Reinforcing organic polymers

Polyvinyl alcohol films can be stiffened and insolubilized in water after incorporation of colloidal silica (671-673). Hard PVA molding material is made from a mixture of the polymer solution and colloidal silica, with glycerol as plasticizer. The heat-pressed sheet was strong, stiff, and impact resistant (674). 

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Composite materials are composed of two or more phases of (mostly) different chemical compositions, by which the combination of the two phases and interface phenomena result in new properties of the composite compared to its individual constituents. An example is fiber-reinforced organic polymers. Classical composite materials have distinct phase boundaries between different macroscopic phases. 

As noted earlier, for the most part, the resulting materials from the use of reinforcements are composites, which are materials that contain strong fibers embedded in a continuous phase. The fibers are called reinforcement and the continuous phase is called the matrix. While the continuous phase can be a metallic alloy or inorganic material, it is typically an organic polymer that is termed a resin. Composites can be fabricated into almost any shape and after hardening, they can be machined, painted, etc., as desired. 

Carbon nanotubes are also of considerable interest with regard to both reinforcement and possible increases in electrical conductivity.89 90 92,93 95-104 There is considerable interest in characterizing the flexibility of these nanotube structures, in minimizing their tendencies to aggregate, and in maximizing their miscibilities with inorganic as well as organic polymers. 

BN fibers are used for reinforcing ceramic materials (e.g., Al203, Si3N4, SiC) to enhance mechanical properties as well as to extend the range of possible applications. They serve as reinforcement of organic polymers (e.g., epoxides, polyether-polyketones, polyphenylensulfides) which exhibit good thermal conductivity and low thermal expansion. 

Potassium titanate has a high refractive index and a low thermal conductivity. Moreover, its size is in the right range to scatter infrared radiation. Thus it has potential use as an insulating and ir-reflective material. Other potential applications of potassium titanate include its use as a filtration medium, a reinforcement material for organic polymers, and an asbestos replacement in friction brakes. Between 1965 and 1972, pigmentary potassium titanate was manufactured in the United States (108). 

Strong graphite fibers are made by pyrolysis, at 1500°C or above, of oriented organic polymer fibers (e.g., those of polyacrylonitrile, polyacrylate esters, or cellulose). When incorporated into plastics the reinforced materials are light and very strong. Other forms of graphite such as foams, foils, or whiskers can also be made. 

It should be noted that reinforcement applications are not limited to organic polymers. Though ceramics are already hard and chemically/thermally resistant, these materials may also be doped with CNTs to improve their inherent brittleness. This has already been proven for the incorporation of 5-10% of CNTs within an alumina matrix. The resultant material exhibits five times the fracture toughness and seven times greater electrical conductivity relative to undoped AI2O3, with an added property of unidirectional heat conductivity,... 

The intercalation of organic polymers into the interlayer space has also been widely studied since hybridization may not only produce unique materials with high dispersive ability, but may also enhance polymeric properties by nsing nanoscale reinforcements compared to the conventional particnlate-lilled... 

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