|French, Alfred - Al|
|Stipanovic, Robert - Bob|
Submitted to: Journal of Molecular Structure
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2007
Publication Date: 8/21/2007
Citation: Taylor, R.E., French, A.D., Gamble, G.R., Himmelsbach, D.S., Stipanovic, R.D., Thibodeaux, D.P., Wakelyn, P.J., Dybowski, C. 2008. 1H and 13C Solid-state NMR of Gossypium barbadense (Pima) Cotton. Journal of Molecular Structure. 878(1-3):177-184. Interpretive Summary: The interaction of cotton with water is poorly understood, but the results of these interactions are important from several standpoints. Unlike other carbohydrate-based materials, cotton fibers that contain more moisture are stronger than those with less; the energy to dry cotton fabrics is unusually high, and high levels of moisture in cotton in the bale promote changes in the color of the fibers. The purpose of this submission is to provide a better understanding of the moisture-cotton interaction at the molecular level. Several specialized techniques using Nuclear Magnetic Resonance were applied to raw Pima cotton. Major findings included that water is broadly distributed within the fiber, not just in amorphous regions. Another finding was that water accumulates in layers about that are the thickness of 15 molecules of water, based on normal absorbance from the air. These findings are primarily of interest to scientists trying to understand how water impacts cotton behavior so that practical solutions to the problems above and other improvements can be developed.
Technical Abstract: The interaction of water with cellulose and its influence on the nuclear spin dynamics in G. barbadense (Pima) cotton were investigated by 1H and 13C solid-state NMR techniques. 1H spin diffusion results from a Goldman-Shen experiment indicate that the water is multilayered. 1H MAS experiments provide evidence of a range of correlation times for the water, indicative of molecular motion ranging from restricted to relatively mobile. The 1H spin-lattice relaxation time varies with water content and is different for static and MAS conditions. By coupling the Goldman-Shen sequence with 13C CP/MAS, cross-polarization from the molecularly mobile water protons distributes magnetization throughout the cellulose (as opposed to enhancing 13C 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-13C 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.