Atmospheric pressure plasmas for polymer surface modification: Alternating current gliding arcs and ultrasound enhanced plasmas

A plasma is one of the four states of matter. It is useful for industrial and material processing due to high treatment effects and environmental compatibility. Surface modification for adhesion improvement is among the most promising applications for plasmas. Practically it is realized by introducing electrical energy to a gas to generate a plasma as a reactive gas, in which a material surface is exposed.

During plasma surface treatment, addition of polar functional groups, roughening, and removal of weak domains can take place simultaneously. All of them are important to improve adhesion by better interaction with adhesives or uncured polymers in composite manufacturing. For many practical applications, atmospheric pressure plasma processing is much preferable, as it can avoid to use expensive vacuum systems.

In the present thesis, newly developed atmospheric pressure plasmas for surfaceprocessing are summarized. Specifically, a gliding arc and ultrasound enhanced plasma processing were developed. The gliding arc presented is characterized by stable extension of the discharge into air up to several centimetres operated by a high frequency alternating current (AC).

In the optimized conditions, highly oxidative radicals are efficiently produced and used for surface processing. In addition, the discharge may not necessarily extinguish at every half period, but can survive over a plurality of AC periods, suppressing unwanted energy consumption for arc ignition. Ultrasound enhanced plasma processing demonstrated enhanced treatment effects, arc suppression, and improved treatment-uniformity, compared to plasma processing without ultrasonic irradiation.