Surface modification of polyethylene by photochemical introduction of sulfonic acid groups

A photochemical technique for the modification of polyethylene (PE) surfaces was developed. Polyethylene samples were irradiated with UV light in a gas atmosphere containing SO2 and air to achieve a photosulfonation of the surface. The introduction of sulfonic acid groups (-SO3H) onto the PE surface was proved by Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, The influence of the gas composition and the UV irradiation time on the modification reaction were studied by means of contact angle measurements, FTIR spectroscopy, and dyeing with methylene blue. The hydrophilicity of the PE surface increased considerably compared to unreacted PE. The depth of photomodification amounted to several micrometers. A patterned surface modification was obtained by mask projection, The presented method of surface modification is carried out under atmospheric pressure and is considered to be an inexpensive alternative to plasma modification techniques. Because of the large depth of modification, the process may also be useful for the modification of membranes and-in combination with projection lithography-for the manufacture of gratings in thin polymer films (as required for holographic recordings and distributed feedback lasers).