High-performance rayon fibers

Regenerated celluloses High-performance rayon fibers... 

A defect of regular rayon fabric in the absence of a cross-linking finish is its solubility in alkali with consequent loss of strength and dimensional stability. These defects have been largely overcome in the high performance rayons. Mitchell and Daul (43) reported that regular textile grade rayon staple fiber accounts for 70-80% of the output of the rayon industry. 

Rayon-based reinforcing fibers, as a result of their high price of > 800 DM/kg, are only of minor importance. A comparison of the production figures for high performance C-fibers and standard C-fibers shows that the importance of the high performance HT- and HM-C-fibers has steadily increased (see Table 5.2-11). 

The high-performance rayons overcome this disadvantage. The HWM fiber has cotton like mechanical properties and a caustic resistance that allows mercerization. It is compatible in blends with all grades of cotton where it adds strength, improved luster and appearance, and a softer hand. In blends with nylon, polyester, acrylics, and triacetate, it has good strength retention after resination, and the blended fabrics have superior wash-and-wear performance and resistance to pilling. 

PEN-based fibers extend the performance of polyesters. PEN fibers have excellent heat resistance, modulus, and dimensional stability relative to PET and demonstrate better retention of mechanical properties in a hot/wet environment and offer improved chemical resistance versus PET fibers (see Polyesters, Fibers). With naphthalate modification, polyester fibers can meet the application requirements, which are currently served by other high performance industrial fibers such as rayon, nylon-6,6, aramids, poly(phenylene sulfide) (PPS), and even steel. 

Producers of PAN-based carbon fiber include Toray, Toho Beslon, Mitsubishi Rayon, and Asahi Kasai Carbon in Japan Hercules, Amoco Performance Products, BASE Stmctural Materials, Eortafil (Akzo), and Mitsubishi Rayon in the United States and Akzo, Sigri, and Soficar in Europe. Primary suppHers of high performance pitch-based carbon fibers include Amoco Performance Products, Mitsubishi Kasai, and Tonen Corp. 

The reinforcement of rubbers using nylon, rayon, vinyl, and polyester fibers was reported by various authors [10,58,73-75]. Because of the design flexibility and suitable end-use applications, high-performance fibers such as glass, carbon, and aramid also find extensive applications in short fiber-reinforced mbbers. A brief description of some of the major high-performance fibers commonly used in short fiber-rubber composites is given below ... 

In addition to rayon, pitch, and PAN, many polymeric materials have been used to make carbon fibers. However, only the big three, rayon, pitch, and PAN, have endured the high-performance markets. Their price has dropped over the years, but remains high, accounting for over one-half of the production costs, too high for the GP markets. The literature supports that recycled petrochemical polymers and fibers and renewable cellulosics and lignins, which are inexpensive and widely available, may be potential feedstocks for GP carbon fibers. ... 

Much less ordered than PAN-based high-strength CFs are the isotropic CFs. They are produced by the carbonization of isotropic pitch fibers (or other fibrous precursors such as phenolic resins or cellulose, including rayon), without any attempt to obtain a preferred orientation of the polyaromatic molecules in the fiber direction. Consequently, they have a random nanotexture and belong to the low modulus class of CFs [16]. Rather than being used for high-performance reinforcement purposes, they find their application as thermal insulators for furnaces or as reinforcements for cement [1]. Another important use of isotropic CFs is as a feedstock for the production of activated carbon fibers, a material dealt with in Section 2.4.4. 

Of the fibers listed in Table II only the polyesters, polyamides, spandexes, acetates, and rayon are discussed in this chapter. While the acrylics and modacrylics are the third most important class of commercial fibers because their polymerization chemistry is also discussed in other chapters concerned with vinyl addition emulsion polymerizations, it will only be briefly summarized here. For the same reason polypropylene polymerization chemistry is also not covered in this section. However, two additional topics, carbon fiber formation and polybenzimidazoles have been included on the basis of the current Interest in high-performance fibers for composite materials. 

The majority of commercial carbon fibers are produced from polyacrylonitrile (PAN) fibers. In fact, HTA-12K PAN-based carbon fibers are the most commonly used commercial carbon fiber (15). PAN-based fibers are the strongest commercially available carbon fibers and dominate structural applications. Mesophase pitch-based carbon fibers represent a smaller but significant market niche. These fibers develop exceptional moduli and excel in lattice-based properties, including stiffness and thermal conductivity (1). Rayon-based fibers are used in heat shielding and in missile nosecones (16). Carbon fibers made from high performance pol5oners (17-19) or from chemical vapor deposition of hydrocarbons, such as benzene or methane, display imique properties that make them potentially attractive futime alternatives (20-22). 

The first carbonization of cellulose-based fibers dates back to Thomas Edison, who carbonized a natural cellulose filament for use as an incandescent lamp filament. In the mid-1950s, the Carbon Wool Corporation introduced the first commercial carbonized rayon fibers (79). PAN- and pitch-based carbon fibers have replaced rayon-based fibers in most high performance applications however, they continue to find use as ablative materials in missile nosecones and heat shielding (16). Additionally, the combination of low cost, ease of handling, and high natural porosity makes rayon an attractive precursor for activated carbon fibers (see CELLULOSE Fibers, Regenerated). 

For applications that do not require exceptional mechanical properties, carbon fibers made from high performance aramid polymers show considerable potential. These aramid fibers do not require stabilization prior to carbonization, which substantially simplifies the production process. Rayon-based carbon fibers continue to appear in some composite applications, but have become key substrates for the development of activated carbon fibers. These ACFs develop a microp-orous surface structure that is ideal for adsorption of low levels of volatile organic compounds. 

Rayon High modulus rayon-carbon fiber. U.S.A. [9] Sparked high performance cf industry in U.S.A. 

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