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A Study of Certain Natural Dyes I‐The Adsorption of Brazilwood and Logwood Colouring Matters by Fibres
Author(s) -
Arshid F. M.,
Desai J. N.,
Duff D. J.,
Giles C. H.,
Jain S. K.,
Macnral I. R.
Publication year - 1954
Publication title -
journal of the society of dyers and colourists
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.297
H-Index - 49
eISSN - 1478-4408
pISSN - 0037-9859
DOI - 10.1111/j.1478-4408.1954.tb02043.x
Subject(s) - adsorption , chemistry , hydrogen bond , cellulose acetate , cellulose , haematoxylin , van der waals force , wool , polymer chemistry , hydrolysis , organic chemistry , molecule , inorganic chemistry , materials science , composite material , medicine , staining , pathology
The adsorption properties of hæmatein, the colouring matter from logwood, and its leueo compound, haEmatoxylin, together with brazilein, the colouring matter from brazilwood, have been studied on several types of fibre. Brazilein and haEmatein are weak acids and are adsorbed by wool or nylon appreciably only from acid solutions, probably by hydrogen bonding between the fibre and the undissociated hæmatein or brazilein molecules, as well as by acid‐base combination with the charged amino groups in the fibre. Very high adsorption values observed at about pH 1.0 may be indicative of some hydrolytic breakdown of the fibre. In solutions less acid than about pH 7 adsorption is very low on account of the mutual repulsion between the colouring matter anions and the negatively charged fibre. HaEmatoxylin is a tetrahydric phenol and has the very unusual property, in a single substance, of appreciable substantivity for cellulose as well as for cellulose acetate, nylon, and protein fibres. A study of the apparent heat of adsorption, of the nature of the isotherms, and of the affinities leads to the conclusion that its adsorption by cellulose acetate, nylon, and wool is most probably attributable to the formation of hydrogen bonds with the fibre, those formed by nylon and wool being stronger than those formed by cellulose acetate. The adsorption by cellulose, studied by the same means, appears to be of a different nature and to be attributable to weaker forces, probably van der Waals attraction. Since hæmatoxylin, with four strong hydrogen‐bonding groups, does not seem to form hydrogen bonds with cellulose in water, it is unlikely that any dyes can do so, and their adsorption may therefore be due to physical attraction and not to hydrogen bonding. Some evidence is given that hæmatoxylin may act as a cross‐linking agent between the peptide groups in the molecular chains of proteins. Analytical methods for the colouring matters are evaluated. Refractometry was used in determining the adsorption of haEmatoxylin. A simple and effective method of packing loose fibres for adsorption tests is described.