Accuracy of alternate oven drying procedures

Authors: Funk, Paul; Hardin Iv, Robert; Terrazas, Albert; Armijo, Carlos; Whitelock, Derek; Pelletier, Mathew; Wanjura, John; Holt, Gregory; Delhom, Christopher; Yeater, Kathleen

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/4/2018
Publication Date: 5/31/2018
Citation: Funk, P.A., Hardin Iv, R.G., Terrazas, A.A., Armijo, C.B., Whitelock, D.P., Pelletier, M.G., Wanjura, J.D., Holt, G.A., Delhom, C.D., Yeater, K.M. 2018. Accuracy of alternate oven drying procedures. National Cotton Council Beltwide Cotton Conference. p. 909-916. Available: https://www.cotton.org/beltwide/index-printable.cfm?page=proceedings

Interpretive Summary: The four ARS laboratories that perform various types of post-harvest research cooperated to re-evaluate moisture content determination procedures that were developed in the 1960's. The introduction of electronic balances, plastic food storage bags with integral zipper closures, express air freight package shipping, and high-capacity ovens has changed some aspects of the gravimetric methods we follow, and each team currently practices slightly different procedures. These differing procedures were compared, and the potential differences in results are presented. Weighing samples outside of high-capacity ovens makes no difference when determining change in moisture content (for example, before and after a drying system), but it results in an apparent moisture content that is half of one percent higher than the value determined by weighing samples inside of the drying oven. We also quantified the influence of sample density, trash content, excess drying time, and variations in sample storage and handling. These effects were less, and storage and handling differences were negligible.

Technical Abstract: Cotton post-harvest processing research frequently requires moisture content determination for seed cotton, cotton seed, and cotton lint. Standard procedures as documented in 1972 and as currently practiced were analyzed to estimate measurement uncertainty. Understanding the source and magnitude of errors will aid in increasing precision and interpreting results. Four types of seed cotton (with from 9.4 to 36.8% foreign matter) and one variety of lint were stored for > 30 days in a controlled environment (21 C, 65% RH) and thoroughly blended to reach uniform moisture content. Drying baskets (652 cc) were loaded, in random order, with 25, 35, 50, 71 and 100 grams of material; wet weights were determined in the controlled environment. Additional samples were placed in plastic zipper bags and sent by air freight or stored on-site. Replicated sets of seed cotton and lint samples were weighed inside a drying oven, then outside of it while still hot. Some samples were dried for twice the recommended time. Sample location in the ovens was tracked. Weighing hot dry samples outside of the drying oven increased apparent moisture content approximately half of one percent. Smaller differences in apparent moisture content were found when halving or doubling the amount of material in drying baskets, or doubling the drying time. Foreign matter had a minor influence on apparent moisture content. Storage for three days and shipping by airfreight in plastic zipper bags did not measurably change the apparent moisture content. Sample location within the drying oven made no difference.