Polydopamine-coated silk yarn for improving the light fastness of natural dyes

One of the problems occasionally associated with the use of natural dyes in the dyeing of silk is the susceptibility of the dyed yarn to fading in light. While a number of approaches have been used to address this problem, the use of polydopamine (PDA), a known agent with photo-protective properties, has not been assessed previously. In this study, silk was pretreated with nano-particulate PDA formed in situ by oxidation of a dopamine solution, then dyed with lac dye or annatto dye as model natural dyes. Photofading rates were significantly reduced in the case of annatto-dyed, PDA-coated silk relative to uncoated silk, while wash fastness was unaffected and remained only moderately good. In contrast, no significant change was seen in photofading rates with treated or untreated lac-dyed silk, and wash fastness was also unaffected. The PDA did not adversely affect resultant colour values if the concentration of the dopamine precursor was kept low. When this was done, acceptable colours were obtained in the dyed silk. Further investigation is warranted of PDA as a photofading protectant and mordant with other natural dyes on silk and other fibres.