A new method to determine the exact values of the fiber identity period of polyamides

A method to determine the exact fiber identity periods (FIP) of polyamides from the X-ray meridional reflections has been found, which is essential especially for the γ forms of polyamides with large values of the FIP. The basic concept of this method is that the γ form has two kinds of reflections, the peak positions of which are shifted from the corresponding reciprocal-lattice points to the wide- and small-angle directions, so that the true FIP is between the maximum and minimum values calculated from the former and latter kinds of reflections, respectively. For an example, this method was applied to polylauryllactam (nylon 12) and a value of 31.92±0.02 Å was obtained as a more precise FIP.