Characterization of macromolecular orientation in κ-carrageenan fibers using polarized Fourier-transform infrared spectroscopy

In the current study, polarized infrared (IR) microspectroscopy was employed to characterize the macromolecular orientation in wet-spun and stretched κ-carrageenan fibers. The fibers were shown to be well oriented by X-ray diffraction, suggesting that the κ-carrageenan molecules were generally aligned along the fiber axis direction. Longitudinal fiber pieces of about 10 μm thick were obtained by focused ion beam (FIB) micromilling. The fiber pieces were examined by polarized IR in transmission mode. Several bands, including those characteristic of κ-carrageenan at 845 and 930 cm⁻¹, were polarization-dependent, demonstrating polarized IR as a useful tool to evaluate macromolecular orientation in carrageenan fibers. Band assignments were discussed by considering the general alignment of molecules and the polarization dependence of vibration modes, and our results agreed well with band assignments from previous reports.