Kevlar electrical properties

Humidity affects the strength and rigidity while also reducing electrical properties, but it serves as a plasticizer and enhances toughness. The novel types like 6-10, 11 and 12 are definitely more expensive, but they are unique due to lower sensitivity to water as well as improved chemical resistance. The water repellency increases with the length of the methylene groups. There are also several copolymers, some within the family, like 6-6/6 or 6-6/6-10. Other Nylons of limited utility are termed 4, 7, 8 or 9. Novel developments are mainly in the aromatic polyamides like Kevlar... 

Table 2.36 Thermal and Electrical Properties of Kevlar 49 Fabric/Epoxy...

Kevlar Trademark for a group of DuPont aromatic polyimides that are frequently used as fibers in reinforced plastics and composites. Major characteristics are low thermal expansion, light weight, and good electrical properties, coupled with stiffness in laminated form. One special application area is in high-performance circuit boards requiring low x-y axis thermal expansion. 

Fillers. Fillers used in molding compounds are glass fibers, aromatic polyamide fibers (like Kevlar and Arenka), mineral flour (mica, silica, wollastonite, talcum, and calcium carbonate), wood flour, cellulose, and caibon fibers. Fillers reduce shrinkage during cure, give higher compressive strength and stiffness, and improve thermal resistance, electrical properties, and flame retardancy. 

Aerogels are quasi-stable, low-density, three-dimensional assemblies of nanoparticles, which have usually poor mechanical properties. A facile one-pot synthesis of Kevlar-like aerogels based on the reaction of multifunctional isocyanates and carboxylic acids has been reported [57]. The materials exhibit an ultimate compressive strength, a high specific energy absorption, and a thermal conductivity like foamed PS. By a pyrolysis process at 800 °C, the materials can be converted to a porous, electrically conducting carbon with a high surface area. 

A major use of Kevlar is in rigid and soft body armour protective applications. Kevlar fabric is bullet and fragment resistant, lightweight, flexible and comfortable, has excellent thermal properties, is resistant to cuts and chemicals and is flame resistant and self-extinguishing. The uses include bulletproof vests, chainsaw leg protection and military uses for helmets and armoured vehicles, cargo containers, armour shields and cockpit doors. Kevlar and Nomex fabrics are used in the construction of flame-resistant protective clothing used in petroleum and petrochemical operations, by utility workers, NASA astronauts, racing drivers and their crews, the military and any industry where there is a chance of flash fire exposure or electric arc flash or blast. 

Heeger s research group obtained monofilament conductive fibers from a blend of polyaniline and poly(/ -phenyleneterephthalamide) (Kevlar from DuPont) [88]. The monofilament fibers, with different concentrations of polyaniline, were wet-spun from a solution of the component polymers in sulfuric acid, into a 1 N sulfuric acid solution. In the process, a draw ratio of 7 20 and an extrusion speed of 0.12-0.3mmin enabled the continuous production of bobbins. These were sprayed with deionized water to prevent fiber collapse and to remove the excess of sulfuric acid. The bobbins were immersed in HCl to protonate the polyaniline and dried in a vacuum oven. Pure polyaniline fibers were also wet spun by the same method. The Kevlar fibers become brittle with an increase in the concentration of polyaniline. In general, the mechanical properties of the fibers change proportionally to the concentration of polyaniline. Enhancement of the strain at break occurs at the expense of electrical conductivity. The most significant result from this work was the observation that small amounts of polyamide improved markedly the mechanical properties of polyaniline fibers, while retaining its conductivity (10 S cm ). 

The remaining sector of the laminate industry is the so-called industrial laminates. These materials have a diverse range of applications in such fields as electrical/electronics, construction, leisure, aircraft, boats and others. Sometimes paper is used as the fibre component, but usually more exotic materials such as glass fibre, polyester, cotton, carbon fibre and Kevlar are found. Fibre choice is dictated by the very special properties required of the laminate such as (a variety of) electriccil characteristics. 

In the 1970s, a paradigm shift occurred when polymers with more specific properties started to be produced. This included various liquid crystalline polymers leading, for example, to the production of superstrong fibers such as Aramid / Kevlar [12]. The development of functional polymers for the conduction of light and electricity and optical switches also started then [13]. In the near future this will probably lead to highly effective and flexible polymer solar cells [14]. 

---