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.
1. Oxidation of cotton occurs during oven drying moisture measurements. A popular method for measuring moisture in cotton is based on weight loss during drying in an oven; all the weight loss is assumed to result from evaporation of the water. If other changes happen to the cotton during drying, then the results may require correction to give values that reflect the actual water content. Oven-treated cotton samples were examined with Attenuated Total Reflection-Fourier Transform Infrared spectroscopy, colorimetry, and observation of particulate matter. All methods suggested that cotton oxidation takes place when the Standard Oven Drying method is used. Cotton oxidation was positively identified by comparing the spectra of oven-treated cotton samples and synthesized 2,3 cellulose dialdehyde. This study is important to the textile industry since moisture content can be linked to cotton quality parameters and cotton processing methods.
2. Moisture content in cotton traceable to water content. Moisture content is the phrase used to describe the weight lost from putting a cotton sample in a drying oven, even though other processes also occur that change the weight of the sample. Water content refers to the amount of water determined by the Karl Fischer Titration (KFT) method. ARS scientists in New Orleans, LA hypothesized that moisture data that were collected at moisture equilibrium can be corrected to be comparable to water content. Correction factors were developed for four different oven methods and the adjusted results for Mississippi cultivars were on the same level as the water content. These corrections allow the use of the less costly and widely used oven drying methods to get more accurate results.
3. Industry-supported, ARS-developed technique aids moisture analysis. The range of water content in U.S. cottons measured at standard textile testing temperature and humidity is small, less than 1%. Therefore precise data are needed to differentiate the samples, but several factors can influence the results. Methods of blending the sample and for conditioning it (in a standard test lab or a special closed chamber with extra control of the humidity) as well as number of repeat tests all strongly influenced the results. This was learned using Split-Sample Correlation, a technique previously developed by ARS researchers and collaborators in New Orleans, LA for Near Infrared spectroscopy aided by industry funds.
4. Instruments for measuring fiber moisture compared. Research by ARS scientists in New Orleans, LA established the capabilities of several moisture measurement instruments and methods when compared to Standard Oven Drying (SOD) and the ARS-developed Karl Fischer Titration (KFT) reference methods. The best technical results were given by thermal weight loss and Near Infrared spectroscopy units, whereas the least expensive dielectric units were only satisfactory and gave poorer agreement with the reference methods. A Comparison Matrix was developed to assist in selecting the optimal moisture system, considering types of sampling, speed, size, etc. and accuracy. Preliminary results showed that the KFT method could serve as a calibration method instead of SOD for other moisture measurement instruments. These results for the KFT method as reference strongly demonstrate that various instruments must be calibrated to the oven and KFT methods in order to compare directly the method agreement for those instruments to both the oven and KFT reference methods.
5. Crystallite size is the primary factor in cotton crystallinity. For more than 50 years, cotton fibers were described as being composed of crystalline and amorphous zones, with a percent crystallinity to denote the fraction in the crystalline regions. But this gives only a rough idea. ARS researchers in New Orleans, LA showed that the X-ray diffraction pattern observed for a typical cotton can be re-created by assuming that the crystal is approximately six nanometers in diameter but is otherwise perfect. This is considerably larger than the crystals in cellulose from other sources. This should be of use in understanding interactions of cotton with moisture and various chemical treatments. Most of these interactions were thought to occur in the non-crystalline regions but such regions must be a small percentage of the total structure.
6. Boundaries placed on Segal’s crystallinity index. X-Ray powder diffraction studies are perhaps the most widely used analysis of cotton and other materials that are composed of cellulose. One procedure that has been widely used for these analyses is the Segal Crystallinity Index, developed by ARS Researchers in New Orleans,LA some 55 years ago. With the ability to calculate diffraction patterns that give different values of crystallinity based on different sizes of crystals (see previous accomplishment), patterns were calculated for different sizes of cellulose in its native crystalline form and also for the crystalline form that results from the mercerization of cotton cloth. The Segal method showed increases in crystallinity as the crystallite sizes increased, as expected. However, for a given size of crystallite, the Segal crystallinity was much higher for fully mercerized cotton than for native cotton. Therefore, the Segal crystallinity values cannot be compared for samples that have fundamental differences.
7. Chemical bonds and weak interactions visualized. The bonds that hold atoms together correspond to concentrations of electrons between those atoms. Previously, the existence of such regions was deduced from the detailed structures of molecules based on a distance criterion. That suffices for typical chemical bonds but cotton structures are also held together by weaker forces that are poorly understood. ARS researchers in New Orleans, LA used Electronic Structure Theory (also called quantum mechanics) calculations and follow-up studies of the electron density to visualize not only the conventional chemical bonds but also the weaker bonds. The roles of these weaker bonds (hydrogen bonds and van der Waals attractions) are poorly understood, but they are a major factor in understanding of the differences between chemically similar molecules such as cellulose and starch. Application of Atoms-in-Molecules theory also permitted quantification of these weak interactions for comparisons with other structures.Von Hoven, T.M., Montalvo Jr, J.G., Byler, R.K. 2012. Preliminary assestment of lint cotton water content in gin-drying temperature studies. Journal of Cotton Science. 16:282-292.