Textile Research Journal

An apparatus has been constructed to rub filaments together under controlled mechanical and ambient conditions and to measure the charge remaining after separa tion. The apparatus is similar to that of Hersh and Montgomery, with refinements to ohtain better control of mechanical variables and to allow variation of ambient pressure. A photomultiplier has been added near the filaments to detect the incidence of electrical breakdown of the atmosphere. Many of Hersh's findings for 45°-45° rubs have been confirmed, specifically those on reproducibility and triboelectric series. On the other hand, some findings have not been substantiated when the range of vari ahles is extended. For nylon rubbed on polyethylene. the charge q shows a square-root dependence on the normal force F, in place of the linear dependence found by Hersh; the charge shows an inverse proportionality with diameter d, in contrast with the inde pendence noted by Hersh. For tantalum rubbed on nylon. the charge is found to depend on a combination of velocity v. conductivity σ, and presumably dielectric con stant . together with a characteristic distance l to be determined empirically. If the charge dependence on length of rub L is taken to he the proportionality found by Hersh. the combined relation is suggested, where the sign and the magnitude of c are in principle determined by the details of the band structure, but in practice are fixed experimentally. No detailed theoretical picture has been obtained to justify the rest of the expression, and it must be considered at present as an empirical relation whose generality and basis remain to be established.

The contraction of nylon yarn resulting from the sorption of HCl has been studied under various conditions. Tension applied to the yarn during the sorption of the gas reduces the contraction in a way that can be explained by the theory of reaction rates. It is shown that the uptake of HCl, however, is not affected noticeably by tensioning the yarn. The contraction appears to be largely dependent on the rate of diffusion of the HCl. A coefficient of diffusion has been calculated for this rate at 22° C. The effect of drawing has also been investigated, and it was found that the greater the draw ratio, the greater the contraction, but the previous history of the yarn is very important in this respect. Twisted nylon filament has also been observed to untwist during HCl sorption. This untwisting also appears to be a rate process.

Force-extension data for a large number of wool fibers of various types have been analyzed in detail by statistical methods in order to determine the effects of fiber crimp and cross-sectional area on mechanical behavior. During the initial stages of crimp removal, the extensional behavior is controlled by fiber bending; during later stages of crimp removal, this behavior is controlled by both fiber bending and extension. Finally, as the crimp removal approaches completion, the behavior is controlled by the exten sional modulus of the fiber. This modulus is perturbed by differential bending strains associated with crimp removal which act to decrease the modulus below that for an un crimped fiber. Generally good correlation has been found between visual estimates of crimp and mechanical estimates based on analysis of the low-extension region of the fotce-extension curve. The methods of crimp evaluation used indicate that within a group of fibers taken from the same Rambouillet sheep the crimp level increases with increasing fiber diameter, and among fibers taken from sheep of different breeds the crimp level decreases with increasing fiber diameter. It is also observed that the rupture properties, breaking stress and breaking extension. generally increase with increasing fiber diameter.

The extent to which wool may be iodinated with alcoholic solutions of iodine at 22.2°C. has been examined as a function of the size of the alcohol molecule. With a solution of iodine in methanol or ethanol, the limiting amount of combined iodine is approximately what would be expected if the whole of the tyrosine were converted into 3 : 5-di-iodotyro sine. When. however, a solution of iodine in n-propanol is used, the reaction proceeds more slowly and comes to an end when the amount of combined iodine is less than half the theoretical value. This result, and the fact that solutions of iodine in n-butanol and n-pentanol give so small an extent of iodination as to suggest that reaction is restricted to the surface of the fibers, confirm an earlier deduction from the elastic properties of wool fibers in alcohols of increasing molecular weight [6] that the fine structure of wool is inaccessible to molecules larger than those of n-propanol.

A basic understanding of any textile dyeing process is concerned with those factors , which influence the distribution of dye molecules between an external phase, primarily aqueous, and the fiber phase. An adequate description of the factors affecting the dyeing of acetate fibers with the disperse dye class must include:

1. a detailed description of the dyes in terms of their chemical and physical prop erties and their behavior in the aqueous and fiber phases,

2. the influence of the degree of acetylation of the cellulose upon the dyeing rate and affinity for the disperse dyes,

3. the relationship of specific dye structure tp dyeability and colorfastness on secondary and tricellulose acetate, and

4. a discussion of the mechanism of accelerant or carrier dyeing as applied to cel- . lulose triacetate.

White the data presented do not rigorously support either the solution dyeing or the site dyeing hypothesis, sufficient empirical observations are presented which will increase the control and economy of dyeing with the disperse dyes.

In package dyeing with vat dyes by the pigment method, the finely dispersed pig ment is circulated through the package and exhausts on the fiber in the oxidized state. The degree of pigmentation varies greatly from one part of the package to another, resulting in initial unlevelness of the package. The degree of levelness of the final dyeing will depend on the amount of migration that takes place after the pigment is reduced to the leuco vat dye. Dyes having leucos with high affinity for the fiber, as is shown by measurements of the free energy of dyeing, migrate less and produce less level package dyeings.

Reducing the particle size of the pigment sometimes gives more level pigmentation at the beginning, but this is not necessarily reflected in more level final dyeings. The vat acid process also leads to more uniform pigmentation, but still does not give level dyeings in every case; it is also quite inconvenient. Retarding agents promote levelness by tying up leuco and slowing the strike, but are uneconomical because much dye is left in the bath. Solvents slow the rate of dyeing and promote levelness, but also interfere with exhaustion and are very expensive. A higher temperature (212°-220° F.) during the pigmentation and reduction shifts the equilibrium in favor of the dye bath and promotes levelness; the temperature can then be lowered to put the remaining dye on the fiber. However, pressure machines are necessary; also. many dyes are unstable at the higher temperatures.

A migration test for vat dyes, whereby a dyed and undyed skein are placed in a caustic-hydro solution and allowed to reach equilibrium, has been found to give a good indication of the dye's leveling ability.

The physico-chemical approach to the understanding and elucidation of a phe nomenon proceeds in three stages.

The first stage consists of the collection of reasonably accurate quantitative data. In the second stage qualitative or rough quantitative explanations of the observed trends are put forward,, and in the final stage the whole phenomenon is made amenable to precise treatment in mathematical terms. The development of dyeing theory passed fairly rapidly through the first and second stages during the 1930's and is now struggling to enter the third stage.