Moisture Gradients in Centrifuged Samples

Abstract

in their article &dquo;Swelling Capacities of Fibers in Water: Part II: Centrifuge Studies&dquo; [9] described an interesting new freezing technique for measuring moisture gradients.They also discussed some of the data given in a recent paper of ours [7]. On the basis of this discussion they arrived at some deductions which call for comment. The theoretical treatment of Welo et al.has points of similarity with ours. It differs principally in considering the capillary water among fibers to be present as &dquo;aggregates,&dquo; the volume of which is proportional to the cube of the linear dimensions of the air-water-fiber line at which surface tension acts. This consideration, among others, leads to two deductions which differ from ours. It introduces a two-thirds exponential into the effects of the centrifugal acceleration and, more important, it eliminates any consideration of a length factor independent of the dimensions of the air-water-fiber line which supports the capillary water. In our treatment we considered this independent length factor, which was effectively the dimension of the sample of fibers in the direction of the centrifugal acceleration. Our treatment starts from the assumption that in assemblies of hydrophilic fibers there are continuous water columns throughout. The basis for this assumption is well established. The earliest reference to it was made by Socrates in Plato's Symposium [3] . It is a traditional method of siphoning and filtering liquids from vessel to vessel [2]. An ordinary cotton cloth left hanging over the side of a bucket of water demonstrates the presence .of continuous columns of water in the cloth; whether the cloth is crumpled or straight, after a short time the contents of the bucket are on the floor. In a rerent paper [6] it was shown that suction forces are capable of maintaining continuous columns of water even when opposed by forces equivalent to very large centrifugal fields. There is an elementary physics experiment which shows that capillary rise is independent of the straightness or crookedness of the capillary in the direction of the gravitational field, as shown in Figure 1. It is thus irrelevant whether the fibers, which have capillary channels between them, are convoluted or straight. The only important dimensions are: (1 ) the effective length of the air-water

Contribution of Swelling to Water-Resistant Cotton Fabrics

“…The high values have not been fully explained but are comparable with examples of other high values quoted in one of the original publications [ 1, p. 53].. The chance that the yarns and fabrics of fine, immature cotton held more water in their capillary systems in the centrifuge tests and that it might be mistaken for water of swelling is ruled out by the method of extrapolation used [8].…”

“…The centrifuge was used in the manner described by Welo and his associates ( 12 and Preston [8 ] for the estimation of the weight of the water of swelling [ 1 ]. This water, as regain retained by the dry cotton, is considered to be additive as volume to the volume of cotton that corresponds with its density in water, 1.61 ( 5, p. 95 1.…”

A- Preliminary Report on Fully Acetylated Cotton

“…This moisture content is slightly below that of solvent-spun triacetate and suggests the possibility of quick drying characteristics. Also, comparative values of water retention on centrifuging, extrapolated to infinite speed by the methods of ~'Velo [ 15 1 and Pre:,to11 and Bimkar [12). are 30, 8.4, and 7.c1': for typical untreated cotton, solvent-spun triacetate, and F.B cotton stock, respectively.…”

Application of the Specific Gravity Gradient Column to the Quantitative Determination of Additives in a Base Material

“…Preston and Nimkar [5] have suggested the use of hollow glass floats for this purpose. In special instances, refractive index determinations can also be used.…”

“…Columns have been used by Boyer, Spencer, and Wiley [1] to follow polymerization and crystallization in synthetic polymers, and by Tessler, Woodberry, and Mark [6] to examine influences of spinning variables on synthetic fibers and to follow differential digestion of cellulose. Preston and Nimkar [5], who have shown the value of the method in identifying natural and synthetic fibers in mixtures, have also extended the inherent ability of the columns to provide precise data even for small particles by viewing short lengths of individual fibers through polarizing screens.…”