Aramid producers

Differences in densities can be large, especially when we compare organic fibers (1-1.5 g cm ) with glass fibers (2.5 g cm ) or steel cord (7.8 g cm ). Therefore, aramid producers may argue that their product is five times stronger than steel (in g denier" or N tex ), while steel cord producers can rightfully respond that steel has the same strength (in GPa). 

Composites. The history of phenoHc resin composites goes back to the early development of phenoHc materials, when wood flour, minerals, and colorants were combined with phenoHc resins to produce mol ding compounds. In later appHcations, resin varnishes were developed for kraft paper and textile fabrics to make decorative and industrial laminates. Although phenoHcs have been well characterized in glass-reinforced composites, new developments continue in this area, such as new systems for Hquid-injection molding (LIM) and sheet-molding compounds (SMC). More compHcated composite systems are based on aramid and graphite fibers. 

Introduced in 1972, the whoUy aromatic polyamide, poly i ra-phenylene teraphthalamide), termed aramid, was the subject of extensive evaluation as a tire cord in all types of tires (8,14). As of the late 1990s, however, only specialized appHcations have emerged for aramid tire cord that draw on their high strength-to-weight ratio to produce tires with lower weight (16). 

Standard Test Methods for Tire Yarns, Cords, and Woven Fabrics. ASTM standard D885M-94 includes test methods for characterizing tire cord twist, break strength, elongation at break, modulus, tenacity, work-to-break, toughness, stiffness, growth, and dip pickup for industrial filament yams made from organic base fibers, cords twisted from such yams, and fabrics woven from these cords that are produced specifically for use in the manufacture of pneumatic tires. These test methods apply to nylon, polyester, rayon, and aramid yams, tire cords, and woven fabrics. 

Adhesion. Commercially available 1- or 2-coat adhesive systems produce mbber failure in bonds between ethylene—acryflc elastomer and metal (14). Adhesion to nylon, polyester, or aramid fiber cord or fabric is greatest when the cord or fabric have been treated with carboxylated nitrile mbber latex. 

Epoxide resins reinforced with carbon and Aramid fibres have been used in small boats, where it is claimed that products of equal stiffness and more useable space may be produced with a 40% saving in weight over traditional polyester/ glass fibre composites. Aramid fibre-reinforced epoxide resins have been developed in the United States to replace steel helmets for military purposes. Printed circuit board bases also provide a substantial outlet for epoxide resins. One recent survey indicates that over one-quarter of epoxide resin production in Western Europe is used for this application. The laminates also find some use in chermical engineering plant and in tooling. 

Compare the energy absorption capabilities of composites produced using carbon fibres, aramid fibres and glass fibres. Comment on the meaning of the answer. The data in Fig. 3.2 may be used. 

Aramides, aromatic polyesters, polypenzazoles 25,000 20 500 Electronic connectors and precision thermosplast parts some producers buy advanced intermediates... 

Kevlar Fibers. Table IX shows results obtained with Kevlar 950 fibers. The crystallinity of this aromatic polyamide is only slightly higher than that for the aliphatic polyamide samples that we studied (Table VI). But in Kevlar, as for PET fibers, the disorder parameter k is smaller than in PA 66 fibers. Thermal treatment at 220°C for 1 hour in slack conditions does not substantially increase the average crystallinity of the Kevlar 950 fibers and produces more distortions. Consequently, we conclude that the behavior of this Aramid fiber during our annealing treatment is similar to PA 66 as far as crystallinity is concerned. Kevlar 950 is also similar to PET fiber with regard to the behavior of the disorder parameter. 

It is produced from a liquid solution in a process similar to that by which viscose rayon is made. The final product consists of long fibers with the lowest density of all commonly used reinforcements. Aramid s rigidity and strength are intermediate between those of glass and carhon. 

Wool and Visil fiber are blended to improve latter s fiber properties, but the flammability of the blend is also reduced. Cotton-wool blends are quite common as well. Aramids are blended with many fibers for different applications. Nomex can be blended with FR viscose and FR wool to produce fire-blocking fabric, e.g., for aircraft seats.4 Nomex blended with Kevlar shows better performance than 100% Nomex in fire fighters outer protective garments.26 Various blends of glass fibers with aramids, melamine fibers, PVC fibers, and polyester have been reported for use in fire-protective nonwoven veils for upholstery and mattresses.92... 

---