Effects of additives on atmospheric pressure gliding arc applied to the modification of polypropylene

• Published in: Surface & coatings technology 2019-08, Vol.372, p.45-55
• Main Authors: Jelínek, P., Polášková, K., Jeník, F., Jeníková, Z., Dostál, L., Dvořáková, E., Cerman, J., Šourková, H., Buršíková, V., Špatenka, P., Zajíčková, L.
• Format: Article
• Language: English
• Subjects: Additives; Adhesion tests; Adhesive bonding; Adhesive joints; Adhesive strength; Adhesives; Air flow; Argon; Chemical bonds; Contact angle; Cross flow; Electric arcs; Error analysis; Ethanol; Filaments; Functional groups; Gas dynamics simulations; Gliding; Gliding arc; Nonuniformity; PECVD; Photoelectrons; Plasma; Plasma diagnostics; Plasma treatment of polymers; Polypropylene; Surface characterization methods; Surface treatment; Tensile strength; VOCs; Volatile organic compounds; Wettability
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2019.04.035

The polypropylene (PP) strips were modified with the industrial gliding arc discharge working in air flow at 50 Hz. The experiments aimed at increased wettability and improved strength of the epoxy adhesive DP190 bond with PP. While working only in dry air, the deterioration of the plasma treatment uniformity was observed at higher treatment speeds than 100 mm/s. At the same time, the tensile strength of the adhesive bond and the atomic concentrations of O and N decreased whereas the water contact angle (WCA) measurement error increased. The fast camera measurements revealed that the PP surface was treated by the direct contact with active plasma filaments. The non-uniformity of the PP surface treatment for increased treatment speed can be explained by taking into account the stochastic character of the filament propagation direction and the characteristic time scales of the process. As an improvement of the gliding arc treatment technology a new geometry utilizing the gas cross flow was proposed with the help of gas dynamic simulations. The addition of argon cross flow led to an improvement of the treatment uniformity and, for the optimized conditions, the measured tensile strength of the adhesive bond to PP was 6.5 times higher than for the untreated PP sample. The treatments with the cross flow of argon mixed with water vapors and volatile organic compounds (VOCs), ethanol and isopropanol, did not increase the tensile strength of the adhesive joint even though the wettability was higher for the mixtures with VOCs. Since the concentration of functional groups measured by X-ray photoelectron spectroscopy was well correlated with the tensile strength of adhesive joints, WCA measurements cannot be used as the only parameter judging the success of the plasma treatment aimed at an improvement of adhesive joint strength. •High speed camera revealed long plasma filaments propagating along polymer surface.•Gas cross flow addition into the air gliding arc was proposed using gas dynamics simulations.•Argon cross flow improved the width and the uniformity of the plasma treatment.•Tensile strength of adhesive bond to polypropylene was improved up to six times.