Location: Cotton Structure and Quality Research
Title: Novel studies of non-aqueous volatiles in lint Cotton moisture tests by complementary thermal methods Authors
Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 2, 2011
Publication Date: July 31, 2011
Citation: Cheuk, S.Y., Montalvo Jr, J.G., Von Hoven, T.M. 2011. Novel studies of non-aqueous volatiles in lint cotton moisture tests by complementary thermal methods. Journal of Cotton Science. 15:179-188. Interpretive Summary: Water affects cotton fiber properties, making its accurate determination important. The usual method uses a conventional oven set at 105°C (221°F) and all weight loss is attributed to water. Past research have suggested a bias associated with this method, but there is no explanation as to why this bias exists. Karl Fischer titration is the gold standard for determining water concentrations in various substances and recently being used to measure moisture levels in cotton. The weight loss as a result of oven drying is significantly greater than what is established by KFT. The objective of the three experiments in this study was to determine the cause of the additional weight loss attributed to oven drying. First, using a modified distillation apparatus, a cotton samples were heated under various dry gases at 105°C, mimicking the oven drying method. The distillates were condensed and analyzed for the presence of organic compounds. Only the cotton samples dried in air contained organic compounds. Second, preheated (105°C) dry gases were directly injected in to the cotton samples sealed in a vial. Argon did not dry the cotton samples after 3 hours. Cotton samples dried using dry air resulted in a higher dry weight indicated by KFT. Cotton samples dried under nitrogen were accomplished at 75°C and may give rise to a new method of accurate moisture determination. Third, differences in color between untreated cotton and oven dried cotton were quantified and have positive correlation to the difference between oven drying and KFT.
Technical Abstract: Moisture affects economical and rheological properties of cotton, making its accurate determination important. A significant difference in moisture contents between the current and most cited standard oven drying ASTM method (ASTM D 2495, SOD) and volumetric Karl Fischer Titration (KFT) has been established. The former weight loss, all attributed to water, is greater, but the cause is just being elucidated. The objective of the three experiments in this study was to determine the basis for the greater weight loss by SOD. First, various gases (dry air, N2, and Ar) were used to dry 50 g of two commercial cottons in a distillation setup. Distillates were analyzed for total organic carbon content and glassware residue was collected. Organic compounds and a significant amount of residue were found from cotton samples dried in air. The second experiment used the same gases plus helium, directly injected into vials containing cotton samples at 105°C. Argon did not dry the cotton samples after 3 h. Within an hour, drying cotton in dry air resulted in a higher dry weight suggesting oxidation of the cotton samples. For the third experiment, colorimetry data on oven dried cotton at 105°C and 150°C also implied the SOD method oxidizes the cotton samples. Moisture analysis by near-infrared spectroscopy (absorbance at 1930-1940 nm) confirmed drying in N2 could be done at a lower temperature (75°C, dubbed Low Temperature Distillation, LTD) than stated in ASTM D 2495. Comparative studies between LTD and KFT resulted in mean differences of 0.1% actual moisture content.