Durable Hydrophobic Cellulose Fabric Prepared with Polycarboxylic

Ind. Eng. Chem. Res. 2010, 49, 9135–9142

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Durable Hydrophobic Cellulose Fabric Prepared with Polycarboxylic Acid Catalyzed Silica Sol Wenqi Huang,†,‡ Yang Song,§ Yanjun Xing,*,†,‡ and Jinjin Dai† College of Chemistry, Chemical Engineering and Biotechnology, Donghua UniVersity, Shanghai 201620, China, Key Laboratory of Science & Technology of Eco-Textile (Donghua UniVersity), Ministry of Education, Shanghai 201620, China, and National Engineering Research Center for Dyeing & Finishing of Textiles, Shanghai 201620, China

Nine polycarboxylic acids (PAs) were employed in silica sol to offer an alternative approach in improving washing durability of the hydrophobic cellulose fabric by the sol-gel method. Polycarboxylic acids played a twofold role since they work not only as catalysts in hydrolyzing silica precursor but more importantly as cross-linkers to bind silica coating to cellulose substrate. Washing durability of hydrophobic cellulose fabric finished by the sol-gel method was obviously enhanced. The polycarboxylic acid with the proper number of carboxylic acid groups and distance between the terminal carboxylic acid groups could enhance the washing durability of the hydrophobicity of the cotton fabric by the sol-gel method. 1,2,3,4-Butanetetracarboxylic acid (BTCA) led to the best durability of hydrophobic cellulose fabric with a water contact angle of 138.6° (recovery percentage 96.5%) after washing 30 times. The effect of BTCA on durability was also characterized by scanning electron microscopy (SEM). This study suggested that the organic-inorganic sol-gel hybrid using PA as a catalyst is appropriate for achieving a durable hydrophobic cellulose fabric. 1. Introduction The sol-gel technique has been applied to the fabrication of superhydrophobic surfaces on cellulose fabrics.1-7 The silica coating prepared from the sol-gel technique could first serve as a carrier to covalently bind hydrophobic additives.1-3 The introduced silica layer also provides a certain surface roughness for the superhydrophobic surface on the cellulose fiber.3-7 Furthermore, the silica layer could form a heterogeneous coating to decrease the hydrophilicity of the cellulose fiber caused by forming a network around cellulose fibers. It could be predicted that the silica coating could be destroyed by mechanical or swelling behavior during their lifetime.8 In order to improve the washing durability, silane coupling agents2,9,10 or synthesized silane polymers11,12 have been used as cross-linkers. However, a silane coupling agent will influence the reaction kinetics of the sol-gel polymerization, especially silanes exhibiting bulky organic chains that could lead to lower reactivity under both acidic as well as alkaline conditions.13 Furthermore, water solubility and pH-sensitivity varied greatly with different silane coupling agents,14 leading to extra requirements of organic solvents and catalysts. Although silane coupling agents are used to improve coating durability on cellulose fabric, the surface of the cellulose fibers is markedly less reactive than that of the inorganic oxides onto which the silanes are usually applied with silane coupling agents.14-16 Most silica sols are prepared starting from the hydrolysis of alkoxysilane precursors like TEOS. Widely used catalysts are mineral acids or derivative salts.17 However, most of the reported mineral acids are liquid and too strong to be suitable for industrial manufacturing. Heavy demand for necessary labor * To whom correspondence should be addressed. Tel.: +86-2167792729. Fax: +86-21-67792306-804. E-mail: [email protected]. † College of Chemistry, Chemical Engineering and Biotechnology, Donghua University. ‡ Key Laboratory of Science & Technology of Eco-Textile, Donghua University. § National Engineering Research Center for Dyeing & Finishing of Textiles.

protection articles and labor protection facilities shall send the cost up. Moreover, the finishing machinery will also be eroded in the acidic conditions. Polycarboxylic acids (PAs), a kind of organic acid, appear to have a number of advantages over mineral acids as a catalyst. As a hydrolysis catalyst, the acidity of PA is strong enough to hydrolyze alkoxysilane precursors and on the other hand far weaker than mineral acid. This indicated that the working risk and erosions of processing equipment will be alleviated by using PAs as a catalyst. In addition, most of the PAs are solid, which would greatly facilitate packing and delivery in industrial manufacturing. As a silica network modifier, polycarboxylic acid could cocondense with Si-OH groups, leading to the formation of interfacial ester bonds.18,19 The introduction of organic chains into the SiO2 polymeric matrix is known to increase the flexibility of the organic-inorganic network.20 As a result, compatibility of the silica coating could be improved as the stripping off of anchored silane caused by rigid structure is reduced. Polycarboxylic acid has also been used as a heterogeneous cross-linker to improve the adhesion of the inorganic-organic interface.21,22 Moreover various PAs have been investigated as cross-linkers for durable press finishing of cellulose fabric,23-29 implying PA’s advantage of better application on cellulose material over a silane coupling agent. In this regard, polycarboxylic acid was proposed to be capable as a cross-linker to connect the heterogeneous silica functional layer to cellulose fabric. In this paper, nine commercially available nontoxic PAs containing two to four carboxylic acid groups were hired to work not only as catalysts in hydrolyzing silica precursor but more importantly cross-linkers to bind silica coating to the cellulose substrate. It hopes to offer an alternative approach in improving the washing durability of hydrophobic cellulose fabric finished by the sol-gel method (Scheme 1).

10.1021/ie1012695  2010 American Chemical Society Published on Web 08/31/2010

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Ind. Eng. Chem. Res., Vol. 49, No. 19, 2010

Scheme 1

2. Experimental Section 2.1. Materials. Native cotton fabric (20s × 16s, 128 ends/ in. × 60 picks/in.) was pretreated by singeing, desizing, scouring, bleaching, and mercerizing. Tetraethoxyorthosilicate (TEOS) and hexadecyltrimethoxysilane (HDTMS) were purchased from Fluka. Malonic acid (C3A), succinic acid (C4A), glutaric acid (C5A), adipic acid (C6A), maleic acid (MA), DLmalic acid (MAA), tartaric acid (TA), citric acid (CA), hydrochloric acid (HCl), and sodium hypophosphite monohydrate (NaH2PO2) were from Sinopharm Chemical Reagent Co. Ltd. 1,2,3,4-Butanetetracarboxylic acid (BTCA) was purchased from Alfa Aesar. All chemicals were used directly without further purification. 2.2. Preparation of Polycarboxylic Acid Catalyzed Silica Sol. Silica sol was prepared via hydrolysis of TEOS in aqueous solution, according to the following procedure: An aqueous solution of TEOS (Si% ) 1, w/w), polycarboxylic acid and NaH2PO2 (6%, w/w) was sonicated for 60 min by a SK2200H ultrasonic cleaner (90 W, 59 kHz, China). All the polycarboxylic acid solutions maintain the same carboxyl concentration of 1.03 M. Then the mixture was stirred for another 30 min at 60 °C, and a homogeneous solution was obtained. 2.3. Coating with PA-Sol and Surface Modification of Treated Cotton Fabrics with HDTMS. Cellulose fabrics were immersed in the silica sol, padded with a pickup of 75%, and dried at 80 °C. After that, all treated fabrics were immersed in ethanol solution of hydrolyzed HDTMS (4 wt %) for 5 min, padded with a pickup of 75%, and dried at 80 °C before cured at 170 °C for 2.5 min. The final treated cotton fabrics were referred to as sample C3A, C4A, C5A, C6A, MA, MAA, TA, CA, and BTCA, respectively, according to the polycarboxylic acid used; the fabric treated with HCl-sol would be referred to as sample N in the following discussion. 2.4. Instruments and Characterization. The average particle size of silica sol was measured on Zetasizer nano ZS particle size and zeta potential analyzer (Zetasizer Nano ZS,

Table 1. Standard Spray Test Ratings ratings

explanation

100

no wetting of, and no adherence of small drops to, the sprayed surface no wetting of, but adherence of small drops to, the sprayed surface wetting of the sprayed surface only at small discrete areas wetting of half of the sprayed surface; this usually occurs through the merging of small discrete wetting areas wetting of the whole of the sprayed surface

90 80 70 50

Malvern, Britain). The surface morphology of the sample was observed using scanning electron microscopy (SEM, JSM5600LV, Jeol, Japan). 2.5. Water Repellency Test. All samples were put in the standard atmosphere balance chamber for 24 h before water repellency tests. The water contact angle (WCA) was measured using an optical video contact angle instrument (OCA 40, Dataphysics, Germany) at ambient temperature. All WCAs were determined at 30 s after a water droplet of 5 µL was placed on a cotton substrate. All reported WCA values were averaged from 10 measurements at different positions of the same sample. The spray test was performed according to AATCC Test Method 22-2005.30 Substrates (18 cm × 18 cm) were fixed at an angle of 45° under a spray nozzle at a distance of 15 cm. Then, 250 mL of water was sprayed onto substrates during 30 s. Each test specimen is assigned a rating corresponding to the nearest standard in the standard spray test ratings (Table 1). Intermediate ratings can be used for ratings of 50 or higher. Hydrostatic press test was performed according to AATCC Test Method 127-2003.30 The hydrostatic head supported by a fabric is a measure of the opposition to the passage of water through the substrate. A specimen is subjected to a steadily increasing pressure of water on one face under standard conditions, until penetration occurs in three places. The pressure at which water penetrates the substrate at the third place is noted. Evaluation results were described by water pressure (centimeters of H2O).


Figure 1. Particle size of silica sol catalyzed with different polycarboxylic acids at the same carboxyl concentration.

2.6. Evaluation of Durability. Durability of water repellency of the textile fabric was evaluated by performing water repellency measurements of washed textile fabrics. Laundering was carried out by subjecting treated fabrics according to the AATCC Test Method 61-2006.30 Samples were washed using a laundering machine (WASHTEC-P, Roaches International Ltd. England) at 40 °C in the presence of 50 stainless steel balls with the existence of standard reference detergent. One washing cycle (45 min) is approximate to five times of commercial laundering. The washed textiles were annealed at 120 °C during 30 min to simulate an iron procedure after washing and drying. Afterward, water repellency tests were performed. 3. Results and Discussion 3.1. Catalyst Effects on Sol Preparation. It is reported that polycondensation is the rate limiting step of the silica network formation in the acid-catalyzed sol-gel synthesis.17 Particle sizes of the silica sol catalyzed with different PAs were then measured at the same period to compare hydrolysis and condensation rates among the PA catalysts (Figure 1). Since the condensation process was known as pH-dependent, pH values of the resulting sols were also measured to help understand the final effect of an acidic catalyst.17 Results showed that the investigated silica sols had different pH values even at the same carboxyl concentration. All pH values were kept constant during the experimental period. This indicated that the hydrolysis of TEOS is rapid and complete. Moreover, the final pH sequence of the silica sol is the same as the pKa sequence of the investigated polycarboxylic acids.31 This indicated that the preparation of silica sol catalyzed by polycarboxylic acids

Figure 2. Water contact angle measurement of treated cellulose fabrics.

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also followed the ordinary reaction: hydrolysis of the precursor material and subsequent condensation reactions.17 However, since investigated PAs are organic acids and also to be used as cross-linkers, a larger amount is required than that of mineral inorganic acid to guarantee the complete hydrolysis of TEOS and enough esterification with cellulose.23-29 As a result, overall hydrolysis and condensation rates of PAsols differed from HCl catalyzed sol. It is observed that the gelation times of PA-sols are longer than that of the HCl-sol. For the silica sol prepared with BTCA and C4A, no gelation was found in 2 months. Figure 1 revealed that the particle size of silica sol is related to the pH value. The silica sols around pH 2 (the final pH value) showed smaller particle size among all sols. It could be presumed that a pH value of 2 seemed to be a turning point, as the particle size of the sol went up with an increasing pH value when the pH > 2, while sol-MA with pH 1.62 also showed a larger particle size than sol-C3A (pH 2.02). The polymerization process was divided into three approximate pH domains: pH 7.32 pH 2 appears as a boundary, since the point of zero charge (PZC) and the isoelectric point (IEP) both are in the range pH 1-3. It is generally assumed that above the IEP, the condensation rate is proportional to [OH-], and the polymerization rate is proportional to [H+] below pH 2. Therefore, the rate of particle growth and linking of particles into networks increased steadily between pH 2 and pH 7. The overall condensation rate of the silica sol catalyzed by PAs is C6A > C5A > C4A > BTCA > MAA > CA > MA > TA > C3A. The particle size of sols catalyzed by bicarboxylic acids (C6A > C5A > C4A > MAA > MA > TA > C3A) might also suggest condensation to be favored by longer organic chains for imparting better flexibility for the SiO2 polymeric matrix. The size distribution of PA-sols applied in subsequent coatings was controlled between 20-30 nm, since particle diameters smaller that 50 nm (“nanosols”) are preferred in the chemically or physically modified silica sols applied in the coating of textiles.1 3.2. Wettability and Washing Durability of PA Samples. The wettability of cotton fabric samples is mostly commonly characterized by water contact angle (WCA). It could be seen from Figure 2 that all samples (including sample N) exhibited good hydrophobicity with WCAs above 140° before washing. The variations of WCAs were probably caused by residual SHP and PAs, as the before-washing WCAs went down with better solubility of the corresponding PA. Different from sample N, all PA treated samples (except sample C6A) showed

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Table 2. Spray Test Ratings of Treated Cellulose Fabrics washing times sample

0

5

15

30

HCl C3A C4A MA MAA TA C5A C6A CA BTCA

100 95 95 95 95 95 95 95 95 95

80 90 95 95 90 90 95 90 95 95

70 80 85 85 85 80 85 75 85 85

60 75 75 75 75 70 70 70 75 80

similar phenomena that they showed higher WCAs after the first washing cycle (equal to five times washing) than the WCAs before washing, which also confirmed the existence of residual hydrophilic SHP and PA. Three factors account for the WCA increase of five-timewashed PA samples: good durability of resulted coating, elimination of residual hydrophilic components (SHP and PAs), and rougher fiber surface after the first washing cycle. Since fine crystallites of PA and SHP are embedded in the even silica coating on drying, the removal of these crystallites would lead to increased surface roughness accordingly.33 All samples showed a different decrease of WCAs after repeated washing. The decrease of WCAs increased with the increase of washing cycles. Sample N showed the most obvious decrease during washing. WCAs of all PA samples are much higher than that of sample N at all washing cycles. Even the worst sample TA showed a better hydrophobicity than sample N with WCA larger than 15° after 30 times of washing. This obviously indicated that the use of PA improved the washing durability of hydrophobicity. However, the fiber ends protruded from the surface of cotton fabric to make the determination of the baseline more difficult. The testing error of WCAs indicated that more methods of testing are needed to sufficiently evaluate water repellent properties of textiles. It reported that spray rating (Table 2) and hydrostatic pressure (Figure 3) could give more dynamic information about the water resistance of fabrics and a better indication of the repellency effect.34 The spray test evaluates the water repellent property in a more practical way, as it simulates a more customary condition like rain. Like WCA results, all samples exhibited a spray rating above 95 before washing, indicating good water repellency gained from the sol-gel process. Moreover, PA samples showed higher spray rating than that of sample N, even after different

Figure 3. Hydrostatic pressures of treated cellulose fabrics.

washing cycles. This also suggested the effectiveness of PAs in the improvement of washing durability. As wetting behavior of the hydrophobic cotton fabric could be described by the equation of the Cassie-Baxter state, hydrostatic pressure is also an important factor to consider for water penetration.6,35 Moreover, water resistance depends not only on the hydrophobicity of fibers and yarns but also fabric construction. As shown in Figure 3, it was found that all hydrophobic-treated samples showed an increased resistance to water penetration (more than 36 cm H2O) as compared with native cotton fabric (0 cm H2O). It might be due to the presence of silica particles on the surface of cellulose fibers, which increased the friction between fibers. As a result, the resistance to block water flow through the fabric increased. Although water resistance of all samples declined clearly after washing, all ester-bridged samples exhibited better resistance than sample N. The high hydrostatic pressure indicated that there was still a hydrophobic silica coating that remained on cellulose fabric even after 30 times of washing. 3.3. FTIR Spectra of BTCA Catalyzed Silica Gels and BTCA-Sol Treated Cellulose. FTIR spectra of BTCA catalyzed gels are compared with that of silica gel catalyzed by HCl in Figure 4. In Figure 4a, a strong and sharp peak at 1711 cm-1 is assigned to carboxyl acid groups (-COOH) introduced by BTCA. The band at 1089 cm-1 due to H-P-H wagging vibration and the band at 2384 cm-1 due to the P-H stretching vibration were caused by hypophosphite (SHP),36 which served as a catalyst in the esterification between PA and cellulose. Stretching vibrations of Si-O(H) bonds give rise to an absorption band at 810-950 cm-1.37 After rinsed with distilled water, the BTCA catalyzed silica gel (Figure 4b) does not show a significant difference compared with that of HCl (Figure 4c). A broad intensive band with a maximum at 3434 cm-1 arises from several vibration modes of the -OH groups. The strong bands in the region 1060-1200 cm-1 can be assigned to the asymmetric stretching vibrations of the Si-O-Si bonds of silica components.38 The broader and more complex Si-O-Si absorption in this region, showing two or more overlapping bands, implies the siloxane chains become longer or branched.39 The band at 1643 cm-1 could be due to deformation vibrations of -OH groups and confirms the presence of bound water. The similarity of parts b and c of Figure 4 implies that before the curing process, BTCA does not alter the structure of the resulting silica sol but worked only as a catalyst to accelerate hydrolysis and condensation of silicone


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Figure 5. FTIR spectra of (a) native cellulose fabric; (b) BTCA treated cellulose fabric; (c) BTCA-sol treated cellulose fabric.

Figure 4. FTIR spectra of (a) BTCA catalyzed silica gel; (b) BTCA catalyzed silica gel rinsed with distilled water; (c) HCl catalyzed silica gel; (d) BTCA catalyzed silica sol oven-dried at 80 °C, heated at 170 °C for 3 min, then rinsed with distilled water.

precursor. FTIR spectra of other PA-gels after rinsing show a similar phenomena (not shown). Figure 4d showed a FTIR spectrum of a cured BTCA catalyzed silica sol after repeated rinsing. When esterification occurs between PA and -OH, the carbonyls retained in three forms: ester, carboxylic acid, and carboxylate anion.24 As shown in Figure 4d, the band at 1565 cm-1 can be assigned to the carbonyl of the carboxylate anion, and carbonyls of the carboxylic acid and the ester were proposed to overlap at 1719 cm-1. These two bands confirmed the formation of ester bonds between Si-OH and BTCA as a result of the curing process. Furthermore, a decrease of the bands at 1643, 959, and 810 cm-1 implied the reduction of Si-OH groups, which could be due to esterification as well as further condensation between the Si-OH groups under curing. FTIR spectra corresponding to the cellulose samples before and after treatment with BTCA and BTCA-sol (both with SHP at 170 °C for 3 min) are shown in Figure 5. The washing process with distilled water was performed following curing to remove residual compounds. Compared with native cellulose, a new band at 1722 cm-1 in Figure 5b confirmed esterification between PA and cellulose.23-29 In Figure 5c, peaks of SiO2 were overlapped by broad bands of cellulose due to a low content of silica on fabric. However, the band at 1722 cm-1 is obvious, indicating the formation of ester bonds between cellulose-OH/ Si-OH and BTCA. In addition, the decreases of peak intensity of the treated cellulose were detected after treated with sol. As reported before, such changes indicate the increase of roughness of the cotton fabric surface.40-42 Since esterification occurs for BTCA with both Si-OH and cellulose, ester bridges linking the silica coating to the cellulose fabric are established by BTCA. After coating on the fiber

surface, carboxylic acid groups of PA would attach to cellulosesOH and SisOH by hydrogen bonds, and a celluloses OC(dO)sPA-C(dO)OsSi linkage is proposed to form during the curing process. These linkages would thus enhance washing durability of the treated cellulose fabric. The formation of cellulosesOC(dO)sPAsC(dO)Oscellulose and sSisOC (dO)sPAsC(dO)O-Sis bridges might also occur to generate a more complex cross-linking network in the silica sol coated cellulose fabric. 3.4. Structural Effect of Polycarboxylic Acids on Washing Durability of Hydrophobicity. From the results of the water contact angle, the spray test, and the hydrostatic pressure (Figures 2 and 3 and Table 2), varied wettability and durability were observed on cellulose fabrics treated with different PA sols. It was expected that the best performance would be obtained with PA, TEOS, and hydrophobic agent to provide good anchoring of the silica coating, a hydrophobic interface, and chemical interaction with the cellulose substrate. It could be seen that the number of carboxylic acid groups in the PA molecule (R(COOH)n) shows a significant influence on washing durability (Figures 2 and 3 and Table 2). The results showed that the durability of these PA samples increases generally in the order of dicarboxylic acid (n ) 2, C4A, MA, MAA, and TA) < tricarboxylic acid (n ) 3, CA) < tetracarboxylic acid (n ) 4, BTCA). It is reported that the carboxylic acids with more carboxyl acid groups could be more easily grafted onto cellulose fiber.22,23 The resulting interaction sites by grafting could also increase the resistance of the washing of the coating.27 Moreover, more carboxylic acid groups indicated more siloxane ester bonds formed between the silanol -OH group and the PA molecule. As a result, the increased flexibility of the silica network interlinked by PA increases the compatibility between the silica coating and the cellulose fiber. It could be concluded that the more carboxylic acid groups in the PA molecule, the more hydrophobicity of the cellulose fabrics preserved after washing. It could be generally concluded that washing durability of samples treated by dicarboxylic acids (HOOC-(CHR)mCOOH) catalyzed sol follows the order of m ) 2 (C4A, MA, MAA, and TA) > m ) 3 (C5A) ≈ m ) 1 (C3A) > m ) 4 (C6A). Esterification of PAs would be greatly favored when anhydride intermediates are formed during esterification, which depends largely on the distance between terminal carboxylic acid groups.29 On the basis of extensive studies, the formation of five-membered cyclic anhydride intermediates (m ) 2) is more effective than that of six-membered cyclic anhydride intermediates (m ) 3).38 In the case of C3A (m ) 1) and C6A

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Figure 6. SEM morphology of (a) native cellulose fabric; (b) sample N; (c) 30 times washed sample N; (d) sample BTCA; (e) 5 times washed sample BTCA; (f) 30 times washed sample BTCA.

(m ) 4), the acidity of reaction (pH) is a critical parameter for ester formation without formation of an anhydride. It was reported that a pH < 2 strongly favors esterification, and ester formation decreases rapidly with increased pH, whereas almost no esters are produced at a pH > 5.43 Therefore, better performance of sample C3A compared with C6A was expected. The effect of PAs with different functional groups and structures on washing durability was investigated (samples MAA, TA, and MA). However, the reported controversial effect of hydroxyl group on esterification of PAs was not found.27,44 The results of samples C4A (without -OH), MAA (with one -OH in a molecule), and TA (two -OH) showed the washing durability of hydrophobicity decreased with increasing number of hydroxyl groups in the PA molecule. The reduced hydrophobicity could be due to the increased surface -OH group, which is an effective adsorptive site for water molecules. The increased surface -OH group includes not only a newborn silanol group from the silica coating after washing but also the exposed hydroxyl group in the PA molecule in the silica coating. As a perfect specimen, sample BTCA shows remarkable hydrophobicity and washing durability. Sample BTCA particularly exhibited a high contact angle of 138.6° with the recovery

of 96.5% and more than 75% water resistance even after 30 washing times. This feature can be attributed to the most maximum number of carboxylic acid groups in the molecule (n ) 4). Moreover, the BTCA molecule also has enough distance between the two terminal carboxylic acid groups (m ) 4). The results suggested that polycarboxylic acid, with the proper number of carboxylic acid groups and distance between terminal carboxylic acid groups, could be used as bridge molecules to improve the washing durability of the hydrophobicity of the cotton fabric by the sol-gel method. 3.5. Morphology of Superhydrophobic Cellulose Fabrics. The surface morphologies of samples N and BTCA before and after home laundering cycles were measured using SEM (Figure 6). The surface morphology of the native cellulose fabric was also measured for comparison. A typical longitudinal fibril structure with natural veins, which was clearly observed on native cellulose fiber (Figure 6a), disappeared after silica sol coating and HDTMS treatment. The vanished characteristic parallel ridges and grooves could be due to the weakly cross-linked condensation layer formed by silica sols hydrolyzed under acidic conditions.45 The analysis in both samples N (Figure 6b) and BTCA (Figure 6d) showed that there


was a coating of silica gel on the surface of the fabric/fiber. However, there was no significant difference observed on the surface of samples N and BTCA before washing. Surface roughness of sample BTCA increased obviously after the first washing cycle (Figure 6e). It implies the elimination of embedded PA and SHP crystallites led to increased surface roughness accordingly.33 The rougher coating surface served as an argument for PA samples exhibiting larger WCAs after the first washing cycle than before washing. After 30 laundering times, a cluster of broken fragments could be clearly observed among fibers on sample N (Figure 6c), which implied that the silica coating on sample N was cracked after washing. Part of the silica coating was preserved on the fiber (area 1 in Figure 6c), and cracked fragments were observed adhering to the fiber surface (area 2 in Figure 6c) or scattering between fibers (area 3 in Figure 6c). Moreover, the vanished parallel ridges and grooves tended to appear again, indicating seriously flaking off of deposited SiO2 coating. In the image of 30-time-washed sample BTCA (Figure 6f), few morphology changes were observed compared with 5-timewashed sample BTCA (Figure 6e). As compared with 30-timewashed sample N (Figure 6c), the integrity of the hydrophobic coating on the surface of sample BTCA was largely preserved. These results implied that the silica coating of sample BTCA had a much stronger adhesion to cellulose fiber than that of sample N. It is also suggested that the bridges introduced by BTCA between cellulose-OH and Si-OH had played a most important role in the enhancement of the silica coating adhesion. 4. Conclusions All nine polycarboxylic acids used in this work have been proven effective in improving the washing durability of hydrophobic cellulose fabrics achieved by sol-gel technology. The results indicated that PAs played a dual role based on their acidity and multifunctionality. In the stage of sol preparation, polycarboxylic acids served only as acidic catalysts without changing the structure of resulting silica sol. Polycarboxylic acids worked as a cross-linker by forming ester bonds with cellulose-OH and Si-OH after the PA-sols coated cellulose were cured. Polycarboxylic acid with the proper number of carboxylic acid groups and distance between terminal carboxylic acid groups could effectively improve the washing durability of hydrophobicity. Among various PAs, 1,2,3,4-butanetetracarboxylic acid (BTCA) gave the best performance (i.e., hydrophobicity and its washing durability). After 30 times washing, the BTCA employed hydrophobic cellulose fabric still presented a high contact angle above 138°, while that of the non-PA counterpart was less than 110°. The morphology study by SEM also confirmed the enhanced coating adhesion imparted by BTCA. This study demonstrated that the organic-inorganic sol-gel hybrid using PA as the catalyst is appropriate for achieving a durable hydrophobic cellulose fabric. Acknowledgment The research was supported by the Shanghai Natural Science Foundation (Grant No. 10ZR1400500) and the Fundamental Research Funds for the Central Universities (Grant No. 9D10508). Literature Cited (1) Mahltig, B.; Haufe, H.; Bo¨ttcher, H. Functionalisation of Textiles by Inorganic Sol-Gel Coatings. J. Mater. Chem. 2005, 15, 4385.

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(2) Daoud, W. A.; Xin, J. H.; Tao, X. Superhydrophobic Silica Nanocomposite Coating by a Low-Temperature Process. J. Am. Ceram. Soc. 2004, 87, 1782. (3) Li, Z.; Xing, Y.; Dai, J. Superhydrophobic Surfaces Prepared from Water Glass and Non-Fluorinated Alkylsilane on Cotton Substrates. Appl. Surf. Sci. 2008, 254, 2131. (4) Barthlott, W.; Neinhuis, C. Purity of the Sacred Lotus, or Escape from Contamination in Biological Surfaces. Planta 1997, 202, 1. (5) Barthlott, W.; Neinhuis, C. Louts Effect: Nature’s Model for SelfCleaning Surfaces. Int. Text. Bull. 2001, 47, 8. (6) Cassie, A. B. D.; Baxter, S. Wettability of Porous Surfaces. Trans. Faraday Soc. 1944, 40, 546. (7) Wenzel, R. N. Resistance of Solid Surface to Wetting by Water. J. Ind. Eng. Chem. 1936, 28, 988. (8) Zimmermann, J.; Reifler, F. A.; Fortunato, G.; Gerhardt, L.; Seeger, S. A Simple, One-Step Approach to Durable and Robust Superhydrophobic Textiles. AdV. Funct. Mater. 2008, 18, 3662. (9) Mahltig, B.; Bo¨ttcher, H. Modified Silica Sol Coatings for WaterRepellent Textiles. J. Sol-Gel Sci. Technol. 2003, 27, 43. (10) Roe, B.; Zhang, X. Durable Hydrophobic Textile Fabric Finishing Using Silica Nanoparticles and Mixed Silanes. Text. Res. J. 2009, 79, 1115. (11) Vince, J.; Orel, B.; Vilcˇenik, A.; Fir, M.; Vuk, A. Sˇ.; Jovanovski, V.; Simoneˇieˇ, B. Structural and Water-Repellent Properties of a Urea/ Poly(Dimethylsiloxane) SolsGel Hybrid and its Bonding to Cotton Fabric. Langmuir 2006, 22, 6489. (12) Yeh, J.; Chen, C.; Huang, K. Preparation and Application of Fluorocarbon Polymer/SiO2 Hybrid Materials, Part 2: Water and Oil Repellent Processing for Cotton Fabrics by Sol-Gel Method. J. Appl. Polym. Sci. 2007, 103, 3019. (13) Tan, B.; Rankin, S. E. Study of the Effects of Progressive Changes in Alkoxysilane Structure on Sol-Gel Reactivity. J. Phys. Chem. B 2006, 110, 22353. (14) Plueddemann, E. P. Silane Coupling Agents, 2nd ed.; Plenum: New York, 1991. (15) Krasnoslobodtsev, A. V.; Smirnov, S. N. Effect of Water on Silanization of Silica by Trimethoxysilanes. Langmuir 2002, 18, 3181. (16) Britcher, L. G.; Kehoe, D. C.; Matisons, J. G.; Swincer, A. G. Siloxane Coupling Agents. Macromolecules 1995, 28, 3110. (17) Brinker, C. J.; Scherer, G. W. Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing; Academic Press: Boston, MA, 1990. (18) Hernańdez-Padroń, G.; Rojas, F.; Castanõ, V. M. Ordered SiO2(Phenolic-Formaldehyde Resin) in situ Nanocomposites. Nanotechnology 2004, 15, 98. (19) Leite, E. R.; Carrenõ, N. L. V.; Longo, E.; Pontes, F. M. Development of Metal-SiO2 Nanocomposites in a Single-Step Process by the Polymerizable Complex Method. Chem. Mater. 2002, 14, 3722. (20) Textor, T.; Schro¨ter, F.; Schollmeyer, E. Functionalisation of Textiles with Nanotechnology. Mater. Res. Soc. Symp. Proc. 2006, 920, 1. (21) Meilert, K. T.; Laub, D.; Kiwi, J. Photocatalytic Self-Cleaning of Modified Cotton Textiles by TiO2 Clusters Attached by Chemical Spacers. J. Mol. Catal. A: Chem. 2005, 237, 101. (22) Menaa, B.; Mizuno, M.; Takahashi, M.; Tokuda, Y.; Yoko, T. Polycarboxylic Acids as Network Modifiers for Water Durability Improvement of Inorganic-Organic Hybrid Tin-Silico-Phosphate Low-Melting Glasses. J. Solid State Chem. 2006, 179, 492. (23) Schramm, C.; Rinderer, B.; Bobleter, O. Kinetic Data for the Crosslinking Reaction of Polycarboxylic Acids with Cellulose. J. Soc. Dyers Colour. 1997, 113, 346. (24) Yang, C. Q. Characterizing Ester Crosslinkages in Cotton Cellulose with FT-IR Photoacoustic Spectroscopy. Text. Res. J. 1991, 61, 298. (25) Yang, C. Q. FT-IR Spectroscopy Study of the Ester Crosslinking Mechanism of Cotton Cellulose. Text. Res. J. 1991, 61, 433. (26) Yang, C. Q. Infrared Spectroscopy Studies of the Cyclic Anhydride as the Intermediate for the Ester Crosslinking of Cotton Cellulose by Polycarboxylic Acids. 1. Identification of the Cyclic Anhydride Intermediate. J. Polym. Sci., Part A: Polym. 1993, 31, 1187. (27) Yang, C. Q.; Wang, X.; Kang, I. Ester Crosslinking of Cotton Fabric by Polymeric Carboxylic Acids and Citric Acid. Text. Res. J. 1997, 67, 334. (28) Gu, X.; Yang, C. Q. FTIR Spectroscopy Study of the Formation of Cyclic Anhydride Intermediates of Polycarboxylic Acids Catalyzed by Sodium Hypophosphite. Text. Res. J. 2000, 70, 64. (29) Mao, Z.; Yang, C. Q. IR Spectroscopy Study of Cyclic Anhydride as Intermediate for Ester Crosslinking of Cotton Cellulose by Polycarboxylic Acids. V. Comparison of 1,2,4-Butanetricarboxylic Acid and 1,2,3Propanetricarboxylic Acid. J. Appl. Polym. Sci. 2001, 81, 2142. (30) American Association of Textile Chemists and Colorists (AATCC). AATCC Technical Manual; AATCC: Research Triangle Park, NC, 2007.

9142


(31) Dean, J. A. Lange’s Handbook of Chemistry, 15th ed.; McGrawHill Inc.: New York, 1999. (32) Iler, R. K. The Chemistry of Silica; Wiley: New York, 1979. (33) Isobe, H.; Utsumi, S.; Yamamoto, K.; Kanoh, H.; Kaneko, K. Micropore to Macropore Structure-Designed Silicas with Regulated Condensation of Silicic Acid Nanoparticles. Langmuir 2005, 21, 8042. (34) Shekar, R. I.; Kasturiya, N.; Raj, H.; Mathur, G. N. Studies on Effect of Water Repellent Treatment on Flame Retardant Properties of Fabric. J. Ind. Text. 2001, 30, 222. (35) Hoefnagels, H. F.; Wu, D.; de With, G.; Ming, W. Biomimetic Superhydrophobic and Highly Oleophobic Cotton Textiles. Langmuir 2007, 23, 13158. (36) Morris, C. E.; Morris, N. M.; Trask-Morrell, B. J. Interaction of Meso-1,2,3,4-Butanetetracarboxylic Acid with Phosphorus-Containing Catalysts for Esterification Cross-Linking of Cellulose. Ind. Eng. Chem. Res. 1996, 35, 950. (37) Almeida, R. M.; Guiton, T. A.; Pantano, C. G. Characterization of Silica Gels by Infrared Reflection Spectroscopy. J. Non-Cryst. Solids 1990, 121, 193. (38) Schramm, C.; Binder, W. H.; Tessadri, R. Durable Press Finishing of Cotton Fabric with 1,2,3,4-Butanetetracarboxylic Acid and TEOP/ GPTMS. J. Sol-Gel Sci. Technol. 2004, 29, 155.

(39) Launer, P. J. In Silicone Compounds Register and ReView; Arkles, B., Eds.; Petrarch Systems:Bristol, PA, 1987. (40) Li, F.; Xing, Y.; Ding, X. Silica Xerogel Coating on the Surface of Natural and Synthetic Fabrics. Surf. Coat. Technol. 2008, 202, 4721. (41) Cu, X.; Raghavan, D.; Nguyen, T.; VanLandingham, M. R.; Yebassa, D. Characterization of Polyester Degradation Using Tapping Mode Atomic Force Microscopy: Exposure to Alkaline Solution at Room Temperature. Polym. Degrad. Stab. 2001, 74, 139. (42) Colthup, N. B.; Daly, L. H.; Wiberley, S. E.; Introp, P. Introduction to Infrared and Raman Spectroscopy, 3rd ed.; Academic: Boston, MA, 1990. (43) Pantze, A.; Karlsson, O.; Westermark, U. Esterification of Carboxylic Acids on Celluloseic Material: Solid State Reactions. Holzforschung 2008, 62, 136. (44) Pantze, A. Studies of Ester Formation on a Cellulose Matrix. Licentiate Thesis, Lulea˚ University of Technology, 1996. (45) Claessens, H. A.; Straten, M. A. V.; Kirkland, J. J. Effect of Buffers on Silica-Based Column Stability in Reversed-Phase High-Performance Liquid Chromatography. J. Chromatogr., A 1996, 728, 259.

ReceiVed for reView June 11, 2010 ReVised manuscript receiVed August 1, 2010 Accepted August 15, 2010 IE1012695

Durable Hydrophobic Cellulose Fabric Prepared with Polycarboxylic

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