Aramid fibers structure

Kalanta J. and Drzal L.T. (1990a). Structural properties of aramid fibers and their influence on fiber adhesion. In Proc. ICC/-2, Controlled Interphases in Composite Materials (H. Ishida ed.), Elsevier, New York, pp. 685 690. 

The value of the epoxy resins lies in their reactivity with a variety of chemical groups. This enhanced reactivity also means that the surface chemistry of the reinforcement which the epoxies are cured against, can alter the local structure in the interphase regionJl). The most common reinforcement surfaces cured in contact with the epoxies are carbon/graphite fibers, glass fibers, aramid fibers and metal oxides. The surface chemistry of these reinforcement surfaces is quite diverse and in many cases can be the reason for alteration of the interphase epoxy structure as compared to the bulk. 

Figure 4.21 (a) Bonding in an aramid fiber. Strong covalent bonding in the fiber direction and weak hydrogen bonding in the transverse direction, (b) Schematic representation of the supramolecular structure of Kevlar 49 (after Dobbs et al, 1980). 

Both polyethylene and aramid fibers have increasing applications in a variety of armor products. Body armor is a high performance system for protection against rifle bullets. Armor containing these fibers together with a polymeric matrix in the form a composite can provide ballistic protection as well as structural... 

Besides the aliphatic and aliphatic/aromatic nylons, aromatic polyamides have excellent capability to form fibers. Among aromatic polyamides the most common are Kevlar or poly(imino-1,4-phenyleneiminocarbonyl-1,4-phenylenecarbonyl) or poly(phenylene terephthalimide), and Nomex or poly(phenylene isophthalimide). These compounds are included in a group of polyamides known as aramids. The structures of Kevlar and Nomex are shown below ... 

Epoxy resins are by far the most widely used polymer matrices for advanced structural composites and, if carbon, glass, and aramid fiber reinforced epoxies... 

Table 4 compares the mechanical properties of various organic fibers, graphite/carbon fibers, ceramic fibers, and glass fibers, and lists commercially important applications. One major application of organic fibers, such as Spectra and aramid fibers, is in ballistic In contrast, graphite, ceramic fibers, and glass fibers are primarily used in structural applications. One of the reasons that organic fibers find little... 

Srinivasan, G. and Reneker, D.H., 1995. Structure and morphology of small diameter electrospun aramid fibers, Polym. Int., 36, pp. 195-201. 

In practice, a short gauge length. 10 mm for a 2 mm thick specimen of unidirectionally reinforced material, or 25 mm for a 4 mm thick fabric or mat reinforced specimen, is most frequently used. A framework has been developed in order to rationalize the many test methods and the even greater number of loading fixtures jigs. The final failure will frequently be by local microbuckling. or kinking, of bundles of fibers. A similar failure occurs in individual carbon and aramid fibers, which have a fibrillar structure. 

Techniques for production of 3-D structures of high tenacity aramid fiber have also been developed, offering excellent fatigue resistance to abrasion, flexure, and stretching. One such system is on a wire frame basis, with mechanized frame building, and it is proposed as reinforcement for concrete pillars and other structures. As well as the strength of the fiber, this application exploits the high chemical resistance of aramid to acids, alkalis, and cement. 

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