Kevlar

I want to introduct something about Low Frequency Data Transmission Cable. Features: 1) Operating temperature: -5 ~ 70°C 2) Operating voltage: 250V 3) Testing voltage: 1,200V 4) Operating capacitance: ≤120nF/km (800Hz) 5) Operating inductance: 0.7mH/km 6) Characteristic impedance: 85 ohms 7) Insulation resistance: ≥100M ohms x km (after inundation) 8) Bending radius: 15 times of the cable's outer diameter 9) Fire-retardant performance: IEC 60332-1 10) RoHS instruction: accord with RoHS instruction 2002/95/EC 11) Testing standards for insulation and sheath mechanical performance: IEC 60811 12) Cable construction: a) Conductor: bare Cu wire, multi-wires stranded into bundles, accord with class 5 of IEC 60228 b) Insulation: environmental-protective 70°C half hard PVC insulation material, with colored cores c) Cores: cabling after twisting, with mylar coiling around d) Screening layer: tinned Cu wire braiding into screening layer, coverage rate ≥8
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Kevlar's molecular structure; BOLD: monomer unit; DASHED: hydrogen bonds.
Kevlar is the registered trademark for a light, strong para-aramid synthetic fiber, related to other aramids such as Nomex and Technora.
Developed at DuPont in 1965 by Stephanie Kwolek it was first commercially used in the early 1970s as a replacement for steel in racing tires. Typically it is spun into ropes or fabric sheets that can be used as such or as an ingredient in composite material components.
Currently, Kevlar has many applications, ranging from bicycle tires and racing sails to body armor because of its high strength-to-weight ratioamously: "...5 times stronger than steel on an equal weight basis..."
A similar fiber called Twaron with roughly the same chemical structure was introduced by Akzo in 1978, and now manufactured by Teijin.
Contents
1 Properties
2 Production
3 Chemical properties
4 Thermal properties
5 Applications
5.1 Armor
5.2 Rope and cable
5.3 Sports equipment
5.4 Audio equipment
5.5 Electricity generation
5.6 Drumheads
5.7 Woodwind reeds
5.8 Fiber Optic Cable
5.9 Building construction
5.10 Brakes
5.11 Expansion joints and hoses
6 Composite materials
7 See also
8 References
9 External links
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Properties
When Kevlar is spun, the resulting fiber has great tensile strength (ca. 3 620 MPa), and a relative density of 1.44. When used as a woven material, it is suitable for mooring lines and other underwater applications.
There are three grades of Kevlar: (i) Kevlar, (ii) Kevlar 29, and (iii) Kevlar 49. Typically, Kevlar is used as reinforcement in tires and rubber mechanical goods. Kevlar 29's industrial applications are as cables, in asbestos replacement, brake linings, and body armor. Kevlar 49 has the greatest tensile strength of all the aramids, and is used in plastic reinforcement for boat hulls, airplanes, and bicycles. The ultraviolet light component of sunlight degrades and decomposes Kevlar, a problem known as UV degradation, and so it is rarely used outdoors without protection against sunlight.
Production
Kevlar is synthesised in solution from the monomers 1,4-phenylene-diamine (para-phenylenediamine) and terephthaloyl chloride in a condensation reaction yielding hydrochloric acid as a byproduct. The result has liquid-crystalline behaviour, and mechanical drawing orients the polymer chains in the fiber's direction. Hexamethylphosphoramide (HMPA) was the polymerization solvent first used, but toxicology tests demonstrated it provoked tumors in the noses of rats, so DuPont replaced it by a N-methyl-pyrrolidone and calcium chloride as the solvent. As this process was patented by Akzo (see above) in the production of Twaron, a patent war ensued.
Kevlar (poly paraphenylene terephthalamide) production is expensive because of the difficulties arising from using concentrated sulfuric acid, needed to keep the water-insoluble polymer in solution during its synthesis and spinning.
Chemical properties
Fibers of Kevlar consist of long molecular chains produced from PPTA (poly-paraphenylene terephthalamide). There are many inter-chain bonds making the material extremely strong. Kevlar derives part of its high strength from inter-molecular hydrogen bonds formed between the carbonyl groups and protons on neighboring polymer chains and the partial pi stacking of the benzenoid aromatic stacking interactions between stacked strands. These interactions have a greater influence on Kevlar than the van der Waals interactions and chain length that typically influence the properties of other synthetic polymers and fibers such as Dyneema. The presence of salts and certain other impurities, especially calcium, could interfere with the strand interactions and caution is used to avoid inclusion in its production. Kevlar's structure consists of relatively rigid molecules which tend to form mostly planar sheet-like structures rather like silk protein.
Thermal properties
For a polymer, Kevlar has very good resistance to high temperatures, and maintains its strength and resilience down to cryogenic temperatures (-196); indeed, it is slightly stronger at low temperatures.
At higher temperatures the tensile strength is immediately reduced by about 10-20%, and after some hours the strength progressively reduces further. For example at 160 about 10% reduction in strength occurs after 500 hours. At 260 50% strength reduction occurs after 70 hours.Kevlar
At 450 Kevlar sublimates.
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