The fiber/fiber interface influences strongly the mechanical properties of a composite paper material. Polyethylene (PE) pulp fiber was treated, for surface modification to improve adhesion with conventional paper fiber, using ozone in aqueous medium, and fluorinated gases. X-ray photoelectron spectroscopy (XPS) was used to analyze the surface of conventional paper fiber as well as the variation of the chemical composition and the O/C atomic ratio, within the surface level of the PE pulp fiber after the treatments. The thermodynamic surface characteristics of the fiber were then determined using the inverse gas chromatography (IGC) technique at infinite dilution. Following Fowkes＇ approach, acid/base surface characteristics were obtained. The variation of surface thermodynamic properties due to treatments were compared to the variation of the chemical compositions as obtained by XPS.