Ramie cellulose study

Selection of Ramie Cellulose for Study. Ramie cellulose was selected for study because it is highly oriented and fairly... 

FRENCH ETAL. X-ray Diffraction Studies of Ramie Cellulose I... 

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. 

Polymorphy. Cellulose polymorphy within the cellulose I family was studied by comparing the Raman spectra of VaIonia and ramie cellulose. Solid state NMR spectra indicate that the I, form predominates in Valonia while the Ig form predominates in ramie (17-18). 

It was observed In earlier studies of controlled alkall-mercerlzatlon of ramie cellulose that the crystal structure of native cellulose Is transformed to cellulose II through a series of crystalline alkali-cellulose complexes (1,2). The relationships between these "Na-celluloses" and their pathways of transformation are Illustrated In Fig. 1. It has further been observed that all of the transformations are crystal-to-crystal phase changes, not Involving Intermediate amorphous phases. All of the experimental evidence has suggested... 

A study on extrusion of functionalized ramie cellulose whiskers chemically modified the cellulose whiskers by grafting organic acid chlorides (Scheme 23.1) presenting different lengths of the aliphatic chain by an esterification reaction [68]. 

The crystal structure of native ramie cellulose was shown to be similar to that recently reported for Valonia cellulose. The earlier conclusion that the ramie diffraction data could not be satisfied by a conventional cellulose model is refuted. R (an indication of diffraction error) values of 0.158, 0.185, and 0.175 were obtained for anti-parallel, parallel up, and parallel down alignments respectively. The author considers that the anti-parallel model provides the best accounting for the ramie data and is therefore probably the correct model for both cotton and ramie cellulose. The changes in crystallinity and physical characteristics of microcrystalline cellulose which occur on grinding have been studied. Under one set of grinding conditions, the specific surface area rose... 

Acetylation rates have also been studied by Centola37 who treated natural and mercerized ramie fibers for varying times with acetic anhydride and sodium acetate and examined the reaction products chemically and by X-ray diffraction. The reagent was considered to penetrate into the interior of fibers. A heterogeneous micellar reaction was believed to occur that converted a semi-permeable elastic membrane around the micelles into the triacetate. The rate of acetylation of mercerized ramie was observed to be faster than that of unmercerized fiber. Centola concluded that about 40 % of the cellulose in native ramie is amorphous and acetylates rapidly. 

The studies of Miles and Craik [13] merit special attention since they obtained the following X-ray diagrams of ramie (Chinese nettle) cellulose, which is notable for a distinctly crystalline structure (Fig. 83). 

Results. We have made a detailed study of the effect of using both the Jones and the Stokes corrections on crystallite size measurements obtained from the most crystalline samples of cellulose I and II, Ramie and Fortisan (18). Our conclusion was that the Jones corrections were always within 5% of the Stokes corrections for both half-width and integral breadth. Current practise is always to use a Stokes deconvolution procedure for the correction of all resolved peak profiles, evaluating an... 

Cellulose microcrystals can be suspended in dilute solution. Turbidity measurements suggest that the particles are not highly associated in the absence of added salt. In the presence of a low salt concentration, large aggregates are formed, as was shown by a study of light scattering by suspensions of ramie microcrystals 15). When the salt concentration is further increased, the microcrystals precipitate. Since the microcrystals... 

Cellulose, which Is one of the most abundant organic substances found In nature, has been extensively studied by various techniques such as x-ray scattering, electron microscopy, IR and Raman spectroscopy, NMR spectroscopy etc. However, the crystal structure and noncrystalline state are not yet solved for cotton, ramie, bacterial and valonla celluloses which can be easily obtained in pure form. Cross-polarization/magic angle spinning(CP/MAS) C NMR spectroscopy is a promising new method to study these unsolved problems of cellulose, because this method is very sensitive to local molecular conformations and dynamics. 

Current fiber x-ray diffraction studies, including new calculations by the authors, are reviewed. Because of different conventions used to describe the crystal structure of native cellulose, the preferred parallel structure described as "up by Gardner and Blackwell for Valonia corresponds to the "down" structure that was strongly rejected for ramie by Woodcock and Sarko. 

The previous studies (1-3) suggested that the higher plant celluloses, like cotton and ramie, were rich in Ig while the content was appreciable if not dominant in the algal celluloses and the bacterial cellulose obtained from Acetobacter xylinum. In Figure 2 the considerable contrast between the spectra of cotton linter cellulose, both dry (2A) and wet (2B), and algal cellulose (2C) from Valonla ventricosa is Illustrated. Because the lateral... 

Cellulose orientation in the plane perpendicular to the chain axis was studied by recording spectra of ramie cross sections with different polarizations of the incident light relative to the cell wall surface. 

More recently, Atalla and VanderHart (17-18) have studied the solid-state NMR spectra of several forms of native cellulose. They concluded that native celluloses appear to be composites of two distinct crystalline forms of cellulose called 1, and Ig. The proportions of I j and Ig in the composite varies depending on the source of the cellulose. In algal and bacterial cellulose, the I, form dominates, whereas the Ig form dominates in ramie, cotton, and wood pulp. These results are consistent with the data from diffrac-tometry and infrared spectroscopy in that algal and bacterial cellulose are similar to each other but different from other native celluloses. 

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. 

In the second class of experiments, spectra were recorded from ramie fiber cross-sections. The plane of polarization of the incident light was changed relative to plane of the cell wall by rotating the cross-sections around the optical axis of the microscope axis (see Figure 2b). The information from these spectra was used to study the orientation of the cellulose in the plane perpendicular to the chain axis. 

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