CP MAS C-13 NMR ANALYSIS OF THE CRYSTAL TRANSFORMATION INDUCED FOR VALONIA CELLULOSE BY ANNEALING AT HIGH-TEMPERATURES

The crystal transformation of Valonia cellulose induced in a dilute alkaline solution at high temperatures has been examined in detail by high-resolution solid-state C-13 NMR spectroscopy. The C1 and C4 resonance lines, which are characteristic triplets for the celluloses from primitive organisms, markedly undergo changes in relative intensities of the constituent lines with increasing annealing temperature, and those lines are finally converted to doublets with almost equivalent intensities. Such spectral changes have been successfully analyzed in terms of the composite crystal model in which native cellulose crystals are assumed to be composites of two allomorphs, celluloses I(alpha) and I(beta) resulting in confirmation of the validity of the composite crystal model. Moreover, the fraction of cellulose I(alpha) is found to be reduced from 0.64 for intact Valonia cellulose to about 0.12 by annealing as a result of the crystal transformation from cellulose I(alpha) to I(beta).