1H and 13C solid-state NMR of Gossypium barbadense (Pima) cotton

The interaction of water with cellulose and its influence oil the nuclear spin dynamics in Gossypium barbadense (Pima) cotton were investigated by H-1 and C-13 solid-state NMR techniques. H-1 spin diffusion results from a Goldman-Shen experiment indicate that the water is multilayered. (1) H MAS experiments provide evidence of a range of correlation times for the water, indicative of molecular motion ranging from restricted to relatively mobile. The (1) H spin-lattice relaxation time varies with water content and is different for static and MAS conditions. By coupling the Goldman-Shen sequence with C-13 CP/MAS, cross-polarization from the molecularly mobile water protons distributes magnetization throughout the cellulose (as opposed to enhancing (13) C resonances from only the crystalline or the amorphous domains or from only the surface of the cellulose). However, spatial localization of the combined Goldman-Shen- C-13 CP/MAS experiment using both short mixing and contact times yields a spectrum consistent with predominantly the I-beta polymorph of cellulose. Longer mixing times and the same, short contact time yield a spectrum that is indicative of an increased I-alpha. polymorph content in the crystallite interiors relative to the smaller values found with short mixing times. Published by Elsevier B.V.