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Applied Surface Science 257 (2011) 4165–4170

Contents lists available at ScienceDirect

Applied Surface Science

journa l homepage: www.e lsev ier .com/ locate /apsusc

urface treatment of aramid fiber by air dielectric barrier discharge plasma attmospheric pressure

aixia Jiaa, Ping Chena,b,∗, Wei Liua,c, Bin Lia, Qian Wanga

Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education) & Faculty of Chemical, Environmental and Biological Science and Technology,alian University of Technology, Dalian 116024, ChinaLiaoning Key Laboratory of Advanced Polymer Matrix Composites Manufacturing Technology, Shenyang Aerospace University, Shenyang 110034, ChinaDalian University of Education, Dalian 116021, China

r t i c l e i n f o

rticle history:eceived 1 October 2010eceived in revised form6 November 2010ccepted 29 November 2010vailable online 9 December 2010

a b s t r a c t

Aramid fiber samples are treated by air dielectric barrier discharge (DBD) plasma at atmospheric pressure;the plasma treatment time is investigated as the major parameter. The effects of this treatment on thefiber surface physical and chemical properties are studied by using surface characterization techniques.Scanning electron microscopy (SEM) is performed to determine the surface morphology changes, X-rayphotoelectron spectroscopy (XPS) is analyzed to reveal the surface chemical composition variations anddynamic contact angle analysis (DCAA) is used to examine the changes of the fiber surface wettability. In

eywords:ramid fiberir DBD plasmareatment timeurface characterizationetting behavior

addition, the wetting behavior of a kind of thermoplastic resin, poly(phthalazinone ether sulfone ketone)(PPESK), on aramid fiber surface is also observed by SEM photos. The study shows that there seems to bean optimum treatment condition for surface modification of aramid fiber by the air DBD plasma. In thispaper, after the 12 s, 27.6 W/cm3 plasma treatment the aramid fiber surface roughness is significantlyimproved, some new oxygen-containing groups such as C–O, C O and O C–O are generated on the fibersurface and the fiber surface wettability is greatly enhanced, which results in the better wetting behavior

sma-t

of PPESK resin on the pla

. Introduction

Aramid fiber, combining high specific modulus and strengthith excellent thermal stability and chemical inertness, is one of

he best candidates as reinforcement for high-performance com-osites. However, the employing aramid fiber as reinforcementas been limited by poor fiber/matrix interfacial adhesion, becausef the fiber having smooth surface and inert chemical structure,hich prevents interfacial bonding with most of the commercially

vailable resins used in composites [1–5]. In order to optimize theramid-fiber/matrix adhesion, a variety of research efforts haveeen directed towards the improvement of fiber surface proper-ies by various surface treatment techniques [6–11]. Traditionalhemical treatments are often accompanied by the use of water

nd/or organic solvents, thus pose such problems as the disposalf drained water and recovery of organic solvents, which arenergy-, time- and cost-intensive and involve pollution of wateresources. Therefore, non-thermal plasma technology, which is effi-

∗ Corresponding author at: Dalian University of Technology, Department of Poly-er Material, Zhongshan Road 158-42#, Dalian, Liaoning 116012, China.

el.: +86 0411 89393866.E-mail address: chenping 898@126.com (P. Chen).

169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.apsusc.2010.11.190

reated aramid fiber.© 2010 Elsevier B.V. All rights reserved.

cient and environmentally friendly, has been extensively studied[12,13].

Plasma techniques may work in very flexible conditions. Incomparison with that at low and medium pressure, plasmas atatmospheric pressure are predominantly studied recently, e.g.dielectric barrier discharge (DBD) plasma, which can not only sep-arate the fiber bundles into individual filaments and modify thefiber surface without altering the bulk properties, but also has theadvantages of operating at atmospheric pressure and easy forma-tion of uniform and stable plasmas, avoiding the need of expensivevacuum equipment and permitting continuous processing of fibersurfaces. This approach has proved to be a promising method and isincreasingly used for polymeric fiber or film surface modifications[14–16]. However, until now, only little research [17,18] is doneon the relationship between the air DBD plasma treatment and thesurface properties of aramid fiber.

In this paper, the influence of DBD plasma treatment in airat atmospheric pressure on aramid fiber surface is studied. Vari-ous different treatment durations have been explored to optimize

the modification, and the physical and chemical changes on thetreated fiber surface induced by the plasma are investigated.The surface morphology was examined using scanning electronmicroscopy (SEM), the surface chemical composition was analyzedby X-ray photoelectron spectroscopy (XPS), and the surface wet-

4166 C. Jia et al. / Applied Surface Scien

tIps

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Fig. 1. Schematic representation of the air DBD plasma set-up.

ability was measured by dynamic contact angle analysis (DCAA).n addition, the wetting behavior of a kind of thermoplastic resin,oly(phthalazinone ether sulfone ketone) (PPESK), on aramid fiberurface was also illustrated by SEM photos.

. Experimental

.1. Materials

Twaron aramid yarn used in this study was received fromkzo Nobel Co. Ltd., Arnhem. The fiber samples were cleaned withcetone at room temperature before proceeding air DBD plasmaurface modification in order to remove the surface oily finish, andhen they were dried in an air oven at 110 ◦C for 3 h. The resin ofhich the wetting behavior on Twaron fiber was observed was

hermoplastic poly(phthalazinone ether sulfone ketone), whichas supplied by Dalian Polymer New Material Co. Ltd., China.

.2. Air DBD plasma treatment

The schematic diagram of the dielectric barrier discharge appa-atus is shown in Fig. 1 and the detailed description about the set-upas reported in previous work [18]. When a high AC voltage with an

utput frequency of 27 kHz was applied continuously, a filamentaryielectric barrier discharge would take place, which was uniformnd stable. Twaron fiber samples were treated by means of goinghrough the DBD plasma region at a constant speed. During thereatment process the system was always exposed to atmospherehrough the air hole of the DBD experiment set-up.

The essential parameters about the DBD apparatus are shownn Table 1. The treatment durations were successively set as 6 s,2 s and 18 s, which was carried out by the fiber entrainment speedeing 1.56 cm/s and the fiber going through the discharge region

wo, four, and six times respectively with every treatment timeasting for 3 s. And it is important to note that after the air DBDlasma treatment the fiber samples kept staying in the DBD set-upor 12 h in order to incorporate more oxygen from the environ-

able 1ssential parameters about the DBD treatment in this study.

Parameters Description

Electrode diameter (material) 4.7 cm (steel)Discharge gap 0.3 cmBarrier thickness (material) 0.1 cm (quartz)Discharge power (power density) 143.5 W (27.6 W/cm3)Discharge atmosphere and pressure Air and at atmosphere pressureTreatment time 0 s (untreated), 6 s, 12 s, 18 s

ce 257 (2011) 4165–4170

mental atmosphere according to the post-plasma oxidation effect[19].

2.3. SEM

Scanning electron microscopy (SEM; QUANTA 200, FEI) wasselected to observe the surface morphologies of Twaron fiber. Andthe wetting behavior of the PPESK resin on the fiber filamentswas also studied by SEM photos; the samples were prepared byimpregnating the filaments with PPESK solution which was madeby dissolving the PPESK resin into N,N-dimethylacetamide (DMAc)solvent, and then drying the fiber/resin samples in an air oven(120 ◦C/1 h, 175 ◦C/3 h) to remove DMAc completely; it is importantto note that the volume fraction of Twaron fiber in every sample wasset to about 60%. The pressure of the chamber for SEM measurementwas less than 60 Pa and the magnification was set at 5000×.

2.4. XPS

The surface chemical composition of Twaron fiber was ana-lyzed by X-ray photoelectron spectroscopy (XPS; ESCALAB 250,Thermo), making use of monochromatic Al K� (h� = 1486.6 eV)X-ray source (15 kV, 250 W) radiation from a dual Al–Mg anode.The measurements were performed at an operating vacuum lowerthan 3.0 × 10−9 mbar. Spectra were acquired at a take-off angle of90◦ relatively to the sample surface. The pass energy and energystep set for elemental quantification were 100 eV and 1 eV, respec-tively, and for C1s peak shape identification purpose the passenergy and energy step were fixed at 20 eV and 0.05 eV, respec-tively. The non-linear least squares fitting (NLLSF) program with aGaussian–Lorentzian production function was used for curve fittingof C1s spectra.

2.5. DCAA

The surface free energy and contact angles of Twaron fiber weremeasured through a dynamic contact angle analysis system (DCAA;DCA-322, Thermo). The fiber sample was cut into about 1 cm inlength and fixed indirectly to a wire hook suspended from themicrobalance of the system. The fiber was immersed into the test-ing liquid media by raising the elevating stage at a constant speed of1 mm/min and then the dynamic contact angles (�) were obtainedschematically by the measurement. There are two equations (Eqs.(1) and (2)) as follows, from which the surface free energy can becalculated:

�l(1 + cos �) = 2√

�ps �p

l + 2√

�ds �d

l (1)

�total = �ps + �d

s (2)

where � is the dynamic contact angle between fiber and testingliquid which is calculated by the computer program, � l is the sur-face tension of the testing liquid, � total stands for total surface freeenergy of the fiber, and �p

s and �ds are the polar component and

the dispersive component of total surface free energy, respectively[20]. In our experiment, water (polar solvent; its surface tensionis 72.3 mN/m) and diiodomethane (non-polar solvent; its surfacetension is 50.8 mN/m) were chosen as testing liquids.

3. Results and discussion

3.1. Surface morphology of Twaron fiber

SEM was used to investigate the surface morphology changes ofTwaron fiber before and after the air DBD plasma treatment. In Fig. 2is shown a comparison of the SEM images of the untreated fiber and

C. Jia et al. / Applied Surface Science 257 (2011) 4165–4170 4167

F e: (a) 0 s (untreated); (b) plasma treated for 6 s; (c) plasma treated for 12 s; (d) plasmat

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Table 2XPS surface element analysis of Twaron fiber before and after treatment.

Samples Chemical composition [at.%] Atomic ratio

C O N O/C N/C

0 s (untreated) 78.9 14.0 7.1 0.177 0.090

ig. 2. SEM photographs of the untreated and air DBD plasma treated fiber surfacreated for 18 s.

he fiber samples after the plasma treatment for 6 s, 12 s and 18 st 27.6 W/cm3. It can be seen that after 6 s treatment (Fig. 2b) theurface of the fiber is uneven and clearly different from that of thentreated one (Fig. 2a), which is clean and smooth. When the fiber isreated for 12 s by the air DBD plasma (Fig. 2c), the irregular surfaceith apparent bulges and ruts can be observed. However, when the

reatment time increases further to 18 s (Fig. 2d), it is surprising thathere is obvious damage present on the fiber involving the surfaceeeling off, which maybe implies that the bulk is affected by the

ong time plasma treatment.The results show that surface roughness of Twaron fiber

ncreases with increasing plasma treatment time. The changesf Twaron fiber surface features before and after the treatmentre mainly caused by the etching effects and oxidative reactionsnduced by the plasma processing. The results also show that there

ay be an optimum treatment time of the air DBD plasma for theodification of Twaron fiber surface physical properties.

.2. Surface chemical composition of Twaron fiber

XPS technique was used to analyze the surface chemical compo-ition of Twaron fiber. The results of XPS analysis of the untreated

nd plasma-treated fiber samples are given in Table 2. It can beeen that the surface chemical composition of Twaron fiber expe-iences little change after the air DBD plasma treatment for 6 s;he slight decrease of oxygen (O) concentration and the ratio ofxygen to carbon atoms (O/C) may be due to the removal of the

Plasma treated for 6 s 79.3 13.5 7.2 0.170 0.091Plasma treated for 12 s 75.5 17.6 6.9 0.233 0.091Plasma treated for 18 s 83.1 12.6 4.3 0.152 0.052

small amount of residual oily finish arriving from the commercialfiber surface by plasma etching effects [19]. After the plasma treat-ment time increases to 12 s, the O concentration increases evidentlyfrom 13.5% to 17.6% and the O/C increases from 0.170 to 0.233;the nitrogen (N) concentration and the ratio of nitrogen to car-bon atoms (N/C) have not shown obvious change. However, whenthe treatment time increases from 12 s to 18 s, it is observed thatthe C concentration increases and O and N concentrations decreasesharply with the O/C from 0.233 to 0.152 and N/C from 0.091 to0.052.

The changes of fiber surface chemical composition show that asuitable processing time (12 s in this study) of air DBD plasma canintroduce much oxygen onto aramid fiber surface and increase the

ratio of oxygen to carbon atoms, the shorter treatment time (6 s inthis study) does not have significant influence on the fiber surfacechemical composition, and a long treatment time (18 s in this study)might cause the decreases of oxygen and nitrogen concentrations,which can be explained by the mechanism that surface modifica-

4168 C. Jia et al. / Applied Surface Science 257 (2011) 4165–4170

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ig. 3. C1s spectra of the untreated and air DBD plasma treated fiber surface: (a) 0 s8 s.

ion is dominant at beginning and then is overwhelmed by surfacetching at a later stage of the process [21]. These observations areomplemented by the change of the XPS C1s spectrum as a func-ion of treatment time, as shown in Fig. 3. The C1s spectrum of theber samples can be fitted to four peaks with binding energies ofbout 284.6 eV (C–C), 286.0 eV (C–O), 287.8 eV (C O) and 289.0 eVO C–O), and the concentrations of these carbon-containing func-ional groups on aramid fiber surface are given in Table 3 which arealculated from the relevant peak areas in the C1s spectrum.

The peak intensities and peak areas of C1s spectrum experienceistinct variation from the untreated to the plasma treated samples.ompared to the untreated fiber (Fig. 3a), the C–C concentrationecreases sharply from 74.1% to 68.5%, while the concentrations ofxygen functional groups such as C–O, C O and O C–O increaserom 13.3%, 6.0% and 6.6% to 17.8%, 6.8% and 6.9%, respectively,fter the air DBD plasma treatment for 12 s (Fig. 3c). In addition,t can be found that the contributions of C–O and O C–O declinefter the plasma treatment for 6 s (Fig. 3b) owing to the removal

f the residual surface oily finish and the contributions of oxygen-ontaining groups obviously decrease after the plasma treatmentor 18 s (Fig. 3d) caused by the plasma etching effects, which agreesell with the discussion above about the variations of surface com-

able 3orrelative functional groups of Twaron fiber surface.

Samples Concentrations of correlative functionalgroups (%)

C–C C–O C O O C–O

0 s (untreated) 74.1 13.3 6.0 6.6Plasma treated for 6 s 77.5 9.3 8.5 4.7Plasma treated for 12 s 68.5 17.8 6.8 6.9Plasma treated for 18 s 89.3 5.3 3.6 1.8

eated); (b) plasma treated for 6 s; (c) plasma treated for 12 s; (d) plasma treated for

position. The results indicate that some new oxygen-containingpolar groups (C–O, C O and O C–O) can be introduced to Twaronfiber surface by the ions, electrons and UV radiation [10] after the12 s air DBD plasma treatment, which could enhance the adhesionproperties of aramid fiber via improving the fiber surface chemicalinertness and increasing the fiber surface free energy [21].

3.3. Surface wettability of Twaron fiber

Surface free energy of aramid fiber, which can be derived fromthe dynamic contact angle measurements, is used to study theeffects of different air DBD plasma treatment durations on thefiber surface wettability. The advancing contact angles and surfacefree energy, consisting of polar and dispersive components, of theuntreated and plasma treated fiber samples are given in Table 4.

The advancing contact angles (�) of water decline by degreesfrom 64.3◦ for the untreated sample to 42.3◦ for the sample aftera 27.6 W/cm3 and 12 s air DBD plasma treatment, and the polarcomponent (�p) of surface free energy and the total surface freeenergy (� total) increase gradually from 11.5 mJ/m2 and 50.6 mJ/m2

to 24.4 mJ/m2 and 62.6 mJ/m2, respectively. As for the advancingcontact angles of diiodomethane and the dispersive component(�d) of surface free energy, the changes are not distinct. When thefiber is treated for 18 s by the air DBD plasma, it can be seen thatthe total surface free energy increases further to 66.6 mJ/m2. Thiscould be explained by the fact that the air DBD plasma increasesthe surface roughness of Twaron fiber as illustrated by SEM pho-tos and introduces some new polar groups onto the fiber surface as

shown by XPS measurements, together improving the fiber surfacewettability. After the 18 s air DBD plasma treatment, Twaron fibersurface morphology is changed to a great extent (Fig. 2d), whichmight bring the fiber higher surface free energy but implies thatthe bulk properties may be affected.

C. Jia et al. / Applied Surface Science 257 (2011) 4165–4170 4169

Table 4Advancing contact angles and surface free energy of Twaron fiber before and after treatment.

Samples Contact angle (�) ± SDa (◦) Surface free energy (mJ/m2)

Water Diiodomethane �p �d � total = �p + �d

0 s (untreated) 64.3(2.5) 41.0(2.0) 11.5 39.1 50.6

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Plasma treated for 6 s 48.6(2.4) 47.4(1.8)Plasma treated for 12 s 42.3(0.4) 42.7(2.7)Plasma treated for 18 s 35.9(2.7) 41.1(2.3)

a Standard deviation.

.4. The wetting behavior of PPESK resin on Twaron fiber

As for the purpose of this paper, the modification of air DBDlasma on Twaron fiber surface is to make the treated fiber haveractical application as reinforcement agents in resin matrix com-osites. We all know that the fiber/matrix interface governs theverall performance of composites, and from a practical point ofiew, good wetting behavior of resin on fiber surface plays anmportant role in the formation of interface with excellent perfor-

ance. In this paper, the influence of air DBD plasma treatmentimes on the wetting behavior of a kind of thermoplastic resin,oly(phthalazinone ether sulfone ketone), on Twaron fiber was alsotudied by SEM measurements. The surface morphologies of the

ntreated and plasma treated Twaron filaments impregnated withPESK resin are shown in Fig. 4.

The four samples all show that there is more or less PPESKesin adhering to Twaron fiber surface before and after the air DBDlasma treatment. For the untreated sample (Fig. 4a), only a lit-

ig. 4. The wetting behavior of PPESK resin on Twaron fiber surface: (a) 0 s (untreated); (

21.8 35.7 57.524.4 38.2 62.627.5 39.1 66.6

tle resin is on the fiber surface and some smooth fiber surface isvisible. After the fiber is treated for 6 s (Fig. 4b), there is a littlemore PPESK resin being observed and we can also see some undu-lations on the sample. When the fiber is treated for 12 s (Fig. 4c),the fiber is covered with more resin evenly and it can be foundthat the resin is present among the fiber filaments as well. Afterthe treatment time lasts for 18 s (Fig. 4d), there is a mass of PPESKresin on the fiber surface, however, the resin has a nonuniformdistribution.

The results indicate that the PPESK resin could show a bet-ter wetting behavior on Twaron fiber surface when the fiber istreated for 12 s by the air DBD plasma at 27.6 W/cm3, which agreeswith the results of SEM, XPS and DCAA measurements shown in

above sections, showing that suitable treatment of the plasma canincrease the surface roughness of Twaron fiber and improve thesurface chemical inertness, enhancing the fiber surface wettabil-ity and leading to good interfacial adhesion between the fiber andmatrix.

b) plasma treated for 6 s; (c) plasma treated for 12 s; (d) plasma treated for 18 s.

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. Conclusions

The experimental results presented in this study show that their DBD plasma at atmospheric pressure can effectively modifywaron fiber surface adhesion properties, the plasma treatmentime has great influence on fiber surface physical features andhemical compositions and there might be an optimum treatmentondition existing for the fiber modification. The results indicatehat after a 12 s, 27.6 W/cm3 plasma treatment, the aramid fiberurface roughness is evidently improved as illustrated by SEM,he concentrations of oxygen and oxygen-containing functionalroups on the fiber surface increase significantly as determinedith XPS, and the fiber surface wettability derived from DCAA is

reatly enhanced. The improvements of the physical and chemicalroperties induced by the air DBD plasma could account for theetter wetting behavior of PPESK resin on plasma-treated Twaronramid fiber.

cknowledgements

This work was funded by the National Natural Science Foun-ation of China (No. 50743012), National Defense 11th 5-yearrogram Foundational Research Program (No. A3520060215), andiaoning Province Innovation Organization (No. LT2010083). Inddition, the authors are indebted to Mr. Xinglin Li for XPS analysisnd Dr. Litao Shi for his skillful experimental assistance.

eferences

[1] J.S. Lin, Effect of surface modification by bromination and metalation on Kevlarfibre-epoxy adhesion, Eur. Polym. J. 38 (2002) 79–86.

[2] L. Liu, Y.D. Huang, Z.Q. Zhang, Z.X. Jiang, L.N. Wu, Ultrasonic treatment of aramidfiber surface and its effect on the interface of aramid/epoxy composites, Appl.Surf. Sci. 254 (2008) 2594–2599.

[3] P.J. de Lange, E. Mäder, K. Mai, R.J. Young, I. Ahmad, Characterization andmicromechanical testing of the interphase of aramid-reinforced epoxy com-posites, Compos. Part A 32 (2001) 331–342.

[4] S.P. Lee, K.S. Chian, C.Y. Yue, H.C. Looi, Effects of bromination and hydrolysistreatments on the morphology and tensile properties of Kevlar-29 fibres, J.Mater. Sci. Lett. 13 (1994) 305–309.

[

[

ce 257 (2011) 4165–4170

[5] S.J. Park, M.K. Seo, T.J. Ma, D.R. Lee, Effect of chemical treatment of Kevlar fiberson mechanical interfacial properties of composites, J. Colloid Interface Sci. 252(2002) 249–255.

[6] H. Watanabe, M. Furukawa, T. Takata, M. Yamamoto, Surface improve-ments of aramid fibers by physical treatments, Macromol. Symp. 159 (2000)131–141.

[7] T.K. Lin, S.J. Wu, J.G. Lai, S.S. Shyu, The Effect of chemical treatment on reinforce-ment/matrix interaction in Kevlar-fiber/bismaleimide composites, Compos.Sci. Technol. 60 (2000) 1873–1878.

[8] P.A. Tarantili, A.G. Andreopoulos, Mechanical properties of epoxies rein-forced with chloride-treated aramid fibers, J. Appl. Polym. Sci. 65 (1997)267–276.

[9] R.J. Day, K.D. Hewson, P.A. Lovell, Surface modification and its effect on theinterfacial properties of model aramid-fibre/epoxy composites, Compos. Sci.Technol. 62 (2002) 153–166.

10] S. Mukhopadhyay, R. Fangueiro, Physical modification of natural fibers andthermoplastic films for composites—a review, J. Thermoplast. Compos. Mater.22 (2009) 135–162.

11] Y. Katoh, T. Nozawa, L.L. Snead, T. Hinoki, Effect of neutron irradiation on tensileproperties of unidirectional silicon carbide composites, J. Nucl. Mater. 367–370(2007) 774–779.

12] R.Z. Li, L. Ye, Y.W. Mai, Application of plasma technologies in fibre-reinforcedpolymer composites: a review of recent developments, Compos. Part A 28A(1997) 73–86.

13] N. De Geyter, R. Morent, C. Leys, Surface modification of a polyester non-wovenwith a dielectric barrier discharge in air at medium pressure, Surf. Coat. Technol.201 (2006) 2460–2466.

14] K.L. Wang, W.C. Wang, D.Z. Yang, Y. Huo, D.Z. Wang, Surface modification ofpolypropylene non-woven fabric using atmospheric nitrogen dielectric barrierdischarge plasma, Appl. Surf. Sci. 256 (2010) 6859–6864.

15] G. Borcia, C.A. Anderson, N.M.D. Brown, Surface treatment of natural and syn-thetic textiles using a dielectric barrier discharge, Surf. Coat. Technol. 201(2006) 3074–3081.

16] G. Borcia, C.A. Anderson, N.M.D. Brown, Using a nitrogen dielectric barrier dis-charge for surface treatment, Plasma Sources Sci. Technol. 14 (2005) 259–267.

17] M. Xi, Y.L. Li, S.Y. Shang, D.H. Li, Y.X. Yin, X.Y. Dai, Surface modification of aramidfiber by air DBD plasma at atmospheric pressure with continuous on-line pro-cessing, Surf. Coat. Technol. 202 (2008) 6029–6033.

18] C.X. Jia, P. Chen, B. Li, Q. Wang, C. Lu, Q. Yu, Effect of Twaron fiber surfacetreatment by air dielectric barrier discharge plasma on the interfacial adhesionin fiber reinforced composites, Surf. Coat. Technol. 204 (2010) 3668–3675.

19] L. Tusek, M. Nitschke, C. Werner, K.S. Kleinschek, V. Ribitsch, Surface character-isation of NH3 plasma treated polyamide 6 foils, Colloids Surf. A: Physicochem.

Eng. Aspects 195 (2001) 81–95.

20] P. Chen, C. Lu, Q. Yu, Y. Gao, J.F. Li, X.L. Li, Influence of fiber wettability on theinterfacial adhesion of continuous fiber-reinforced PPESK composite, J. Appl.Polym. Sci. 102 (2006) 2544–2551.

21] C.-M. Chan, T.-M. Ko, H. Hiraoka, Polymer surface modification by plasmas andphotons, Surf. Sci. Rep. 24 (1996) 1–54.