Para-aramid

The photodegradation of para-aramid in an 0 atmosphere allows the differentiation between the accelerated experimental photooxidative conditions from its usual daylight exposure effects. This study illustrated an estimation of the rates of photooxidation of a commercial para-aramid product (i.e., DuPont s Kevlar-29 woven fabric) based on the oxygen-18-labelled carbon dioxide ( CC and CC ) decarboxylated from the sample. The oxygen-18-labelled atoms, which are inserted in the macromolecules, were analyzed for the photodegradation processes. This technique also allows the radial l O-distribution measurement from the fiber surface toward the fiber center. 

Silica, Some Silicates, Coal Dust and para-Aramid Fibrils... 

The rigid rod chains in para-aramids tend to form so-called liquid crystals when they are dissolved in polar solvents or heated to certain temperatures. The polymers showing liquid crystalline behavior in melts are called the thermotropic liquid crystalline polymers, and those showing similar properties in solution are called the lyotropic liquid crystalline polymers. These liquid crystals exist in three distinct phases according to their specific structures (Fig. 12.25). 

Poly(p-phenylene terephthalamide) PPD-T, also called para-aramid, can be polymerized to a fiber-forming molecular weight by polycondensation of terephthaloyl chloride and 1,4-phenylene diamine. 

Searl A. 1997. A comparative study of the clearance of respirable para-aramid, chrysotile and glass fibres from rat lungs. Ann Occup Hyg 41 217-233. 

Warheit DB, Snajdr SI, Hartsky MA, et al. 1997. Lung proliferative and clearance responses to inhaled para-aramid REP in exposed hamsters and rats Comparisons with chrysotile asbestos fibers. Environ Health Perspect Suppl 105 1219-1222. 

Kevlar (Du Pont) and Twaron (Enka/Akzo) are trade names for the all para aramid, poly(p-phenylene terephthalamide), produced by these companies (Eq. 21.18). 

Continuous glass filament Rock (stone) wool Slag wool Para-Aramid Wollanstonite Sepiolite... 

The first verification of the theoretical predictions of Onsager and of Flory that rod-like molecular chains might exhibit liquid-crystalline properties (see section 1.3.2 and chapter 12) was obtained in the 1960s and fibres from para-aramid polymers were commercialised under the name of Kevlar in 1970. These materials are very stiff and have excellent thermal stability many other materials of this class of rigid main-chain liquid-crystal polymers have been developed. They cannot, however, be processed by the more conventional processing techniques and this led to the development in the 1980s of another group of liquid-crystal polymers, the thermoplastic co-polyesters. 

P. D. Yarborough and H. M. Ghorashi. Process for restoring the natural appearance of para-aramid clothing. US Patent 6 669 741, assigned to E. I. du Pont de Nemours and Company (Wilmington, DE), December 30,2003. 

I. V. Slugin, G. B. Sklyarova, A. I. Kashirin, and L. V. Tkacheva. Rusar para-aramid fibers for composite materials for constraction applications. Fibre Chemistry, 38 25-26, 2006. 

D. B. Warheit. A review of inhalation toxicology studies with para-aramid fibrils. Am. Occupat. Hyg., 39(5) 691-697, October 1995. 

D. B. Warheit, K. L. Reed, J. D. Stonehuemer, A. J. Ohio, and T. R. Webb. Biodegradability of para-aramid respirable-sized fiber-shaped particulates (RFP) in human lung cells. Toxicol. Sci., 89 296-303, 2006. 

A significant development is a technique for pulping or fibrillation that greatly increases the surface area of short-length fibers of para-aramid, and renders them suitable for reinforcement of plastics and elastomers. A typical staple fiber will have a surface area of about 0.1 m /g, but the compounding process increases this to 7-9 mVg, so increasing the area available for adhesion to the matrix plastic. The bond achieved will... 

Aramid para-aramid, 2.8 Pa strength, 70 GPa modulus chopped staple or fibrid (pulp) 10-150 g/m2 Tensile strength up to 8 N/mm Density 80 kg/mm Improved impact resistance Smooth finish Good wear resistance Can be blended with conductive fiber Superior temperature resistance Aerospace adhesive carriers Automotive improved stone impact resistance Defence radar cross section Recreation skis, snow and surf boards, surf boards, canoes Industrial substrate for friction products wear resistance for high-speed rolls Electrical printed circuit boards... 

L G P Dalmolen, J Willing, A Goksoyr and P Osen, Para-aramid fibre-reinforced composite bellmouths for a floating production platform . Conference on Structural Materials in Marine Environments, London, loM/MTD/IMechE/ IMarE, 11-12 May 1994, pp 109-118. 

In para-aramids, the links are formed on the opposite comers of the rings. Para-aramids do not melt, bnt decompose above 430 °C. They absorb a small amount of water due to their low moisture regain. Kevlar, in particular, starts to decompose only above 550 °C. ... 

Staple fibre Kevlar yams with two different linear densities were sourced from Aramex-Game, Germany, and one of the yams was doubled locally without any twist, coded as K2. This is mainly to increase the linear density of the yam to enable the use of thicker yam. Tilsa is a para-aramid yam from Tilsatec, with a similar linear density to that of the Kevlar yams from Aramex-Game. Several dope-dyed para-aramid yams were sourced from Tilsatec in various linear densities. 

Since para-aramid yam is the most widely used yam in cut resistance fabrics, ring spun staple fibre aramid yams were chosen to be used in one face of the weft-knitted fabric. A composite yam had to be used for the other face of the fabric. It is imperative that the most suitable yams for each face of the fabric are chosen. 

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