Mercerized ramie conformation

Cellulose polymorphy was studied by comparing the spectra of Valonia, ramie, and mercerized ramie. It appears that the conformation of the cellulose backbone is the same in Valonia and ramie celluloses, but that the hydrogen bonding patterns are different. Mercerized cellulose and native celluloses differ in both their backbone conformations and hydrogen bonding patterns. 

The cellulose I spectra were also compared with spectra of ceTTulose II recorded from a mercerized ramie fiber. Figures 7 and 8 show the Raman spectra of these three celluloses. Spectra were recorded with the electric vector of the incident light parallel and perpendicular to the chain axis. These spectra can be divided into two regions. The region below 1600 cm (Figure 7) is most sensitive to the conformation of the cellulose backbone (especially below 700 cm" ). 

Influence of Physical Structure. The hydrolytic behavior of cellulose is much influenced by its physical structure and lateral order [121-132]. Wood cellulose was hydrolyzed twice as fast as cotton [125]. Hydrolysis rate was significantly increased by physical or chemical pretreatment, with the effect depending on the source of cellulose. Hill and coworkers [127,128] reported that mercerization increased the hydrolysis rate of cotton (by 40%) and of ramie (7%), whereas the opposite effect was observed for linen and a-cellulose samples showing an approximately 30% reduction. Based on kinetic analysis, they concluded that the end-attach model proposed by Sharpies [121] can only be applied to the cellulose II structure and not to the cellulose I crystallite. Thus, the conformation of cellulose is also a significant factor affecting its reactivity and possibly the hydrolytic mechanism as well. 

The use of synchrotron X-ray data collected from ramie fibers after ad hoc treatment in NaOH provided a revised crystal-structure determination of mercerized cellulose II at 1 A resolution." The unit-cell dimensions of the P2i monochnic space group are a = 8.10 A, h = 9.04 k,c= 10.36 k,y= 117.1°. As with the regenerated cellulose, the chains are located on the 2i axes of the cell. This indicates that the different ways of preparing cellulose II result in similar crystal and molecular structures. The crystal structure consists of antiparallel chains having different conformations, but with the... 

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