Low-Temperature Dyeing of Silk Fabric Using Atmospheric Pressure Helium/Nitrogen Plasma

Silk fabric was plasma treated in an indigenously developed atmospheric pressure plasma reactor in the presence of helium and nitrogen (He/N-2) gaseous mixture at a discharge voltage of 5 kV and frequency of 21-23 kHz. The samples were plasma treated for 1 to 10 min with a constant nitrogen flow of 50 ml/min. They were also plasma treated in varying nitrogen flow rates in the range of 33.3 to 225 ml/min, keeping a constant helium (He) flow rate at 450 ml/min. The effects of plasma treatment time and nitrogen (N-2) gas flow rates on water wicking, physical and chemical properties of the fabric surface along with rate of dyeing were investigated in details. The formation of amine groups in the plasma treated samples helps in faster exhaustion of acid dye even at a lower temperature. It was possible to dye the plasma treated silk fabric at 40 degrees C temperature instead of 90 degrees C, as is used conventionally. Due to higher dye exhaustion, the plasma treated sample showed a deeper shade. The physical and chemical properties of the samples were analyzed using SEM, ATR-FTIR, secondary ion mass spectrometer (SIMS), and XRD. Results indicate that water took only 408 s and 309 s to travel up to a height of 6 cm in the plasma treated samples for 4 min and 10 min, respectively. This was much shorter as compared to 696 s observed in the untreated (control) sample. The effects of plasma treatment time and the amount of nitrogen (N-2) gas flow had a similar effect on water wicking. The plasma treatment time and N-2 gas flow rates showed only marginal effects on mechanical properties of silk.