Progress 07/16/09 to 07/27/10
Outputs
Progress Report Objectives (from AD-416) Characterize how processing-related properties of cotton from different cultivars and growth environments vary in response to moisture. Determine cotton fiber structure changes affected by moisture and relate the structural changes to fiber attributes, especially breakage. Determine the mechanisms of cotton fiber breakage with varying moisture content. It is unknown why moisture strengthens cotton. Determine molecular weight and molecular weight distributions of cellulose in raw fibers and fabrics of different varieties of cotton grown under different environmental conditions. Approach (from AD-416) We will use moisture sorption isotherms as well as water of imbibition and moisture regain. Light and electron microscopy will be used to monitor changes in structure and breakage patterns with moisture. Energy dispersive x-ray data in the scanning electron microscope will show the depth and uniformity of penetration of solutes, indicating moisture accessible areas. X-ray diffraction studies will indicate the sizes and orientations of the crystallites, another indication of moisture accessible surfaces, and molecular modeling will be used to assist the understanding of noncrystalline regions and breakage mechanism. A new reference method for moisture in cotton by Karl Fischer Titrtion with iodine reagent is automated with, for example a turntable for 35 sample vials. Insequence, each sample vial is heated to 150� C to evaporate the water from the cotton. Released water is transported into the working medium (solvent) and titrated with the chemical, iodine. One problem is that errors can result from accumulation of iodine reaction products and other molecules in the solvent. Instead of replacing the solvent after 6 samples, the usual workaround, we placed "blank" vials in the turntable to allow time for re-equilibration. Error was significantly reduced. A second proposed reference method, Low Temperature Distillation, is based on weight loss. The cotton is dried at 75� C under nitrogen. The loss of all water is confirmed by Near Infrared (NIR) spectroscopy. We are investigating a less expensive sensor. Having two methods avoids relying on just one, with unknown biases, when producing reference cottons with known moisture content. Calibration of refrence materials is possible for the first time. Theory studies guided data analysis and a pilot collaborative study is underway. Fourteen laboratory moisture measurement instruments and the reference oven moisture method were tested. Thermal, NIR, microwave, and chemical techniques were evaluated on the same domestic and international cotton samples. The NIR and small thermal weight loss analyzers gave the best correlations and = 5% outliers. The inexpensive, hand held, resistance- based instruments were least accurate. A Comparative Matrix shows the advantages and disadvantages of each instrument. Some of these techniques were compared against the above Karl Fischer Titration and present standard oven methods. Results were reported at the International Cotton Conference in Bremen, Germany, in March 2010. The Young's modules (elasticity) of cellulose was calculated with both quantum mechanics (QM) and empirical (MM) methods. QM provided independent checks of the MM on short cellulose models, and MM force fields allowed use of larger, more representative models of cellulose. Larger models gave values close to recent experiments. Diffraction patterns were calculated for models with different crystal shapes and 4 to 169 cellulose chains, with and without water, and with and without molecular dynamics displacements from the original coordinates. Model crystals at 327� C changed structure. The electron density of a short fragment of cellulose was determined by X-ray diffraction and QM. Attractive short contacts were found and the infinite chains of hydrogen bonds were characterized. Lone pairs of electrons were revealed. Work at Tulane University under SCA 6435-44000-072-02S gave contact angles for water drops on model cellulose surfaces that had varying chemical modifications so that they would attract less water. A model cellulose crystal dissolved in model solvent at high termperature. Work at University of Georgia under SCA 6435-44000-072-03S has sought to modify the modeling software so model crystals did not twist. Many approaches were tried, but the crystals still twisted. Accomplishments 01 Cooperation/Support from Stakeholders. Because there were more ideas within the project team than could be studied, additional funding from outside sources was requested. A project on validating the Karl Fischer Titration reference method for moisture in cotton and preparing a draft standard procedure in American Society for Testing and Materials (ASTM) format was funded by Cotton Incorporated in CY 2009. A project on studyi the difference between moisture content in cotton by standard oven dryin and the new Karl Fischer Titration (KFT) reference method was funded by The Cotton Foundation (National Cotton Council) in FY 2010. A project on moisture movement in cotton was funded by Cotton Incorporated, with the bulk of funding going to collaborators at Tulane University and Universi of Georgia. 02 ARS Headquarters Funded Postdoc Program. Because a major stakeholder wanted results published more quickly than would be possible using existing staff, additional funds were sought to support a postdoctoral scientist. A project on paired reference methods for moisture in cotton was funded in CYs 2009-2010. 03 ASTM Draft Standard Method for Moisture in Cotton by Karl Fischer Titration (KFT). A new standard reference method was needed for moisture in cotton. The scope of this test method covers the determination of tot moisture (free and bound) in raw and lint cotton conditioned to moisture equilibrium at the standard atmosphere for testing textiles. Extensive research has documented that other chemical compounds in cotton do not interfere with this test method. Commercially available instrumentation specified in this test method. Calibration and standardization utilize commercially available water standards and reagents. Significance and us acceptance testing of commercial shipments of lint cotton, manufacturing control and calibration of fast, indirect sensors to measure water. Precision: the averaged repeatability standard deviation (single analyst of eight lint cottons measured on two different days was: raw, 0.106 % a 0.078 % total moisture; and cleaned, 0.061% and 0.052 % total moisture. 04 Difference Between Moisture Contents in Cotton by Standard Oven Drying a Karl Fischer Titration (KFT). A new standard reference method for determining the amount of moisture in cotton was needed, as was the relationship of the results by the old and new methods. Moisture content by Standard Oven Drying was determined to be significantly higher � by about 03% to 0.7% � than by our proposed new standard method, Karl Fisch Titration. In Standard Oven Drying (at 105� C in air), all of the loss i weight is attributed to moisture. In contrast, the KFT method (fast, ove drying at 150� C in nitrogen) is highly selective for water. It turned o that there is no difference in results between the two methods when otherwise Standard Oven Drying is carried out in an inert atmosphere rather than air. We believe that the underlying mechanism for the increased weight loss in oven drying in air is oxidative decomposition o the sample material. In the past 70 years, moisture analysis of cotton b oven drying in air has been the reference method worldwide. Knowledge of the actual moisture content is an important financial consideration and can help to provide the U.S. cotton industry a world marketplace advanta 05 Paired Reference Methods for Moisture in Cotton. A second independent reference method for moisture in cotton was needed to validate the KFT method. Low Temperature Distillation (LTD) was developed. The weighed sample is placed in a sealed vial with inlet and outlet needles. Heating in an oven at 75� C with dry nitrogen injected into the fiber matrix for 45 minutes removes all of the moisture in the cotton, as confirmed by in vitro Near Infrared (NIR) spectra taken through the glass walls of the container. Because this new method is highly selective for moisture in cotton, weight loss is directly related to moisture content. Also, heati at the lower temperature compared to Standard Oven Drying ensures that only water is distilled from the cotton. Averaged difference in moisture content between the paired methods (KFT and LTD) for 20 cottons examined was: LTD � KFT = 7.06% - 7.04% = 0.02%. The paired reference methods produced equivalent averaged moisture contents. This work opens up a new kind of oven drying and challenges the biased Standard Oven Drying technique. 06 Effects of Gaseous Atmosphere on Moisture Loss and Regain of Commercial Cottons. Another deficiency with the Standard Oven Drying method (at 105 in air) for moisture in cotton is the lack of regain of the original moisture content, thus the lack of retention of the initial properties o the fiber. Four dry gases (argon, nitrogen, helium and air) were used to observe weight loss (75� C and 45 minutes treatment) and regain. Results were verified by NIR and KFT. The averaged moisture content under nitrog at 75� C was within 0.1% of the KFT values. After the water was removed, the dried samples were reconditioned in the standard textile atmosphere (in air at 70�C and 65% RH) for 48 hours and the weights recorded. The sample weights after reconditioning were equivalent to the original weights taken just before the weight loss treatment. Thus, hysteresis wa prevented by drying under nitrogen. These results surprised the research team. Now we have evidence for the first time that oxygen -- rather than just drying -- is involved in the mechanisms leading to hysteresis. In other work with the different gases, helium was able to remove the moisture in cotton, but argon, even at 105� C for 3 hours, failed to remove all of the water. 07 Modulus Calculations Using Model Cellulose Molecules and Crystals. Computer models of cellulose were used to better understand the basic physical properties of cotton cellulose. We calculated the Young�s modul of cellulose models of different lengths and number of strands. Although hydrogen bonds only exhibit a fraction of the strength of covalent bonds our modeling methods suggest that hydrogen bonding plays a crucial role the molecular stiffness (resistance to deformation) of cellulose. Calculations with analogue models incapable of undergoing hydrogen bondi place this contribution close to 50%. Calculations with a model containi multiple cellulose strands revealed that most of this contribution comes from intramolecular hydrogen bonding. While shorter cellulose models exhibited modest modulus values, longer cellulose models (i.e. more than 20 glucose units) provided modulus values comparable to reported experimental and theoretical determinations. Since changes in moisture a expected to affect hydrogen bonding, our findings could guide our understanding of the effect of moisture on cotton structure and physical properties (i.e.; fiber strength and elongation). 08 Symmetry of Cellulose Molecules. The cotton fiber is composed of many small crystals of cellulose and intervening amorphous regions. A general picture of the arrangement of the atoms inside the crystals is available but there is a controversy over whether the crystals are normally untwisted (symmetric) or twisted in close-up view. It is widely thought that there is an inherent tendency for the individual cellulose molecule to twist, which could affect the shape of the crystals. QM calculations and a review of the crystal structure literature showed numerous example of untwisted molecules with the same general structure as cellulose. Thi suggests that any inherent tendency to twist is small.
Impacts
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Publications
- Montalvo Jr, J.G., Von Hoven, T.M., Cheuk, S.Y., Schlinder, A. 2010. Preliminary Studies of Non-aqueous Volatiles in Lint Cotton Moisture Tests by Thermal Methods. Textile Research Journal. p. 1-17.
- French, A.D., Johnson, G.P. 2009. Cellulose and the twofold screw axis: Modeling and experimental arguments. Cellulose. 16:959-973.
- Stevens, E.D., Dowd, M.K., Johnson, G.P., French, A.D. 2010. Experimental and Theoretical Electron Density Distribution of Alpha,Alpha-Trehalose Dihydrate. Carbohydrate Research. 345:1469-1481.
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