P-Aramid fiber

E. Dommershuijzen, "Super Single Truck Tyre Carcasses A Challenge For P-Aramid Fibers," Conference Proceedings ACS, Rubber Division, Odando, Fla., Paper 53, Oct. 1993, p. 7.012. 

A small amount of p-aramid fiber (Armos and Rusar) is produced in Russia. Both are copolymers based on diaminophenylbenzimidazole—a unique but expensive monomer. 

The almost perfect orientation of p-aramid fibers is reflected in the anisotropic behavior of its thermal expansion coefficient. The linear expansion coefficient for these materials is negative (Table 13.2). Because the volumetric thermal expansion coefficient is not affected by orientation, the radial coefficient must increase as fiber orientation increases. The negative expansion coefficient of these materials has opened a whole field of applications in electronics (see section 13.8.4.2). 

Kwolek [106] demonstrated in her early work at DuPont that p-aramid fibers could be spun from amide and salt solutions using a conventional wet-spinning process. These solutions were typically of low concentration. The resulting fibers had low strength but high modulus after heat treatment. In later development,p-aramid fibers were spun from more concentrated solutions using dry-jet wet-spinning processes [107]. These solutions contained aramid polymer above a critical solids concentration and were anisotropic. 

As m-aramid fibers are best known for their flame resistance, p-aramid fibers are universally recognized as the material of choice for ballistic protection. While p-aramids do play a critical role in this application we will attempt to show that their unusual properties are also suitable for a wide variety of other end-uses. 

Zylon (PBO fiber) represents the next generation of fibers with strength and moduli nearly twice as high as those of p-aramide fibers... 

The dissolution point of Zylon is 100 °C higher than that of p-aramide fibers. 

Aramid fiber has a highly ordered fibrillar stmcture with a propensity for fibrillation attributable to the lack of lateral forces between macromolecules. As the /7-aramid content of a fabric increases above 5%, the extent of fibrillation of the p-aramid fibers increases and the actual fibrillations can become more noticeable and objectionable. With the wear, abrasion and laundering that occurs as the fabric article is used over time, fabrics lose their esthetic appeal. 

Aramid products have now been commercially available for nearly 40 years. Table 2 provides a summary of current (as of 1999) capacities to produce these products, with total worldwide capacities of 19,000 t of m-aramid fiber, 43,000 t of p-aramid fiber, and 6001 ofp-aramid film. Table 8 shows total world consumption of Aramid fibers between 1979 and 1998 (33), indicating sales near 90% of capacity for m-aramid and near 60% for p-aramid. Sales of both types have been increasing at a rate of over 4.5%/year for the past 10 years. 

The basic development and the first commercial introduction of aramid materials were done by DuPont, which continues to be the largest producer. MPDI fiber products (staple, continuous filament, yarn, and floe) under the trademark Nomex are produced by DuPont in the United States and Spain. The only other major MPDI producer is Teijin, with its fiber product Teijinconex produced in Japan. The situation is very similar with the PPTA manufacturers. The first and largest manufacturer, DuPont, produces essentially all product forms except films. DuPont s PPTA fibers are known under the trademark Kevlar , p-Aramid fiber is also produced in Ireland and Japan. The other producer of PPTA is Teijin Co., which produces two basic fibers Twaron based on PPTA, and Technora based on the ODA-PPTA copolymer. A small amount of p-aramid fibers (Armos and Rusar ) are produced in Russia, both being based on SVM copolymer [6]. 

Hydrophylicity of amide linkage leads to moisture absorption by all aramids. The skin-core structure of the p-aramid fibers plays an important role in the moisture absorption, which is critical for many structural applications of the FRP on their basis. Thus, Fhkuda and Kawai found that the ultrahigh modulus Kevlar 149 has a moisture uptake of 1% (20°C, 55% relative humidity), while in the regular brand Kevlar 29 it is -7% under the same conditions [34], Apparently, above a certain concentration, the water molecules could upset the intermolecular hydrogen bond formation (Figure 8.2) and affect the mechanical properties, as seen by the comparison of the mechanical properties of Kevlar 29 and Kevlar 149. The same authors found that the diffusion coefficient through the skincore structure of the Kevlar fiber is also of importance in the skin the trend is Kevlar 149 > Kevlar 29 > Kevlar 49 and in the core it is reversed Kevlar 29 > Kevlar 49 > Kevlar 149. 

It is worth noting that the better performance of the Armos and Rusar fibers comes at very elevated price related with the high monomer costs, lower productivity spinning process and large energy consumption. These products apparently still do not meet the Western standards as far as quality and uniformity are concerned [45] but nevertheless could be a basis for future p-aramid fiber improvements. 

Properties of p-aramid fiber reinforced polymer composites... 

The FRPs for demanding structural applications comprising continuous p-aramid fiber reinforcements are most frequently based on epoxy matrices [54-56]. The main reasons... 

Hahn C (2000) Characteristics of p-aramid fibers in friction and sealing materials, J Ind Text... 

Tsimpris C W, Wartalski J and Ferradino A G (2001) Compounding with p-aramid fiber elastomers. Rubber World 224 35. 

Slugin I V, Sklyarova G B, Kashirin A I and Tkacheva I V (2006) Rusar p-aramid fibers for composites materials with construction application, Fiber Chemistry 38 25-26. 

Perepelkin K E, Andreeva I V, Pakshver E A and Morgoeva 1 Yu (2003) Thermal characteristics of p-aramid fibers, Fiber Chemistry 35 265-269. 

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