2012 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.
New industry supported methods to measure water in cotton fiber samples are being developed. Difficulty in holding samples at standard testing conditions of 70° Farenheit and 65% relative humidity (RH) was reduced by putting the samples inside an insulated chamber to control temperature and a salt solution in the chamber maintained humidity. Progress was also made by separating the total water content in raw cotton into fractions, such as the water in the botanical trash and the water in the fiber’s cellulose. Mathematical relationships that describe the way that water content is affected by changes in growth, harvesting, and ginning could provide a blueprint to improve those processes.
Fifteen moisture measurement instruments and methods were compared to the standard oven and the SRRC-developed Karl Fischer Titration (KFT) reference methods. Moderate-to-very good method agreement results were observed for twelve of the units. A Comparison Matrix was updated to assist selection of the best overall moisture system for their needs. Initially, selected instruments were calibrated to the KFT method. The methods agreed well and the work was expanded to include different temperatures and relative humidities. Initial results at high air moisture (80° Farenheit/75% RH) were unexpected. Each moisture measurement method responded differently to increased temperature and RH. New and replicate evaluations are underway at expanded temperature/RH ranges.
The effect of moisture on bundle strength, elongation and fracture morphology of cotton fibers was further examined. Increases of fiber strength and elongation with higher moisture content were confirmed. Infrared microscopy (IR) showed different spectroscopic bands for cotton samples before and after fracture. Electron microscopy showed different fracture morphology for samples broken at different humidity levels.
The evolution of spectroscopic bands associated with moisture was observed with IR microscopy on dry cotton webs that were later exposed to water. Also, X-ray diffraction was used to examine the crystallinity (which affects physical properties) of cotton fibers harvested at different days post-anthesis (after flowering) and compared to progression of fiber properties and IR bands.
The nature of the nanoparticles that make up most of the cotton cellulose was explored in collaboration with scientists at the Louisiana State University AgCenter. Previously observed, very different self-assembled physical states of freeze-dried nanoparticles made from native and mercerized cotton are hypothesized to result from different concentrations of the particles, leading to ideas of how the fiber structures might be modified in the future.
Collaborators in Austria and Japan were assisted by explaining the right-handed twist of a short fragment of normally untwisted or left-handed cellulose that had been chemically modified to have the ability to generate electrical current, allowing the potential of photocell garments. It is because the chemical modifications were applied to the first and third glucose units in the molecule (but not the second) that the structure would be right-handed.
A method to determine water content of botanical trash in baled cotton. Baled cotton contains extraneous contamination from plant parts such as leaf and stem; the water concentration in the botanical trash is unknown. ARS scientists in New Orleans, LA, mechanically cleaned the cotton to remove the trash and manually separated entrained lint from the trash particles. The isolated botanical trash was analyzed for water by the Karl Fischer Titration reference test method, developed and validated by ARS scientists. Results indicated unexpectedly high water concentration (15%), about twice that in the cleaned cotton. These findings are important to the industry in monitoring water control in botanical trash to rule out excess water as a source of fiber degradation and color-grade changes during bale storage.
Lint cotton water content in gin-drying temperature studies. The Karl Fischer technology to measure water in cotton was applied to detecting the influence of cultivar, defoliation time (a procedure commonly use to remove leaves before harvest), and gin-drying temperature on water content of lint cotton. ARS scientists in New Orleans, LA, in collaboration with ARS scientists in Stoneville, Mississippi, subjected the cultivars to two possible defoliation dates and gin-drying temperatures. In addition, the ginned lint was cleaned by mechanical processing, and also scoured and bleached. Overall, mean water content was about 7.8% at moisture equilibrium (70° Farenheit and 65% relative humidity) and the within cultivar range of only 0.2% for raw cotton decreased to less than 0.1% for the scoured material. These findings demonstrate that the different genetic backgrounds of U.S. cultivars, defoliation time, and current gin-drying temperatures influence to a slight extent the range of the equilibrium water content at standard conditions. The precursor to accurate online methods in the industry to detect the small variability in this important property of cotton is sound calibration cottons data, as demonstrated by Karl Fischer Titration technology.
Modeling water content in raw cotton. One factor contributing to the water level is the presence of botanical trash which has a water concentration about twice that of the cleaned fibers (15% compared to only 7.5%). The lack of mathematical models to simulate the influence of the trash material on the total water content does not allow for understanding what quantities influence the process and what relations exist between them. Two models were developed by ARS scientists in New Orleans, LA, and both were tested on raw cottons supplied by ARS scientists in Stoneville, Mississippi. Clearly, the mass fraction of the trash rather than the water concentration in the contaminant is the controlling factor in establishing the difference in water content before and after mechanical cleaning. The industry is advised that a maximum of about 0.5% of the total water content in raw cotton may come from the botanical trash, which is greater than the expected change in water content associated with within-cultivar range in fiber maturity.
Quantum mechanics studies of cellobiose, the shortest cellulose molecule. The complex structure of cotton cellulose and its relationship to water are not sufficiently understood to permit knowledge-based modifications for improved utilization of cotton. Work was carried out by ARS scientists in New Orleans,LA, with collaboration by scientists from the University of Minnesota and the Budapest University of Technology and Economics in Hungary. A model to mimic the effect of being in water was effective in explaining the difference between the experimentally observed structure in vacuum and those in crystal structures and solution. New interactions that stabilize the structure were revealed, and there was less inherent tendency to twist than was found in studies with more rapid computations.
Review of experimental crystal structures and theoretical modeling. The complex structure of cotton cellulose and its relationship to water are not sufficiently understood to permit knowledge-based modifications for improved utilization of cotton. An ARS scientist in New Orleans, LA, reviewed the implications of theoretical computer modeling and the experimental crystal structures of related small molecules for cellulose structure. Literature data on the shape of the individual glucose units and the geometry of the linkage between the units in small molecules were collected for comparison with inherently less accurate data on cellulose itself. Water was not observed in any of the crystal structures, but the structure of the shortest cellulose chain is very different when water or related molecules are present than when the small molecules are isolated. This long-term research is important for developing structure function relationships on which improvements to cotton utilization can be based.
Diffraction patterns from computer models of cellulose crystals. Cotton fibers are composed in large part of small crystals of the molecule cellulose. Many of its chemical reactions are thought to occur in non-crystalline regions, but there is little understanding of those regions. ARS scientists in New Orleans,LA, in collaboration with a Centre National de la Recherche Scientifique (CNRS) scientist from Grenoble, France, have pioneered the calculation of diffraction patterns from various models that could correspond to components of cotton fibers. These patterns were compared with experimental patterns for various cellulosic materials including cotton. This is an advance in understanding the diffraction pattern of cotton that follows purely experimental work done more than 50 years ago at the ARS facility in New Orleans,LA. Such studies are carried out with the aim of understanding the relationship between structure and properties.
Water content of U.S. cottons. The amount of water in cotton critically influences its properties (mechanical, geometrical, and electrical) in textile processing. The cotton industry has sought implementation of more accurate standard test methods to measure the amount of water in cotton at moisture equilibrium – 70° Farenheit and 65% relative humidity. ARS scientists in New Orleans, LA, in collaboration with the American Society for Testing and Materials (ASTM) developed D7785-12, the automated Karl Fischer Titration test method for water in lint cotton, raw (baled) and processed. The system warms the cotton and transfers the released water vapor into a titration cell where it chemically reacts with a measured quantity of Karl Fischer reagent to produce the water content in the sample, about 7.5%. This technology can be utilized by industry to calibrate online sensors to monitor the concentration of water in cotton, which will greatly enhance processing improvement to benefit cotton consumption.
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