Electrodialytic Estimation of Ash and of Acidic and Basic Groups in Textile Fibres

Abstract

Considerable practical interest attaches to the ash of textile fibres. It is well known, for example, that the electrical properties of textiles such as cotton, silk, and wool depend to a considerable extent upon the nature and amount of inorganic substances in the fibres. In addition, this ash content influences the uptake of mois ture and dyestuffs, as well as the ability of the fibre to combine with certain softening or finishing agents.

The method of combustion usually employed for the estimation of the ash yields results which acquire significance in terms of equivalents only when an estimate of the composition of the ash can be made. Since the ash may contain substances, such as sulfate in the case of wool, which are not in the unburned fibre, but which are formed during the combustion process, its composition is un certain at best.

It is shown by recent work of the research associates of the Textile Foundation at the National Bureau of Standards that the hydrogen-ion equivalence of the cationic ash of fibres (the total content of the cations of bases whether free, or combined with acids, or with the acid groups of the fibres) may be obtained di rectly, without ignition, by existing electrodialytic procedures which hace been hitherto applied principally to biological solutions. Only simple and inexpensive equipment is required. The content of any given anion in the sample may be similarly determined. By dupli cating the procedure on a larger scale, the method has been used to obtain samples of fibrous materials of very low ash content. A simple extension of the method which permits the quantitative de termination of the acidic and basic groups in the material consists in combining them with suitable tightly bound cations or anions which are subsequently estimated by the electrodialytic procedure.

Examples are given of the application of the method to de waxed and to depectinized cotton. In both cases the results are shown to correspond with the capacity of the fibres to bind acid. Examples are also given of ash determinations on wool fibres and on samples of wool cloth at several stages in processing subsequent to the carbonizing process. A comparison of the results with the ash obtained gravimetrically on similar samples, after combustion, permits the estimation of the average equivalent weight of the constituents of the ash, and aids in their identification. It is shown that the largest part of the ash of untreated wool, as ob tained by combustion, consists of sulfates. Since sulfates are not present to an appreciable extent in washed (defatted) root-wool fibres, the presence of this anion in the ash of such fibres must be attributed to the oxidation of the sulfur of the wool during com bustion. The much larger ash remaining after carbonizing, neu tralizing, and rinsing is also in the form of sulfates, but at these stages most of the sulfate has been contributed by the sulfuric acid in the carbinizing process.