Effects of Heat-Drying on the Physical and Chemical Properties of Cottons

The poor spinnability of some lots of gin-dried cotton has been attributed to over heating of the seed cotton. To determine what changes in the lint might be responsible, two series of gin-dried cottons and one series that was flash-heated in the laboratory were studied. Appropriate physical and chemical properties of the lint were measured, such as fiber length distribution, single-fiber and fiber-bundle strength and elongation, moisture regain, nepping potential, fiber friction, microscopical swelling, alkali swelling, wet tability, fluorescence, copper number, carboxyl content, pH, infrared spectra, and wax properties. Limited spinning and weaving tests allowed yarn and fabric properties to be measured. Nearly all tests showed no evidence of radical permanent changes in lint properties. The one significant finding was an altered fiber length distribution in some heated lots such that the proportion of shorter fibers was increased while the percentage of long fibers was slightly decreased. This change appeared to be correlated with poorer yarn appearance and uniformity, a slight reduction in yarn and fabric strength, and poorer resistance to flex-abrasion. A blend of unheated lint with enough short (cut) fibers to give a fiber-length distribution approximately the same as that of a gin-overheated lot produced yarns and fabric with properties in close agreement with the overheated lot whose fiber-length distribution was approximated by the blending. Laboratory tests showed that fiber strength was lower when tested immediately after heating—that is, when the moisture regain was temporarily greatly reduced. From this finding it is deduced that the change in length distribution is the result of excessive fiber breakage when lint is subjected to mechanical agitation at too low a moisture content.