- Email: [email protected]
Application of radiation-crosslinked polytetrafluoroethylene to fiber-reinforced composite materials
Radiation Physics and Chemistry 60 (2001) 467–471
Application of radiation-crosslinked polytetrafluoroethylene to fiber-reinforced composite materials Akihiro Oshima*, Akira Udagawa, Yousuke Morita Japan Atomic Energy Research Institute, Takasaki Radiation Chemistry Research Establishment, Watanuki-eho 1233, Takasaki, Gunma 370-1292, Japan
Abstract Plain-woven carbon fiber-filled polytetrafluoroethylene (PTFE) composites were fabricated by radiation-crosslinking under selective conditions. High mechanical and frictional properties are found in the composite materials compared with crosslinked PTFE without fiber. The composite materials with optional shapes, which are laminated after electron beam (EB) crosslinking treatment of each mono-layer could also be fabricated. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Crosslinked PTFE; Plain-woven carbon fiber; Composite materials
1. Introduction Recently, in our previous studies on irradiation temperature effects of fluorinated polymers (Tabata, 1992; Oshima, 1994, 1997; Oshima et al., 1994, 1995, 1997a, b; Tabata et al., 1996; Katoh et al., 1999; Tabata and Oshima, 1999; Ikeda et al., 2000), it was found that the crosslinked polytetrafluoroethylene (PTFE) has been attained by irradiation in its molten state just above the melting temperature (3278C) under oxygen-free atmosphere (Tabata, 1992; Oshima, 1994, 1997; Oshima et al., 1994, 1995, 1997b; Sun et al., 1994; Tabata et al., 1996; Katoh et al., 1999). The obtained crosslinked PTFE shows remarkable improvements in radiation resistance (Oshima, 1994, 1997; Oshima et al., 1997c; Tabata et al., 1996), mechanical properties (Oshima, 1994, 1997; Oshima et al., 1994, 1995), frictional properties (Oshima et al., 1997d), visible light transparency (Oshima, 1994, 1997; Oshima et al., 1997c, d) and other properties, compared with those of non-crosslinked PTFE. *Corresponding author. Tel: +81-27-346-9442; fax: +81-27346-9687. E-mail address: [email protected] (A. Oshima).
High-performance fiber-reinforced PTFE composites have not been developed, because PTFE has high viscosity (1010–1011 P) at 3808C in its molten state (Nishioka and Watanabe, 1957), is insoluble to most chemical solvents and shows low adhesion (Fox and Zisman, 1950). A ready-made PTFE composite has been produced by PTFE fine powder filled with 10–20 wt% of carbon or glass-chopped fibers. However, they show poor mechanical properties, for there is hardly any fiber–resin adhesion. It would be useful to develop continuous fiber-reinforced PTFE composites with high mechanical properties. Uni-directional carbon fiber composites have been fabricated by the electron beam crosslinking technique of PTFE under selective conditions (Oshima et al., 1999). In this method, the composites are limited in size due to limited radiation penetration, or temperature distribution. In this study, we tried to fabricate the crosslinked PTFE composite with optional shapes by means of laminate molding after crosslinking within carbon fiber-woven mono-layer pre-form. The dependence of mechanical properties on its production technique was studied for the carbon fiber composites so produced.
0969-806X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 0 ) 0 0 4 1 6 - 3
468
A. Oshima et al. / Radiation Physics and Chemistry 60 (2001) 467–471
2. Experimental 2.1. Materials The materials used were an aqueous dispersion of PTFE fine powder (FLUON1 AD1; average diameter of particles: 0.25 mm, concentration: 60 wt%, Mn: 1.4 106, Asahi–Glass fluoropolymers Co. Ltd.), and the plain-woven carbon fabric (TORAYCA1 T-300; average diameter of fibers: 9 mm, TORAY Co. Ltd.). Material samples were prepared by the polymer dispersion impregnation method described in a previous paper (Oshima et al., 1999). The impregnated materials based on PTFE and plain-woven carbon fabrics were dried at 1508C for 24 h in a vacuum oven prior to sintering of PTFE powder. Sintering was carried out at 3508C for 10 min under a pressure of 3 MPa by a hot press machine. Then the samples were allowed to cool down to ambient temperature under pressure. The pre-forms consist of mono-layer, and laminates with multi-layers, prepared as mentioned above. 2.2. Irradiation The preformed composite materials were put in an irradiation vessel with a heating device (Haruyama et al., 1995). The materials were irradiated up to 500 kGy with a dose rate of 0.12 kGys 1 by electron beam (EB), 2 MeV, under oxygen-free atmosphere at 3358C 58C. 2.3. Measurements Flexural properties were measured by the three-point bending test; interlaminar shear strength (ILSS) test also was carried out at ambient temperature using an INSTRON (type 4302). The thickness of the specimen was 2 mm. The crosshead speed in the bending test was
Fig. 1. Flexural properties of PTFE resin and crosslinked PTFE composite with 500 kGy irradiation.
2 mm/min with a span length of 32 mm. In addition, the crosshead speed in the ILSS test was 1 mm/min with a span length of 14 mm. Flexural strength, flexural modulus and ILSS of the test pieces were calculated from the stress–strain curves obtained. Coefficients of friction and abrasion were measured by using thrust-type frictional testing machine at ambient temperature. The testing pressures were 20, 35 and 50 kgf/cm2, and the velocities were 10, 20 and 30 m/min against the standard friction material of S45C stainless-steel ring.
3. Results and discussions The composites are laminated with 12 layers after EBcrosslinking treatment (500 kGy for crosslinking) of each monolayer, and the sample dimensions are length 140 mm width 80 mm thickness 2 mm. Fig. 1 shows the flexural properties of PTFE resin and the crosslinked PTFE composites with 500 kGy EB irradiation. The flexural properties of the crosslinked composites were higher than those of commercial PTFE composites, and much higher than those of PTFE resin. These show that the PTFE composites with high mechanical properties are obtained by the EB-crosslinking technique. The flexural strength and the modulus of the crosslinked composite laminated with 12 layers before EBcrosslinking treatment, were about 125 MPa and 24 GPa, respectively. In addition, the strength and the modulus of the composite laminated with the same layers after the crosslinking within monolayer pre-form were about 138 MPa and 28 GPa, respectively. Flexural properties of the crosslinked composites laminated after the crosslinking hardly changed, compared with the composites laminated before the crosslinking. It is found that the fiber-reinforced composites with optional shapes such as thick board or plank could be fabricated by means of laminated molding after crosslinking within the monolayers. Therefore, the crosslinked composites with optional shapes can be produced by using smallsized irradiation equipment such as low-energy electron accelerator facility (voltage: 300–800 kV class). However, the flexural properties of the composites are poorer, compared with those of the usual polymer composites, and also they are low as compared with the theoretical values calculated from each parameter. Though the ILSS of the crosslinked PTFE composites changes sharply with crosslinking dose, these values are about 13 times lower than that of usual polymer composites. We expected chemical bonding between PTFE and the fibers; however, it appears that fiber–resin adhesion is negligible in these composites. When three-point bending test was carried out, fracture mode of the composites indicated that fracture
A. Oshima et al. / Radiation Physics and Chemistry 60 (2001) 467–471
energy was released gradually with the displacement, as shown in Fig. 2. The fracture surfaces after three-point bending test observed by scanning electron microscope are shown in Fig. 3. The toughness of the resin matrix was guessed to be poor in this composite. Especially, in the case of the composite laminated after the crosslinking, the delamination could easily take place, compared with that laminated before the crosslinking. Therefore, fabrication of the crosslinked PTFE compo-
Fig. 2. Typical stress–strain curve of crosslinked PTFE composites: crosslinking dose is 500 kGy.
Fig. 3. SEM photograph of the fracture surfaces after threepoint bending test.
469
sites with higher mechanical properties is required to enhance the toughness of the crosslinked PTFE and fiber–resin adhesion. Table 1 shows the frictional properties of PTFE, crosslinked PTFE resin (100 kGy for crosslinking) and the crosslinked composite (100 kGy for crosslinking). All coefficient of friction values are very low compared with the other hydrocarbon polymers and hardly change by EB-crosslinking or reinforcing fiber in it. However, the coefficient of abrasion decreases drastically with crosslinking or with reinforcing fiber in it; the value decreases by three or four orders of magnitude after crosslinking and in the fiber-reinforced samples. Thus, the abrasion was greatly improved by crosslinking and reinforcing fiber in it. The PV value, which is pressure by velocity, shows a severe condition of frictional environment. In case of PV=200, the abrasion of PTFE resin shows abnormal phenomenon. However, by only crosslinking, the abrasion was much improved and the coefficient of abrasion was better than glass or carbon-chopped fibers filled PTFE using frictional materials. The coefficient of abrasion for the crosslinked composites is about four times smaller than that of the crosslinked PTFE resin. The crosslinked composites are kept until PV=1050 and abraded at PV=1500 under frictional environment, as seen in Table 1. The crosslinked resin is kept until PV=200 and abraded at PV=400. Thus, the coefficient of abrasion is much improved by the crosslinking and the reinforcing fiber. It is seen that the appearance of the crosslinking and the reinforcing effects are supposed to be a morphological change of PTFE from non-crosslinking to crosslinking, because there is hardly an adhesion between PTFE and the fibers even in the presence of crosslinking. That is, the morphology of PTFE is changed from a discontinuous stratum of a pile of random crystal phase to a continual stratum of a visco-elastically amorphous one by radiation crosslinking (Oshima, 1997; Oshima et al., 1997e). According to our previous studies on radiation resistance of the uni-directional crosslinked PTFE composites (Oshima et al., 1999), the radiation resistance is about six times higher than that of the crosslinked resin, and about 4000 times higher than uni-directional non-crosslinked PTFE composites. The high radiation resistance of the crosslinked composites is caused by radiation resistance of crosslinked PTFE and outside radiation protection effects from the carbon fiber in the composite. That is, the improvement of radiation resistance could be explained by selective energy or charge transfer to the crosslinking sites in matrix, and the protection effect to radiation, which come from the carbon fibers in the composite (Yamaoka and Tagawa, 1984). Therefore, it is expected to apply this composite in fields requiring high frictional properties and high radiation resistance.
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A. Oshima et al. / Radiation Physics and Chemistry 60 (2001) 467–471
Table 1 The frictional properties of crosslinked matrix resin (100 kGy-crosslinking) and crosslinked PTFE composite (100 kGy-crosslinking, Vf 54.3%)
Non-crosslinked PTFE resin Crosslinked PTFE resin Crosslinked PTFE composite
Coefficient of friction
Coefficient of abrasion ( 10 10cm3 kgfm 1)
Pressure (kgf cm 2)
Velocity (m min 1)
0.14
Abnormal abrasion
20
10
200
0.13
775
20
10
200
0.15> 0.10
High abrasion 200
20 20
20 10
400 200
0.08 0.15 0.15>
220 190 High abrasion
20 35 50
20 30 30
400 1050 1500
4. Conclusion The plain-woven carbon fiber-reinforced crosslinked PTFE composites with optional shapes are fabricated by means of laminated molding after EB-crosslinking treatment within monolayer pre-form. In the three-point bending test, the flexural strength and the modulus are higher than those of a ready-made composite. The composites show high frictional properties, that is, the coefficient of friction value is very low compared with the other hydrocarbon polymers, and also the abrasion is better than that of crosslinked PTFE without fiber.
Acknowledgements The authors would like to acknowledge continuing encouragement by Prof. Y. Tabata of the University of Tokyo. They wish to thank Dr. Yoshimura of Mitsui Chemical Co. Ltd. for measuring the frictional properties of materials, Mr. A. Hiroki of Gunma University for SEM observation, and the operation staffs of first electron accelerator in JAERI Takasaki.
References Fox, H.W., Zisman, W.A., 1950. The spreading of liquids on low energy surfaces. I. polytetrafluoroethylene. J. Colloid Sci. 5, 514. Haruyama, Y., Oshima, A., Ikeda, S., Sunaga, H., Takizawa, H., Seguchi, T., 1995. Development of high temperature electron beam irradiation vessel. Report. Japan Atomic. Energy Research Institute, JAERI-Tech, 95-003. Ikeda, S., Oshima, A., Tabata, Y., 2000. Temperature effects on radiation induced phenomena in fluorinated polymeric systems } change of mechanical and thermal properties }. Proceedings of International Symposium on Prospects for Application of Radiation Towards the 21st Century, Tokyo, Japan.
Value of PV
Katoh, E., Sugisawa, H., Oshima, A., Tabata, Y., Seguchi, T., Yamazaki, T., 1999. evidence for radiation induced crosslinking in polytetrafluoroethylene by means of high-resolution solid state 19F high-speed MAS NMR. Radiat. Phys. Chem. 54, 165. Nishioka, A., Watanabe, M., 1957. Viscosity and elasticity of polytetrafluoroethylene resin above the melting point. J. Polym. Sci. 24, 298. Oshima, A., 1994. Irradiation effects on fluorinated-polymers under severe environment } studies on irradiation temperature effects of fluorinated-polymers. The Master Thesis of Tokai University. Oshima, A., 1997. Studies on radiation induced crosslinking of polytetrafluoroethylene (PTFE). The Doctor Thesis of Tokai University. Oshima, A., Seguchi, T., Tabata, Y., 1994. Radiation induced crosslinking of polytetrafluoroethylene. Proceedings of the 14th International Symposium on Fluorine Chemistry. Yokohama, Japan, p. 278. Oshima, A., Tabata, Y., Kudoh, H., Seguchi, T., 1995. Radiation induced crosslinking of polytetrafluoroethylene. Radiat. Phys. Chem. 45, 269. Oshima, A., Ikeda, S., Seguchi, T., Tabata, Y., 1997a. Temperature effect on radiation induced reactions in ethylene and tetrafluoroethylene copolymer (ETFE). Radiat. Phys. Chem. 50, 519. Oshima, A., Ikeda, S., Kudoh, H., Seguchi, T., Tabata, Y., 1997b. Temperature effects on radiation induced phenomena in polytetrafluoroethylene (PTFE) } change of G-value }. Radiat. Phys. Chem. 50, 611. Oshima, A., Ikeda, S., Seguchi, T., Tabata, Y., 1997c. Improvement of radiation resistance for polytetrafluoroethylene (PTFE) by radiation crosslinking. Radiat. Phys. Chem. 49, 279. Oshima, A., Ikeda, S., Seguchi, T., Tabata, Y., 1997d. Development of advanced fluoropolymer for nuclear environment. J. Adv. Sci. 9, 60. Oshima, A., Ikeda, S., Seguchi, T., Tabata, Y., 1997e. Change of molecular motion of polytetrafluoroethylene (PTFE) by radiation induced crosslinking. Radiat. Phys. Chem. 49, 581. Oshima, A., Udagawa, A., Morita, Y., 1999. Radiation processing for PTFE composite reinforced with carbon fiber. Proceedings of Seventh International Conference on Radia-
A. Oshima et al. / Radiation Physics and Chemistry 60 (2001) 467–471 tion Curing (RadTech Asia ‘99). Kualalumpur, Malaysia, pp. 507–512, August 1999. Sun, J., Zhang, Y., Zhong, X., Zhu, X., 1994. Modification of polytetrafluoroethylene by radiation-1. Improvement in high temperature properties and radiation stability. Radiat. Phys. Chem. 44, 655. Tabata, Y., 1992. Solid state reaction in radiation chemistry. Proceedings of Taniguchi Conference. Sapporo, Japan, pp. 118–120, June 1992.
471
Tabata, Y., Oshima, A., Takashika, K., Seguchi, T., 1996. Temperature effects on radiation induced phenomena in polymers. Radiat. Phys. Chem. 48, 563. Tabata, Y., Oshima, A., 1999. Temperature dependence of radiation effects on polymers. Macromolecular Symposia, Vol. 143, p. 337. Yamaoka, H., Tagawa, S., 1984. Recent studies on radiation effects of organic insulators, J. At. Energy Soc. Jpn. (Nihon Genshiryoku gakkai-shi) 26(9), 739 (in Japanese).
Application of radiation-crosslinked polytetrafluoroethylene to fiber-reinforced composite materials Akihiro Oshima*, Akira Udagawa, Yousuke Morita Japan Atomic Energy Research Institute, Takasaki Radiation Chemistry Research Establishment, Watanuki-eho 1233, Takasaki, Gunma 370-1292, Japan
Abstract Plain-woven carbon fiber-filled polytetrafluoroethylene (PTFE) composites were fabricated by radiation-crosslinking under selective conditions. High mechanical and frictional properties are found in the composite materials compared with crosslinked PTFE without fiber. The composite materials with optional shapes, which are laminated after electron beam (EB) crosslinking treatment of each mono-layer could also be fabricated. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Crosslinked PTFE; Plain-woven carbon fiber; Composite materials
1. Introduction Recently, in our previous studies on irradiation temperature effects of fluorinated polymers (Tabata, 1992; Oshima, 1994, 1997; Oshima et al., 1994, 1995, 1997a, b; Tabata et al., 1996; Katoh et al., 1999; Tabata and Oshima, 1999; Ikeda et al., 2000), it was found that the crosslinked polytetrafluoroethylene (PTFE) has been attained by irradiation in its molten state just above the melting temperature (3278C) under oxygen-free atmosphere (Tabata, 1992; Oshima, 1994, 1997; Oshima et al., 1994, 1995, 1997b; Sun et al., 1994; Tabata et al., 1996; Katoh et al., 1999). The obtained crosslinked PTFE shows remarkable improvements in radiation resistance (Oshima, 1994, 1997; Oshima et al., 1997c; Tabata et al., 1996), mechanical properties (Oshima, 1994, 1997; Oshima et al., 1994, 1995), frictional properties (Oshima et al., 1997d), visible light transparency (Oshima, 1994, 1997; Oshima et al., 1997c, d) and other properties, compared with those of non-crosslinked PTFE. *Corresponding author. Tel: +81-27-346-9442; fax: +81-27346-9687. E-mail address: [email protected] (A. Oshima).
High-performance fiber-reinforced PTFE composites have not been developed, because PTFE has high viscosity (1010–1011 P) at 3808C in its molten state (Nishioka and Watanabe, 1957), is insoluble to most chemical solvents and shows low adhesion (Fox and Zisman, 1950). A ready-made PTFE composite has been produced by PTFE fine powder filled with 10–20 wt% of carbon or glass-chopped fibers. However, they show poor mechanical properties, for there is hardly any fiber–resin adhesion. It would be useful to develop continuous fiber-reinforced PTFE composites with high mechanical properties. Uni-directional carbon fiber composites have been fabricated by the electron beam crosslinking technique of PTFE under selective conditions (Oshima et al., 1999). In this method, the composites are limited in size due to limited radiation penetration, or temperature distribution. In this study, we tried to fabricate the crosslinked PTFE composite with optional shapes by means of laminate molding after crosslinking within carbon fiber-woven mono-layer pre-form. The dependence of mechanical properties on its production technique was studied for the carbon fiber composites so produced.
0969-806X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 0 ) 0 0 4 1 6 - 3
468
A. Oshima et al. / Radiation Physics and Chemistry 60 (2001) 467–471
2. Experimental 2.1. Materials The materials used were an aqueous dispersion of PTFE fine powder (FLUON1 AD1; average diameter of particles: 0.25 mm, concentration: 60 wt%, Mn: 1.4 106, Asahi–Glass fluoropolymers Co. Ltd.), and the plain-woven carbon fabric (TORAYCA1 T-300; average diameter of fibers: 9 mm, TORAY Co. Ltd.). Material samples were prepared by the polymer dispersion impregnation method described in a previous paper (Oshima et al., 1999). The impregnated materials based on PTFE and plain-woven carbon fabrics were dried at 1508C for 24 h in a vacuum oven prior to sintering of PTFE powder. Sintering was carried out at 3508C for 10 min under a pressure of 3 MPa by a hot press machine. Then the samples were allowed to cool down to ambient temperature under pressure. The pre-forms consist of mono-layer, and laminates with multi-layers, prepared as mentioned above. 2.2. Irradiation The preformed composite materials were put in an irradiation vessel with a heating device (Haruyama et al., 1995). The materials were irradiated up to 500 kGy with a dose rate of 0.12 kGys 1 by electron beam (EB), 2 MeV, under oxygen-free atmosphere at 3358C 58C. 2.3. Measurements Flexural properties were measured by the three-point bending test; interlaminar shear strength (ILSS) test also was carried out at ambient temperature using an INSTRON (type 4302). The thickness of the specimen was 2 mm. The crosshead speed in the bending test was
Fig. 1. Flexural properties of PTFE resin and crosslinked PTFE composite with 500 kGy irradiation.
2 mm/min with a span length of 32 mm. In addition, the crosshead speed in the ILSS test was 1 mm/min with a span length of 14 mm. Flexural strength, flexural modulus and ILSS of the test pieces were calculated from the stress–strain curves obtained. Coefficients of friction and abrasion were measured by using thrust-type frictional testing machine at ambient temperature. The testing pressures were 20, 35 and 50 kgf/cm2, and the velocities were 10, 20 and 30 m/min against the standard friction material of S45C stainless-steel ring.
3. Results and discussions The composites are laminated with 12 layers after EBcrosslinking treatment (500 kGy for crosslinking) of each monolayer, and the sample dimensions are length 140 mm width 80 mm thickness 2 mm. Fig. 1 shows the flexural properties of PTFE resin and the crosslinked PTFE composites with 500 kGy EB irradiation. The flexural properties of the crosslinked composites were higher than those of commercial PTFE composites, and much higher than those of PTFE resin. These show that the PTFE composites with high mechanical properties are obtained by the EB-crosslinking technique. The flexural strength and the modulus of the crosslinked composite laminated with 12 layers before EBcrosslinking treatment, were about 125 MPa and 24 GPa, respectively. In addition, the strength and the modulus of the composite laminated with the same layers after the crosslinking within monolayer pre-form were about 138 MPa and 28 GPa, respectively. Flexural properties of the crosslinked composites laminated after the crosslinking hardly changed, compared with the composites laminated before the crosslinking. It is found that the fiber-reinforced composites with optional shapes such as thick board or plank could be fabricated by means of laminated molding after crosslinking within the monolayers. Therefore, the crosslinked composites with optional shapes can be produced by using smallsized irradiation equipment such as low-energy electron accelerator facility (voltage: 300–800 kV class). However, the flexural properties of the composites are poorer, compared with those of the usual polymer composites, and also they are low as compared with the theoretical values calculated from each parameter. Though the ILSS of the crosslinked PTFE composites changes sharply with crosslinking dose, these values are about 13 times lower than that of usual polymer composites. We expected chemical bonding between PTFE and the fibers; however, it appears that fiber–resin adhesion is negligible in these composites. When three-point bending test was carried out, fracture mode of the composites indicated that fracture
A. Oshima et al. / Radiation Physics and Chemistry 60 (2001) 467–471
energy was released gradually with the displacement, as shown in Fig. 2. The fracture surfaces after three-point bending test observed by scanning electron microscope are shown in Fig. 3. The toughness of the resin matrix was guessed to be poor in this composite. Especially, in the case of the composite laminated after the crosslinking, the delamination could easily take place, compared with that laminated before the crosslinking. Therefore, fabrication of the crosslinked PTFE compo-
Fig. 2. Typical stress–strain curve of crosslinked PTFE composites: crosslinking dose is 500 kGy.
Fig. 3. SEM photograph of the fracture surfaces after threepoint bending test.
469
sites with higher mechanical properties is required to enhance the toughness of the crosslinked PTFE and fiber–resin adhesion. Table 1 shows the frictional properties of PTFE, crosslinked PTFE resin (100 kGy for crosslinking) and the crosslinked composite (100 kGy for crosslinking). All coefficient of friction values are very low compared with the other hydrocarbon polymers and hardly change by EB-crosslinking or reinforcing fiber in it. However, the coefficient of abrasion decreases drastically with crosslinking or with reinforcing fiber in it; the value decreases by three or four orders of magnitude after crosslinking and in the fiber-reinforced samples. Thus, the abrasion was greatly improved by crosslinking and reinforcing fiber in it. The PV value, which is pressure by velocity, shows a severe condition of frictional environment. In case of PV=200, the abrasion of PTFE resin shows abnormal phenomenon. However, by only crosslinking, the abrasion was much improved and the coefficient of abrasion was better than glass or carbon-chopped fibers filled PTFE using frictional materials. The coefficient of abrasion for the crosslinked composites is about four times smaller than that of the crosslinked PTFE resin. The crosslinked composites are kept until PV=1050 and abraded at PV=1500 under frictional environment, as seen in Table 1. The crosslinked resin is kept until PV=200 and abraded at PV=400. Thus, the coefficient of abrasion is much improved by the crosslinking and the reinforcing fiber. It is seen that the appearance of the crosslinking and the reinforcing effects are supposed to be a morphological change of PTFE from non-crosslinking to crosslinking, because there is hardly an adhesion between PTFE and the fibers even in the presence of crosslinking. That is, the morphology of PTFE is changed from a discontinuous stratum of a pile of random crystal phase to a continual stratum of a visco-elastically amorphous one by radiation crosslinking (Oshima, 1997; Oshima et al., 1997e). According to our previous studies on radiation resistance of the uni-directional crosslinked PTFE composites (Oshima et al., 1999), the radiation resistance is about six times higher than that of the crosslinked resin, and about 4000 times higher than uni-directional non-crosslinked PTFE composites. The high radiation resistance of the crosslinked composites is caused by radiation resistance of crosslinked PTFE and outside radiation protection effects from the carbon fiber in the composite. That is, the improvement of radiation resistance could be explained by selective energy or charge transfer to the crosslinking sites in matrix, and the protection effect to radiation, which come from the carbon fibers in the composite (Yamaoka and Tagawa, 1984). Therefore, it is expected to apply this composite in fields requiring high frictional properties and high radiation resistance.
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A. Oshima et al. / Radiation Physics and Chemistry 60 (2001) 467–471
Table 1 The frictional properties of crosslinked matrix resin (100 kGy-crosslinking) and crosslinked PTFE composite (100 kGy-crosslinking, Vf 54.3%)
Non-crosslinked PTFE resin Crosslinked PTFE resin Crosslinked PTFE composite
Coefficient of friction
Coefficient of abrasion ( 10 10cm3 kgfm 1)
Pressure (kgf cm 2)
Velocity (m min 1)
0.14
Abnormal abrasion
20
10
200
0.13
775
20
10
200
0.15> 0.10
High abrasion 200
20 20
20 10
400 200
0.08 0.15 0.15>
220 190 High abrasion
20 35 50
20 30 30
400 1050 1500
4. Conclusion The plain-woven carbon fiber-reinforced crosslinked PTFE composites with optional shapes are fabricated by means of laminated molding after EB-crosslinking treatment within monolayer pre-form. In the three-point bending test, the flexural strength and the modulus are higher than those of a ready-made composite. The composites show high frictional properties, that is, the coefficient of friction value is very low compared with the other hydrocarbon polymers, and also the abrasion is better than that of crosslinked PTFE without fiber.
Acknowledgements The authors would like to acknowledge continuing encouragement by Prof. Y. Tabata of the University of Tokyo. They wish to thank Dr. Yoshimura of Mitsui Chemical Co. Ltd. for measuring the frictional properties of materials, Mr. A. Hiroki of Gunma University for SEM observation, and the operation staffs of first electron accelerator in JAERI Takasaki.
References Fox, H.W., Zisman, W.A., 1950. The spreading of liquids on low energy surfaces. I. polytetrafluoroethylene. J. Colloid Sci. 5, 514. Haruyama, Y., Oshima, A., Ikeda, S., Sunaga, H., Takizawa, H., Seguchi, T., 1995. Development of high temperature electron beam irradiation vessel. Report. Japan Atomic. Energy Research Institute, JAERI-Tech, 95-003. Ikeda, S., Oshima, A., Tabata, Y., 2000. Temperature effects on radiation induced phenomena in fluorinated polymeric systems } change of mechanical and thermal properties }. Proceedings of International Symposium on Prospects for Application of Radiation Towards the 21st Century, Tokyo, Japan.
Value of PV
Katoh, E., Sugisawa, H., Oshima, A., Tabata, Y., Seguchi, T., Yamazaki, T., 1999. evidence for radiation induced crosslinking in polytetrafluoroethylene by means of high-resolution solid state 19F high-speed MAS NMR. Radiat. Phys. Chem. 54, 165. Nishioka, A., Watanabe, M., 1957. Viscosity and elasticity of polytetrafluoroethylene resin above the melting point. J. Polym. Sci. 24, 298. Oshima, A., 1994. Irradiation effects on fluorinated-polymers under severe environment } studies on irradiation temperature effects of fluorinated-polymers. The Master Thesis of Tokai University. Oshima, A., 1997. Studies on radiation induced crosslinking of polytetrafluoroethylene (PTFE). The Doctor Thesis of Tokai University. Oshima, A., Seguchi, T., Tabata, Y., 1994. Radiation induced crosslinking of polytetrafluoroethylene. Proceedings of the 14th International Symposium on Fluorine Chemistry. Yokohama, Japan, p. 278. Oshima, A., Tabata, Y., Kudoh, H., Seguchi, T., 1995. Radiation induced crosslinking of polytetrafluoroethylene. Radiat. Phys. Chem. 45, 269. Oshima, A., Ikeda, S., Seguchi, T., Tabata, Y., 1997a. Temperature effect on radiation induced reactions in ethylene and tetrafluoroethylene copolymer (ETFE). Radiat. Phys. Chem. 50, 519. Oshima, A., Ikeda, S., Kudoh, H., Seguchi, T., Tabata, Y., 1997b. Temperature effects on radiation induced phenomena in polytetrafluoroethylene (PTFE) } change of G-value }. Radiat. Phys. Chem. 50, 611. Oshima, A., Ikeda, S., Seguchi, T., Tabata, Y., 1997c. Improvement of radiation resistance for polytetrafluoroethylene (PTFE) by radiation crosslinking. Radiat. Phys. Chem. 49, 279. Oshima, A., Ikeda, S., Seguchi, T., Tabata, Y., 1997d. Development of advanced fluoropolymer for nuclear environment. J. Adv. Sci. 9, 60. Oshima, A., Ikeda, S., Seguchi, T., Tabata, Y., 1997e. Change of molecular motion of polytetrafluoroethylene (PTFE) by radiation induced crosslinking. Radiat. Phys. Chem. 49, 581. Oshima, A., Udagawa, A., Morita, Y., 1999. Radiation processing for PTFE composite reinforced with carbon fiber. Proceedings of Seventh International Conference on Radia-
A. Oshima et al. / Radiation Physics and Chemistry 60 (2001) 467–471 tion Curing (RadTech Asia ‘99). Kualalumpur, Malaysia, pp. 507–512, August 1999. Sun, J., Zhang, Y., Zhong, X., Zhu, X., 1994. Modification of polytetrafluoroethylene by radiation-1. Improvement in high temperature properties and radiation stability. Radiat. Phys. Chem. 44, 655. Tabata, Y., 1992. Solid state reaction in radiation chemistry. Proceedings of Taniguchi Conference. Sapporo, Japan, pp. 118–120, June 1992.
471
Tabata, Y., Oshima, A., Takashika, K., Seguchi, T., 1996. Temperature effects on radiation induced phenomena in polymers. Radiat. Phys. Chem. 48, 563. Tabata, Y., Oshima, A., 1999. Temperature dependence of radiation effects on polymers. Macromolecular Symposia, Vol. 143, p. 337. Yamaoka, H., Tagawa, S., 1984. Recent studies on radiation effects of organic insulators, J. At. Energy Soc. Jpn. (Nihon Genshiryoku gakkai-shi) 26(9), 739 (in Japanese).