EVIDENCE OF DISTINCT WATER SPECIES IN CELLULOSIC ENVIRONMENTS FROM BROAD-LINE NMR

In the reported experiments, broad-line NMR measurements were made on water in cellulosic samples. The spectra for oriented rayon at 65% relative humidity and room temperature consisted of a visually apparent doublet (S//D) and a narrow singlet (S//N) which was shifted upfield about 7 ppm from the center of the doublet. Spectra for vacuum-treated rayon consisted of only the narrow singlet, which was orientation dependent. The doublet separation decreases with increasing moisture content and is essentially zero for oriented rayon samples at 100% relative humidity; the resulting spectra due to the collapsed doublet and S//N singlet was an asymmetric line. Temperature-dependent measurements were made on oriented rayon at 65% relative humidity with the fiber axis parallel to the magnetic field; when the temperature was increased from about 0 degree the peak-to-peak linewidth of the doublet halves and the doublet separation decreased. Measurements using oriented cotton samples and randomly packed rayon samples indicated that the NMR line shape of the water spectra depends upon the physical properties of the macromolecular substrate. The doublet component of the spectra is attributed to a water species (S//D) which is highly bonded to the macromolecular substrate.