Part II: Centrifuge Studies

Abstract

In an effort to develop a simple and rapid means of measuring swelling capacities in water of cotton and other fibers in mass, the centrifuge technique has been subjected to a rather extensive study. In this technique the swelling capacity appears as a function of the moisture retention after swelling and centrifuging. Many previous workers have employed the centrifuge empirically for the removal of external, nonswelling water from fibers, but under conditions which have varied greatly as to time and intensity of centrifuging. In the present work, the complication of dealing with the two variables of time and speed of centrifuging simultaneously has been circumvented by noting that straight lines (to a high degree of approximation) were obtained when the moisture regains of the sample were plotted against the squares of the rotational speeds. The intercept of these straight lines on the moisture regain axis was characteristic for a given fiber in a given physical form. The intercept values were shown to be the same and reproducible for any selected centrifuging time of 20 min. or more, provided the minimum acceleration was above 3,200 g. It was found that the zero-speed intercepts on the moisture regain axis, while highly re producible, did not represent true swelling capacities. That the intercept values were too large was shown by the sizable intercepts obtained with glass fibers, which obviously are incapable of swelling. It was found that the excess moisture retentions could be reduced considerably in samples "oriented" so that the axis of the yarns or cords lay parallel to the direction of centrifugal force. Still further reductions occurred on cutting such "oriented" samples after centrifuging and determining the moisture regains of the cut lengths nearest the centrifuge axis. Although it was not found possible to obtain true swelling capacities with the centrifuge, it appears that the technique could be very useful for detecting and measuring differences in water-holding capacity brought about by chemical treatment. A quantitative theory of the behavior of the fiber-water system in the centrifuge was developed, based on simple capillary considerations.