Characteristics of atmospheric pressure N2 cold plasma torch using 60-Hz AC power and its application to polymer surface modification

Atmospheric pressure N2 cold plasmas are generated with a torch-type generator using 60-Hz AC power. High flow rate N2 gas is injected into the plasma generator and high voltage of about 2 kV is introduced into the power electrode through transformer. Discharge characteristics of N2 cold plasma, such as current-voltage profile, gas temperature and radial species in plasma, are measured. As one possible application, the N2 cold plasma is used to modify the surface of polymer, especially polypropylene, for adhesion improvement. Power dissipation in discharge has the maximum value at optimal power electrode position, z=3 mm, which lead to the generation of more energetic electrons capable of creating N2* and N2+ excited states in plasmas effectively. These excited species can induce high population of oxygen and nitrogen atoms on polymer surface through creation of polymer excited states. Maximum bonding strength about 10.5 MPa is obtained at optimal power electrode position.