- Open Access
Multi-jet electrospinning of polystyrene/polyamide 6 blend: thermal and mechanical properties
© The Author(s) 2017
- Received: 16 June 2016
- Accepted: 1 November 2016
- Published: 28 April 2017
Polystyrene (PS) has high thermal resistance thus can be applied as thermally comfortable textile. However, the application is limited due its low mechanical strength. In this study, polyamide 6 (PA6) was blended with PS to improve the mechanical strength of PS, by means of a multi-jet electrospinning. Content ratio of the blend web was measured by chemical immersion test and confocal microscopy analysis. Fiber content was in accordance with the number of syringes used for PS and PA6 respectively. The effects of content ratio on the web morphology, thermal resistance, tensile behavior, air and water vapor permeability, and surface hydrophilicity were investigated. The influence of environmental humidity during electrospinning process on three dimensional (3D) web structure was also reported. PS web produced from higher humidity had more pores and corrugations at the surface. The increased surface roughness and porosity led to the increased hydrophobicity and thermal resistance. Though the blending of PA6 with PS enhanced the mechanical strength, the added PA6 decreased air/water vapor permeability and thermal resistance. The lowered thermal resistance by the addition of PA6 was mainly attributed to higher thermal conductivity of PA6 material and lowered air content with PA6 fibers.
- Multi-jet electrospinning
- Polyamide 6
- Thermal resistance
Electrospinning process is broadly used to obtain membrane-like webs with submicron to micron fibers (Li and Xia 2004). Electrospun nanofibers, with its large surface area and multiple pores, can be used to construct unique functional nanostructures for composites, filtration membranes, biomaterials, and breathable textile fabrics (Greiner and Wendorff 2007; Li and Xia 2004; Pham et al. 2006). Generally, an electrospinning set-up consists of a high voltage source, container (usually syringe) for polymer solution, syringe pump, capillary nozzle, and grounded collector (Pham et al. 2006). When high electric voltage is applied, the surface tension of polymer solution is overcome by the applied electric field. Charged polymer solution forms into jet, forming a Taylor cone, then gets further stretched. Meanwhile, solvent from the polymer jet continuously evaporates and solidifies to form fiber webs on a collector (Reneker and Chun 1996).
Despite the usefulness and availability of electrospinning technique for various product development, its commercial application has been limited mainly due to its poor production efficiency (Teo and Ramakrishna 2006). As ways to increase the polymer throughput and improve productivity, a multi-needle (multi-jet) (Teo and Ramakrishna 2006) setup or roller spinning electrode device (Cengiz et al. 2010; Yener and Jirsak 2012) has been tested. Due to the advantage of multi-jet electrospinning as a simple set-up for blending different fibers with desired ratio (Teo and Ramakrishna 2006), several research groups have applied multi-jet device to fabricate nanofibrous textiles. Park et al. (2013) investigated the efficacy of blending polyurethane/polyamide 6 using an angled dual-nozzle electrospinning set up. Ding et al. (2004) studied the mechanical properties of blended web with poly(vinyl alcohol) and cellulose acetate in different ratio. However, there are few studies that thoroughly examined the influence of blend ratio on the web structure and properties as clothing materials.
Polystyrene (PS) and polyamide 6 (PA6) are widely used for in textile industry (Carrizales et al. 2008; Casper et al. 2004; Marsano et al. 2010; Pai et al. 2009). PS has a potential application as breathable textile with thermal comfort thanks to its high thermal resistance, but its application is limited due to its low mechanical property. If a material such as PA6 with good mechanical property can be blended with PS, the blend web can have practical applications as thermally comfortable clothing with the enhanced mechanical property.
Polystyrene (PS, Mw = 350,000 g/mol) and polyamide 6 (PA6, Mw = 10,000 g/mol) were purchased from Sigma-Aldrich (USA). N,N-dimethylformamide (DMF, 99.8%), tetrahydrofuran (THF, 99.5%), formic acid (≥99.0%) and acetic acid (≥99.0%) were purchased from Daejung Chemicals (Korea) and used as solvents without further purification.
To obtain uniform PS fibers, 18 wt% PS solution was prepared with DMF/THF mixture in a weight ratio of 3/1. 18 wt% PA6 solution was prepared with a formic acid/acetic acid mixture in a weight ratio of 4/1. ES-robot® Electrospinning/spray system (Nano NC, Korea) was used. A multi-jet electrospinning set up is illustrated in Fig. 1. Two syringes with needles (gauge 22G) were placed in the front and back side of grounded stainless drum collector respectively, and polymer solution was ejected toward the collector rotating at a speed of 100 rpm. The ejecting syringe was horizontally moved along the track with a speed of 7 m/min. Electric voltage of 20 kV was applied to the tip, and a collector to tip distance was maintained at 20 cm. Environmental temperature was kept at 25 ± 5 °C and humidity was 40 ± 5 RH % if not specified. To obtain the varied contents of PS and PA6 in the blend web, the number of syringes containing PS or PA6 solutions were varied as 4/0, 3/1, 2/1, 2/2, 1/2, 1/3 and 0/4, and a constant solution feeding rate of 0.2 ml/h was maintained. All webs were made in a thickness range of 56–64 µm. Electrospun webs were collected on an aluminum foil, and dried in vacuum at room temperature for 24 h to evaporate residual solvents.
Determination of PS/PA6 blend ratio
The blend web was observed for its PS and PA6 contents by the chemical immersion test (adjusted KS K ISO 1833 method) and confocal microscopy (LSM 700, Carl Zeiss, Germany) analysis after dyeing the respective fibers with different fluorescent dyes.
The contents of PS and PA6 in the blend electrospun web were investigated by immersing the dried blend web into formic acid to remove the PA6 component. The immersed web was thoroughly washed with formic acid and distilled water then dried. The content of PA6 was calculated by the weight loss of the web.
PS was dyed with rhodamin B (≥95.0%, HPLC grade, Sigma-Aldrich) in 5 µg/ml concentration, and PA6 was dyed with fluorescein isothiocyanate isomer I (FITC, 98.0%, HPLC grade, Sigma-Aldrich) in 5 µg/ml concentration. The confocal microscopy was taken through the web thickness of 60 µm in every 1 µm sectional frames. The images were analyzed by Adobe Photoshop CS4 for the number of pixels in red PS fibers and green PA6 fibers to estimate the respective fiber contents in a blend web.
Fiber morphology was observed by field emission scanning electron microscope (FE-SEM, JSM-7600F, JEOL, Japan). The fiber diameter of each specimen was measured by image analyzing software, Image J (National Institute of Health, USA). Web configuration with varied environmental humidity during electrospinning process was observed by the photo taken by using Digital Single Lens Reflex (EOS 650D, Canon, Japan) to draw a comparison of the appearance of each web.
Tensile properties were assessed by a universal test machine (UTM, WL 2100, Withlab Co. Ltd., Korea) for a specimen in 40 × 10 × 0.06 mm3 in accordance with ASTM D5035 strip method. The gauge length and crosshead speed were 20 mm/min and 10 mm/min, respectively. The average of five measurements was used for analysis.
Air and water vapor permeability
Air permeability of the web was characterized using capillary flow porometer (CFP-1200, PMI, USA), at the maximum pressure of 200 psi and the maximum flow rate of 25,000 ml/min. In this method, the amount of air (ml/s) passing through the specimen was measured as the applied air pressure was increased up to the set maximum pressure.
Water vapor transmission rate (WVTR) was measured according to ASTM E 96 desiccant method. A custom-designed cup was filled with calcium chloride, and the web specimen was fixed onto its opening. Then the assembly was kept at 40 °C, 90% RH. After 1 h, the evaporation of water through the specimen was measured by the weight change of the cup.
Surface hydrophilicity of the blend web was measured by static contact angle (SCA) measurement using a contact angle measurement device (Theta Lite, Attention, KSV Instrument, Finland). 4 μl droplets of distilled water was placed on five different positions on the sample surface, and the SCA on specimens were measured. SCA changes were recorded for 60 s of water contact time on the web surface.
Thermal conductivity of an electrospun web was measured by KES-F7 System (Thermal Labo II: Kato Tech Co. Ltd, Japan). Thermal resistance was measured using a sweating hotplate device (SGHP-8.2, Measurement Technology Northwest, USA), according to the modified ISO 11,092 sweating guarded-hotplate test method. For measurement of thermal resistance, electrospun web specimen was placed 10 mm above the hotplate to simulate a micro-environment of still air between human skin and clothes (Kim and Park 2013).
Blend Ratio of PS/PA6 Webs
Characteristics of the electropsun webs
Number ratio of jets (PS/PA6)
Weight ratio (confocal microscopy analysis)
Blend ratio (immersion test)
Calculated weighta (g/m2)
Measured weight (apparent density) (g/m2)
8.1 ± 0.4
60 ± 4
8.7 ± 0.5
60 ± 3
9.2 ± 0.5
60 ± 2
9.5 ± 0.4
60 ± 4
10.0 ± 0.7
60 ± 1
10.1 ± 0.5
60 ± 2
12.7 ± 0.5
60 ± 1
Electrospun web morphology
In addition to the diameter difference, more distinctive difference between PS and PA6 fibers was observed from the surface configurations as in Fig. 3a, where PS fiber surface shows corrugations and small pores. The surface configuration is a result of interactions among polymer molecule, solvent, and moisture in the environment. A polymer solution such as PS in a mixture solvent of a highly volatile THF and a less volatile DMF can create porosity and/or corrugations by the vapor-induced phase separation (VIPS) (Casper et al. 2004; Fashandi and Karimi 2012; Lin et al. 2010). When a fluid jet of PS solution is exposed to humid environment, the polymer solution undergoes phase separation into polymer-rich and solvent-rich regions. Then the polymer-rich phase solidifies quickly, whereas the solvent-rich phase delays the solidification. Highly volatile THF in solvent-rich region contributes to creating small pores at the surface upon its rather faster evaporation, while low volatile DMF contributes to forming corrugations and grooves at the surface by the growth of pores and evolution of channels.
Pore size range, total pore volume and porosity of PS/PA6 blend webs
Pore size range (µm)
Sample density (g/cm3)
Total pore volume (ml/g)
Air permeability and water vapor permeability
The effect of porosity on water vapor transmission was dominant for S4A0, S3A1, S2A1, S2A2, and S1A2; that is, the increased PA6 content reduced the web porosity, and thus lowered the water vapor transmission. However, when PA6 was further increased in the web content, hydrophilicity by PA6 contributed more to the water vapor transmission, significantly enhancing the water vapor transmission for A4. Thus, when PA6 is blended with PS web, it should be understood that certain comfort properties such as air permeability and water vapor transmission can be compromised in exchange of improved mechanical strength.
As the thermal conductivity of air is as low as 0.025 W/m K, thermal conductivity of textile material is largely influenced by air content (Kim and Park 2013). Thermal conductivity for PS film is reported to range in 0.10–0.13 W/m K (Han and Fina 2011; Hu et al. 2001) and that of PA6 film to be 0.25 W/m K (Han and Fina 2011). Also, a material with higher density and lower air content is likely to have higher thermal conductivity, deteriorating thermal insulation.
Thermal resistance of the web was linearly reduced with higher PA6 content (Fig. 9). As shown in Fig. 3, finer PA6 fibers appeared to interlace with larger PS fibers, forming a complicated and dense pore structure. The results show that the addition of PA6 can enhance the mechanical strength of the web in the expense of comfort factors in terms of thermal resistance, air permeability, and water vapor transmission.
To obtain fibrous webs with the high thermal resistance and reasonable mechanical strength, blend webs with PS and PA6 contents were produced by the multi-jet electrospinning process. Confocal microscopy can be used to examine fiber contents and distribution in the web, while immersion test gave more accurate fiber contents of the blend web. Fiber morphology and 3D structure of PS fibrous web were influenced by the environmental humidity during electrospinning process and solvent selection. PS web produced in higher humidity generated more pores and corrugations at the surface. The increased surface roughness and porosity led to the increased hydrophobicity and thermal resistance.
The addition of PA6 to PS enhanced the mechanical strength. However, the added PA6 deteriorated the comfort properties including air permeability, water vapor transmission rate, and thermal resistance. Water vapor transmission of 100% PA6 web, however, was significantly better than that of blend web due to higher surface hydrophilicity of the web. The lowered thermal resistance by the addition of PA6 is attributed to (1) higher thermal conductivity of PA6 material and (2) lowered air content for compact PA6 structure.
The blend ratio of PS/PA6 influenced on blend web structure, morphology, and properties. Future study is needed for the environmental parameters in electrospinning to produce an optimal 3D web structure to achieve the highest thermal resistance. It is recommended to examine the ways to enhance the mechanical strength of the PS web, probably by lowering the rate of solvent evaporation to allow more time for fiber bonding.
All authors were involved in the design of experiments and result discussion. Also, all authors read and approved the final manuscript.
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP: No 2015R1A2A2A03002760) and the BK21 Plus Project funded by the National Research Foundation of Korea.
On behalf of all authors, the corresponding author states that there is no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Ahn, H. W., Park, C. H., & Chung, S. E. (2011). Waterproof and breathable properties of nanoweb applied clothing. Textile Research Journal, 81, 1438–1447.View ArticleGoogle Scholar
- Bonino, C. A., Efimenko, K., Jeong, S. I., Krebs, M. D., Alsberg, E., & Khan, S. A. (2012). Three-dimensional electrospun alginate nanofiber mats via tailored charge repulsions. Small (Weinheim an der Bergstrasse, Germany), 8, 1928–1936.View ArticleGoogle Scholar
- Carrizales, C., Pelfrey, S., Rincon, R., Eubanks, T. M., Kuang, A., McClure, M. J., et al. (2008). Thermal and mechanical properties of electrospun PMMA, PVC, Nylon 6, and Nylon 6,6. Polymers for Advanced Technology, 19, 124–130.View ArticleGoogle Scholar
- Casper, C. L., Stephens, J. S., Tassi, N. G., Chase, D. B., & Rabolt, J. F. (2004). Controlling surface morphology of electrospun polystyrene fibers: Effect of humidity and molecular weight in the electrospinning process. Macromolecules, 37, 573–578.View ArticleGoogle Scholar
- Cengiz, F., Dao, T. A., & Jirsak, O. (2010). Influence of solution properties on the roller electrospinning of poly(vinyl alcohol). Polymer Engineering & Science, 50, 936–943.View ArticleGoogle Scholar
- Ding, B., Kimura, E., Sato, T., Fujita, S., & Shiratori, S. (2004). Fabrication of blend biodegradable nanofibrous nonwoven mats via multi-jet electrospinning. Polymer, 45, 1895–1902.View ArticleGoogle Scholar
- Fashandi, H., & Karimi, M. (2012). Pore formation in polystyrene fiber by superimposing temperature and relative humidity of electrospinning atmosphere. Polymer, 53, 5832–5849.View ArticleGoogle Scholar
- Gibson, P. (1993). Influencing steady-state heat and water vapor transfer measurements for clothing materials hot plate and upright cup methods of. Textile Research Journal, 63, 749–764.View ArticleGoogle Scholar
- Gotoh, K. (2004). Wettability and surface free energies of polymeric materials exposed to excimer ultraviolet light and particle deposition onto their surfaces in water. In K. Mittal (Ed.), Polymer surface modification: relevance to adhesion (pp. 125–139). Utrecht: VSP.View ArticleGoogle Scholar
- Greiner, A., & Wendorff, J. H. (2007). Electrospinning: A fascinating method for the preparation of ultrathin fibers. Angewante Chemie-International Edition, 46, 5670–5703.View ArticleGoogle Scholar
- Han, Z., & Fina, A. (2011). Thermal conductivity of carbon nanotubes and their polymer nanocomposites: A review. Progress in Polymer Science, 36, 914–944.View ArticleGoogle Scholar
- Harris, M., Appel, G., & Ade, H. (2003). Surface morphology of annealed polystyrene and poly(methyl methacrylate) thin film blends and bilayers. Macromolecules, 36, 3307–3314.View ArticleGoogle Scholar
- Hu, C., Kiene, M., & Ho, P. S. (2001). Thermal conductivity and interfacial thermal resistance of polymeric low k films. Applied Physical Letter, 79, 4121–4123.View ArticleGoogle Scholar
- Kim, K. S., & Park, C. H. (2013). Thermal comfort and waterproof-breathable performance of aluminum-coated polyurethane nanowebs. Textile Research Journal, 83, 1808–1820.View ArticleGoogle Scholar
- Li, D., & Xia, Y. (2004). Electrospinning of nanofibers: Reinventing the wheel? Advanced Materials, 16, 1151–1170.View ArticleGoogle Scholar
- Lin, J., Ding, B., Jianyong, Y., & Hsieh, Y. (2010). Direct fabrication of highly nanoporous polystyrene fibers via electrospinning. ACS Applied Materials & Interfaces, 2, 521–528.View ArticleGoogle Scholar
- Marsano, E., Francis, L., & Giunco, F. (2010). Polyamide 6 nanofibrous nonwovens via electrospinning. Journal of Applied Polymer Science, 117, 1754–1765.Google Scholar
- Miyauchi, Y., Ding, B., & Shiratori, S. (2006). Fabrication of a silver-ragwort-leaf-like super-hydrophobic micro/nanoporous fibrous mat surface by electrospinning. Nanotechnology, 17, 5151–5156.View ArticleGoogle Scholar
- Pai, C. L., Boyce, M. C., & Rutledge, G. C. (2009). Morphology of porous and wrinkled fibers of polystyrene electrospun from dimethylformamide. Macromolecules, 42, 2102–2114.View ArticleGoogle Scholar
- Park, C. H., Kim, C. H., Pant, H. R., Tijing, L. D., Yu, M. H., Kim, Y., et al. (2013). An angled robotic dual-nozzle electrospinning set-up for preparing PU/PA6 nanofiber composites. Textile Research Journal, 83, 311–320.View ArticleGoogle Scholar
- Park, D.-K., Park, S.-J., Baek, W.-I., Kanjwal, M. A., & Kim, H.-Y. (2011). Point-bonded electrospun polystyrene fibrous mats fabricated via the addition of poly(butylacrylate) adhesive. Polymer Engineering & Science, 51, 894–901.View ArticleGoogle Scholar
- Park, Y., Park, C. H., & Kim, J. (2014). A quantitative analysis on the surface roughness and the level of hydrophobicity for superhydrophobic ZnO nanorods grown textiles. Textile Research Journal, 84, 1776–1788.View ArticleGoogle Scholar
- Pham, Q. P., Sharma, U., & Mikos, A. G. (2006). Electrospinning of polymeric nanofibers for tissue engineering applications: A review. Tissue Engineering, 12, 1197–1211.View ArticleGoogle Scholar
- Reneker, D. H., & Chun, I. (1996). Nanometre diameter fibres of polymer, produced by electrospinning. Nanotechnology, 7, 216–223.View ArticleGoogle Scholar
- Sun, B., Long, Y.-Z., Yu, F., Li, M.-M., Zhang, H.-D., Li, W.-J., et al. (2012). Self-assembly of a three-dimensional fibrous polymer sponge by electrospinning. Nanoscale, 4, 2134–2137.View ArticleGoogle Scholar
- Teo, W. E., & Ramakrishna, S. (2006). A review on electrospinning design and nanofibre assemblies. Nanotechnology, 17, 89–106.View ArticleGoogle Scholar
- Wehner, J. A., Miller, B., & Rebenfeld, L. (1988). Dynamics of water vapor transmission through fabric barriers. Textile Research Journal, 58, 581–592.View ArticleGoogle Scholar
- Yener, F., & Jirsak, O. (2012). Comparison between the needle and roller electrospinning of polyvinylbutyral. Journal of Nanomaterials, 2012, 1–6.View ArticleGoogle Scholar