Improving hydrophilicity of polypropylene film using atmospheric pressure plasma jet in argon

In order to study the application of plasma jet in film surface modification, the surfaces of polypropylene (PP) films were modified using atmospheric pressure plasma jet in Ar to improve hydrophilicity. The discharge characteristics were studied by means of voltage and current waveforms measurement, Lissajous figures measurement, light-emission pictures taking, and optical emission spectra measurement, and the surface properties of the untreated and plasma jet treated samples were characterized by means of contact angle and surface energy measurement, providing reference for selecting optimum processing condition in practical application. The influences of discharge and treatment parameters, such as treatment distance, treatment time, and power density on PP surface modification, are studied, the aging effect of treated PP that was exposed to open air was also investigated, and the modification mechanism was discussed. Results show that the generated gas in Ar plasma jet is a typical non-thermal one, in which the main species are OH, N ₂, Ar, and O, and gas temperature is the range of 317 K to 362 K. After atmospheric pressure plasma jet treatment, the water contact angle decreases and surface energy increases, and both of them reach saturated values at certain treatment time. The water contact angle can reach minimum value of 55° after treatment, and the surface energy can reach maximum value of 45.313 mJ/m ². The treatment time can be shortened by decreasing treatment distance and increasing power density, then the treatment efficiency can be improved. Aging effect occurs on the plasma treated PP surface, but the value of water contact angle is still 70.5° even after 10 days storage in ambient air, much lower than that of the untreated one.