Composite-based fibers

Finally, electrospinning is another method used recently to form composite-based fibers from solution. In 2003, Ko and co-workers developed electrospinning as a method to fabricate CNT/polymer composite fibers and yams. Composite dispersions of SWNTs and either poly(lactic acid) or polyacrylonitrile in DMF were initially produced. Then, the dispersion was placed in a pipette with a 0.9-mm nozzle. A wire was placed in the pipette and connected to a steel plate, which was placed 15cm below the nozzle, via a high-voltage power supply of 25 kV. When the power supply was turned on, the composite solution was charged, forcing it out of the... 

Composites. High molecular weight PPS can be combiaed with long (0.6 cm to continuous) fiber to produce advanced composite materials (131). Such materials having PPS as the polymer matrix have been developed by usiag a variety of reinforcements, including glass, carbon, and Kevlar fibers as mat, fabric, and unidirectional reinforcements. Thermoplastic composites based on PPS have found application ia the aircraft, aerospace, automotive, appliance, and recreation markets (see Composite materials, polymer-matrix). 

Tile is based mainly on vinyl chloride and vinyl acetate copolymers. Some polypropylene tile systems have recendy been iatroduced. A petroleum resia is usually employed as an extender and processiag aid conventional vinyl plasticizers and stabilizers also are iacorporated. Reinforcing fibers and limestone constitute the remainder of the tile composition the fibers contribute hot strength for processiag and dimensional stabiHty ia the finished tile, limestone suppHes bulk at an economical cost. Stable pigments are also iacorporated. Siace tile is iastalled oa and below grade level, it is important that the finished product be resistant to the effects of moisture and alkaH. 

The mechanical properties of composites based on the fibers discussed depend not only on the characteristics of the fibers but also on those of the matrix itself as well as on the fiber—matrix interface. 

Poly(phenylene sulfide) (PPS) is another semicrystalline polymer used in the composites industry. PPS-based composites are generally processed at 330°C and subsequently cooled rapidly in order to avoid excessive crystallisation and reduced toughness. The superior fire-retardant characteristics of PPS-based composites result in appHcations where fire resistance is an important design consideration. Laminated composites based on this material have shown poor resistance to transverse impact as a result of the poor adhesion of the fibers to the semicrystalline matrix. A PPS material more recently developed by Phillips Petroleum, AVTEL, has improved fiber—matrix interfacial properties, and promises, therefore, an enhanced resistance to transverse impact (see PoLYAffiRS containing sulfur). 

A number of amorphous thermoplastics are presently employed as matrices in long fiber composites, including polyethersulfone (PES), polysulfone (PSU), and polyetherimide (PEI). AH offer superior resistance to impact loading and higher interlaminar fracture toughnesses than do most epoxies. However, the amorphous nature of such polymers results in a lower solvent resistance, clearly a limitation if composites based on such polymers are to be used in aggressive environments. 

In contrast, there is also current interest in investigating PAN-based fibers in low thermal conductivity composites [62], Such fibers are carbonized at low temperature and offer a substitute to rayon-based carbon fibers in composites designed for solid rocket motor nozzles and exit cones. 

These composites and the information gained from stndying them have set the stage for the next generation of polymer composites, based on high-strength fibers such as the aramids. 

Ethylene-vinyl acetate Fetterman [37] reinforced compounded ethylene-vinyl acetate (EVA) copolymer by using short hbers and found that silane coupling agents were effective at establishing improved hber-matrix adhesion. Das et al. [38] prepared carbon fiber-filled conductive composites based on EVA and studied the electromagnetic interference shielding effectiveness of the composites. 

Scanning and transmission electron microscopies show that CNTs were coated with a homogeneous layer of ECPs (up to 50 nm). In the case of the composites based on TEG, ECP fibers with diameters up to 1 pm are observed on the TEG particles. 

As can be seen from this figure, the heat-resistance was remarkably improved by the drastic changes in the microstructure from amorphous to polycrystalline structure. Another type of SiC-based fiber, SA fiber (2), has a sintered SiC polycrystalline structure and includes very small amounts of aluminum. This fiber exhibits outstanding high temperature strength, coupled with much improved thermal conductivity and thermal stability compared with the Nicalon and Hi-Nicalon fibers. The fabrication cost of the SA fiber is also reduced to near half of that of the Hi-Nicalon Type S [ 17]. The SA fiber makes SiC/SiC composites even more attractive to the many applications [18]. In the next section, the production process, microstructure and physical properties of the SA fiber are explained in detail. 

The high-temperature stability of SiC-based ceramics is well-known, and therefore its composite materials have been investigated for application to high-tem-perature structural materials [19-21]. However, well-known SiC-based fibers and matrix-materials stained with alkali salt are easily oxidized at high temperatures in air [22]. This would be a serious problem when these materials are used near the ocean or in a combustion gas containing alkali elements. In particular, a silicon carbide fiber containing boron (a well-known sintering aid for SiC) over 1 wt% was extensively oxidized under the above condition. In this... 

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