Surface modification of polyethylene by photochemical introduction of sulfonic acid groups

A photochemical technique for the modification of polyethylene (PE) surface s was developed. Polyethylene samples were irradiated with UV light in a ga s atmosphere containing SO2 and air to achieve a photosulfonation of the su rface. The introduction of sulfonic acid groups (-SO3H) onto the PE surface was proved by Fourier transform infrared spectroscopy (FTIR), energy-dispe rsive X-ray spectroscopy, and X-ray photoelectron spectroscopy, The influen ce of the gas composition and the UV irradiation time on the modification r eaction were studied by means of contact angle measurements, FTIR spectrosc opy, and dyeing with methylene blue. The hydrophilicity of the PE surface i ncreased considerably compared to unreacted PE. The depth of photomodificat ion amounted to several micrometers. A patterned surface modification was o btained by mask projection, The presented method of surface modification is carried out under atmospheric pressure and is considered to be an inexpens ive alternative to plasma modification techniques. Because of the large dep th of modification, the process may also be useful for the modification of membranes and-in combination with projection lithography-for the manufactur e of gratings in thin polymer films (as required for holographic recordings and distributed feedback lasers).