Polyaramide fibers

Due to the low density of the parent polymer, UHMW polyethylene fibers have a strength-to-weight ratio even greater than polyaramide fibers. Most common commercial trade names are Spectra , Dyneema or Tekmilon . 

Polyaramide fibers are well known thermosets (see Polymers) having both a high-strength and stiffness combined with an excellent thermal resistance. They are commercialized under the trade names Kevlar and Nomex (E.l. DuPont de Nemours) and Technora and Twaron (Teijin) respectively. 

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Villar-odil S, Suarez-garcia F, Paredes JI, Martinez-Alonso A, Tascon JMD. Activated carbon materials of uniform porosity form polyaramid fibers. Chem Mater 2005 17 5893-5908. 

Villar-Rodil, S., Suarez-Garda, F., Paredes, J.I., et al. (2005).Activated carbon materials of uniform porosity from polyaramid fibers. Chem. Mater., 17, 5893-908. 

One can think of the PTFE dispersion coating process as impregnation of fibrous or porous materials such as glass fiber, woven glass cloth, and polyaramide fibers and fabrics. The composite product combines the properties of PTFE and substrate. The polytetrafluoroethylene coated or impregnated products are characterized by a number of common attributes, Table 5.9. 

Because of its slightly negative coefficient of thermal expansion in the longitudinal directions, composites made with polyaramid fibers exhibit excellent dimensional stability. One special application area is in high-performance electronic circuit boards requiring low x-y axis thermal expansion. 

Pi om a mesoscopic point of view, when a semicrystalline polymer is submitted to a large deformation, the spherulitic structure is gradually broken down, while increasing moleculai orientation. In a tensile deformation, the spherulitic could be reformed ultimately in a new oriented microstructure the oriented fibrillar texture [190]. Such cold processed polymer fibers may have a Young s modulus, which could nearly reach 150 GPa for polyaramid fibers (Kevlar ). The strong link between microstructme and mechanical properties can be easily predicted. 

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