Application of Oxidation and Copigmentation of Anthocyanins from Purple Sweet Potato to Silk Colouration

Abstract

The new silk dyeing methods by utilising oxidation and copigmentation of anthocyanins were researched and compared with metal mordanting dyeing. The used colourant was purple sweet potato pigment (PSPP) and its main components were assumed to contain cyanidin and/or peonidin 3-sophoroside-5-glucosides. PSPP dyes silk fabrics purple and the post-treatment changes the colour. The dyeing method were designed two step treatment (post-treatment dyeing). First is dyeing process with PSPP and second is reaction process by using an appropriate material which are Al(III), Cu(II), Fe(II) compound for the metal mordanting dyeing, sodium periodate (NaIO₄) for the oxidation dyeing, and polyphenol for the copigmentation dyeing, respectively. The colour of the silk dyed with PSPP is bluish purple for the mordanting dyeing with Al(III) or Cu(II), purplish black for the mordanting dyeing with Fe(II), brown for the oxidation dyeing. The copigmentation dyeing gives deeper purple than the PSPP only dyeing. Their dyeability dependence on the pH of PSPP solution was examined at pH = 2.9 ~ 9.1. The PSPP only dyeing and the copigmentation dyeing gives deeper purple at pH = 4.5 ~ 6.9 and the dyeability of the copigmentation dyeing is higher whole of pH. In the mordanting dyeing with Fe(II), the resulting colour is changed from purplish black to blueish black at pH = 2.9 ~ 7.0, and in the oxidation dyeing that is turned from brown to purplish brown at pH = 2.9 ~ 7.0.