NMR investigations of orientational and structural changes in polyamide-6 yarns by drawing

The effect of drawing on the structure and molecular orientation of polyami de-g fibers has been investigated by C-13 solid-state NMR. The molecular or ientation in the fibers is determined using a two-dimensional rotor synchro nized magic-angle spinning ((MAS) experiment. For the highly oriented fiber s order parameters up to (Ps) are determined. By using a 13C Tip filter, th e orientation in the rigid (crystalline + rigid amorphous) and mobile (amor phous) regions are separately determined. The orientation in the rigid phas e increases rapidly at low draw ratios up to A = 3.5 and levels off at high er draw ratios ([P-2])approximate to 0.75). The mobile amorphous phase rema ins disordered for low draw ratios but orients rapidly for draw ratios abov e A = 3.5. By using a 13C TI filter, 13C MAS spectra of the crystalline pha se are obtained, from which the relative amounts of the alpha- and gamma-ph ase can be quantitatively determined using spectral deconvolution. It appea rs that upon drawing the alpha/gamma ratio changes from 60/40 for an undraw n fiber to almost completely a for a fully drawn fiber. The NMR results are qualitatively supported by wide-angle X-ray spectroscopy (WAXS) photos.