Sonicator dyeing of cotton fabric and chemical characterization of the colorant from Melastoma malabathricum P.S. Vankar and V. Tiwari Facility for Ecological and Analytical Testing, Indian Institute of Technology, Kanpur, India, and L.W. Singh and L. Potsangbam Department of Chemistry, Manipur University, Imphal, India Abstract Purpose – The purpose of this paper is to evaluate the dyeing potentials of Melastoma malabathricum whose fruit pulp showed high dye contents. It is an abundantly available shrub in the north eastern forests of India. Design/methodology/approach – Dye extraction was carried out by conventional heating and sonicator. The dyebility of the aqueous extract of melastoma was evaluated for dyeing cotton fabric by two methods – sonication and conventional heating. The purpose of using sonication was for betterment of dye uptake, improved dye adherence and good wash and light fastnesses. Findings – The test results showed that choosing this dyeing method produced improved results. The superiority of sonicator dyeing over conventional dyeing in terms of enhanced resource productivity and as a result, reduced wastes, makes it the established best available technique in the natural dyeing industry. Use of sonicator shows marked enhancement for cotton dyed fabric. Typical bath liquor to fabric ratio for conventional dyeing varies from 20:1 to 15:1 and for sonicator dyeing from only 12:1 to 10:1 thereby reducing specific water and energy consumption by, respectively, 30 and 50 percent. Research limitations/implications – Although natural dyeing has its limitations of fastness, we have tried to overcome this limitation by using sonicator. Practical implications – The method developed for natural dyeing of cotton fabric using sonication in conjunction with metal mordanting has shown marked improvement. Originality/value – The method developed for natural dyeing of cotton fabric using fruit pulp of Melastoma malabathricum under sonication in conjunction with metal mordanting using has shown marked improvement in terms of dye adherence and fastness properties and can thus be recommended for industrial application. Keywords Dyes, Colours technology, Cotton, Plants Paper type Research paper Introduction Melastoma malabathricum of family Melastomataceae is investigated as a source of natural dye in the present paper. Melastoma is a slender undershrub with oblong leaves and has deep purplish blue fruits. The plant grows abundantly in the foothills of Manipur but is also widely found in Sri Lanka and Southeast Asia, including the Philippines and Taiwan, to Papua New Guinea, Australia and the Pacific Islands; also Mauritius, Jamaica, and United States. Melastoma bears fruit, a berry-like capsule with numerous seeds coated with red, sweet astringent pulp (Figure 1). The plants bear the fruit in the months of May-July. Fruits were collected and extracted in water and methanol. Aqueous extract of the fruit pulp is found to be a source of good coloring agent. The fruit is known to contain anthocyanins (Janna et al., 2006) and tannins (Malek et al., 2003). We have also carried out the column chromatographic separation of the crude extract and identified the chemical composition of the colorants by FT-IR, UV-Visible, NMR and Mass spectroscopy and matched with literature values (Figure 2). Materials and methods Materials Substrate Plain weave cotton fabric {105 g/m 2 , Warp/Weft: 30/20 (per in.)} was used in this study for dyeing. Natural dyes The aqueous extract of fruit pulp of M. malabathricum was used as natural dye. Chemicals Tannic acid, alum, ferrous sulphate, stannous chloride, stannic chloride, sodium chloride, and methanol. All these chemicals were of analytical grade. Methods Extraction of natural dyes Fruit pulp was extracted by aqueous extract in sonicator as well as by conventional heating methods. Standardization of The current issue and full text archive of this journal is available at www.emeraldinsight.com/0369-9420.htm Pigment & Resin Technology 38/1 (2009) 38–42 q Emerald Group Publishing Limited [ISSN 0369-9420] [DOI 10.1108/03699420910923562] The authors express their sincere thanks to Department of Science and Technology (DST) for financial support. 38