THE EFFECT OF FLUORINATION ON THE SURFACE CHARACTERISTICS AND ADHESIVE PROPERTIES OF POLYETHYLENE AND POLYPROPYLENE

Polyethylene and polypropylene have been treated with fluorine/nitroge n or fluorine/oxygen/nitrogen mixtures at atmospheric pressure. Change s in surface chemistry and topography as well as depth of fluorination have been examined using Fourier transform infra-red analysis, X-ray photoelectron spectroscopy (X.p.s.), atomic force microscopy (AFM) and ellipsometry. Even very short exposure times caused a large substitut ion of the hydrogen atoms by fluorine. No change in surface topography was noticed at magnifications of up to 5000 times with the scanning e lectron microscope (SEM), but AFM showed that fluorination led to an i ncrease of microroughness. The influence of fluorine or fluorine/oxyge n concentration, as well as time of treatment and time of storage befo re adhesive bonding, on adhesion of polypropylene to steel was investi gated with a bending peel test. Significant improvement in peel streng th was already achieved with minor fluorination intensity. Increase of fluorination intensity did not lead to further improvement in peel st rength. Analysis of the fracture surfaces was carried out with the SEM and by energy dispersive X-ray spectroscopy and X.p.s. The findings s howed that the samples failed cohesively in the polymer or directly be neath the fluorinated layer. A model to describe the formation of spec ific interactions between substrate and adhesive is suggested.