Author
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Anthony, William |
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Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings Publication Acceptance Date: 1/4/2006 Publication Date: 6/10/2006 Citation: Anthony, W.S. 2006. Investigation of the equilibrium moisture contents of u.s. cottons. National Cotton Council Beltwide Cotton Conference. CD ROM pp. 2520-2529. Interpretive Summary: Marketing cotton worldwide is currently based on several different assessments (instrument or manual) of cotton quality depending on the country and marketing association. Instrument classification is used in the United States and Australia but the other countries use manual classification. A major challenge to global use of instrument classification is the need for the samples to be conditioned in expensive environmentally controlled facilities so that the samples reach a common moisture content because moisture content significantly impacts fiber properties. Previous studies indicate that all cottons do not equilibrate at the same moisture content when exposed to the same environmental conditions depending on the moisture history of the sample as well as physiological differences in the cotton fiber. This study investigated drying the sample to zero moisture content before conditioning to alleviate the impact of the history of the sample. In this study of about 750 samples of cotton fiber from the 2004 crop in the United States, only 69% of the samples stored in an uncontrolled environment for several months were in the recommended moisture content range. After storage at recommended conditions for 15 days or more, 90% of the samples were within the recommended range. After drying the samples to zero moisture content and reconditioning them, 95% were within the recommended range. Conditioning the cotton fiber decreased the expected moisture content variability of samples. Drying the cotton to zero moisture content and then reconditioning it reduced the moisture content hysteresis effect 83% suggesting that the moisture content of samples would be more uniform using this procedure. Adoption of this method will improve the repeatability of instrument measurement of fiber quality and enhance adoption of instrument classing globally. Technical Abstract: Globalization of instrument classification of cotton faces a major challenge in environmental conditioning because of the need to evaluate samples at a common moisture content (mc). The mc significantly impacts the fiber properties of strength and length. A mc range of 6.3 to 7.6% (wet basis) is used for testing which is usually achieved with environmental conditions of 70 ±1ºF and 65% ± 2% relative humidity (RH). In this study of about 750 samples of cotton fiber from across the United States, the mc was measured with four methods--oven, portable resistance sensor, Stoneville Stickiness Tester (SST) infrared sensor and SST resistance sensor. For the average mc for these four methods, only 68.8% of the samples stored in an uncontrolled environment for several months were in the recommended mc range. After storage at environmental conditions of 70 ±1ºF and 65% ± 2% RH for 15 days or more in this study, 90.1% of the samples were within the recommended range. After drying the samples to zero mc and reconditioning them, 94.7% were within the recommended range. The strength of fiber samples averaged 28.0 g/tex after conditioning while mc (oven) averaged 6.9%. After drying and reconditioning, strength averaged 27.0 g/tex while mc (oven) averaged 6.6%. Thus, drying and the associated reduction in mc reduced the strength by 1 g/tex on average. The fiber length averaged 1.083 in. and mc averaged 6.9%. When the samples were dried and reconditioned, the length values averaged 1.067 in. while mc averaged 6.6%. Thus, drying reduced the measured length by 0.016 in. After rigorous drying, the samples did not equilibrate at the same mc as before drying and the change in length averaged 0.011 in. In summary, this study confirmed that all cottons do not equilibrate at the same mc when exposed to the same environmental conditions, regardless of measurement method. However, drying the cotton to zero mc and then reconditioning it reduced the mc hysteresis effect from 0.63% to 0.11% or 83% suggesting that the mc of samples would be more uniform using this procedure. Conditioning the cotton fiber decreases the expected mc variability of samples. The minimum and maximum mc values can be decreased either by conditioning or by drying and then conditioning. Drying the cotton to near zero mc reduces mc hysteresis. |
