Comparison between adhesion properties of adhesive bonding and adhesive-free adhesion for heat-assisted plasma-treated polytetrafluoroethylene (PTFE)

Heating during plasma treatment, known as heat-assisted plasma treatment, has recently reported to positively affect the adhesion properties of polytetrafluoroethylene (PTFE). In the present study, the adhesion properties of adhesive bonding and adhesive-free adhesion were compared for plasma-treated PTFE with different plasma treatment times and with or without heating during the plasma treatment. The relations among adhesion strength, plasma treatment time, radical density ratio, surface morphology, and surface hardness were investigated. No correlation was found between the adhesion strength and the radical density ratio or between the adhesion strength and the oxygen-containing-functional-group ratio. In contrast, correlation was observed between the adhesion strength and the surface hardness. In addition, the heat-assisted plasma treatment time affected the recovery of the weak boundary layer on the PTFE surface. Adhesive-free adhesion was found to require a longer heat-assisted plasma treatment time than adhesive bonding in order to achieve a high adhesion strength such as 1 N/mm.