|French, Alfred - Al|
|Stipanovic, Robert - Bob|
Submitted to: Journal of Molecular Structure (Theochem)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2007
Publication Date: 8/7/2008
Citation: Taylor, R.E., French, A.D., Gamble, G.R., Himmelsbach, D.S., Stipanovic, R.D., Thibodeaux, D.P., Wakelyn, P.J., Dybowski, C. 2007. 1h and 13c solid-state NMR of Gossypium barbadense (Pima) cotton. J. Mol. Struct. DOI:10.1016/j.molstruc.207.08.006 Interpretive Summary: The fundamental physical properties of the cotton fiber and how it interacts with its environment are poorly understood. One example is how water that is taken up from the atmosphere interacts with the cotton fiber. Pima cotton was selected for study because of its unique properties including strength. The study found that the moisture is present in the fiber as ordered multiple layers that are at least 14 to 17 layers thick. It also found highly structured cellulose in the interiors for the fiber, whereas the surface of the fiber was primarily unstructured. These results can enhance our understanding of drying mechanisms for cotton textiles and could potentially lead to energy savings.
Technical Abstract: The interaction of water with cellulose and its influence on the nuclear spin dynamics in G. barbadense (Pima) cotton were investigated with 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 changes with water content and changes between 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, the amorphous, or 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 which is primarily composed of the I' polymorph of cellulose. Longer mixing times with the same short contact time yields a spectrum that indicates an increased I' polymorph content relative to the smaller values found with short mixing times. This indicates an increased I' content in the crystallite interiors.