Solid State NMR of Cellulose, Wood, and Pulp

Abstract

High resolution ¹³C NMR of crystalline celluloses is both complementary and supplementary to x-ray diffraction analysis because it is effective both for crystalline an non-crystalline materials. Good spectral quality has been achieved for a range of cellulose samples and spectral elements related to lateral order are observed but some interpretational details are still evolving. The spectrum of a complex material such as wood, shows morphological and conformational features for each chemical component. The resolution achieved is sufficient to allow identification of carbohydrate resonances, methoxyl, and aromatic resonances and methyl and carbonyl resonances of hemicellulose acetyls. The effect of solid state chemical treatments such as acetylation and prehydrolysis are readily detected. The use of interrupted decoupling allows one to separate the lignin and cellulose components of the spectrum. The potential of the technique for rapid ¹³C NMR analysis of paper debris, coated sheets and insoluble resins is now becoming well-established. More complex biosubstances such as grasses, bark, and plant cell wall are being molecularly examined in their true nascent state for the first time. In this paper, a series of spectra are presented covering the various physical states of Esparto grass: native, holocellulose, alkali extracted, pulp; these spectra are compared to Esparto xylan. The line broadening effect of the latter on the C-1 resonance of cellulose demonstrates the difficulty in interpreting effects of fine structure vs. heterocomposition.