PROCEDURES FOR MOISTURE ANALYTICAL TESTS USED IN COTTON GINNING RESEARCH
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Abstract. Cotton post-harvest processing research requires moisture content determination for seed cotton, cottonseed, and lint. Methods for determining moisture content have changed and are no longer consistent between laboratories. This research compared standard procedures documented in 1972 and those currently practiced for finding moisture content by oven drying, and quantified the variability. Seed cotton from four modern cultivars (ranging from 9.4% to 36.8% foreign matter), lint, and cottonseed were brought from dry conditions, blended, and then stored for more than 30 days in a controlled environment (21C, 65% RH) to reach uniform moisture content. Additionally, 150 seed cotton samples were placed in plastic zipper bags and sent by air freight to a distant location and back or stored on-site. Drying baskets (652 cm3) were loaded, in random order, with 25, 35, 50, 71, and 100 g seed cotton or 10, 14, 20, 28, and 40 g lint. Cottonseed was placed in 45 cm3 aluminum cups (10 g) or 800 cm3 aluminum baskets (50 g). Wet weights were determined in the controlled environment. After drying, replicated sets of seed cotton, lint, and cottonseed samples were weighed inside a drying oven and then outside the oven while still hot. Some samples were dried for twice the recommended duration. Sample location in the ovens was tracked. Weighing hot seed cotton samples outside the oven after drying increased apparent moisture content by approximately 0.5% due to air buoyancy; weighing lint samples outside the oven increased apparent moisture content by 1%. Smaller differences in apparent seed cotton moisture content were found when halving or doubling the amount of material in drying baskets or doubling the drying duration. Foreign matter had a minor influence on apparent moisture content. Storage for three days and shipping by air freight in plastic zipper bags did not measurably change the apparent moisture content of seed cotton. Sample location within the drying oven made no difference. Current practices are satisfactory if dry weight location is taken into consideration. Measurement uncertainty has decreased compared to 50 years ago, but the recommended minimum number of samples per treatment was increased slightly for greater statistical power. Keywords: Cotton lint, Cottonseed, Moisture content, Oven drying, Seed cotton.
