Probing Bias Reduction to Improve Comparability of Lint Cotton Water and Moisture Contents at Moisture Equilibrium

Abstract

The Karl Fischer Titration (KFT) standard test method is specific for water in lint cotton and designed for samples conditioned to moisture equilibrium. There is no standard method for equilibrium moisture content by oven drying (OD). The KFT technique is specific for water; in the OD procedure the weight of the loss volatiles at 105 to 110°C is the measure of moisture content, all of which is incorrectly attributed to water. The results from OD we call "moisture content" and from KFT "water content". Different OD procedures, with dissimilar sample conditioning systems, drying ovens, size, and number of weighing bottles in the oven, currently are used to make measurements. Yet, no comprehensive study of the multiple causes of the difference between equilibrium water and moisture content has been reported. To assist with explaining the observed disparity, the present effort develops a list of six potential OD biases. The origin of these biases is incomplete drying and weight change due to side reactions in opposite directions. Using a control cotton, the biases were measured at moisture equilibrium in four different OD procedures. The corrections were applied to the moisture content data from a dozen Mississippi cotton samples analyzed by the same OD methods. Method grand mean results were 7.73% water compared to moisture content before/after bias correction, respectively: 7.19/7.80, 7.50/7.80, 7.42/7.69, and 7.79/7.92. By changing OD features it was possible to suppress one bias over the other. Samples were conditioned to more stringent specifications to provide precise data to test the hypotheses in this research.