Effect of PET Melt Spinning on TiO2 Nanoparticle Aggregation and

Jul 24, 2007 - Poly(ethylene terephthalate) (PET) was incorporated with different amounts of TiO2 nanoparticle and then spun into fibers of different ...
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Effect of PET Melt Spinning on TiO2 Nanoparticle Aggregation and Friction Behavior of Fiber Surface Yung-Pin Huang,*,†,‡ Teng-Ko Chen,† Jing-Wen Tang,‡ Cheng Yeh,‡ and Chin-Heng Tien‡ Department of Chemical and Materials Engineering, National Central UniVersity, Taoyuan County 32001, Taiwan, ROC, and DiVision of AdVanced Fiber Materials and Applications, Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan 300, ROC

Poly(ethylene terephthalate) (PET) was incorporated with different amounts of TiO2 nanoparticle and then spun into fibers of different diameters. Surface properties of these modified fibers were investigated by friction force, scanning electron microscopy, energy dispersive X-ray analysis, and electron spectroscopy for chemical analysis (ESCA). TiO2 nanoparticles showed aggregation on the fiber surface. The number of aggregates increased as the amount of TiO2 nanoparticle increased and/or the diameter of spun fiber decreased. These were evidenced from SEM and also from an increased C(1s)/O(1s) ratio in the ESCA spectra. The aggregates of TiO2 nanoparticle on the fiber surface cause unevenness, leading to a decreased friction-contact area between surface of the sliding fiber and its encountered surface. Thus, the friction force that arose from the interface reduced. In addition, on the basis of different amounts of TiO2, a broad range of fiber frictions could be formed. This would provide promise to potential performance in fiber industry. 1. Introduction Fabric friction is important for the evaluation of fabric quality or hand touch and has been well studied in the literature.1-5 Bueno et al.6 describe a tribology method for the quantization of sanding, which is one of the most famous methods to improve fabric touch. In addition, many other research groups have focused on the evaluation of the fabric friction over a wide range of normal loads and sliding speeds.7-9 However, relationships between the friction of the fabric and the friction of the yarn are very limited. This study will emphasize developing low friction yarns and discuss its relationship with the resulting fabric friction. Surface lubricity and coefficient of friction significantly determine the performance and end use of the fiber. The surface modifying additives are usually copolymerized to or blended with the resin and then processed to their desired product form, for example, fiber, film, and so on. These additives include silicones and the copolymers,10 fluorine containing polymers, and low molecular weight polyolefin waxes.11 However, in the melt spinning process, these additives quickly separate from bulk polymer and migrate to the air-polymer interface. These kinds of surface additives would fade away from the fiber surface after a few home launderings. To author’s best understanding, there has been very limited information of permanent modification on a fiber surface risen directly from the melt spinning stage. Besides the benefit from permanent lowering of the fiber friction that would improve the fabric quality and feel, the applications of poly(ethylene terephthalate) (PET) fibers coated with titania have also been reported for other various uses, such as antifouling, antibacterial, and deodorizing applications,12 because of their photocatalytic properties. In photocatalytic water treatment (a practical process for the degradation of many pollutants), TiO2 is coated on supporting substrates of varying * Corresponding author. Fax: +886 3 5732358. Tel.: +886-35732733. E-mail address: [email protected]. † National Central University. ‡ Industrial Technology Research Institute.

shapes, for example, particles, fibers, and honeycombs to increase the photocatalytic efficiency.13 By plasma and UV irradiation, TiO2 is bonded on polyester textiles, and their photocatalytic activity allowed the almost complete discoloration of coffee and wine stains.14 In addition, by forming a thin layer of TiO2 on the surface of fibers, a new approach to UV-blocking treatment on fabrics is achieved.15 This is attributed to the fact that the titania films can absorb light with an energy that matches or exceeds their band gap energy16 which lies in the UV region of the solar spectrum. Our UV absorption study of this TiO2modified PET fiber hosiery (1.4 wt % and 2.5 wt % TiO2) also revealed a high UPF (ultraviolet protection factor) rating 50+, which was an excellent protection according to the Australian/ New Zealand Standard. This study presented a method to make a permanent surfacemodified fiber based directly on a melt spinning process. To modify the surface of the PET fibers, PET with different amounts of the TiO2 nanoparticles were spun into fibers of different yarn diameter. The added TiO2 particles showed a preference to distribute and aggregate on the fiber surface. The evenness of fiber surface was thus reduced (i.e., friction contact area was decreased), and, therefore, the friction force between the fiber and its friction counterpart is decreased. It is also demonstrated that the effect of surface modification could be maintained after 20 home launderings. 2. Experimental Section 2.1. Materials. Spinning grade TiO2 nanoparticles, which were pretreated with a hydrophobic surface modifier to improve the blending dispersity of the nanoparticles in PET polymer, were obtained from Zig Sheng Industrial Co., Ltd., Taiwan. PET polymer pellets formulated with spinning grade TiO2 nanoparticles at 0.0 wt %, 0.3 wt %, 1.4 wt %, and 2.5 wt % were either obtained from Shinkong Synthetic Fiber Corp., Taiwan, or prepared in our pilot plant via the incorporation of TiO2 nanoparticles during the PET polymerization process17-19 by using ethylene oxide (EO) and terephthalic acid. Analytical grade TiO2 nanoparticles were purchased from Aldrich. Spin finishes formulated with lubricants of EO/PO (ethylene oxide/propylene oxide) random copolymers and emulsifier of

10.1021/ie070248y CCC: $37.00 © 2007 American Chemical Society Published on Web 07/24/2007

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Figure 1. Yarn plate friction device: A, steel sled; B, nylon thread; C, yarn plate; D, pulley; E, steel base; F, tensile crosshead. Table 1. Composition of Spin Finish Recipe EO/PO-50/50-1.7K (wt %)

EO/PO-50/50-5K (wt %)

NP-12 (wt %)

C12AX (wt %)

67.5

14.0

13.5

5.0

NP-12 (polyoxyethylene nonylphenol ether adduct with 12 mol of EO) were used in this study. Two types of EO/PO were formulated in our work. EO/PO of molar ratio 75:25 and with a Mn of 5000 (designated as EO/PO-75/25-5K) was obtained from Schill & Seilacher GmbH & Co., Germany. EO/PO of EO/PO-50/50-1.7K was obtained from SINO-JAPAN Chemical Co., Ltd., Taiwan. The wetting agent of dimethyllaurylamine oxide (C12AX) at 30 wt % concentration, obtained from Taiwan Surfactant Corp., was formulated into the spin finish to improve its wettability on the fiber surface. 2.2. PET Melt Spinning and Spin Finish Application. The spin finish of 10 wt % solid in an aqueous emulsion was applied onto the PET melt spinning yarn at an application ratio of 0.66 wt %. The take-up unit used was Teijin Seiki NS 419 winder, which was set to take up yarns at a speed of 2650 m/min. Denier per filament (dpf) is one of the most useful parameters to describe the single filament fineness of a multi-filament yarn. The PET multi-filament yarns with round filament cross section at 1.67 dpf (120 denier/72 filament), 1.11 dpf (80 denier/72 filament), and 0.83 dpf (120 denier/144 filament) were used for the present study, where lower dpf indicates a finer cross area of the single filament (fiber). An EO/PO based spin finish formulated with NP-12 and C12AX was used to increase the wetting ability of the spin finish.20 It has been observed that better wetting ability of the spin finish will provide better online spin finish distribution on the fiber.20 Table 1 lists the compositions of the spin finish used in this study. 2.3. Measurements of Friction and Rossa SD. According to ASTM D3108-89, the yarn to steel-rod (with 7.98 mm diameter) friction was measured by a R-1083 yarn friction meter (Rothschild, Switzerland) at a wrap angle of 90°. Τhe experiments were conducted at 23 ( 1 °C and 65 ( 2% relative humidity. Three testing speeds (100 m/min, 200 m/min, and 300 m/min) were conducted. A total of 1080 friction data per minute obtained at each speed were averaged and taken as the yarn to steel-rod friction force. On the other hand, for the friction force of steel sled to yarn plate a representative diagram of the slide friction device is shown in Figure 1.9 The device consists of a sled (A) having a contact area of 20 cm2 and a steel plate of 1.5 mm in thickness. The steel sled moved across a yarn plate (C), which was attached to a stationary steel platform (E) fixed with double-sided adhesive tape. A nylon thread (B) attached to the upper crosshead of a tensile tester (F) pulled the steel sled through the pulley (D). The pulley was sufficiently greased to perform smooth rotation, and it was assumed to have negligible friction.

Figure 2. SEM micrograph of the spinning grade TiO2 nanoparticles. Samples were more or less spherical and less than 150 nm in diameter.

The load cell was attached to a constant pulling upper crosshead of a tensile tester. The upper crosshead was pulled at two speeds (100 mm/min and 500 mm/min), each operated at three normal loads of 39, 59, and 78 cN over the yarn plate. The sliding of the steel sled was in the longitudinal direction of the yarns. Three repetitions were carried out, and data were averaged and taken as the friction force of steel sled to yarn plate. The on-line spin finish distribution was measured by a Rossa on-line spin finish analyzer (Cognis Deutschland GmbH, Dusseldorf, Germany). The measurements were conducted at a frequency of 10 kHz, which produced a resolution of approximately 4.4 mm in the yarn length. For each analysis, a total of 28 measurements were averaged. Each measurement provided 8192 detected values, and the interval between measurements was 9.2 s. Thus, from average of all the 28 standard deviations obtained from each analysis, the on-line spin finish distribution on 12.37 km yarn was reported as Rossa SD. 2.4. Analysis of Fiber Surface (ESCA, SEM). The finish oil on the yarn was extracted by ethanol before electron spectroscopy for chemical analysis (ESCA) and scanning electron microscopy/energy dispersive X-ray (SEM/EDX) analysis. ESCA spectra of PET fiber and TiO2-modified PET fibers (obtained in the hosiery fabric form) were obtained from a µ-ESCA (Thermo VG/ESCAlab 250) equipped with Al KR radiation and operated under 200 W electric power. The fabrics were inserted into a vacuum chamber of 10-9 mbar and were analyzed at a takeoff angle of 90°. For the EDX analysis, samples were deposited with a thin layer of platinum by an Edwards S150B sputter coater and followed by an examination with a Hitachi S-4700 field emission scanning electron microscope, which was equipped with an EDX analyzer. 3. Results and Discussion In this study, TiO2 particles were homogeneously stabilized in the PET polymer through the incorporation of TiO2 nanoparticles into the well-known PET polymerization process,17-19 where the spinning grade TiO2 nanoparticles were first mixed with ethylene glycol to become a diluted slurry that was then pumped into a reactor to conduct the step polymerization with terephthalic acid. A steady spinning of this TiO2-modified PET was achieved without a jam on the spinning filter. 3.1. SEM Characterization for TiO2 Nanoparticles and Fiber Surface. The SEM micrograph of the spinning grade TiO2 nanoparticles is given in Figure 2. It reveals that the TiO2

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Figure 3. EDX spectra of TiO2 nanoparticles (a) from analytical grade particles and (b) from spinning grade particles. Titanium and oxygen were the only two elements measured from the analytical grade TiO2 particles; however, a third carbon peak was measured from the spinning grade TiO2.

nanoparticles are more or less spherical and less than 150 nm in diameter. To improve the blending dispersity of the nanoparticles in PET polymer, these spinning grade TiO2 particles were pretreated with a hydrophobic surface modifier. To make sure that the resulting nanoparticles had become hydrophobic, analytical grade and spinning grade TiO2 nanoparticles were separately examined in an EDX microanalysis and are shown in Figure 3 together. Figure 3a reveals that titanium and oxygen are the only two elements on the surface of the analytical grade TiO2 particle, whereas Figure 3b shows that there are three major elements (carbon, titanium, and oxygen) on the surface of the spinning grade TiO2. The ratio of additional carbon atom to the total atoms on surface of the spinning grade TiO2 was found to be about 37%, indicating that there were plenty of carbon atoms resulting from the surface modifier of the TiO2 particles. Figure 4 reveals the SEM morphologies of the surfaces of a 1.67 dpf PET fiber with (a) 0.0 wt % TiO2, (b) 1.4 wt % TiO2,

and (c) 2.5 wt % TiO2, together with that of the 0.83 dpf PET fiber with 2.5 wt % TiO2 (d). From the representative SEM on Figure 4 and some other SEM additional micrographs, it was apparent that the aggregated TiO2 nanoparticles appeared clearly on the fiber surface even if the TiO2 content was as low as 0.3 wt %. In addition, the number of TiO2 aggregates increased as the TiO2 content (wt %) increased. On the other hand, by comparing fibers at different dpf’s but with equivalent content of TiO2 at 2.5 wt %, we found that the 0.83 dpf fiber (Figure 4d) provided a greater number of aggregates on the fiber surface than that of a 1.67 dpf fiber (Figure 4c), whose surface area was much less than that of a 0.83 dpf fiber. It appeared that the TiO2 particles had shown greater preference to distribute and aggregate on the fiber surface. The aggregation of TiO2 particles on the fiber surface may be attributed to the effect of melt spinning on the morphology of PET composite. During the melt spinning process, PET

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Figure 4. SEM pictures of the surface-modified PET fibers: (a) 1.67 dpf with 0.0 wt % TiO2, (b) 1.67 dpf with 1.4 wt % TiO2, (c) 1.67 dpf with 2.5 wt % TiO2, and (d) 0.83 dpf with 2.5 wt % TiO2. The amount of TiO2 and/or the dpf of the PET yarn strongly influence surface morphology of the fiber. Table 2. C(1s)/O(1s) Ratios of TiO2-Modified PET Fibersa amount of TiO2 in PET atomic ratio C(1s)/O(1s) (location 1) C(1s)/O(1s) (location 2) C(1s)/O(1s) (location 3) C(1s)/O(1s) (averaged) C(1s)/O(1s) (after 20 home launderings) a

unmodified PET (1.67 dpf)

0.3 wt % (1.67 dpf)

1.4 wt % (1.67 dpf)

2.5 wt % (1.67 dpf)

1.4 wt % (1.11 dpf)

2.5 wt % (1.11 dpf)

1.4 wt % (0.83 dpf)

2.5 wt % (0.83 dpf)

2.60 2.57 2.59 2.59 2.61

2.65 2.62 2.67 2.65 2.64

2.80 2.82 2.80 2.81 2.78

2.93 2.94 2.91 2.93 2.93

3.21 3.18 3.21 3.20 3.18

3.30 3.27 3.29 3.29 3.31

3.37 3.38 3.35 3.37 3.32

3.43 3.45 3.42 3.43 3.42

Those after 20 home launderings are presented together.

polymer was highly stretched and formed excessive stressinduced crystallization in the spun PET. It has been indicated that the amount of crystalline phase increases with increasing spinning rate up to 7000 m/min.21-23 The crystallization provides the driving force to separate the TiO2 nanoparticles from the bulk PET, and, therefore, the separated TiO2 nanoparticle naturally migrated onto the fiber surface and formed the TiO2 aggregates. The lower the dpf of the fiber, the easier the migration. 3.2. ESCA Studies. In this study, ESCA analysis was used to provide information about the change of element composition on the fiber surface, which was modified with TiO2 nanoparticles. The ESCA spectrum for the spinning grade TiO2 nanoparticles is shown in Figure 5. It shows that there are three major elements (carbon, titanium, and oxygen) on the surface of the spinning grade TiO2. The ratio of titanium to the total atoms on the surface of the spinning grade TiO2 was calculated to be only about 8%. In the ESCA analysis, the depth of electron emission from the surface is only about 10 nm at a takeoff angle of 90°. Consequently, there were plenty of carbon atoms resulting from the surface modifier of the spinning grade TiO2 particles, and a relatively low concentration of titanium atom can be found by ESCA. In addition, the ESCA examination

area was as large as 0.6 mm × 0.6 mm. Thus, the result came out as an average from many fibers with diameters as small as 8.9-13.7 µm. Furthermore, three measurements from different locations of the fabrics were made, and the average obtained was used for our discussion. After close examination, there were no Ti(2p3) and Ti(2p1) that could be found in our ESCA spectra. Thus, the C(1s)/O(1s) ratios were chosen to elucidate the aggregation of TiO2 particles on the fiber surface in this study. The C(1s)/O(1s) ratios calculated from the ESCA spectra for the modified and the unmodified PET fibers, together with the fiber before and after 20 home launderings, are all tabulated in Table 2. Data obtained from three different locations were almost the same, and the average was taken for this study. These data are also graphically shown in Figure 6 with C(1s)/O(1s) ratios plotted against TiO2 wt %. Within the 1.67 dpf series, the PET fiber that contained no TiO2 showed a C(1s)/O(1s) ratio of 2.59, for the low TiO2-containing fiber (0.3 wt % TiO2), it showed a C(1s)/O(1s) ratio of 2.65, and for the high TiO2containing fibers at 1.4 wt % and 2.5 wt %, they showed C(1s)/ O(1s) ratios of 2.81 and 2.93, respectively. Apparently, C(1s)/ O(1s) ratio increased with increasing TiO2 content. In addition, for the 1.11 dpf and 0.83 dpf series at 1.4 wt % and 2.5 wt %

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Figure 5. ESCA survey scan spectrum of the spinning grade TiO2 nanoparticles.

Figure 6. Plots of surface C(1s)/O(1s) atomic ratios against the contents of TiO2 in PET fiber. The C(1s)/O(1s) atomic ratio increased slowly with increasing amount of TiO2 in the 1.67 dpf yarn series. On the other hand, a large increase of C(1s)/O(1s) atomic ratio was observed when dpf of the PET fiber decreased.

TiO2, the C(1s)/O(1s) ratio also increased with increasing TiO2 content. On the other hand, at 1.4 wt % and 2.5 wt % TiO2 content, the C(1s)/O(1s) ratio showed decreased tendency as the dpf of the PET fiber increased. Table 2 also reveals that the C(1s)/O(1s) ratio of the modified PET fiber can be maintained after 20 home launderings, indicating that the surface modification of PET fiber was permanent. When ESCA spectra of the fibers were closely examined, detailed information on the chemical bonding of the surface component can be obtained. Figure 7 shows the ESCA C 1s spectra for a 1.67 dpf PET containing (a) 0.3 wt % TiO2 and (b) 2.5 wt % TiO2. It was observed that the peak ratio of (CC)/(COO) for 2.5 wt % TiO2 PET was apparently higher than that of the 0.3 wt % TiO2 PET. Table 3 summarizes the percentage contribution of C(1s) from the ESCA spectra for various PET fibers. After being modified with TiO2, the peak at 284.6 eV (C-C) increased significantly, whereas the peaks at 286.1 eV (C-O) and 289.0 eV (COO) decreased (Table 3) slightly. On the other hand, as the dpf of the PET yarn (with 2.5 wt % TiO2) varied from 1.67 dpf to 0.83 dpf, the percentage contribution of the C-C peaks largely increased. On the basis of these ESCA analyses, both Figure 7 and Table 3 showed that increasing the TiO2 particles and/or decreasing the dpf of fiber lead to an increased percentage contribution of C-C component on the fiber surface. Because the surface modifier (TiO2 particles) contains a large proportion of C-C component, results from these data indicate that surface modifier has been largely migrated to the fiber surface. 3.3. Friction Force Measurements. Influence of TiO2 on the extent of surface friction was shown in Figure 8, where the

Figure 7. ESCA spectra of C(1s) for 1.67 dpf PET with 0.3 wt % TiO2 (a) and with 2.5 wt % TiO2 (b). The (C-C peak)/(COO peak) ratio of that with 2.5 wt % TiO2 is apparently higher than that with 0.3 wt % TiO2. Table 3. Percentage Contribution of the ESCA C(1s) Component for the Pure and Modified PET Fibers contribution of C(1s) components (%)

yarn code

TiO2 (wt %)

dpf

denier

C-C (284.6 eV)

C-O (286.1 eV)

COO (289.0 eV)

PET-0.0 PET-0.3 PET-1.4 PET-2.5-a PET-2.5-ba PET-2.5-c

0.0 0.3 1.4 2.5 2.5 2.5

1.67 1.67 1.67 1.67 1.11 0.83

120 120 120 120 80 120

66.8 67.3 68.6 69.9 75.1 77.0

17.2 16.8 16.1 15.7 13.9 12.8

16.0 15.9 15.3 14.4 11.0 10.2

a Data were measured from 80 denier PET yarn. Other data were measured from 120 denier PET yarn.

yarn friction force is plotted against the amount of TiO2 in PET fiber. The yarns, which were modified with a smaller amount of TiO2, exhibited higher friction force and large variation among the three testing speeds. On the other hand, yarns with higher amount of TiO2 exhibited lower friction force, and the force varied only very little among the same testing speeds. Comparing results of the friction force (Figure 8) and morphology from the respective SEM (Figure 4), it reveals that friction force decreases with increasing the number of TiO2 aggregates on the fiber surface. It was thus suggested that the aggregation of TiO2 particles on the PET fiber surface could reduce the

Ind. Eng. Chem. Res., Vol. 46, No. 17, 2007 5553 Table 5. Friction Force between Steel Sled and Yarn Plate (with Different TiO2 wt %), Measured at Various Normal Loads and Sliding Speeds friction force (cN) code PET-0.0 PET-0.3 PET-1.4 PET-2.5-a PET-2.5-ba PET-2.5-c

speed (mm/min)

39 cN

59 cN

79 cN

100 500 100 500 100 500 100 500 100 500 100 500

23.3 38.4 19.4 29.1 14.9 21.0 11.7 14.2 10.9 13.4 9.3 11.9

30.3 47.9 26.1 37.5 19.0 28.3 14.2 17.9 13.0 16.6 12.6 16.0

37.2 59.4 30.7 46.9 24.1 34.9 17.5 22.1 16.1 20.9 14.9 19.4

a Data were measured from 80 denier PET yarn. Other data were measured from 120 denier PET yarn.

Table 6. Effect of TiO2 Content on the Rossa SD Obtained from 120 denier/72 filament PET Yarn yarn Figure 8. Influence of percentage TiO2 of a 1.67 dpf PET yarn on the friction force obtained from the friction on the interface between yarn and steel rod. Table 4. Friction Force of Yarn to Steel Rod for the Unmodified and Modified PET Fibers yarn code

TiO2 (wt %)

dpf

PET-0.0 PET-0.3 PET-1.4 PET-2.5-a PET-2.5-ba PET-2.5-c

0.0 0.3 1.4 2.5 2.5 2.5

1.67 1.67 1.67 1.67 1.11 0.83

friction force (cN)

denier

100 m/min

200 m/min

300 m/min

120 120 120 120 80 120

48.1 33.8 15.0 13.4 9.6 14.5

51.1 36.3 16.2 14.2 10.7 15.6

53.5 38.5 16.8 14.5 11.2 16.0

a Data were measured from 80 denier PET yarn. Other data were measured from 120 denier PET yarn.

friction contact area between the fiber and its encountered surface, owing to the uneven fiber surface. Table 4 provides friction forces of various PET yarns. These yarns were distinguished with TiO2 contents of 0.0 wt %, 0.3 wt %, 1.4 wt %, and 2.5 wt %, respectively, and also with their dpf types of 1.67 dpf, 1.11 dpf, and 0.83 dpf, respectively. For the effect of TiO2, it shows that as the amount of TiO2 content increases, friction force between the yarn and the steel rod decreases. This indicated that TiO2 particles could effectively reduce the friction force between the yarn and the steel rod. On the other hand, it was found that a 0.83 dpf yarn (PET-2.5-c) provide almost the same friction force as that of a 1.67 dpf yarn (PET-2.5-a) under equivalent yarn denier (at 120 denier) and TiO2 content (at 2.5 wt %). It is known that a PET-2.5-c yarn contains a higher number of filaments (144 filaments) and, thus, apparently shall have a higher total filament surface area than that of a PET-2.5-a yarn which contains only 72 filaments. However, Figure 4 reveals that there are more TiO2 aggregates that appear on the PET-2.5-c fiber surface. These aggregates greatly reduce the friction contact area on the PET-2.5-c yarn. The effect from yarn dpf and the effect from TiO2 aggregates may just be balanced for these two yarns, leading to similar friction forces between these yarns. The friction force of the 1.11 dpf yarn (PET-2.5-b) was found to be the lowest among those yarns shown in Table 4, and the reason is because both its yarn denier and its filament count

code

TiO2 (wt %)

dpf

denier

Rossa SD

PET-0.0 PET-0.3 PET-1.4 PET-2.5-a

0.0 0.3 1.4 2.5

1.67 1.67 1.67 1.67

120 120 120 120

248 155 99 76

are the lowest and, therefore, its friction area in contact with the steel rod is also the lowest. Because there are a large number of independent weaving needles, weaving a fabric from a traditional weaver unavoidably provides great variations on the fabric surface, especially the friction properties.9 To reduce this effect, PET yarns were wound closely side by side to form a uniform PET yarn layer on a steel plate. This layer was characterized to have a yarn weight of 91 g/m2 and was the so-called yarn plate in this study. Three normal loads (the weight of the steel plate is included) on the yarn plate were performed at 39, 59, and 78 cN, respectively. The results given in Table 5 reveal that the friction force increased with increasing normal load and also with increasing testing speed. Besides, the friction force decreased with the increase of TiO2 content in the fiber. From these data, the fibers with different contents of TiO2 will not only provide a broad range of friction forces from the interface between the sliding yarn and the steel rod but also display a wide range of friction forces between the yarn plate and the sliding steel sled. On the other hand, TiO2-modified fiber should also improve and assist the yarn formation process during melt spinning. Carroll24 studies the effect of surface roughness on the spreading of a fluid on cylindrical material. He finds that the effect of surface roughness is always to lower the contact angle. In our study, the aggregation of TiO2 particles would cause the unevenness (roughness) of the fiber surface, and, thus, it would improve the on-line spin finish distribution along the fiber surface during the finishing process. In our experiment, we found that the on-line spin finish distribution along the fiber surface increased (i.e., Rossa SD decreased) with the increase of TiO2 contents in the fiber (Table 6). It was attributed to the fact that the increase of TiO2 would increase the unevenness (roughness) of the fiber surface and, thus, assist the wetting of spin finish along the fiber surface. It is also reported25 that the variation in mass per unit length along the yarn (UCV %) is decreased with a better on-line spin finish distribution. A low UCV % is preferred for quality control because a high UCV % is usually associated

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with a large variation in strength along the yarn, many visible faults on the fabric surfacee,26 and difficulty in processing. 4. Conclusion Permanent surface modification of PET fiber with low friction property could be achieved by blending TiO2 nanoparticles with PET polymer and then spinning into fibers. The TiO2 nanoparticles showed aggregation on the fiber surface, and the number of aggregates increased with the amount of TiO2 increased. On the other hand, by comparing fibers with equivalent TiO2 content, it was found that the yarn with lower dpf (higher fiber surface area) gave rise to a greater number of TiO2 aggregates than the yarn with higher dpf. It was concluded that the TiO2 aggregates reduced the evenness of the fiber surface, and therefore the friction contact area of the sliding fiber was reduced. Reduction of friction force was mainly arose from the reduction of direct contact surface. The prepared fibers with different contents of TiO2 gave a broad range of yarn friction force, which provides the promise of potential performance in the fiber industry. Literature Cited (1) Carr, W. W.; Posey, J. E.; Tincher, W. C. Frictional characteristics of apparel fabrics. Text. Res. J. 1998, 58, 129. (2) Nishimatsu, T.; Sawaki, T. Study on pile fabrics. Part III. Frictional properties of pile fabrics. J. Text. Mach. Soc. Jpn. 1984, 30, 67. (3) Ajayi, J. O. Fabric smoothness, friction and handle. Text. Res. J. 1992, 62, 52. (4) Virto, L.; Naik, A. Frictional behavior of textile fabrics. Part I. Sliding phenomena of fabrics on metallic and polymeric solid surfaces. Text. Res. J. 1997, 67, 793. (5) Ramkumar, S. S. Tribology of textile materials (note). Indian J. Fiber Text. Res. 2000, 25, 238. (6) Bueno, M.-A.; Lamy, B.; Renner, M.; Pierre, V.-R. Tribological investigation of textile fabrics. Wear 1996, 195, 192. (7) Roedel, C.; Ramkumar, S. S. Surface mechanical property measurements of H1 technology needle punched nonwovens. Text. Res. J. 2003, 73 (5), 381. (8) Ramkumar, S. S.; Shastri, L.; Tock, R. W.; Shelly, D. C.; Smith, M. L.; Seshaiyer, P. An experimental study of frictional properties of friction spun yarns. J. Appl. Polym. Sci. 2003, 88 (10), 2540.

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ReceiVed for reView February 15, 2007 ReVised manuscript receiVed June 16, 2007 Accepted June 19, 2007 IE070248Y