Sonic and Ultrasonic Irradiation of Cotton Fibers

Abstract

An investigation was made of the effects of exposure to sonic and ultrasonic energy on the physical and chemical properties of Deltapine and Acala 4-42 cotton irradiated in partially degassed water. From the results of more than 1300 different tests, it appears that some of the cotton fibers properties can be modified. However, the main changes observed to date appear to be of a physical and not of a chemical nature. Cavitation, specially vaporous cavitation, has been singled out as the main factor responsible for fibers modification. Frequency and acoustic energy density in the liquid phase play a key role only because they indirectly control the intensity of cavitation phenomena. The importance of sample size for uniform irradiation has also been stressed. Irradia tion around 30 kcps with an energy density of 20 watts/liter and a cavitation activity of 220 cavits lead to strong fiber surface modifications and fibers entanglement after a few hours of insonation. Evidence of severe fibrillation has been established not only by optical and electron microscopic techniques but also through alkali swelling tests and Micronaire readings.Generally speaking the Deltapine variety of cotton grown under conditions of natural rainfall seems slightly more susceptible to cavitation effects than Acala 4-42 grown under irrigated conditions. It has also been clearly established that contrary to nonirradiated fibers, ultrasonically treated cotton enables to make paper sheets of acceptable tensile strength. From both the theoretical and experimental viewpoint a rather promising avenue seems to have been opened for future large scale ultrasonic fibrillating of fibers suspension.On the negative side we must mention that due to absorption phenomena high-power sonic irradiation does not seem a very promising tool for trash removal from raw cotton.