Location: Cotton Structure and Quality Research2011 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
Due to its specificity, Karl Fischer Titration (KFT) is being used to measure water in cotton. Processing history affects the moisture values. Raw cotton has the largest range of values, mechanically cleaned less, and scoured and bleached cotton has very little variation. Cotton samples are usually equilibrated in a conditioning room before moisture analysis. Variability in KFT results was significantly reduced by equilibrating in a small environmental chamber that contains an aqueous salt solution to generate constant 65% relative humidity. Various moisture instruments and methods were compared to the oven reference method and new KFT reference method. Agreement between the two methods was very good, with a low number of outliers for several instruments. The number of outliers was higher for the KFT method, due to the instruments being calibrated with the oven method, not the KFT method. Computer models of the crystallites in cotton were tested by calculating their X-ray diffraction patterns and comparing with experimental ones. The fewest cellulose molecules that could give the experimental pattern is 64, instead of the 36 from biosynthesis studies. The models are twisted, perhaps from imperfect modeling. The effect of twist on the calculated patterns is minor but could be detected by careful experiment if real crystals are twisted. Elongation and force were obtained using a Stelometer to break cotton fibers of several varieties that were conditioned at different humidity levels. The measurements changed with varying relative humidity, confirming previous results. Microscopy showed different breaking patterns caused by the different humidity levels. A sampling system for examining moisture diffusion (transport) in cotton bundles was created. Several cotton webs were studied with infrared (IR) spectroscopy before and after drying, showing differences for dried and moist cotton fibers. The IR spectrometer was also used to examine cotton at different days post-anthesis (flowering), and a calibration was developed that correlates IR peak height with fiber maturity. Shapes of the shortest cellulose molecule cellobiose in isolation and in solution were studied with quantum mechanics (QM). The preferred cellobiose shape in solution was consistent with experimental solution studies and crystal structures. When the model was not in solution, results agreed with previous QM studies of isolated molecules and with experiments in the gas phase. Work at Tulane University finalized contact angles for water drops on native and modified model cotton surfaces. A model drop spread out at about 1 m/s. More dissolution of cellulose in water and N-methyl-morpholine-N-oxide (NMMO) solvent was modeled. At the University of Georgia cellulose crystal models were restrained so they did not twist but otherwise are affected by the force field. Those models were then allowed to twist. Modeled diffraction patterns from both showed how twisting of experimental samples could be detected based on analysis of the diffraction spots.
1. An improved technique for measuring water in cotton. The cotton industry has requested a more accurate method to measure water in cotton because the current method is biased. Extensive research by ARS researchers in New Orleans, LA, resulted in the development of an accurate method to measure this important property of cotton. The scope of this test method covers the determination of water in raw and lint cotton conditioned to moisture equilibrium at 70°F and 65% relative humidity. The technique can be applied to acceptance testing of commercial shipments of lint cotton, manufacturing control and calibration of fast, indirect sensors to measure water. The cotton industry, from producer to buyer, benefits.
2. Influence of gin drying temperature, cultivar, and fiber cleaning on water content in lint cotton. Ginners need to know that cotton is not over dried during ginning to prevent adverse affects on mill processing. ARS researchers in Stoneville, MS, gin-dried several cultivars at low and high heat. ARS scientists in New Orleans, LA, cleaned and analyzed lint samples from the gin. Water was measured by Karl Fischer Titration. The amount of water in the scoured and bleached samples within a cultivar was constant, unrelated to gin-drying temperature or maturity. The results suggest that differences in water content in raw lint within a cultivar are really due to changes in gin-drying history and impurities in the cotton. The gins and textile mills benefits from this work.
3. Observed and predicted hydroxyl group orientations. Modeling studies on cellulose and other carbohydrates are typically done with a single isolated molecule and give hydroxyl group orientations that are quite different from solid state experiments. This work brought understanding to this situation. An ARS scientist in New Orleans, LA, collaborated with a scientist in Budapest, Hungary, to determine orientations in cellulose and other carbohydrate structures with Quantum Mechanics energy calculations and statistical studies of experimental structures in the Cambridge Crystal Database. Quantum Mechanics studies of isolated molecules confirmed the attraction of adjacent hydroxyl groups, leading to sequential partial rings of hydrogen-bond like interactions around the individual glucose residues. Use of a solvent model decreased the interaction energy to nearly zero, and the database study showed few examples of the hydrogen bond like interactions that are favored by the isolated molecules. Instead, the hydroxyls were oriented so they could form the stronger hydrogen bonds that are possible with neighboring sugars.
4. Moisture affected cotton fiber properties. Elongation and tenacity were determined with a Stelometer (a mechanical tester for fiber elongation and breaking strength) for several cotton varieties that were conditioned at different humidity levels (50% to 65% RH). Tenacity and elongation values declined with decreasing moisture levels when measured at standard conditions, confirming previous results. Images from optical, infrared, and electron microscopes of the resulting broken cotton fibers indicated that the changes in tenacity and elongation are accompanied by differences in the patterns of breakage.
5. Infra red spectra showed cotton fiber at differnt developmental stages. An FT-IR spectrometer was used to measure the IR spectra of various cotton fiber samples from two related genetic varieties at different days post-anthesis. The spectra reveal band changes with increasing days. The intensities of these bands were compared against the intensity of mature fiber marker bands, and their ratios correlated to reference maturity measurements. From this correlation a “calibration” curve for various cotton cultivars will be produced. Cotton breeders and growers who want to follow fiber development from these maturity measurements and a calibration curve.
French, A.D., Csonka, G.I. 2011. Hydroxyl orientations in cellobiose and other polyhydroxy compounds – modeling versus experiment. Cellulose. 18:897-909, DOI 10.1007/s10570-011-9539-6.