Effects of additives on atmospheric pressure gliding arc applied to themodification of polypropylene

The polypropylene (PP) strips were modified with the industrial gliding arc discharge working in airflow at50 Hz. The experiments aimed at increased wettability and improved strength of the epoxy adhesive DP190 bondwith PP. While working only in dry air, the deterioration of the plasma treatment uniformity was observed athigher treatment speeds than 100 mm/s. At the same time, the tensile strength of the adhesive bond and theatomic concentrations of O and N decreased whereas the water contact angle (WCA) measurement error in-creased. The fast camera measurements revealed that the PP surface was treated by the direct contact with activeplasmafilaments. The non-uniformity of the PP surface treatment for increased treatment speed can be explainedby taking into account the stochastic character of thefilament propagation direction and the characteristic timescales of the process.As an improvement of the gliding arc treatment technology a new geometry utilizing the gas crossflow wasproposed with the help of gas dynamic simulations. The addition of argon crossflow led to an improvement ofthe treatment uniformity and, for the optimized conditions, the measured tensile strength of the adhesive bondto PP was 6.5 times higher than for the untreated PP sample. The treatments with the crossflow of argon mixedwith water vapors and volatile organic compounds (VOCs), ethanol and isopropanol, did not increase the tensilestrength of the adhesive joint even though the wettability was higher for the mixtures with VOCs. Since theconcentration of functional groups measured by X-ray photoelectron spectroscopy was well correlated with thetensile strength of adhesive joints, WCA measurements cannot be used as the only parameter judging the successof the plasma treatment aimed at an improvement of adhesive joint strengt