Vacuum ultraviolet–induced photochemical nitriding of polyolefin surfaces

Abstract

Abstract Film samples of two very pure polyolefins, low‐density polyethylene (LDPE) and biaxially oriented polypropylene (BOPP), were surface‐modified by vacuum ultraviolet (VUV) photochemistry in low‐pressure ammonia. The influence of experimental conditions such as wavelength and intensity (photon flux) of the VUV radiation, ammonia pressure, and treatment duration, as well as the mechanisms involved in the surface modification were discussed. Changes in the surface energy and chemistry were investigated using suitable techniques like contact angle goniometry (surface energy) measurements, X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance infrared spectroscopy, and time‐of‐flight secondary ion mass spectroscopy. We show that chemically bonded nitrogen concentrations [N], up to 25%, can be achieved on the polymer surfaces by VUV photochemistry, and that N is predominantly bonded as amine groups, thus leading to an important increase in the surface energy of treated samples. Finally, XPS, surface energy measurements, and atomic force microscopy were used to characterize possible degradation of the polymer surfaces during the VUV treatments. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3886–3898, 2004