Modification of expanded polytetrafluoroethylene by UV irradiation in reactive and inert atmosphere

The surface properties of expanded polytetrafluoroethylene (ePTFE) can be modified by 172 nm excimer lamp irradiation in ammonia (NH3) or acetylene (C2H2) atmosphere. This surface modification is either related to the substitution of fluorine by nitrogen- and/or hydrogen-containing groups or to the deposition of material from the gas phase. Additional oxygen-containing functionalities are incorporated by reactions with the residual gas and/or oxidation in air after treatment. The changes in surface properties are discussed on the basis of water contact-angle measurements, X-ray photoelectron spectroscopy (XPS) and IR spectroscopy on dense PTFE samples. Surface modification yields a reduction of the tear strength and break-down elongation in tensile tests. Field-emission scanning electron microscopy (FE-SEM) revealed that the tensile failure occurred at the contact of fibrils and nodes in the material. With 193 nm ArF excimer-laser irradiation in NH3 atmosphere, both the modification efficiency and material degradation are considerably lower.