers (Atta et al., 2005; Jang and Kim, 2000a,b; Dutta and Gogoi, 2013; Pourjavadi and Doulabi, 2013). Liu et al. (2013) made reduced graphene oxide coated polyurethane (rGPU) sponges, which were fabricated by way of facile reduction. The rGPU sponge had an oil sorption capacity of more than 80 g g1 and a chloroform sorption capacity of 160 g g1 (the highest reported value). He et al. (2013) fabricated porous reduced graphene oxide (RGO) foam with a maximum oil sorption value of about 122 g g1 for olive oil by three kinds of freeze-drying methods. Liang et al. (2012) prepared carbonaceous nanofiber (CNF) hydrogels and aerogels through a hydrothermal carbonization process. The CNF hydrogels and aerogels had an oil sorption capacity of 40 g g1 for gasoline and diesel oil. However, these materials have many limitations such as high costs, complex fabrication processes, and low stabilities (Wang and Lin, 2013; Nguyen et al., 2012). Electrospinning is well known as an effective technique for producing fibers with diameters ranging from micrometers to nanometers (Reneker and Chun, 1996; Li et al., 2002). Zhu et al. (2011) first reported electrospun polyvinyl chloride (PVC)/polystyrene (PS) sorbents with an oil sorption capacity of 146 g g1. PVC/PS showed a superior selectivity of water and oil, high buoyancy, and could be applied to clear oil spills. Lin et al. (2012a,b), Wu et al. (2012) reported PS fibers with far higher oil sorption capacities than
http://dx.doi.org/10.1016/j.marpolbul.2015.02.012 0025-326X/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
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P. Li et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
Table 1 Tensile properties of as-prepared fibrous sorbents formed in different compositions. Sample
Break strength (MPa)
Elongation at break (%)
F1 F2 F3 F4 F5
14.89 10.43 9.15 4.84 4.18
533.10 483.75 356.74 201.77 158.3
those of polypropylene (PP) fabric. However, PS fibers could be dissolved in gasoline because of their non-polarity. Additionally, PS fibers had a poor mechanical behavior and could be easily destroyed in oil after oil sorption. Polyacrylonitrile (PAN) fibers Nam et al. (1999) have been widely used in industry because of good conductivity, solvent resistance and high strength. However, PAN is hydrophilic and as a result is seldom used in oil sorption. In this paper, the PS/PAN fibrous sorbents were fabricated by electrospinning a blend of PS and PAN. The oil sorption capacities of these fibrous sorbents for pump oil, peanut oil, diesel, and gasoline were investigated.
Fig. 2. Viscosity and conductivity of the PS/PAN solution for different PS/PAN compositions.
2. Experiments 2.1. Materials Polystyrene (PS) with a molecular weight of Mw = 250,000 was purchased from Energy Chemical. Polyacrylonitrile (PAN) with a molecular weight of Mw = 80,000 was purchased from Beijing Yili Fine Chemicals Co., Ltd. N, N-dimethylformamide (DMF) was purchased from Shanghai Chemical Reagents Co., Ltd., China. The oils used for absorption are pump oil (Beijing Si Fang special oil factory), peanut oil (Shandong Lu Hua Group Co., Ltd.), diesel and gasoline (Shandong Qingdao SINOPEC Co., Ltd.). The oil properties investigated are listed in Table 1. 2.2. Method A mixture of PS and PAN was dissolved in DMF by stirring for 4 h to form 18 wt.% solution., Weight ratios of PS/PAN of 0/10, 3/ 7, 5/5, 7/3, 10/0 were named as F1, F2, F3, F4, F5, respectively. The electrospun fibrous fibers were prepared at 25 kV in a relative humidity of 40% at 30 °C, a feed rate of 0.1 mm/s and the distance
between the tip and the collector was fixed at 10 cm. To form fibers with different diameters, the feed rates were set as 0.1 mm/s, 0.15 mm/s, 0.2 mm/s, 0.25 mm/s and 0.3 mm/s. The other conditions are the same as the above study, except that the weight ratio of PS/PAN is 5/5.
2.3. Characterization The morphology of the electrospun fibers was examined by field emission scanning electron microscopy (FE-SEM) (S-4800, Hitachi Ltd., Japan). The fiber diameters were calculated from the SEM images by SmileView. Contact angles of the electrospun fibers were measured by an contact-angle system (SL200B, Kino Inc, USA) at 25 °C. The average contact angle value of both water and oil were obtained by measuring at three different positions of the same sample. The viscosity and electrical conductivity of solution in different compositions were measured by rotational viscometer (NDJ-79, Shanghai Changji Geological Instruments Co., Ltd., China) and digital conductivity meter (DDS-11A, Shanghai Leici Ltd., China), respectively.
Fig. 1. SEM images of PS/PAN fibers formed with weight ratios of (a) 0/10, (b) 3/7, (c) 5/5, (d) 7/3, and (e) 10/0, corresponding to samples F1, F2, F3, F4 and F5, respectively.
Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
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P. Li et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
2.5. Elemental analysis X-ray Photoelectron Spectroscopy (XPS) was recorded by PHI5700. Energy Dispersive Spectrometer (EDS) was recorded by S-4800, Hitachi Ltd., Japan. 2.6. Oil sorption test Approximately 0.15 g of oil sorbent was added into the glass beaker filled with 100 mL of oil. After 60 min of sorption, the wet sorbent was drained for 60 s. The oil sorption capacities for these sorbents were obtained from the following equation (Pourjavadi et al., 2013):
Q ¼ ðm m0 Þ=m0
ð1Þ 1
Fig. 3. Maximum oil sorption capacities of F1–F5 for various oils.
2.4. Mechanical test Tensile strength is measured by universal tensile machine (WDM3020) with a tensile speed of 50 mm/min. All samples were prepared with thickness of 0.02 mm, width of 10 mm and extension interval of 20 mm.
where Q is the oil sorption capacity (g g ), m is the total mass of wet sorbent after the oil drained for 60 s (g), and m0 is the mass of the sorbent before sorption (g). Each sample was independently measured three times, and the average value and standard deviation were calculated. 2.7. Buoyancy test 20 mL vacuum pump oil (dyed with Oil Red) was poured into a beaker containing 150 mL water. 0.15 g of the fiber was gently placed onto the surface of oil.
Fig. 4. Photos of (a) F3, and (b) F5 after sorption of pump oil.
Fig. 5. SEM images of fibers formed by feed rates of (a) 0.1 mm/s, (b) 0.15 mm/s, (c) 0.2 mm/s, (d) 0.25 mm/s, and (e) 0.3 mm/s.
Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
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P. Li et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
Fig. 6. Maximum oil sorption capacities of fibers formed by feed rates of (a) 0.1 mm/s, (b) 0.15 mm/s, (c) 0.2 mm/s, (d) 0.25 mm/s, and (e) 0.3 mm/s.
3. Results and discussion The morphology of fibers with different PS/PAN compositions is observed in Fig. 1. The average fiber diameters are 0.74, 1.07, 1.29, 1.77 and 1.36 lm, for samples F1, F2, F3, F4 and F5, respectively. It is well known that the high surface tension and viscosity of the spinning solution are not conducive to ejection, while the repulsive electric force is favorable for droplet ejection. With a small total force, the acceleration of the jet decreases and the splitting of the jet increases, resulting in thinner fiber diameters (Iksoo, 1955). The PAN solution has a high surface tension that hampers droplet division, which makes it hard for thinner diameters to form. As shown in Fig. 2, increasing the PAN percentage in the polymer mixtures leads to an increase in the viscosity and electrical conductivity of the polymer solution. When the repulsive electric force is the main factor, the fiber diameters will decrease with increasing the PAN content. However, the diameter of F5 is smaller than F4, which may because the viscosity and surface tension play a more important role than repulsive electric. Specific surface area and porosity will increase with a thinner fiber diameter which is favorable for the adsorption and adherence of oil on the fiber surfaces and in the voids. Oil sorption capacity is the most important parameter in oil recovery. Fig. 3 presents the oil sorption capacities of fibers formed with PS/PAN weight ratios of 0/10, 3/7, 5/5, 7/3, and 10/0. For pump oil, peanut oil and diesel oil, a higher weight percentage of PS results in a higher oil sorption capacity. The oil sorption is the result of fiber diameter and oleophilicity. Even though F1 has the minimum diameter, its polarity is the largest, and as a result its oil sorption capacity is the lowest. For gasoline, if the PS content of fibers less than 50%, increase of PS content will decrease the polarity of fibers, therefore, its oil sorption capacity increases. However, F4 and F5 whose PS content is more than 50%, the fibers can dissolve in gasoline because of similarity-intermiscibility theory, which of course will decrease the gasoline sorption capacity., Therefore, F3 has the highest oil capacity in gasoline because the joint effect of dissolving and polarity. The mechanical strength of PAN fiber shows the highest among fibers we tested. The F1, F2 and F3 samples with more PAN can maintain their form after oil sorption, as shown in Fig. 4(a), while the F4 and F5 samples with less PAN are destroyed in high viscosity oils such as pump oil and peanut oil after oil sorption, as shown in Fig. 4(b), big balls of fibers were destroyed into a few small fiber balls. The mechanical properties of the sorbents were evaluated by stress–strain measurements. The break strength and elongation
Fig. 7. X-ray Photoelectron Spectroscopy (XPS) data of the F3 sorbent: (a) the survey spectrum, (b) C1s, and (c) N1s.
at break of the fibers are summarized in Table 1. The mechanical properties of PS sorbent are greatly reinforced by incorporation of PAN. It is obvious that the break strength increases with increasing the content of PAN. At a critical weight ratio of 5/5 of PS/PAN (sample F3), the break strength of the sorbent is 9.15 MPa, which is two times larger compared with pure PS sorbent F5. Meanwhile, the F3 sample shows a relative high elongation at break (356.74%), namely, good toughness. To investigate the relationship between fiber diameter and oil sorption capacity, the sorbents were formed with a variety of feed rates. Fig. 5 shows the SEM images of the fibers formed with
Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
P. Li et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
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Fig. 8. Contact angle photos of a (a) water droplet and (b) diesel oil droplet on the F3 sample surface with contact angles of 144.32° and 0°, respectively.
Table 2 Properties of the studied oils at room temperature (20 °C). Oil
Viscosity (MPa S1)
Density (g cm1)
Qe (g g1)
te (min)
Vacuum pump oil Peanut oil Diesel oil Gasoline
162.30 78.45 4.75 0.30
0.8566 0.9151 0.8449 0.7724
194.85 131.70 66.75 43.38
56.27 16.24 5.161 3.520
various feed rates of 0.1 mm/s, 0.15 mm/s, 0.2 mm/s, 0.25 mm/s and 0.3 mm/s. The average diameters of the corresponding fibers are 1.29, 1.45, 2.12, 2.2 and 2.47 lm, respectively. It is obvious that the fiber diameter will increase with increasing of the feed rate. This is because when feed rates are slow, the charged jet contains few polymer chains and solvents that accelerates the solvent evaporation and subsequent solidification, resulting in a thin diameter. Moreover, the oil sorption capacities of the sorbents formed at different feed rates are shown in Fig. 6. It is observed that the oil sorption capacity of fibers increases with decreasing the feed rate. When the feed rate is 0.1 mm/s, the oil sorption capacities of the fiber are the highest and the maximum sorption capacities of the PS/PAN sorbent for pump oil, peanut oil, diesel, and gasoline were 194.85, 131.70, 66.75, and 43.38 g g1, respectively. This can be attributed to the difference of the fiber diameter, which is related to the specific surface area and porosity of the sorbent. The specific surface area and porosity will increase with decreasing fiber diameter, which provide a large amount of storage volume for sorbed oils. Based on the above results, the fiber sorbent F3 formed by a feed rate of o.1 mm/s is chosen as a sorbent for oil spill cleanup. It is known that microphase separation may happen during the process of polymer blending, resulting in different compositions at the fiber surface compared to the fiber interior. The change of the fiber surface composition will change its polarity, as well as its oil sorption. Therefore, the chemical composition of the fiber was
investigated by XPS and EDS. As can be seen from Fig. 7, XPS was used to examine the chemical composition on the surface of electrospun fibers. The peaks at 284.7 and 399.6 eV were ascribed to C1s and N1s. After calculating the atomic concentrations of C and N elements, we can obtain that C:N = 89.65:10.35. However, the XPS elemental analysis covers the surface to a depth of only 10 nm, while the diameter of the fiber is about 1 lm. As a result, the element distribution from the center to the surface of composite fiber need further investigation. Therefore, we use the EDS analysis method which can probe several microns below the surface. The EDS result shows that C:N ratio of F3 is 87.70:12.30, which is close to the result obtained by XPS. If the mixture of PS and PAN is uniform, the nominal atomic ratio of C:N is 87.63:12.37. The XPS and EDS results are consistent with this prediction. The wettability of the electrospun fiber was measured by the contact angle of a water and diesel oil droplet, as shown in Fig. 8. It is shown that the water and diesel oil contact angles on F3 sample are 144.32° and 0°, respectively, indicating that the fiber sorbent is oleophilic and hydrophobic. The hydrophobicity and oleophilicity of F3 sample is determined by low surface tension and surface structure. Table 2 shows the tendency of maximum oil sorption capacity is: pump oil > peanut oil > diesel oil > gasoline. The oil sorption capacity is determined by oil properties and fiber properties. The increase of the oil viscosity can lead to two different effects: on one hand, high viscosity can inhibit the oil entering the interior of the fibers; on the other hand, with the increase of oil viscosity, the oil can be more likely to adhere to the surface and voids of the fibers. The details about the maximum oil sorption capacity and sorption rate were discussed in another paper (Qiao et al., 2014). Buoyancy is another important parameter for sorbents used in oil spill cleanup on the water surface. A sorbent with high buoyancy Zhu et al. (2011) can keep floating over the water surface before and after oil sorption, which is helpful for both the oil sorption and removing the used sorbent from the oil spill area. Fig. 9 shows the
Fig. 9. Oil sorption behaviors of pump oil in oil–water bath at times of (a) 10 s, (b) 10 min, and (c) 60 min.
Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
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oil sorption behaviors of the sorbent F3 with increasing time. When the F3 sorbent is placed on the surface of oil over the water, the sorbent floats on the surface and keeps absorbing the oil. After 10 min, the thickness of the oil layer over the water surface decreases significantly, showing that a large amount of oil is absorbed by the sorbent. 60 min later, the F3 sorbent could absorb almost all pump oil and while still floating on the water. This high buoyancy before and after sorption makes PS/PAN a promising sorbent for oil spill cleanups. 4. Conclusion Electrospun fibers with different weight ratios of PS/PAN were investigated. The oil sorption capacity of fibers is a joint result of the chemical composition and the specific surface area related to fiber diameter size. The addition of PAN greatly reinforces the mechanical properties of PS fibers. It is shown that the weight ratio of 5/5 for PS/PAN results in high oil capacities while maintaining good mechanical strength. Moreover, sorbents were obtained by different feed rates and it is demonstrated that the oil sorption capacity increases with decreasing of the fiber diameter. The maximum sorption capacities of the PS/PAN sorbent for pump oil, peanut oil, diesel, and gasoline were 194.85, 131.70, 66.75, and 43.38 g g1, respectively. Additionally, the sorbent exhibits quick oil sorption speed as well as high buoyancy, which has great potential for use in oil spill cleanup. Acknowledgments The work was supported by the NSFC (National Natural Science Foundation of China) under Grant 51203186, the Converging Research Center Program funded by Korean Ministry of Education (2013K000415), the Shandong Provincial Natural Science Foundation (contract Grant No. ZR2010BQ026) and the Fundamental Research Funds for the Central Universities. References Singh, V., Kendall, R.J., Hake, K., Ramkumar, S., 2013. Crude oil sorption by raw cotton. Ind. Eng. Chem. Res. 52, 6277–6281. Buist, I., Potter, S., Nedwed, T., Mullin, J., 2011. Herding surfactants to contract and thicken oil spills in pack ice for in situ burning. Cold Reg. Sci. Technol. 67, 3–23. Roulia, M., Chassapis, K., Fotinopoulos, C.H., Savvidis, T.H., Katakis, D., 2003. Dispersion and sorption of oil spills by emulsifier-modified expanded perlite. Spill Sci. Technol. B, 425–431. Broje, V., Keller, A.A., 2006. Improved mechanical oil spill recovery using an optimized geometry for the skimmer surface. Environ. Sci. Technol. 40, 7914– 7918. Boopathy, R., Shields, S., Nunna, S., 2012. Biodegradation of crude oil from the BP oil spill in the marsh sediments of southeast Louisiana, USA. Appl. Biochem. Biotechnol. 167, 1560. Li, H., Liu, L., Yang, F., 2013. Oleophilic polyurethane foams for oil spill cleanup. Proc. Environ. Sci. 18, 528–533. Ceylan, D., Dogu, S., Karacik, B., Yakan, S.D., Okay, O.S., Okay, A.O., 2009. Evaluation of butyl rubber as sorbent material for the removal of oil and polycyclic aromatic hydrocarbons from seawater. Environ. Sci. Technol. 43, 3846–3852. Choi, S.J., Kwon, T.H., Im, H., Moon, D.I., Baek, D.J., Seol, M.L., Choi, Y.K., 2011. A polydimethylsiloxane(PDMS) sponge for the selective absorption of oil from water. ACS Appl. Mater. Interface 3, 4552–4556. Wu, L., Zhang, J., Li, B., Wang, A., 2014. Mechanical-and oil-durable superhydrophobic polyester materials for selective oil absorption and oil/ water separation. J. Colloid Interface Sci. 413, 112–117. Chu, Y., Pan, Q., 2012. Three-dimensionally macroporous Fe/C nanocomposites as highly selective oil-absorption materials. ACS Appl. Mater. Interface 4, 2420– 2425.
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Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water Li Peng a,⇑, Qiao Ying a, Zhao Lili a, Yao Dahu b, Sun Haixiang a,⇑, Hou Yingfei a, Li Shuo c, Li Qi d a
State Key Laboratory of Heavy Oil Processing, China University of Petroleum (East China), Qingdao, Shandong 266580, China School of Chemical Engineering & Pharmaceutical, Henan University of Science and Technology, Luoyang, Henan 471023, China c Shandong Hi-tech Chemical Group, Dongying, Shandong 257105, China d Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, Jiangsu 215123, China b
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: PS/PAN fiber Electrospinning Oil sorption capacity Mechanical property
a b s t r a c t A mechanically robust and high-capacity oil sorbent is prepared by electrospinning a blend of polystyrene (PS) and polyacrylonitrile (PAN). The morphology, oil sorption capacity and mechanical property of the fibers formed in different compositions are investigated in detail. It is shown that the oil sorption capacity is a result of both the chemical composition and the specific surface area which related to diameter size. The addition of PAN as a component in fibrous sorbents can significantly improve the mechanical properties of PS fibers. Moreover, the oil sorption capacity increases with decreasing fiber diameter. The results also show that the maximum sorption capacities of the PS/PAN sorbent for pump oil, peanut oil, diesel, and gasoline were 194.85, 131.70, 66.75, and 43.38 g g1, respectively. Additionally, the sorbent exhibits quick oil sorption speed as well as high buoyancy, which make it a promising candidate for use as an oil spill cleanup sorbent. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Oil spill accidents often take place during transportation and storage of oil, causing huge economic losses as well as environmental pollution. In recent years, with the frequent occurrence of oil spills (Singh et al., 2013) at sea, such as the Exxon Valdez oil spill (1989), the Gulf of Mexico oil spill (2010) and the ConocoPhillips Bohai oil spill (2011), it is imperative to find a reliable method for cleaning up spilled oil at sea. There are a variety of methods for dealing with oil spills, such as situ burning (Buist et al., 2011), dispersion (Roulia et al., 2003), mechanical collection (Broje and Keller, 2006), bioremediation (Boopathy et al., 2012), and the use of sorption materials (Li et al., 2013; Ceylan et al., 2009; Choi et al., 2011; Wu et al., 2014; Chu and Pan, 2012). Among these existing methods, there has been extensive research on oil sorption materials because they are efficient, economical, and provide for easy oil recovery. Currently, oil sorbent materials are divided into three types: inorganic mineral products, organic natural products, and synthetic organic products (Choi and Moreau, 1993). These materials include zeolites (Choi and Cloud, 1992), activated carbon (Bayat et al., 2005), organoclays (Adebajo et al., 2003), straws (Sun et al., ⇑ Corresponding authors. Tel.: +86 18754277990. E-mail addresses: [email protected] (P. Li), [email protected] (H. Sun).
2002), fibers (Annunciado et al., 2005), sponges (Zhou et al., 2013), and alkyl acrylate copolymers (Atta et al., 2005; Jang and Kim, 2000a,b; Dutta and Gogoi, 2013; Pourjavadi and Doulabi, 2013). Liu et al. (2013) made reduced graphene oxide coated polyurethane (rGPU) sponges, which were fabricated by way of facile reduction. The rGPU sponge had an oil sorption capacity of more than 80 g g1 and a chloroform sorption capacity of 160 g g1 (the highest reported value). He et al. (2013) fabricated porous reduced graphene oxide (RGO) foam with a maximum oil sorption value of about 122 g g1 for olive oil by three kinds of freeze-drying methods. Liang et al. (2012) prepared carbonaceous nanofiber (CNF) hydrogels and aerogels through a hydrothermal carbonization process. The CNF hydrogels and aerogels had an oil sorption capacity of 40 g g1 for gasoline and diesel oil. However, these materials have many limitations such as high costs, complex fabrication processes, and low stabilities (Wang and Lin, 2013; Nguyen et al., 2012). Electrospinning is well known as an effective technique for producing fibers with diameters ranging from micrometers to nanometers (Reneker and Chun, 1996; Li et al., 2002). Zhu et al. (2011) first reported electrospun polyvinyl chloride (PVC)/polystyrene (PS) sorbents with an oil sorption capacity of 146 g g1. PVC/PS showed a superior selectivity of water and oil, high buoyancy, and could be applied to clear oil spills. Lin et al. (2012a,b), Wu et al. (2012) reported PS fibers with far higher oil sorption capacities than
http://dx.doi.org/10.1016/j.marpolbul.2015.02.012 0025-326X/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
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Table 1 Tensile properties of as-prepared fibrous sorbents formed in different compositions. Sample
Break strength (MPa)
Elongation at break (%)
F1 F2 F3 F4 F5
14.89 10.43 9.15 4.84 4.18
533.10 483.75 356.74 201.77 158.3
those of polypropylene (PP) fabric. However, PS fibers could be dissolved in gasoline because of their non-polarity. Additionally, PS fibers had a poor mechanical behavior and could be easily destroyed in oil after oil sorption. Polyacrylonitrile (PAN) fibers Nam et al. (1999) have been widely used in industry because of good conductivity, solvent resistance and high strength. However, PAN is hydrophilic and as a result is seldom used in oil sorption. In this paper, the PS/PAN fibrous sorbents were fabricated by electrospinning a blend of PS and PAN. The oil sorption capacities of these fibrous sorbents for pump oil, peanut oil, diesel, and gasoline were investigated.
Fig. 2. Viscosity and conductivity of the PS/PAN solution for different PS/PAN compositions.
2. Experiments 2.1. Materials Polystyrene (PS) with a molecular weight of Mw = 250,000 was purchased from Energy Chemical. Polyacrylonitrile (PAN) with a molecular weight of Mw = 80,000 was purchased from Beijing Yili Fine Chemicals Co., Ltd. N, N-dimethylformamide (DMF) was purchased from Shanghai Chemical Reagents Co., Ltd., China. The oils used for absorption are pump oil (Beijing Si Fang special oil factory), peanut oil (Shandong Lu Hua Group Co., Ltd.), diesel and gasoline (Shandong Qingdao SINOPEC Co., Ltd.). The oil properties investigated are listed in Table 1. 2.2. Method A mixture of PS and PAN was dissolved in DMF by stirring for 4 h to form 18 wt.% solution., Weight ratios of PS/PAN of 0/10, 3/ 7, 5/5, 7/3, 10/0 were named as F1, F2, F3, F4, F5, respectively. The electrospun fibrous fibers were prepared at 25 kV in a relative humidity of 40% at 30 °C, a feed rate of 0.1 mm/s and the distance
between the tip and the collector was fixed at 10 cm. To form fibers with different diameters, the feed rates were set as 0.1 mm/s, 0.15 mm/s, 0.2 mm/s, 0.25 mm/s and 0.3 mm/s. The other conditions are the same as the above study, except that the weight ratio of PS/PAN is 5/5.
2.3. Characterization The morphology of the electrospun fibers was examined by field emission scanning electron microscopy (FE-SEM) (S-4800, Hitachi Ltd., Japan). The fiber diameters were calculated from the SEM images by SmileView. Contact angles of the electrospun fibers were measured by an contact-angle system (SL200B, Kino Inc, USA) at 25 °C. The average contact angle value of both water and oil were obtained by measuring at three different positions of the same sample. The viscosity and electrical conductivity of solution in different compositions were measured by rotational viscometer (NDJ-79, Shanghai Changji Geological Instruments Co., Ltd., China) and digital conductivity meter (DDS-11A, Shanghai Leici Ltd., China), respectively.
Fig. 1. SEM images of PS/PAN fibers formed with weight ratios of (a) 0/10, (b) 3/7, (c) 5/5, (d) 7/3, and (e) 10/0, corresponding to samples F1, F2, F3, F4 and F5, respectively.
Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
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P. Li et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
2.5. Elemental analysis X-ray Photoelectron Spectroscopy (XPS) was recorded by PHI5700. Energy Dispersive Spectrometer (EDS) was recorded by S-4800, Hitachi Ltd., Japan. 2.6. Oil sorption test Approximately 0.15 g of oil sorbent was added into the glass beaker filled with 100 mL of oil. After 60 min of sorption, the wet sorbent was drained for 60 s. The oil sorption capacities for these sorbents were obtained from the following equation (Pourjavadi et al., 2013):
Q ¼ ðm m0 Þ=m0
ð1Þ 1
Fig. 3. Maximum oil sorption capacities of F1–F5 for various oils.
2.4. Mechanical test Tensile strength is measured by universal tensile machine (WDM3020) with a tensile speed of 50 mm/min. All samples were prepared with thickness of 0.02 mm, width of 10 mm and extension interval of 20 mm.
where Q is the oil sorption capacity (g g ), m is the total mass of wet sorbent after the oil drained for 60 s (g), and m0 is the mass of the sorbent before sorption (g). Each sample was independently measured three times, and the average value and standard deviation were calculated. 2.7. Buoyancy test 20 mL vacuum pump oil (dyed with Oil Red) was poured into a beaker containing 150 mL water. 0.15 g of the fiber was gently placed onto the surface of oil.
Fig. 4. Photos of (a) F3, and (b) F5 after sorption of pump oil.
Fig. 5. SEM images of fibers formed by feed rates of (a) 0.1 mm/s, (b) 0.15 mm/s, (c) 0.2 mm/s, (d) 0.25 mm/s, and (e) 0.3 mm/s.
Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
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P. Li et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
Fig. 6. Maximum oil sorption capacities of fibers formed by feed rates of (a) 0.1 mm/s, (b) 0.15 mm/s, (c) 0.2 mm/s, (d) 0.25 mm/s, and (e) 0.3 mm/s.
3. Results and discussion The morphology of fibers with different PS/PAN compositions is observed in Fig. 1. The average fiber diameters are 0.74, 1.07, 1.29, 1.77 and 1.36 lm, for samples F1, F2, F3, F4 and F5, respectively. It is well known that the high surface tension and viscosity of the spinning solution are not conducive to ejection, while the repulsive electric force is favorable for droplet ejection. With a small total force, the acceleration of the jet decreases and the splitting of the jet increases, resulting in thinner fiber diameters (Iksoo, 1955). The PAN solution has a high surface tension that hampers droplet division, which makes it hard for thinner diameters to form. As shown in Fig. 2, increasing the PAN percentage in the polymer mixtures leads to an increase in the viscosity and electrical conductivity of the polymer solution. When the repulsive electric force is the main factor, the fiber diameters will decrease with increasing the PAN content. However, the diameter of F5 is smaller than F4, which may because the viscosity and surface tension play a more important role than repulsive electric. Specific surface area and porosity will increase with a thinner fiber diameter which is favorable for the adsorption and adherence of oil on the fiber surfaces and in the voids. Oil sorption capacity is the most important parameter in oil recovery. Fig. 3 presents the oil sorption capacities of fibers formed with PS/PAN weight ratios of 0/10, 3/7, 5/5, 7/3, and 10/0. For pump oil, peanut oil and diesel oil, a higher weight percentage of PS results in a higher oil sorption capacity. The oil sorption is the result of fiber diameter and oleophilicity. Even though F1 has the minimum diameter, its polarity is the largest, and as a result its oil sorption capacity is the lowest. For gasoline, if the PS content of fibers less than 50%, increase of PS content will decrease the polarity of fibers, therefore, its oil sorption capacity increases. However, F4 and F5 whose PS content is more than 50%, the fibers can dissolve in gasoline because of similarity-intermiscibility theory, which of course will decrease the gasoline sorption capacity., Therefore, F3 has the highest oil capacity in gasoline because the joint effect of dissolving and polarity. The mechanical strength of PAN fiber shows the highest among fibers we tested. The F1, F2 and F3 samples with more PAN can maintain their form after oil sorption, as shown in Fig. 4(a), while the F4 and F5 samples with less PAN are destroyed in high viscosity oils such as pump oil and peanut oil after oil sorption, as shown in Fig. 4(b), big balls of fibers were destroyed into a few small fiber balls. The mechanical properties of the sorbents were evaluated by stress–strain measurements. The break strength and elongation
Fig. 7. X-ray Photoelectron Spectroscopy (XPS) data of the F3 sorbent: (a) the survey spectrum, (b) C1s, and (c) N1s.
at break of the fibers are summarized in Table 1. The mechanical properties of PS sorbent are greatly reinforced by incorporation of PAN. It is obvious that the break strength increases with increasing the content of PAN. At a critical weight ratio of 5/5 of PS/PAN (sample F3), the break strength of the sorbent is 9.15 MPa, which is two times larger compared with pure PS sorbent F5. Meanwhile, the F3 sample shows a relative high elongation at break (356.74%), namely, good toughness. To investigate the relationship between fiber diameter and oil sorption capacity, the sorbents were formed with a variety of feed rates. Fig. 5 shows the SEM images of the fibers formed with
Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
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Fig. 8. Contact angle photos of a (a) water droplet and (b) diesel oil droplet on the F3 sample surface with contact angles of 144.32° and 0°, respectively.
Table 2 Properties of the studied oils at room temperature (20 °C). Oil
Viscosity (MPa S1)
Density (g cm1)
Qe (g g1)
te (min)
Vacuum pump oil Peanut oil Diesel oil Gasoline
162.30 78.45 4.75 0.30
0.8566 0.9151 0.8449 0.7724
194.85 131.70 66.75 43.38
56.27 16.24 5.161 3.520
various feed rates of 0.1 mm/s, 0.15 mm/s, 0.2 mm/s, 0.25 mm/s and 0.3 mm/s. The average diameters of the corresponding fibers are 1.29, 1.45, 2.12, 2.2 and 2.47 lm, respectively. It is obvious that the fiber diameter will increase with increasing of the feed rate. This is because when feed rates are slow, the charged jet contains few polymer chains and solvents that accelerates the solvent evaporation and subsequent solidification, resulting in a thin diameter. Moreover, the oil sorption capacities of the sorbents formed at different feed rates are shown in Fig. 6. It is observed that the oil sorption capacity of fibers increases with decreasing the feed rate. When the feed rate is 0.1 mm/s, the oil sorption capacities of the fiber are the highest and the maximum sorption capacities of the PS/PAN sorbent for pump oil, peanut oil, diesel, and gasoline were 194.85, 131.70, 66.75, and 43.38 g g1, respectively. This can be attributed to the difference of the fiber diameter, which is related to the specific surface area and porosity of the sorbent. The specific surface area and porosity will increase with decreasing fiber diameter, which provide a large amount of storage volume for sorbed oils. Based on the above results, the fiber sorbent F3 formed by a feed rate of o.1 mm/s is chosen as a sorbent for oil spill cleanup. It is known that microphase separation may happen during the process of polymer blending, resulting in different compositions at the fiber surface compared to the fiber interior. The change of the fiber surface composition will change its polarity, as well as its oil sorption. Therefore, the chemical composition of the fiber was
investigated by XPS and EDS. As can be seen from Fig. 7, XPS was used to examine the chemical composition on the surface of electrospun fibers. The peaks at 284.7 and 399.6 eV were ascribed to C1s and N1s. After calculating the atomic concentrations of C and N elements, we can obtain that C:N = 89.65:10.35. However, the XPS elemental analysis covers the surface to a depth of only 10 nm, while the diameter of the fiber is about 1 lm. As a result, the element distribution from the center to the surface of composite fiber need further investigation. Therefore, we use the EDS analysis method which can probe several microns below the surface. The EDS result shows that C:N ratio of F3 is 87.70:12.30, which is close to the result obtained by XPS. If the mixture of PS and PAN is uniform, the nominal atomic ratio of C:N is 87.63:12.37. The XPS and EDS results are consistent with this prediction. The wettability of the electrospun fiber was measured by the contact angle of a water and diesel oil droplet, as shown in Fig. 8. It is shown that the water and diesel oil contact angles on F3 sample are 144.32° and 0°, respectively, indicating that the fiber sorbent is oleophilic and hydrophobic. The hydrophobicity and oleophilicity of F3 sample is determined by low surface tension and surface structure. Table 2 shows the tendency of maximum oil sorption capacity is: pump oil > peanut oil > diesel oil > gasoline. The oil sorption capacity is determined by oil properties and fiber properties. The increase of the oil viscosity can lead to two different effects: on one hand, high viscosity can inhibit the oil entering the interior of the fibers; on the other hand, with the increase of oil viscosity, the oil can be more likely to adhere to the surface and voids of the fibers. The details about the maximum oil sorption capacity and sorption rate were discussed in another paper (Qiao et al., 2014). Buoyancy is another important parameter for sorbents used in oil spill cleanup on the water surface. A sorbent with high buoyancy Zhu et al. (2011) can keep floating over the water surface before and after oil sorption, which is helpful for both the oil sorption and removing the used sorbent from the oil spill area. Fig. 9 shows the
Fig. 9. Oil sorption behaviors of pump oil in oil–water bath at times of (a) 10 s, (b) 10 min, and (c) 60 min.
Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
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oil sorption behaviors of the sorbent F3 with increasing time. When the F3 sorbent is placed on the surface of oil over the water, the sorbent floats on the surface and keeps absorbing the oil. After 10 min, the thickness of the oil layer over the water surface decreases significantly, showing that a large amount of oil is absorbed by the sorbent. 60 min later, the F3 sorbent could absorb almost all pump oil and while still floating on the water. This high buoyancy before and after sorption makes PS/PAN a promising sorbent for oil spill cleanups. 4. Conclusion Electrospun fibers with different weight ratios of PS/PAN were investigated. The oil sorption capacity of fibers is a joint result of the chemical composition and the specific surface area related to fiber diameter size. The addition of PAN greatly reinforces the mechanical properties of PS fibers. It is shown that the weight ratio of 5/5 for PS/PAN results in high oil capacities while maintaining good mechanical strength. Moreover, sorbents were obtained by different feed rates and it is demonstrated that the oil sorption capacity increases with decreasing of the fiber diameter. The maximum sorption capacities of the PS/PAN sorbent for pump oil, peanut oil, diesel, and gasoline were 194.85, 131.70, 66.75, and 43.38 g g1, respectively. Additionally, the sorbent exhibits quick oil sorption speed as well as high buoyancy, which has great potential for use in oil spill cleanup. Acknowledgments The work was supported by the NSFC (National Natural Science Foundation of China) under Grant 51203186, the Converging Research Center Program funded by Korean Ministry of Education (2013K000415), the Shandong Provincial Natural Science Foundation (contract Grant No. ZR2010BQ026) and the Fundamental Research Funds for the Central Universities. References Singh, V., Kendall, R.J., Hake, K., Ramkumar, S., 2013. Crude oil sorption by raw cotton. Ind. Eng. Chem. Res. 52, 6277–6281. Buist, I., Potter, S., Nedwed, T., Mullin, J., 2011. Herding surfactants to contract and thicken oil spills in pack ice for in situ burning. Cold Reg. Sci. Technol. 67, 3–23. Roulia, M., Chassapis, K., Fotinopoulos, C.H., Savvidis, T.H., Katakis, D., 2003. Dispersion and sorption of oil spills by emulsifier-modified expanded perlite. Spill Sci. Technol. B, 425–431. Broje, V., Keller, A.A., 2006. Improved mechanical oil spill recovery using an optimized geometry for the skimmer surface. Environ. Sci. Technol. 40, 7914– 7918. Boopathy, R., Shields, S., Nunna, S., 2012. Biodegradation of crude oil from the BP oil spill in the marsh sediments of southeast Louisiana, USA. Appl. Biochem. Biotechnol. 167, 1560. Li, H., Liu, L., Yang, F., 2013. Oleophilic polyurethane foams for oil spill cleanup. Proc. Environ. Sci. 18, 528–533. Ceylan, D., Dogu, S., Karacik, B., Yakan, S.D., Okay, O.S., Okay, A.O., 2009. Evaluation of butyl rubber as sorbent material for the removal of oil and polycyclic aromatic hydrocarbons from seawater. Environ. Sci. Technol. 43, 3846–3852. Choi, S.J., Kwon, T.H., Im, H., Moon, D.I., Baek, D.J., Seol, M.L., Choi, Y.K., 2011. A polydimethylsiloxane(PDMS) sponge for the selective absorption of oil from water. ACS Appl. Mater. Interface 3, 4552–4556. Wu, L., Zhang, J., Li, B., Wang, A., 2014. Mechanical-and oil-durable superhydrophobic polyester materials for selective oil absorption and oil/ water separation. J. Colloid Interface Sci. 413, 112–117. Chu, Y., Pan, Q., 2012. Three-dimensionally macroporous Fe/C nanocomposites as highly selective oil-absorption materials. ACS Appl. Mater. Interface 4, 2420– 2425.
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Please cite this article in press as: Li, P., et al. Electrospun PS/PAN fibers with improved mechanical property for removal of oil from water. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.02.012
