INDIGOFERA TINCTORIA (BLUE)
Indigo ( indigotin, ~2. 2 ' - biindoline-3,3'dione) is one of the oldest colouring agents known, having been found in the wrappings of Egyptian mummies. Its natural sources are 'dyer's woad' (lsatis tinetoria), a plant indigenous to Europe, and the indigo-plant (lndigofera tinctoria or sumatrana), native to India and Java. Immediately after harvesting, the leaves and stalk of the plant are steeped in water. Fermentation sets in and indican (2) is hydrolysed to gluco e and indoxyl (3). The resulting aqueou olution is decanted and aerated to oxidize indoxyl to indigo.
Conversion of indigo precursor into indigo
Excavation in the Indus valley indicates that indigo dye was used in India since ancient times. The association of indigo with India is reflected in the Greek word for the dye, indikón (coming from India). The Romans Latinised the term to indicum, which passed into Italian dialect and eventually into English as the word ‘indigo’. The dye was also known to ancient civilisations in Mesopotamia, Egypt, Greece, Rome, Britain, Peru, Iran and Africa. Indigo was also the foundation of centuries old textile traditions throughout West Africa (Kriger and Connah, 2006). Thus indigo is one of the oldest dyes used by mankind.
The traditional reducing agent used is sodium dithionite (Na2S2O4) because of its effective reduction for indigo dyes. It is also called sodium hydrosulphite or hydrose. Typically, the amount of Na2S2O4 that is industrially used in the reduction reaction of indigo dyeing is more than the stoichiometric amount, resulting in a large amount of by-products from the process e.g. sulfite (SO32-) and sulfate (SO42-) ions as shown in below Equation.
These ions can cause ecological problems, for example, SO32- can be easily oxidized to SO42-and the high concentration of SO42- can cause corrosion in concrete pipes.
Researchers highlight the use of copperas method was followed by the zinc–lime method for indigo reduction and this is metal based chemical technique. These methods were not satisfactory due to heavy precipitates of ferrous and zinc hydroxide. Also highlighted the use of eco-friendly reducing agents such as Alpha-hydroxy ketones (more expensive product), Gulcose (need high temperature) etc. Hence, search of NATURAL REDUCING AGENT & NATURAL ALKALI is Inevitable. Michel’s technique, which is based on the traditional indigo vats of Morocco, India and Provence, relies on the chemical reactions between a mineral alkali and a natural reducing agent to remove excess oxygen (a chemical process called reduction) , which liberates the indigo dye molecule, allowing it to attach to fibers and bond. These natural reducing agents include dried and fresh fruits, minerals, and flavanoids.
Keeping all these in mind, with continuous R&D, we were able to find new solution for the reduction of natural indigo dyes using natural reducing agent (different from all other researchers & dyers) and also eco-friendly alkali which was never tired before for the indigo dye reduction purpose.