To enhance the bondability of polyetheretherketone (PEEK), surface treatment
techniques of plasma and corona discharge have been evaluated. The results have
shown that these two methods are effective and practical. The treated materials not
only reach their highest possible joint strength, but also show very promising joint
durability. In addition, the various environments, e. g. atmosphere, heat, water, and
solvent, have little effects on the enhanced bondability of the treated materials.
By using Contact Angle Measurement, Scanning Electron Microscopy (SEM), X-ray
Photoelectron Spectroscopy (XPS) and Time of Flight Secondaty Ion Mass
Spectrometry (TOF-SIMS) to characterise the PEEK surfaces before and after
treatment, it was established that the lack of active chemical groups, which if present
can form strong interatomic and intermolecular forces across the adhesive/PEEK
interface, is the main cause for the poor bondability of the untreated PEEK. Both
plasma and corona discharge treatment introduce such active functional groups, for
instance, hydroxyl, carboxylic acid, amine and etc., onto the surface of PEEK film and
so greatly enhance the intrinsic adhesion at the interface between treated PEEK
surfaces and epoxy adhesive, as confirmed by the TOF-SIMS interfacial analysis.
It is deduced that low molecular weight molecules (LMWM) are formed on treated
surfaces, which contain high concentration of oxygen and/or nitrogen, and can be
removed by solvent washing. The removal of LMWM will drastically reduce the
wettability of the treated surfaces, but does not impair the enhanced bondability.
It has been found that both plasma and corona discharge treated surfaces are in a
thermodynamically unstable state. When exposed to the atmosphere, the treated
surfaces tend to lose their improved wettability and decrease their surface polarity.
Increasing temperature can not only accelerate these processes but also change the
surface chemical structures of the treated materials back to that of the untreated films
to some extent, as revealed by the TOF-SIMS analysis. Water immersion, on the
contrary, tend to reverse the above processes
