Effect of Plasma Gas Flow Direction on Hydrophilicity of Polymer by Small Zone Cold Plasma Treatment and Hydrophobic Plasma Treatment

Plasma treatment is the most popular surface modification process of polymers. A small cold plasma zone treatment is an important modification technique in modern industry. In this study, the effect of gas flow direction on plasma treatment was investigated. In order to decrease the plasma zone area, we added a separate cylinder to surround the upper electrode. The separate cylinder is effective in limiting the plasma discharge area, and we could find a light and dark area in the vacuum chamber. After O2 plasma treatment, the result shows that only PP nonwoven in the discharge area became hydrophilic, but the other position away from the plasma zone was not affected. The water adsorption of PP nonwoven increased from 34.8% to 537.4%. When the sample is further from the plasma zone, near the up stream of gas flow, the surface property is less hydrophilic. The water contact angle analysis of PS and glass shows the same results as those of PP nonwoven. But PET in plasma zone or dark zone (plasma zone: 75 to 31 , dark zone: 75 to 52 ) both show hydrophilic property. The wettability effect in the dark zone may be due to the UV-light irradiation in the process of plasma excitation.