Phytochemical profiling, optimization of extraction and application of natural dyes from selected indigenous plants in Uganda

Abstract

Globally, textile dyeing with natural dyes (NatD) reduced tremendously with the introduction of synthetic dyes in the mid 19th Century. Later studies reported that the use of synthetic dyes is not eco-safe and cause human health problems. This shifted researchers’ attentions on NatD as alternatives. In Uganda, many dye-yielding indeginous plants have been identified but facts about the nature of these dyes and methods for their extractions and applications on fabrics is still limited. In this study, the phytoconstituents of dyes from selected plants were determined, their extraction and application on cotton and silk were optimized. Four dye-yielding plant species identified from preious studies were selected namely; Albizia coriaria, Vitellaria paradoxa, Morinda lucida and Haranguna madagascariensis. Phytochemical profiles were determined using chromatography, UV-Vis and FTIR spectroscopy. UV-Vis spectrometry was used in a method that was developed for fast quantification of dyes from plant extracts. Variables for extraction of dyes and their application on cotton and silk fabrics were optimized. Adsorption-kinetic of fabrics mordant dyeing was studied. Dyestuffs from A. coriaria and V. paradoxa constitute of gallotannins and proanthocynidins respectively. Flavonoids and traces of hydrolyzable tannins and anthraquinones constitute dyes from M. lucida and H. madagascariensis plants. The new method was validated and successfully used for quantification of dyes from plant samples. Appreciable dye extraction yield (10 % w/w dry basis) and acceptable filterability was achieved by use of dilute sodium bicarbonate solutions (0.65 to 0.8 % w/w ) and by the optimized sample particle sizes (0.5 to 0.7 mm), material to liquor ratios (M: L) of (1:40 to 1:45), and extraction times (30 to 40 mins). Mordants used improved on fastness to between fairly good (3) and excellent (5) and mordanting method is unique to a plant. Stronger and more brilliant shades in terms of k/s values were registered on silk. Simultaneous mordanting (SM) and post mordanting (PM) dyeing using M. lucida dye extract followed pseudo second order (PSO) reaction model (chemisorption) and mordanting followed pseudo first order (PFO) model (physisorption). Greater dye adsorption was recorded in PM method. Dyeing followed Langmuir and Freundlich isotherm models therefore there is homogenous fibre surface cover with monolayers of dye. From PSO model, dyeing speed is improved by increasing the dye concentrations. More studies should be conducted on methods of preservation of extracted dyes. Additionally, more investigation is needed on the use of the natural dyes for cosmetics, food, leather and drugs.