See discussions, stats, and author profiles for this publication at: http://www.researchgate.net/publication/282320932 Atmospheric pressure plasma treatment of wool fabric structures ARTICLE in JOURNAL OF ELECTROSTATICS · OCTOBER 2015 Impact Factor: 0.86 · DOI: 10.1016/j.elstat.2015.07.004 READS 28 6 AUTHORS, INCLUDING: Lutfi Oksuz IEEE ICOPS 98 PUBLICATIONS 563 CITATIONS SEE PROFILE Ferhat Bozduman T.C. Süleyman Demirel Üniversitesi 16 PUBLICATIONS 11 CITATIONS SEE PROFILE Neslihan Nohut T.C. Süleyman Demirel Üniversitesi 8 PUBLICATIONS 2 CITATIONS SEE PROFILE Aysegul Uygun Oksuz T.C. Süleyman Demirel Üniversitesi 61 PUBLICATIONS 498 CITATIONS SEE PROFILE All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately. Available from: Neslihan Nohut Retrieved on: 04 December 2015
Atmospheric pressure plasma treatment of wool fabric structures
Esin Eren a, Lutfi Oksuz b, *, Ali Ihsan Komur c, Ferhat Bozduman b,Neslihan Nohut Maslakci c, Aysegul Uygun Oksuz c
a Suleyman Demirel University, Hydrogen Technologies Research and Application Center, 32260 Isparta, Turkeyb Suleyman Demirel University, Faculty of Arts and Science, Department of Physics, 32260 Isparta, Turkeyc Suleyman Demirel University, Faculty of Arts and Science, Department of Chemistry, 32260 Isparta, Turkey
a r t i c l e i n f o
Article history:Received 27 March 2015Received in revised form10 July 2015Accepted 10 July 2015Available online xxx
Polyaniline-wool (PAN-WF), poly(3,4-ethylenedioxythiophene)-wool (PEDOT-WF), polypyrrole-wool(PPy-WF) fabrics were successfully prepared via atmospheric pressure plasma process. Scanning elec-tron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), Fourier Transform Infrared Spec-troscopy (FTIR) and four-probe resistance measurements were used to study the properties of the plasmapolymer coated wool fabrics. The effects of the addition of iodine doping on the morphology and elec-trical properties of the fabrics were examined. The lowest electrical resistance was measured to be7.7 � 103 U cm for PEDOT-I2-WF sample after washing with water two times.
Many great investigations and new techniques have beenfocused on the study of textile to improve surface properties suchas wetting, antistatic, electrical conduction, penetration, and so on[1e3]. Both low-pressure and atmospheric pressure plasma sys-tems were used for novel antistatic acquisition; processing fibers,yarns, fabric [4e6]. Plasmas generate a high density of free radicalsvia disassociating molecules through electro collisions and photo-chemical processes that allow it to disrupt the chemical bonds inthe fiber polymer. As a result, new chemical species form on fiberand polymer surfaces [7,8]. Aside from plasma activation or plasmamodification process, plasma is used to deposit chemical materialsonto wide variety of substrate by plasma polymerization or plasmagrafting techniques [8]. Since the depth of plasma modification hasfrom tens to hundreds nanometers, plasma can be used tomaterialssurface modification without changing their bulk properties [9].The plasma polymerization has advantageous including the envi-ronmental friendliness of the solvent-free process, the depositionof ultra-thin films with thickness directly proportional to deposi-tion time, the deposition of pinhole free films without dimensionalchanges associated with solvent evaporation [10,11].
The plasma polymerization process starts with gas ionization.
Plasma is generated via supplying energy to an ordinary neutral gasand converting from the gas atoms to charged and excited speciessuch as electrons, radicals and excited atoms. The collisions amongthese particles cause various kinds of reactions including plasma-phase and radical initiated polymerization in plasma [12]. Themechanism of plasma polymerization is difficult to explain exactlydue to a great number of elementary processes [12,13]. Early studyindicates that the number of adsorbed molecules on electrode haveeffect onto rate of polymerization. Moreover, they found that therewas no polymer on the anode in a dc discharge and their resultsshowed that the positive ions occurred in the negative glow viaelectron bombardment of the monomer molecules played animportant role in polymer formation [13,14]. However, recently ar-ticles have been put emphasis on the role of free radicals in plasmapolymerization and the rather random nature of plasma-phase re-actions such as ionization via collisions [13]. It is well known thatthe interaction between radical and molecule for plasma polymer-ization brings about a higher concentration of free radicals in a nonequilibrium plasma and faster rates of radicalemolecule reactionwhen compared to ionemolecule reaction [12,15].
Wool is good substrate for plasma modification due to outer-most part of fiber that is consisted of lipid layers and ionizablefunctional groups. Moreover, the fiber surface is divided into fourcoaxial layers of different chemical compound including epicuticle,exocuticle that is highly cross-linked by cystine bridges, the lesscross-linked endocuticle, the cell membrane complex (CMC)[5,8,16]. According to several investigations including the effect of
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plasma treatment on wool, the changing performance of wool arerelated to surface-specific changes of the protein fiber via theplasma treatment [16].
Compared to high and low pressure plasmas, atmosphericpressure plasma systems have an exciting alternative due to in-lineprocess capabilities, low production costs. The shape and size of theplasma systems are simply altered in atmospheric pressure systems[10,11,17,18]. Atmospheric pressure discharges have made it avail-able to treat polymers surfaces rapidly, continuously, uniformlywithout using expensive equipment like vacuum [19]. Atmosphericpressure non-thermal plasmas are generally excited via a dielectricbarrier discharge, plasma jet or diffuse discharge [20,21]. This workaims to investigate antistatic and surface properties of atmosphericpressured plasma-induced graft polymerized (APPGP) conductingpolymer coated wool fabrics. As conducting polymers, polyaniline
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(PAn), polypyrrole (PPy), poly(3,4-ethylenedioxythiophene)(PEDOT) were selected because of their advantages that includerelatively high conductivity, light-weight, inexpensive, flexible, etc[22]. Polymer-coated fabrics were characterized by means ofscanning electron microscopy-energy dispersive X-ray spectros-copy (SEM-EDS), Fourier transform infrared (FTIR) and electricalresistance measurements.
2. Experimental
2.1. Materials
Wool fabric was supplied from Yunsa/Turkey Company. 3,4-Ethylenedioxythiophene (EDOT, Aldrich), aniline (An,
Fig. 4. Photo images (a) PAN-I2-WF after washing with water (b) PEDOT-I2-
SigmaeAldrich), pyrrole (Py, Aldrich), Iodine solution (Aldrich)were used as received.
2.2. Experimental procedure
Each monomer (2 mL) was drop-casted on wool fabric(3 cm � 3 cm). After drying in air at room temperature, APPGPprocess was applied ontowool fabrics in 3 cm distance for 10min. Asingle electrode plasma jet was used as plasma source (Fig. 1). Thetotal argon flow rate was fixed at 7 L/min at room temperature. Thegenerator's voltage and current were set at 3000 Vrms and 30 mA,sine wave respectively. The frequency was 55 kHz. Also, the plasmapolymer coated wool samples were doped via 1 wt% iodine solu-tions, dried in air, stored in a standard atmosphere of 20± 2 �C and
WF after washing with water (c) PPy-I2-WF after washing with water.
Fig. 5. Logarithmic resistance vs number of washing cycles of PEDOT-I2-WF sample.
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65 ± 3% relative humidity. The abbreviations of all samples aresummarized in Table 1.
2.3. Characterization
Fourier transform infrared (FTIR) spectra were recorded be-tween 400 and 4000 cm�1 with a 4 cm�1 resolution on a PerkinElmer Spectrum BX FTIR system (Beaconsfield, Beuckinghamshire,HP91QA, England). SEM images were taken on a Scanning electronmicroscope model Tescan Vega II LSU. The elemental analysis wasconducted by EDS measurements (Oxford Instruments, Swift-ED).The electrical resistance (Res) was measured at standard climateconditions (20 ± 2 �C, 65 ± 3% RH) using a standard four-probemethod with a PCIDAS6014 current source, a voltmeter and atemperature controller.
3. Results and discussion
3.1. Photo images of samples
Fig. 2aeg shows photo images of samples. While WF has bronzemetallic brown color (Fig. 2g), the color of PAN-WF is linear fawncolor as seen Fig. 2a. This sample indicated paste fawn brown colorupon treatment with iodine (Fig. 2b). Depending on oxidation ratioand doping time, polyaniline shows different color changeincluding yellow, green, blue, violet, brown [23,24]. In case ofPEDOT-I2-WF sample, the color varied from light blue to dark grayupon iodine doping (Fig. 2ced). PEDOT is well known of cathodiccolored conducting polymer. The color of PEDOT film changes fromlight to dark blue. It's darker shades include black or grey. Thisproperty allows it to have wide applications such as chemical andbiochemical sensors, antistatic coatings, electrically switchablewindows, and polymeric light-emitting diodes [25,26]. PPy-WFsample showed a color change from light fawn brown to bronzemetallic brown upon iodine doping. This behavior is an funda-mental feature of the electroactive conducting polymers containingPPy [23,27].
3.2. FTIR results
The FTIR spectra of all samples are shown in Fig. 3aec. Thespectrum of PPAN-WF indicated the peak at 3445 cm�1 attributedto NeH stretching (Fig. 3a). The bands observed around 1540 and1508 cm�1 have been attributed to stretching of N ¼ Quinine(Q) ¼ N and N-Benzenoid (B)eN, respectively. The presence of ar-omatic ring has been confirmed with the peaks at 1654 and1458 cm�1 even after plasma deposition of polymer fabrics. The
CeN stretching band of amine was observed at 1237 cm�1. It wasconcluded from FTIR spectra of PAN fabrics that the aromatic ring isnot destroyed in the polymer structure. It is also seen that upondoping with iodine, NeH stretching bands at 3445 cm�1 wasshifted lower wavenumber (Fig. 3a). This shifting might haveconfirmed the interactions between the doping anion and theamine nitrogen sites of polyaniline [24,28e31].
The spectrum of PEDOT-WF sample indicated that the 1234 and1056 cm�1 bands are characteristic of CeOeC asymmetric andsymmetric stretching coming from ethylenedioxy group, respec-tively (Fig. 3b). The intensity of these peaks increased upon dopingwith iodine. It is explained by formation of stronger band. Theabove result is consistent with resistance results after washingwithwater. The band at ~670 cm�1 corresponds to the CeS stretching.C]C and CeC stretching bands were observed around 1508 cm�1
and 1380 cm�1 [32].In the FTIR spectra of PPy-WF (Fig. 3c), the peak at 3421 cm�1 is
typical of the NeH stretching. The eNH bending vibration bandand/or aromatic C]C stretching peak were observed at 1654 cm�1.This indicates the presence of the aromatic cyclic structure in thepolypyrrole chain. The band at 1239 cm�1 belongs to CeNstretching and/or NeH aromatic bending [33]. This peak was shif-ted lower wavenumbers upon treatment with iodine. Additionally,the FTIR spectra of all fabrics show the broader peaks that arehighly disordered nature of plasma polymers [24].
3.3. Electrical resistance results
The electrical resistance results were given in Table 1. The initialelectrical resistance of wool fabric was 7.7 � 104 U cm and itchanged in the range of 1.0 � 104e3.3 � 104 U cm after plasmapolymer coatings. Plasma deposition of polymer fabrics have lowerelectrical resistance than untreated wool fabric. The decrease inelectrical resistance after argon plasma treatment can be attributedto the formation of oxygen vacancies on fabric surface by ionbombardment, whichmay act as donors [34]. The value of electricalresistance was measured as 3.3� 104U cm for PPy-WF sample. Thisvalue is better than that of PPy films prepared via conventionalmethods such as AC plasma polymerization [33]. Since the con-ductivities of PPy and PAN are related to the eNe species thatoccurred from eNHe groups, it is assumed that the charge transfercomplex from such eNe species in plasma deposited pyrrole andaniline is not stable [33]. Moreover, although remaining radicalselongate conjugated system, doping may cause a partial degrada-tion of that conjugated system [35]. Thus, after iodine doping,higher resistance of PPy-I2-WF, PAN-I2-WF fabrics were obtained(Table 1).
The increase in resistance of PEDOT-I2-WF sample was shown inTable 1. The enhancement of resistance is assigned to diffusion ofabsorbed doping ions out of layers due to post-doping exposure toair [36,37]. Moreover, the number of charge carriers and their inter-and intra-chain mobility is responsible for the measured resistance[37]. It is hypothesized that the difference in the rate of formation ofcharge carriers is due to a difference in conjugation length [37]. Thehigh electrical resistance such as PPy-I2-WF fabric is associatedwith the very small number of carriers [37]. When the delocaliza-tion of charge carriers is lower, the energy barrier for hopping ishigher. Thus, the hopping efficiency was based on the conjugationlength. It is inferred that the number of charge carriers decreasesdue to a decrease in conjugation length after iodine doping additionfor all fabrics. With increasing energy barrier for hopping, electricalresistance increased [37].
In order to study the ageing effect, the electrical resistancemeasurements were repeated after several months. The electricalresistance of plasma-deposited polymer fabrics are in the range of
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3 � 104e5 � 104 U cm. It should also be noted that even afterextensive ageing time, there was no polymer degradation on fabric.Additionally, EDS results indicated that there was no chemicaldegradation after even atmospheric-pressure plasma treatment.Moreover, our ageing effect results indicate that these films have ahigh degree of cross-linking, which limits the polymer chainmovement and therefore limits the fraction of mobile groupswhichcan move away from the surface [38]. After extensive ageing time,electrical resistance of PAN-I2-WF and PPy-I2-WF samples wasobtained as 7� 104U cm,1.2� 105U cm, respectively. These resultswere similar with that of PAN-I2-WF and PPy-I2-WF samples.However, after several months, PEDOT-I2-WF fabric has tendency torevert back to the plasma-deposited PEDOT state.
The stability of the electrical resistance of PAN-I2-WF, PPy-I2-WF, PEDOT-I2-WF fabrics against washing with water were inves-tigated (Fig. 4). PAN-I2-WF, PPy-I2-WF and PEDOT-I2-WF haveresistance values of 7.1 � 105, 7.7 � 105, 1.2 � 104 U cm afterwashing with water, respectively. It is be concluded that the elec-trical resistance via washing changed depending on the degree ofanion dedoping and the removal of the polymer deposit on thefabric [39,40]. Good adhesion of the PEDOT layer onwool fabric wasformed, that allow it to bemore stable than PAN, PPy coated fabrics.In addition, the effect of the number of water washing cycles onelectrical resistance of PEDOT-I2-WF fabric was studied, as shownvia the plot presented in Fig. 5. Trend of decrease of electricalresistance was obtained until washing cycle two times. We figure
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out that the decrease of electrical resistance might be due to theformation of a conductive moisture layer over the fabric surface[41,42] Electrical resistance expressed as <108 U sq is normallysufficient to use antistatic applications [43]. Thus this work can beintended to improve antistatic properties [41].
3.4. SEM and EDS results
Scanning electron microscopy images of the wool fabric beforeand after coated with each polymer are shown in Fig. 6. As it is seenin Fig. 6g, the wool fabric before plasma deposition process showsfibril structure with smooth surface. When compared to each thecoated fabric via plasma-induced graft polymerization, the fibersurface of PEDOT-WF fabric showsmore dense covering of polymer,as shown in Fig. 6c. All SEM images show that after iodine dopingtreatment, iodine doping took out of layers, resulting in enhance-ment in resistance (Fig. 6b, d, f).
The component of all prepared samples was determined viaEDS, as shown in Table 2. Ratio of carbon to nitrogen (C/N), carbonto oxygen (C/O) and carbon to sulfur (C/S) of wool fabric wascalculated as 2.37, 1.74, 15.57, respectively. Elemental analysis resultof PEDOT-WF shows that the elements C, O and S are mainly fromthe monomer EDOT. The amount of S content increased afterplasma deposition as a result of decreasing ratio of C/S from 15.57 to10.73. This indicates the formation of PEDOT on wool fabric [44].
EDS analysis results of PPy-WF and PAN-WF reveal that the C/Nratio increased from 2.37 to 2.78 and 2.47, respectively. It isexplained by formation of weaker CeN bond. In our study, argonwas used as carrier gas in plasma-induced graft polymerizationprocess. It contains large and heavy molecules that might attackand break the CeN bonds easily. Moreover, it has been suggestedthat an enhancement in the number of between electrons andother plasma species that allow it to have loss of N from fabric [33].The above results are consistent with previous literature [45,46].The same situation was formed after doping process. This isconsistent with resistance result, indicating that this fabric have therelatively weaker CeN bond.
4. Conclusions
PAN-WF, PEDOT-WF, PPy-WF fabrics were successfully synthe-sized through atmospheric pressure plasma-induced graft poly-merization. FTIR results proved the polymer formation on woolfabric. After iodine doping, the all fabrics showed the increasedresistance since iodine doping took out of layers. However, ourresults have shown that PEDOT-I2-WF is more stable than PAN-I2-WF and PPy-I2-WF fabrics after washing treatment. PEDOT-I2-WFfabric has the decrease in electrical resistance until washing cycletwo times. As a result, this fabric is shown to be promising candi-dates for antistatic applications.
Acknowledgements
Authors gratefully acknowledge the 1509- TÜB_ITAK
International Industrial R & D Projects Grant Programme (ProjectNo: 9110021) for financial support to this study.
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