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Nature has gifted us more than 500 dye-yielding plant species. Coloring agents of these plants are derived from roots, leaves, barks, trunks or fruits. All colors of rainbow are obtained from plants. Natural dyes have better bio degradability and generally have higher compatibility with the environment. They are non toxic, non-allergic to skin, non-carcinogenic, easily available and renewable. 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 and rub fastness are considered for textile fibers.
The outer skin of onion contains different phytochemicals which are responsible for giving colour, antimicrobial and antioxidant properties to the fabric. In this study, natural colourants were extracted using different solvents. The dye potential of the colourants obtained from the onion skin dye was evaluated by colouring cotton fabric. Bio mordanting of cotton fabric was done by using biopolymer before dyeing to improve the dyeabilty of cotton fabric with natural dye. L*, a*, b*, C*and H* values and k/s value was studied. Study about the different fastness tests were undertaken by using standard test methods. The chitosan mordanted cotton fabric showed higher k/s value. Good light fastness, wash fastness, rubbing fastness and perspiration fastness. From an ecological point of view, dyeing of cotton fabric with natural dye with bio mordanting may better alternative to conventional mordanting with chemicals.
Key words: Chitosan, Onion skin dye, Cotton, Dyeing, Natural dye