Alternative Surface Treatment for the Enhanced Adhesion of Polytetrafluoroethylene Films via Atmospheric Pressure Nitrogen Plasma

Abstract

Polytetrafluoroethylene (PTFE) presents a notably challenging surface for enhancing its adhesion properties. Here, a surface modification of PTFE via atmospheric pressure nitrogen plasma is presented. This treatment produces peel strength values comparable to conventional wet chemical treatments. Indeed, plasma-treated surfaces were compared with those obtained with heat-treated PTFE and conventional chemically etched PTFE. All plasma treatments resulted in altered wettability, increased surface roughness, partial defluorination of the substrates, and the incorporation of oxygen and nitrogen functional groups on the polymer surface. Similar surface topologies were observed between the thermally treated and plasma-treated PTFEs, suggesting that the plasma approach induced a heating process on the substrate. The effect of these outcomes on the adhesive response of plasma-treated substrates was investigated by 180°and T-peel tests with different adhesives (acrylic adhesive, acrylic adhesive tape, and rubber adhesive tape). Peel test results showed a drastic increase in the adhesion of plasma-treated PTFE compared to the untreated PTFE films, reaching similar or higher values to those obtained with the chemically etched PTFE. Additionally, the evolution of the bonding properties of plasma-treated surfaces was studied over time. The peel strength increased from ≈0 N/cm (untreated) to 1.7 ± 1.2 N/cm when measured by a 180°peel test with an acrylic adhesive. There was also an increase from 0.3 ± 0.1 and 2.5 ± 0.2 N/cm to 5.3 ± 0.1 and 9.2 ± 0.6 N/cm when measured by the Tpeel test with acrylic and rubber adhesive tapes, respectively. The results revealed that the measured peel strength stabilized after 15 days, remaining constant over 365 days. The remarkable results highlight the possibility of replacing conventional solvent-based chemical processes with a dry atmospheric pressure treatment and also emphasize the potential, lower environmental impact, and cost effectiveness of a nitrogen-based plasma process compared to the wet chemical etching approaches commonly used in the industry today for the surface treatment of fluoropolymers.