Kevlar Applications

Technical Bulletin, Kevlar Applications, Sealants and Adhesive Group, DuPont Company, Wilmington, DE, 2001. 

Kevlar fibers are very strong which makes Kevlar a popular choice m applications where the ratio of strength to weight is important For example a cable made from Kevlar weighs only one fifth as much as a steel one but is just as strong Kevlar is also used to make lightweight bulletproof vests... 

Applications. The polyamides have important appHcations. The very high degree of polymer orientation that is achieved when Hquid crystalline solutions are extmded imparts exceptionally high strengths and moduli to polyamide fibers and films. Du Pont markets such polymers, eg, Kevlar, and Monsanto has a similar product, eg, X-500, which consists of polyamide and hydra2ide-type polymers (31) (see High performance fibers Polyamides, fibers). 

Composites. High molecular weight PPS can be combiaed with long (0.6 cm to continuous) fiber to produce advanced composite materials (131). Such materials having PPS as the polymer matrix have been developed by usiag a variety of reinforcements, including glass, carbon, and Kevlar fibers as mat, fabric, and unidirectional reinforcements. Thermoplastic composites based on PPS have found application ia the aircraft, aerospace, automotive, appliance, and recreation markets (see Composite materials, polymer-matrix). 

Fiber-reinforced plastics have been widely accepted as materials for structural and nonstructural applications in recent years. The main reasons for interest in FRPs for structural applications are their high specific modulus and strength of the reinforcing fibers. Glass, carbon, Kevlar, and boron fibers are commonly used for reinforcement. However, these are very expensive and, therefore, their use is limited to aerospace applications. 

V-belts are the most commonly used belt in industrial power transmission applications. In addition to V-belts, there are round belts (e.g., O-rings) and flat belts, which are often reinforced with steel or Kevlar. Round belts are generally used in light-duty applications while reinforced flat belts are used in high-temperature applications such as automobiles. 

Scientists and engineers at the University of Exeter are investigating whether natural fibers tike hemp and sisal could be used to make sustainable and eco-friendly brake pads [39]. The technology of brake pads turned green with the replacement of asbestos by aramids (hke Kevlar of DuPont) in the 1980s. Kevlar is very expensive and eco-friendly alternatives like hemp, jute, sisal, nettle, and flax are much, much cheaper. A breakthrough in this application will revolutionize brake manufacture and protect the environment. 

The number of such examples, however, is not high. In many other examples of advanced-performance materials, such as DuPont s Kevlar and Allied Signal s SPECTRA, the volume applications associated with system-for-system substitution has not yet occurred at a level necessary to pay back the development and commercialization costs already expended. High-performance ceramics is another area in which the early promise has yet to materialize. The consequences of Eckstut s life-cycle dynamics have been overcapacity and severe rationalization in high-performance carbon fiber businesses, some specialty alloy activities, and high-performance polymer composites. Thus, with critical technologies that involve advanced-performance materials, we need to better understand how to exploit their value in a commercially viable way. 

Polymers containing no secondary or tertiary C-H or are aromatic (PEEK or Kevlar ) or perfluorpolymers (PTFE) are generally resistant to oxidation and require no anti-oxidant additives. However, the high temperature necessary for curing or fabrication of high performance polymers (especially for aerospace applications) can cause oxidation. For this reason, these materials are often prepared and fabricated under a nitrogen atmosphere. 

Fig. 3.24 Applicable flow-through cells forthe CEM Voyager 5 mL Kevlar-reinforced Teflon coil (left),10 mLglasscoil (center), active flow cell (right).

Modern life and civilization opened the way to other important practical applications of heterocycles, for example dyestuffs, copolymers, solvents, photographic sensitizers and developers, and in the rubber industry antioxidants and vulcanization accelerators. Some of the sturdiest polymers, such as Kevlar, have aromatic rings. Melamines (2,4,6-triamino-substituted s-triazines) are monomers with numerous applications as both homopolymers and copolymers. Scheme 9 shows a few examples of compounds with various applications in our daily life, having in common the same building block, the aromatic s-triazine. 

When she first synthesized KEVLAR , Stephanie Kwolek did not know that it would eventually be used in bulletproof vests or protective gloves. She did, however, understand the theories behind the properties that make it suitable for such applications—the theories of intermolecular and intramolecular forces. This is not always the case. Often scientists discover a material that has useful or interesting properties, but are unable to explain them. 

Many advanced materials, such as KEVLAR , have applications that depend on their chemical inertness. What hazards do such materials pose for the environment In your opinion, do the benefits of using these materials outweigh the long-term risks associated with their use Give reasons to justify your answer. 

The most widespread and widely known are Kevlar and Twaron. AF are used especially in high- and medium-performance applications they are also used with other fibres to create a hybrid reinforcement. 

Suzuki cross-coupling has found applications in the preparation of specialty polymers, too. Rigid rod polymers may have very useful properties (the well-known Kevlar, poly(p-phenyleneterephtalamide) belongs to this family, too) but they are typically difficult to synthetize, characterize and process. Such materials with good solubility in organic solvents [38] or in water [39] were obtained in the reactions of bifunctional starting compounds under conventional Suzuki conditions with [Pd(PPh3)4] and [Pd(TPPMS)3] catalysts, respectively (Scheme 6.15). 

Observations for cured epoxy resins and resins derived from 1,2-polybutadlene crosslinked with t-butylstyrene are reported. These resins find applications in aerospace industry, including high performance, Kevlar 49, filament wound, pressure vessels on Skylab and the Space Shuttle. 

Duvis, T., Papaspyrides, C.D. and Skourlis, T. (1993). Polyamide coating on carbon fibers and potential application in carbon/Kevlar/epoxy hybrid composites. Composites Sci. Technol. 48, 127-133. 

Working with a solution is needed for polymers which above their melting point would degrade (example aromatic polyamide fibres such as Kevlar and Twaron). For fibres the removal of the solvent is not too problematic. In e.g. injection moulding applications solvents caimot be used here thermotropic LCP s have to be used. Since these would degrade during processing, they are diluted by copolymerisation (example poly-hydroxy-benzoic acid - co - PETP)... 

Perhaps the most widely utilized (and studied) lyotropic LCP is poly j -phenylene terephthalamide (PPTA), more commonly known as Kevlar (see Figure 1.70). Kevlar belongs to the class of aramids that are well known for their LCP properties. Because these polymers are crystalline in solution, they are often spun into filaments, from which the solvent is subsequently removed in order to retain the aligned polymer structure. The result is a highly oriented, strong filament that can be used for a wide variety of structural applications. Most thermotropic LCPs are polyesters or copolymers that can be melted and molded into strong, durable objects. 

The chemical composition of the composite constituents and the interphase is not limited to any particular material class. There are metal-matrix, ceramic-matrix, and polymer-matrix composites, all of which find industrially relevant applications. Similarly, reinforcements in important commercial composites are made of such materials as steel. E-glass, and Kevlar . Many times a bonding agent is added to the fibers prior to compounding to create an interphase of a specified chemistry. We will describe specific component chemistries in subsequent sections. 

Other Reinforcement Materials. Other materials that have been used in tire compounds for reinforcement are chopped wire (brass-coated), cotton and nylon flock, chopped nylon strands, polyethylene, zinc oxide, and chopped Kevlar. Most of these materials have very limited application and some are obsolete. Others are used more extensively in solid mbber industrial tires than in pneumatics. 

The most spectacular application example to date is perhaps the Aberfeldy footbridge over the river Tay in Scotland (see Fig. 11.4). This bridge is 113-m long, has a deck width of 2.2 m, and a main span of 113 m [4]. The entire deck structure, hand rails, and A-frame towers are pultruded composites, and the cable stays are Kevlar ropes. The deck structure is assembled from a modular system of pultruded 6-m long, hollow components, which consist of 70 percent by weight of E glass and 30 percent pigmented isophtalic polyester resin. 

Commercial applications have been identified primarily in the electronics industry where requirements for dimensional stability, mechanical properties, and high temperature resistance make these systems attractive in advanced circuit board technology. Other commercial applications include high temperature membranes and filters where these materials offer performance improvements over glass, Kevlar, and graphite composites. Industrial development of these types of materials will most likely be dependent on monomer cost and advances in various product properties requirements. 

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