PTFE fabric composite reinforced with surface modified nanometer ZnO

Available online at www.sciencedirect.com

Wear 265 (2008) 311–318

Friction and wear behavior of hybrid glass/PTFE fabric composite reinforced with surface modified nanometer ZnO Feng-hua Su a,b , Zhao-zhu Zhang a,∗ , Wei-min Liu a a

State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China b Graduate School of the Chinese Academy of Sciences, Beijing 100039, China Received 21 March 2007; received in revised form 31 August 2007; accepted 22 October 2007 Available online 20 December 2007

Abstract Nano-ZnO was successfully grafted with 2,4-toluenediisocyanate (TDI) and ␤-aminoethyltrimethoxylsilane (OB551) to avoid the agglomeration of nano-ZnO in composite. The hybrid glass/PTFE fabric composites reinforced with the untreated, OB551 and TDI modified nano-ZnO, respectively, were prepared by dip-coating of the hybrid fabric in a phenolic adhesive resin containing the nanoparticles to be incorporated and the successive curing. The friction and wear behaviors of various nano-ZnO reinforced hybrid glass/PTFE fabric composites sliding against AISI-1045 steel in a pin-on-disk configuration were evaluated on a Xuanwu-III high-temperature friction and wear tester, with the unfilled one as a reference. The morphologies of the worn surfaces of the composites and of the counterpart pins were analyzed using scanning electron microscopy. In addition, FTIR spectrum was taken to characterize the untreated and treated nano-ZnO. It is found that the untreated and treated nano-ZnO reinforced hybrid glass/PTFE fabric composites exhibit improved wear resistance and friction-reduction in comparison with the unfilled one. The TDI modified nano-ZnO reinforced composite can obtain the best friction and wear performance under different applied load; followed by the OB551 modified nano-ZnO reinforced one. Sliding conditions, such as environmental temperature and lubricating condition, significantly affect the tribo-performances of the unfilled and filled hybrid glass/PTFE fabric composites. © 2007 Elsevier B.V. All rights reserved. Keywords: Hybrid glass/PTFE fabric composite; Nano-ZnO filler; Surface treatment; Phenolic resin; Friction and wear

1. Introduction Nowadays, many attempts have been made to develop nanoparticles filled polymer composite to improve the tribological property of them [1–8]. Sawyer et al. [1] have reported that the wear resistance of PTFE can be improved 600× as the nano-Al2 O3 filler concentration of 20%, however, the friction coefficient of the composite increase over unfilled sample. Li et al. [2] investigated the effect of nano-ZnO filler on the friction and wear properties of polytetrafluoroethylene (PTFE) and pointed out that the anti-wear property of the polymer can be improved without sacrificing friction-reducing abilities. Wang et al. [3,4] have incorporated nano-Si3 N4 and nano-SiO2 into polyetheretherketone (PEEK) to improve the friction and wear behavior of PEEK. Many researches have systemically illustrated the particular action of nanoparticles during the friction

∗

Corresponding author. Tel.: +86 931 4968098. E-mail address: [email protected] (Z.-z. Zhang).

0043-1648/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2007.10.013

process compared to the traditional micro-particles filler. On the one hand, the nano-fillers possess decreased angularity, and thus they are less abrasive as compared to the conventional micrometer-sized fillers [5,6]. On the other hand, a better adhesion between polymer and nanoparticles is expected due to the high surface area of the nanoparticles, which is believed to avoid the particles pulling-out, and thus to reduce the wear [6,7]. However, the friction and wear properties of fabric composite reinforced with nanoparticles have not been systemically evaluated, even though many researchers have reported the friction and wear properties of the polymer composite filled with glass fabric, carbon fabric and Kevlar fabric [9–12]. Our previous studies have illustrated the prominent action of fabric composite in the tribological application as bearing liner materials when compared to the traditional polymer and coating composite [13–16]. Moreover, in many tribological application of nanocomposites, the surface of nanoparticles has not been pre-treated with chemical means, despite the fact that the nanocomposites often perform better than microcomposites. Owing to the particular

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size of nanoparticles, their specific surface area becomes larger which results in the probability of nanopariticles to agglomerate. An addition of such agglomerate nanoparticles to the polymer or fabric composites are not sufficient for reaching a homogeneous dispersion state and thus degrade the improvement of tribological properties of the nanocomposites. Therefore, the unique nano-effect of nanoparticles filler cannot be fully brought into play. In view of the existing problem, the authors proposed a special approach based on the nano-ZnO successfully grafted with 2,4-toluenediisocyanate (TDI) and ␤-aminoethyltrimethoxylsilane (OB551) to avoid the agglomeration of nanoparticles in the fabric composite. In fact, the grafting method has proved to be an effective way for strengthening thermoplastics at a rather low nano-filler content [17,18]. Our previous studies have reported the friction and wear properties of fabric composite with the simplex fabric such as glass fabric, carbon fabric and Nomex fabric [13,15,16]. However, to the best of our knowledge, the friction and wear properties of fabric composite composed of hybrid fabric, such as the hybrid glass/PTFE fabric, have not been extensively studied [14]. Especially, the friction and wear properties of the hybrid fabric composite reinforced with surface modified nanoparticles have not been reported in any journals. With this respective in mind, we prepared the hybrid glass/PTFE fabric composites reinforced with untreated, TDI and OB551 modified nano-ZnO and evaluated the tribo-performance of the composites expecting to broad the application of hybrid glass/PTFE fabric composite as bearings liner materials. 2. Experiment 2.1. Materials The plain hybrid glass/PTFE fabric was weaved with Eglass fibers and PTFE fibers made in our country, and the picture of hybrid glass/PTFE fabric has been given in the reported paper [14]. The phenolic adhesive resin (204 phenolic adhesive) was provided by Shanghai Xingguang Chemical Plant of China. Nano-ZnO (15–25 nm) was provided by Zhejiang Hongcheng Material Inc., China. Ethanol, toluene, acetone and 2,4-toluenediisocyanate (TDI), which are the analysis grade reagent, were purchased from Tianjin No. 1 Chemical Reagent Plant, China. ␤-aminoethyltrimethoxylsilane (OB551) was purchased from Diamond New Material of Chemical Inc., Hubei Province of China. No. 20 mechanical oil is the normal used mechanical oil, which is purchased from commercial market.

and cleaned with acetone and eventually dried in vacuum at 100 ◦ C for 2 h. 50.0 ml ethanol, 7.5 ml ␤-aminoethyltrimethoxylsilane (OB551) and 2.0 g nano-ZnO were added into a flask and stirred with the assistance of ultrasonic for 10 min. And the solution was heated at 80 ◦ C until the reaction had been completed for 5 h. Then the OB551 modified nano-ZnO was filtrated and cleaned with distilled water and eventually dried in vacuum at 100 ◦ C for 2 h. 2.3. Preparation of composites According to a series of screening tests, the optimum mass fraction of nano-ZnO in adhesive resin is 4%. The various nanoZnO was evenly dispersed in the adhesive with the assistance of ultrasonic stirring. The hybrid glass/PTFE fabric after pretreatment (dipped in acetone for 24 h, followed by boiling in distilled water for 10 min and cleaning with acetone in an ultrasonic bath) was immersed in the mixed adhesive to allow the coating by the adhesive mixture containing the various nanoZnO with 4% mass fraction. The immersing of the hybrid glass/PTFE fabric in the mixed adhesive and the successive drying and pressing the coated glass/PTFE fabric around 60 ◦ C were repeated until the adhesive was used up. The hybrid glass/PTFE fabric composite about 400–450 um thick was obtained. The mass concentration of phenolic adhesive resin, glass fabric and PTFE fabric in the hybrid glass/PTFE fabric composite is about 40, 32 and 28%, respectively. Finally, the various nano-ZnO reinforced hybrid glass/PTFE fabric composites were affixed on the AISI-1045 steel surface using the phenolic resin adhesive and cured at 180 ◦ C for 2 h under 0.10–0.20 MPa. And the surface of AISI-1045 steel disc (to be coated by the fabric composites coating) have been polished with 280 and 350 grade waterproof sand paper to a surface roughness about Ra = 0.30–0.45 um. The unfilled hybrid glass/PTFE fabric composite (abridged as Composite-I) was prepared in the same manner except that no nano-ZnO filler was introduced into the phenolic resin. And the untreated, OB551 and TDI grafted nano-ZnO reinforced hybrid glass/PTFE fabric composite was abridged as Composite-II, Composite-III and Composite-IV, respectively.

2.2. Modification of nano-ZnO In a flask 2.0 g of nano-ZnO, 1.0 ml of 2,4toluenediisocyanate (TDI) were added and stirred at room temperature for 10 min, and then 50.0 ml of toluene was added into the flask. Then the solution was heated to 80 ◦ C in nitrogen until the reaction continued for 3 h. After the reaction have completed after 3 h, the TDI modified nano-ZnO was filtrated

Fig. 1. Schematic diagram of the pin-on-disc (pin: φ 2.0 mm and disc: φ 44.0 mm) friction and wear tester: P, applied load; 1, counterpart pin; 2, composites coated AISI-1045 steel disc; 3, electric furnace; 4, themocouple and 5, the circinal groove placed with the steel disc.

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The friction and wear behaviors of Composite-I, CompositeII, Composite-III and Composite-IV sliding against AISI-1045 steel pin with a diameter 2 mm were evaluated on an Xuanwu-III high-temperature friction and wear tester. The friction experiment was conducted under dry sliding condition or under water and oil lubricated condition. The AISI-1045 steel disc coated with fabric composite was fixed in the circinal grooves during the friction process, and the distilled water or No. 20 mechanical oil was directly added into circinal grooves beforehand under water or oil lubricating condition. Fig. 1 shows the schematic diagram of the test rig. Prior to the tests, the pin was successively mechanically polished with 350, 700, and 900 grade waterproof abrasive paper, to a surface roughness Ra = 0.10–0.15 um, and

measurement in the mid-infrared (4500–400 cm−1 ) was performed. FTIR spectra was recorded on powders samples, dispersed in dry KBr using Bruker IFS/66v. From Fig. 2(A), the peak appeared at 3500 cm−1 was ascribed to the stretching band of hydroxyl group in untreated nano-ZnO, which disappeared in the OB551 and TDI treated nano-ZnO (see Fig. 2(B and C)). As shown in Fig. 2(B), some new spectra appeared in the OB551 treated nano-ZnO in comparison with the untreated one. The characteristic stretching bands from methylene and methyl groups can be observed at 2850 and 2925 cm−1 . The band centered at 1000–1100 cm−1 results from the contributions from Si O Si stretching bands. The peak at 3300 cm−1 was assigned to the stretching vibration of N H. The results showed that nano-ZnO have been successfully grafted with OB551. The possible chemical reaction might be as follows:

then cleaned with acetone. The sliding was performed at a humidity of 20–40% with a sliding speed of 0.26 or 0.39 m/s, and a normal load within 117.6–227.4 N, a temperature of 15–180 ◦ C and over a period of 2 h except for otherwise indication. At the end of each test, the composite coating on the steel was cleaned and dried, then its wear volume loss (V) was obtained by measuring the wear scar and wear depth on a micrometer (±0.001 mm). The wear rate (w = V /pL) represents the wear

As show in Fig. 2(C), the characteristic stretching bands from methyl groups can be observed at 2925 cm−1 . The characteristic stretching bands from –NCO can be observed at about 2270 cm−1 . The peak at 1650 cm−1 was ascribed to the stretching bands of C O, and the peak at about 3300 cm−1 was assigned to the stretching band of N H. The results illustrated that the nano-ZnO have successfully grafted with TDI. The possible chemical reaction might be as follows:

2.4. Friction and wear test

volume per unit applied load and of sliding distance, and it was still calculated using the same formula even the tested composites sample was unable to endure sliding for 2 h. During the test the friction force was measured with a sensor and fed into a computer continuously. The friction coefficient was the result of the ratio of the measured force and the applied load. The environmental temperature of frictional condition was controlled by the electric furnace and was monitored with a thermocouple in the furnace. Each experiment was carried out three times and average value was considered. The relative errors to measure the friction coefficient and wear volume loss are ±5 and ±10%, respectively. The morphology of the worn composite surfaces was analyzed on a JSM-5600LV scanning electron microscope (SEM).

3.2. Friction and wear property Table 1 presents the comparison of friction coefficients and wear rates of Composites-I, II, III, IV at 196.0 N, room

3. Results and discussion 3.1. FTIR spectra of various nano-ZnO In order to investigate the possible chemical reaction between nano-ZnO and OB551 or TDI, FTIR spectroscopy

Fig. 2. FTIR spectra of (A) untreated nano-ZnO, (B) OB551 treated nano-ZnO and (C) TDI treated nano-ZnO.

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Table 1 Comparisons of the friction coefficients and wear rates of unfilled and various nano-ZnO filled hybrid glass/PTFE fabric composites (196.0 N, room temperature, 0.26 m/s), (the data marked with “*” represents the composites cannot endure sliding 120 min at this condition) Sample/parameter

Friction coefficient μ

Wear rate (×10 −14 m3 (N m)−1 )

Composite-I Composite-II Composite-III Composite-IV

0.073* 0.068 0.072 0.065

17.6* 5.66 3.82 3.21

temperature and 0.26 m/s. It can be seen that the untreated, OB551 and TDI grafted nano-ZnO can significantly improve the friction-reduction and wear resistance and enhance loadcarrying capacity of hybrid glass/PTFE fabric composite. The Composite-IV can obtain the best anti-wear and frictionreducing abilities, followed by Composite-III. In the subsequent section, the friction and wear properties of Composite-I and Composite-IV will be systemically and comparatively discussed under different sliding condition. Table 2 illustrates that the addition of TDI grafted nanoZnO can reduce the friction coefficient and wear rate of hybrid glass/PTFE fabric composite under the dry sliding condition at 117.6 N, 0.26 m/s and room temperature. However, the wear rate of the Composite-IV increases rapidly even though the friction coefficient deceases under the oil or water lubricating condition. The results indicate that the hybrid glass/PTFE fabric composite is unsuitable to apply under the oil or water lubricating condition. Fig. 3 indicates that TDI grafted nano-ZnO can significantly improve the friction reduction and wear resistance of hybrid glass/PTFE fabric composite under different applied load, especially under high load. Moreover, TDI grafted nano-ZnO can greatly enhance the load-carrying capacity of hybrid glass/PTFE fabric composite because the Composite-I is unable to endure sliding for 2 h at the load of 196.0 N. The friction coefficients of Composite-I and Composite-IV decrease with increasing applied load except the friction coefficient of Composite-I at 196.0 N. However, the wear rates of them increase with the increase of load. And the wear rate of the Composite-I increases Table 2 Comparisons of the friction coefficients and wear rates of Composite-I and Composite-IV under different lubricated condition (117.6 N, room temperature and 0.26 m/s), (the data marked with “*” represents the composites cannot endure sliding 120 min at this condition) Sample/parameter

Friction coefficient μ

Wear rate (×10−14 m3 (N m)−1 )

Composite-I at dry sliding condition Composite-IV at dry sliding condition Composite-IV at water sliding condition Composite-IV at oil sliding condition

0.079

2.14

0.076

1.72

0.070

7.32

0.060*

16.7*

Fig. 3. Effect of applied loads on the friction coefficients and wear rates of Composite-I and Composite-IV. (0.26 m/s, room temperature and dry sliding condition.) (The data marked with “*” represents that the composite cannot endure sliding for 120 min at this condition.)

rapidly from 180.3 to 196.0 N, which is related to the wear life of the composite at this sliding condition. Influence of the sliding speed and load on the friction and wear behavior of Composite-IV was investigated (see Fig. 4). It is seen that the friction coefficient of Composite-IV gradually decrease while the wear rate of it gradually increase with increasing applied load under the different sliding speed. The friction coefficient and wear rate of Composite-IV at higher speed (0.39 m/s) is lower than that at lower speed (0.26 m/s) under different load. One possible effect that contributes to the reduction of the friction coefficient at high sliding velocity is the polishing effect. Namely the worn surface could be polished very rapidly at the high sliding speed, which at last result in the reduced friction coefficient. On the other hand, the great increase of the sliding distance within 120 min corresponds to the reduced wear rate of the composite although the wear depth might increase. In order to broad the application of Composite-IV as bearing liner materials under different sliding environment, Fig. 5 shows the influence of environmental temperature on the friction and wear behavior of the composite at 164.6 N and 0.26 m/s. The results show that the friction coefficient of the Composite-IV decreases while the wear rate of it increases with increasing environmental temperature. As the environmental temperature increases to 180 ◦ C, Composite-IV cannot endure sliding for

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Fig. 5. Effect of environmental temperature on the friction and wear properties of Composite-IV. (164.6 N, 0.26 m/s and dry sliding condition.) (The data marked with “*” indicated that the composites cannot endure sliding for 120 min at this condition.)

Fig. 4. Variation of friction coefficient and wear rate of Composite-IV under different sliding speed with increasing applied load. (Room temperature and dry sliding condition.)

120 min at the load of 164.6 N and 0.26 m/s indicating that the composite is suitable to the tribological applications at ambient and moderately elevated temperatures. That the worn surface can be polished to a certain extent owing to softening of the

adhesive resin can explain the decreasing friction coefficient of the composites with the increase of environmental temperature [16]. On the other hand, the temperature at the friction interface between composite and counterpart pin greatly increase with increasing environmental temperature, which might induce an accelerative breakage of the matrix especially in the interfacial region [19]. As a result, the wear rate of Composite-IV increases with increasing environmental temperature. 3.3. SEM analysis of the composites structure Fig. 6 shows the SEM micrograph of the cross-section of these composites, which directly reflects structural integrity of them. From Fig. 6, it is obviously observed that some holes and

Fig. 6. SEM micrographs of the cross-section of (a) Composite-I, (b) Composite-II, (c) Composite-III and (d) Composite-IV.

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cracks exist in the Composite-I, and the hybrid glass/PTFE fabric cannot compactly bond with the adhesive (see Fig. 6(a)), which corresponds to the poor tribological properties of CompositeI. And, the bonding strength between the hybrid glass/PTFE fabric and the resin binder doped with untreated nano-ZnO seems to be increased to some extent as compared with the unfilled one. However, some holes and cracks still exist in the cross-section of Composite-II (see Fig. 6(b)), which is attributed to the slightly improved wear-resistance and friction-reduction

nanoparticles and the resin when the pretreated nanoparticles are mechanically mixed with a thermosetting resin. In this paper, the mutual action between the OB551 grafted nano-ZnO and the phenolic adhesive resin might be hydrogen chemical bond and chain entanglement, while the chemical reaction and chain entanglement might have been occurred between TDI grafted nano-ZnO and phenolic adhesive resin. The possible chemical reaction between OB551 and TDI grafted nano-ZnO with phenolic resin adhesive might be as follows:

of this composite. The hybrid glass/PTFE fabric is well bonded with the adhesive resin doped with OB551 or TDI grafted nano-ZnO (see Fig. 6(c and d)). Especially, Composite-IV, the interface between hybrid glass/PTFE fabric and adhesive resin becomes blurry (see Fig. 6(d)) indicating that TDI grafted nano-ZnO does contribute to improve the structural integrity of Composite-IV. As shown in many paper [19–21], the following stages of wear mechanisms of fiber or fabric composite can be recognized: (a) matrix wear and fiber thinning, (b) fiber broken, (c) interfacial debonding and (d) fiber peeling-off. Therefore, the structural integrity of the composite greatly affects the friction and wears performance of the fabric composite. Due to the specific high surface activity and energy and small size effect, many physical and chemical defects exist on the surface of nanoparticles, so the particles have a lot of physical and chemical binding opportunities with the adhesive resin chains. As a result, the structural integrity of the various nano-ZnO reinforced hybrid glass/PTFE fabric composite have been improved (see Fig. 6(b)) in comparison with unfilled one, which correspond to the improvement of tribo-performance of the reinforced composite (see Table 1). However, the nanoparticles are very easy to agglomerate owing to the small size of the particles if no specific surface treatment is applied beforehand. And an addition of such agglomerated nanoparticle to the fabric composite will lead to an inhomogeneous dispersion state of nanoparticles, which eventually affects the reinforced effect of nanoparticle. When the nano-ZnO was treated with OB551 or TDI beforehand, on the one hand, the agglomeration of nano-ZnO in hybrid glass/PTFE fabric composite can be avoided. On the other hand, the filler/matrix adhesion would be substantially enhanced by chain entanglement and/or chemical bonding between the chemical functional group grafted on the

Therefore, the structural integrity of the Composite-III and Composite-IV are significantly improved, especially Composite-IV (see Fig. 6(d)). Accordingly, it can be rationally understood the best tribo-performance of Composite-IV (see Table 1).

3.4. SEM analysis of the worn surface Fig. 7 presents the feature of the worn surfaces of the Composite-I and Composite-IV at different sliding conditions. It can be seen that the serious breakage of the matrix occurred and most of the glass or PTFE fibers were pulled out and cut from Composite-I matrix after sliding 90 min at 196.0 N (see Fig. 7(a)). The characteristic of Composite-I might be attributed to the bad structural integrity of the composite. By the careful observation of the friction process of Composite-I, the major wear mechanism of Composite-I is the severe fatigue wear, which gradually results in fiber broken, interfacial debonding and fiber peeling-off. Contrary to Fig. 7(a), the worn surface of Composite-IV is smooth after sliding 120 min at 196.0 N, and the wear debris composed of nano-ZnO like roll are squeezed into the worn surface (see Fig. 7(b)). Nano-ZnO in the compressed wear debris on the worn surface might have acted as three body roller bearing and further increase the wear resistance and load-carrying capacity of Composite-IV owing to the particular mechanical properties of nano-ZnO [5]. With the increase of sliding speed to 0.39 m/s, the worn surface of the Composite-IV is also smooth after sliding 120 min at 196.0 N (see Fig. 7(c)). But it is characterized with some adhesive wear owing to the increase of the friction heat caused by the increased sliding speed (see Fig. 7(c)). However, the worn surface of Composite-IV at 117.6 N after sliding 120 min was characterized with obvious

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Fig. 7. SEM micrographs of the worn surface of Composite-I and Composite-IV. ((a) Composite-I, 196.0 N, 90 min, 0.26 m/s; (b) Composite-IV, 196.0 N, 120 min, 0.26 m/s; (c) Composite-IV, 196.0 N, 120 min, 0.39 m/s and (d) Composite-IV, 117.6 N, 120 min, 0.26 m/s under water lubrication.)

corrosive patch, scuffed groove and worn crack under water lubricated condition (see Fig. 7(d)), which indicates that the major wear mechanism of Composite-IV under water lubricated condition is corrosive wear. The corrosiveness of water to the composite corresponded to the poor tribological properties of Composite-IV under water lubricated condition. Because the Composite-IV is unable to endure sliding for 120 min at

117.6 N under oil lubricated condition, the SEM micrograph of the worn surface of the composite cannot been provided in manuscript. Fig. 8 presents the SEM micrographs of the transfer films formed on the counterpart pin sliding against the Composite-I and Composite-IV under different sliding condition. In case of the counterpart pin sliding against the Composite-I, the trans-

Fig. 8. SEM micrographs of the worn steel surfaces sliding against (a) Composite-I at 180.3 N; (b) Composite-IV at 180.3 N, (d) Composite-IV at 117.6 N under water lubricated sliding; (c) energy dispersive X-ray analysis of Zn element on (b) (Room temperature, 2 h.)

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fer film is very thick and appears to be lumpy (see Fig. 8(a)). In comparison with Fig. 8(a), the transfer film formed on the counterpart pin sliding against Composite-IV is very smooth, uniform and thin (see Fig. 8 (b)). The uniform distribution of Zn element on the worn surface of the counterpart pin sliding against Composite-IV also confirms the formation of a uniform transfer film thereon (see Fig. 8(c)). However, no signs of the transfer film are observed and many signs of scuffing are shown on the counterpart pin sliding against Composite-IV under water-lubricated condition (see Fig. 8(d)). Therefore, no transfer film formed on the counterpart pin and the boundary lubricating action of water or oil are another major reason for the decreased friction coefficient and poor wear life of the Composite-IV under water or oil lubricated condition. 4. Conclusion 1. Nano-ZnO has been successfully grafted with 2,4toluenediisocyanate (TDI) and ␤-aminoethyltrimethoxylsilane (OB551). The filling of various 4% nano-ZnO into hybrid glass/PTFE fabric composite can obviously improve the wear resistance and friction reduction of the composite. And the Composite-IV can obtain the best anti-wear and friction-reducing abilities, followed by the Composite-III. 2. The improved and best tribo-performance of Composite-IV can be attributed to five factors, i.e., (a) the agglomeration of nano-ZnO in fabric composite has been avoided; (b) the structural integrity of the hybrid glass/PTFE fabric composite has been improved; (c) a thin and uniform transfer film has formed on the counterpart pin; (d) the particular mechanical and anti-wear action of nano-ZnO during the friction process due to the particular mechanical property of nanoparticle and (e) nano-ZnO in the wear debris squeezed on the worn surface of Composite-IV has acted as three body roller bearings. 3. Sliding condition, such as environmental temperature, applied load, sliding speed and lubricating condition, significantly affect the friction and wear performance of the unfilled and filled hybrid glass/PTFE fabric composite. And the hybrid glass/PTFE fabric composite is unsuitable to apply under the water or oil lubricating condition. Acknowledgements The authors are grateful to the National Natural Science Foundation of China (Grant No. 50421502), “973” program (Grant 2007CB607601) for financial support. References [1] W.G. Sawyer, K.D. Freudenberg, P. Bhimaraj, L.S. Schadler, A study on the friction and wear behavior of PTFE filled with alumina nanoparticles, Wear 254 (2003) 573–580.

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