Article pubs.acs.org/IECR
Antimicrobial Polyacrylonitrile/m‑Aramid Hybrid Composite Sam Soo Kim† and Jaewoong Lee*,‡ †
Department of Textile Engineering & Technology, Yeungnam University, Gyeongsan 712-749, South Korea Korean Intellectual Property Office, Daejeon, 302-701, South Korea
‡
ABSTRACT: Antimicrobial polyacrylonitrile (PAN)/m-aramid hybrid film was prepared. PAN and m-aramid were dissolved in dimethyl sulfoxide, thin-layered on a glass plate, and then coagulated in distilled water. The morphology of the PAN/m-aramid hybrid film was analyzed by scanning electron microscopy. The molecular interaction between PAN and m-aramid was assessed by dynamic mechanical analysis. The antimicrobial efficacy was measured by a swatch test using bacterial suspensions. The PAN/ m-aramid hybrid film produced a 7-log reduction against Escherichia coli and Staphylococcus aureus within 5-min contact time.
1. INTRODUCTION Synthetic fibers, in general, have been prepared with polymeric materials that possess outstanding fiber-forming properties. In the fiber industry, polyester, nylon, and acrylic have been employed as major synthetic fibers. Among those fibers, acrylic is defined as a fiber composed of at least 85% polyacrylonitrile (PAN) units, and acrylic fibers are used in socks, sweaters, and blankets. After dissolving an acrylic polymer in N,N-dimethyl acetamide (DMAc) or N,N-dimethyl formamide (DMF), a dryor wet-spinning process is used to produce acrylic fibers.1−5 PAN consists of nitrile groups (CN) on alkyl backbones, and several polymers have been blended with PAN or acrylic. For instance, cellulose,6 poly(vinyl chloride),7 polymethylhydrosiloxane,8 and polyvinylidine fluoride9 have been used for blending. On the other hand, fibers including PAN or acrylic comprise one appropriate substrate for a microorganism. In particular, Lee et al. suggested antimicrobial acrylic/polystyrene hydantoin (PSH)-blended fiber.10 Nam et al. studied PAN/ ammonium chitosan chloride-blended fiber.11 However, the antimicrobial acrylic and the PAN fiber lost strength and elongation properties after being blended with PSH and ammonium chitosan chloride, respectively. Poly(m-phenylene isophthalamide), known as m-aramid, has been used for industrial applications such as fire fighter’s cloth, as a thermal filter in a power plant, and as a membrane in an electric transformer.12−16 Interestingly, Sun et al. proposed maramid fiber for antimicrobial application as an N-halamine precursor,17 and Lee et al. reported that oxidative chlorine on m-aramid was relatively stable.18 As an N-halamine precursor, m-aramid could change into an N-halamine after chlorination. Oxidative chlorine released from the N-halamine might transfer to bacteria and inactivate the bacteria.17 Because every repeating unit in m-aramid possesses pi electrons and an amide group (CONH), m-aramid is simply hydrophilic, and this characteristic could allow hydrogen bonding with other materials. The aim of this study was to produce an antimicrobial PAN/ m-aramid hybrid film. In addition, the molecular interaction between PAN and m-aramid was ascertained. The morphology of the films was detected using scanning electron microscopy (SEM). The films were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectrosco© 2013 American Chemical Society
py (XPS), X-ray diffractometry (XRD), and differential scanning calorimetry (DSC). Dynamic mechanical analysis (DMA) was used to detect molecular interactions. Mechanical properties of the films were also reported. The antimicrobial efficacy of the films was assessed by contact with bacterial solutions.
2. EXPERIMENTAL SECTION 2.1. Materials. Polyacrylonitrile (PAN) was purchased from Sigma-Aldrich (St. Louis, MO, USA), and the weight-average molecular weight of the PAN was 150 000. m-Aramid, a fiber product, was provided by Yantai Spandex (Yantai, China) and the m-aramid fiber was scoured with distilled water (∼60 °C), ethanol, and acetone and then dried overnight at ambient temperatures. Each part of the scouring process other than drying was repeated at least once. Dimethyl sulfoxide (DMSO) and lithium chloride anhydrous (LiCl) were purchased from Daejung Chemicals (Shiheung, Korea) and used without further purification. 2.2. Preparation of PAN/m-Aramid Hybrid Film. mAramid was dissolved in DMSO with LiCl, which was used as a catalyst to dissolve m-aramid. The ratio of PAN and m-aramid was varied at 100/0, 95/5, 85/15, 75/25, 50/50, 25/75, and 0/ 100 wt %. The concentration of the solutions was fixed at 15 wt %. A homogeneous 15 wt % PAN/m-aramid (50/50 wt %) solution was prepared by adding 7.5 g of m-aramid fiber into 100 mL of DMSO including 6 g of LiCl, while stirring at 120 °C for 4 h followed by cooling at 80 °C. Then, 7.5 g of PAN powder was added into the m-aramid solution with additional stirring at 80 °C for 6 h. The film was produced under a filmmaking process using Baker applicator (YBA-4, Yoshimitsu Seiki, Tokyo, Japan). The solution was thin-layered on a glass plate using a Baker applicator; the glass plate was then dipped into distilled water at ambient temperature. The coagulated film was dipped into boiling water for 10 min followed by rinsing with a large excess of distilled water. The film was sandwiched using a nonwoven fabric to minimize rolling up of the edge, and Received: Revised: Accepted: Published: 10297
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Figure 1. Surface images of PAN/m-aramid hybrid films: (a) 100/0, (b) 50/50, (c) 25/75, and (d) 0/100 wt %.
were used as the internal reflection elements. The film was held against one side of the Ge crystal. The background spectra were obtained with a Ge crystal and nitrogen gas in the absence of the film. After drying at 105 °C for 2 h, the FTIR spectra of the films were scanned from 700 to 4000 cm−1 for 64 scans at a 2 cm−1 resolution. 2.6. X-ray Photoelectron Spectroscopy (XPS). XPS was used to show that oxygen, which is present in m-aramid, and chlorine existed on the PAN/m-aramid hybrid film after chlorination. XPS measurements were conducted using a Quantera SXM (ULVAC-PHI, Ulvac, Tokyo, Japan). Monochromate Al was used as an X-ray source. Beam size, beam power, electron source, and pass energy were 100 lm, 100 W, 18 kV, and 26 eV, respectively. 2.7. X-ray Diffractometry (XRD). XRD (D/Max, Rigaku, Tokyo, Japan) was performed to examine crystal formation under the molecular interaction between PAN and m-aramid. Cu Kα radiation (wavelength=1.5418 Å) was used as an incident X-ray source (40 kV, 200 mA) and the films were scanned from 10 to 80° 2θ at a rate of 2°/min. 2.8. Differential Scanning Calorimetry (DSC). The thermal behavior of the films was examined by DSC (DSC 2920, TA Instruments, New Castle, DE, USA) in the temperature range from 25 to 300 °C under nitrogen purge gas and at a heating rate of 20 °C/min. 2.9. Dynamic Mechanical Analysis (DMA). DMA was performed on the samples of size 20 mm × 10 mm × 0.1 mm using a dynamic mechanical analyzer (N535−0001, PerkinElmer, Waltham, MA, USA), which was used for the evaluation of dynamic moduli and mechanical damping (tan δ) under nitrogen purge gas in a temperature range of 10 to 280 °C at a frequency of 1 Hz and heating rate of 2 °C/min.
then the film was dried at ambient temperature for 24 h. The thickness of the film was approximately 100 μm. 2.3. Chlorination. A 150-mL aliquot of commercial bleach (Yuhan-Clorox, Seoul, Korea), which contained 4% hypochlorite, was diluted with 850 mL of distilled water. The pH of the diluted solution was buffered to 7.5 with acetic acid and the films were soaked in the solution at an ambient temperature for 60 min. The chlorinated films were rinsed with a large excess of distilled water and dried at 45 °C for 2 h to remove the unbonded chlorine. An iodometric titration procedure was used to analyze the oxidative chlorine content as previously described.18 The [Cl+]% in the sample was calculated using the following equation: [Cl+]% =
V × N × 35.45 W × 2 × 10
where [Cl+]% is the wt % of oxidative chlorine on the sample, V is equal to the volume of the titrant (sodium thiosulfate solution (mL)), N is equal to the normality of the titrant, and W is the weight of the sample (g). The following constants were used: 35.45, the molecular weight of Cl; 2, the change in the oxidation state of Cl during titration; and 10, to normalize the units in numerator and denominator to give the % Cl. 2.4. Scanning Electron Microscopy (SEM). The films were coated with platinum under an argon purge before the observations. The resulting samples were observed by SEM (Hitachi S-4100, Tokyo, Japan) at a 15 kV accelerating voltage. 2.5. Fourier Transform Infrared Spectroscopy (FTIR). The surface of the films was examined by FTIR (Spectrum 100, PerkinElmer, Waltham, MA, USA) spectroscopy in attenuated total reflectance (ATR) mode. Germanium (Ge) ATR crystals 10298
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Figure 2. SEM images of the opposite sides of PAN/m-aramid hybrid films: (a) 100/0, (b) 50/50, (c) 25/75, and (d) 0/100 wt %.
Figure 3. SEM images of the cross sections of PAN/m-aramid hybrid films: (a) 100/0, (b) 50/50, (c) 25/75, and (d) 0/100 wt %.
2.10. Universal Testing Machine. The tensile strength and elongation at break were assessed in a universal testing
machine (Model 3345, Instron, Canton, MA, USA) at a cross head speed of 300 mm/min according to the KS K 0521: 2006 10299
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Figure 4. FTIR spectra of PAN/m-aramid hybrid films: (a) 100/0, (b) 95/5, (c) 85/15, (d) 75/25, (e) 50/50, (f) 25/75, and (g) 0/100 wt %.
method. The gauge length (distance between jaws) was 200 mm. Ten samples were tested in each case and the average was taken. 2.11. Antimicrobial Test. The films were challenged with E. coli (KCTC 2441) and Staphylococcus aureus (KCTC 1621) using the modified AATCC Test Method 100−2004. The both bacteria were incubated under optimal medium condition and temperature. A 1 mL of the culture fluid was then diluted with 9 mL of sterile distilled water followed by incubation using streak-plate method at 37 °C for 24 h. The total bacteria of E. coli and Staphylococcus aureus were 2.67 × 107 cfu/mL and 1.84 × 107 cfu/mL, respectively. Bacterial suspensions (25 μL) prepared with pH 7 phosphate buffer were added to 1 in2 sample swatches. A second swatch was sandwiched over the first to ensure contact between the suspension and the films. At contact times of 5, 10, 30, and 120 min, the samples were quenched with 5.0 mL of sterile 0.85% saline solution. The quenched samples were then diluted with pH 7 phosphate buffer and plated on Typticase soy agar. The plates were incubated at 37 °C for 24 h, and the number of bacteria was counted to determine the presence or absence of viable bacteria. The antimicrobial test was replicated three times.
Figure 5. XPS spectra of PAN/m-aramid hybrid films: (a) 100/0, (b) 95/5, (c) 85/15, (d) 75/25, (e) 50/50, (f) 25/75, and (g) 0/100 wt %.
relatively low rate because the glass plate might hinder the exchange between DMSO and distilled water. Regarding the size of voids, the m-aramid film possessed smaller voids than the PAN film. On the basis of this phenomenon, m-aramid dissolved in DMSO was presumed to be a relatively proper polymer for coagulation in distilled water. In the case of the PAN/m-aramid film, the size of the voids tended to be smaller with increased portion of m-aramid. In other words, the PAN/ m-aramid (25/75 wt %) film possessed somewhat smaller voids than the PAN/m-aramid (50/50 wt %) film. On the other hand, the voids on the opposite sides of the films may have a negative effect on the mechanical properties of the films. We will discuss the mechanical properties of the films in detail in a later section. Because the surfaces of the films that contacted the air showed a relatively flat surface, unlike the opposite sides of the films, an increased coagulation rate might be one possible method by which to protect against void formation on the films. To enhance the coagulation rate of PAN/m-aramid
3. RESULTS AND DISCUSSION 3.1. Morphology of PAN/m-Aramid Hybrid Film. PAN and m-aramid were dissolved in DMSO, and this solvent was exchanged with distilled water during the coagulation process. The SEM images of PAN/m-aramid films were measured and are shown in Figure 1, Figure 2, and Figure 3. PAN, PAN/maramid hybrid, and m-aramid films revealed that surfaces of the films in direct contact with distilled water showed relatively flat surfaces. (Figure 1) On the other hand, the opposite sides of the films that contacted the glass plate possessed numerous voids ranging from tens to thousands nanometers (Figure 2). The solution thin-layered on the glass plate was dipped into distilled water to produce the film. Therefore, the surface of the thin-layered solution that contacted the air was assumed to coagulate first. On the other hand, the side of the thin-layered solution that contacted the glass plate might coagulate at a 10300
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Figure 6. XPS spectra of PAN/m-aramid hybrid films: (a) 100/0 wt %, (a′) chlorinated sample of 100/0 wt %, (b) 50/50 wt %, (b′) chlorinated sample of 50/50 wt %, (c) 0/100 wt %, and (c′) chlorinated sample of 0/100 wt %.
Figure 9. DSC curves of PAN/m-aramid hybrid films: (a) 100/0, (b) 95/5, (c) 85/15, (d) 75/25, (e) 50/50, (f) 25/75, and (g) 0/100 wt %. Figure 7. X-ray diffraction patterns of PAN/m-aramid hybrid films: (a) 100/0, (b) 95/5, (c) 85/15, (d) 75/25, (e) 50/50, (f) 25/75, and (g) 0/100 wt %.
Figure 10. Tensile strength of PAN/m-aramid composites: (a) 100/0, (b) 95/5, (c) 85/15, (d) 75/25, (e) 50/50, (f) 25/75, and (g) 0/100 wt %. Figure 8. Tan δ of PAN/m-aramid hybrid films: (a) 100/0, (b) 95/5, (c) 85/15, (d) 75/25, (e) 50/50, (f) 25/75, and (g) 0/100 wt %.
in its repeating unit, and m-aramid possesses sufficient pi electrons and an amide group in its repeating unit. Thus, hydrogen bonding and molecular interactions between PAN and m-aramid would be expected. To detect functional groups in the films, FTIR was performed, and the spectra of the films are shown in Figure 4. The FTIR spectrum of the PAN film
dissolved in DMSO, the temperature of the coagulation bath might be increased.19 3.2. Molecular Interaction between PAN and mAramid in the Hybrid Film. PAN contains a nitrile group 10301
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the other hand, the spectra of the m-aramid film and the PAN/ m-aramid hybrid films revealed an oxygen peak (O1s) at a binding energy of 530.5 eV. Therefore, this oxygen peak was presumed to indicate the existence of m-aramid in the PAN/maramid film. During the coagulation of a blended solution containing two different polymers, crystallization of each polymer in the blend might occur and the molecular interaction between the two polymers might affect the crystal formation. XRD was used to confirm the crystal of the films, and XRD spectra are shown in Figure 7. The distinctive peak of PAN was shown at 16.3° 2θ.2,3 In addition, the distinctive peaks of m-aramid appeared at 13.5 and 23° 2θ.19 The crystal intensity of the m-aramid film was relatively weak. No additional drawing for the film was presumed to be the reason for the weak intensity of crystal. Even though the coagulation process between the PAN film and the m-aramid film was identical, the PAN film showed higher crystal intensity than the m-aramid film. This suggested that PAN dissolved in DMSO was crystallized with higher crystallinity than m-aramid in distilled water. We confirmed that the distinctive peaks of PAN coexisted with the distinguished peak of m-aramid in the PAN/m-aramid hybrid films. However, the shift of the 2θ peak that might prove the molecular interaction between PAN and m-aramid was not found. A general method to confirm the molecular interaction between different polymers is to determine the glass transition temperature (Tg) of the blended polymer. DMA was used to measure the Tg21 of the films and the results are shown in Figure 8. The changing temperature of tan δ of m-aramid film was observed at 275 °C, which was defined as Tg of m-aramid.22 When the portion of PAN in the PAN/m-aramid film was increased, Tg shifted to a lower temperature. On the other hand, the Tg of the PAN film was 102 °C.9 Even if the portion of m-aramid in PAN/m-aramid hybrid film was enhanced, a shift of the Tg of PAN was not observed. On the basis of the Tg shift of m-aramid, a molecular interaction between PAN and maramid existed, and PAN and m-aramid were partially miscible. Interestingly, it is worth noting that m-aramid is relatively more affected by molecular interaction than PAN in the PAN/maramid film. 3.3. Thermal and Mechanical Properties. To examine the thermal properties of the films, DSC was performed and the results are shown in Figure 9. Because PAN is decomposed below its melting point, a melting endotherm of PAN could not be detected under thermal analysis. In the case of the PAN film, an exothermic transition was detected at 266 °C. This was thought to indicate a cyclization reaction between two nitrile groups in a repeating unit and an adjacent repeating unit.23 The exothermic transition showed a tendency to shift to higher temperature with increasing ratio of m-aramid in PAN/maramid films. For instance, PAN/m-aramid (50/50 wt %) and PAN/m-aramid (25/75 wt %) showed an exothermic transition at 270 and 282 °C, respectively. Thus, the cyclization reaction of PAN required somewhat increased energy when m-aramid was present. The molecular interaction between nitrile groups and m-aramid was assumed to hinder the cyclization reaction. In addition, the increased temperature of the exothermic transition indicated that PAN/m-aramid hybrid films possessed a higher thermal stability than the PAN film. In terms of applications of the PAN/m-aramid hybrid films, the mechanical properties of the films should be considered. To measure the mechanical properties of the films, tensile strength and elongation at break were evaluated and are shown in Figure
Figure 11. Elongation at the break of PAN/m-aramid hybrid films: (a) 100/0, (b) 95/5, (c) 85/15, (d) 75/25, (e) 50/50, (f) 25/75, and (g) 0/100 wt %.
Figure 12. FTIR spectra of PAN/m-aramid hybrid films: (a) 100/0 wt %, (a′) chlorinated sample of 100/0 wt %, (b) 50/50 wt %, (b′) chlorinated sample of 50/50 wt %, (c) 0/100 wt %, and (c′) chlorinated sample of 0/100 wt %.
revealed its distinctive absorption feature at about 2243 cm−1, which was assigned to a CN stretching peak.7,11 On the other hand, FTIR spectrum of the m-aramid film showed distinguished absorption peaks at 3253, 1651, 1580, and 1532 cm−1, which were assigned to the N−H stretching vibration, amide CO stretching, CC stretching vibration of the aromatic ring and N−H in-plane bending modes, respectively.20 The intensity of the absorption peak at about 2243 cm−1 was reduced when the portion of m-aramid in the PAN/ m-aramid film was increased. On the other hand, the intensity of the distinguished absorption peaks of m-aramid, was reduced with increasing PAN ratio in the blended films. In addition, the distinguished peaks of both PAN and m-aramid appeared in the PAN/m-aramid hybrid films. Therefore, PAN and m-aramid were obviously blended in one film. However, we could not observe an FTIR band shift to prove molecular interaction. Compared to PAN, m-aramid only possesses oxygen in its chemical structure. Thus, the existence of oxygen might be a sign of m-aramid in the PAN/m-aramid hybrid film. XPS was employed to inspect atomics on the surface layer of the films and the XPS spectra of the films are shown in Figure 5. The XPS spectrum of the PAN film showed no peak for oxygen. On 10302
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Table 1. Antimicrobial Efficacy of the Films Escherichia colia wt % 100/0 95/5 0/100 100/0 95/5 0/100 100/0 95/5 0/100 100/0 95/5 0/100 100/0 95/5e 0/100f 100/0 95/5e 0/100f 100/0 95/5e 0/100f 100/0 95/5e 0/100f
contact time (min) 5
10
30
120
5 10
30
120
bacterial no. (cfu/mL) 2.47 2.50 1.51 2.42 2.48 1.63 2.48 2.41 1.61 2.12 2.44 9.80
± ± ± ± ± ± ± ± ± ± ± ±
2.43 0 0 2.42 0 0 1.84 0 0 8.70 0 0
±
±
±
±
c
Staphylococcus aureusb log reduction
unchlorinated PAN/m-aramid 0.25 × 107 NDd 7 NDd 0.22 × 10 7 0.52 × 10 0.08 0.30 × 107 NDd 0.15 × 107 NDd 7 0.05 0.34 × 10 0.38 × 107 NDd 0.21 × 107 NDd 7 0.20 × 10 0.06 NDd 0.14 × 107 7 0.16 × 10 NDd 0.44 × 106 0.27 chlorinated PAN/m-aramid 0.13 × 107 NDd 7.26 7.26 0.23 × 107 NDd 7.26 7.26 0.11 × 107 0.01d 7.26 7.26 0.50 × 106 0.33 7.26 7.26
bacterial no. (cfu/mL)c
log reduction
1.58 1.60 1.64 1.69 1.54 1.62 1.73 1.51 1.54 1.63 1.56 1.12
± ± ± ± ± ± ± ± ± ± ± ±
107 107 107 107 107 107 107 107 107 107 107 107
0.23 0.22 0.21 0.20 0.24 0.20 0.19 0.25 0.19 0.21 0.23 0.23
1.63 0 0 1.67 0 0 1.72 0 0 1.57 0 0
± 0.15 × 107
0.21 7.43 7.43 0.20 7.43 7.43 0.19 7.43 7.43 0.23 7.43 7.43
0.10 0.26 0.11 0.58 0.33 0.21 0.29 0.38 0.27 0.10 0.13 0.34
× × × × × × × × × × × ×
± 0.36 × 107
± 0.37 × 107
± 0.22 × 107
Total bacteria: 1.84 × 107 cfu/sample. bTotal bacteria: 2.67 × 107 cfu/sample. cBacterial no. data are expressed as mean ± standard deviation of a triplicate analysis. dNo determination. e[Cl+]%: 0.21. f[Cl+]%: 3.05.
a
absorption peaks at 1653 and 1656 cm−1, which represented the CO stretch band of m-aramid, were shifted to 1673 and 1672 cm−1, respectively. This band shift of a CO band to higher wavenumbers after chlorination was reported in previous research of an N-halamine precursor that contained an N−H in an amide group changed into N−Cl.25,26 We assumed that the chlorine in an N−Cl bond adjacent to a CO bond would possess relatively high electronegativity. Therefore, the energy for stretching the CO bond might vary and the FTIR wavenumbers of the CO might shift. XPS spectra of the films before and after chlorination were evaluated (Figure 6). The chlorine peaks at 200 and 271 eV, which were assigned to Cl 2p and Cl 2s, respectively,27 were only shown in the XPS spectra of the PAN/m-aramid (50/50 wt %) and the m-aramid film after chlorination. This also indicated that the m-aramid in the PAN/m-aramid film had changed into an N-halamine structure. The antimicrobial efficacy of chlorinated and unchlorinated PAN/m-aramid hybrid films was evaluated and the results are shown in Table 1. The films in this study possessed numerous voids on one of two surfaces (Figure 2), and the antimicrobial property of the films varied with different surface areas. Thus, equivalent surfaces of the films were used in the swatch test to minimize the effect of surface area. A pronounced antimicrobial property was not observed in the unchlorinated films. More specifically, unchlorinated PAN, m-aramid, PAN/m-aramid (95/5, wt%), and chlorinated PAN films showed no significant antimicrobial effect. On the other hand, the chlorinated PAN/ m-aramid and m-aramid films exhibited antimicrobial properties against both E. coli (Gram-negative) and Staph. aureus (Gram-
10 and Figure 11. The strength of the m-aramid film was approximately 400% higher than that of the PAN film. In addition, the strength of the films was enhanced with increasing m-aramid ratio in the films. The big strength gap between the PAN film and the m-aramid film was assumed to be attributed to the voids on one side of the films. In other words, the voids on the PAN film were relatively large, unlike the voids on the m-aramid film, and the relatively large voids on the PAN film were presumed to negatively affect the film strength. On the other hand, elongation at the break of the films was dramatically enhanced with the increasing ratio of m-aramid (Figure 11). Relatively high elongation at the break of m-aramid might be attributed to the enhanced elongation properties of the PAN/m-aramid hybrid films. After chlorination, the strength and elongation at the break of the films were decreased. We assumed that sodium hypochlorite (NaOCl) in the bleach may cause degradation of the polymer formed as a thin film during the chlorination. 3.4. Antimicrobial Efficacy. As outlined in the introduction, the aim of this study was to produce an antimicrobial PAN/m-aramid hybrid composite. In the antimicrobial mechanism of PAN/m-aramid hybrid composite, the amide group in m-aramid changes into an N-halamine after chlorination, followed by the release of oxidative chlorine from the N-halamine, which would attach to a negative charge of a microorganism.18,20 This would fatally hinder the metabolism of the microorganism and the microorganism would become inactive.24 To examine the change of m-aramid into an N-halamine structure, FTIR was performed (Figure 12). On the spectra of m-aramid and PAN/m-aramid film, 10303
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positive) with 7-log reduction within 5-min contact time. PAN/ m-aramid (95/5, wt %) film revealed 0.21% of the oxidative chlorine (Table 1). According to our previous research,18,20 0.20% of the oxidative chlorine was sufficient to inactivate bacteria. Thus, 0.21% of oxidative chlorine of the film can be enough to inactivate bacteria.
4. CONCLUSIONS Dissolved PAN and m-aramid in DMSO were coagulated into films in distilled water, and a molecular interaction between PAN and m-aramid was proven. The PAN/m-aramid films showed better thermal stability than the PAN film. The chlorinated PAN/m-aramid films exhibited antimicrobial efficacy against Gram-negative and Gram-positive bacteria. The PAN/m-aramid hybrid composite, which possessed relatively enhanced thermal stability and predominant antimicrobial efficacy, will broaden the applications of PAN and the PAN-related industry. For instance, the hybrid composite can be applied as an antimicrobial textile including socks and sweater. In addition, because PAN is the precursor of carbon fiber, the hybrid composite would be used as a precursor of novel carbon fibers. The formation of voids on the surface of the PAN/m-aramid films should be protected through adjustment of the coagulation conditions. In addition, reduced mechanical properties after chlorination might be improved using a relatively mild solution with lower concentration of the bleach.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: +82-42-481-8716. Fax: +82-42-472-3558. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This study was supported by the Yeungnam University Research Grant in 2012. In addition, the authors wish to thank Dr. Byungjoo Seo, Department of Applied Microbiology and Biotechnology, Yeungnam University, for the preparation of the antimicrobial test. The authors are also grateful to Jimin Lee for her helpful discussion and for preparing the samples.
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REFERENCES
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dx.doi.org/10.1021/ie400636z | Ind. Eng. Chem. Res. 2013, 52, 10297−10304
