Most. Halima Khatun et al. / Rajshahi University Journal of Environmental Science, 6, 111-117, 2017 111 OPTIMIZATION OF ALKALINE EXTRACTION OF NATURAL DYE FROM Acacia catechu AND ITS DYEING ON SILK FABRICS Most. Halima Khatun 1 , Ayesha Akhter 2 , H. Jahan Kadri 2 and M. G. Mostafa 1* 1 Institute of Environmental Science, University of Rajshahi, Rajshahi 6205, Bangladesh 2 Bangladesh Council of Scientific and Industrial Research (BCSIR) Laboratories, Rajshahi 6206, Bangladesh Abstract This study aimed at the potential application of ‘Acacia catechu’ a natural dye as a brown colorant for natural silk. The natural dye was extracted from the raw Khair (cutch) by aqueous, alkaline, acidic, and alcoholic medium using the standard procedure. The alkaline extraction condition of the natural dye from the raw Khair was optimized. The dyeing was carried out with and without the use of mordants and the colorfastness properties of the fabrics were determined. The optimized alkaline extraction conditions for pH and temperature were found to be 12 and 90ºC, respectively. The UV-VIS Spectrophotometric analysis result confirmed the presence of catechin compound in Khair dye. The results of the colorfastness properties of the dyed silk fabrics using different mordants were found to be fair to good. Keywords: Acacia catechu, Absorbance, Dyeing, Mordant, Colorfastness. 1. Introduction Natural dyes are gaining popularity due to its lower environmental impacts and simple dye processing method. Local plants are a potential source of natural dyes. Dyes derived from natural materials such as plant leaves, roots, bark, insect secretions, and minerals were the only dyes available for the coloring of textiles until the discovery of the first synthetic dye in 1856 (Druding, 1982). The advent of synthetic dyes caused a rapid decline in the use of natural dyes, which was completely replaced by the former within a century. However, environmental issues in the production and application of synthetic dyes revived consumer interest in natural dyes during the last few decades of the twentieth century. Several synthetic colorants have been banned because they cause allergy-like symptoms or are carcinogens (Ratna and Padhi 2012; Melgoza et al., 2004; Kulkarni et al., 2011). Due to harmful and toxic effects of the dyeing effluent, researchers have diverted their interest towards in dyeing. Natural colorants are non-carcinogenic, non-toxic and biodegradable in nature (Banchero, 2012; Adeel et al., 2013; Padthy and Rathy 1990; Eom et al., 2001). Natural dyes are mostly non-substantive and usually applied to textiles with the help of mordants. Mordants are metal salts which produce an affinity between the fabric and the dye (Vankar et al., 2009; Samanta and Agarwal 2009). Potash alum, ferrous sulphate, copper sulfate, stannous chloride etc. are the commonly used mordants. Color fastness is the resistance of a material to change any of its color characteristics or extent of transfer of its colorants to adjacent white materials in touch. Generally, light fastness, wash fastness, rub fastness (Dry and Wet) and perspiration fastness are considered for textile fibers. Acacia catechu (A. catechu) is a medium-sized, deciduous, thorny tree which grows up to 15 meters tall. It is a native of Central and East Africa, Southern Asia, Bhutan, Thailand, China, India, Myanmar, Nepal and Pakistan (Vankar, 2002). Acacia catechu grows in abundance in the northern part of Bangladesh, especially in Rajshahi district. Main chemical constituents of Acacia catechu from the heartwood are catechin and epicatechin (Lakshmi et al., 2011). The powdered heartwood of A. catechu contains tannin phyto-constituents. Catechin is a type of natural phenol and an antioxidant. It is a secondary metabolite of the plant that belongs to the chemical family of flavonoids. It is used for dyeing of fabrics with different mordants. It yields brown, Corresponding author’s address: mgmostafa@ru.ac.bd