Valonia cellulose spectra

In the 0-H stretching region (3200-3600 cm ), however, significant differences are observed between all three celluloses. These differences are most prominent in the spectra recorded with the electric vector parallel to the fiber axis (Figure 8a-c). The frequency as well as the broadness of the peaks varies in this region. The spectra of Valonia cellulose have a peak at 3231 cm that is not observed in the ramie spectra. The spectra of native ramie on the other hand, have a peak at 3429 cm that is not observed in Valonia. The spectrum of mercerized ramie recorded with the elec-... 

Figure 4.8 IR spectrum of cellulose 4 (Valonia) at room temperature (upper spectrum) and difference spectrum of sample at room temperature minus at 115 °C (lower spectrum). Spectra are offset for clarity.

Two classes of experiments were conducted. In both sets of experiments, fibers in which the cellulose chains are oriented parallel to the fiber axis were used. In the first class of experiments, the plane of polarization of the incident light was changed relative to the axis of the fibers by rotating the fibers around the optical axis of the microscope (see Figure 2a). The dependence of the band intensities on the polarization of the incident light was studied to determine the directional character of the vibrational motions. This information was used to advance the assignment of the Raman spectrum of cellulose. Spectra from Valonia, ramie, and mercerized ramie fibers, which have different allomorphic compositions, were compared to study the structural differences between the allo-morphs. 

The differences between the spectra of ramie and Valonia are quite small compared to the differences between native cellulose and cellulose II (see Figure 7). In the spectra of ramie and Valonia, the different peak widths and relative intensities can be attributed to the difference in the crystallite sizes. In the spectrum of cellulose II, however, the frequency and number of peaks is significantly different. In previous publications, the differences between the spectra of celluloses I and II have been interpreted as evidence for different conformations in celluloses I and II (40-41). The spectral differences which are indicative of conformational change are not observed in the spectra of ramie and Valonia. Since ramie and Valonia have different I to Ip ratios, it would appear that celluloses 1 and Ip must have similar molecular conformations. 

Figure 1. CP/MAS C-NMR spectra recorded at 7.05 T on cellulose / isolated from different sources and one hr aft pulp. From bottom to top the sources are Valonia, Cladophora, Halocynthia, and cotton linters. The top spectrum is bleached birch krcft pulp that contains hemicelluloses. (Reproduced with permission from reference 16. Copyright 1999).

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