Aromatic adjacent hydrogen reflectance

Figure 5. Spectral area for aromatic 1 adjacent hydrogen at 884 crrrl (curve fitting) vs. reflectance.

A distinctive structural feature of PpPTA and other para-aromatic polyamide fibres is the pleated sheet, which is shown in Fig. 13c, 13d and 13e. It was for the first time observed by Ballou in dark-field images taken from meridional reflections of the ED pattern [132]. This phenomenon has been extensively studied by Dobb et al. [125]. The pleated sheet consists of parallel-oriented chains, which are hydrogen bonded along the direction of the crystallographic b-axis. They are usually oriented perpendicular to the surface of the filament, i.e., in the circular cross-section the b-axes are directed preferably along the radius, as shown in Fig. 14. The angle between adjacent planes of the pleat is about 170° and the distanee between two pleats is about 250 nm, but both values may vary along the radius of the fibre cross-section. 

---