Effect of Surface Treatment on Titania-Modified PET Fiber Using

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Ind. Eng. Chem. Res. 2009, 48, 8487–8492

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Effect of Surface Treatment on Titania-Modified PET Fiber Using Polyethylene Nanoparticles Yung-Pin Huang,* Jing-Wen Tang, Fen-Mei Chang, and Chin-Heng Tien DiVision of AdVanced Fiber and Bio Materials Research, Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan 300, R.O.C

Polyethylene (PE) nanoparticles were newly prepared by a combination of ultrasonication and low-temperatureinduced crystallization in poly(ethylene glycol). These PE particles were formulated into spin finishes and applied to the surface of titania-modified poly(ethylene terephthalate) (PET) fibers that had a higher relative concentration of titania (TiO2) nanoparticles at the fiber surface than in the interior core as evidenced by SEM/EDX mapping studies. Aggregations of TiO2 nanoparticles were found to appear on the surface of such fibers, which led to a decreased contact area and, thus, an increased contact pressure between the sliding fiber and its encountered surface. The effect of plowing by the sliding fiber on its counterpart was observed and studied as a function of the PE nanoparticle size, and the corresponding data on the friction force among three values of fiber fineness were also obtained. We found that the fiber friction force decreased and the plowing effect on its counterpart increased when the fiber fineness decreased. In addition, we found that the minimum plowing effect was obtained when the size of the PE nanoparticles was comparable to the size of the TiO2 aggregations that appeared on the surface of the titania-modified PET fibers. 1. Introduction Applications of poly(ethylene terephthalate) (PET) fibers coated with titania (TiO2) have been reported for a variety uses,1-3 because of their photocatalytic properties. In photocatalytic water treatment for the degradation of pollutants, titania is coated on supporting particles, fibers, and honeycombs to increase the photocatalytic efficiency.2 Using plasma and ultraviolet (UV) irradiation, titania can be bonded to polyester textiles, and the photocatalytic activity of the coating allows for the almost complete discoloration of coffee and wine stains.3 Also, TiO2 has been found to form a homogeneous thin film on the fiber surface when applied by the sol-gel method and shows efficient stain-cleaning effects upon exposure to solar light.4-6 The antimicrobial effects of titania-coated textiles have also been investigated by plasma grafting of titania nanoparticles,7 by dipcoating to fix apatite-coated TiO2,8 and by the sol-gel method to load Ag/TiO2.9 In addition, because a titania film can absorb light with an energy that matches or exceeds the energy of its band gap,10 a UV-blocking fabric was achieved11 by forming a titania film on the fiber surface by the sol-gel process. Our UPF (ultraviolet protection factor) study12 of this TiO2-modified PET fiber hosiery gave a high rating of >50, which is excellent UV protection according to Standard AS/NZS 4399. On the other hand, because surface lubricity and friction coefficient can significantly affect the performance and end use of PET fibers, high-lubricity silicone13 additives and polyolefin waxes14 have been copolymerized or blended with PET resins and then processed into product form, such as high-surfacelubricity fibers. For example, we incorporated TiO2 particles into PET fibers to make fibers with a permanent low-friction surface.12 These TiO2 particles on the fiber surface show aggregation and cause surface unevenness, which leads to a decreased contact area between the sliding fiber and any surface it encounters; thus, a lower-friction fiber surface is achieved. It was also found that the uneven surface of TiO2-modified fibers can improve and assist the spreading of spin finishes during * To whom correspondence should be addressed. Fax: +886 3 5732358. Tel.: +886 3 5732733. E-mail: [email protected].

the high-speed melt-spinning process. Carroll15 studied the effect of surface roughness on the spreading of a fluid on cylindrical material. He found that the effect of surface roughness is always to reduce the contact angle of the wetting liquid. In our previous studies,12,16,17 TiO2 aggregation was found to improve the wetting ability of the spin finish spreading along the fiber surface and, thus, assist in the reduction of fiber evenness (UCV, %). A low UCV is preferred for fiber quality control, whereas a high UCV is usually associated with a variation in fiber strength and many visible faults on the fabric surface.18 In this study, a method was developed to make polyethylene (PE) nanoparticles by a combination of ultrasonication and lowtemperature-induced crystallization in poly(ethylene glycol) (PEG). These PE nanoparticles were formulated into spin finishes and applied to titania-modified PET fibers. We focused on the relationships among the morphology of the TiO2 aggregations appearing on the fiber surface, the effects of plowing by a sliding fiber on its counterpart, and the size of the PE nanoparticles adhered to the fiber surface. 2. Materials and Methods 2.1. Materials. PET polymer pellets incorporated with spinning-grade TiO2 nanoparticles at 0.3 and 2.5 wt % were either obtained from Shinkong Synthetic Fiber Corporation, Taipei, Taiwan, or prepared in our pilot plant by the PET polymerization process,12,19 where the spinning-grade TiO2 particles were first mixed with ethylene glycol to form a dilute slurry, which was then pumped into a reactor to conduct the step polymerization with terephthalic acid. Polyethylene, with a number-average molecular weight (Mn) of 1000 and a d90 grain size (grain size at which 90% of the sample is finer) of 12.62 µm, was purchased from Sasol Wax Ltd., Sasolburg, South Africa. Poly(ethylene glycol) with an average molecular weight of 300 (PEG 300) was obtained from Sigma-Aldrich. Two types of ethylene oxide/ propylene oxide (EO/PO) random copolymer were formulated in our work. EO/PO with a molar ratio of 75/25 and an Mn of 5000 (EO/PO-75/25-5K) was obtained from Schill & Seilacher GmbH & Co., Heilbronn, Germany. EO/PO with a molar ratio

10.1021/ie900811r CCC: $40.75  2009 American Chemical Society Published on Web 07/27/2009

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Table 1. Preparation Conditions and Average Sizes of PE Particle Suspensions batch no.

PE (mg)

PEG 300 (mg)

concentration (wt %)

amplitude of sonication (%)

cooling temperature (°C)

1 2 3 4 5 6 7 8 9 10 11 12

0.1 0.25 0.1 0.25 0.1 0.25 0.1 0.25 0.1 0.25 0.1 0.25

10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0

1.0 2.5 1.0 2.5 1.0 2.5 1.0 2.5 1.0 2.5 1.0 2.5

10 10 30 30 50 50 10 10 10 10 10 10

-10 -10 -10 -10 -10 -10 -20 -20 0 0 +25 +25

a

particle morphology spherical spherical between cylindrical between cylindrical cylindrical cylindrical spherical spherical between cylindrical between cylindrical irregular irregular

and spherical and spherical

and spherical and spherical

avg sizea (µm) 0.055 0.088 0.081 0.355 0.133 0.551 0.045 0.065 1.151 1.825 ∼3 ∼5

Average of at least 20 particles; the size of an individual particle was taken as the mean of its longest and shortest dimensions.

Table 2. Compositions of Spin Finish Recipes recipe

composition (wt %)

EO/PO-50/50-1.7K EO/PO-50/50-5K suspension of 1.0 wt % PE particles in PEG 300 C12AX

47.0 15.0 33.0 5.0

of 50/50 and an Mn of 1700 (EO/PO-50/50-1.7K) was obtained from Sino-Japan Chemical Co. Ltd., Taipei, Taiwan. Dimethyllaurylamine oxide (C12AX) at 30 wt % concentration, obtained from Taiwan Surfactant Corporation (Taipei, Taiwan), was formulated into the spin finish to increase its wetting ability on the fiber surface. 2.2. Methods. 2.2.1. Preparation of PE Particles in the Spin Finish. PE nanoparticles have been synthesized for different applications. Fowler et al.20 used PE particles as cleansing agent components in the cosmetics industry. Yarovoy et al.21 studied the influence of submicrometer-size PE particles on cell response: They used hot decalin to dissolve polyethylene polymer and added, with vigorous stirring, hot tetraglyme (nonsolvent) to this solution. Microdroplets of PE solution were formed and dispersed in this high-temperature mixture. Upon cooling, the temperature-induced crystallization of PE particles occurred. Chen et al.22 used decalin and tetraglyme to synthesize polyethylene particles containing iron oxide nanoparticles for use in biomedical applications. These methods all require tedious synthesis and separation procedures to make PE particles and also might fail to produce the particles in the desired yields. In this article, we present an easy method for the synthesis of PE nanoparticles that requires no separation process prior to use in fiber application. In our typical preparation, a dilute (1.0 wt %) and transparent suspension (25 mL) of PE polymer was made using PEG 300 at 150 °C and ultrasonicating at 60% amplitude in a 50-mL vial. The ultrasonication device used was a Sonicator 3000 (MISONIX Inc., Farmingdale, NY). During ultrasonication, the suspension was rapidly cooled to -10 °C (or lower). After 30 s, the ultrasonication amplitude was reduced to 10-50%, and the vial was kept at the above temperature for at least 2.5 min. Table 1 provides an overview of the preparation condition for 12 different batches of low-temperature-induced crystallized PE particle suspensions, which were subsequently formulated into an EO/PO-based spin finish. Table 2 lists the compositions of the spin finishes used in this study. 2.2.2. PET Melt Spinning and Spin Finish Application. The spin finish of 10 wt % solid in an aqueous system was applied to the PET melt spinning fibers at an application ratio of 0.66 wt % solid. The takeup unit used was a Teijin Seiki NS 419 winder, which was set to take up fiber at a speed of 2650 m/min. Denier per filament (dpf) is one of the most useful parameters for describing the fineness of a single filament (i.e.,

fiber), where 1.0 dpf corresponds to a 9000-m-long filament with a weight of 1.0 g and lower values indicate that the crosssectional area of the fiber is finer. PET multifilament yarns with round filament cross sections of 1.40 dpf (50 denier/36 filaments), 1.10 dpf (79 denier/72 filaments), and 0.90 dpf (65 denier /72 filaments) were used for the present study. 2.2.3. Measurements of Friction and Abrasion. According to standard method ASTM D3108-89, the fiber to steel-rod (with a 7.98-mm diameter) friction was measured with a R-1083 yarn friction meter (Rothschild Instruments, Zu¨rich, Switzerland) at a wrap angle of 90°. Τhe experiments were conducted at 23 ( 1 °C and (65 ( 2)% relative humidity (RH). Three testing speeds (100, 200, and 300 m/min) were used. A total of 1080 friction data points per minute obtained at each speed were averaged and taken as the fiber to steel-rod friction force. The effect of plowing by the sliding fibers on a copper plate (abrasion value) was measured with an abrasion meter (Honigmann Industrielle Elektronik GmbH, Wuppertal, Germany). Τhe experiments were conducted at 23 ( 1 °C and (65 ( 2)% RH. The testing speed was 250 m/min, and the testing interval was 20 min. The pretension was controlled to 0.2 cN/denier, and the detected initial value was set to 20 µm. Three measurements were made to determine each abrasion value of the copper plate, and the means are reported herein. 2.2.4. Mapping of Titania in Fiber Cross Section (SEM/EDX). The finish oil on the fiber was extracted by ethanol before scanning electron microscopy/energy dispersive X-ray (SEM/EDX) mapping studies. SEM images for longitudinal and cross-sectional specimens of the titania-modified PET fibers were obtained. To prepare the cross section of a fiber, a hooktail needle was inserted into the circular hole of an aluminum plate to hook a bundle of fiber, and then the needle was pulled back so that the fiber was tightly jammed in the hole. We cut the fiber along the surface of the aluminum plate with a knife to give a trimmed fiber cross section for SEM observation. Samples were typically deposited with a thin layer of platinum using an Edwards S150B sputter coater and then examined with a Hitachi S-4700 field emission scanning electron microscope equipped with an EDX analyzer. At a magnification factor of about 5000, we studied the location and distribution of TiO2 particles within the fiber samples (Figure 1). 3. Results and Discussion 3.1. Characterization of the Prepared PE Particles. SEM samples of PE particles were prepared by placing a drop of the suspension of PE particles in water (1:1000) on a supporting surface and letting the water evaporate. From Table 1, it can be seen that a decrease in the amplitude of sonication gave

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Figure 1. Locations of EDX data collection for the illustration of the distance from the fiber surface (label 1) into the core (label 5).

smaller particles (batch nos. 1, 3, and 5). The effect of sonication at the cooling step, where interparticle collisions occur, might lead to agglomeration and changes in the particle morphology. Particle morphology was found to be cylindrical at 50% amplitude; in contrast, the particles were more or less spherical at 10% amplitude. Figure 2 shows some representative SEM micrographs of the PE particles. The effect of the PE concentration on the size of the particles was tested (Table 1), and it was found that a lower suspension concentration resulted in a significantly smaller size of the particles (batch nos. 1 and 2). Yarovoy et al.21 derived a relationship between the average diameter of submicrometersize PE particles and the concentration of PE polymer, proposing that the PE particle size is roughly proportional to the cubic root of the highly dilute ( 1.1 dpf > 1.4 dpf. This indicates that the lower dpf of the yarn, the more TiO2 aggregates on the fiber surface. Figure 4 shows the SEM morphologies of PET longitudinal fibers of 0.90, 1.10, and 1.40 dpf with 2.5 wt % TiO2 and 1.10 dpf with 0.3 wt % TiO2. From the representative SEM images in Figure 4 and some additional SEM micrographs, it is apparent that the aggregated TiO2 particles appeared clearly on the fiber surface and the aggregation size was about 400-600 nm. This can be attributed to the effect of melt spinning on the morphology of the PET composite. It has been indicated that the amount of crystalline phase increases with increasing spinning rate up to 7000 m/min;24-26 this crystallization could provide the driving force to separate the TiO2 particles from the bulk PET and, therefore, cause them to migrate onto the fiber surface and form TiO2 aggregates. In addition, a comparison of the micrographs of Figure 4a (0.90 dpf) and Figure 4c (1.40 dpf) reveals that greater numbers of TiO2 aggregates appeared the surface of the fibers with smaller fineness. In addition, comparison of the surface morphologies from the respective SEM images (Figure 4b,d) reveals that greater numbers of TiO2 aggregates appeared on the surface of the fibers with 2.5 wt % TiO2 than on those with 0.3 wt % TiO2 fiber. 3.3. Friction Force and Abrasion Measurements. Introduction fillers of solid lubricants are used to improve the wear resistance of the matrix material. Bahadur and Gong27 found that polytetrafluoroethylene (PTFE) powder can be used in most polymers to reduce the effects of wear. Tian and Huang28 found that PTFE is effective fillers for distinct effects on the wear behavior of a polyurethane (PU) coating. Li et al.29 found that graphite powder is able to increase the wear resistance of the epoxy composite greatly. Song et al.30 found that phenolic coating filled with 10 wt % graphite exhibits better antiwear ability than the unfilled coating. In our study, solid lubricants of PE nanoparticles were newly prepared and filled in the spin finish of titania-modifed PET fibers. We found that the PE particles are effective fillers to increase the wear resistance of the sliding fiber counterpart. Aggregation of TiO2 particles occurring on the titania-modifed PET fiber surface can lead to a decreased contact area, and thus (according to the relationship of contact force ) contact pressure × contact area), an increased contact pressure between the sliding fibers and the encountered surface is established. Therefore, a severe plowing effect on the fiber encountered surface was surely found. In this regard, it is of practical importance to reduce this severe plowing effect on the processing machinery of titania-modified PET fibers. The effects of the amount of TiO2 on the extent of fiber friction and the abrasion value of the copper plate are reported in Table 4, where PE particles of batch no. 10 (with an average size of 1.825 µm) were applied to the fiber surface. These were distinguished in terms of their TiO2 contents of 0.3 and 2.5 wt % and also in terms of their fineness values of 1.4, 1.1, and 0.9 dpf. From Table 4, one can see that, for fibers with 2.5 wt % TiO2, the order of increasing friction force/denier was 0.9 dpf < 1.1 dpf < 1.4 dpf, whereas the order of increasing abrasion/ denier value was 1.4 dpf < 1.1 dpf < 0.9 dpf. This indicates

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Figure 2. SEM images of PE particles fabricated at -10 °C temperature: batch nos. (a) 1, (b) 3, and (c) 5 (all from Table 1). It was found that the decrease in the amplitude of sonication gave smaller particles.

Figure 3. SEM images of fabricated PE particles cooled at different temperatures: batch nos. (a) 7, (b) 9, and (c) 11 (all from Table 1). It was found that a decrease in the cooling temperature gave smaller particles. Table 3. EDX Analysis of the Titanium/Carbon Atom Ratios of the TiO2-Modified PET Fiber As a Function of Depth from the Fiber Surface (Label 1) to the Core (Label 5) yarn

titanium/carbon atom ratio (%)

code

titania (wt %)

dpf

denier

label 1 (surface)

label 2

1.4f-2.5t 1.1f-2.5t 0.9f-2.5t 1.1f-0.3t

2.5 2.5 2.5 0.3

1.4 1.1 0.9 1.1

50 79 65 79

1.08 1.21 1.79 0.21

1.02 1.08 1.31 0.17

that an inverse relationship between friction force/denier and abrasion/denier value was established for all of the 2.5 wt % TiO2 fibers in Table 4. Moreover, comparison of the 1.1f-2.5t and 1.1f-0.3t data in Table 4 reveals that the fibers with 2.5 wt % TiO2 had a higher abrasion value and a lower friction force than the 0.3 wt % TiO2 fibers. This is attributed to the fact that the fibers with 2.5 wt % TiO2 would cause separation of the sliding fiber and the encountered surface and would typically have a smaller contact area than the equivalent 0.3 wt % TiO2 fibers, for which a low friction force and a relatively strong plowing effect on the counterpart was observed.

Figure 4. SEM images of longitudinal PET fibers of (a) 0.90, (b) 1.10, and (c) 1.40 dpf yarn with 2.5 wt % TiO2 and (d) 1.10 dpf yarn with 0.3 wt % TiO2. Both the amount of TiO2 and the dpf of the PET yarn strongly influence the morphology of the fiber surface.

label 0.95 0.76 0.75 0.12

3

label 0.87 0.62 0.53 0.07

4

label 5 (core) 0.82 0.52 0.30 0.02

The influence of the PE particle size on the abrasion value of the copper plate is shown in Figure 5, where the abrasion/ denier values are plotted against the PE particle size. The fibers to which smaller particles of PE had been applied exhibited lower abrasion values and smaller variations among yarns of different dpf values. On the other hand, fibers to which larger PE particles had been applied exhibited higher abrasion values and larger variations among yarns of different dpf values. This shows that lower abrasion values were attained when the PE particle size was below 550 nm, which was comparable to the TiO2 aggregation size appearing on the fiber surface. The friction behavior of the spin-finished fiber can be well predicted using hydrodynamic lubrication theory,31 whereas no clear understanding of the mechanisms that cause the reduced abrasion levels (due to the presence of TiO2 aggregations and PE particles at the friction interface) has been documented. Orband et al.32 observed that there is a critical particle diameter (dcrit) below which the cohesiveness of particles33 rapidly increases, resulting in the formation of a layer of high interparticle cohesive energy. Mill et al.34 conducted a Stanley pendulum friction test on a glass surface of sufficient roughness with the presence of particulate contamination at the friction interface and found that, for d < dcrit, the particles tend to clump together (and a degree of mechanical interlocking within the asperities of glass roughness occurs) and pass through the contact in a shear deformation action. In Figure 5, lower abrasion values occurred with PE particles of less than 0.55 µm (somewhat like dcrit). In this case, a degree of mechanical interlocking probably occurred, where some of the PE particles were interlocked within the asperities of the fiber surface roughness (which caused the roughness to be reduced) and some other particles tended to clump together and passed through the contact in a shear deformation action (which caused the fiber

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a

Table 4. Friction Force/Denier of Fiber to Steel-Rod and Abrasion/Denier Values of Copper-Plate for the Yarns with Different dpf Values and Sliding Speeds yarn

friction force/denier (cN)

abrasion/denier (µm)

code

titania (wt %)

dpf

denier

100 m/min

200 m/min

300 m/min

250 m/min

1.4f-2.5t 1.1f-2.5t 0.9f-2.5t 1.1f-0.3t

2.5 2.5 2.5 0.3

1.4 1.1 0.9 1.1

50 79 65 79

0.14 0.13 0.12 0.23

0.16 0.15 0.14 0.32

0.18 0.17 0.14 0.39

0.76 0.90 1.10 0.06

a

Yarns were treated with PE particles of batch no. 10 (avg size ) 1.825 µm).

Figure 5. Plots of abrasion/denier values against the PE particle sizes applied to the TiO2-modified PET fiber. With smaller PE particles, lower abrasion/ denier values were exhibited. The lowest abrasion/denier value was obtained when the diameter of the PE particles was comparable to 550 nm (batch no. 6).

friction force to increase and the abrasion value of the copper plate to decrease). Figure 6 shows SEM micrographs of a new surface and a few worn surfaces of the copper plate encountered by 1.1f-2.5t yarn to which with PE particles of three different sizes (551, 1151, and 1825 nm) were applied. The new surface of the copper plate (Figure 6a) shows the original porous, rough, and discontinuous machine marks. The worn surfaces encountered by the sliding fiber that was surface-treated with 551-nm PE particles was characterized by slightly scuffing (Figure 6b), and its abrasion/denier value was 0.18 µm (Figure 5). In contrast, more scuffing lines were observed for a PE particle size of 1151 nm (Figure 6c), which had an abrasion/denier value of 0.49 µm (Figure 5). Moreover, the fiber surface to which 1825-nm PE particles had been applied showed the most obvious and severe plowing effect, and its worn surface had an abrasion/denier value of 0.89 µm (Figure 5); this high abrasion/denier value accounts for its severe plowing effect on the copper plate. Mill et al.34 found that, for d > dcrit, the particles behave in a more discrete fashion and are able to roll/tumble through the contact independently of the other particles, in which case a continual entrainment of particles is required for the tumbling to be

Figure 6. SEM images of the (a) new copper-plate surface and the worn surfaces encountered by 1.1f-2.5t yarn whose finish was filled with (b) 550-nm PE particles (batch no. 6), (c) 1151-nm PE particles (batch no. 9), and (d) 1825-nm PE particles (batch no. 10).

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maintained. In Figure 6c,d, the severe plowing effect on the copper plate was probably due to the shortage of continual entrainment of particles required for the tumbling to be maintained, in which case the contact (of the fiber asperities and the copper plate) was remade, so that the plowing effect on the copper plate was high. 4. Conclusions Micrometer-, submicrometer-, and nanosized PE particles were newly fabricated by a combination of ultrasonication and low-temperature-induced crystallization in PEG. Two main factors, the cooling temperature and the amplitude of sonication, determined the size (from 0.045 to 5 µm) of the PE particles. These PE particles were formulated into spin finishes and applied to the surface of titania-modified PET fibers, which showed the formation of TiO2 aggregations on the fiber surface and a decreasing concentration of titana from the fiber surface to the core. These TiO2 aggregations could result in a lowfriction fiber and, thus, a high plowing effect on the encountered surface. Moreover, an inverse relationship between the fiber friction force and the abrasion value of its counterpart was found, where the yarn with a lower dpf value gave rise to a larger abrasion value (and a smaller fiber friction force) than the yarn with a higher dpf. From these measurements, in combination with SEM images, we concluded that the size of the PE particles that were applied to the surface of titania-modified PET fibers played a dominant effect on the abrasion value of the encountered copper plate. This showed that lower abrasion values were attained with PE particle sizes below 550 nm, which was comparable to the size of TiO2 aggregations appearing on the fiber surface. The prepared fibers with different contents of TiO2 gave a broad range of yarn friction forces and a high UPF rating of >50, which would provide potential performance in the fiber industry. On the other hand, given the continuing interest in the fabrication of polymer particles suitable for biology and other different application fields, the easy method presented herein might enable the synthesis of PE nanoparticles in desirable yields and, thus, show promise in numerous fields, especially to reduce the plowing effects of sliding titania-modified PET fibers on their counterparts. Literature Cited (1) Toshiki, S.; Nobuko, K.; Hideyuki, H. Fiber. Japanese Patent Application JP09225781, 1997. (2) Kaneko, M.; Okura, I. Photocatalysis Science and Technology; Kodasha/Springer: Tokyo, 2002. (3) Bozzi, A.; Yuranova, T.; Kiwi, J. Self-Cleaning of Wool-Polyamide and Polyester Textiles by TiO2-Rutile Modification under Daylight Irradiation at Ambient Temperature. J. Photochem. Photobiol. A: Chem. 2005, 172, 27. (4) Uddin, M. J.; Cesano, F.; Bonino, F.; Bodiga, S.; Spoto, G.; Scarano, D.; Zecchina, A. Photoactive TiO2 films on cellulose fibres: Synthesis and characterization. J. Photochem. Photobiol. A: Chem. 2007, 189, 286. (5) Uddin, M. J.; Cesano, F.; Bonino, F.; Bertarione, S.; Bodiga, S.; Spoto, G.; Scarano, D.; Zecchina, A. Tailoring the activity of Ti-based photocatalysts by playing with surface morphology and silver doping. J. Photochem. Photobiol. A: Chem. 2008, 196, 165. (6) Uddin, M. J.; Cesano, F.; Scarano, D.; Bonino, F.; Agostini, G.; Spoto, G.; Bodiga, S.; Zecchina, A. Cotton Textile Fibers Coated by Au/ TiO2 Films: Synthetic, Characterization and Self Cleaning Properties. J. Photochem. Photobiol. A: Chem. 2008, 199, 64. (7) Daoud, W. A.; Xin, J. H.; Zhang, Y. H. Surface Functionalization of Cellulose Fibers with Titanium Dioxide Nanoparticles and Their Combined Bactericidal Activities. Surf. Sci. 2005, 599, 69.

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ReceiVed for reView May 18, 2009 ReVised manuscript receiVed July 14, 2009 Accepted July 16, 2009 IE900811R