Surface modification of clay‐coated paper by atmospheric‐pressure plasma in air

The aim of this work was the wettability improvement of clay-coated paper by ambient air plasma exposure. Industrial corona with a volume dielectric barrier discharge in cylindrical configuration was used as a plasma source; the exposure times varied from 0.25 up to 5 s. Water contact angle (WCA) measurement and surface free energy (SFE) evaluation were carried out for the estimation of wettability changes. Plasma treatment in the duration of 0.25 s was sufficient to decrease the WCA almost to the half of the original value, which was 76 degrees. SFE of paper has increased by 40%-50% after plasma treatment. Long-term ageing effect study of treated samples was carried out up to 3 months after the treatment. WCA did not reach the original value even after 3 months, and it was still 20%-30% lower. O/C ratio increased from 0.7 to 1.8 in case of 5-s plasma treatment, and the new chemical bonds (C=O, O-C=O) were created on the surface.