Native cellulose crystalline morphology

In an effort to further validate the proposal that the Iq, and forms were the primary constituents of native celluloses, VanderHart and Atalla undertook another extensive study to exclude the possibility that experimental artifacts contributed to the key spectral features assigned to the two forms. A number of possible sources of distinctive spectral features were explored. The first was the question whether the surface layers associated with crystalline domains within particular morphological features in the native celluloses could give rise to features other than those of the core crystalline domains. The second was whether variations in the anisotropic... 

With the wide acceptance of the proposal of the two crystalline forms (I and I/3) came the challenge of understanding the differences between them and their relationship to each other within the morphology of native cellulosic tissues. A number of complementary approaches were pursued by different investigators in the search for answers. Some were based on further application of solid-state C NMR to the study of different celluloses as well as to celluloses that had been subjected to different modifying treatments. Others were based on the application of Raman and infrared spectroscopy to new classes of cellulosic samples. Others were still based on the refinement of electron microscopic and diffractometric methods. The results of these investigations will be presented in summary. 

T,he chemical structure of cellulose chains was established by Haworth and Hibbert more than 40 years ago. Native cellulose occurs in solid state and in partly crystalline form. A schematic model for the native cellulose lattice was worked out about 1930 by Meyer, Mark, and Misch. The basic morphology of native cellulose could not be resolved, however, before electron microscopy with high resolution was developed and applied. During the last two decades, it has been amply shown and is now generally accepted that native cellulose basically is composed of microfibrils of a width 100 A. or less as was reviewed in 1956 (12). 

The oxidation of different cellulosic materials by TEMPO catalysis has highlighted the importance of the substrate morphology [36]. Crystalline native celluloses were unaffected even after long reaction times, whereas amorphous celluloses were promptly oxidized at Cg. 

The hypothesis (1-3) that all native celluloses are a composite of two crystalline allomorphs, designated and Ig, has been further tested using C solid state NMR. In particular, two alternate origins of sharp resonance features were considered in addition to the usual origin, the crystalline unit cell. The first source is ordered layers on crystal surfaces the second is possible anistropic bulk magnetic susceptibility (ABMS) shifts associated with well defined fibril patterns (tertiary morphology). 

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