NMR Investigations of Orientational and Structural Changes in Polyamide-6 Yarns by Drawing

The effect of drawing on the structure and molecular orientation of polyamide-6 fibers has been investigated by 13 C solid-state NMR. The molecular orientation in the fibers is determined using a two-dimensional rotor synchronized magic-angle spinning (MAS) experiment. For the highly oriented fibers order parameters up to 〈 P 6 〉 are determined. By using a 13 C T 1 ρ filter, the orientation in the rigid (crystalline + rigid amorphous) and mobile (amorphous) regions are separately determined. The orientation in the rigid phase increases rapidly at low draw ratios up to λ = 3.5 and levels off at higher draw ratios (〈 P 2 〉 ≈ 0.75). The mobile amorphous phase remains disordered for low draw ratios but orients rapidly for draw ratios above λ = 3.5. By using a 13 C T 1 filter, 13 C MAS spectra of the crystalline phase are obtained, from which the relative amounts of the α- and γ-phase can be quantitatively determined using spectral deconvolution. It appears that upon drawing the α / γ ratio changes from 60 / 40 for an undrawn fiber to almost completely α for a fully drawn fiber. The NMR results are qualitatively supported by wide-angle X-ray spectroscopy (WAXS) photos.