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Cotton and wool fabrics have been dyed in the absence of mordants with annatto and ultrafiltrated annatto powder. Τhe optimum dyeing conditions were determined as far as the quantity of salt and dyebath pH are concerned. The dyeing properties of annatto and ultrafiltrated annatto were studied by monitoring the dye uptake in various time intervals and temperatures of dyeing. The adsorption isotherms for both annatto and ultrafiltrated annatto were studied. It was found that adsorption of annatto on cotton follows a BET-type adsorption isotherm indicating a multilayer formation of molecules onto cotton, whereas the adsorption of ultrafiltrated annatto follows a Freundlich-type monolayer adsorption. Adsorption of both annatto and ultrafiltrated annatto on cotton occurs through the formation of Van der Waals forces between annatto molecules and cotton substrate. The adsorption on wool of both annatto and ultrafiltrated annatto follows a Freudlich-type adsorption isotherm indicating a monolayer formation occurring between the positively-charged wool substrate and the negatively-charged annatto molecules. The dyeing behavior of natural annatto resembles that of the synthetic direct and acid dyes commonly applied for dyeing cotton and wool. Thus, annatto and ultrafiltrated annatto can successfully replace the synthetic yellow dye component in the dyeing of cotton and wool fibers.

Study of the Dyeing Properties of Annatto and Ultrafiltrated Annatto as Colourants for Natural Fibres