Improvement in hydrophobicity of polyester fabric finished with fluorochemicals via aminolysis and comparing with nano-silica particles

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1 Colloid Polym Sci (2011) 289: DOI /s ORIGINAL CONTRIBUTION Improvement in hydrophobicity of polyester fabric finished with fluorochemicals via aminolysis and comparing with nano-silica particles Zahra Mazrouei-Sebdani & Akbar Khoddami & Shadpour Mallakpour Received: 12 December 2010 / Revised: 2 March 2011 /Accepted: 20 March 2011 /Published online: 14 April 2011 # Springer-Verlag 2011 Abstract For the fabrication of the lotus-type fibers, a combination of two major requirements, low surface energy and the magnified of the degree of roughness, should be utilized. In this research, the possible surface roughening effect of aminolysis of the polyester fibers was applied to manipulated surface topography while fluorocarbon polymer layer generates low surface energy. The results were compared with the method that created variety of surface roughness by changing the size of the nano-silica particles using the 3M water/oil repellency test, sliding (tilt) angle, microscopy (SEM), decay of hydrophobicity, self-cleaning, and tensile properties. The results indicated the usefulness of the conventional polyester aminolysis process to control surface roughness for enhancement of fabric hydrophobicity with sliding angle as low as 12. Keywords Superhydrophobic surface. Aminolysis. Nanoparticles. Polyester fabric. Surface roughness Introduction The wettability of solid surface is an important property of material that is controlled by the chemical composition and Z. Mazrouei-Sebdani : A. Khoddami (*) Department of Textile Engineering, Isfahan University of Technology, Isfahan , Iran khoddami@cc.iut.ac.ir S. Mallakpour Organic Polymer Chemistry Research Laboratory, Department of Chemistry, Isfahan University of Technology, Isfahan , Iran S. Mallakpour Nanotechnology and Advanced Materials Institute, Isfahan University of Technology, Isfahan , Iran geometry of the surface [1 3]. For the solid substrate, when the water contact angle is larger than 150, it is called superhydrophobic surface [3 8]. While the search on superhydrophobic surfaces dates back a long time [9 17], generally the main approach has been to mimic the lotus leaf effect with self-cleaning properties on textiles [10]. There have been attempts to fabricate superhydrophobic fiber and textiles in a different ways as varied as electrospinning, sol gel, plasma polymerization, and coating [1, 5, 18 29], but no research work has been reported applying aminolysis of polyester in order to manipulate the fiber surface roughness. Nanoparticles have been generally used as a simple way to change surface roughness to fabricate lotus-type textiles, but some of these nanoparticles could penetrate person skin by releasing from the finished fabric surface and cause healthiness troubles. Also, resulting textile could be uncomfortable to wear. Therefore, replacing the nanoparticles could be a priority for textile industries. In this paper, adopting the traditional textile finishing process, fabricating superhydrophobic polyester has been investigated. To achieve the necessary topography, three different methods were examined including: (1) changing the size of the nano-silica particles, (2) aminolysis of polyester, and (3) using the nano-silica particles on the amine-treated samples. The required low surface energy layer was obtained by a fluorochemical for all samples. Experimental Materials Polyester fabric with plain weave (100%, 120 g/m 2 ) was used as a substrate. All chemicals were of analytic grade from Merck, Germany. Nano-silica particles, SNOTEX O (10 20 nm), SNOTEX OL (40 50 nm), MP-4540 ( nm),

2 1036 Colloid Polym Sci (2011) 289: Table 1 Water repellency and physical properties of fluorochemical-treated polyester fabrics Fluorochemical (g/l) Sliding angle ( ) Tenacity change (%) Water and oil repellency 3M test Before wash After wash After wash and hot-pressing Water Oil Water Oil Water Oil ± ± ± ± ± ±1.6 a a Minus shows the tenacity loss and MP-1040 ( nm), were supplied by Nissan Chemical America Corporation. The selected fluorocarbon was Rucostar EEE from Rudolf, Germany, and the used nonionic detergent was Sera Wet C-NR from DyStar. Fabric preparation The polyester fabric was firstly washed to remove any possible impurities which can adversely affect the surface treatments by 1 ml/l non-ionic detergent and 0.2 g/l sodium carbonate (ph 8 9) with L/R of 30:1 at C for 45 min. Then, samples were rinsed for 60 min and air dried without any tension. Polyester fabric treatment with the fluorochemical The scoured polyester fabrics were impregnated in a treatment baths containing 30, 45, and 60 g/l Rucostar EEE, acetic acid to adjust ph, and propane 2-ol, 5 ml/l added to the baths as a wetting agent. Subsequently, the sample was passed through a two-roll laboratory padder (Mathis, Switzerland). This treatment gave a wet pickup of Table 2 Water repellency and physical properties of fluorochemical nanoparticle-treated polyester fabrics Nanoparticle Add on dry (%) Sliding angle ( ) Water and oil repellency 3M test Tenacity change (%) Before wash After wash After wash and hot-pressing Water Oil Water Oil Water Oil 17.9± ±2.5 SNOTEX O (10 20 nm) ± ± ± ±0.5 a ± w ± ± ±2.6 SNOTEX OL (40 50 nm) ±o ± ± ± ± ± ± ±0.5 MP-1040 ( nm) ± ± ± ± ± ± ± ±2.9 MP-4540 ( nm) ± ± ± ± ± ± ± ±0.8 a Minus shows the tenacity loss

3 Colloid Polym Sci (2011) 289: %. After drying (2 min, 100 C), the fabric was cured for 2 min at 180 C in a lab dryer (Warner Mathis AG, Niederhasli/Zurich, Switzerland). Polyester fabric treatment with the fluorochemical and nano-silica particles The nano-silica particles co-applied with the optimum concentration of the fluorochemical, Rucostar EEE 45 g/l, according to the abovementioned conditions with a wide range of particle size from 10 to 400 nm and with different concentrations. It should be mentioned that nanoparticles were stirred for 20 min by Ultrasonic lab devices (UP200 H, 200 W, 24 khz, 65% amplitude) and subsequently 10 min by electronic mixer (1KA-COMBIMAG RED, Drehzahl-Electronic, and 900 rpm). During stirring of the solution using the electronic mixer, propane 2-ol and Rucostar EEE were added and the samples treatment was carried out by the pad-dry-cure method under the abovementioned conditions. Aminolysis of the polyester fabric, and treatment with the fluorochemical and fluorochemical nanoparticles Aminolysis of scoured polyester samples was carried out with 30%, 32%, 34%, 36%, and 38% methyl amine, L/R of 15:1, for 150 min at 30 C. To investigate the effect of salts on the aminolysis and subsequent hydrophobicity imparted by fluorocarbon finishing, ammonium chloride salt in 0.5, 1, 2, and 5 g/l was used in the optimum conditions of aminolysis bath containing 30% methyl amine. After aminolysis, the samples were left in distilled water for 20 min and air dried without any tension. All amine-treated samples were finished with the optimum concentration of the fluorochemical, Rucostar EEE 45 g/l, according to the abovementioned conditions, with or without the selected size and concentration of the nano-silica particle, MP-4540, nm, and 0.4% dry add on, respectively. Fig. 1 Sliding angle of polyester fabrics treated by different amount of nano-silica particles versus of nanoparticle size hemispherical, the fabric passes the test. Samples are rated as pass or fail of the appropriate test liquid, W 10. The rating given to a sample is for the highest test liquid remaining visible after 15 s. In general, water repellency rating of 2 or greater is desirable [31]. For the oil repellency, the samples are placed flat on a smooth, horizontal surface. Beginning with the lowest numbered test oil, small droplets (approximately 5 mm in diameter) are placed onto the sample using a pipette. The droplets are observed for 30 s from a 45 angle. If the droplet neither wets the fabric nor has any sign of wicking, the test is repeated using the next numbered oil. This is continued until an oil sample is found to either wet the fabric or show signs of wicking. The oil repellency rating is deemed to be the highest numbered test oil which does not wet the fabric within 30 s. Wetting of a substrate is normally seen by darkening of the substrate at the liquid substrate interface. On dark colored samples, wetting can be detected by loss of sparkle within the droplet [32]. In addition, the reorientation of fluorocarbon polymer chains after wet processing was evaluated in accordance with AATCC Test Method tests No. 2A by Polymat (AHIBA1000 Datacolor; Zurich, Switzerland) in Evaluation methods To study the level of the samples hydrophobicity, both sliding angle [30] and the 3M oil and water repellency tests [31, 32] were examined. Sliding angle of samples was measured by an instrument built at faculty with 15 tests for each sample. The samples were tested for water repellency using the water/alcohol drop test. The samples are placed flat on a smooth, horizontal surface. Beginning with the lowest numbered test liquid, three small droplets (approximately 5 mm in diameter) are placed onto the sample using a pipette. The droplets are observed for 10 s. If after 10 s, two of the three droplets are still visible as spherical to Fig. 2 Sliding angles of polyester fabrics treated with different nanosilica particles size versus of amount of nanoparticles

4 1038 Colloid Polym Sci (2011) 289: Fig. 3 SEM micrographs of a untreated polyester and treated fabric with b 45 g/l fluorochemical, c 45 g/l fluorochemical 0.2% nano-silica particles (10 20 nm), and d 45 g/l fluorochemical 0.4% nano-silica particles ( nm) order to assess how samples keep their performance after washing and hot-pressing (120 C for 2 min). Determination of fabric tensile properties was carried out according to ASTM: D strip method on an Instron 5564 with gauge length of 0.15 m, crosshead speed of 100 mm/min, and ten tests for each sample. Scanning electron microscopy (SEM; Hitachi S-300N) was applied to study the samples surface structure. Also, the Lotus effect was evaluated using photographic method by Canon camera model macro in which selfcleaning properties were compared before and after water drop movement on the surface uniformly covered with carbon black. Table 3 Water repellency and tenacity loss of amine-treated polyester fabrics finished with fluorochemical and fluorochemical nanoparticles Finish Amine concentration (%) Sliding angle ( ) 3M water and oil repellency test Tenacity loss (%) Before wash After wash After wash and hot-pressing Water Oil Water Oil Water Oil Unfinished ± ± ± ± ±0.7 Fluorochemical ± ± ± ± ± ± ± W ± ± ±1.0 Fluorochemical and nanoparticle ± ± ± ± ± ± ± ± ± W ±0.9

5 Colloid Polym Sci (2011) 289: Result and discussions Polyester fabrics treatment with fluorochemical According to Table 1, fluorocarbon finishing regardless of the applied concentration leads to maximum oil and water repellency with 3M water repellency of 10 and oil repellency of 8 for three samples. The sliding angle of the sample treated with 60 g/l fluorochemical is not statistically different from the second sample, but the sample treated with 45 g/l shows lower sliding angle than the sample treated with 30 g/l fluorochemical. So, the increase in the fluorocarbon concentration results in better hydrophobic film coverage and consequently lower sliding angle. In addition, samples treated with 30 and 45 g/l of the fluorochemical have more tenacity at the same range while the third sample shows an adverse effect on the strength. The reduction in tenacity could be due to the imparted sample stiffness attained by higher concentration of fluorochemical. Accordingly, the concentration of 45 g/l was chosen as an optimum concentration for further experiments, while economic aspect was also considered. Furthermore, improving sliding angle can be manipulated by changing surface roughness with more important role than the fluorochemical concentration. Fig. 4 Sliding angles of aminolysed polyester fabrics finished with fluorochemical and fluorochemical nanoparticles versus amine concentration film. The differences between the sliding angle of the coated samples with 0.4%, 0.6%, and 0.8% concentration of Snowtex OL (40 50 nm) and MP-1040 ( nm) and the sample treated with just fluorochemical are not statistically significant. In both cases, using lower nanoparticles concentration, 0.2% (dry add on), results in lower Polyester fabrics treatment with fluorochemical and nano-silica particles Creating surface roughness using the nanoparticles show that the sliding angle is deeply affected by the size and amount of nanoparticles (Table 2). By applying a mixture of nanoparticles and fluorochemical, fluorochemical chains migrated to the outer surface because of lower surface energy and covered the fiber surface which carried nanoparticles resulting in water and oil repellency with grade of 10 and 8, respectively. Migration of low surface energy molecular chains to outmost surface has already been reported [8, 22]. Figures 1 and 2 compared the sliding angles of samples treated with different size and concentration of the nanoparticles. It can be implied that the sliding angles decreased gradually when the nanoparticle size increased (Fig. 1). Similar behavior was observed when the nanoparticles concentration decreased (Fig. 2). The sliding angles of the samples coated with smaller nanoparticles, nm, are higher than the sliding angle of sample treated with just fluorochemical. When it is considered that the finishing was applied on the woven fabrics with natural surface roughness, then this phenomenon could be due to the nanoparticle aggregation (Fig. 1c), with possible reducing fabric surface roughness, in comparison with the sample covered with only fluorocarbon Fig. 5 SEM micrographs of aminolysed polyester fabrics finished with fluorochemical nanoparticles. a 500 and b, c 1,000

6 1040 Colloid Polym Sci (2011) 289: Table 4 Water repellency of amine-treated polyester fabrics in presence of ammonium chloride salt finished with fluorochemical and fluorochemical nanoparticles Treatment Ammonium chloride concentration (g/l) Sliding angle ( ) 3M water and oil repellency test Before wash After wash After wash and hot-pressing Water Oil Water Oil Water Oil Fluorochemical ± ± W ± W ± Fluorochemical and nanoparticle ± W ± ± ± W sliding angles of 13.9 and 13.2 for Snowtex OL and MP1040, respectively. All nm nanoparticles treated samples reveal sliding angle of less than 15. So the best result, sliding angle of 12.5±0.5, was accomplished by 0.4% (dry add on) nanoparticles with size of nm. The decrease in sliding angle is attributed to the introduction of double roughness with the original roughness appearing from the fabric structure itself and the next from the layer of the nanoparticles. A double-scale roughness provides the appropriate topography to develop superhydrophobic, self-cleaning surfaces [33]. The effect of fabric structure on hydrophobicity can be proven by comparing the sliding angle of fluorochemical-treated smooth polyester film (30.5±1.9 ), Melinex, with the fabric (17.9±0.7 ). The results lead to the conclusion that the larger the nanoparticle size and the lower the concentration, the lower the sliding angle. The SEM micrographs reveal acceptable distribution of this nanoparticle (Mp4540, nm) on the fabric surface (Fig. 3). Furthermore, evaluation of the samples tensile properties (Table 2) shows an increase in the samples tenacities in most cases, indicating no negative effect of the applied process on the samples strength which is so important for industrial application. This effect could be due to the more adhesion between fibers that resulted in better force distribution. kind, and textiles comfort [27], developing a simple method for replacing nanoparticles in the manufacturing process of super hydrophobic surfaces on textiles by harmless and flexible materials is very crucial. In this work, to create surface roughness, replacement of nanoparticles with possible roughening effect of polyester aminolysis was investigated. The polyester aminolysis is well known as a common process to make fibers hydrophilic. Some chemical and morphological changes can be generated on the polyester fabric by amine action [34 36]. This irregular surface after aminolysis could possibly be directed to proper roughness for enhancement of repellent properties after being finished with the fluorochemical. Accordingly, as can be seen at Table 3, amine-treated samples after both fluorocarbon and fluorocarbon nanoparticle finishings showed the highest values for 3M oil and water repellency. According to Fig. 4, in both cases, with or without nanoparticles, the sliding angle of samples shows a gradual Aminolysis of the polyester fabric, and treatment with the fluorochemical and fluorochemical nanoparticles Nanoparticles have been used as a simple way to fabricate lotus-type textiles. However, due to the adverse effect of these nanoparticles on environment, human Fig. 6 Sliding angles of aminolysed polyester fabrics finished with fluorochemical and fluorochemical nanoparticles versus that of ammonium chloride concentration

7 Colloid Polym Sci (2011) 289: Fig. 7 Self-cleaning properties of repellent finished polyester fabrics, a covered by carbon black and b d after movement of water droplet. b Fluorochemical-, c fluorochemical nanoparticle-, and d amine and fluorochemicaltreated samples increase with the increase of methyl amine concentration so that the sliding angle of aminolysed sample with a concentration of 30% is less than those treated with a higher concentration. Generally, in each group (with or without nanoparticles), the differences between the sliding angles of amine-treated samples are not statistically significant except for the treated sample with 30% amine. Furthermore, the results (Table 3) indicate that aminolysis created proper roughness so that there is no necessity to use the nanoparticles. Because, in all tested conditions, the sliding angles of the fluorocarbon-finished samples were lower or at the same range as those samples finished with fluorocarbon nanoparticles after aminolysis. Aminolysis with 30% methyl amine and finishing with just fluorocarbon resulted in similar repellent properties to the condition in which the polyester fabric after aminolysis was finished with 0.4% nanoparticles, with size of nm, and fluorocarbon. Measurement of tensile properties (Table 3) showed the adverse effect of aminolysis on the fabric tenacity. However, after being finished with the fluorocarbon, there was not any further decrease in tensile properties. In addition, a little improvement in tenacity was observed. Figure 5 shows SEM micrographs of methyl aminetreated samples after treatment with fluorochemical nanoparticles. Amine reaction is selective, and amorphous regions are degraded in the initial stage of treatment leading to cracks on the surface of fibers [35, 36]. Different etchings in amorphous and crystalline regions as well as internal stress that remained in the fibers are the factors that lead to cracks on the surface [36]. The fluorocarbon film on the topmost surface layer brings the low surface energy, coupled with created cracks and rough surface, of the aminolysis initiate more hydrophobicity, with the best result (sliding angle of 12 ) achieved by 30% methyl amine treatment, without applying nanoparticles. It seems that the double-scale topography (pits/fabric structure) of the polyester surface is mimicking the lotus leaf effect which is compatible with previous finding about the binary length scale topography ( 2 μm fiber/ 50 μm woven bundle) of the microfiber polyester that is responsible for promoting its water repellency as compared to conventional polyester fabric [37, 38]. Amine reaction of polyester fiber can be affected by the salts [39, 40]. Therefore, the effect of ammonium chloride on the creating rough surface during aminolysis was investigated. The results presented in Table 4 and Fig. 6 indicated that ammonium chloride changes the aminolysis in the way that improved the sliding angles due to the possible roughening effect. Also, a direct relation between the increase of salt concentrations from 0.5 to Table 5 White increase percentage of some repellent finished polyester fabrics Treatment Whiteness increase (%) Sliding angle ( ) Fluorochemical (45 g/l) ±0.7 Fluorochemical (45 g/l) and nanoparticles (0.4%) ±0.5 Aminolysis (30%) and fluorochemical (45 g/l) ±0.6

8 1042 Colloid Polym Sci (2011) 289: g/l and the improvement of decreasing sliding angles was observed. Reorientation of fluorochemical chains during wash By applying a polymer containing both fluorinated and hydrophilic polymer segments, the required surface energy in air or in an aqueous environment can be obtained [41]. Thus, the hybrid fluorochemical functions effectively as a stain repellent in air and also as an effective oily soil release finish in washing. But as can be seen in Tables 1, 2, and 3, the reorientation of Rocustar EEE during air drying is incomplete. The repellent properties show remarkable decrease in both oil and water repellencies due to the dual action of the fluorochemicals resulted from the reorientation of hydrophobic chains. Hydrophobic moieties present at the air/ polymer interface move away from the surface into the bulk of the polymer by immersing into water [42]. Amine fluorochemical-treated samples show the same trends as the fluorochemical- and fluorochemical nanoparticle-treated samples and similar deficiency of molecular reorientation after washing. Decay of the repellency after wet treatment is not due to removing of the hydrophobic moieties because they retrieve their original repellency performance after hot-pressing at 120 C. So, migrations of hydrophobic moieties caused by the water are at least partially reversible. The buried Fig. 9 Cleaning of the surface under the drop movement, a one and b several times fluorine-containing moieties migrate toward the surface on heat treatment [43]. In spite of the decay of hydrophobicity after washing, all treated samples show minimum 3M water repellency of 1 2 which is fair enough for water repelling and obtaining selfcleaning effect. Self-cleaning properties of the repellent finished samples Quantitative and qualitative evaluations of the samples selfcleaning were carried out using photographs of the samples coated with thin layer of carbon black before and after passing Fig. 8 Water drops after transition over the blacked surface Fig. 10 Collection of contamination at the drop surface when it contacts superhydrophobic surface

9 Colloid Polym Sci (2011) 289: water droplets on the surface (Fig. 7). A water droplet was deposited on the surface with dropper, and the surface was tilted until the droplet could slide. Movement of the droplets over the repellent finished fabrics caused the black powder to be gathered and made the fabrics cleans. In quantitative analysis, the increase in whiteness percentage of the finished samples as compared with the same sample before passing the water droplet was evaluated using Matlab software (Table 5). The increase in self-cleaning effect is quite clear with adding the nanoparticles and aminolysis on the surface of the samples with more amounts of washed particles away comparing to fluorochemical-treated sample (Table 5 and Fig. 7). Although aminolysed sample shows lower white increase percentage than nanoparticle-treated sample, still it could have enough functionality like nanoparticles in which proper surface roughness was achieved as a result of surface cracks. It is obvious that the interaction between the droplet and the black particles had been adequate to overcome the low adhesion between the fabric and the particles similar to lotus leaf [33] (Fig.7). In fact, the particles stuck to the water drop rolling across the surface (Fig. 8). Some black particles, which are stuck among the woven bundles, could not be removed by the water droplet which moves on the pinnacle of the rough surface. However, in order to remove almost all the particles between fabric structures, passing the droplet gently back and forth for several times are adequate (Fig. 9). In addition, it is revealed in Fig. 10 that in each place where the water drop first touches the surface, the contamination will be collected at the drop surface which aids the surface cleaning by rain. These experiments indicate the parameters affecting self-cleaning properties and pave the way to assess successful biomimetic of lotus leaf effect on textile objectively in addition to subjective measurement. Conclusion Improvement of hydrophobicity was investigated on polyester fabric using aminolysis method. A required dual-scale surface roughness was created by both woven structure and creation of cracks caused by amine treatment and compared with the method of using nanoparticles. The results indicated that surface topography with proper roughness could be created with moderate aminolysis of polyester fabric, 30% methyl amine, for 150 min at 30 C. Fabrication of superhydrophobic textiles with an aminolysis method of polyester fabric can be achieved without application of expensive nanoparticles, required a complicated method to be dispersed, deteriorated fabrics handle, and made garment uncomfortable. 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