Rotational disorder in poly(p-phenylene terephthalamide) fibers by X-ray diffraction with a 100 nm beam

Single fibers of poly(p-phenylene terephthalamide) (PPTA; brand names Kevlar(x), where x = 29, 49, 149) have been scanned with an about 100 nm synchrotron radiation X-ray beam normal to the fiber axis. Models of rotational disorder of the crystalline domains are discussed based on Monte Carlo simulations of the spatial variation of the 110/200 reflection intensities. For Kevlar(149) the principal disorder appears to be a rotational domain-disorder across the fiber. The data suggest also the presence of a core and possibly a skin layer, which are both more disordered. Kevlar(29,49) appear to have the same type of layering but with different volume fractions. There is also some evidence for a volume fraction without rotational correlation, which might be related to a morphology formed at the onset of coagulation.