Aramids solutions

Picken SJ (1990) Orientational order in aramid solutions. PhD thesis, University of Utrecht... 

Picken SJ, "Orientational Order in Aramid Solutions", PhD Thesis, Utrecht, 1990 Rodriguez F, Polym Lett 10 (1972) 455. 

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. 

In air gap spinning, aramid solution is forced through a spinneret whose face is in contact only with a gas, usually air. After traveling a short distance through the air, the solution enters a coagulant in the form of a fine jet. 

The structure of the sohd state of nematic aramid solutions will be discussed in Sect. 3.4. 

Table 1. Results of a least squares fit of the clearing temperature (T j) versus concentration (c) measurements, to relation (8) for various aromatic aramid solutions. The standard deviations of A and a are shown in parentheses...

Fig. 3. Schematic structure of a single domain in an aramid solution. Each domain contains several blobs of dimension L,. The director n is the average orientation of the molecules inside the domain...

Fibrids are film-like particles that are formed when aramid solutions are precipitated in a non-solvent under high shear [20,21]. The dimensions of as-formed fibrids are aronnd 100 mm X 700 mm x 0.01 mm. Fibrids have a high surface area, around 200-300 m /g, and can function as a thixotrope or a reinforcing agent in composite, sealing, coating, and elastomer applications [22,23], and also in aramid papers. 

Picken S J, Aerts J, Visser R and Northolt M G (1990) Structure and rheology of aramid solutions X-ray scattering measurements. Macromolecules 23 3849-3854. 

While aliphatic-containing polyamides are given the name nylons, those in which at least 85% of the amide groups are attached to an aromatic are called aramids. Aramids are stronger and tougher than nylons but they are also more difficult to solubilize and fabricate. Because the presence of the aromatic groups causes the aramids to be stiff, they often form liquid crystals (LCs) that are present in a nematic EC state in concentrated solution. 

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