Cotton Quality and Fiber Properties

The increased use of drying and cleaning equipment at cotton gins has occasioned complaints from spinners that the "quality" characteristics of cottons are being lowered due to "over drying" of the seed cotton prior to ginning. The present study was undertaken to clarify the effects of overdrying on the processing characteristics of cotton and to determine any changes in fiber properties relating thereto. Three 2-bale lots of cotton were prepared from a homogeneous batch of hand-picked seed cotton by drying in three parts before ginning. The first part was passed through the driers with unheated air. For the second part the air in the first drying tower was heated to 450°F ; the air in the second tower was unheated. For the third part the air in both drying towers was heated to temperatures between 170° and 290°F. Both heated cottons were dried to 3.8% moisture in the lint, well below the recommended minimum of 5%. The cottons were evaluated by means of a small preliminary spinning trial and a full-scale processing trial. Samples taken during the trials were studied to determine the properties of the fibers and the fiber assemblies. The greatest processing difference between the cottons was in the spinning end-breakage rates, which increased as much as 21.4% due to excessive drying for the high-temperature-dried sample. The yarns showed a decrease in strength, evenness, and yarn-appearance grade for the heated cottons, with similar results for roving samples. Raw-cotton samples exhibited only minor differences in fiber properties when examined by conventional methods. Alkali- centrifuge values indicated significant fiber surface damage with heating; and there was evidence to indicate a greater crystallinity for the heated cottons. Tests for the fiber number-length distributions showed that both before and especially after processing through roving the excessively dried cottons consisted of more short and fewer long fibers than the control cotton. It is believed that the presence of many short fibers is the main cause of processing difficulties and reduced yarn quality.