Polydopamine-dyed eri silk yarn for the improvement of wash and light fastness properties

Abstract

In this research, eri silk yarn was dyed with polydopamine (PDA) formed in situ by oxidation of a dopamine (DA) solution under alkaline condition at pH 8.5 in the presence of oxygen. Eri silk yarn was immersed in different initial concentrations of DA solution (0.010 – 5.00 mg mL−1) for 24 h, after which the yarn changed to a black/brown color. This indicated that PDA could adhere on the surface of eri silk yarn via Schiff base reactions and/or Michael-type additions. The surface morphologies of PDA-dyed silk yarn in different initial concentrations of DA solution were characterized using a field emission scanning electron microscope (FE-SEM) and Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopic analysis. It was found that the surface of eri silk yarn became obviously rough, which indicated that PDA was successfully dyed on the surface of eri silk yarn. In addition, all dyed eri silk yarn exhibited a shade of brownish to black with different CIE L*, a*, and b* values. In addition, the color fastness to light and washing of the PDA-dyed eri silk yarn samples using 1.00 – 5.00 mg mL−1 DA solutions were found to be at very good rating levels of 6 and 4-5, respectively. Therefore, PDA could act as both a dye for eri silk itself and as a photo-protective agent.