P-Aramids

E. Dommershuij2en, "Super Single TmckTyre Carcasses A Challenge Eor P-Aramid Eibers," Conference Proceedings ACS, Rubber Division, Orlando, Fla., Paper 53, Oct. 1993, p. 7.012. 

Antimony trioxide production p-Aramid respirable fibres (1) (s) - -... 

Aramid honeycombs find use in the fields of aerospace, transport equipment, etc. Aramid honeycomb sheets comprising a nylon-type resin, particularly a p-aramid honeycomb resin, have flame retardant, tough and other excellent properties required for a honeycomb core structure. However, the method of fabrication of aramid honeycombs is a rather complicated process. The process is described in detail in the literature. ... 

A p-aramid polymer supporting a catalyst agent has been presented for several reactions. The composition exhibits an improved catalytic activity in comparison to m-aramid polymer catalyst support. The actual catalyst agent is adhered on or within the support. 

Inhalation toxicology studies with fihrils made from p-aramid have been documented. Responses were detected, but the interpretation of these studies were regarded as controversial. There is some evidence for the biodegradabihty of p-aramid respirable-sized fiber-shaped particulates, which concept was supported in subsequent studies. Actually, material safety data sheets report the possibihty of lung injury, if fiber dust is inhaled for a prolonged time. On the other hand, aramids are not considered to be dangerous by skin contact or by ingestion. 

H. Werlich, W. ZwUling, and U. Wecker. Process for preparing p-aramide paper, p-aramide pulp, and the use of the paper and the pulp. EP Patent 1277 880, assigned to Teijin Twaron Gmbh (DE), January 22, 2003. 

D. B. Warheit, K. L. Reed, K. E. Pinkerton, and T. R. Webb. Biodegradability of inhaled p-aramid respirable fiber-shaped particulates (RFP) Mechanisms of RFP shortening and evidence of reversibility of pulmonary lesions. Toxicol. Lett., 127(l-3) 259-267, Febmary 2002. 

Various nonwoven structures have been developed as well. The least important among sheet structures are films. There are two film products (see Section 13.3) based onp-aramids and none on m-aramids. The significant cost differential is the most likely reason for this situation. On the other hand a very large market has been developed for papers based on both p-aramids and m-aramids. In general, these papers are based on short fibers (floe) and a binder (fibrids), but other components have been explored as well. A very small market exists for particles other than fibrids and pulps. 

The situation is very similar on the para side of chemistry. The first and the largest producer—DuPont—has three facilities throughout the world. The largest one in the United States produces essentially all product forms except films. Fiber is also produced in Ireland and Japan. The other producer of p-aramids is Teijin Co., which produces two basic fibers Twaron based on PPTA and Technora based on a copolymer. Twaron is produced in the Netherlands while Technora is manufactured in Japan. 

A small amount of p-aramid fiber (Armos and Rusar) is produced in Russia. Both are copolymers based on diaminophenylbenzimidazole—a unique but expensive monomer. 

There are two producers of p-aramid film. The first one was Toray with its Mictron film based on a copolymer and Asahi with a product (Aramica ) based on PPTA homopolymer. 

The almost perfect orientation of p-aramid fibers is reflected in the anisotropic behavior of its thermal expansion coefficient. The linear expansion coefficient for these materials is negative (Table 13.2). Because the volumetric thermal expansion coefficient is not affected by orientation, the radial coefficient must increase as fiber orientation increases. The negative expansion coefficient of these materials has opened a whole field of applications in electronics (see section 13.8.4.2). 

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