Surface modification and adhesion improvement of expanded poly(tetrafluoroethylene) films by plasma graft polymerization

In this investigation, we attempted to improve the peel strength of expanded poly(tetrafluoroethylene) (ePTFE) film by O2 RF plasma treatment and grafting polymerization with hydrophilic monomers of acrylamide (AAm), glycidyl methacrylate (GMA) and 2-hydroxyethyl methacrylate (HEMA). The surface properties of the modified film were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total refraction-Fourier transform infrared (FTIR-ATR), contact angle meter (CA), atomic force microscopy (AFM) and scanning electron microscopy (SEM). It was found that heavy etching reaction was induced by the oxygen plasma treatment. Small molecular weight segments such as -CFX were formed due to the etching phenomenon on the ePTFE surface. By increasing the power of plasma, this phenomenon was more significant. These -CFX segments might be re-deposited onto the ePTFE surface by physical adsorption and lead to the decrease of peel strength from 3.65 N/cm to 1.05 N/cm. In addition, the adhesion properties of the oxygen plasma pretreated ePTFE films could be further improved by post-grafting polymerization of AAm onto the surface of ePTFE film. A 50 W oxygen plasma treatment for 60 s and grafting polymerization of 20 wt.% AAm at 80 °C for 3 h gave an improvement of ePTFE peel strength from 2.47 to 6.22 N/cm.