Aramid Films

Aromatic PA films are produced by casting a polymer solution in sulfuric acid onto an endless belt. In addition, the solution contains nucroparticles of silica to improve the surface properties. The casting solution is guided after intermediate heating into a coagulation bath and the film is released from the belt and post treated. 

It is possible to condense the aramide directly in an NMP solution and cast the solution. This process directly produces a transparent film from an aromatic polyamide dope without requiring the step of dissolving the aromatic polyamide in concentrated sulfuric acid. The process does not require any acid resistant equipment and is inexpensive.  

A procedure for the production of a film has been reported as follows  

In NMP, 0,85 mol 2-chloro-p-phenylenediamine, and 0.15 mol 4,4 -di-aminodiphenyl ether are dissolved. 0.985 mol 2-chloroterephthaloyl chloride is added. After 2 hours, the polymerization is complete. The mixture is then neutralized with lithium hydroxide. The polymer solution is filtered and cast onto an endless belt. The solvent is evaporated at 160°C. A 

Properties of an aramid fiber are shown in Table 13.2. Extensive tables of chemical stability are given in the literature. Nomex can be chlorinated without any significant decomposition, however, Kevlar decomposes under the same conditions of chlorination. Experiments with model compounds revealed that the p-diaminophenylene moiety is oxidized to a quin-one intermediate when treated with h)q)ochlorous acid, that is not stable. In contrast, with Nomex such a reaction mechanism is not possible.  

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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. 

There are two examples of commercial p-aramid films. Toray produces a terpolymer film under the trade name Mictron, while Asahi introduced a PPTA homopolymer film called... 

Aramid films have been in development since the late 1990s by several Japanese companies including Toray, Teijin, and Asahi. As with fibers, aramid solutions can be extruded through flat dies to form films. The conventional wet process can be employed to produce unidirectional and bi-oriented films from isotropic aramid solutions. Production of films from anisotropic solutions requires unique processes as shown by the example of PPTA film. 

Film Prop6rti6S. The two commercial aramid films are both based on PPTA. Aramica is a homopolymer, while Mictron is most likely a copolymer or a terpolymer. They provide excellent strength and stiffness, along with high temperature stability. Table 7 lists some of the key properties of these materials. 

Aramid products have now been commercially available for nearly 40 years. Table 2 provides a summary of current (as of 1999) capacities to produce these products, with total worldwide capacities of 19,000 t of m-aramid fiber, 43,000 t of p-aramid fiber, and 6001 ofp-aramid film. Table 8 shows total world consumption of Aramid fibers between 1979 and 1998 (33), indicating sales near 90% of capacity for m-aramid and near 60% for p-aramid. Sales of both types have been increasing at a rate of over 4.5%/year for the past 10 years. 

Sato, S., Arisaka, Y., Matsumura, S., (1999). Surface design of Aramid film for future ME tapes, IEEE Trans. Magn., Vol. 35, No. 5, pp.2760-2762, ISSN 0018-9464 Seki, A. Kondo, H., (1991). FTIR Reflection Absorption Spevtra of Novel Lubricant Layer on the Magnetic Thin Film Media, /. Magn. Soc. Jpn, Vol. 15, No. SuupL, S2. p>p.745-749... 

Thianthrene and thioether-containing aromatic dicarboxylic acids were readily synthesized by nucleophilic aromatic substitution. Polyamides obtained from the dacids splayed good thermal stabilities and solubilities enhanced over typical aramids. Films displayed good toughness and flexibility, consistent with high molecular weight and low crystallinity. 

Cast PTFE films can be laminated with different substrates, most frequently with PTFE-coated glass and aramid fabrics. They also can be metallized, in particular with aluminum for use in electronics. Other applications include as release films for the manufacture of composite materials for aerospace vehicles, in electronics and electrical industries, as selective membranes, and in the chemical industry. 

In plastic films, Toray is a major world producer of BOPP film sold under the Torayfan trade name. In addition Toray offers Lumirror (polyester) film, Torelina (PPS) and Mictron (aramid). 

Research and development in fluid jet technology led to its widespread use in film and web processing, mixers, reactors, and fiber processing. Applications to fibers alone includes Taslan bulked yams, jet piddlers, draw-jets, interlaced yams, bulk-crimped carpet fibers (BCF), and spunbonded products such as Reemay polyester, Typar polypropylene (PP), and Tyvek olefins. New fibers also were introduced Nomex aramid, especially suited for high-temperature applications Lycra spandex, an elastic textile yam Qiana nylon, with a silklike appearance and Kevlar aramid, used in products ranging from tires to bullet-resistant vests. 

The reinforcing fabrics used were aramid (Kevlar DuPont) and poly(p-pheny-lene-2,6-benzobisoxazole) (PBO) (Zylon Toyobo). The fabrics were first treated with a 1.5% solution of HB PAMAM (AD-102), dried, then interleaved with an epoxy film structural adhesive (epoxy stage B on polyester net), and compression-molded for 90 min at 120 °C. For the aramid-based composite, FM-73 (Cy-tec) was used as the matrix. For the PBO-based composite, AF-191 (3M) was used as the matrix. The laminates were cut into strips and tested for interlaminar shear strength (ASTM D-2344) using a three-point bending instrament. 

Aramid polymers are much more expensive than the aliphatic polyamides. The use of aramid polymers is limited to those applications that justify the high cost. The present U.S. market is about 20 million pounds per year. The applications are those where one needs very high flame resistance (clothing for firefighters and welders, welder s protective shield, upholstery and drapes), heat resistance (ironing board covers, insulation film for electrical motors and transformers, aerospace and military), dimensional stability (fire hose, V- and conveyor belts), or strength and modulus (circuit boards, bulletproof vests, fiber optic and power lines, ship mooring ropes, automobile tire cord, puncture-resistant bicycle tires). 

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