《纺织复合材料》课程参考文献（Fiber-Reinforced Composites，THIRD EDITION）08 Polymer Nanocomposites

decomposition temperature can range up to 1200C.The reaction is conducted in presence of other gases,such as hydrogen sulfide and ammonia,which act as growth promoters.Cylindrical carbon nanofibers grow on the catalyst particles and are collected at the bottom of the reactor.Impurities on their surface, such as tar and other aromatic hydrocarbons,are removed by a subsequent process called pyrolitic stripping,which involves heating them to about 1000C in a reducing atmosphere.Heat treatment at temperatures up to 3000C is used to graphitize their surface and achieve higher tensile strength and tensile modulus.However,the optimum heat treatment temperature for maximum mechanical properties is found to be close to 1500C [5]. The diameter of carbon nanofibers and the orientation of graphite layers in carbon nanofibers with respect to their axis depend on the carbon-containing gas,the catalyst type,and the processing conditions,such as gas flow rate and temperature [7,8].The catalyst particle size also influences the diameter. Several different morphologies of carbon nanofibers have been observed [8,9]:platelet,in which the graphite layers are stacked normal to the fiber axis; hollow tubular construction,in which the graphite layers are parallel to the fiber axis,and fishbone or herringbone (with or without a hollow core),in which graphite layers are at an angle between 10 and 45 with the fiber axis(Figure 8.3).Single-wall and double-wall morphologies have been observed in heat- treated carbon nanofibers [10].Some of the graphite layers in both single-wall and double-wall morphologies are folded,the diameter of the folds remaining close to I nm. Table 8.2 lists the properties of a commercial carbon nanofiber(Pyrograf III)(Figure 8.4)as reported by its manufacturer (Applied Sciences,Inc.).The tensile modulus value listed in Table 8.2 is 600 GPa;however it should be noted that owing to the variety of morphologies observed in carbon nanofibers,they exhibit a range of modulus values,from as low as 110 GPa to as high as 700 GPa.Studies on vapor-grown carbon fibers (VGCF)[11],which are an order of (a) (b) (c) (d) (e) (0 FIGURE 8.3 Different morphologies of carbon nanofibers.(a)Graphite layers stacked normal to the fiber axis;(b)Hollow tubular construction with graphite layers parallel to the fiber axis;(c)and (d)Fishbone or herringbone morphology with graphite layers at an angle with the fiber axis;(e)Fishbone morphology with end loops;and (f)Double- walled morphology. 2007 by Taylor Francis Group,LLC

decomposition temperature can range up to 12008C. The reaction is conducted in presence of other gases, such as hydrogen sulfide and ammonia, which act as growth promoters. Cylindrical carbon nanofibers grow on the catalyst particles and are collected at the bottom of the reactor. Impurities on their surface, such as tar and other aromatic hydrocarbons, are removed by a subsequent process called pyrolitic stripping, which involves heating them to about 10008C in a reducing atmosphere. Heat treatment at temperatures up to 30008C is used to graphitize their surface and achieve higher tensile strength and tensile modulus. However, the optimum heat treatment temperature for maximum mechanical properties is found to be close to 15008C [5]. The diameter of carbon nanofibers and the orientation of graphite layers in carbon nanofibers with respect to their axis depend on the carbon-containing gas, the catalyst type, and the processing conditions, such as gas flow rate and temperature [7,8]. The catalyst particle size also influences the diameter. Several different morphologies of carbon nanofibers have been observed [8,9]: platelet, in which the graphite layers are stacked normal to the fiber axis; hollow tubular construction, in which the graphite layers are parallel to the fiber axis, and fishbone or herringbone (with or without a hollow core), in which graphite layers are at an angle between 108 and 458 with the fiber axis (Figure 8.3). Single-wall and double-wall morphologies have been observed in heat￾treated carbon nanofibers [10]. Some of the graphite layers in both single-wall and double-wall morphologies are folded, the diameter of the folds remaining close to 1 nm. Table 8.2 lists the properties of a commercial carbon nanofiber (Pyrograf III) (Figure 8.4) as reported by its manufacturer (Applied Sciences, Inc.). The tensile modulus value listed in Table 8.2 is 600 GPa; however it should be noted that owing to the variety of morphologies observed in carbon nanofibers, they exhibit a range of modulus values, from as low as 110 GPa to as high as 700 GPa. Studies on vapor-grown carbon fibers (VGCF) [11], which are an order of (a) (b) (c) (d) (e) (f) FIGURE 8.3 Different morphologies of carbon nanofibers. (a) Graphite layers stacked normal to the fiber axis; (b) Hollow tubular construction with graphite layers parallel to the fiber axis; (c) and (d) Fishbone or herringbone morphology with graphite layers at an angle with the fiber axis; (e) Fishbone morphology with end loops; and (f) Double￾walled morphology.
2007 by Taylor & Francis Group, LLC

TABLE 8.2 Properties of Vapor-Grown Carbon Nanofibers Carbon Nanofibers" Properties Pyrotically Stripped Diameter(nm) 60-200 Density (g/cm) 1.8 Tensile Modulus(GPa） 600 Tensile Strength(GPa) 7 Coefficient of thermal expansion(10C) -1.0 Electrical resistivity (n cm) 55 a Pyrograf III,produced by Applied Sciences,Inc. magnitude larger in diameter than the VGCNF,have shown that tensile modulus decreases with increasing diameter,whereas tensile strength decreases with both increasing diameter and increasing length. Carbon nanofibers have been incorporated into several different thermo- plastic and thermoset polymers.The results of carbon nanofiber addition on the mechanical properties of the resulting composite have been mixed. 0.2um FIGURE 8.4 Photograph of carbon nanofibers.(Courtesy of Applied Sciences,Inc. With permission.) 2007 by Taylor Francis Group.LLC

magnitude larger in diameter than the VGCNF, have shown that tensile modulus decreases with increasing diameter, whereas tensile strength decreases with both increasing diameter and increasing length. Carbon nanofibers have been incorporated into several different thermo￾plastic and thermoset polymers. The results of carbon nanofiber addition on the mechanical properties of the resulting composite have been mixed. TABLE 8.2 Properties of Vapor-Grown Carbon Nanofibers Carbon Nanofibersa Properties Pyrotically Stripped Diameter (nm) 60–200 Density (g=cm3 ) 1.8 Tensile Modulus (GPa) 600 Tensile Strength (GPa) 7 Coefficient of thermal expansion (106 =8C) 1.0 Electrical resistivity (mV cm) 55 a Pyrograf III, produced by Applied Sciences, Inc. FIGURE 8.4 Photograph of carbon nanofibers. (Courtesy of Applied Sciences, Inc. With permission.)
2007 by Taylor & Francis Group, LLC.

In general,incorporation of carbon nanofibers in thermoplastics has shown modest to high improvement in modulus and strength,whereas their incorpor- ation in thermosets has shown relatively smaller improvements.An example of each is given as follows. Finegan et al.[12]conducted a study on the tensile properties of carbon nanofiber-reinforced polypropylene.The nanofibers were produced with a variety of processing conditions (different carbon-containing gases,different gas flow rates,with and without graphitization).A variety of surface treatments were applied on the nanofibers.The composite tensile specimens with 15 vol%nanofi- bers were prepared using melt processing (injection molding).In all cases,they observed an increase in both tensile modulus and strength compared with poly- propylene itself.However,the amount of increase was influenced by the nanofiber production condition and the surface treatment.When the surface treatment involved surface oxidation in a CO2 atmosphere at 850C,the tensile modulus and strength of the composite were 4 GPa and 70 MPa,respectively,both of which were greater than three times the corresponding values for polypropylene. Patton et al.[13]reported the effect of carbon nanofiber addition to epoxy. The epoxy resin was diluted using acetone as the solvent.The diluted epoxy was then infused into the carbon nanofiber mat.After removing the solvent,the epoxy-soaked mat was cured at 120C and then postcured.Various nanofiber surface treatments were tried.The highest improvement in flexural modulus and strength was observed with carbon nanofibers that were heated in air at 400C for 30 min.With~18 vol%of carbon nanofibers,the flexural modulus of the composite was nearly twice that of epoxy,but the increase in flexural strength was only about 36%. 8.3 CARBON NANOTUBES Carbon nanotubes were discovered in 1991,and within a short period of time, have attracted a great deal of research and commercial interest due to their potential applications in a variety of fields,such as structural composites, energy storage devices,electronic systems,biosensors,and drug delivery sys- tems [14].Their unique structure gives them exceptional mechanical,thermal, electrical,and optical properties.Their elastic modulus is reported to be >1 TPa,which is close to that of diamond and 3-4 times higher than that of carbon fibers.They are thermally stable up to 2800C in vacuum;their thermal con- ductivity is about twice that of diamond and their electric conductivity is 1000 times higher than that of copper. 8.3.1 STRUCTURE Carbon nanotubes are produced in two forms,single-walled nanotubes (SWNT)and multiwalled nanotubes (MWNT).SWNT is a seamless hollow cylinder and can be visualized as formed by rolling a sheet of graphite layer, 2007 by Taylor Francis Group,LLC

In general, incorporation of carbon nanofibers in thermoplastics has shown modest to high improvement in modulus and strength, whereas their incorpor￾ation in thermosets has shown relatively smaller improvements. An example of each is given as follows. Finegan et al. [12] conducted a study on the tensile properties of carbon nanofiber-reinforced polypropylene. The nanofibers were produced with a variety of processing conditions (different carbon-containing gases, different gas flow rates, with and without graphitization). A variety of surface treatments were applied on the nanofibers. The composite tensile specimens with 15 vol% nanofi￾bers were prepared using melt processing (injection molding). In all cases, they observed an increase in both tensile modulus and strength compared with poly￾propylene itself. However, the amount of increase was influenced by the nanofiber production condition and the surface treatment. When the surface treatment involved surface oxidation in a CO2 atmosphere at 8508C, the tensile modulus and strength of the composite were 4 GPa and 70 MPa, respectively, both of which were greater than three times the corresponding values for polypropylene. Patton et al. [13] reported the effect of carbon nanofiber addition to epoxy. The epoxy resin was diluted using acetone as the solvent. The diluted epoxy was then infused into the carbon nanofiber mat. After removing the solvent, the epoxy-soaked mat was cured at 1208C and then postcured. Various nanofiber surface treatments were tried. The highest improvement in flexural modulus and strength was observed with carbon nanofibers that were heated in air at 4008C for 30 min. With ~18 vol% of carbon nanofibers, the flexural modulus of the composite was nearly twice that of epoxy, but the increase in flexural strength was only about 36%. 8.3 CARBON NANOTUBES Carbon nanotubes were discovered in 1991, and within a short period of time, have attracted a great deal of research and commercial interest due to their potential applications in a variety of fields, such as structural composites, energy storage devices, electronic systems, biosensors, and drug delivery sys￾tems [14]. Their unique structure gives them exceptional mechanical, thermal, electrical, and optical properties. Their elastic modulus is reported to be >1 TPa, which is close to that of diamond and 3–4 times higher than that of carbon fibers. They are thermally stable up to 28008C in vacuum; their thermal con￾ductivity is about twice that of diamond and their electric conductivity is 1000 times higher than that of copper. 8.3.1 STRUCTURE Carbon nanotubes are produced in two forms, single-walled nanotubes (SWNT) and multiwalled nanotubes (MWNT). SWNT is a seamless hollow cylinder and can be visualized as formed by rolling a sheet of graphite layer,
2007 by Taylor & Francis Group, LLC