Location: Cotton Structure and Quality Research2013 Annual Report
1a. Objectives (from AD-416):
Objective 1: Develop new or improved industry-supported methods to measure moisture in cotton fiber. Sub-objective 1a: Develop and implement accurate reference methods to replace the existing standard oven-drying methods to alleviate the biases in the latter methods. Sub-objective 1b: Develop more accurate techniques to measure the “free” and “bound” water contents in cotton for use in understanding which quality indicator correlates best with the fiber properties. Objective 2: Determine the bases for the interaction of moisture with cotton structures and resulting fiber properties. Sub-objective 2a: Determine the structures and interactions of cotton cellulose crystals and amorphous regions at the molecular level. Sub-objective 2b: Determine the impact of moisture interaction/moisture levels on fiber physical properties and on the transport properties of moisture between cotton fibers. Sub-objective 2c: Improve the understanding of factors that control molecular shape and reactivity for cotton.
1b. Approach (from AD-416):
This research is a comprehensive effort to optimize the measurement of the amount of water in cotton fiber by both reference and rapid, indirect methods, to understand the structural bases for the interaction of water with cotton, to determine the implications of water for cotton performance properties, and to develop means of optimizing the effects of water on cotton performance. The first objective develops a more accurate measure of the water in cotton fiber. Karl Fischer Titration (KFT) and Low Temperature Distillation (LTD) techniques will be used to develop new fiber reference moisture methods. Solvent extraction techniques, followed by the KFT method for moisture, will be used to separate and measure the free water and bound water fractions of the total moisture level. The second objective develops a deeper understanding of fiber structure at the molecular, crystallite, and microfibrillar levels, how water interacts with, and moves within, these entities, and how these levels are affected by water. Theoretical and experimental molecular modeling and X-ray diffraction studies will be used to characterize and establish new structural features. A large number of rapid moisture measurement techniques (chemical, electric, spectroscopy, gravimetric) will be compared to the present oven and new reference moisture methods. Environmentally controlled chambers, in combination with sensors, will be used to monitor moisture transport through a specified mass/density of cotton fiber and to characterize moisture impacts (e.g., strength/ breakage) on cotton fiber by varying the relative humidity and temperature. Light and electron microscopy and molecular spectroscopy will be used to monitor changes in structure and breakage patterns with moisture.
3. Progress Report:
ARS scientists in New Orleans, LA studied water content in raw (bale) cotton, in mechanically cleaned lint and in scoured and bleached fiber, all at moisture equilibrium. The raw cotton had the highest water content, implying that the botanical trash in cotton that had not been cleaned has higher water content. In one set of cottons with the same growing conditions, water content depended little on micronaire. Samples from across the country had a complex relationship with micronaire and inconsistent values for water in the main locations of water in raw cotton. A bias of 0.2-0.7% had been found when comparing standard oven drying (SOD) to the Karl Fischer Titration (KFT) method for water content. The causes of bias in the moisture loss measurement were indicated by Attenuated Total Reflection-Fourier Transform Infrared spectroscopy on SOD cotton. Evidence of oxidation was confirmed with a spectrum of synthesized 2,3 cellulose aldehyde that was similar to that of SOD cotton. Colorimetry and particulate matter also indicated that other processes happen during SOD. The organization of moisture in cotton fibers before and after exposure to water was examined by mid-infrared microscopy and 3D image analysis to give a partial picture of moisture transport in the fibers. Studies of cotton fibers harvested at various developmental stages sought to confirm earlier findings of changes in infrared spectra during secondary cell wall deposition. However, experiments with deuterated fibers signaled that the hydrogen bonds of the crystalline part of cotton fibers are maintained during secondary cell wall development. Also, X-ray diffraction data indicated a gradual increase in crystallite size from 3.8 to 4.9 nm for fibers harvested between 20 and 36 days after flowering. Nuclear magnetic resonance spectra showed gradual loss of the relative amount of amorphous component in cotton fibers during secondary cell wall development. X-ray diffraction patterns calculated from model cotton structures were studied with an eye to simplifying the results, related to Objective 2. Emphasis was on unifying conventions and developing ways to exploit the atomic arrangements in cellulose from work at national and international laboratories. Work showed that the twisting in model crystals would not substantially affect the calculated diffraction patterns. Electron densities of models of cellulose were analyzed to better understand the forces among the molecules, related to Objective 2. Pairs of model cellulose molecules were arranged according to published data and their details studied with Atoms-in-Molecules (AIM) theory. The pairs were also energy-minimized, adjusting each atom according to quantum mechanics theory to give the most likely structure. Surrounding water molecules were also considered. A precursor of 2,5 dihydroxy [1,4] benzquinone was discovered and analyzed. The new molecule results from oxidation of cotton. AIM methods found an unusual additional bond that may be important in devising ways to avoid progression to the quinone molecule that has an intense yellow color. This relates to a modified objective in the project plan for next year.