Effect of pulse voltage slew rate on the uniformity of polypropylene surface hydrophilic modification by nanosecond pulsed dielectric barrier discharge

To improve the hydrophilicity of polypropylene (PP) surface and the uniformity of the treatment effect, the nanosecond pulsed nitrogen dielectric barrier discharge (DBD) is used to process PP surface. The discharge characteristics of the DBD with different pulse rise times (from 50 ns to 500 ns) are investigated by electrical and optical diagnostic methods and the corresponding treatment effect and uniformity of the treated PP surfaces are characterized by measuring the value and radial distribution of the water contact angle (WCA) cross the PP surface. The results show that when the pulse rise time is 50 ns, not only the discharge become more uniform but also the emission spectral intensity is higher compared to other conditions. For hydrophilic modification effect, as the pulse rise time increases from 50 ns to 500 ns, the WCA average values changes from 47° to 55°. And for the uniformity of the PP surface treatment, the results show that the uniformity of the DBD-treated PP surface under 50 ns pulse rise time (3° variation). The faster pulse voltage slew rate enhances the reduced field in discharge space and promote the electron avalanche fusion, which leads to better discharge and treatment uniformities.