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Electrospinning of ABS nanofibers and their high filtration performance

Electrospinning of ABS nanofibers and their high filtration performance Acrylonitrile–butadiene–styrene (ABS) is a commercial polymer for widely industrial applications due to its good mechanical and physical properties. However, there are only countable reports regarding its fibers from electrospinning. Comprehensive investigation on its optimized electrospinning parameters is missing. Herein, ABS fibers with different fiber diameters were produced by electrospinning. The electrospinning conditions, including the solvents, solution concentrations and amounts of different salt additives, have been comprehensively investigated. The morphologies of electrospun ABS fibers are studied by scanning electron microscopy and Raman spectroscopy. Different fiber diameters and coating densities are applied for filtration applications, which showed excellent filtration performance. The filtration efficiency of up to 99%, low pressure drop of < 30 Pa, and high filtration quality factor of up to 0.477 are achieved from the electrospun ABS fibers coated on microfibrous polypropylene substrates. In addition, the electrospun ABS fibers also shows good thermal stability and other applications such as oil/water separation. Keywords Acrylonitrile–butadiene–styrene fiber · Electrospinning · Filtration · Oil–water separation Introduction because of its good physical and mechanical properties, such as excellent chemical resistance, dimensional stabil- Acrylonitrile–butadiene–styrene (ABS) is a commercial ity, impact-resistant and toughness [1, 2]. Although ABS terpolymer made by polymerizing acrylonitrile and styrene has been comprehensively investigated and applied in many in the presence of polybutadiene. It has broad applications areas, only countable studies on its fibers and applications for light, rigid and molded products, such as piping, musi- in fiber morphology are available. Electrospinning is a facial cal instruments, golf club heads, automotive body parts, technology to produce fibers with diameters in the range wheel covers, enclosures, protective headgear and toys, from sub-nanometers to tens of micrometers and electrospun fibers have been applied in almost all fields, including tissue engineering, composites, actuators, catalysts, filtration and Electronic supplementary material The online version of this sponges [3–17]. In 2014, ABS and ABS/zeolite compos- article (https ://doi.org/10.1007/s4276 5-019-00026 -7) contains ite fibers were firstly prepared by electrospinning technol- supplementary material, which is available to authorized users. ogy, but the fibers have a broad diameter distribution and * Shaohua Jiang no application was presented [18]. In another report, pure shaohua.jiang@njfu.edu.cn ABS fibers and their conductive ABS/copper composite b fi - * Andreas Greiner ers were fabricated via electrospinning and electroless metal greiner@uni-bayreuth.de deposition, respectively [19]. However, comprehensive investigation on the formation of ABS electrospun fibers is Macromolecular Chemistry, Bavarian Polymer Institute, University of Bayreuth, Universitätsstraße 30, missing in this report. Very recently, N,N-dimethylforma- 95440 Bayreuth, Germany mide (DMF), N,N-dimethylacetamide (DMAc), and tetrahy- Bavarian Polymer Institute (BPI), University of Bayreuth, drofuran (THF), were reported as solvents for the electro- Universitätsstraße 30, 95440 Bayreuth, Germany spinning of ABS, and the obtained ABS electrospun fibers Present Address: College of Materials Science were used for air filtration [20]. The results indicate that the and Engineering, Nanjing Forestry University, DMF and DMAc were suitable solvents for electrospinning, Nanjing 210037, China Vol:.(1234567890) 1 3 Advanced Fiber Materials (2020) 2:34–43 35 but there are still many beads on fibers. Additionally, the collecting the fibers with aluminum paper on a horizontal filtration results suggest a relatively high pressure drop and rotating disc. The samples for the filtration and adhesion low quality factor which could be because of the beaded test were prepared by coating the fibers on polypropylene ABS fibers and the self-standing thick membranes. microfiber filter substrate for different lengths of time. Therefore, it is still necessary to find out optimized elec- trospinning parameters for the fabrication of beads-free elec- Characterizations trospun ABS fibers and investigate the relationship between the fiber structures and filtration performance. In this work, The electrospun fiber morphology was measured by we choose a mixture of dimethyl sulfoxide (DMSO) and scanning electron microscopy (SEM, Zeiss LEO 1530, chloroform (CHCl ) as solvent for the electrospinning of EHT = 3  kV). All the samples were coated with 3.0  nm ABS. The electrospinning parameters to achieve homoge- platinum before scanning. The fiber diameter was measured nous and beads-free ABS fibers are optimized. To decrease by ImageJ software. The pore size of nonwoven electrospun the pressure drop and obtain high filtration quality factor, a ABS was measured by a pore size meter (TOPAS, PSM165). commercial microfibrous polypropylene substrate (MFPP) The filtration measurement for salt particles was performed is used to coating a very thin layer of electrospun ABS fib- on MFP 2000 from P ALAS with a white light-scattering ers. With the above strategies, electrospun ABS fibers with spectrometer, Welas digital 2100 (particle size detection fiber diameter in the range from hundreds of nanometers range: 0.2–10.0 μm). to several micrometers are obtained. The novel composite A confocal WITec alpha 300 RA + imaging system equip- filters (ABS electrospun fibers on MFPP) also show high ment with a UHTS 300 spectrometer and a back-illuminated filtration efficiency, low pressure drop and high filtration Andor Newton 970 EMCCD camera was used for Raman quality factor. imaging. Raman spectra were acquired using an excita- tion wavelength of 532 nm and an integration time of 0.7 s −1 pixel (100 × objective, NA = 0.9, step size 100 nm, soft- Experimental ware WITec Control FOUR 4.1). All spectra were subjected to a cosmic ray removal routine and baseline correction. The Materials spatial distribution of SAN and PB particles in the fibers was determined by basis analysis using the Raman spectra Acrylonitrile–Butadiene–Styrene (ABS, Novodur H701, of the neat components as references (software WITec Pro- M = 210 kDa, Styrolution Group GmbH), DMSO (99.5%, ject FOUR 4.1). The neat Styrene-Acrylonitrile (SAN) and Gruessing GmbH), CHCl (99%, Sigma-Aldrich), sodium polybutadiene (PB) particles were obtained by extracting dodecyl sulfate (SDS, 99%, Sigma-Aldrich) and perfluoro- ABS with acetone, which dissolves SAN selectively. decalin (oil, 95%, density 1.908 g/mL, Sigma-Aldrich) were used as received. Pyridine-formic acid salt (PF) was pre- pared by mixing pyridine (99.9%) and formic acid (98%) Results and discussion (1:1 molar ratio). Microfibrous PP substrate (fiber diameter of 23 ± 4 µm) was used for coating electrospun ABS fib- Electrospinning of ABS ers. The commercial filter (MGK-P95%, 90 g/m , thickness 0.5 mm) was provide by Shanghai Mingguan Purification In previous reports, acetone and DMSO were used as sol- Materials Co., Ltd, which was prepared by melt-spinning. vents for electrospinning ABS [18, 19]. However, there are disadvantages using these two solvents. Acetone has a low Preparation of electrospun ABS fibers boiling point of 56.5 °C and high vapor pressure of 24.6 kPa (20 °C) [21], which lead to a fast evaporation during electro- The ABS solutions for electrospinning were prepared spinning. Therefore, ABS precipitates easily at the electro- according to the component composition in Table S1. The spinning nozzle, disturbing the continuous jet formation. By ABS pellets were dissolved in mixture solvent of DMSO and comparison, DMSO has a very high boiling point of 189 °C CHCl (wt/wt, 1/1) with different concentrations. Different and very low vapor pressure of 55 Pa (20 °C) [21], causing amounts of SDS were added to the ABS solution to adjust deposition of wet fibers gluing together and losing fiber mor - the conductivity of the solutions. Thirty-one ABS solutions phology. Chloroform is another common solvent for elec- (S1–S31) were prepared. The electrospinning was performed trospinning. It has a slightly higher boiling point of 61.2 °C by applying a high voltage of 12–20 kV, collecting distance and lesser vapor pressure of 21.1 kPa than acetone [21]. of 15–20 cm and flow rate of 0.6 mL/h. The samples for fiber Similar to acetone, it is also a good solvent for ABS. Our ini- morphology, pore size and heat resistance were prepared by tial studies on the electrospinning of ABS/CHCl solutions 1 3 36 Advanced Fiber Materials (2020) 2:34–43 showed a blockage of the electrospinning nozzle due to the fast solidic fi ation of the solution at the nozzle tip. Therefore, in this work, a solvent mixture of DMSO and CHCl with equal weight ratio was used for the electrospinning. The initial investigation was focused on the electrospin- ning of ABS solutions with high concentrations (S1: 25 wt%, S2: 20 wt% and S6: 15 wt%). These three solutions showed very good electrospinnability with the continuous electrospinning process. The increased concentration is beneficial to eliminate the beads on the fibers, but the fiber diameter also increases (Fig. 1). The electrospun fibers from 25 to 20 wt% ABS solution showed bead-free fibers and the average fiber diameters were 2800 ± 350 and 2180 ± 390 nm, respectively. The 15 wt% ABS solution led to a quite dif- ferent fiber morphology. Many beads were observed on the fibers and the average fiber diameter was decreased greatly to 598 ± 254 nm. Higher magnification SEM images showed that the fiber surface was rough with particles embedded in the fibers. These particles could be from the PB dispersed in the styrene-acrylonitrile matrix in ABS, which is inherent during ABS synthesis. Confocal two-dimensional (2D) Raman imaging was performed in order to probe the spatial distribution of SAN and PB in the fibers. It can be clearly deduced from the Fig. 2 Raman imaging of ABS fibers (sample S25). a Optical micro- color-coded 2D Raman images shown in Fig. 2 that the sup- graph with marked position for Raman x, y-imaging. b Color-coded confocal 2D Raman image showing the spatial distribution of SAN porting fiber consists of SAN and the embedded particles (red) and PB particles (pink) in the electrospun ABS fibers; c the dis- correspond to the PB particles in the ABS. tribution of PB particles (blue) for means of clarity. d Raman spectra Conductivity plays an important role in the electrospin- of SAN (red) and PB particles (blue) ning process and the b fi er morphology. The addition of salts in the electrospinning solutions could change the conduc- tivity significantly. In this work, we first investigated the Fig. 1 Fiber morphology of electrospun ABS fibers spun from a mixture of DMSO: CHCl (1:1 wt: wt) with concentrations of 25 wt% (a, a′), 20 wt% (b, b′) and 15 wt% (c, c′) 1 3 Advanced Fiber Materials (2020) 2:34–43 37 which was seven times more than that by adding PF (9.1 µs/ cm). A further increase of the amount of SDS led to greatly increased conductivity but also introduced the problem for the electrospinnability that big droplets were formed during the electrospinning process. The addition of salts (SDS and PF) also affected the fiber morphologies significantly. Figure  4 shows the fiber mor - phologies electrospun from ABS solutions (20 wt%) with different amounts of SDS from 0.1 to 8 wt% and PF from 0.1 to 1.0 wt%. Compared to the fibers from the ABS solu- tion without salt additives, the addition of salt is useful to decrease the fiber diameters. A small amount of SDS (0.1, 0.2 and 0.5 wt%) led to a decrease of the fiber diameter to 1150 ± 346, 926 ± 151 and 908 ± 208  nm, respectively, which was half the diameter of the fibers from the solution without salts (2180 ± 390 nm). Interestingly, this relatively Fig. 3 Effect of salt additives (SDS and PF) on the conductivity of high salt amount led to the fact that the fiber was branched the ABS solution (20 wt%) with very fine fibers, which could be attributed to the strong repelling effect from the high conductivity. In comparison to the fibers from solution without additives, the addition of addition of a small amount of SDS and PF on the solution PF could also decrease the fiber diameter but not much more conductivity, the electrospinnability and the fiber morphol- than the addition of SDS, which could be due to the weak ogy. Figure 3 presents the relationship between the conduc- effect on conductivity from PF (Fig.  4). tivity of ABS solutions (20 wt%) and the added amount of More solutions with different ABS concentrations and SDS and PF salts. The addition of both SDS and PF into different amounts of salt additives of SDS and PF were the ABS solutions could increase the conductivity, but SDS prepared according to the Table S1 (1–5) to optimize the exhibits a much more obvious effect. With the addition of electrospinning conditions to achieve a good electrospin- 1 wt%, SDS increased the conductivity up to 68.5 µs/cm, ning process and obtain fibers with small diameters. The Fig. 4 Effect of the amount of SDS and PF on the fiber morphologies 1 3 38 Advanced Fiber Materials (2020) 2:34–43 salt. Fixing the ABS concentration to 10 wt% and changing the SDS amount (0.1, 0.2, 0.25, 0.3, 0.35 and 0.4 wt%) can- not change the fiber diameter much. However, by fixing the SDS amount to 0.2 wt% and changing the ABS concentra- tion from 20 wt% to 10 wt%, it is easy to get tunable fiber diameters from 1 µm to 150 nm (Figure S1). Due to the hydrophobicity of ABS, the self-standing porous electrospun membrane showed the efficient separa- tion of oil and water. In this work, we also tried to find some applications for electrospun ABS fibers. The electrospun ABS fibrous membrane could be used for oil/water separa- tion due to the hydrophobicity with a water contact angle of 130 (Fig. 6, SI Video). The mixture with oil (perfluorodeca- lin, 3 mL) and water (dyed with Rhodamine B, 9 mL) was filled into the container equipped with ABS fibrous separator (thickness: 0.1 mm; diameter: 15 mm). After about 6 min, the oil/water mixture separated. The clear oil dripped into the collector and the red water was kept on the top of the ABS filter. These findings made electrospun ABS fibrous membranes possible for oil/water separation. Pore size and coating density Fig. 5 The concentration of ABS and SDS on the electrospinnabil- Pore size and coating density are very important parameters ity (a) and fiber diameters (b). The electrospinnability was defined by for achieving the high filtration efficiency when randomly rates: 10—very good; 9—good (a small number of beads); 8—good oriented fibers are coated on a filter substrate. In this work, (many beads); 7—good (beads and ununiformed coating); 6—com- mon (big droplets); and 4—bad (beads, big droplets and ununiformed we first prepared electrospun ABS nonwoven fibers with coating) different fiber diameters and then measured the pore size of these nonwoven fibers. Figure  7a plots the relationship cross effect of ABS concentration and additive amounts on between the fiber diameter and the pore size. Interestingly, the electrospinnability and fiber diameter is shown in Fig.  5. the b fi er diameter showed a linear relationship with the aver - It is obvious that the fiber diameter decreases as the ABS age pore size. When the fiber diameter came down to 300 nm concentration decreases (0 wt% SDS) and a small amount from 2800 nm, the average pore size dropped dramatically of SDS up to 0.2 wt% is useful to decrease the fiber diam- to 2 µm from 13.5 µm. If the fiber diameter decreases to eter. Increasing the salt amount by more is not expected to 100 nm, then the average pore size could drop to even about further decrease the fiber diameter, but the fiber diameter is 1 µm. These fine fibers and small pore size would greatly still much smaller than the fibers from a solution without improve the filtration efficiency. Fig. 6 Oil/water separation by electrospun ABS membrane 1 3 Advanced Fiber Materials (2020) 2:34–43 39 Fig. 7 Relationship of fiber diameter and pore size (a) and coating time-dependent coating density (b) of electrospun ABS fibers Commercial filters usually have a coating of electrospun Filtration efficiency fibers with a weight per area in the range of 0.3–0.8 g/m . We established a simple method to measure the coating den- The filtration measurement was performed to evaluate the sity (weight per area, g/m ) of electrospun ABS fibers on effect of the electrospun fiber diameter and the coating time MFPP (9 × 9  cm ): (1) Electrospinning ABS fibers on the (coating density) on the filtration efficiency in comparison substrates for different time (0.5, 1, 2, 4, 6 and 8 min); (2) to the blank MFPP samples (MFPP-01 and MFPP-02) and Drying the samples in a vacuum oven at 55 °C for 18 h to the commercial filter (C-Filter). Before we measured the remove residual solvents; (3) Put the substrate with coat- filtration efficiency, we first checked the fiber morphology ing fibers on balance (0.01 mg deviation) and set weight to of MFPP and C-Filter. As shown in Figure S2, the MFPP 0.00 mg; (4) Remove the coating fibers from the substrate; was composed of smooth fibers. The average fiber diam- (5) Put the substrate on balance again and a minus value was eters are 23 ± 4 µm and junctions between the fibers were obtained. The absolute value is the weight of the coating observed. A commercial filter contains two layers. One layer fibers on the substrate; (6) Repeat 4 times for each sam- is a substrate layer with a homogeneous fiber diameter of ple. Figure 7b shows that the coating density was linearly 16.5 ± 1.1 µm and the other layer is composed of much thin- increased with the coating time. When the coating time was ner fibers with ununiformed fiber diameters of 1.3 ± 1.2 µm. 2, 4 and 6 min, the coating weight per area was in the com- The two layers were glued together to improve the adhesion. mercial range, which implied the commercial application of The electrospun fiber diameter and the coating density this coating filters. play a crucial role in the filtration efficiency of salt par - ticles (0.2–10 μm) (Fig. 9). As expected, the microfiber Heat resistance fibrous MFPP (MFPP-01 and MFPP-02) showed the worst filtration efficiency due to their large pore size. A coating Due to the heat pressing process during the fabrication of of electrospun ABS fibers on the substrate improved the filters, it is necessary to evaluate the heat resistance of elec- filtration efficiency. When fixing the coating time to 2 min, trospun ABS nonwovens. As shown in Fig. 8, the ABS non- the coating layer with a fiber diameter of 428 nm showed wovens could stand the same shape under 110 °C for 2 min. much better filtration efficiency than that with 2800 nm Higher temperatures led to the shrinkage of the nonwovens. fiber diameter. The same results were also found when the The SEM images showed that no changes were found in coating time was fixed to 4 and 6 min. Two exceptional the fiber morphology when the heating temperature reached samples were outside the rule of fiber diameter-related around 110 °C. When the samples were heated between 120 filtration efficiency. The first one is the sample coated with and 130 °C, the fibers became smoother due to the melting electrospun fibers of 598 nm. This sample showed worse of the dispersed polybutadiene particles. In addition, junc- filtration efficiency than the sample coated with electro - tions between the fibers were also observed due to the partial spun fibers of 2800 nm, which could be due to the large melting of ABS fibers. beads on the fibers. Another exceptional sample was the filter coating with 149 nm ABS fibers, which showed very bad filtration efficiency among all coating samples. This could be due to the quite inhomogeneous coating on the 1 3 40 Advanced Fiber Materials (2020) 2:34–43 Fig. 8 SEM images of electrospun ABS fibers after heat treatment and photos (insert) of the heat resistance of electrospun ABS fiber nonwovens at different temperatures for different times. Sample: S6 with original size of 2 × 2 cm MFPP (Fig.  9d). As the coating time (coating density) showed a differential pressure of 13.5 Pa. By comparison, increased, the filtration efficiency also improved. When the samples coated with 457 and 428 nm for 2 and 4 min, the fiber diameter was 428 nm and the coating time was respectively, which showed comparable filtration efficiency, 2 min, the filtration efficiency was as good as the com- presented similar or a little higher differential pressure. mercial filter (C-filter) with the particle size larger than Ashby figures of coating density-dependent pressure drop 2.5 μm. When the coating time was 4 min, the coated filter and the quality factor (QF) from different filter mediums were showed comparable filtration efficiency to the commercial plotted to compare the quality of the filter prepared in this work filter and when the coating time was increased to 6 min, to other filter mediums. As illustrated in Fig.  11, the filters in the coating filter showed even better filtration efficiency this work showed a much better filtration performance in terms than the commercial filter (Fig.  9). of the pressure drop and QF. When comparing the pressure Differential pressure (pressure drop) is an important drop of different filter mediums (pressure drop > 30 Pa), the parameter to evaluate the efficiency of filters. It is defined ABS filters occupied a very important area where the small as the pressure difference between the two sides of the filter pressure drop < 30 Pa could be achieved with a sample coating during the filtration test. Electrospun ABS fibers on MFPP, density smaller than 0.8 g/m (Fig. 11a). The quality of the smaller fiber diameter and increasing the coating time gen- filters could be evaluated by QF based on the comprehensive erally lead to the increase of differential pressure (Fig.  10). evaluation on the pressure drop and filtration drop. It can be Due to the large pore size, the MFPP showed the smallest calculated by the following equation: differential pressure of 1.98 Pa, while the commercial filter 1 3 Advanced Fiber Materials (2020) 2:34–43 41 Fig. 9 Comparison of filtration efficiency of MFPP (substrate with- coating times of a 2 min, b 4 min and c 6 min. d Ununiformed coat- out coating), commercial filter (C-Filter) and the filters coating with ing with electrospun ABS fiber (149  nm) on MFPP before and after electrospun ABS fibers with different fiber diameters and different filtration Fig. 10 Differential pressure of MFPP, commercial filter (C-Filter) and filters by coating electrospun ABS fibers with different fiber diameters and different coating times 1 3 42 Advanced Fiber Materials (2020) 2:34–43 the range of 200–2000 nm were successfully prepared by electrospinning. This electrospun ABS membrane showed thermal stability up to 110 °C for 2 min. Comparable filtra- tion efficiency to commercial filter was achieved by coating electrospun ABS fibers on MFPP. The filtration efficiency improved as the fiber diameter decreased and the coating time increased. Compared to the commercial PA fiber fil- ter, electrospun ABS fibers might be better electrically charged. Unfortunately, the adhesion between electrospun ABS fibers and MFPP was bad but could be improved by electrospraying glue or hot-pressing. The electrospun ABS fibrous membranes were also successfully applied for oil/ water separation. Acknowledgments Open Access funding provided by Projekt DEAL. Compliance with ethical standards Conflict of interest There are no conflicts to declare. Open Access This article is licensed under a Creative Commons Attri- bution 4.0 International License, which permits use, sharing, adapta- tion, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are Fig. 11 Ashby plot of coating density-dependent pressure drop (a) included in the article’s Creative Commons licence, unless indicated and quality factor (QF) (b) for different filter mediums: Alumina [23], otherwise in a credit line to the material. If material is not included in MWNT [22], PP [24–27], PAN [28, 29], PAN/silica [30], silica [31], the article’s Creative Commons licence and your intended use is not PA [32, 33], PU [34], polysulfone [35] and PI [36] permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativ ecommons .or g/licenses/b y/4.0/. − ln (1 − ) QF = ΔP where η and ΔP are the filtration efficiency and the pres- References sure drop between the upstream and downstream pressure, respectively. The higher the QF is, the more efficient the 1. Kulich DM, Gaggar SK, Lowry V, Stepien R. Acrylonitrile–Buta- filters are [22]. Figure  11b plotted the Ashby figure of QF for diene–Styrene polymers. Encyclopedia of polymer science and technology. New York: Wiley; 2002. the 300 nm particle size in this work in comparison to other 2. Rutkowski JV, Levin BC. 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Electrospinning of ABS nanofibers and their high filtration performance

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Springer Journals
Copyright
Copyright © The Author(s) 2020
ISSN
2524-7921
eISSN
2524-793X
DOI
10.1007/s42765-019-00026-7
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Abstract

Acrylonitrile–butadiene–styrene (ABS) is a commercial polymer for widely industrial applications due to its good mechanical and physical properties. However, there are only countable reports regarding its fibers from electrospinning. Comprehensive investigation on its optimized electrospinning parameters is missing. Herein, ABS fibers with different fiber diameters were produced by electrospinning. The electrospinning conditions, including the solvents, solution concentrations and amounts of different salt additives, have been comprehensively investigated. The morphologies of electrospun ABS fibers are studied by scanning electron microscopy and Raman spectroscopy. Different fiber diameters and coating densities are applied for filtration applications, which showed excellent filtration performance. The filtration efficiency of up to 99%, low pressure drop of < 30 Pa, and high filtration quality factor of up to 0.477 are achieved from the electrospun ABS fibers coated on microfibrous polypropylene substrates. In addition, the electrospun ABS fibers also shows good thermal stability and other applications such as oil/water separation. Keywords Acrylonitrile–butadiene–styrene fiber · Electrospinning · Filtration · Oil–water separation Introduction because of its good physical and mechanical properties, such as excellent chemical resistance, dimensional stabil- Acrylonitrile–butadiene–styrene (ABS) is a commercial ity, impact-resistant and toughness [1, 2]. Although ABS terpolymer made by polymerizing acrylonitrile and styrene has been comprehensively investigated and applied in many in the presence of polybutadiene. It has broad applications areas, only countable studies on its fibers and applications for light, rigid and molded products, such as piping, musi- in fiber morphology are available. Electrospinning is a facial cal instruments, golf club heads, automotive body parts, technology to produce fibers with diameters in the range wheel covers, enclosures, protective headgear and toys, from sub-nanometers to tens of micrometers and electrospun fibers have been applied in almost all fields, including tissue engineering, composites, actuators, catalysts, filtration and Electronic supplementary material The online version of this sponges [3–17]. In 2014, ABS and ABS/zeolite compos- article (https ://doi.org/10.1007/s4276 5-019-00026 -7) contains ite fibers were firstly prepared by electrospinning technol- supplementary material, which is available to authorized users. ogy, but the fibers have a broad diameter distribution and * Shaohua Jiang no application was presented [18]. In another report, pure shaohua.jiang@njfu.edu.cn ABS fibers and their conductive ABS/copper composite b fi - * Andreas Greiner ers were fabricated via electrospinning and electroless metal greiner@uni-bayreuth.de deposition, respectively [19]. However, comprehensive investigation on the formation of ABS electrospun fibers is Macromolecular Chemistry, Bavarian Polymer Institute, University of Bayreuth, Universitätsstraße 30, missing in this report. Very recently, N,N-dimethylforma- 95440 Bayreuth, Germany mide (DMF), N,N-dimethylacetamide (DMAc), and tetrahy- Bavarian Polymer Institute (BPI), University of Bayreuth, drofuran (THF), were reported as solvents for the electro- Universitätsstraße 30, 95440 Bayreuth, Germany spinning of ABS, and the obtained ABS electrospun fibers Present Address: College of Materials Science were used for air filtration [20]. The results indicate that the and Engineering, Nanjing Forestry University, DMF and DMAc were suitable solvents for electrospinning, Nanjing 210037, China Vol:.(1234567890) 1 3 Advanced Fiber Materials (2020) 2:34–43 35 but there are still many beads on fibers. Additionally, the collecting the fibers with aluminum paper on a horizontal filtration results suggest a relatively high pressure drop and rotating disc. The samples for the filtration and adhesion low quality factor which could be because of the beaded test were prepared by coating the fibers on polypropylene ABS fibers and the self-standing thick membranes. microfiber filter substrate for different lengths of time. Therefore, it is still necessary to find out optimized elec- trospinning parameters for the fabrication of beads-free elec- Characterizations trospun ABS fibers and investigate the relationship between the fiber structures and filtration performance. In this work, The electrospun fiber morphology was measured by we choose a mixture of dimethyl sulfoxide (DMSO) and scanning electron microscopy (SEM, Zeiss LEO 1530, chloroform (CHCl ) as solvent for the electrospinning of EHT = 3  kV). All the samples were coated with 3.0  nm ABS. The electrospinning parameters to achieve homoge- platinum before scanning. The fiber diameter was measured nous and beads-free ABS fibers are optimized. To decrease by ImageJ software. The pore size of nonwoven electrospun the pressure drop and obtain high filtration quality factor, a ABS was measured by a pore size meter (TOPAS, PSM165). commercial microfibrous polypropylene substrate (MFPP) The filtration measurement for salt particles was performed is used to coating a very thin layer of electrospun ABS fib- on MFP 2000 from P ALAS with a white light-scattering ers. With the above strategies, electrospun ABS fibers with spectrometer, Welas digital 2100 (particle size detection fiber diameter in the range from hundreds of nanometers range: 0.2–10.0 μm). to several micrometers are obtained. The novel composite A confocal WITec alpha 300 RA + imaging system equip- filters (ABS electrospun fibers on MFPP) also show high ment with a UHTS 300 spectrometer and a back-illuminated filtration efficiency, low pressure drop and high filtration Andor Newton 970 EMCCD camera was used for Raman quality factor. imaging. Raman spectra were acquired using an excita- tion wavelength of 532 nm and an integration time of 0.7 s −1 pixel (100 × objective, NA = 0.9, step size 100 nm, soft- Experimental ware WITec Control FOUR 4.1). All spectra were subjected to a cosmic ray removal routine and baseline correction. The Materials spatial distribution of SAN and PB particles in the fibers was determined by basis analysis using the Raman spectra Acrylonitrile–Butadiene–Styrene (ABS, Novodur H701, of the neat components as references (software WITec Pro- M = 210 kDa, Styrolution Group GmbH), DMSO (99.5%, ject FOUR 4.1). The neat Styrene-Acrylonitrile (SAN) and Gruessing GmbH), CHCl (99%, Sigma-Aldrich), sodium polybutadiene (PB) particles were obtained by extracting dodecyl sulfate (SDS, 99%, Sigma-Aldrich) and perfluoro- ABS with acetone, which dissolves SAN selectively. decalin (oil, 95%, density 1.908 g/mL, Sigma-Aldrich) were used as received. Pyridine-formic acid salt (PF) was pre- pared by mixing pyridine (99.9%) and formic acid (98%) Results and discussion (1:1 molar ratio). Microfibrous PP substrate (fiber diameter of 23 ± 4 µm) was used for coating electrospun ABS fib- Electrospinning of ABS ers. The commercial filter (MGK-P95%, 90 g/m , thickness 0.5 mm) was provide by Shanghai Mingguan Purification In previous reports, acetone and DMSO were used as sol- Materials Co., Ltd, which was prepared by melt-spinning. vents for electrospinning ABS [18, 19]. However, there are disadvantages using these two solvents. Acetone has a low Preparation of electrospun ABS fibers boiling point of 56.5 °C and high vapor pressure of 24.6 kPa (20 °C) [21], which lead to a fast evaporation during electro- The ABS solutions for electrospinning were prepared spinning. Therefore, ABS precipitates easily at the electro- according to the component composition in Table S1. The spinning nozzle, disturbing the continuous jet formation. By ABS pellets were dissolved in mixture solvent of DMSO and comparison, DMSO has a very high boiling point of 189 °C CHCl (wt/wt, 1/1) with different concentrations. Different and very low vapor pressure of 55 Pa (20 °C) [21], causing amounts of SDS were added to the ABS solution to adjust deposition of wet fibers gluing together and losing fiber mor - the conductivity of the solutions. Thirty-one ABS solutions phology. Chloroform is another common solvent for elec- (S1–S31) were prepared. The electrospinning was performed trospinning. It has a slightly higher boiling point of 61.2 °C by applying a high voltage of 12–20 kV, collecting distance and lesser vapor pressure of 21.1 kPa than acetone [21]. of 15–20 cm and flow rate of 0.6 mL/h. The samples for fiber Similar to acetone, it is also a good solvent for ABS. Our ini- morphology, pore size and heat resistance were prepared by tial studies on the electrospinning of ABS/CHCl solutions 1 3 36 Advanced Fiber Materials (2020) 2:34–43 showed a blockage of the electrospinning nozzle due to the fast solidic fi ation of the solution at the nozzle tip. Therefore, in this work, a solvent mixture of DMSO and CHCl with equal weight ratio was used for the electrospinning. The initial investigation was focused on the electrospin- ning of ABS solutions with high concentrations (S1: 25 wt%, S2: 20 wt% and S6: 15 wt%). These three solutions showed very good electrospinnability with the continuous electrospinning process. The increased concentration is beneficial to eliminate the beads on the fibers, but the fiber diameter also increases (Fig. 1). The electrospun fibers from 25 to 20 wt% ABS solution showed bead-free fibers and the average fiber diameters were 2800 ± 350 and 2180 ± 390 nm, respectively. The 15 wt% ABS solution led to a quite dif- ferent fiber morphology. Many beads were observed on the fibers and the average fiber diameter was decreased greatly to 598 ± 254 nm. Higher magnification SEM images showed that the fiber surface was rough with particles embedded in the fibers. These particles could be from the PB dispersed in the styrene-acrylonitrile matrix in ABS, which is inherent during ABS synthesis. Confocal two-dimensional (2D) Raman imaging was performed in order to probe the spatial distribution of SAN and PB in the fibers. It can be clearly deduced from the Fig. 2 Raman imaging of ABS fibers (sample S25). a Optical micro- color-coded 2D Raman images shown in Fig. 2 that the sup- graph with marked position for Raman x, y-imaging. b Color-coded confocal 2D Raman image showing the spatial distribution of SAN porting fiber consists of SAN and the embedded particles (red) and PB particles (pink) in the electrospun ABS fibers; c the dis- correspond to the PB particles in the ABS. tribution of PB particles (blue) for means of clarity. d Raman spectra Conductivity plays an important role in the electrospin- of SAN (red) and PB particles (blue) ning process and the b fi er morphology. The addition of salts in the electrospinning solutions could change the conduc- tivity significantly. In this work, we first investigated the Fig. 1 Fiber morphology of electrospun ABS fibers spun from a mixture of DMSO: CHCl (1:1 wt: wt) with concentrations of 25 wt% (a, a′), 20 wt% (b, b′) and 15 wt% (c, c′) 1 3 Advanced Fiber Materials (2020) 2:34–43 37 which was seven times more than that by adding PF (9.1 µs/ cm). A further increase of the amount of SDS led to greatly increased conductivity but also introduced the problem for the electrospinnability that big droplets were formed during the electrospinning process. The addition of salts (SDS and PF) also affected the fiber morphologies significantly. Figure  4 shows the fiber mor - phologies electrospun from ABS solutions (20 wt%) with different amounts of SDS from 0.1 to 8 wt% and PF from 0.1 to 1.0 wt%. Compared to the fibers from the ABS solu- tion without salt additives, the addition of salt is useful to decrease the fiber diameters. A small amount of SDS (0.1, 0.2 and 0.5 wt%) led to a decrease of the fiber diameter to 1150 ± 346, 926 ± 151 and 908 ± 208  nm, respectively, which was half the diameter of the fibers from the solution without salts (2180 ± 390 nm). Interestingly, this relatively Fig. 3 Effect of salt additives (SDS and PF) on the conductivity of high salt amount led to the fact that the fiber was branched the ABS solution (20 wt%) with very fine fibers, which could be attributed to the strong repelling effect from the high conductivity. In comparison to the fibers from solution without additives, the addition of addition of a small amount of SDS and PF on the solution PF could also decrease the fiber diameter but not much more conductivity, the electrospinnability and the fiber morphol- than the addition of SDS, which could be due to the weak ogy. Figure 3 presents the relationship between the conduc- effect on conductivity from PF (Fig.  4). tivity of ABS solutions (20 wt%) and the added amount of More solutions with different ABS concentrations and SDS and PF salts. The addition of both SDS and PF into different amounts of salt additives of SDS and PF were the ABS solutions could increase the conductivity, but SDS prepared according to the Table S1 (1–5) to optimize the exhibits a much more obvious effect. With the addition of electrospinning conditions to achieve a good electrospin- 1 wt%, SDS increased the conductivity up to 68.5 µs/cm, ning process and obtain fibers with small diameters. The Fig. 4 Effect of the amount of SDS and PF on the fiber morphologies 1 3 38 Advanced Fiber Materials (2020) 2:34–43 salt. Fixing the ABS concentration to 10 wt% and changing the SDS amount (0.1, 0.2, 0.25, 0.3, 0.35 and 0.4 wt%) can- not change the fiber diameter much. However, by fixing the SDS amount to 0.2 wt% and changing the ABS concentra- tion from 20 wt% to 10 wt%, it is easy to get tunable fiber diameters from 1 µm to 150 nm (Figure S1). Due to the hydrophobicity of ABS, the self-standing porous electrospun membrane showed the efficient separa- tion of oil and water. In this work, we also tried to find some applications for electrospun ABS fibers. The electrospun ABS fibrous membrane could be used for oil/water separa- tion due to the hydrophobicity with a water contact angle of 130 (Fig. 6, SI Video). The mixture with oil (perfluorodeca- lin, 3 mL) and water (dyed with Rhodamine B, 9 mL) was filled into the container equipped with ABS fibrous separator (thickness: 0.1 mm; diameter: 15 mm). After about 6 min, the oil/water mixture separated. The clear oil dripped into the collector and the red water was kept on the top of the ABS filter. These findings made electrospun ABS fibrous membranes possible for oil/water separation. Pore size and coating density Fig. 5 The concentration of ABS and SDS on the electrospinnabil- Pore size and coating density are very important parameters ity (a) and fiber diameters (b). The electrospinnability was defined by for achieving the high filtration efficiency when randomly rates: 10—very good; 9—good (a small number of beads); 8—good oriented fibers are coated on a filter substrate. In this work, (many beads); 7—good (beads and ununiformed coating); 6—com- mon (big droplets); and 4—bad (beads, big droplets and ununiformed we first prepared electrospun ABS nonwoven fibers with coating) different fiber diameters and then measured the pore size of these nonwoven fibers. Figure  7a plots the relationship cross effect of ABS concentration and additive amounts on between the fiber diameter and the pore size. Interestingly, the electrospinnability and fiber diameter is shown in Fig.  5. the b fi er diameter showed a linear relationship with the aver - It is obvious that the fiber diameter decreases as the ABS age pore size. When the fiber diameter came down to 300 nm concentration decreases (0 wt% SDS) and a small amount from 2800 nm, the average pore size dropped dramatically of SDS up to 0.2 wt% is useful to decrease the fiber diam- to 2 µm from 13.5 µm. If the fiber diameter decreases to eter. Increasing the salt amount by more is not expected to 100 nm, then the average pore size could drop to even about further decrease the fiber diameter, but the fiber diameter is 1 µm. These fine fibers and small pore size would greatly still much smaller than the fibers from a solution without improve the filtration efficiency. Fig. 6 Oil/water separation by electrospun ABS membrane 1 3 Advanced Fiber Materials (2020) 2:34–43 39 Fig. 7 Relationship of fiber diameter and pore size (a) and coating time-dependent coating density (b) of electrospun ABS fibers Commercial filters usually have a coating of electrospun Filtration efficiency fibers with a weight per area in the range of 0.3–0.8 g/m . We established a simple method to measure the coating den- The filtration measurement was performed to evaluate the sity (weight per area, g/m ) of electrospun ABS fibers on effect of the electrospun fiber diameter and the coating time MFPP (9 × 9  cm ): (1) Electrospinning ABS fibers on the (coating density) on the filtration efficiency in comparison substrates for different time (0.5, 1, 2, 4, 6 and 8 min); (2) to the blank MFPP samples (MFPP-01 and MFPP-02) and Drying the samples in a vacuum oven at 55 °C for 18 h to the commercial filter (C-Filter). Before we measured the remove residual solvents; (3) Put the substrate with coat- filtration efficiency, we first checked the fiber morphology ing fibers on balance (0.01 mg deviation) and set weight to of MFPP and C-Filter. As shown in Figure S2, the MFPP 0.00 mg; (4) Remove the coating fibers from the substrate; was composed of smooth fibers. The average fiber diam- (5) Put the substrate on balance again and a minus value was eters are 23 ± 4 µm and junctions between the fibers were obtained. The absolute value is the weight of the coating observed. A commercial filter contains two layers. One layer fibers on the substrate; (6) Repeat 4 times for each sam- is a substrate layer with a homogeneous fiber diameter of ple. Figure 7b shows that the coating density was linearly 16.5 ± 1.1 µm and the other layer is composed of much thin- increased with the coating time. When the coating time was ner fibers with ununiformed fiber diameters of 1.3 ± 1.2 µm. 2, 4 and 6 min, the coating weight per area was in the com- The two layers were glued together to improve the adhesion. mercial range, which implied the commercial application of The electrospun fiber diameter and the coating density this coating filters. play a crucial role in the filtration efficiency of salt par - ticles (0.2–10 μm) (Fig. 9). As expected, the microfiber Heat resistance fibrous MFPP (MFPP-01 and MFPP-02) showed the worst filtration efficiency due to their large pore size. A coating Due to the heat pressing process during the fabrication of of electrospun ABS fibers on the substrate improved the filters, it is necessary to evaluate the heat resistance of elec- filtration efficiency. When fixing the coating time to 2 min, trospun ABS nonwovens. As shown in Fig. 8, the ABS non- the coating layer with a fiber diameter of 428 nm showed wovens could stand the same shape under 110 °C for 2 min. much better filtration efficiency than that with 2800 nm Higher temperatures led to the shrinkage of the nonwovens. fiber diameter. The same results were also found when the The SEM images showed that no changes were found in coating time was fixed to 4 and 6 min. Two exceptional the fiber morphology when the heating temperature reached samples were outside the rule of fiber diameter-related around 110 °C. When the samples were heated between 120 filtration efficiency. The first one is the sample coated with and 130 °C, the fibers became smoother due to the melting electrospun fibers of 598 nm. This sample showed worse of the dispersed polybutadiene particles. In addition, junc- filtration efficiency than the sample coated with electro - tions between the fibers were also observed due to the partial spun fibers of 2800 nm, which could be due to the large melting of ABS fibers. beads on the fibers. Another exceptional sample was the filter coating with 149 nm ABS fibers, which showed very bad filtration efficiency among all coating samples. This could be due to the quite inhomogeneous coating on the 1 3 40 Advanced Fiber Materials (2020) 2:34–43 Fig. 8 SEM images of electrospun ABS fibers after heat treatment and photos (insert) of the heat resistance of electrospun ABS fiber nonwovens at different temperatures for different times. Sample: S6 with original size of 2 × 2 cm MFPP (Fig.  9d). As the coating time (coating density) showed a differential pressure of 13.5 Pa. By comparison, increased, the filtration efficiency also improved. When the samples coated with 457 and 428 nm for 2 and 4 min, the fiber diameter was 428 nm and the coating time was respectively, which showed comparable filtration efficiency, 2 min, the filtration efficiency was as good as the com- presented similar or a little higher differential pressure. mercial filter (C-filter) with the particle size larger than Ashby figures of coating density-dependent pressure drop 2.5 μm. When the coating time was 4 min, the coated filter and the quality factor (QF) from different filter mediums were showed comparable filtration efficiency to the commercial plotted to compare the quality of the filter prepared in this work filter and when the coating time was increased to 6 min, to other filter mediums. As illustrated in Fig.  11, the filters in the coating filter showed even better filtration efficiency this work showed a much better filtration performance in terms than the commercial filter (Fig.  9). of the pressure drop and QF. When comparing the pressure Differential pressure (pressure drop) is an important drop of different filter mediums (pressure drop > 30 Pa), the parameter to evaluate the efficiency of filters. It is defined ABS filters occupied a very important area where the small as the pressure difference between the two sides of the filter pressure drop < 30 Pa could be achieved with a sample coating during the filtration test. Electrospun ABS fibers on MFPP, density smaller than 0.8 g/m (Fig. 11a). The quality of the smaller fiber diameter and increasing the coating time gen- filters could be evaluated by QF based on the comprehensive erally lead to the increase of differential pressure (Fig.  10). evaluation on the pressure drop and filtration drop. It can be Due to the large pore size, the MFPP showed the smallest calculated by the following equation: differential pressure of 1.98 Pa, while the commercial filter 1 3 Advanced Fiber Materials (2020) 2:34–43 41 Fig. 9 Comparison of filtration efficiency of MFPP (substrate with- coating times of a 2 min, b 4 min and c 6 min. d Ununiformed coat- out coating), commercial filter (C-Filter) and the filters coating with ing with electrospun ABS fiber (149  nm) on MFPP before and after electrospun ABS fibers with different fiber diameters and different filtration Fig. 10 Differential pressure of MFPP, commercial filter (C-Filter) and filters by coating electrospun ABS fibers with different fiber diameters and different coating times 1 3 42 Advanced Fiber Materials (2020) 2:34–43 the range of 200–2000 nm were successfully prepared by electrospinning. This electrospun ABS membrane showed thermal stability up to 110 °C for 2 min. Comparable filtra- tion efficiency to commercial filter was achieved by coating electrospun ABS fibers on MFPP. The filtration efficiency improved as the fiber diameter decreased and the coating time increased. Compared to the commercial PA fiber fil- ter, electrospun ABS fibers might be better electrically charged. Unfortunately, the adhesion between electrospun ABS fibers and MFPP was bad but could be improved by electrospraying glue or hot-pressing. The electrospun ABS fibrous membranes were also successfully applied for oil/ water separation. Acknowledgments Open Access funding provided by Projekt DEAL. Compliance with ethical standards Conflict of interest There are no conflicts to declare. Open Access This article is licensed under a Creative Commons Attri- bution 4.0 International License, which permits use, sharing, adapta- tion, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are Fig. 11 Ashby plot of coating density-dependent pressure drop (a) included in the article’s Creative Commons licence, unless indicated and quality factor (QF) (b) for different filter mediums: Alumina [23], otherwise in a credit line to the material. 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"Advanced Fiber Materials"Springer Journals

Published: Feb 23, 2020

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