Surface Treatment of Cotton Yarn by Underwater Capillary Electrical Discharge

An alternating current (50 Hz) capillary underwater discharge in aqueous solution of NaH₂PO₄·2H₂O is used for surface treatment of cotton yarn. The capillary discharge emits of ultraviolet radiation in the wavelength range 280–340 nm (OH band). The process of bubble generation and expansion inside the capillary results in the formation of weak shock waves. The effect on cotton yarn exposed to the discharge is quantified by a liquid wicking rate test. The treatment effect strongly depends both on the distance between plasma and cotton yarn and on the voltage. The maximum effect is observed at an applied voltage of 5.8 kV and at 1.5 mm distance to the plasma zone. Analysis of the experimental data shows that the changes in cotton yarn hydrophilicity cannot be explained solely by the locally overheated water. The nonlinear dependence of the treatment effect on the applied voltage is delivered to be due to the generation of weak shock waves in the capillary discharge.