Influence of absorbed moisture on solubility of poly(vinyl alcohol) film during atmospheric pressure plasma jet treatment

Moisture in the hydrophilic material may potentially influence the plasma treatment effect. In order to understand how moisture absorbed into PVA affects the result of plasma treatment to the polymer, atactic poly(vinyl alcohol) (PVA) films with moisture regain (MR) of 2.5%, 9.3% and 78.3% corresponding to 10%, 65% and 98% relative humidity (RH), respectively were exposed to atmospheric pressure plasma jet. Another group was annealed at 140 °C for 20 min to discern the thermal effects from those due to plasma treatment. Scanning electron microscope (SEM) showed lamellae crystal structures were on the surface of the films with 65% and 98% RH, while some bubbles or salt grains appeared on the surface of film with 10% RH and the annealed film respectively. X-ray photoelectron spectroscopy (XPS) analysis indicated that oxygen concentration increased for plasma treated films with 65% and 98% RH and decreased for that with 10% RH. X-ray diffraction analysis (XRD) shows an increase in crystallinity in all the plasma treated films. It was found that the solubility of all the treated films was decreased, especially for the plasma treated film under 98% RH which is nearly insoluble in water at 50 °C for 20 min.