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A study on washing resistance of pp-HMDSO films deposited on wool fabrics for anti-pilling purposes
Surface & Coatings Technology 224 (2013) 109–113
Contents lists available at SciVerse ScienceDirect
Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat
A study on washing resistance of pp-HMDSO films deposited on wool fabrics for anti-pilling purposes A. Montarsolo a,⁎, R. Mossotti a, R. Innocenti a, E. Vassallo b a b
C.N.R. National Research Council -ISMAC-Institute for Macromolecular Studies, Corso G. Pella 16, 13900 Biella, Italy C.N.R. National Research Council -IFP-Institute of Plasma Physics, via R. Cozzi 53, 20125 Milano, Italy
a r t i c l e
i n f o
Article history: Received 21 September 2012 Accepted in revised form 9 March 2013 Available online 17 March 2013 Keywords: PECVD HMDSO Wool fabrics Adhesion Washing resistance Pilling
a b s t r a c t In this work plasma polymerized coatings for anti-pilling purposes were deposited on knitted wool fabrics by means of a capacitively coupled RF discharge reactor using hexamethyldisiloxane as precursor. Their resistance to dry and wet cleaning was investigated and compared to that of a wet chemically deposited coating. Different gas mixtures and pre-treatment steps were tested to adjust the plasma process and to improve the film adhesion. An evaluation of the silica-like coatings behaviour to the washing stresses was performed by means of Fourier transform infrared and x-ray photoelectron spectroscopy. Anti-pilling performances of untreated, plasmatreated, and wet chemically treated wool fabrics were assessed. © 2013 Elsevier B.V. All rights reserved.
1. Introduction The textile industry is looking for applications which lead to products with additional properties in a cost-effective and eco-sustainable way. In this respect we have studied in a previous work [1], a method to solve an important issue in the textile field that is the fabrics tendency to pill. Abrasion from normal wear and cleaning causes the fibres to unravel and the loose ends to ball up on the fabric surface. This complex phenomenon is attributable to several factors comprising fibre, yarn and fabrics characteristics. To our knowledge no group of specific anti-pilling products exists and textile auxiliary producers mostly recommend chemical products that are primarily used for other purposes for anti-pilling finishes [2]. Moreover these products are usually applied on textile substrates in an aqueous bath or in foulard, using great amount of heated water and the production of polluting liquid effluents. In our study silicon containing thin films (Si:Ox:Cy:Hz) were deposited on knitted wool fabrics, by plasma-enhanced chemical vapor deposition (PECVD) in a low pressure plasma equipment, using hexamethyldisiloxane (HMDSO) as monomer and argon and oxygen as feed gases. The plasma treated samples compared with chemically treated and untreated samples, exhibited an improvement of about two grades as regards the standard pilling assessment. The results showed that this kind of treatments could represent an efficient technique to reduce pill formation on knitted wool fabrics and could also allow significant reductions of
⁎ Corresponding author. Tel.: +39 0158493043; fax: +39 0158408387. E-mail address: [email protected] (A. Montarsolo). 0257-8972/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.surfcoat.2013.03.007
water, energy, and chemical consumption. Because of the poor resistance of these coatings to the washing stress, further investigations were required for an industrial application of the method. In general, due to the numerous ways a plasma interacts with a polymer surface, the gas type and plasma conditions must be adjusted to the polymer type in order to achieve a good adhesion of the deposited coatings. Glow discharges of non-polymerizing gases like argon or oxygen are usually used to prepare the substrate surface prior to the following deposition step. In particular argon is a commonly used inert gas for the pre-treatment of polymer surfaces and an Ar plasma can be applied to clean the surface before reactive gases are applied [3] to remove low molecular weight materials [3] and to improve the adhesive characteristics of polymers [4]. Oxygen and oxygen-containing plasma can at the same time etch the polymer surface and form oxygenated functional groups. The balance of these two processes depends on the operation parameters [3]. O2 plasma pre-treatment can be carried out to roughen the surface resulting in an enhanced contact area at the beginning film growth [5]. Moreover, oxygen plays an important role in the deposition of the silicon-containing monomer in that the dilution of HMDSO with oxygen allows to increase the inorganic character of the coating [6]. The aim of this work was to study various plasma process operating conditions in order to guarantee durability of the anti-pilling coating on the wool surface to washing stress and dry cleaning. In particular, the number of plasma process steps and operational parameters including gas type were adjusted to improve adhesion of the thin film deposited. Morphologies of fibre surfaces were investigated using scanning electron microscopy (SEM). The pilling behaviour of untreated, plasma treated and wet chemically treated samples was assessed with modified
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A. Montarsolo et al. / Surface & Coatings Technology 224 (2013) 109–113
Martindale abrasion testing method and washing resistance of plasmadeposited coatings and wet chemically-treated samples was evaluated by means of Fourier transform infrared (FT-IR) and x-ray photoelectron spectroscopy (XPS).
2. Materials and methods
2.5. Washing test Washing resistance was investigated according to UNI EN ISO 26330. An Electrolux Wascator FOM71MP-Lab washing machine was used. Two 8A wash cycle at 30 ± 3 °C was used, with the total load of 2Kg for 15 min. The washing test was carried out on polymerized samples and wet chemically treated sample.
2.1. Materials 2.6. Dry cleaning The experiments were carried out on 100% knitted wool fabrics (292 g/m 2) and the dimensions of samples were 30 cm × 30 cm. The purities of both argon and oxygen were more than 99.99% (Siad S.p.A., Italy) and HMDSO [(CH3)3-Si-O-Si-(CH3)] monomer was chemical reagent of grade 98% A.R.; (Sigma Aldrich, Germany). Prior to the plasma treatments, the fabrics were previously scoured with petroleum ether (A.R. grade) for 3 h using Soxhlet extraction to remove sizing agents, followed by rinsing with deionized hot (T = 50 °C) and cool (room temperature) water for 1 h. Before and after the treatment, they were transported in a dry box to minimize humidity.
2.2. Plasma treatment
Dry cleaning was performed according to UNI EN ISO 105-X05 using an organic solvent (CCl4) The test was carried out with a Linitest (URAI S.p.A) machinery at room temperature for 30 min. The dry cleaning test was carried out on polymerized samples and wet chemically treated sample.
2.7. Pilling behaviour The determination of the propensity to pilling of knitted was assessed with modified Martindale method. Nu-Martindale Abrasion and Pilling Tester from James H. Heal & Co. Ltd was used. The samples were placed under standard laboratory conditions (65% R.H. and 20 °C) for 24 h before testing. The pilling tests were carried on untreated, plasma treated and wet chemical treated samples.
Plasma treatments were carried out in the lab scale low pressure plasma reactor of the Institute for Macromolecular Studies, National Research Council, Biella, Italy. The discharge was powered by an RF (13.56 MHz) generator coupled to the capacitively-coupled electrodes by a fully tunable matching network. The sample was fixed to a roller below electrodes that was set at 4 rpm of working speed. This configuration allowed a homogeneous plasma deposition on all the substrate surface. In the deposition step (Step 2) the pressure, the treatment time and the discharge power were kept constant at 2 Pa, 5 min, 40 W, respectively. The combination of different gas mixtures and number of steps used are shown in Table 1. The samples 1 and 2 were pre-treated with argon and oxygen plasma, respectively, while in the case of sample 3, the silicon-like film was directly deposited onto substrate. Ar and O2 flux was fixed at 20 sccm while the HMDSO flux was 3 sccm.
Attenuated total reflectance FT-IR (ATR-FT-IR) spectroscopy measurements of untreated, plasma treated, wet chemical treated samples were carried out using an FT-IR Nexus 510 spectrometer (Thermo Nicolet) provided with a ATR accessory (Specac Ltd.) equipped with a Zn Se crystal with a 45° angle of incidence. Furthermore, FT-IR spectra of plasma treated and wet chemical treated samples were acquired after dry cleaning and washing test. Data were collected from 400 cm −1 to 4000 cm −1 wavelength range with 100 scans and a spectral resolution of 4 cm −1.
2.3. Wet chemical anti-pilling treatment
2.9. XPS analysis
Knitted wool fabrics were treated with an aqueous solution (pH adjusted to 5.5 with 2% o.w.f acetic acid) containing 2,5% o.w.f of aminomodified silicone emulsion (CT-80, Bilab, Italy) at 40 °C for 20 min. The material-to-liquor ratio was 1:50. The fabrics were dried at room temperature until constant weight. This treatment was used as a reference to evaluate the effectiveness and durability of plasma treatment in reducing pilling tendency.
The composition of elements of the deposited layer was studied by XPS using a monochromatic Al radiation at 1486.6 eV, VSW model TA10 and a hemispherical analyzer equipped with a single channel detector. XPS measurements were performed at a pressure of 1 × 10−6 Pa. The pass energy of the hemisphere analyzer was maintained at 187.8 eV for survey scan and 29.3 eV for high-resolution scan while the take off angle was fixed at 45°. Binding energies of XPS spectra were corrected by referencing the C1s signal of adventitious hydrocarbon to 285 eV. XPS data fittings were carried out with PHI multipack™ software using the Gauss-Lorenz model and Shirley background.
2.4. SEM analysis Morphological characterization of treated and untreated wool fabrics was carried out with a LEO 435VP scanning electron microscope from LEO Electron Microscopy Ltd.
2.8. FT-IR analysis
3. Results and discussion 3.1. SEM analysis
Table 1 Plasma treatment operating conditions.
Sample 1 Sample 2 Sample 3
Step 1
Step 2
Ar 50 W 3 min 20 Pa O2 50 W 3 min 20 Pa –
HMDSO/O2/Ar HMDSO/O2/Ar HMDSO/O2/Ar
Fig. 1 shows SEM micrographs of untreated and Sample 1–3 knitted wool fabrics. The thin inorganic coating of the treated samples was not visible and the morphology of the fibres appeared practically unchanged compared to the untreated wool sample. Samples 1 and 2, that were subjected to a preliminary plasma activation with Ar and O2 gas respectively, showed an increased roughness due to the appearance of microcraters distributed all along the surface and to the re-deposition of etched material on the surface [7].
A. Montarsolo et al. / Surface & Coatings Technology 224 (2013) 109–113
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Fig. 1. SEM images (3500 ×) of a) untreated wool fabric, b) Sample 1, c) Sample 2, d) Sample 3.
3.2. FT-IR analysis In our previous work we studied the chemical structure of the deposited film under varying process parameters [1]. The measurements showed that the gas mixture ratio used in the discharge resulted in the formation of a film with an inorganic (quartz–like) character. Not all of the typical absorption bands of this kind of coating [8–11] were clearly visible on the treated samples due to the overlapping with the
Fig. 2. FT-IR spectra of untreated wool fabric (a), Sample 3 before (b) and after washing (c) and dry cleaning (d) tests.
wool signals making difficult the FT-IR spectral interpretation. However, the analysis of samples after deposition highlighted the presence of a broad band between 1000 cm−1 and 1100 cm−1 and a narrow band around 1270 cm−1. The band observed at around 1030 cm−1 is due to the asymmetric Si–O stretching vibration in the Si–O–Si bond, and the shoulder at 1274 cm−1 is attributed to the asymmetric deformation vibration of CH3 groups in the molecule Si–(CH3)x. In this paper we used this information to verify the permanence of the pp-HMDSO coating deposited under various conditions after washing
Fig. 3. FT-IR spectra of untreated wool fabric (a), wet chemically treated wool fabric before (b) and after washing (c) and dry cleaning tests (d).
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A. Montarsolo et al. / Surface & Coatings Technology 224 (2013) 109–113 Table 2 Functional composition of the deposited film determined by fitting of Si2p, C1s, O1s. Before washing
C1s% O1s% Si 2p % C/Si O/Si
Fig. 4. O1s peak of a deposit formed from HDMSO/O2/Ar plasma at 2 Pa and 40 W (Sample 3), before (thick line) and after washing.
cycle in the Wascator machine, and after dry cleaning. The washing resistance of the plasma thin films was also compared to that of a conventional wet chemical treatment. Fig. 2 illustrates FT-IR spectra of plasma treated sample 3 compared to the untreated wool fabric. Sample 3 showed the best resistance to washing and dry cleaning tests where it can be seen that the absorption bands attributable to the SiO2 like coating after 2 washing cycles in the Wascator machine and even after 10 dry cleanings these are still present in the case of the single step plasma process (HMDSO/O2/Ar, 5 min, 40 W, 2 Pa). On the contrary, signals referring to the coating disappeared in samples 1 and 2 (spectra not shown) after washing tests. These results are difficult to explain because most authors generally report, as stated in the Introduction, that a substrate pre-treatment with non-polymerizing gases like argon or oxygen usually improves the adhesion of the film deposited later. However, it is well known that film adhesion and aging effects depend strongly on the polymer type, the internal stresses in the plasma deposited coating, and the storage conditions [12]. Plasma deposited films are often characterized by high internal stresses that may lead to long-term film stability problems and poor adhesion [13,14]. Moreover, the plasma treatment can subject the substrate to a heat load depending on the plasma operating parameters, as well as the distance between the sample and plasma region. The substrate cools when the plasma is switched off and difference in thermal expansion coefficients between the inorganic coating and the substrate can cause stress build up in the coating. The coating relieves the stress by cracking and accelerated water and oxygen diffusion
After 1st washing
Sample 1
Sample 2
Sample 3
Sample 1
Sample 2
Sample 3
55.4 28.2 9.6 5.8 2.9
50.2 34.1 10.5 4.8 3.2
36.1 45 18.9 1.9 2.4
86.2 8.5 1.1 78.4 7.7
85.8 9.3 1.3 66 7.2
47.1 38.9 14.0 3.4 2.8
through the cracks leading to de-lamination. Thus, a pre-treatment step and thus extending the exposure of the substrate to the plasma can adversely affect film adhesion and this behaviour is elsewhere primarily attributed [15,16] to increase heating of the substrate. Another way to explain the lower adhesion following plasma pre-treatment is the modification of fibre surface morphology. As is well-known, oxygen or argon pre-treatments can produce surface morphological changes (roughness and surface bond scission) which may weaken the mechanical properties of the fibres [17,18]. This effect could account also for the decreasing coating adhesion. In Fig. 3, FT-IR spectra of untreated wool fabric, wet chemicallytreated wool fabric (before and after washing and dry cleaning tests) are reported. Some of the characteristic signals of polysiloxanes were identified in the wet chemically-treated sample namely the shoulder near 1260 cm−1 is due to symmetric methyl deformation, while at 1000–1100 cm−1 the double band is assigned to Si–O–Si stretching bonds. Moreover, close to 800 cm−1 a CH3 rocking vibration is observed and the band at around 2960 cm−1 is due to the asymmetric stretching of the C–H bond in methyl groups [19]. It's evident that the wet chemical treatment is characterized by a very low resistance to both durability tests in that after only one washing cycle the absorption bands of the amino modified silicon emulsion are no longer visible and the same behaviour was found after only two dry cleaning tests. 3.3. XPS analysis The XPS characterization of plasma coated fabrics was used to confirm the presence of the coating after washing tests. Figs. 4 and 5 show XPS Si2p and O1s spectra of Sample 3. The broad scan XPS spectra of these films reveal the presence of distinct bands at binding energies (BE) which correspond to Si2p C1s, O1s core levels. The signal analyses of the Si2p and O1s before and after the washing tests confirm that the silicon-like thin film is still deposited on the substrate. For each element the relative atomic concentration of the species was estimated from the area below the spectral lines and after normalization to the atomic sensitivity factors given in literature [20]. XPS analysis of samples 1, 2 and 3 showed that after the washing cycle the O/Si ratio for sample 3 (≈2) did not change significantly (Table 2), thus the silicon-like structure is kept. Data obtained seem to confirm FT-IR results, where the signals attributable to the coating disappeared for Sample 2 and 3 after washing. Analysis of high-resolution XPS data gives a possible explanation for the increased resistance to washing of the plasma coatings obtained without an activation step: as seen in Table 3, Sample 3 showed an higher Si2p atomic % and C–Si Pick Area % compared (for example) to Table 3 Survey scan and high-resolution XPS data comparison between Sample 1 and Sample 3. Atomic %
Fig. 5. Si2p peak of a deposit formed from HDMSO/O2/Ar plasma at 2 Pa and 40 W (Sample 3), before (thick line) and after washing.
Peak area %
Survey scan
Sample 3
Sample 1
C1s high resolution
Sample 3
Sample 1
C1s O1s Si 2p
36.1 45 18.9
55.4 28.2 9.6
C–Si C–C C–O C=O
25.83 52.92 11.7 9.55
2.33 66.29 16.59 14.8
A. Montarsolo et al. / Surface & Coatings Technology 224 (2013) 109–113 Table 4 Pilling grade assigned untreated, plasma treated and wet chemically treated samples before and after washing tests. Sample
Pilling grade
Pilling grade after washing test
Pilling grade after dry cleaning test
Sample 3 Wet chemically treated Untreated
3 1–2 1
2–3 1 –
2–3 1 –
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FT-IR and XPS analyses revealed that best results were obtained with a single step of deposition using a HMDSO/O2/Ar mixture. Moreover, plasma treated sample showed an improvement about two grades in the pilling standard scale and this trend was maintained after the washing and dry cleaning tests. Acknowledgment The authors would like to thank Dr. Eng. Monica Periolatto for additional XPS measurements.
Sample 1. This seems to indicate that a single deposition step led to an increased amount of SiO2-like deposited layer. 3.4. Pilling test Table 4 shows the pilling grades determined for untreated, wet chemically treated and sample 3 wool fabrics after 7000 rubbings. The plasma treated sample, compared with chemically treated and untreated samples, showed an improvement of about two grades. These experimental results are in accordance with our previous work [1] that underlined the efficiency of silica-like plasma deposited coatings in the reduction of the fabric pilling behaviour. Pilling tendency was studied also after one washing and one dry cleaning test. The coated sample 3 showed a little decreasement of pilling grade after washing cycles and this is probably due to the partial removal of the film. However, after washing the plasma treated sample showed better pilling behaviour compared with the untreated wool fabric and with the sample treated by wet chemical method. 4. Conclusions Silicon-like thin films were deposited on knitted wool fabrics by PECVD method to improve pilling behaviour. Different plasma treatment conditions were tested to enhance the adhesion of plasma coatings and their resistance to washing and dry cleaning cycles was evaluated and compared to that of an untreated sample and a conventional wet chemically treated sample.
References [1] R. Mossotti, G. Lopardo, R. Innocenti, G. Mazzuchetti, F. Rombaldoni, A. Montarsolo, et al., Text. Res. J. 79 (2009) 853. [2] W. Schindler, P.J. Hauser, Chemical Finishing of Textiles, Woodhead Publishing Ltd., Cambridge, 2004, p. 129. [3] C. Kan, C.M. Yuen, Text. Prog. 39 (3) (2007) 121. [4] I.S. Bae, S.H. Cho, S.B. Lee, Y. Kim, J.H. Boo, Surf. Coat. Technol. 193 (2005) 142. [5] D. Hegemann, U. Vohrer, C. Oehr, R. Riedel, Surf. Coat. Technol. 116–119 (1999) 1033. [6] D. Hegemann, D.J. Balazs, in: R. Shishoo (Ed.), Plasma Technologies for Textiles, Woodhead Publishing Ltd, Cambridge, 2007, p. 158. [7] C.W. Kan, in: A. Méndez-Vilas, J. Díaz (Eds.), Formatex, 2007, p. 683. [8] M. Walker, F. Meermann, J. Schneider, K. Bazzoun, J. Feichtinger, A. Schulz, et al., Surf. Coat. Technol. 200 (2005) 947. [9] J. Schwarz, M. Schmidt, A. Ohl, Surf. Coat. Technol. 98 (1998) 859. [10] M. Creatore, F. Palumbo, R. D'Agostino, Pure Appl. Chem. 74 (3) (2002) 407. [11] G.F. Leu, A. Brockhaus, J. Engemann, Surf. Coat. Technol. 174–175 (2003) 928. [12] D. Hegemann, H. Brunner, C. Oehr, Nucl. Instr. Meth. B 208 (2003) 281. [13] S.M. Rossnagel, J.J. Cuomo, W.D. Westwood, Handbook of Plasma Processing Technology: Fundamentals, Etching, Deposition, and Surface Interactions, Noyes Publications, New York, 1990. 344. [14] R.F. Bunshah, Handbook of Deposition Technologies for Films and Coatings: Science Technology and Applications, 2nd ed. Noyes Publications, Westwood, 1994. 352. [15] G.R. Alcott, J.L. Linden, M.C.M. Van de Sanden, Mater. Res. Soc. Symp. Proc. 726 (2002) 297. [16] G.R. Alcott, D.J. Eijkman, C.P.G. Schrauwen, J.L. Linden, M.C.M. Van de Sanden, 10th Neues Dresdner Vakuum technisches Kolloquium Proceedings, 2002, p. 55. [17] M. Radetic, P. Jovancic, N. Puac, Z.L. Petrovic, Z. Saponjic, Text. Res. J. 79 (2009) 558. [18] Q. Wei, Y. Liu, D. Hou, F. Huang, J. Mater. Proc. Technol. 194 (2007) 89. [19] M.C. Gutierrez, M. Lopez-Mesas, M.T. Lacorte, J. Cegarra, Fibers Polym. 10 (4) (2009) 437. [20] J.F. Moulder, W.F. Stckle, P.E. Sobol, K.D. Bomben, Handbook of X-Ray Photoelectron Spectroscopy, Ed. Physical Electronics, Inc., Minnesota, 1995.
Contents lists available at SciVerse ScienceDirect
Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat
A study on washing resistance of pp-HMDSO films deposited on wool fabrics for anti-pilling purposes A. Montarsolo a,⁎, R. Mossotti a, R. Innocenti a, E. Vassallo b a b
C.N.R. National Research Council -ISMAC-Institute for Macromolecular Studies, Corso G. Pella 16, 13900 Biella, Italy C.N.R. National Research Council -IFP-Institute of Plasma Physics, via R. Cozzi 53, 20125 Milano, Italy
a r t i c l e
i n f o
Article history: Received 21 September 2012 Accepted in revised form 9 March 2013 Available online 17 March 2013 Keywords: PECVD HMDSO Wool fabrics Adhesion Washing resistance Pilling
a b s t r a c t In this work plasma polymerized coatings for anti-pilling purposes were deposited on knitted wool fabrics by means of a capacitively coupled RF discharge reactor using hexamethyldisiloxane as precursor. Their resistance to dry and wet cleaning was investigated and compared to that of a wet chemically deposited coating. Different gas mixtures and pre-treatment steps were tested to adjust the plasma process and to improve the film adhesion. An evaluation of the silica-like coatings behaviour to the washing stresses was performed by means of Fourier transform infrared and x-ray photoelectron spectroscopy. Anti-pilling performances of untreated, plasmatreated, and wet chemically treated wool fabrics were assessed. © 2013 Elsevier B.V. All rights reserved.
1. Introduction The textile industry is looking for applications which lead to products with additional properties in a cost-effective and eco-sustainable way. In this respect we have studied in a previous work [1], a method to solve an important issue in the textile field that is the fabrics tendency to pill. Abrasion from normal wear and cleaning causes the fibres to unravel and the loose ends to ball up on the fabric surface. This complex phenomenon is attributable to several factors comprising fibre, yarn and fabrics characteristics. To our knowledge no group of specific anti-pilling products exists and textile auxiliary producers mostly recommend chemical products that are primarily used for other purposes for anti-pilling finishes [2]. Moreover these products are usually applied on textile substrates in an aqueous bath or in foulard, using great amount of heated water and the production of polluting liquid effluents. In our study silicon containing thin films (Si:Ox:Cy:Hz) were deposited on knitted wool fabrics, by plasma-enhanced chemical vapor deposition (PECVD) in a low pressure plasma equipment, using hexamethyldisiloxane (HMDSO) as monomer and argon and oxygen as feed gases. The plasma treated samples compared with chemically treated and untreated samples, exhibited an improvement of about two grades as regards the standard pilling assessment. The results showed that this kind of treatments could represent an efficient technique to reduce pill formation on knitted wool fabrics and could also allow significant reductions of
⁎ Corresponding author. Tel.: +39 0158493043; fax: +39 0158408387. E-mail address: [email protected] (A. Montarsolo). 0257-8972/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.surfcoat.2013.03.007
water, energy, and chemical consumption. Because of the poor resistance of these coatings to the washing stress, further investigations were required for an industrial application of the method. In general, due to the numerous ways a plasma interacts with a polymer surface, the gas type and plasma conditions must be adjusted to the polymer type in order to achieve a good adhesion of the deposited coatings. Glow discharges of non-polymerizing gases like argon or oxygen are usually used to prepare the substrate surface prior to the following deposition step. In particular argon is a commonly used inert gas for the pre-treatment of polymer surfaces and an Ar plasma can be applied to clean the surface before reactive gases are applied [3] to remove low molecular weight materials [3] and to improve the adhesive characteristics of polymers [4]. Oxygen and oxygen-containing plasma can at the same time etch the polymer surface and form oxygenated functional groups. The balance of these two processes depends on the operation parameters [3]. O2 plasma pre-treatment can be carried out to roughen the surface resulting in an enhanced contact area at the beginning film growth [5]. Moreover, oxygen plays an important role in the deposition of the silicon-containing monomer in that the dilution of HMDSO with oxygen allows to increase the inorganic character of the coating [6]. The aim of this work was to study various plasma process operating conditions in order to guarantee durability of the anti-pilling coating on the wool surface to washing stress and dry cleaning. In particular, the number of plasma process steps and operational parameters including gas type were adjusted to improve adhesion of the thin film deposited. Morphologies of fibre surfaces were investigated using scanning electron microscopy (SEM). The pilling behaviour of untreated, plasma treated and wet chemically treated samples was assessed with modified
110
A. Montarsolo et al. / Surface & Coatings Technology 224 (2013) 109–113
Martindale abrasion testing method and washing resistance of plasmadeposited coatings and wet chemically-treated samples was evaluated by means of Fourier transform infrared (FT-IR) and x-ray photoelectron spectroscopy (XPS).
2. Materials and methods
2.5. Washing test Washing resistance was investigated according to UNI EN ISO 26330. An Electrolux Wascator FOM71MP-Lab washing machine was used. Two 8A wash cycle at 30 ± 3 °C was used, with the total load of 2Kg for 15 min. The washing test was carried out on polymerized samples and wet chemically treated sample.
2.1. Materials 2.6. Dry cleaning The experiments were carried out on 100% knitted wool fabrics (292 g/m 2) and the dimensions of samples were 30 cm × 30 cm. The purities of both argon and oxygen were more than 99.99% (Siad S.p.A., Italy) and HMDSO [(CH3)3-Si-O-Si-(CH3)] monomer was chemical reagent of grade 98% A.R.; (Sigma Aldrich, Germany). Prior to the plasma treatments, the fabrics were previously scoured with petroleum ether (A.R. grade) for 3 h using Soxhlet extraction to remove sizing agents, followed by rinsing with deionized hot (T = 50 °C) and cool (room temperature) water for 1 h. Before and after the treatment, they were transported in a dry box to minimize humidity.
2.2. Plasma treatment
Dry cleaning was performed according to UNI EN ISO 105-X05 using an organic solvent (CCl4) The test was carried out with a Linitest (URAI S.p.A) machinery at room temperature for 30 min. The dry cleaning test was carried out on polymerized samples and wet chemically treated sample.
2.7. Pilling behaviour The determination of the propensity to pilling of knitted was assessed with modified Martindale method. Nu-Martindale Abrasion and Pilling Tester from James H. Heal & Co. Ltd was used. The samples were placed under standard laboratory conditions (65% R.H. and 20 °C) for 24 h before testing. The pilling tests were carried on untreated, plasma treated and wet chemical treated samples.
Plasma treatments were carried out in the lab scale low pressure plasma reactor of the Institute for Macromolecular Studies, National Research Council, Biella, Italy. The discharge was powered by an RF (13.56 MHz) generator coupled to the capacitively-coupled electrodes by a fully tunable matching network. The sample was fixed to a roller below electrodes that was set at 4 rpm of working speed. This configuration allowed a homogeneous plasma deposition on all the substrate surface. In the deposition step (Step 2) the pressure, the treatment time and the discharge power were kept constant at 2 Pa, 5 min, 40 W, respectively. The combination of different gas mixtures and number of steps used are shown in Table 1. The samples 1 and 2 were pre-treated with argon and oxygen plasma, respectively, while in the case of sample 3, the silicon-like film was directly deposited onto substrate. Ar and O2 flux was fixed at 20 sccm while the HMDSO flux was 3 sccm.
Attenuated total reflectance FT-IR (ATR-FT-IR) spectroscopy measurements of untreated, plasma treated, wet chemical treated samples were carried out using an FT-IR Nexus 510 spectrometer (Thermo Nicolet) provided with a ATR accessory (Specac Ltd.) equipped with a Zn Se crystal with a 45° angle of incidence. Furthermore, FT-IR spectra of plasma treated and wet chemical treated samples were acquired after dry cleaning and washing test. Data were collected from 400 cm −1 to 4000 cm −1 wavelength range with 100 scans and a spectral resolution of 4 cm −1.
2.3. Wet chemical anti-pilling treatment
2.9. XPS analysis
Knitted wool fabrics were treated with an aqueous solution (pH adjusted to 5.5 with 2% o.w.f acetic acid) containing 2,5% o.w.f of aminomodified silicone emulsion (CT-80, Bilab, Italy) at 40 °C for 20 min. The material-to-liquor ratio was 1:50. The fabrics were dried at room temperature until constant weight. This treatment was used as a reference to evaluate the effectiveness and durability of plasma treatment in reducing pilling tendency.
The composition of elements of the deposited layer was studied by XPS using a monochromatic Al radiation at 1486.6 eV, VSW model TA10 and a hemispherical analyzer equipped with a single channel detector. XPS measurements were performed at a pressure of 1 × 10−6 Pa. The pass energy of the hemisphere analyzer was maintained at 187.8 eV for survey scan and 29.3 eV for high-resolution scan while the take off angle was fixed at 45°. Binding energies of XPS spectra were corrected by referencing the C1s signal of adventitious hydrocarbon to 285 eV. XPS data fittings were carried out with PHI multipack™ software using the Gauss-Lorenz model and Shirley background.
2.4. SEM analysis Morphological characterization of treated and untreated wool fabrics was carried out with a LEO 435VP scanning electron microscope from LEO Electron Microscopy Ltd.
2.8. FT-IR analysis
3. Results and discussion 3.1. SEM analysis
Table 1 Plasma treatment operating conditions.
Sample 1 Sample 2 Sample 3
Step 1
Step 2
Ar 50 W 3 min 20 Pa O2 50 W 3 min 20 Pa –
HMDSO/O2/Ar HMDSO/O2/Ar HMDSO/O2/Ar
Fig. 1 shows SEM micrographs of untreated and Sample 1–3 knitted wool fabrics. The thin inorganic coating of the treated samples was not visible and the morphology of the fibres appeared practically unchanged compared to the untreated wool sample. Samples 1 and 2, that were subjected to a preliminary plasma activation with Ar and O2 gas respectively, showed an increased roughness due to the appearance of microcraters distributed all along the surface and to the re-deposition of etched material on the surface [7].
A. Montarsolo et al. / Surface & Coatings Technology 224 (2013) 109–113
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Fig. 1. SEM images (3500 ×) of a) untreated wool fabric, b) Sample 1, c) Sample 2, d) Sample 3.
3.2. FT-IR analysis In our previous work we studied the chemical structure of the deposited film under varying process parameters [1]. The measurements showed that the gas mixture ratio used in the discharge resulted in the formation of a film with an inorganic (quartz–like) character. Not all of the typical absorption bands of this kind of coating [8–11] were clearly visible on the treated samples due to the overlapping with the
Fig. 2. FT-IR spectra of untreated wool fabric (a), Sample 3 before (b) and after washing (c) and dry cleaning (d) tests.
wool signals making difficult the FT-IR spectral interpretation. However, the analysis of samples after deposition highlighted the presence of a broad band between 1000 cm−1 and 1100 cm−1 and a narrow band around 1270 cm−1. The band observed at around 1030 cm−1 is due to the asymmetric Si–O stretching vibration in the Si–O–Si bond, and the shoulder at 1274 cm−1 is attributed to the asymmetric deformation vibration of CH3 groups in the molecule Si–(CH3)x. In this paper we used this information to verify the permanence of the pp-HMDSO coating deposited under various conditions after washing
Fig. 3. FT-IR spectra of untreated wool fabric (a), wet chemically treated wool fabric before (b) and after washing (c) and dry cleaning tests (d).
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A. Montarsolo et al. / Surface & Coatings Technology 224 (2013) 109–113 Table 2 Functional composition of the deposited film determined by fitting of Si2p, C1s, O1s. Before washing
C1s% O1s% Si 2p % C/Si O/Si
Fig. 4. O1s peak of a deposit formed from HDMSO/O2/Ar plasma at 2 Pa and 40 W (Sample 3), before (thick line) and after washing.
cycle in the Wascator machine, and after dry cleaning. The washing resistance of the plasma thin films was also compared to that of a conventional wet chemical treatment. Fig. 2 illustrates FT-IR spectra of plasma treated sample 3 compared to the untreated wool fabric. Sample 3 showed the best resistance to washing and dry cleaning tests where it can be seen that the absorption bands attributable to the SiO2 like coating after 2 washing cycles in the Wascator machine and even after 10 dry cleanings these are still present in the case of the single step plasma process (HMDSO/O2/Ar, 5 min, 40 W, 2 Pa). On the contrary, signals referring to the coating disappeared in samples 1 and 2 (spectra not shown) after washing tests. These results are difficult to explain because most authors generally report, as stated in the Introduction, that a substrate pre-treatment with non-polymerizing gases like argon or oxygen usually improves the adhesion of the film deposited later. However, it is well known that film adhesion and aging effects depend strongly on the polymer type, the internal stresses in the plasma deposited coating, and the storage conditions [12]. Plasma deposited films are often characterized by high internal stresses that may lead to long-term film stability problems and poor adhesion [13,14]. Moreover, the plasma treatment can subject the substrate to a heat load depending on the plasma operating parameters, as well as the distance between the sample and plasma region. The substrate cools when the plasma is switched off and difference in thermal expansion coefficients between the inorganic coating and the substrate can cause stress build up in the coating. The coating relieves the stress by cracking and accelerated water and oxygen diffusion
After 1st washing
Sample 1
Sample 2
Sample 3
Sample 1
Sample 2
Sample 3
55.4 28.2 9.6 5.8 2.9
50.2 34.1 10.5 4.8 3.2
36.1 45 18.9 1.9 2.4
86.2 8.5 1.1 78.4 7.7
85.8 9.3 1.3 66 7.2
47.1 38.9 14.0 3.4 2.8
through the cracks leading to de-lamination. Thus, a pre-treatment step and thus extending the exposure of the substrate to the plasma can adversely affect film adhesion and this behaviour is elsewhere primarily attributed [15,16] to increase heating of the substrate. Another way to explain the lower adhesion following plasma pre-treatment is the modification of fibre surface morphology. As is well-known, oxygen or argon pre-treatments can produce surface morphological changes (roughness and surface bond scission) which may weaken the mechanical properties of the fibres [17,18]. This effect could account also for the decreasing coating adhesion. In Fig. 3, FT-IR spectra of untreated wool fabric, wet chemicallytreated wool fabric (before and after washing and dry cleaning tests) are reported. Some of the characteristic signals of polysiloxanes were identified in the wet chemically-treated sample namely the shoulder near 1260 cm−1 is due to symmetric methyl deformation, while at 1000–1100 cm−1 the double band is assigned to Si–O–Si stretching bonds. Moreover, close to 800 cm−1 a CH3 rocking vibration is observed and the band at around 2960 cm−1 is due to the asymmetric stretching of the C–H bond in methyl groups [19]. It's evident that the wet chemical treatment is characterized by a very low resistance to both durability tests in that after only one washing cycle the absorption bands of the amino modified silicon emulsion are no longer visible and the same behaviour was found after only two dry cleaning tests. 3.3. XPS analysis The XPS characterization of plasma coated fabrics was used to confirm the presence of the coating after washing tests. Figs. 4 and 5 show XPS Si2p and O1s spectra of Sample 3. The broad scan XPS spectra of these films reveal the presence of distinct bands at binding energies (BE) which correspond to Si2p C1s, O1s core levels. The signal analyses of the Si2p and O1s before and after the washing tests confirm that the silicon-like thin film is still deposited on the substrate. For each element the relative atomic concentration of the species was estimated from the area below the spectral lines and after normalization to the atomic sensitivity factors given in literature [20]. XPS analysis of samples 1, 2 and 3 showed that after the washing cycle the O/Si ratio for sample 3 (≈2) did not change significantly (Table 2), thus the silicon-like structure is kept. Data obtained seem to confirm FT-IR results, where the signals attributable to the coating disappeared for Sample 2 and 3 after washing. Analysis of high-resolution XPS data gives a possible explanation for the increased resistance to washing of the plasma coatings obtained without an activation step: as seen in Table 3, Sample 3 showed an higher Si2p atomic % and C–Si Pick Area % compared (for example) to Table 3 Survey scan and high-resolution XPS data comparison between Sample 1 and Sample 3. Atomic %
Fig. 5. Si2p peak of a deposit formed from HDMSO/O2/Ar plasma at 2 Pa and 40 W (Sample 3), before (thick line) and after washing.
Peak area %
Survey scan
Sample 3
Sample 1
C1s high resolution
Sample 3
Sample 1
C1s O1s Si 2p
36.1 45 18.9
55.4 28.2 9.6
C–Si C–C C–O C=O
25.83 52.92 11.7 9.55
2.33 66.29 16.59 14.8
A. Montarsolo et al. / Surface & Coatings Technology 224 (2013) 109–113 Table 4 Pilling grade assigned untreated, plasma treated and wet chemically treated samples before and after washing tests. Sample
Pilling grade
Pilling grade after washing test
Pilling grade after dry cleaning test
Sample 3 Wet chemically treated Untreated
3 1–2 1
2–3 1 –
2–3 1 –
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FT-IR and XPS analyses revealed that best results were obtained with a single step of deposition using a HMDSO/O2/Ar mixture. Moreover, plasma treated sample showed an improvement about two grades in the pilling standard scale and this trend was maintained after the washing and dry cleaning tests. Acknowledgment The authors would like to thank Dr. Eng. Monica Periolatto for additional XPS measurements.
Sample 1. This seems to indicate that a single deposition step led to an increased amount of SiO2-like deposited layer. 3.4. Pilling test Table 4 shows the pilling grades determined for untreated, wet chemically treated and sample 3 wool fabrics after 7000 rubbings. The plasma treated sample, compared with chemically treated and untreated samples, showed an improvement of about two grades. These experimental results are in accordance with our previous work [1] that underlined the efficiency of silica-like plasma deposited coatings in the reduction of the fabric pilling behaviour. Pilling tendency was studied also after one washing and one dry cleaning test. The coated sample 3 showed a little decreasement of pilling grade after washing cycles and this is probably due to the partial removal of the film. However, after washing the plasma treated sample showed better pilling behaviour compared with the untreated wool fabric and with the sample treated by wet chemical method. 4. Conclusions Silicon-like thin films were deposited on knitted wool fabrics by PECVD method to improve pilling behaviour. Different plasma treatment conditions were tested to enhance the adhesion of plasma coatings and their resistance to washing and dry cleaning cycles was evaluated and compared to that of an untreated sample and a conventional wet chemically treated sample.
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