Textile Research Journal

Research on the apparent densities of cellulose fibers in different liquids gives information concerning inner fiber structure which may be useful in characterizing certain desirable prop erties of cotton fibers. The following report describes an investigation of some factors involved in evaluating density data in terms of fiber structure. The interpretation is made of some experimentally determined densities of cotton and rayon fibers in benzene and in dioctyl phthalate —two liquids differing greatly in molecular dimensions—and in mercury, a nonwetting liquid. In the last case, the "over-all density" of a fiber, defined as the average density of all material within the outer wall of the fiber, is determined by a method utilizing a mercury-pressure volumenometer.

In the case of the wetting liquids, higher densities were obtained with benzene—which has the smaller molecule; this indicates that the fibers have pore spaces which in size approach the dimensions of the molecule. When the cotton fibers are cut into short sections, about 1 mm. long, more of these pores and intrafiber channels are open to the liquid medium; a higher density is, therefore, obtained for the cut fibers than for the whole fibers. Pore-space values within the fiber are calculated and compared with values obtained by other methods. The significance of these observations in the consideration of fiber structure is discussed.

The previous paper in this series discussed the uncatalyzed autoxidation of alkali cellulose and suggested that the reaction proceeds via a chain mechanism involving transient free radicals. The present paper describes the effect of certain transition metal catalysts on the kinetics of oxygen absorption and cellulose depolymerization. It is further shown that the reaction is subject to catalysis by substances which generate free radicals and by the presence of certain other autoxidizable substances. Silver and gold compounds behave as inhibitors, as do some typical organic antioxidants. The results provide further evidence for the free-radical chain character of the reaction. Possible depolymerization processes are discussed in terms of this approach.

Native cotton and commercial viscose rayon were degraded by using a saturated solution of hydrogen chloride (about 43%) in methanol at 0° C. It was found that, on the average, 8.1 bonds in native cotton suffered methanolysis during the first 6 hrs. of the reaction, whereas in the ensuing period of 666 hrs. only 1.6 bonds became cleaved. The results indicate that the initial reaction comes to a practical standstill after about the same stage of degradation has been reached as in the mild hydrolytic scission of the same materials (D.P. ∼ 250 for cotton, and D.P. ∼ 60 for viscose rayon).

In order to gain information as to the nature of the methoxyl groups in the methanolyzed products, a study of the rate of hydrolysis of the latter was made. Evidently, if the classical concept of cellulose structure is correct—that is, if only normal methyl. glucopyranoside end groups are present—then the rate of acid hydrolysis, as measured by the increase in the reducing power, should be of the order of magnitude shown by the normal methyl glucopyranosides. On the other hand, a very fast rate of hydrolysis, which is characteristic for the open-chain dimethyl acetals of the sugars, would constitute evidence for the presence of such types of residues; hence, it would favor the new concept of cellulose structure.

The results showed that more than one-half of the material in the case of viscose rayon and about one-half in that of native cotton were hydrolyzed by 0.05N HCl at 60°C in a period of 48 hrs., which is shorter beyond all comparison than the half-life (3,450 hrs.) of methyl α-gluco pyranoside under identical conditions. These results are considered to supply the chemical proof for the presence of the acid-sensitive, open-chain glucose residues which were suggested in the new formula for cellulose.

A quantitative laboratory method for evaluating levelness of acid wool dyes is described. The procedure consists of running half of a normal yarn-dye cycle and then making additions of white yarn and dye liquor equal in amount to those in the original batch. The second half of the cycle is then run, and the yarns are removed. Reflectances of the two dyed yarns are determined on a G. E. recording spectrophotometer and a "levelness index" is calculated as the ratio of dye concentration on the yarn added at the mid-point of the cycle to that on the yarn started at the beginning of the cycle.

The technical background of the test method is outlined and the results of tests on repre sentative dyes are tabulated. It is shown that the test method has sufficient flexibility to permit examinations of the effects of dyeing variables on levelness. An example is cited showing the effect of salt concentration on levelness of Alizarine Cyanine Green CG ex. (C. I. 1078).

The example above is applied to plant production, and the levelness of 500-pound Hussong stock-dyed batches is evaluated by spectrophotometer reflectances, converted to dye concen tration, of stratified samples from the batches of stock. It is shown that the coefficient of dye concentration variation among the 8 samples from a plant batch is proportional to the laboratory "levelness index."

The "dispersion staining" method is used for observing textile fibers in colors which aid in the determination of their structure and in their identification. Fibers which are classified as striated or microscopically structureless are distinguished by this technique without the need for any special preparation of the fiber. A sample is mounted in a liquid of high dispersion which has a refractive index near that of the fiber and the fiber is identified by the resulting coloration, using an ordinary compound microscope set-up for dark-field illumination.