Y. Yu, Z. Yu, and J. Zhao (Eds.): CSEEE 2011, Part II, CCIS 159, pp. 348–353, 2011. © Springer-Verlag Berlin Heidelberg 2011

Electrospinning Polyurethane (PU) /Inorganic-Particles Nanofibers for Antibacterial Applications

Xiao-jian Han1,*, Zheng-ming Huang2, Chen Huang1, and Chuang-long He3

1 College of light-textile Engineering and Art, Anhui Agricultural University, 130 West Changjiang Rd., 230036 Hefei, China

2 School of Aerospace Engineering & Applied Mechanics, Tongji University, 1239 Siping Road, 200092 Shanghai, China

3 Institute of Biological Sciences and Biotechnology, Donghua University, 1882 West Yanan Rd, 201620 Shanghai, China

xiaojianhan@gmail.com, huangzm@tongji.edu.cn, silkhch@163.com, hcl@dhu.edu.cn

Abstract. A blend-electrospinning technique was applied to transfer polyurethane (PU)/inorganic particles solutions into nanofibers, in which titanium dioxide (TiO2), cuprum (Cu) or/and silver (Ag) nanoparticles were packed. The resultant nanofibers were subsequently characterized by means of scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR) and anti-bacterial test. Experimental results have shown that when the ratio of PU solution and titanium dioxide sol was in 3.5:1, 89.55% of the escherichia coli and 82.35% of the staphylococcus aureus bacteria were killed after a light activation treatment. Without any photocatalysis, however, an introduction of Ag or/and Cu nanoparticles into the PU/TiO2 (in the ratio of 3.5:1) nanofibers led to a significant improvement in their anti-bacterial ability without photocatalysis.

Keywords: Nanofibers, Electrospinning, Anti-Bacterial Performance.

1 Introduction

Recently, preparation of polymer nanofiber films containing inorganic nanoparticles has drawn great attention because the resultant nanocomposites can exhibit the outstanding characteristics of both inorganic nanoparticles (e.g., the quantum size effect and high ratio of surface atoms to innersphere atoms etc.) and polymer nanofibers (e.g., the high specific surface area and good interpenetrating capacity in other materials etc.) [1]. Titanium dioxide is an important material for a variety of applications such as catalytic devices [2], solar cells [3], and other optoelectronic devices [4].

Conventionally, it is extremely difficult to disperse TiO2 powder homogeneously into the polymer solution due to the easy agglomeration of nanoparticles. There are a few investigations of electrospinning polymer/TiO2 sol-gel for application in * Corresponding author.

Electrospinning Polyurethane (PU) /Inorganic-Particles 349

photocatalysts [5], solar cells [6] and other optoelectronic devices[4] reported. He etc al. [5] have investigated the electrospinning parameters of electrospun polyvinyl alcohol (PVA)–Pt/TiO2 composite nanosize fiber and the degradation rate of PVA by photocatalytic oxidation under UV irradiation. Viswanathamurthi etc al. [6] reported the electrospun poly (vinylacetate)/titanium dioxide hybrid fibers and obtained the pure ceramic metal oxide fibers through high temperature calcination of the composite.

In this work we fabricated PU/TiO2 ultrafine fibrous membranes using a sol-gel electrospinning technique. In order to carry out their fine anti-bacterial ability without photocatalysis, a proper content of Ag or/and Cu was added into the PU/TiO2 ultrafine fibers. The resulting composite ultrafine fibers are designated as PU (TiO2, Cu), PU (TiO2, Ag), or PU (TiO2, Cu, Ag) respectively. The nanofibrous mats obtained by this technique can be used for filter media with high filtration efficiency (FE) and low air resistance, or bacterial protective clothing, depending on the PU polymer and TiO2, which was also doped by silver or (and) copper, being used.

2 Experiments

2.1 Materials and Electrospinning

Polyurethane (PU, Elastollan 1185A) was purchased from Jinjiang plastic Ltd. (Shanghai), whereas Tetrahydrofuran (THF), dimethylformamide (DMF) and acetic acid were from Chemical Reagent Co. Ltd (Shanghai). Tetrabutyl titanate, was acquired from Runjie Chemical Reagent Co. Ltd (Shanghai). Copric nitrate (Cu(NO3)2) and Silver Nitrate (AgNO3) were obtained from Zhenxin Reagent Co. Ltd (Shanghai) and NO. 1 Reagent Co. Ltd (Shanghai), respectively.

The devised experimental setup basically includes a spinneret apparatus with an inner steel capillary (inner diameter, 0.8 mm) coaxially located inside an outer plastic nozzle (inner diameter, 2.0 mm), which is fixed no a grounded hob, made a co-axial configuration at the tip. A syringe pump (model WZ-50C2, Zhejiang University Medical Instrument Co., Ltd) is for delivering solution through Teflon tube connecting the syringe with the inner capillaries (needles), a high voltage DC generator (Beijing Machinery & Electricity Institute) exerts a 20-30 KV voltage to spinning solutions through inner needle, and the negative terminal is attached to a aluminium foil covered collector (cathode) with ability to move to and fro in horizontal direction to collect the random fibers.

2.2 Morphology and Fourier Transformed Infrared Spectroscopy (FTIR)

The morphology of collected fibers was observed under a environmental scanning electron microscopy (ESEM, PHILIPS XL 30, Netherland) with a accelerating voltage of 20 kV.

Infrared spectroscopies of the nanofiber membranes, whose spectral range was from 4000 to 500 cm−1 with a resolution of 4 cm−1, were obtained in terms of EQUINOX 55 (Bruker, Germany) under a 6.10 kHz scanner velocity.

350 X. Han et al.

2.3 Antibacterial Test

The in vitro antibacterial activities of PU fibers with nanoparticles were examined according to AATCC100 standard. The following microorganisms were used: Gram-positive taphylococcus aureus (S. aureus, ATCC 6538)) and Gram-negative Escherichia coli (E. coli, ATCC 2592). The counts were used to calculate the surviving number of bacteria by the GB/T 4789.2-2003 standard (Microbiological examination of food hygiene Detection of aerobic bacterial count). The anti-bacterial efficacy (ABE in %) of the specimen was calculated according to the following equation.

ABE（ ） （ － ）% = A B / A×100 (1)

where A (cfu/g)and B (cfu/g) stood for the average numbers of viable bacterial colonies of the blank control in the electrospun PU nanofibrous membrane and PU/inorganic specimen, respectively.

3 Results and Discussion

3.1 Fiber Morphology and FTIR Analysis

Fig.1 shows the SEM images of PU (TiO2, Cu), PU(TiO2, Ag) and PU (TiO2, Cu, Ag) fibers, electrospun by the solution made from Cu (NO3)2 and (or) AgNO3, PU/TiO2 solution (weight ratio, 3.5:1) in the molar ratio (Cu/Ti, 2/100, Ag/Ti, 2/100), respectively. Even though the content of Cu and (or) Ag introduced into PU/TiO2 solution is small, there is a strong interaction between AgNO3 (or Cu(NO3)2) and PU molecular chains, which promoted phase separation of PU . This would change many parameters of mixture, such as solution concentration and surface tension. Therefore, the fine morphology of PU (TiO2, metal particle) could be obtained in more harder electrospinning parameters (voltage, flow rate, the distance between the tip and the collector), than that of PU/TiO2. For example, in the process of electrospinning PU (TiO2, Ag), the environmental condition of the voltage (26-27kv)， the distance (13-14cm) and the flow rate (1.6ml/h) could be distinguished from the respective parameters of PU/TiO2. Even the same flow rate of PU (TiO2, Cu) solution was used as that of PU/TiO2 solution in electrospinning, the other parameters should be different (the voltage, 25kv， the distance, 13-14cm) for successfully fabricating PU (TiO2, Cu) membrane without flaw on the resultant membrane. In the present study, the average diameter of the bead on the PU (TiO2, metal particle) fibers corresponding to Cu, Ag, Cu and Ag, as shown in Fig.1 (b)- (d), were 320 nm, 461 nm, and 1350 nm, respectively. The average diameter of PU/TiO2 (3.5:1) fibers was 862 nm (Fig.1 (a)). This is because the strong interaction between AgNO3 (or Cu(NO3)2) and PU molecular chains slows the viscosity and the higher voltage applied in electrospinning, which increases the charge density of polymer jet and favors stretching or drawing of the jet, leads to in smaller diameter fibers. So Figs.1 (b) and (c) favours more thinner fibers without or less beads than Figs.1 (a). But too much metal particles in the PU (TiO2, Cu, Ag) solution will weaken the electrospinning capability of mixture. So the average diameter of bead in the electrospun PU (TiO2, Cu, Ag) fibers (Fig.1 (d)) is the most and dispersed less symmetrically in PU (TiO2, metal particle) system.

Electrospinning Polyurethane (PU) /Inorganic-Particles 351

Fig. 1. (a) SEM images of PU/TiO2 (3.5:1), (b) PU (TiO2, 3.5:1, Ag), (c) PU(TiO2, 3.5:1, Cu), (d) PU(TiO2, 3.5:1, Cu，Ag)

Fig. 2. FT-IR spectra of fibers: (a) PU/TiO2 (3.5:1), (b) PU (TiO2, 3.5:1, Ag), (c) PU (TiO2, 3.5:1, Cu), (d) PU (TiO2, 3.5:1, Cu, Ag)

From Fig.2, the FT-IR spectra of the PU polymer, we can see the following characteristics: a strong absorbing peak appeared in the 1700-1670 cm-1 region owing to the stretching vibration of C=O bond in carbamate (R-O-C (=O)-NHR). In general, the high frequency absorbing peaks corresponding to a mono-substituent and to a disubstituted compound may occur in the region of 1736-1700 cm-1. A combination of the both gave rise to the peak of 1730 cm-1. Attributed to C=O stretch of amido ester, there was also a 1701cm-1 region. The characteristic bands of alkyl aether produced the wide 1106 cm-1 (1150-1060 cm-1) and 1079 cm-1 regions because of the C-O-C asymmetrical flexing vibration. Howerever, less difference from the FTIR of the PU (TiO2, metal particle) (Fig.2 (b)-(d)) specimen and PU/TiO2 (3.5:1) (Fig.2 (a)) could be found resulted from small amount of Ag and (or) Cu in PU (TiO2, metal particle) system, and the characteristic absorption peaks might not be reflected in this point. Hence, we may conclude that the structure of the TiO2, encapsulated by the PU polymer fibers, was formed in this regard.

a

5um

b

5um

d

5um

c

5um

352 X. Han et al.

3.2 Antibacterial Test

It is believed that the antimicrobial activity TiO2 nanoparticles is dependent on their free radical of hydroxide radical, produced by the process of photooxidation after absorbing the light with the wavelength (below 385 nm), whose oxidizing potential energy could kill almost all the microorganism. The fluorescent light will activate the bonding electron on the conduction band. So the photoelectrons (e-) on the valence band and holes (h+) on the conduction band was produced, and both of them could be separated and migrated to the surface of TiO2 nanoparticles. Morever, the photoelectrons (e-) on the valence band, containing high reducibility with adsorbent oxygen molecule (O2) on the surface to form superoxide anion (•O2-), can induce the further reaction with water (H2O) to produce super-hydroxide radical (•OOH) and oxyful (H2O2), which could be synthetized by the reciprocity of the active hydroxide radical (•OH). The resultant O2- , which contains the strong reducing property, can decompose the organotrophic bacteria and the materials that is necessary for them to survive. Morever, the •OH, H2O2 and •OOH might produce many articulated oxidation reaction along with biomacromolecule, such as the esters, protein, enzyme and nucleic acid, and so on, to destroy the construction of biological cell. Table 1 shows the ABE of various electrospun samples for escherichia coli and staphylococcus aureus. It shows that the process of electrospinning PU/TiO2 sol-gel produced the superfine fibers and intercept the agglomeration of TiO2 nanoparticles, successfully. When these bacteria were incubated on the nanofibers, the ABE of PU/TiO2 (3.5:1) specimen cultured in the fluorescent light, was 82.35% and 89.55% for Gram-positive S. aureus and Gram-negative E. coli, respectively, that is a good example to testify the function of TiO2 particles.

Table 1. Antibacterial Efficiency of Various Electrospun Samples

Antibacterial Efficiency (％) Sample

S. aureus E. coli

PU/TiO2 (3.5:1) Incubating in sunlight for

about 24h 82.35 89.55

PU (TiO2, 3.5:1, Cu) 75.05 91.00 PU (TiO2, 3.5:1, Ag) 92.37 93.20

PU (TiO2, 3.5:1, Cu, Ag)

Incubating in camera obscura for about 24h

93.54 95.13

Besides, in this study, the antimicrobial activity of the PU/TiO2 (3.5:1) nanofibers containing Cu and (or) Ag nanoparticles was tested against S. aureus and E. coli in the camera obscura. The free electron should be inclined to migrate to Ag+ and (or) Cu2+ in the process of experiment, which would separate electrons (e-) and holes (h+) that can be realized by the special environment of fluorescent light for single TiO2 nanoparticles, and the necessary •OH, H2O2 and •OOH for killing microbe can be produced. So, without the factor of illumination, all the PU(TiO2, 3.5:1, metals) shows better function in the antimicrobial activity than PU/TiO2 system does even in the fluorescent light, except the PU (TiO2, 3.5:1, Cu, Ag) membrane against S. aureus (75.05%). The number of bacteria from the PU (TiO2, 3.5:1, Ag) and PU (TiO2, 3.5:1, Cu, Ag) membranes, was reduced

Electrospinning Polyurethane (PU) /Inorganic-Particles 353

more than 90% after 24 h incubation, indicating that the TiO2 nanoparticles, modified by Ag+ (Ag+ and Cu2+) ions, successfully inhibited the growth of these bacteria, that is also caused by good antimicrobial performance of Ag+ in itself. Because of the poorer modifying performance from Cu2+ ions, the antimicrobial activity of PU (TiO2, 3.5:1, Cu) nanofibers (75.05% (S. aureus), 91.00% (E. coli), respectively) was less than that of PU (TiO2, 3.5:1, Ag) and PU (TiO2, 3.5:1, Cu, Ag) one.

4 Conclusion

In this paper, we realized blend-electrospinning of PU/ inorganic particles system, in which TiO2, Cu or (and) Ag nanoparticles were packed by sol-gel way. Experimental results have shown that when the ratio of PU solution (7wt%) and TiO2 sol was 3.5:1, 89.55 percent of the escherichia coli bacteria and 82.35 percent of staphylococcus aureus were killed with light activation. Morever, the attachment of Ag or (and) Cu nanoparticles into PU/ TiO2 (3.5:1) nanofibers leads to a significant antibacterial performance without photocatalysis.

Acknowledgements. The authors are grateful for the financial support of the natural science item of Anhui university and college research (Grant KJ2009A029Z), item to stable and subsidize talent's research (yj 2008-8), Anhui provincial young talents fund (2011SQRL048ZD) for their financial support.

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