Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: February 1, 2003
Publication Date: June 1, 2003
Citation: French, A.D., Goynes Jr, W.R., Rousselle, M.A., Thibodeaux, D.P. 2004. Cotton fiber and moisture - some of the basics. In: Proceedings of the National Cotton Council Beltwide Cotton Conference, Jan. 5-9, 2004, San Antonio, TX. p. 2990-2994. Interpretive Summary: Currently there is much interest in the relationship between cotton fiber and water. One reason is that water is being added to the cotton at the gin, which certainly increases the weight of the baled cotton. It may also help the cotton to have better properties during classification, which determines the price paid to the grower. It is not widely thought that the improvements are durable, but this is a topic of study, as is the response of different varieties to moisture. As part of work to develop deeper understanding of how water causes cotton fibers to have improved properties, we have examined a number of possible locations for the water. If the water is located on the surface of fairly coarse structures, it will exist in multiple layers, a proposed source of improvement in testing properties. This paper covers this examination and also looks at some properties of water-to-water interactions, as determined with computerized molecular modeling. These interactions can be estimated at very high levels of theory, while molecules as large as the cellulose molecules in cotton require much more approximate methods. Those empirical methods can be guided by the high-level methods. Results from this work are primarily of interest to scientists working on fiber structure and moisture-related problems.
Technical Abstract: The possible locations of water molecules in cotton fibers are explored based on fiber size, crystallite size, known crystal structures of cellulose hydrates, and cross-sections of swollen cotton fibers. A 5% moisture content, a normal value for room conditions, corresponds to roughly 760 monolayers of water if it all goes on the external fiber surface, or about 0.3 monolayers if it were able to access all surfaces of the crystallites that are indicated by x-ray diffraction studies. Additional information on hydrogen bonding, the major mechanism for the interaction of water and cotton, is provided by studies of water clusters with quantum mechanics. These theoretical studies show variation on the order of 10% in the length of hydrogen bonds, depending on the position of the water relative to other water molecules. These poorly understood fine distinctions are not found with studies based on available empirical force fields, the only method fast enough to be used for production studies on large molecules such as cellulose, so the empirical methods must be modified appropriately.