Natural colorant from the bark of Macaranga peltata: kinetic and adsorption studies on silk

The colour component from the bark of Macaranga peltata has been extracted and, using spectral techniques, the main colouring ingredient has been identified as ellagic acid. The dyeing properties of the extract on silk have been studied. The colour coordinates of the dyed samples were found to be in the yellow–red quadrant of the colour space diagram and the dyed samples exhibited acceptable fastness properties. The effect of temperature and dye concentration on the rate of dyeing has been studied. Adsorption studies revealed that the process fits well with the Langmuir isotherm model. The thermodynamic parameters of the dyeing process have been evaluated using an Arrhenius plot. The experimental results revealed that the adsorption was exothermic and spontaneous in nature, and exhibited first‐order kinetics. Further, the effect of electrolyte on rate of dyeing has also been recorded. The rate of adsorption increases as the disrupting effect of the added electrolyte cation increases and follows the order: Al³⁺ > Ca²⁺ > Na⁺.