Surface & Coatings Technology 228 (2013) S607–S610

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Surface & Coatings Technology

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Effect of atmospheric pressure plasma treatment on wettability and dryability ofsynthetic textile fibres

C.W. Kan ⁎, C.W.M. YuenInstitute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

⁎ Corresponding author. Tel.: +852 2766 6531; fax:E-mail address: tccwk@inet.polyu.edu.hk (C.W. Kan)

0257-8972/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.surfcoat.2011.10.061

a b s t r a c t

a r t i c l e i n f o

Available online 3 December 2011

Keywords:WettabilityDryabilityPlasmaPolyesterPolyamide

Polyester and polyamide fabrics were treated with plasma under atmospheric pressure for different dura-tions, 3, 5 and 7 s. The wettability of polyester and polyamide fabrics, measured in terms of contact angleand longitudinal wicking, was improved after plasma treatment. The oxygen content of the fabrics wasincreased indicating that hydrophilic groups had been introduced into the fabric leading to the improvedwettability. However, there was no obvious improvement in dryability because bulk properties of the fibresdid not change. Moreover, with the help of plasma treatment, water repellency of the fabrics was greatlyimproved when water repellency finishing agent was added.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Wettability is not only an important property for textiles during pro-cesses such as dyeing and finishing, but it also provides comfort when ahuman body wears a garment. In addition, wettability can be valuablefor characterizing fibre surfaces, liquid transport, interaction of fibreswith liquids and surfactants, and their adhesion with polymers. Otherthan wettability, dryability is also an important property for comfort.In order to keep the wearer dry and comfortable during vigorous activ-ities, garments should have the ability to transport the perspirationfrom the body, i.e. from innerwear to outerwear. Plasma treatment af-fects surface properties of textile materials without altering their bulkproperties much [1–6]; wettability and dryability of textile materialsare closely related to their surface properties. The effect of plasma treat-ment on these properties was studied and results are reported in thispaper.

2. Experimental

2.1. Materials

100% raw polyester and polyamide woven fabrics were used andtheir specifications were shown in Table 1.

2.2. Atmospheric pressure plasma (APP) treatment

APP treatment of synthetic fabrics was carried out by an atmo-spheric pressure plasma jet (APPJ) apparatus (Surfx Technologies,

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US). The APPJ produced a stable discharge at atmospheric pressurewith radio frequency of 13.56 MHz. The APP treatment was carriedout using a rectangular jet nozzle mounted vertically above the fabricand the APP treatment setup was shown in Fig. 1. The distance be-tween the nozzle and the fabric surface was set at 6 mm and treat-ment time was 3, 5 and 7 s. Helium with a flow rate of 10 l/min andoxygen with a flow rate of 0.3 l/min were used as carrier and reactivegases, respectively. After APP treatment, the fabrics were conditionedat 21±1 °C with a relative humidity of 65±2% for 24 h before furtherprocessing.

2.3. Contact angle measurement

A Tantec Contact Angle Metre was used for measuring the contactangle. A water drop with droplet size of 1 μl was dropped on the fabricsurface. Image of the water droplet was projected and magnified to thecontact anglemicrometre. The contact angle wasmeasured immediatelyafter the droplet was placed on the fabric surface.

2.4. Longitudinal wicking test

Longitudinal wicking was used to study the water uptake rate. A1 cm×15 cm fabric strip was suspended vertically with its 1 cm ofits lower edge immersed in a reservoir of distilled water. No pressurewas applied to enhance the flow of water since that affects the truewicking process. The rise of the water was then monitored. It was as-sumed that the water uptake rate was consistent in front, back andinterior part of the fabric strip. In order to indicate the water riseclearly, a water-pen was used to mark the graduated scale on the fab-ric surface. The time for water uptake was recorded at 5 cm and10 cm intervals, when the marking started to blur.

Table 1Fabric specifications.

Specification Polyester Polyamide

Yarn count Warp (tex) 10 20Weft (tex) 10 25

Fabric density Warp (ends/cm) 15 55Weft (picks/cm) 17 35

Fabric weight (g/cm2) 0.02 0.8

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2.5. Dryability

Dry fabric sample (2 g) was first weighed and was then wettedwith deionised water. A 100% increase in the original weight was ob-served on wetting. The wetted fabric samples were then put understandard conditions of 21±1 °C temperature and relatively humidityof 65±2%. Weight of fabric samples was measured at intervals of5 min for 180 min.

2.6. Water repellent treatment and evaluation

A commercial water repellent finishing agent was used as receivedfor treating the fabrics for comparison purposes. 20 g/l of finishingagent was prepared and was padded onto the fabric using a paddingmachine (Labortex Co. Ltd., Taiwan) at a pressure of 2.6 kg/m2 andpadding speed of 2.5 rpm for a wet pick-up of 80%. The padded fabricswere dried in an oven at 80 °C for 2 min and then cured at 170 °C for30 s. The treated fabric was conditioned under standard condition of65±2% relatively humidity and 21±1 °C for at least 24 h prior to fur-ther evaluation by AATCC Test Method 22-2005 (water repellency:spray test).

2.7. Durability test

Durability of fabric samples was evaluated by subjecting them tovarying number of washing cycles, 1, 5 and 10. One washing cyclemeans one washing process followed by one tumble drying process.The washing process was performed in normal regular mode whilethe drying mode was tumble drying at 60 °C. The fabric sampleswere washed at 49 °C with 100 g detergent and the time requiredfor the whole washing cycle was 30 min, and the drying time was25 min.

2.8. X-ray photoelectron spectroscopy (XPS)

Chemical composition of the surface of fabric samples was ana-lysed by XPS. The XPS spectra were obtained from the Perkin ElmerPHI 5600 combined spectrophotometer with an AlKα X-rays emitterbeing operated at 1486.6 eV, 350 W and working pressure of7.3×10−9 Torr. The peak positions were corrected for charging inrelation to hydrocarbon intensities of C1s (285 eV), O1s (533 eV) andN1s (400 eV).

Fig. 1. Schematic diagram of APP treatment.

3. Results and discussion

3.1. Contact angle measurement

Table 2 shows contact angles of polyester and polyamide fabricswith different APP treatments. Untreated polyester fabric has an aver-age contact angle of 87.5° because of the hydrophobic nature andtight structure of the polyester fabric used in this study. On theother hand, the water droplet is absorbed into the fabric immediatelywhen the fabric was treated with plasma using oxygen. It is believedthat fabric treated with oxygen plasma has increased number of polargroups on its surface, like carbonyl group, hydroxyl group and car-boxyl group, which are hydrophilic in nature and lead to substantialreduction in surface tension of APP treated polyester fabric [7, 8].Untreated polyamide fabric has an average contact angle of 86º butthe water droplet is absorbed into the fabric immediately and a zerocontact angle was observed after APP treatment. Similar to the APPtreatment of polyester, oxygen plasma may induce hydroxyl and car-boxylic acid functional groups which are hydrophilic in nature onfibre surface and improve wettability [7, 8]. Based on the results ofcontact angle measurement, it can be concluded that APP treatmentwith oxygen reduces surface tension of polyester and polyamide fab-rics which facilitates the subsequent textile wet processing such asdyeing. However, the contact angle after 3, 5 and 7 s plasma treat-ment achieved the same result. Therefore, the contact angle maynot be a good measure to distinguish the effectiveness of APP treat-ment with oxygen under different treatment durations.

3.2. Longitudinal wicking test

Fig. 2(a) and (b) illustrates wicking properties of APP treated poly-amide and polyester fabrics, respectively. In the case of polyamidefabric, it was observed that the wicking rate was improved whenpolyamide fabrics were treated with oxygen plasma for different du-rations. It is shown that the wicking improvement is directly propor-tional to the treatment duration. With the longest treatment time, i.e.7 s, improvement in the wicking rate was the highest. The reasons forthis improvement could be the introduction of hydrophilic functionalgroups onto the fabric surface and it may also be attributed to the ox-ygen plasma etching effect on the fibre surface resulting in increase insurface area of the fibre which enhances the capillary effect to trans-port the liquid [7, 8]. Therefore, the water uptake rate is faster withincreased APP treatment time. In addition, it is also found that thewicking rate was relatively constant when the water level reachedthe 10 cm interval.

In the case of polyester fabric, there was a significant improve-ment in the wicking rate after APP treatment. The untreated polyesterfabric took 40 s for water uptaking and it still could reach only the5 cm interval. However, that was not the case for plasma treatedpolyester fabric, as shown in Fig. 2(b). After polyester fabrics are trea-ted with oxygen plasma, about 20 s required for transporting the liq-uid from the waterbath to the 5 cm interval of the fabric strip. Themain reason was the introduction of hydrophilic functional groupsonto the fabric surface and it may also be attributed to the oxygenplasma etching effect on the fibre surface which increases surfacearea of the fibre and enhances the capillary effect to transport theliquid [7, 8]. Moreover, it was observed that there was only slight im-provement when APP treatment time was increased from 3 to 5 s.

Table 2Results of contact angle.

Sample Untreated 3 secondAPP-treated

5 secondAPP-treated

7 secondAPP-treated

Polyamide 86° 0° 0° 0°Polyester 87.5° 0° 0° 0°

Fig. 2. Wicking property of (a) polyamide fabrics and (b) polyester fabrics.

Fig. 3. Dryability of polyamide and polyester fabric samples.

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This may be owing to the swelling of fibres caused by absorption ofliquid which reduces the capillary space among fibres and, therefore,limits the water uptake rate within the fabric strip. On the other hand,due to the limited length of the fabric strip, the capillary flow and dif-fusion of liquid is fast at the interval of 10 cm also resulting in no dis-tinct improvement when APP treatment time is increased from 3 to5 s.

3.3. Dryability

Dryability of fabric samples was interpreted by calculating theweight loss of the wet fabric samples of fabric treated with APP for dif-ferent durations. Fig. 3 shows dryability of polyamide and polyester fab-rics treatedwith APP for different durations. For individual fabric, it wasobserved that there were no significant differences between dryingrates of untreated and oxygen plasma-treated fabrics and thereforethe curves are overlappedwith eachother. Experimental results suggestthat oxygen plasma treatment can enhancewettability of fabrics but notdryability. The reason is that as the oxygen plasma treatment introduceshydrophilic functional groups to the fibre surface only but no significant

Table 3Water repellency property.

Samplea I II IIIWashing cycle 0 1 5 10 0 1 5 10 0Polyesterb 70 70 70 70 0 0 0 0 100 1Polyamideb 70 70 70 70 0 0 0 0 100 1

a Fabric code: I — untreated fabric; II — fabric treated with 3 second APP; III — fabric treachemical finishing agent only; and V — fabric treated with finishing agent and then treated

b Water repellency rating: 100 — no sticking or wetting of upper surface; 90 — slight rand70 — partial wetting of whole of upper surface; 50 — complete wetting of whole of upper s

alteration occurs in the bulk portion, i.e. no change in the amorphousand crystalline regions of the fibre. Moisture adsorption dependsmuch on the arrangement of amorphous and crystalline regions insidethe fibre. If there is no significant change in these regions, no obviouseffect will be introduced to the overall dryability of the fabric. Whenthe two different types of fibres w compared, it was found that polyes-ter fabric samples had a higher degree of weight loss compared to poly-amide fabric samples since polyamide fibre contains more polar groupssuch as \NH2, which are hydrophilic in nature, than polyester. Thispolar group holds more water molecules in the fibre through varioustypes of physical attraction. Hence, water stays more firmly in thefibre, resulting in lesser weight loss.

3.4. Water repellency

Water repellent properties of different polyamide and polyesterfabrics are shown in Table 3.

Table 3 shows that both polyester and polyamide fabrics wereaffected similarly by various treatments. APP treated fabrics (SampleII) did not have the same water repellency properties as untreatedfabrics (Sample I). It is true that the oxygen plasma can enhancewettability of the fabrics by imposing oxygen content to the fabricsurface. Therefore, no water repellency property can be obtained. Be-sides, untreated fabric (Sample I) did not have good water repellencysince the water droplets can penetrate through the pores in the fabricstructure, resulting in poor water repellency. Fabric samples treatedwith oxygen plasma, followed by treating with finishing agent (Sam-ple III), as well as fabric sample treated with finishing agent only(Sample IV), generally had desirable water repellent properties.Sample III indicated better results than Sample IV. The reason maybe the etching action on the fabric surface during the oxygen plasmatreatment leading to higher fibre surface area [8]. As a result, largerquantities of finishing agents will be absorbed and available for crosslink-ing with the fibre during the curing process. Consequently, the samplehad higher water repellency property which is desirable. It is interestingto note that if the fabric is treated first with finishing agent and is thentreated with plasma (Sample V), the situation is totally different. No

IV V1 5 10 0 1 5 10 0 1 5 10

00 100 100 90 90 90 90 80 80 80 8000 100 100 90 90 90 90 80 80 80 80

ted with 3 second APP and then treated with finishing agent; IV — fabric treated withwith 3 second APP.om sticking or wetting of upper surface; 80 — wetting of upper surface at spray point;urface; and 0 — complete wetting of whole upper and lower surfaces.

Table 4Elemental composition ratio of fabric surface determined by XPS.

Samples Untreatedpolyester

APP treatedpolyester

Untreatedpolyamide

APP treatedpolyamide

O/C ratio 0.30 0.60 0.20 0.42N/C ratio – – 0.15 0.17

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desirable water repellency property can be obtained in that case becausethe plasma etching process results in peeling off offinishing agent and ex-posing the hydrophilic fabric surface. Fabrics treated with the finishingagent can obtain the desirable water repellency properties but not as du-rable as when the fabric is first APP treated and is then treated with thefinishing agent.

When the effect of washing cycle was taken into consideration, itwas observed that the number of washing cycles did not have any sig-nificant effect on water repellency of the differently treated fabrics.The untreated sample, i.e. Sample I, did not experience any improve-ment of water repellency after the washing process. Fabric treatedwith APP only, i.e. Sample II, retained the plasma effect even after10 washing cycles and all fabric samples were completely wetted.The complete wetting indicates a permanent hydrophilicity wasintroduced to the fibre surface which was originally hydrophobic innature. Fabric samples treated with APP and then treated with finish-ing agent, i.e. Sample III (only treated with finishing agent, withoutAPP treatment) and the water repellency was retained even after 10washing cycles. From the results of Sample III, it can be concludedthat the APP treatment enhances the adhesion of finishing agent tothe fibre surface. In addition, the finishing agent remained coatedwell on the fibre surface after 10 washing cycles. When Sample Vwas taken into consideration, it revealed that water repellency wasreduced when compared with Samples III and IV but it was still betterthan untreated samples. Moreover, the washing process did not showany significant effect on Sample V.

3.5. XPS analysis

Table 4 shows the XPS elemental composition data for differentpolyester and polyamide fabric surfaces, and the evolution of oxygento carbon ratio (O/C ratio) is also presented. The change in the O/Cratio with respect to the untreated polyester fabric sample was usedfor studying the surface modification due to the APP treatment. Itwas observed that the O/C ratio was increased after APP treatment,indicating that the APP treated polyester fibre surface had higher ox-ygen content than the untreated polyester fibre surface. This wasmainly due to the fact that a large number of oxygen polar functional

groups were introduced into the polyester fabric surface during APPtreatment [9, 10]. Hence, the amount of moisture that adhered onthe hydrophilic polyester fabric surface was increased tremendouslyafter the APP treatment.

Oxygen plasma treatment is known to be effective in modifyingfibre morphology and improving hydrophilic properties by inducingpolar functional groups, such as \CO\, \C_O, and \COOH, on thefibre surface [9, 10]. In this paper, XPS analysis is used to provide in-formation about changes in the chemical composition and chemicalstate of polyamide by the plasma treatment. The O/C and N/C atomicratios for untreated and oxygen plasma treated samples are statedin Table 4. The results show that after the APP treatment, the O/Cand N/C ratios increase, suggesting that oxidation had occurred andoxygen atoms are incorporated into the surface of polyamide fabric.

4. Conclusions

It is believed that functional groups like carbonyl group, hydroxylgroup and carboxyl group were formed after APP treatment with ox-ygen, leading to hydrophilic surface of polyamide and polyester fab-rics. Apart from formation of polar groups, the plasma etching effectenhancing the capillary flow was another reason causing improvedwettability. On the other hand, the APP treatment with oxygen didnot show any significant improvement in dryability, compared withuntreated fabrics. With the use of XPS analysis, it was generally ob-served that the oxygen plasma treatment imparted oxygen contentto the fabric surface. APP treatment using oxygen together with treat-ing of finishing agent resulted in desirable water repellency propertywith good durability that lasted even after 10 washing cycles.

Acknowledgments

Authors would like to thank the financial support from The HongKong Polytechnic University for this work.

References

[1] J. Yip, K. Chan, K.M. Sin, K.S. Lau, Color. Technol. 118 (2002) 26.[2] K.K. Wong, X.M. Tao, C.W.M. Yuen, K.W. Yeung, Text. Res. J. 71 (1) (2001) 49.[3] K.K. Wong, X.M. Tao, C.W.M. Yuen, K.W. Yeung, Text. Res. J. 69 (11) (1999) 846.[4] C.W. Kan, K. Chan, C.W.M. Yuen, M.H. Miao, Text. Res. J. 69 (6) (1999) 407.[5] I. Holme, Int. Dyer 188 (5) (2003) 7.[6] T. Wakida, H. Kawamura, S. Jincherl, T. Takagishi, Sen-I Gakkaishi 43 (1987) 384.[7] R. Morent, N. De Geyter, J. Verschuren, K. De Clerck, P. Kiekens, C. Leys, Surf. Coat.

Technol. 202 (2008) 3427.[8] C.X. Wang, Y.P. Qiu, Surf. Coat. Technol. 201 (2007) 6273.[9] R.R. Deshmukh, N.V. Bhat, Mater. Res. Innov. 7 (2003) 283.

[10] L.H. Lin, C.C. Wang, C.W. Chen, K.M. Chen, Surf. Coat. Technol. 201 (2006) 674.